Photo: Giane Cane & Salt Cedar along the Rio Grande, Big Bend National Park, Texas. © 2017 Delena Norris-Tull
Why should we be concerned with the damage caused by invasive plant species?
Summary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, July 2020.
Here are some of the reasons provided by various scientists and agencies:
"The fundamental basis of the community is agriculture" (‘Abdu’l-Bahá, The Promulgation of Universal Peace, p. 217).)
“Invasive exotic plants constitute 8 to 47 percent of the total flora of most States in the United States… There are approximately 4,500 exotic species in the United States that have established naturalized populations and at least 15 percent of these cause severe harm” (Sieg, et al, 2010, p. 35).
Dix & Britton, 2010, p. 1, state, “Invasive species significantly impact U.S. ecosystems and are one of the greatest threats to forest, rangeland, and urban forest health. They have contributed to increases in fire frequency and intensity; reduced water resources, forest growth, and timber; and negatively affected native species and their habitats throughout the United States. Global trade, climate change, and innovations in human transportation are just a few of the factors that have increased the rate of invasive species introduction and the costs associated with their prevention, quarantine, and management. Forest and rangeland managers urgently need effective management techniques to reduce invasive species’ effects.”
Some invasive plant species have impacted wildlife and livestock, either directly, such as by poisoning livestock or wildlife, or indirectly, by altering habitats.
For example, salt cedar (Tamarix spp.) and Russian olive (Elaeagnus angustifolia) were both introduced into the US as ornamental trees. Salt cedar has created problems along the Rio Grande, as it’s long taproots have displaced native shrubs and trees along the river, and its high rate of evapotranspiration reduces water availability in the river. Both species “invade moist pastures and rangeland and cause serious forage-production and soil-water losses” (Carman & Brotherson, 1982).
But removal of invasive species, which have often become embedded into native habitats for decades, can cause issues of its own. Salt cedar provides “suitable habitat for the endangered southwestern willow flycatcher… and other avian species that nest in midcanopy vegetation, but poor habitat for many other avian species” (Sheley, et al, 2011).” Sheley, et al., 2011, describe various studies that have shown increases in wildlife when invasive species have been removed, and several cases in which removal methods have had a negative impact on wildlife.
And Nandina domestica, an invasive shrub that has been widely used as an ornamental, has berries that are toxic to humans but also have caused the death of various animals, including domestic dogs and cats, livestock, and wildlife (particularly native birds). The berries contain cyanide, among other toxic chemicals (Cywinski, 2022).
Defining the problem of invasive plants
Wilcove, et al., 1998, reminded us that, “Biologists are nearly unanimous in their belief that humanity is in the process of extirpating a significant portion of the earth’s species.”
According to Wilson, 1992, the manner in which we are doing so falls into four major categories, overexploitation (including hunting and fishing), habitat destruction, the introduction of non-native (alien) species, and the spread of diseases carried by alien species. Wilcove, et al., 1998, add pollution to Wilson’s list. And they expect climate change to be an important factor in the future. Wilcove, et al., 1998, point out that, “In general, scientists agree that habitat destruction is currently the primary lethal agent, followed by the spread of alien species…. However, apart from several notable exceptions – including studies of North American fishes…, endangered plants and animals in the United States…, aquatic organisms,…and imperiled birds… - few quantitative studies of threats to species have been conducted. Much more studies are needed to provide conservationists, land stewards, and decision makers with a better understanding of the relationships between specific human activities and the loss of biodiversity.”
By analyzing the data on human activities that have threatened “1880 (75%) of the 2490 imperiled species, subspecies, and populations,” Wilcove, et al, 1998, “used the resulting database to determine the relative significance of the major threats” to native species. While acknowledging that data on various species was often sparse, they concluded that habitat degradation (affecting 85% of imperiled species) and the introduction of alien species (affecting 49% of imperiled species) account for the vast majority of threats to native species. They found that pollution was the third most prevalent threat (affecting 24% of imperiled species).
Habitat degradation is closely linked to the introduction of alien species. Whenever and wherever natural habitats are altered, non-native species, particularly plants, can be expected to enter the ecosystem, especially if native plant species are not rapidly re-planted in the damaged areas.
Wilcove, et al., 1998, found that siltation (a form of pollution) is a major threat to aquatic organisms. Siltation is closely linked to both habitat degradation and the introduction of alien species. These three major threats to native species (habitat degradation, introduction of alien species, and pollution) are all closely interlinked.
Habitat degradation
Using data from the US EPA on endangered species (including both species currently listed as endangered, and species proposed for listing), Wilcove, et al., 1998, identified 11 major categories of habitat destruction and degradation and examined the extent to which they contribute to plants and animals becoming endangered. For the following activities, they calculated the following: “agriculture (affecting 38% of endangered species), commercial development (35%), water development (30% when agricultural diversion is included),…and infrastructure development (17%)…. Within the category of infrastructure development, roads affect a wide array of species (15% of all endangered species).” Other forms of habitat degradation also have a significant impact on native species: outdoor recreation, especially the use of off-road vehicles, affects 27% of endangered species. Logging (affecting 12% of endangered species), mining (11%), and grazing (22%) also are important contributors to loss of species. “Livestock grazing… is particularly harmful to plants, affecting 33% of endangered plant species compared to 14% of endangered animals.” And they found that “168 species (14%) are threatened by disruption of fire regimens in the ecosystem...Of these, 85 (7%) are threatened by fire suppression and 83 (7%) are threatened by controlled or uncontrolled fires.” The remaining forms of habitat degradation affect the following percentages of endangered species: military activities (4%), dams, impoundments, and other barriers (17%), and pollutants (particularly siltation and nutrient inputs) (20%).
Introduction to the research on invasive species
In 2010, teams of researchers conducted reviews of the research on invasive species, in order to facilitate the development of a twenty-year research agenda for the US Forest Service. This external review included research on the following categories of invasive species: insects, plants, terrestrial animals, aquatic organisms, and invasive soil organisms. This valuable research review was coalesced by teams of Forest Service researchers into 12 visionary papers to “identify future invasive species research issues and priorities and provide the Forest Service and its partners with a framework for programming and budgeting.” Their recommendations were published in the report, A dynamic invasive species research vision: Opportunities and priorities 2009-2029 (Dix & Britton, 2010).
In that document, Britton, et al., 2010, p. 4, state, “Invasive species are defined in Executive Order 13112: ‘Invasive species are those species that are not native to the ecosystem under consideration and whose introduction causes or is likely to cause economic or environmental harm. Invasive species include: plants, animals, fish, insects, diseases, invertebrates, and others.’ The Forest Service [Research and Development] invasive species research program includes research on species that are not native to the United States and those that are native but are advancing to invade other areas due to the increased connectivity of ecosystems and changing environmental conditions. Our research is conducted throughout the continental United States; in the tropical forests of Hawaii, the western Pacific, and Puerto Rico; and internationally. We conduct research at a variety of scales in wilderness, watersheds, old-growth forests, wetlands, aquatic systems, urban interface forests, grasslands, plantations, and utility corridors.”
As a result of the external research review, Forest Service Research and Development teams identified four overarching priorities for future research on invasive species (Britton, et al., 2010, p. 3-4):
I strongly encourage reading the Dix & Britton, 2010, document. I include in these webpages my own summaries of the research on invasive plant species. The external review conducted for the US Forest Service Report is now over ten years old and does not examine a number of the topics I include in these webpages, such as the history of the development of State laws related to invasive species, the history of the use of herbicides, research on herbicides, research on the factors that facilitate biological invasions, the challenges and limitations of biocontrol agents, and the challenges of rangeland restoration.
References:
Links to next sections:
Why should we be concerned with the damage caused by invasive plant species?
Summary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, July 2020.
Here are some of the reasons provided by various scientists and agencies:
- Some invasive plant species have displaced native plant species in the natural landscape. Approximately 400 of the 958 (42%) native plant species listed as threatened or endangered in the U.S. are impacted by non-native species (Pimentel, Zuniga, & Morrison, 2004). Wilcove, et al, 1998, estimate the percentage higher, at 49%.
- A number of invasive plant species are expanding their ranges at an alarmingly rapid rate.
- Some species, such as cheatgrass, are already facilitating an increase in Western wildfires.
"The fundamental basis of the community is agriculture" (‘Abdu’l-Bahá, The Promulgation of Universal Peace, p. 217).)
“Invasive exotic plants constitute 8 to 47 percent of the total flora of most States in the United States… There are approximately 4,500 exotic species in the United States that have established naturalized populations and at least 15 percent of these cause severe harm” (Sieg, et al, 2010, p. 35).
Dix & Britton, 2010, p. 1, state, “Invasive species significantly impact U.S. ecosystems and are one of the greatest threats to forest, rangeland, and urban forest health. They have contributed to increases in fire frequency and intensity; reduced water resources, forest growth, and timber; and negatively affected native species and their habitats throughout the United States. Global trade, climate change, and innovations in human transportation are just a few of the factors that have increased the rate of invasive species introduction and the costs associated with their prevention, quarantine, and management. Forest and rangeland managers urgently need effective management techniques to reduce invasive species’ effects.”
Some invasive plant species have impacted wildlife and livestock, either directly, such as by poisoning livestock or wildlife, or indirectly, by altering habitats.
For example, salt cedar (Tamarix spp.) and Russian olive (Elaeagnus angustifolia) were both introduced into the US as ornamental trees. Salt cedar has created problems along the Rio Grande, as it’s long taproots have displaced native shrubs and trees along the river, and its high rate of evapotranspiration reduces water availability in the river. Both species “invade moist pastures and rangeland and cause serious forage-production and soil-water losses” (Carman & Brotherson, 1982).
But removal of invasive species, which have often become embedded into native habitats for decades, can cause issues of its own. Salt cedar provides “suitable habitat for the endangered southwestern willow flycatcher… and other avian species that nest in midcanopy vegetation, but poor habitat for many other avian species” (Sheley, et al, 2011).” Sheley, et al., 2011, describe various studies that have shown increases in wildlife when invasive species have been removed, and several cases in which removal methods have had a negative impact on wildlife.
And Nandina domestica, an invasive shrub that has been widely used as an ornamental, has berries that are toxic to humans but also have caused the death of various animals, including domestic dogs and cats, livestock, and wildlife (particularly native birds). The berries contain cyanide, among other toxic chemicals (Cywinski, 2022).
Defining the problem of invasive plants
Wilcove, et al., 1998, reminded us that, “Biologists are nearly unanimous in their belief that humanity is in the process of extirpating a significant portion of the earth’s species.”
According to Wilson, 1992, the manner in which we are doing so falls into four major categories, overexploitation (including hunting and fishing), habitat destruction, the introduction of non-native (alien) species, and the spread of diseases carried by alien species. Wilcove, et al., 1998, add pollution to Wilson’s list. And they expect climate change to be an important factor in the future. Wilcove, et al., 1998, point out that, “In general, scientists agree that habitat destruction is currently the primary lethal agent, followed by the spread of alien species…. However, apart from several notable exceptions – including studies of North American fishes…, endangered plants and animals in the United States…, aquatic organisms,…and imperiled birds… - few quantitative studies of threats to species have been conducted. Much more studies are needed to provide conservationists, land stewards, and decision makers with a better understanding of the relationships between specific human activities and the loss of biodiversity.”
By analyzing the data on human activities that have threatened “1880 (75%) of the 2490 imperiled species, subspecies, and populations,” Wilcove, et al, 1998, “used the resulting database to determine the relative significance of the major threats” to native species. While acknowledging that data on various species was often sparse, they concluded that habitat degradation (affecting 85% of imperiled species) and the introduction of alien species (affecting 49% of imperiled species) account for the vast majority of threats to native species. They found that pollution was the third most prevalent threat (affecting 24% of imperiled species).
Habitat degradation is closely linked to the introduction of alien species. Whenever and wherever natural habitats are altered, non-native species, particularly plants, can be expected to enter the ecosystem, especially if native plant species are not rapidly re-planted in the damaged areas.
Wilcove, et al., 1998, found that siltation (a form of pollution) is a major threat to aquatic organisms. Siltation is closely linked to both habitat degradation and the introduction of alien species. These three major threats to native species (habitat degradation, introduction of alien species, and pollution) are all closely interlinked.
Habitat degradation
Using data from the US EPA on endangered species (including both species currently listed as endangered, and species proposed for listing), Wilcove, et al., 1998, identified 11 major categories of habitat destruction and degradation and examined the extent to which they contribute to plants and animals becoming endangered. For the following activities, they calculated the following: “agriculture (affecting 38% of endangered species), commercial development (35%), water development (30% when agricultural diversion is included),…and infrastructure development (17%)…. Within the category of infrastructure development, roads affect a wide array of species (15% of all endangered species).” Other forms of habitat degradation also have a significant impact on native species: outdoor recreation, especially the use of off-road vehicles, affects 27% of endangered species. Logging (affecting 12% of endangered species), mining (11%), and grazing (22%) also are important contributors to loss of species. “Livestock grazing… is particularly harmful to plants, affecting 33% of endangered plant species compared to 14% of endangered animals.” And they found that “168 species (14%) are threatened by disruption of fire regimens in the ecosystem...Of these, 85 (7%) are threatened by fire suppression and 83 (7%) are threatened by controlled or uncontrolled fires.” The remaining forms of habitat degradation affect the following percentages of endangered species: military activities (4%), dams, impoundments, and other barriers (17%), and pollutants (particularly siltation and nutrient inputs) (20%).
Introduction to the research on invasive species
In 2010, teams of researchers conducted reviews of the research on invasive species, in order to facilitate the development of a twenty-year research agenda for the US Forest Service. This external review included research on the following categories of invasive species: insects, plants, terrestrial animals, aquatic organisms, and invasive soil organisms. This valuable research review was coalesced by teams of Forest Service researchers into 12 visionary papers to “identify future invasive species research issues and priorities and provide the Forest Service and its partners with a framework for programming and budgeting.” Their recommendations were published in the report, A dynamic invasive species research vision: Opportunities and priorities 2009-2029 (Dix & Britton, 2010).
In that document, Britton, et al., 2010, p. 4, state, “Invasive species are defined in Executive Order 13112: ‘Invasive species are those species that are not native to the ecosystem under consideration and whose introduction causes or is likely to cause economic or environmental harm. Invasive species include: plants, animals, fish, insects, diseases, invertebrates, and others.’ The Forest Service [Research and Development] invasive species research program includes research on species that are not native to the United States and those that are native but are advancing to invade other areas due to the increased connectivity of ecosystems and changing environmental conditions. Our research is conducted throughout the continental United States; in the tropical forests of Hawaii, the western Pacific, and Puerto Rico; and internationally. We conduct research at a variety of scales in wilderness, watersheds, old-growth forests, wetlands, aquatic systems, urban interface forests, grasslands, plantations, and utility corridors.”
As a result of the external research review, Forest Service Research and Development teams identified four overarching priorities for future research on invasive species (Britton, et al., 2010, p. 3-4):
- “Quantify Invasive Species Biology, Ecology, Interactions, and Effects
- Predicting and Prioritizing Invasive Species
- Identifying and Detecting Invasive Species
- Managing Invasive Species and Altered Systems”
I strongly encourage reading the Dix & Britton, 2010, document. I include in these webpages my own summaries of the research on invasive plant species. The external review conducted for the US Forest Service Report is now over ten years old and does not examine a number of the topics I include in these webpages, such as the history of the development of State laws related to invasive species, the history of the use of herbicides, research on herbicides, research on the factors that facilitate biological invasions, the challenges and limitations of biocontrol agents, and the challenges of rangeland restoration.
References:
- Britton, et al. (May, 2010). Invasive species overarching priorities to 2029. In M.E. Dix & K. Britton (Eds.), A dynamic invasive species research vision: Opportunities and priorities 2009-2029. Washington, D.C.: USDA Forest Service.
- Carman, J.G., & Brotherson, J.D. (July 1982). Comparisons of Sites Infested and Not Infested with Saltcedar (Tamarix pentandra) and Russian Olive (Elaeagnus angustifolia). Weed Science, 30(4): 360-364.
- Cywinski, R. (Winter 2022). What’s so dangerous about invasive species: Nandina domestica? Texas Native Plants 40(1): 14-15. Fredericksburg, TX: Native Plant Society of Texas.
- Dix, M.E., & Britton, K. (Eds.). (May, 2010). A dynamic invasive species research vision: Opportunities and priorities 2009-2029. Washington, D.C.: USDA Forest Service.
- Merritt, W.J. (2002). A special regard for agriculture. Knoxville, Tennessee: Stonehaven Press.
- Pimental, D., Zuniga, R. & Morrison, D. (December, 2004). Update on the environmental and economic costs associated with alien-invasive species in the United States. Ecological Economics: 52 (2005), 273– 288.
- Sheley, R.L., James, J.J., Rinella, M. J., Blumenthal, D., & DiTomaso, J.M. (2011). Invasive plant management on anticipated conservation benefits: A scientific assessment. In D.D. Briske (Ed.) Conservation benefits of rangeland practices: Assessment, recommendation, and knowledge gaps (pp. 293-336). USDA Natural Resources Conservation Service.
- Sieg, C.H., et al. (May, 2010). The role of the Forest Service in nonnative invasive plant research. In M.E. Dix & K. Britton (Eds.), A dynamic invasive species research vision: Opportunities and priorities 2009-2029. Washington, D.C.: USDA Forest Service.
- Wilcove, D.S., Rothstein, D., Dubow, J., Phillips, A., & Losos, E. (1998). Quantifying threats to imperiled species in the United States. BioScience, 48: 607-615.
- Wilson, E.O. (1992). The Diversity of Life. Cambridge, MA: Belknap Press.
Links to next sections: