Photo: Shepherdia argentea, Buffaloberry, southwest Montana. © 2020 Delena Norris-Tull
Native plants: Their role in ecosystems and in the restoration of damaged lands
Summaries of the research and commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, June, 2020.
The Federal Native Plant Conservation Committee defined a native plant as a species “that occurs naturally in a particular habitat, ecosystem, or region… without direct or indirect human actions” (1994 Memorandum of Understanding that formed the Federal Native Plant Conservation Committee, whose work is continued under the Plant Conservation Alliance (PCA), a public-private partnership between 15 Federal Agencies and 400+ non-Federal cooperators, funded through the BLM). The PCA works “collaboratively to solve the problems of native plant conservation and native habitat restoration, ensuring the sustainability of our ecosystems.”
The Plant Conservation Alliance has developed a National Seed Strategy: “a public-private collaboration to increase the supply of native seeds for restoration projects to ensure ecosystem resilience and the health and prosperity of future generations.”
Ecosystems are based on native plants. Native plants provide nectar and pollen for butterflies, birds, for native and introduced bees, and for some species of bats. Bees, butterflies, birds, and bats facilitate the growth of native plants, agricultural crops, and landscaping plants by carrying pollen from plant to plant. Bird and bats also promote the growth of native and agricultural plant species by consuming many insects. In addition to the important agricultural pollination and honey-producing services provided by the introduced honey bee species, the thousands of native bee species pollinate native and agricultural and landscaping crops. And a number of tropical fruits rely on pollination by bats. Wildlife utilize native plants throughout the year. Plant seeds and fruits provide food for birds and bats. Plant leaves provide food for a wide variety of insects. Native plants provide shelter and nesting habitats for birds. Insects, in turn, provide food for birds and other wildlife. Birds and bats eat many different species of insects, and are extremely important in controlling many of the insects that impact agricultural crops, saving farmers billions of dollars annually in insect pest control costs. And, of course, plants provide oxygen for us all to use.
And, not to be forgotten, we must remember that plants provide great beauty. In the research I cite in the section, Invasive Success Hypotheses, the role and the importance of plant diversity is described. But one aspect that is not mentioned in the scientific research is that plant diversity, like human diversity, provides us with an awe-inspiring world of beauty.
Farmers that promote the growth of natural ecosystems near their agricultural lands increase the numbers of both introduced honey bees and native bees available to pollinate their crops.
In the drought-prone regions of the Western States, many native plant species are well adapted to growing under conditions of drought. Local native plants are adapted to local climate and soils. When attempting to re-establish native plants in a disturbed site, it is often necessary to irrigate the area in the first season. Once re-established, native plants require little or no irrigation or fertilization. Once drought-tolerant native plants are established, they will maintain themselves. In addition, once established, native plants typically do not require the use of pesticides or herbicides. However, refer to the sections on Climate Change for some concerns regarding what could potentially happen as local climates change, and local native plants potentially become less well adapted to local conditions.
I grew up in a household where my mother imparted to me her love of plants, both native and non-native. And, since I lived in Texas for many of my formative years, I had become accustomed to a State Highway Department that promoted landscaping and maintenance of highway rights-of-way using native plants.
Soon after its formation in 1917, Texas Highway Department staff noticed that native wildflowers were often the first plants to regrow in disturbed sections of the highways. The Department implemented policies to promote growing native plants along Texas roadsides. These policies remain in place today, and have turned Texas roadways into popular tourist attractions. Many visitors from both in-state and out-of-state travel along the Texas roadsides in the Spring, to view the large displays of beautiful native wildflowers.
When the Texas Department of Transportation started growing native plants along highways, they quickly discovered that native plants and seeds were in short supply. The policies of the Texas DOT eventually spawned a new agri-business. Landscapers and plant growers began raising native plants, both for landscaping and for seed. Today, the Texas DOT buys and plants 30,000 wildflower seeds each year. They also plant native grasses, forbs, and shrubs. The TxDOT has developed highway maintenance procedures that encourage native wildflowers and grasses to naturally re-seed, where feasible. Those procedures are detailed below.
As First Lady, Lady Bird Johnson, the wife of President Lyndon Baines Johnson, initiated a project to beautify Washington, D.C., by having millions of flowers planted. She is quoted as saying, “Where flowers bloom, so does hope.” She was also instrumental in facilitating the passage of Federal legislation, the Highway Beautification Act (HBA) of 1965 (nicknamed “Lady Bird’s Bill”), which limited the placement of advertising billboards along the Federal Interstate Highway system, and required the removal of junkyards from view of the highways, and encouraged scenic enhancement of Federal highways. I remember this change when I was a child, because prior to the implementation of that Federal law, thousands of giant billboards obstructed the travelers’ views of the beautiful country in which we live. The HBA has always been controversial because it limits advertising by local businesses, already disadvantaged by the placement of the newly expanding Federal Highways, which tend to route travelers away from rural towns. The law has been amended numerous times, and, although the HBA is essentially still in effect, the amendments allow more billboard advertising near places of business.
Thanks to the nationwide beautification projects inspired by First Lady, Lady Bird Johnson, many communities were inspired to landscape public lands with beautiful flowers. Lady Bird, upon returning to Texas after Johnson’s term as President ended, inspired many Texas communities to landscape public spaces, and she provided grants to assist communities in doing so, with a focus on Texas native plants, especially wildflowers.
In 1982, Lady Bird Johnson and actress Helen Hayes worked together to establish the Lady Bird Johnson Wildflower Center, now part of the University of Texas, in Austin, Texas. Lady Bird donated the land for the original site of the Center. In the 1980s, I conducted several workshops for teachers at the Center, to educate teachers on Texas native plants. The Center was eventually moved and expanded to a larger piece of land and renamed The Lady Bird Johnson Wildflower Center, a center focused on native plant conservation, sustainable landscapes, and research on native plants, and which hosts an extensive online native plants database. It is now also the Botanic Garden of Texas. The Center has also created the Texas Seed Bank, where seeds from native Texas plants are collected and stored, for research projects.
By the time I moved away from Texas in 1990, I was so accustomed to seeing native plants along public roadways, that I was quite shocked to realize that planting native species along roadways was not common in other States.
If you review the laws of the Western States related to control of invasive plant species [Refer to the section State Laws], you will find that half of them do not prohibit naming native plants as “noxious weeds.” And State laws typically do not mention re-seeding infested lands with native plants, as part of Integrated Vegetation Management (IVM), probably because the initial laws related only to noxious weeds growing within farmland. Some States have figured out that growing local native plants can be an important agricultural business. But many States do not yet effectively utilize and promote landscaping and roadside planting with native plants, often due to the lack of availability of inexpensive native plants and seeds, native to the State and the region of the State, where the plants and seeds are needed.
Refer to the section Why We Need Plants for detailed information of the role of plants in the maintenance of life on Earth. For additional valuable information about the importance of native plants within ecosystems, refer to the 2019 UN Global Assessment Report on Biodiversity and Ecosystem Services .
I have been surprised at the lack of emphasis on planting native seed and native plants in some States, after removal of weeds with herbicides or biocontrol. There are many sites where either herbicides or biocontrol agents have reduced one species of invasive plant within an area, and then within a year or two, that area is re-infested with the same or a different invasive species. Unless a plan is in place to revegetate the area after treatment, we appear to be wasting our resources and perpetuating the problem.
Many of the interviews included here, show that weed management remains identified with herbicide use, despite the rapidly emerging problems of herbicide-resistance and health concerns due to decades of overuse of herbicides [Refer to the sections on Herbicides for details]. My interviews with individuals who have worked in the field of Weed Management for decades, have provided me with some insights into this issue.
In the not-too-distant past, and in some cases still today, a number of native plant species have been treated as weeds, and have been subjected to eradication attempts. A number of States still allow native plant species to be included on the State list of invasive species, often due to toxicities in some plant species that can result in livestock losses [Refer to the section State Laws].
Here are a few examples of native plants that have been treated as weeds and thus targeted for reduction or eradication:
In my 2017 interview with Phil Westra, Weed Scientist at Colorado State University, he told me, “Colorado has a suite of warm and cool season native grasses that are used in re-seeding projects. But the seed is expensive – about $200 per acre.”
In my interview with Dr. George Beck, Weed Scientist at Colorado State University, he stated that, “The US Natural Resources Conservation Service [NRCS; formerly the US Soil Conservation Service] has demonstrated that native plants will endure longer than non-natives.
“In Colorado, we have state-level Conservation Districts. These are the longest-standing fighters of weeds. They are loosely connected to the NRCS and the USDA.
“We initially focused on re-seeding native grass species. We are starting to realize that we also need native forbs and shrubs in our re-seeding projects, particularly because these native species attract pollinators and other insects that provide a crucial food source for birds, such as quail and grouse.”
George Beck told me, “Invasive species are the biggest problem in the western US. In Colorado now there is tremendous importance being placed on re-planting with native species. Almost all re-seeding now is with natives. Except where the soil is so bad, in which case we might plant a non-native brome grass for grazing.”
George went on to say, “Colorado weed law states that native plant species cannot be designated as noxious weeds. We had a lot of pressure from farmers and ranchers to add some native species to the noxious weed list. We worked with the Sierra Club, who helped get into law the fact that only non-natives should be designated as noxious weeds. A local community can remove natives on local lands, but they cannot force their neighbors to do so on their lands.”
Sheley, Svejcar, and Maxwell, 1996, proposed “a theoretical framework for developing successional weed management strategies on rangeland.” They point out that, up to that point, weed management strategies had focused on “simply controlling weeds, with limited regard to the existing or resulting plant community.” They proposed that the objective of weed management “could be to develop a healthy plant community that is relatively weed-resistant, while meeting land-use objectives, such as forage production, wildlife habitat development, or recreational land maintenance.” They go on to propose that, “A healthy, weed-resistant plant community consists of a diverse group of species which occupy most of the niches…. Weed-resistant plant communities effectively use resources over time and space.” And they state that, “Ecologically-based weed management requires that scientists and managers develop strategies that are based on our current understanding of succession…. Ultimately, the goal is to direct weed infested communities on a trajectory toward more desirable plant communities.” They create a synthesis of previous models of plant succession, to create a model for how to achieve the goal of attaining “desirable plant communities.”
Sheley, Svejcar, and Maxwell, 1996, stated that, “Managing succession requires knowledge of three components corresponding to the three general causes of succession: disturbance, colonization, and species performance…. We can design the disturbance regime and attempt to control colonization and species performance through management. Successional management must be viewed as an ongoing process moving from one successional component to the next or repeating a single component through time. This model is driven by both naturally occurring and human-induced processes.”
Sheley, et al., 1996, describe the three successional components:
Component one: “Designed disturbance. Disturbance plays a central role in initiating and altering successional pathways… Natural disturbances, such as landslides, fire, and severe climatic conditions initiate, retard, or accelerate succession, or alter successional pathways…. Weed management strategies have included designed disturbance, such as cultivation, burning, and herbicide application for decades.”
Note from Delena: Unfortunately, in many locations, previous and even current weed management strategies have completed the “designed disturbance” but have ignored the fact that additional steps are needed to achieve a weed-limited setting. Sheley, et al., 1996, point out that, “if roadside disturbance provides a staging area for weed invasion, emphasis could be placed on roadside revegetation with competitive native perennial species.”
Sheley, etal., 1996, component two:
“Controlled colonization… is the intentional alteration of availability and establishment of various plant species… Controlled colonization efforts are directed toward influencing seed banks, propagule pools, and regulation of safe sites for germination and establishment of desirable species. Weed seed banks can be depleted through attrition if seed production is prevented or significantly reduced.”
Some research has shown that livestock grazing can be effective in reducing some weed seed banks (Olson, et al, 1997; Olson, et al, 1998), but caution that grazing can also reduce desired species. Biocontrol agents also help reduce weed seed banks.
However, controlled colonization also means encouraging the growth of, and the seed bank of, the desired species. Too often, this step is ignored. Sheley, et al., 1996, propose that livestock can also be used to assist in revegetation with desired species by adding native plant seed to the hay. They also propose that, in some cases, such as when soil is so depleted of nutrients that native perennials are difficult to establish, planting a less desirable but ephemeral/annual species can enhance the soil, making colonization by desired perennial species more feasible.
Note from Delena: Unfortunately, in many locations where controlled colonization is used, e.g., when grazing or biocontrol are used to reduce weeds, the third step in managing the successional process is not incorporated.
Sheley, et al., 1996, component three:
“Controlled species performance… involves manipulating the relative growth and reproduction of plant species in an attempt to shift community dynamics in a desirable direction. Biological and chemical weed control, grazing, plant and plant-part removal, altering resource availability, and competitive plantings are techniques to create differential species performance.” However, they also point out that, “plant communities can be shifted toward desirable species providing propagules are present and establishment occurs.” In other words, native plants must either be already present, or native seed or native propagules must be purposefully planted. Unfortunately, in many cases, the soil is so depleted that native seed or native plants are no longer present, or native perennials may not establish due to lack of soil nutrients. In some cases, the native seed will take too long to germinate and thus will not compete with the weed species.
In some cases, too much nutrients, for example, too much nitrogen in the soil, necessary for early successional annual species, can inhibit the growth of later successional species, which are typically the desired species. McLendon and Redente, 1991, found that, “The addition of nitrogen… altered succession by slowing the rate of succession and allowing annuals to dominate …. Dominance of disturbed nutrient-rich sites by annuals may be a function of two major factors: seed availability and rapid potential growth rate.” [Refer to the chapter “Restoration of prairies, steppes, and deserts” for a more detailed account of their research.]
Herron, Sheley, Maxwell, and Jacobsen, 2001, tested the hypothesis that “succession from a weedy plant community toward a desired late-seral [native] plant community could be accelerated by altering nutrient availability.” Herron, et al., 2001, believe that “bluebunch wheatgrass has a lower N requirement than spotted knapweed, and, therefore, has the ability to out-compete spotted knapweed at lower N levels…. Our study provides initial evidence supporting the theory that nutrient levels can be altered to accelerate successional change from a weedy plant community toward a desired plant community. Ephemeral cover crops or mid-seral species could be used in restoration projects to lower N availability. Lower N availability could accelerate the establishment and domination of late-seral species over earlier successional weedy species.”
George Beck introduced me to the work by Sheley, et al. He told me, “Around 1996, Dr. Roger Sheley and Bruce Maxwell, at Montana State University, published a synthesis paper on successional weed management practices. This concept transformed how we thought about weed management (Sheley, Svejcar, & Maxwell, 1996). It is based on:
1 – site availability
2 – differential species diversity, and
3 – differential species performance.”
George said, “As a result of this paper, many more agencies became interested, as well as many more private landowners. We need diversity in the land. At any moment, certain plant species are being favored by the environment and other plant species are not. For example, some plants are more drought tolerant than others, and some are more tolerant of storms. Different plant species flower and seed at different times of the year. Different plant species provide forage for insects, birds, mammals, etc., at different times of the year. A successional system includes all these diverse elements.
“In successional weed management, you incorporate the following:
1 – designed disturbance
2 – controlled colonization
3 – controlled species performance
“An example I have used in my CSU classes is from my own land, an example on a small acreage: I bought a home that includes an old wheat field. It had lots of weeds initially. Here’s what I did on the land:
1 – I used Roundup (glyphosate) to kill field bindweed. And I used an aerator to pull plugs out of the field. This was my designed disturbance.
2 – I broadcast native grass seed. This was my controlled colonization.
3 – I watered the seed, to better control species performance.
“This process worked well on my small acreage.
“We need a variety of native grasses in rangeland. Some are more drought tolerant than others. Competition is the most important component of getting rid of weeds – but it is not sufficient. For example, if I simply broadcast native seed across a field infested with Canada thistle, I get nothing. But if I treat the field with herbicide, I’ll get a period of time with reduced Canada thistle. That’s when I can plant the native grasses.
“In my opinion, by using these techniques, we can diffuse most of the concerns about the use of herbicides or biocontrols, by minimizing how much herbicides we use. Once the native species are back in the system, we don’t have to continue using herbicides.”
Of course, one of the limitations of relying on plant succession in weed management is dealing with the possibility of another unplanned disturbance, which presents the possibility of having to start the whole process over. However, if a seed bank of native species remains in the soil after the disturbance event, it may be easier to re-establish diverse perennial native species.
Harris, 1967, reviewed decades of research and reports on the reduction of the native perennial, bluebunch wheatgrass, and the subsequent spread of the introduced annual, cheatgrass, in Western States. Bluebunch wheatgrass previously was the dominant plant species in the intermountain region of the Western US and Canada. Heavy livestock grazing in Eastern Washington facilitated the spread of cheatgrass as early as the 1930s. Cheatgrass also spread in abandoned fields and repeatedly burned areas. Harris, 1967, demonstrated that, although both species germinate in the fall, cheatgrass has faster and deeper winter root growth, which allows it to dominate in the spring. Cheatgrass completes seeding and begins to die back by late May. Harris demonstrated that cheatgrass preempts resources from perennial bluebunch wheatgrass, by reducing soil moisture before wheatgrass begins its main period of growth in late April.
Carpinelli, Sheley, and Maxwell, 2004, point out that, “During the early stages of secondary succession (e.g., revegetation), availability of light, water, and nutrients may be particularly high relative to the demand by a sparse community of establishing plants. In this case, resource preemption may be more important than competition in determining community dynamics. Those plants with the highest growth rates have the highest likelihood of establishing… Knowledge of the initial growth rate of a species may be the best predictor of the short-term outcome of a revegetation effort.” However, in an experiment they conducted to test this hypothesis, they grew three non-native perennial forage species often used in revegetation projects (crested wheatgrass, intermediate wheatgrass, and alfalfa), and spotted knapweed, a perennial non-native invasive. Both forage grasses have a higher growth rate than either alfalfa or knapweed. Carpinelli, et al., 2004, assumed that because the forage plants occupied different niches, they would jointly dominate all available niches, and thus outcompete the knapweed. Contrary to the predicted results, the increased species richness created by the three forage species did not create an environment limiting to the growth of knapweed. In this experiment, all four species were planted simultaneously. Thus, the sites did not start out with an established species richness, which has been shown to limit weed growth. Carpinelli, et al., 2004, think that “spotted knapweed was able to preempt resources from desirable species in the second growing season, or that spotted knapweed was able to outcompete the desirable species regardless of the degree of niche occupation by desirable species.” Refer to the chapter, “Invasive Species Success Hypotheses” for a discussion of the research by Adler, et al., 2010, on “niche differences,” which challenges the assumption that all the niches in an ecosystem are already filled by the native plant community, before the invasive species enters the scene.
An additional issue to consider is the possibility that revegetation with non-native species, regardless of their desirability as forage, does not simulate the natural ecosystem that existed prior to the disturbance that either removed or reduced the native species in the environment. Thus, this type of revegetation may take more inputs to achieve a successful outcome.
From my interview with Slade Franklin, Weed and Pest Coordinator for the Wyoming Department of Agriculture: “In my job, I focus on removal of invasive species, but not on re-planting. The Wyoming DOT does the re-planting. Sometimes, we don’t have to re-plant, because native perennial bunch grasses have come back in. For example, in some of the early treatments for medusahead and Ventenata in north central Wyoming, we saw the re-emergence of native perennials after the treatment of the non-native annual grasses. In some places in the state, such as the Red Desert in southcentral Wyoming, the natural state of the landscape includes quite a bit of bare ground, so you have to think about how much native seed planting to include.
“The range management teams from the BLM and the USFS do the re-planting on federal lands. There are a number of grass seed nurseries in Wyoming that provide native seed for re-planting.”
However, having different agencies in charge of different aspects of the treatment of damaged lands can result in a disjointed process, with significant time delays between removal and re-seeding.
In the 2013 interview Lars Baker [retired Fremont County, Wyoming, Weed and Pest Supervisor] had with Becky McMillen, Lars explained, “We have removed nutrients from the soil, over the decades of farming and ranching. So now much of our land is poor for farming.
“Weeds are the direct result of how humans have disturbed the land. Native sagebrush range developed over thousands of years. Now that we have disturbed it, we cannot restore it simply by stopping irrigation. The problems we have today with cheatgrass are due to the fact that we have caused so much destruction to the ecological systems.
“Wyoming tried to grow dry-land wheat, but there is not enough rainfall for this to be successful. It failed. So now when we plant native grass seed, they often will not grow, because there is no longer enough rainfall.
“Booth, D.T., & Vogel, 2006, conducted research and found that native plants today are becoming maladapted to current environmental conditions, due to climate change.”
In a 2018 visit to the NRCS Laramie County Field Office, Cheyenne, Wyoming, I interviewed Jim Cochran, District Manager, and Jim Pike, District Conservationist. Here are some notes on the use of native seed in Wyoming, from that interview.
Jim Pike: “We will provide funds for native plant seed if asked by the landowners. However, landowners are often reluctant to use native plants because they take longer to establish. On state-owned lands we will use more native seed. Landowners prefer non-native grasses.
“Native legume seeds are too expensive, about $100 an acre. So we don’t use the natives as much as we could. On cropland we use a mix of natives and non-natives that seems to be working well….”
Jim Pike: “It is challenging to have success with native seed when the cropland has been degraded to such a low level of organic matter. It has been my observation that you need about 3% organic matter in the soil for the soil to be productive. This is not something that we have research on, but it’s been my observation. Most farms around here are now at about 1% organic matter.
“There is enough native seed available. There are more companies producing seed, but it is still too expensive. In mining reclamation projects, they can afford the expensive seed, but there is not as much money available for restoring agricultural land.”
Jim Cochran: “We’re seeing more homeowners who want native lawns, using buffalo grass and blue gramma. About ten years ago, the County Conservation Districts put an emphasis on re-seeding degraded lands.”
Jim Pike: “I’ve been doing a mix of about 30% sainfoin [a non-native perennial legume that is excellent for nitrogen fixation and does not cause bloat in livestock]; 30% intermediate and pubescent wheatgrass [non-native grasses]; some Western and thickspike wheatgrass [native grasses]; orchardgrass [non-native]; and 10 to 15% slender wheatgrass [native grass]. Slender establishes quickly. The native grasses hold their own. The non-natives do not seem to out-compete them…. Natives do not do as well on irrigated lands due to diseases promoted by the water.
“The research says that planting natives with non-natives is not a good idea because the non-natives will out-compete the natives. But I’m having good success with this mix of natives and non-natives.”
Rights-of-way provide important sites for revegetation with native plants
A helpful guide on the value of revegetating highway rights-of-way with native plants is Roadside use of native plants (2000), edited by Bonnie Harper-Lore and Maggie Wilson.
Texas DOT procedures for promotion of native plants along Texas roadsides
Because the Texas DOT procedures for maintaining roadways may be helpful to other States, I include extensive excerpts from Texas Department of Transportation’s Roadside Vegetation Management Manual (revised May 2018). The Manual highlights the importance the State places on the promotion of native vegetation in Texas, and provides information on the importance of native plants. The full Manual is available on the Texas DOT website at http://onlinemanuals.txdot.gov/manuals/AlphaList.html#l_R
Which native plants should we use in revegetation projects?
Those State, County, and Federal Agencies that are attempting to utilize native plants and native seed in their revegetation programs have had to deal with a serious question. “Native plants” differ, not only from State to State, but from region to region within each State. So the question becomes, which native plants should we use to replenish the plant populations on abused lands? Should we only use native plants and seeds from the plants locally native to the specific State and the specific region of that State, that we are attempting to revegetate? And, must we only use seed grown from wild plants, or can we use seed developed from cultivars of native plants?
Research projects conducted by the Great Basin Native Plant Project examine the potential impact of climate change on plant species native to the Great Basin. On the Project website, the Annual Progress Reports describe the findings of these research projects. The research supports the importance of genetic variability as the best option for surviving climate changes. On page 1 of the 2017 Progress Report, the researchers state: “Given the speed and severity with which natural communities are being altered by anthropogenic factors, the application of an evolutionary perspective to restoration ecology is more important than ever. Adjusting seed-selection priorities to account for the existence of locally adapted, intraspecific variation in the Great Basin will promote the maintenance and recovery of resilient, self-sustaining vegetation communities in this region.”
Some of the research conducted by the Great Basin Native Plant Project points to the potential problems when using commercial native plant seed (cultivars) that does not have the degree of genetic variability found in wild plant populations. Massatti, et al, 2017, state: “Recent research has focused on ensuring that native plant materials are ‘appropriate’ for restoration sites... From a genetic perspective, appropriate native plant materials are those that avoid, or mitigate, risks associated with the mixing of local and nonlocal genotypes... For example, nonlocal genotypes may not be adapted to the local environment at a restoration site and therefore have lower fitness... In addition, nonlocal genotypes are increasingly being implicated in negatively impacting local plant and animal species... Furthermore, the intraspecific hybridization of local and nonlocal genotypes could result in outbreeding depression due to the introgression of maladapted genes or hybrid breakdown…, or nonlocal genotypes may prove to be better adapted to local ones and become invasive... Regardless of the potential intraspecific or interspecific impacts resulting from using nonlocal genotypes in restoration treatments, genetic diversity has been recognized as a unit of conservation concern…, suggesting the maintenance of geographic patterns of genetic variation by avoiding the mixture of local and nonlocal genotypes should be an implicit restoration goal... Therefore, gathering information on the genetics of native plants important to restoration is imperative for making the appropriate seed sourcing decisions for ecosystem restoration” (pages 54-63 of the 2017 Annual Report).
Cultivars, or “cultivated varieties,” are plants that have been selected for their desirable characteristics, and then bred to maintain/enhance those advantageous qualities. Many, many cultivars have been developed from many species of ornamental and crop-plants. But cultivars can also be developed from wild, native plant species.
Booth and Vogel, 2006, have attempted to address questions of concern regarding the use of native plant cultivars in restoration projects. Their results challenge the recommendations from Massatti, et al. Booth and Vogel summarize their question as follows: “Controversy exists over the seed source to be preferred and the intended outcome of revegetation projects. We have agreement that disturbed sites need to be stabilized, erosion minimized, and basic ecosystem processes maintained, but disagreement on the extent that revegetation should exactly reproduce the predisturbance plant community and within-species genetic composition. It is a question of priorities. Should preferential use of local plant materials be advocated as the best method to preserve genetic composition, or should available cultivars of native species, and other source identified materials, be employed as the most expedient means for timely soil stabilization and long-term ecosystem-process restoration?”
Booth and Vogel, 2006, found that research had been conducted on very few native plant species and their cultivars, and thus the knowledge base is lacking to definitively answer this question. “One of the basic assumptions for using local ecotypes in revegetation is that they are best adapted to the climate and site of the area…. Since rangeland revegetation projects are expected to produce indefinitely sustainable plant populations, a preference for local ecotypes implies an assumption that the current climate will also continue indefinitely into the future.” They point out the problems with that assumption, by referencing the “evidence that at least 20 glacial-interglacial cycles have influenced the floristic regions of North America.” In addition, movements and food producing practices of Native American populations over the past 12,000 years have influenced North American vegetation patterns, as Native Americans have harvested and eventually farmed many native and introduced plant species.
Booth and Vogel, 2006, point to the rapid changes occurring as a result of global climate change. And they pose the possibility that “composite populations and cultivars with broad genetic bases” are perhaps more likely to adapt to the climatic changes of future centuries, than are local ecotypes. They remind us that, “Genetic diversity, both within and among species, is the foundation of sustainable populations.” They list research that has demonstrated that local plant populations may have reduced population fitness over time, due to inbreeding, and thus, a reduction in the local gene pool, and thus reduction in genetic diversity. They further point out that cultivar development projects, such as those conducted during the droughts of the 1930s and the recent Soil Bank and Conservation Reserve Programs, have focused on developing cultivars by collecting wild plant materials from broad geographic areas, thus broadening the gene pool for each species, then testing them at multiple sites, and selecting the best adapted individuals. These carefully selected cultivars can be produced in commercial seed fields, thus greatly reducing the cost, compared to locally harvested seed from wild stands.
Recent research has verified that cultivars can maintain significant genetic diversity over fairly long periods of time, as a number of native plant cultivars have been used extensively for over 50 years in the Great Plains and Intermountain West, where millions of acres were planted using cultivars. However, Booth and Vogel, 2006, point out that very little research has as yet been conducted, using DNA markers, to examine whether the use of cultivars has had a negative impact or a positive impact on the genetic diversity of local native plant populations. There has also been concern, but little research to test the question, whether native plant cultivars are able to out-compete local native plant populations. However, there is abundant evidence that the use of these native plant cultivars has had “immeasurable benefit to soil and water conservation, forage production, and wildlife habitat.”
As an alternative to using cultivars, when using locally harvested seed, Stutz (1982) advocated using a mix of seed sources to increase the genetic diversity at the revegetation site. The greater the genetic diversity, the greater the likelihood that some parts of the population will survive changes to the locality, such as the changes wrought by climate change.
Booth and Vogel, 2006, cite research that “the adaptation areas of many native plant cultivars are very extensive,” and that they are able to grow and thrive in multiple Hardiness Zones, thus giving these cultivars a decent shot at surviving future climatic shifts. Vogel and others have developed Plant Adaptation Regions (PARs), for use in classifying plant cultivars, not just based on the USDA Plant Hardiness Zones in which they can grow, but also on their ability to grow in a variety of geographic regions, which can then predict their adaptability for surviving climatic shifts. Much more of this research is needed. They claim that, “As long as plant-materials seed stocks are grown in areas with similar photo-periods and a minimal-length growing season, there should not be genetic shifts in the populations during seed production.”
Booth and Vogel, 2006, concluded that the lack of availability of locally harvested native seed, and the cost of attaining that seed, makes reliance on locally-sourced native seed often not feasible. And they make the case for the use of native plant cultivars that can be produced much more economically, and that may potentially result in increased genetic diversity and increased adaptability. Because these cultivars are often planted in settings where on-going monitoring occurs, it is possible to pay attention to undue consequences over time. “Monitored projects, seeded with cultivars and other certified seed sources, have been generally successful and approved because they have restored fundamental ecosystem processes and because no calamitous consequences of using non-local seed have been observed in or around the projects.” They state that, “Revegetation is about performance in the face of challenging environmental conditions and highly competitive invasive weeds. Common-sense budgetary constraints and concern for fundamental ecological processes – including genetic mixing and sorting – and invasive-weed exclusion should be the priority for revegetation considerations.”
In summary, I share the concerns expressed by Massatti, et al., 2017, but also recognize the challenges Booth and Vogel point out, that make it often not feasible to use only local genotypes of native plants in habitat restoration. Given the rapidity with which habitat destruction is occurring, along with the speed at which climate change is occurring, I suspect we will never have an ideal solution.
In her book Braiding Sweetgrass, Dr. Robin Wall Kimmerer, a plant ecologist and a tribal member of the Citizen Potawatomi Nation, provides a different perspective on ecological restoration, using the example of the heavily polluted Onondaga Lake, in New York.
“We may not be able to restore the Onondaga watershed to its pre-industrial condition. The land, plants, animals, and their allies among the human people are making small steps, but ultimately it is the earth that will restore the structure and function, the ecosystem services. We might debate the authenticity of the desired reference ecosystem, but she will decide. We're not in control. What we are in control of is our relationship to the earth. Nature herself is a moving target, especially in an era of rapid climate change. Species composition may change, but relationship endures. It is the most authentic facet of the restoration. Here is where our most challenging and most rewarding work lies, in restoring a relationship of respect, responsibility, and reciprocity. And love” (Kimmerer, 2013, p. 336).
Also refer to the section Rangeland Restoration, for further details on sagebrush steppe ecosystems which extend beyond the Great Basin region, and for further information on revegetation within highway rights-of-way.
References:
Next Sections:
Native plants: Their role in ecosystems and in the restoration of damaged lands
Summaries of the research and commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, June, 2020.
The Federal Native Plant Conservation Committee defined a native plant as a species “that occurs naturally in a particular habitat, ecosystem, or region… without direct or indirect human actions” (1994 Memorandum of Understanding that formed the Federal Native Plant Conservation Committee, whose work is continued under the Plant Conservation Alliance (PCA), a public-private partnership between 15 Federal Agencies and 400+ non-Federal cooperators, funded through the BLM). The PCA works “collaboratively to solve the problems of native plant conservation and native habitat restoration, ensuring the sustainability of our ecosystems.”
The Plant Conservation Alliance has developed a National Seed Strategy: “a public-private collaboration to increase the supply of native seeds for restoration projects to ensure ecosystem resilience and the health and prosperity of future generations.”
Ecosystems are based on native plants. Native plants provide nectar and pollen for butterflies, birds, for native and introduced bees, and for some species of bats. Bees, butterflies, birds, and bats facilitate the growth of native plants, agricultural crops, and landscaping plants by carrying pollen from plant to plant. Bird and bats also promote the growth of native and agricultural plant species by consuming many insects. In addition to the important agricultural pollination and honey-producing services provided by the introduced honey bee species, the thousands of native bee species pollinate native and agricultural and landscaping crops. And a number of tropical fruits rely on pollination by bats. Wildlife utilize native plants throughout the year. Plant seeds and fruits provide food for birds and bats. Plant leaves provide food for a wide variety of insects. Native plants provide shelter and nesting habitats for birds. Insects, in turn, provide food for birds and other wildlife. Birds and bats eat many different species of insects, and are extremely important in controlling many of the insects that impact agricultural crops, saving farmers billions of dollars annually in insect pest control costs. And, of course, plants provide oxygen for us all to use.
And, not to be forgotten, we must remember that plants provide great beauty. In the research I cite in the section, Invasive Success Hypotheses, the role and the importance of plant diversity is described. But one aspect that is not mentioned in the scientific research is that plant diversity, like human diversity, provides us with an awe-inspiring world of beauty.
Farmers that promote the growth of natural ecosystems near their agricultural lands increase the numbers of both introduced honey bees and native bees available to pollinate their crops.
In the drought-prone regions of the Western States, many native plant species are well adapted to growing under conditions of drought. Local native plants are adapted to local climate and soils. When attempting to re-establish native plants in a disturbed site, it is often necessary to irrigate the area in the first season. Once re-established, native plants require little or no irrigation or fertilization. Once drought-tolerant native plants are established, they will maintain themselves. In addition, once established, native plants typically do not require the use of pesticides or herbicides. However, refer to the sections on Climate Change for some concerns regarding what could potentially happen as local climates change, and local native plants potentially become less well adapted to local conditions.
I grew up in a household where my mother imparted to me her love of plants, both native and non-native. And, since I lived in Texas for many of my formative years, I had become accustomed to a State Highway Department that promoted landscaping and maintenance of highway rights-of-way using native plants.
Soon after its formation in 1917, Texas Highway Department staff noticed that native wildflowers were often the first plants to regrow in disturbed sections of the highways. The Department implemented policies to promote growing native plants along Texas roadsides. These policies remain in place today, and have turned Texas roadways into popular tourist attractions. Many visitors from both in-state and out-of-state travel along the Texas roadsides in the Spring, to view the large displays of beautiful native wildflowers.
When the Texas Department of Transportation started growing native plants along highways, they quickly discovered that native plants and seeds were in short supply. The policies of the Texas DOT eventually spawned a new agri-business. Landscapers and plant growers began raising native plants, both for landscaping and for seed. Today, the Texas DOT buys and plants 30,000 wildflower seeds each year. They also plant native grasses, forbs, and shrubs. The TxDOT has developed highway maintenance procedures that encourage native wildflowers and grasses to naturally re-seed, where feasible. Those procedures are detailed below.
As First Lady, Lady Bird Johnson, the wife of President Lyndon Baines Johnson, initiated a project to beautify Washington, D.C., by having millions of flowers planted. She is quoted as saying, “Where flowers bloom, so does hope.” She was also instrumental in facilitating the passage of Federal legislation, the Highway Beautification Act (HBA) of 1965 (nicknamed “Lady Bird’s Bill”), which limited the placement of advertising billboards along the Federal Interstate Highway system, and required the removal of junkyards from view of the highways, and encouraged scenic enhancement of Federal highways. I remember this change when I was a child, because prior to the implementation of that Federal law, thousands of giant billboards obstructed the travelers’ views of the beautiful country in which we live. The HBA has always been controversial because it limits advertising by local businesses, already disadvantaged by the placement of the newly expanding Federal Highways, which tend to route travelers away from rural towns. The law has been amended numerous times, and, although the HBA is essentially still in effect, the amendments allow more billboard advertising near places of business.
Thanks to the nationwide beautification projects inspired by First Lady, Lady Bird Johnson, many communities were inspired to landscape public lands with beautiful flowers. Lady Bird, upon returning to Texas after Johnson’s term as President ended, inspired many Texas communities to landscape public spaces, and she provided grants to assist communities in doing so, with a focus on Texas native plants, especially wildflowers.
In 1982, Lady Bird Johnson and actress Helen Hayes worked together to establish the Lady Bird Johnson Wildflower Center, now part of the University of Texas, in Austin, Texas. Lady Bird donated the land for the original site of the Center. In the 1980s, I conducted several workshops for teachers at the Center, to educate teachers on Texas native plants. The Center was eventually moved and expanded to a larger piece of land and renamed The Lady Bird Johnson Wildflower Center, a center focused on native plant conservation, sustainable landscapes, and research on native plants, and which hosts an extensive online native plants database. It is now also the Botanic Garden of Texas. The Center has also created the Texas Seed Bank, where seeds from native Texas plants are collected and stored, for research projects.
By the time I moved away from Texas in 1990, I was so accustomed to seeing native plants along public roadways, that I was quite shocked to realize that planting native species along roadways was not common in other States.
If you review the laws of the Western States related to control of invasive plant species [Refer to the section State Laws], you will find that half of them do not prohibit naming native plants as “noxious weeds.” And State laws typically do not mention re-seeding infested lands with native plants, as part of Integrated Vegetation Management (IVM), probably because the initial laws related only to noxious weeds growing within farmland. Some States have figured out that growing local native plants can be an important agricultural business. But many States do not yet effectively utilize and promote landscaping and roadside planting with native plants, often due to the lack of availability of inexpensive native plants and seeds, native to the State and the region of the State, where the plants and seeds are needed.
Refer to the section Why We Need Plants for detailed information of the role of plants in the maintenance of life on Earth. For additional valuable information about the importance of native plants within ecosystems, refer to the 2019 UN Global Assessment Report on Biodiversity and Ecosystem Services .
I have been surprised at the lack of emphasis on planting native seed and native plants in some States, after removal of weeds with herbicides or biocontrol. There are many sites where either herbicides or biocontrol agents have reduced one species of invasive plant within an area, and then within a year or two, that area is re-infested with the same or a different invasive species. Unless a plan is in place to revegetate the area after treatment, we appear to be wasting our resources and perpetuating the problem.
Many of the interviews included here, show that weed management remains identified with herbicide use, despite the rapidly emerging problems of herbicide-resistance and health concerns due to decades of overuse of herbicides [Refer to the sections on Herbicides for details]. My interviews with individuals who have worked in the field of Weed Management for decades, have provided me with some insights into this issue.
In the not-too-distant past, and in some cases still today, a number of native plant species have been treated as weeds, and have been subjected to eradication attempts. A number of States still allow native plant species to be included on the State list of invasive species, often due to toxicities in some plant species that can result in livestock losses [Refer to the section State Laws].
Here are a few examples of native plants that have been treated as weeds and thus targeted for reduction or eradication:
- Gambel oak (Engle & Bonham, 1980)
- Huisache and mesquite (Bovey, et al., 1990)
- Yaupon (Bovey, et al., 1990)
- Currants
- Rocky Mountain juniper
In my 2017 interview with Phil Westra, Weed Scientist at Colorado State University, he told me, “Colorado has a suite of warm and cool season native grasses that are used in re-seeding projects. But the seed is expensive – about $200 per acre.”
In my interview with Dr. George Beck, Weed Scientist at Colorado State University, he stated that, “The US Natural Resources Conservation Service [NRCS; formerly the US Soil Conservation Service] has demonstrated that native plants will endure longer than non-natives.
“In Colorado, we have state-level Conservation Districts. These are the longest-standing fighters of weeds. They are loosely connected to the NRCS and the USDA.
“We initially focused on re-seeding native grass species. We are starting to realize that we also need native forbs and shrubs in our re-seeding projects, particularly because these native species attract pollinators and other insects that provide a crucial food source for birds, such as quail and grouse.”
George Beck told me, “Invasive species are the biggest problem in the western US. In Colorado now there is tremendous importance being placed on re-planting with native species. Almost all re-seeding now is with natives. Except where the soil is so bad, in which case we might plant a non-native brome grass for grazing.”
George went on to say, “Colorado weed law states that native plant species cannot be designated as noxious weeds. We had a lot of pressure from farmers and ranchers to add some native species to the noxious weed list. We worked with the Sierra Club, who helped get into law the fact that only non-natives should be designated as noxious weeds. A local community can remove natives on local lands, but they cannot force their neighbors to do so on their lands.”
Sheley, Svejcar, and Maxwell, 1996, proposed “a theoretical framework for developing successional weed management strategies on rangeland.” They point out that, up to that point, weed management strategies had focused on “simply controlling weeds, with limited regard to the existing or resulting plant community.” They proposed that the objective of weed management “could be to develop a healthy plant community that is relatively weed-resistant, while meeting land-use objectives, such as forage production, wildlife habitat development, or recreational land maintenance.” They go on to propose that, “A healthy, weed-resistant plant community consists of a diverse group of species which occupy most of the niches…. Weed-resistant plant communities effectively use resources over time and space.” And they state that, “Ecologically-based weed management requires that scientists and managers develop strategies that are based on our current understanding of succession…. Ultimately, the goal is to direct weed infested communities on a trajectory toward more desirable plant communities.” They create a synthesis of previous models of plant succession, to create a model for how to achieve the goal of attaining “desirable plant communities.”
Sheley, Svejcar, and Maxwell, 1996, stated that, “Managing succession requires knowledge of three components corresponding to the three general causes of succession: disturbance, colonization, and species performance…. We can design the disturbance regime and attempt to control colonization and species performance through management. Successional management must be viewed as an ongoing process moving from one successional component to the next or repeating a single component through time. This model is driven by both naturally occurring and human-induced processes.”
Sheley, et al., 1996, describe the three successional components:
Component one: “Designed disturbance. Disturbance plays a central role in initiating and altering successional pathways… Natural disturbances, such as landslides, fire, and severe climatic conditions initiate, retard, or accelerate succession, or alter successional pathways…. Weed management strategies have included designed disturbance, such as cultivation, burning, and herbicide application for decades.”
Note from Delena: Unfortunately, in many locations, previous and even current weed management strategies have completed the “designed disturbance” but have ignored the fact that additional steps are needed to achieve a weed-limited setting. Sheley, et al., 1996, point out that, “if roadside disturbance provides a staging area for weed invasion, emphasis could be placed on roadside revegetation with competitive native perennial species.”
Sheley, etal., 1996, component two:
“Controlled colonization… is the intentional alteration of availability and establishment of various plant species… Controlled colonization efforts are directed toward influencing seed banks, propagule pools, and regulation of safe sites for germination and establishment of desirable species. Weed seed banks can be depleted through attrition if seed production is prevented or significantly reduced.”
Some research has shown that livestock grazing can be effective in reducing some weed seed banks (Olson, et al, 1997; Olson, et al, 1998), but caution that grazing can also reduce desired species. Biocontrol agents also help reduce weed seed banks.
However, controlled colonization also means encouraging the growth of, and the seed bank of, the desired species. Too often, this step is ignored. Sheley, et al., 1996, propose that livestock can also be used to assist in revegetation with desired species by adding native plant seed to the hay. They also propose that, in some cases, such as when soil is so depleted of nutrients that native perennials are difficult to establish, planting a less desirable but ephemeral/annual species can enhance the soil, making colonization by desired perennial species more feasible.
Note from Delena: Unfortunately, in many locations where controlled colonization is used, e.g., when grazing or biocontrol are used to reduce weeds, the third step in managing the successional process is not incorporated.
Sheley, et al., 1996, component three:
“Controlled species performance… involves manipulating the relative growth and reproduction of plant species in an attempt to shift community dynamics in a desirable direction. Biological and chemical weed control, grazing, plant and plant-part removal, altering resource availability, and competitive plantings are techniques to create differential species performance.” However, they also point out that, “plant communities can be shifted toward desirable species providing propagules are present and establishment occurs.” In other words, native plants must either be already present, or native seed or native propagules must be purposefully planted. Unfortunately, in many cases, the soil is so depleted that native seed or native plants are no longer present, or native perennials may not establish due to lack of soil nutrients. In some cases, the native seed will take too long to germinate and thus will not compete with the weed species.
In some cases, too much nutrients, for example, too much nitrogen in the soil, necessary for early successional annual species, can inhibit the growth of later successional species, which are typically the desired species. McLendon and Redente, 1991, found that, “The addition of nitrogen… altered succession by slowing the rate of succession and allowing annuals to dominate …. Dominance of disturbed nutrient-rich sites by annuals may be a function of two major factors: seed availability and rapid potential growth rate.” [Refer to the chapter “Restoration of prairies, steppes, and deserts” for a more detailed account of their research.]
Herron, Sheley, Maxwell, and Jacobsen, 2001, tested the hypothesis that “succession from a weedy plant community toward a desired late-seral [native] plant community could be accelerated by altering nutrient availability.” Herron, et al., 2001, believe that “bluebunch wheatgrass has a lower N requirement than spotted knapweed, and, therefore, has the ability to out-compete spotted knapweed at lower N levels…. Our study provides initial evidence supporting the theory that nutrient levels can be altered to accelerate successional change from a weedy plant community toward a desired plant community. Ephemeral cover crops or mid-seral species could be used in restoration projects to lower N availability. Lower N availability could accelerate the establishment and domination of late-seral species over earlier successional weedy species.”
George Beck introduced me to the work by Sheley, et al. He told me, “Around 1996, Dr. Roger Sheley and Bruce Maxwell, at Montana State University, published a synthesis paper on successional weed management practices. This concept transformed how we thought about weed management (Sheley, Svejcar, & Maxwell, 1996). It is based on:
1 – site availability
2 – differential species diversity, and
3 – differential species performance.”
George said, “As a result of this paper, many more agencies became interested, as well as many more private landowners. We need diversity in the land. At any moment, certain plant species are being favored by the environment and other plant species are not. For example, some plants are more drought tolerant than others, and some are more tolerant of storms. Different plant species flower and seed at different times of the year. Different plant species provide forage for insects, birds, mammals, etc., at different times of the year. A successional system includes all these diverse elements.
“In successional weed management, you incorporate the following:
1 – designed disturbance
2 – controlled colonization
3 – controlled species performance
“An example I have used in my CSU classes is from my own land, an example on a small acreage: I bought a home that includes an old wheat field. It had lots of weeds initially. Here’s what I did on the land:
1 – I used Roundup (glyphosate) to kill field bindweed. And I used an aerator to pull plugs out of the field. This was my designed disturbance.
2 – I broadcast native grass seed. This was my controlled colonization.
3 – I watered the seed, to better control species performance.
“This process worked well on my small acreage.
“We need a variety of native grasses in rangeland. Some are more drought tolerant than others. Competition is the most important component of getting rid of weeds – but it is not sufficient. For example, if I simply broadcast native seed across a field infested with Canada thistle, I get nothing. But if I treat the field with herbicide, I’ll get a period of time with reduced Canada thistle. That’s when I can plant the native grasses.
“In my opinion, by using these techniques, we can diffuse most of the concerns about the use of herbicides or biocontrols, by minimizing how much herbicides we use. Once the native species are back in the system, we don’t have to continue using herbicides.”
Of course, one of the limitations of relying on plant succession in weed management is dealing with the possibility of another unplanned disturbance, which presents the possibility of having to start the whole process over. However, if a seed bank of native species remains in the soil after the disturbance event, it may be easier to re-establish diverse perennial native species.
Harris, 1967, reviewed decades of research and reports on the reduction of the native perennial, bluebunch wheatgrass, and the subsequent spread of the introduced annual, cheatgrass, in Western States. Bluebunch wheatgrass previously was the dominant plant species in the intermountain region of the Western US and Canada. Heavy livestock grazing in Eastern Washington facilitated the spread of cheatgrass as early as the 1930s. Cheatgrass also spread in abandoned fields and repeatedly burned areas. Harris, 1967, demonstrated that, although both species germinate in the fall, cheatgrass has faster and deeper winter root growth, which allows it to dominate in the spring. Cheatgrass completes seeding and begins to die back by late May. Harris demonstrated that cheatgrass preempts resources from perennial bluebunch wheatgrass, by reducing soil moisture before wheatgrass begins its main period of growth in late April.
Carpinelli, Sheley, and Maxwell, 2004, point out that, “During the early stages of secondary succession (e.g., revegetation), availability of light, water, and nutrients may be particularly high relative to the demand by a sparse community of establishing plants. In this case, resource preemption may be more important than competition in determining community dynamics. Those plants with the highest growth rates have the highest likelihood of establishing… Knowledge of the initial growth rate of a species may be the best predictor of the short-term outcome of a revegetation effort.” However, in an experiment they conducted to test this hypothesis, they grew three non-native perennial forage species often used in revegetation projects (crested wheatgrass, intermediate wheatgrass, and alfalfa), and spotted knapweed, a perennial non-native invasive. Both forage grasses have a higher growth rate than either alfalfa or knapweed. Carpinelli, et al., 2004, assumed that because the forage plants occupied different niches, they would jointly dominate all available niches, and thus outcompete the knapweed. Contrary to the predicted results, the increased species richness created by the three forage species did not create an environment limiting to the growth of knapweed. In this experiment, all four species were planted simultaneously. Thus, the sites did not start out with an established species richness, which has been shown to limit weed growth. Carpinelli, et al., 2004, think that “spotted knapweed was able to preempt resources from desirable species in the second growing season, or that spotted knapweed was able to outcompete the desirable species regardless of the degree of niche occupation by desirable species.” Refer to the chapter, “Invasive Species Success Hypotheses” for a discussion of the research by Adler, et al., 2010, on “niche differences,” which challenges the assumption that all the niches in an ecosystem are already filled by the native plant community, before the invasive species enters the scene.
An additional issue to consider is the possibility that revegetation with non-native species, regardless of their desirability as forage, does not simulate the natural ecosystem that existed prior to the disturbance that either removed or reduced the native species in the environment. Thus, this type of revegetation may take more inputs to achieve a successful outcome.
From my interview with Slade Franklin, Weed and Pest Coordinator for the Wyoming Department of Agriculture: “In my job, I focus on removal of invasive species, but not on re-planting. The Wyoming DOT does the re-planting. Sometimes, we don’t have to re-plant, because native perennial bunch grasses have come back in. For example, in some of the early treatments for medusahead and Ventenata in north central Wyoming, we saw the re-emergence of native perennials after the treatment of the non-native annual grasses. In some places in the state, such as the Red Desert in southcentral Wyoming, the natural state of the landscape includes quite a bit of bare ground, so you have to think about how much native seed planting to include.
“The range management teams from the BLM and the USFS do the re-planting on federal lands. There are a number of grass seed nurseries in Wyoming that provide native seed for re-planting.”
However, having different agencies in charge of different aspects of the treatment of damaged lands can result in a disjointed process, with significant time delays between removal and re-seeding.
In the 2013 interview Lars Baker [retired Fremont County, Wyoming, Weed and Pest Supervisor] had with Becky McMillen, Lars explained, “We have removed nutrients from the soil, over the decades of farming and ranching. So now much of our land is poor for farming.
“Weeds are the direct result of how humans have disturbed the land. Native sagebrush range developed over thousands of years. Now that we have disturbed it, we cannot restore it simply by stopping irrigation. The problems we have today with cheatgrass are due to the fact that we have caused so much destruction to the ecological systems.
“Wyoming tried to grow dry-land wheat, but there is not enough rainfall for this to be successful. It failed. So now when we plant native grass seed, they often will not grow, because there is no longer enough rainfall.
“Booth, D.T., & Vogel, 2006, conducted research and found that native plants today are becoming maladapted to current environmental conditions, due to climate change.”
In a 2018 visit to the NRCS Laramie County Field Office, Cheyenne, Wyoming, I interviewed Jim Cochran, District Manager, and Jim Pike, District Conservationist. Here are some notes on the use of native seed in Wyoming, from that interview.
Jim Pike: “We will provide funds for native plant seed if asked by the landowners. However, landowners are often reluctant to use native plants because they take longer to establish. On state-owned lands we will use more native seed. Landowners prefer non-native grasses.
“Native legume seeds are too expensive, about $100 an acre. So we don’t use the natives as much as we could. On cropland we use a mix of natives and non-natives that seems to be working well….”
Jim Pike: “It is challenging to have success with native seed when the cropland has been degraded to such a low level of organic matter. It has been my observation that you need about 3% organic matter in the soil for the soil to be productive. This is not something that we have research on, but it’s been my observation. Most farms around here are now at about 1% organic matter.
“There is enough native seed available. There are more companies producing seed, but it is still too expensive. In mining reclamation projects, they can afford the expensive seed, but there is not as much money available for restoring agricultural land.”
Jim Cochran: “We’re seeing more homeowners who want native lawns, using buffalo grass and blue gramma. About ten years ago, the County Conservation Districts put an emphasis on re-seeding degraded lands.”
Jim Pike: “I’ve been doing a mix of about 30% sainfoin [a non-native perennial legume that is excellent for nitrogen fixation and does not cause bloat in livestock]; 30% intermediate and pubescent wheatgrass [non-native grasses]; some Western and thickspike wheatgrass [native grasses]; orchardgrass [non-native]; and 10 to 15% slender wheatgrass [native grass]. Slender establishes quickly. The native grasses hold their own. The non-natives do not seem to out-compete them…. Natives do not do as well on irrigated lands due to diseases promoted by the water.
“The research says that planting natives with non-natives is not a good idea because the non-natives will out-compete the natives. But I’m having good success with this mix of natives and non-natives.”
Rights-of-way provide important sites for revegetation with native plants
A helpful guide on the value of revegetating highway rights-of-way with native plants is Roadside use of native plants (2000), edited by Bonnie Harper-Lore and Maggie Wilson.
Texas DOT procedures for promotion of native plants along Texas roadsides
Because the Texas DOT procedures for maintaining roadways may be helpful to other States, I include extensive excerpts from Texas Department of Transportation’s Roadside Vegetation Management Manual (revised May 2018). The Manual highlights the importance the State places on the promotion of native vegetation in Texas, and provides information on the importance of native plants. The full Manual is available on the Texas DOT website at http://onlinemanuals.txdot.gov/manuals/AlphaList.html#l_R
Which native plants should we use in revegetation projects?
Those State, County, and Federal Agencies that are attempting to utilize native plants and native seed in their revegetation programs have had to deal with a serious question. “Native plants” differ, not only from State to State, but from region to region within each State. So the question becomes, which native plants should we use to replenish the plant populations on abused lands? Should we only use native plants and seeds from the plants locally native to the specific State and the specific region of that State, that we are attempting to revegetate? And, must we only use seed grown from wild plants, or can we use seed developed from cultivars of native plants?
Research projects conducted by the Great Basin Native Plant Project examine the potential impact of climate change on plant species native to the Great Basin. On the Project website, the Annual Progress Reports describe the findings of these research projects. The research supports the importance of genetic variability as the best option for surviving climate changes. On page 1 of the 2017 Progress Report, the researchers state: “Given the speed and severity with which natural communities are being altered by anthropogenic factors, the application of an evolutionary perspective to restoration ecology is more important than ever. Adjusting seed-selection priorities to account for the existence of locally adapted, intraspecific variation in the Great Basin will promote the maintenance and recovery of resilient, self-sustaining vegetation communities in this region.”
Some of the research conducted by the Great Basin Native Plant Project points to the potential problems when using commercial native plant seed (cultivars) that does not have the degree of genetic variability found in wild plant populations. Massatti, et al, 2017, state: “Recent research has focused on ensuring that native plant materials are ‘appropriate’ for restoration sites... From a genetic perspective, appropriate native plant materials are those that avoid, or mitigate, risks associated with the mixing of local and nonlocal genotypes... For example, nonlocal genotypes may not be adapted to the local environment at a restoration site and therefore have lower fitness... In addition, nonlocal genotypes are increasingly being implicated in negatively impacting local plant and animal species... Furthermore, the intraspecific hybridization of local and nonlocal genotypes could result in outbreeding depression due to the introgression of maladapted genes or hybrid breakdown…, or nonlocal genotypes may prove to be better adapted to local ones and become invasive... Regardless of the potential intraspecific or interspecific impacts resulting from using nonlocal genotypes in restoration treatments, genetic diversity has been recognized as a unit of conservation concern…, suggesting the maintenance of geographic patterns of genetic variation by avoiding the mixture of local and nonlocal genotypes should be an implicit restoration goal... Therefore, gathering information on the genetics of native plants important to restoration is imperative for making the appropriate seed sourcing decisions for ecosystem restoration” (pages 54-63 of the 2017 Annual Report).
Cultivars, or “cultivated varieties,” are plants that have been selected for their desirable characteristics, and then bred to maintain/enhance those advantageous qualities. Many, many cultivars have been developed from many species of ornamental and crop-plants. But cultivars can also be developed from wild, native plant species.
Booth and Vogel, 2006, have attempted to address questions of concern regarding the use of native plant cultivars in restoration projects. Their results challenge the recommendations from Massatti, et al. Booth and Vogel summarize their question as follows: “Controversy exists over the seed source to be preferred and the intended outcome of revegetation projects. We have agreement that disturbed sites need to be stabilized, erosion minimized, and basic ecosystem processes maintained, but disagreement on the extent that revegetation should exactly reproduce the predisturbance plant community and within-species genetic composition. It is a question of priorities. Should preferential use of local plant materials be advocated as the best method to preserve genetic composition, or should available cultivars of native species, and other source identified materials, be employed as the most expedient means for timely soil stabilization and long-term ecosystem-process restoration?”
Booth and Vogel, 2006, found that research had been conducted on very few native plant species and their cultivars, and thus the knowledge base is lacking to definitively answer this question. “One of the basic assumptions for using local ecotypes in revegetation is that they are best adapted to the climate and site of the area…. Since rangeland revegetation projects are expected to produce indefinitely sustainable plant populations, a preference for local ecotypes implies an assumption that the current climate will also continue indefinitely into the future.” They point out the problems with that assumption, by referencing the “evidence that at least 20 glacial-interglacial cycles have influenced the floristic regions of North America.” In addition, movements and food producing practices of Native American populations over the past 12,000 years have influenced North American vegetation patterns, as Native Americans have harvested and eventually farmed many native and introduced plant species.
Booth and Vogel, 2006, point to the rapid changes occurring as a result of global climate change. And they pose the possibility that “composite populations and cultivars with broad genetic bases” are perhaps more likely to adapt to the climatic changes of future centuries, than are local ecotypes. They remind us that, “Genetic diversity, both within and among species, is the foundation of sustainable populations.” They list research that has demonstrated that local plant populations may have reduced population fitness over time, due to inbreeding, and thus, a reduction in the local gene pool, and thus reduction in genetic diversity. They further point out that cultivar development projects, such as those conducted during the droughts of the 1930s and the recent Soil Bank and Conservation Reserve Programs, have focused on developing cultivars by collecting wild plant materials from broad geographic areas, thus broadening the gene pool for each species, then testing them at multiple sites, and selecting the best adapted individuals. These carefully selected cultivars can be produced in commercial seed fields, thus greatly reducing the cost, compared to locally harvested seed from wild stands.
Recent research has verified that cultivars can maintain significant genetic diversity over fairly long periods of time, as a number of native plant cultivars have been used extensively for over 50 years in the Great Plains and Intermountain West, where millions of acres were planted using cultivars. However, Booth and Vogel, 2006, point out that very little research has as yet been conducted, using DNA markers, to examine whether the use of cultivars has had a negative impact or a positive impact on the genetic diversity of local native plant populations. There has also been concern, but little research to test the question, whether native plant cultivars are able to out-compete local native plant populations. However, there is abundant evidence that the use of these native plant cultivars has had “immeasurable benefit to soil and water conservation, forage production, and wildlife habitat.”
As an alternative to using cultivars, when using locally harvested seed, Stutz (1982) advocated using a mix of seed sources to increase the genetic diversity at the revegetation site. The greater the genetic diversity, the greater the likelihood that some parts of the population will survive changes to the locality, such as the changes wrought by climate change.
Booth and Vogel, 2006, cite research that “the adaptation areas of many native plant cultivars are very extensive,” and that they are able to grow and thrive in multiple Hardiness Zones, thus giving these cultivars a decent shot at surviving future climatic shifts. Vogel and others have developed Plant Adaptation Regions (PARs), for use in classifying plant cultivars, not just based on the USDA Plant Hardiness Zones in which they can grow, but also on their ability to grow in a variety of geographic regions, which can then predict their adaptability for surviving climatic shifts. Much more of this research is needed. They claim that, “As long as plant-materials seed stocks are grown in areas with similar photo-periods and a minimal-length growing season, there should not be genetic shifts in the populations during seed production.”
Booth and Vogel, 2006, concluded that the lack of availability of locally harvested native seed, and the cost of attaining that seed, makes reliance on locally-sourced native seed often not feasible. And they make the case for the use of native plant cultivars that can be produced much more economically, and that may potentially result in increased genetic diversity and increased adaptability. Because these cultivars are often planted in settings where on-going monitoring occurs, it is possible to pay attention to undue consequences over time. “Monitored projects, seeded with cultivars and other certified seed sources, have been generally successful and approved because they have restored fundamental ecosystem processes and because no calamitous consequences of using non-local seed have been observed in or around the projects.” They state that, “Revegetation is about performance in the face of challenging environmental conditions and highly competitive invasive weeds. Common-sense budgetary constraints and concern for fundamental ecological processes – including genetic mixing and sorting – and invasive-weed exclusion should be the priority for revegetation considerations.”
In summary, I share the concerns expressed by Massatti, et al., 2017, but also recognize the challenges Booth and Vogel point out, that make it often not feasible to use only local genotypes of native plants in habitat restoration. Given the rapidity with which habitat destruction is occurring, along with the speed at which climate change is occurring, I suspect we will never have an ideal solution.
In her book Braiding Sweetgrass, Dr. Robin Wall Kimmerer, a plant ecologist and a tribal member of the Citizen Potawatomi Nation, provides a different perspective on ecological restoration, using the example of the heavily polluted Onondaga Lake, in New York.
“We may not be able to restore the Onondaga watershed to its pre-industrial condition. The land, plants, animals, and their allies among the human people are making small steps, but ultimately it is the earth that will restore the structure and function, the ecosystem services. We might debate the authenticity of the desired reference ecosystem, but she will decide. We're not in control. What we are in control of is our relationship to the earth. Nature herself is a moving target, especially in an era of rapid climate change. Species composition may change, but relationship endures. It is the most authentic facet of the restoration. Here is where our most challenging and most rewarding work lies, in restoring a relationship of respect, responsibility, and reciprocity. And love” (Kimmerer, 2013, p. 336).
Also refer to the section Rangeland Restoration, for further details on sagebrush steppe ecosystems which extend beyond the Great Basin region, and for further information on revegetation within highway rights-of-way.
References:
- Booth, D.T., & Vogel, K.P. (Oct., 2006). Revegetation priorities. Rangelands, 28 (5): 24-30.
- Bovey, R.W., Meyer, R.E., & Whisenant, S.G. (1990). Effect of simulated rainfall on herbicide performance in Huisache (Acacia farnesiana) and Honey Mesquite (Prosopis glandulosa). Weed Technology, 4:26-30.
- Carpinelli, M.F., Sheley, R.L., & Maxwell, B.D. (Jan., 2004). Revegetating weed-infested rangeland with niche-differentiated desirable species. Journal of Range Management, 57: 97-105.
- Engle, D.M., & Bonham, C.D. (Sep., 1980). Nonstructural carbohydrates in roots of Gambel Oak sprouts following herbicide treatment. Journal of Range Management, 33 (5): 390-394.
- Harper-Lore, B., & Wilson M. (2000). Roadside use of native plants. Washington D.C.: Island Press. Originally published by the US Department of Transportation.
- Harris, G.A. (1967). Some competitive relationships between Agropyron spicatum and Bromus tectorum. Ecological Monographs, 37: 89-111.
- Herron, G.J., Sheley, R.L., Maxwell, B.D., & Jacobsen, J.S. (Sept, 2001). Influence of nutrient availability on the interaction between spotted knapweed and bluebunch wheatgrass. Restoration Ecology, 9 (3): 326-331.
- Massatti, R., Prendeville, H., Larson, S., Richardson, B., Waldron, B., & Kilkenny, F. (2017). Population Genetics of Bluebunch Wheatgrass (Pseudoroegneria spicata), in Great Basin Native Plant Project, 2017 Progress Report, pages 54-63. USDA Rocky Mountain Research Station & USDI BLM, Boise ID.
- Sheley, R.L., Svejcar, T.J., & Maxwell, B.D. (Oct.-Dec., 1996). A theoretical framework for developing successional weed management strategies on rangeland. Weed Technology, 10 (4): 766-773.
- Stutz, H. C. 1982. Broad gene pools required for disturbed lands. In: E. F. Aldon, W. R. Oaks [Eds.], Symposium: Reclamation of mined lands in the Southwest. Albuquerque, NM: Soil Conservation Society of America, New Mexico Chapter. p 113−118.
- Stutz, H. C. 1989. Evolution of shrubs. In: C. M. McKell [Ed.]. The biology and utilization of shrubs. San Diego, CA: Academic Press Inc. p 323−340.
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