Photo: Columbia River, Sagebrush habitat, Washington. © 2017 Delena Norris-Tull
Species Richness: Its role in maintaining plant diversity
Summaries of the research and commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, July 2020.
Sun, Müller-Scharer, Maron, and Schaffner (2015), followed up on previous work, including the work conducted by Maron and Marler (2007, 2008).
Sun, et al., 2015, further examined the impact of plant diversity on the reduction of expansion of invasive species. They combined experimental data with observational field data. They created 42 mixed-species plots of native perennial plant groupings of grasses and perennials, in a grassland in Switzerland. Plant groups ranged from two to 16 species, and represented natural plant assemblages found in European grasslands. The functional diversity of the species included grasses and forbs that varied in the timing and depth of resource uptake. For example, forb groups had diverse flowering times, and diverse rhizomes, stolons, root crowns, and taproots. Seeds were germinated in a greenhouse, and then the seedlings were planted in the grasslands, after the ground had been treated with RoundUp two weeks prior to transplanting. Plant assemblages were grown from March 2010 to autumn 2012.
In addition to the sixteen species in natural assemblages, they chose seven target species, to introduce into the field plots. They grew seeds from four Asteraceae species native to Swiss grasslands (Senecio jacobaea, Leucanthemum vulgare, Carduus nutans, and Centaurea stoebe) that can become locally dominant in their native settings, and that are invasive in North American grasslands. And they chose three Asteraceae species that are invasive non-natives in Switzerland (Senecio inaequidens, Aster lanceolatus, and Rudbeckia laciniata). These seven species were germinated in a greenhouse and then transplanted into the field plots in April 2012.
Sun, et al., 2015, estimated the percentage cover of all native plants in September 2010, and compared that with cover in autumn 2012. They measured aboveground biomass by cuttings taken in autumn 2012, eight months after transplanting the target species. And they counted the number of seedlings that survived in each subplot, and collected, dried, and weighed them. They also measured the biomass of the target species grown in monocultures in the field.
In addition, Sun, et al., 2015, used field surveys to assess the “correlative relationship between the target alien invader or native biomass and resident native species richness.” They measured aboveground biomass of target species and resident species in natural field settings in Switzerland. They surveyed field settings in areas that included two of the target invasive alien species and/or dominant target native Swiss species. And they visited a few such sites in France. They collected density data of target species of each Swiss plot in 2012.
In the plant assemblages treatments, Sun, et al., 2015, found that, prior to the transplants, “resident [native plant] cover in subplots was generally higher than 75% and did not differ among the diversity treatments… At harvest, the biomass of the background native community in the uninvaded subplots… increased with increasing diversity…. The biomass of transplanted target invasive alien species and native [target] species in all native recipient subplots was significantly lower than in subplots in which the target species were grown in monocultures (on average, 97% lower).”
Sun, et al., 2015, found that, “The analysis of biomass and survival of target species revealed a significant species type x species richness interaction… Species richness had a strong negative effect on the biomass… and survival… of target invasive alien plants, whereas there were no significant effects of resident diversity on biomass… and survival… of target native plants. Biomass of the native community was, however, not correlated with the biomass and survival of target alien and native species… The biomass of Centaurea stoebe in native community subplots was remarkably lower than in the monoculture (on average, 99% lower)… However, neither resident species richness nor background native biomass affected the biomass… or survival… of C. stoebe. Total biomass of assemblages invaded by C. stoebe was similar to that of the paired uninvaded assemblages.”
In the field surveys, Sun, et al., 2015, found that, “Across all field sites monitored over the 2 years, biomass of invasive alien target species decreased significantly with increasing resident diversity… Biomass of the native dominant target species, however, was not correlated with the background species richness… We found that the total plot biomass of invasive target species was significantly higher than that of native target species… However, the density of invasive alien target species was not larger than that of the native target species… in the second-year survey.”
Sun, et al., 2015, stated that, “Our results suggest fundamental differences in competitive interactions between invasive alien species and resident species in the home versus invaded community. The results…indicate that local species richness is a good predictor of the performance of invasive alien species but not of native species.” Their results confirm prior studies that indicate that native species richness, or higher native plant diversity, can reduce invasion by alien species. But higher native plant diversity does not reduce the tendency of some native species to become dominant in an ecosystem.
Reference:
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Species Richness: Its role in maintaining plant diversity
Summaries of the research and commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, July 2020.
Sun, Müller-Scharer, Maron, and Schaffner (2015), followed up on previous work, including the work conducted by Maron and Marler (2007, 2008).
Sun, et al., 2015, further examined the impact of plant diversity on the reduction of expansion of invasive species. They combined experimental data with observational field data. They created 42 mixed-species plots of native perennial plant groupings of grasses and perennials, in a grassland in Switzerland. Plant groups ranged from two to 16 species, and represented natural plant assemblages found in European grasslands. The functional diversity of the species included grasses and forbs that varied in the timing and depth of resource uptake. For example, forb groups had diverse flowering times, and diverse rhizomes, stolons, root crowns, and taproots. Seeds were germinated in a greenhouse, and then the seedlings were planted in the grasslands, after the ground had been treated with RoundUp two weeks prior to transplanting. Plant assemblages were grown from March 2010 to autumn 2012.
In addition to the sixteen species in natural assemblages, they chose seven target species, to introduce into the field plots. They grew seeds from four Asteraceae species native to Swiss grasslands (Senecio jacobaea, Leucanthemum vulgare, Carduus nutans, and Centaurea stoebe) that can become locally dominant in their native settings, and that are invasive in North American grasslands. And they chose three Asteraceae species that are invasive non-natives in Switzerland (Senecio inaequidens, Aster lanceolatus, and Rudbeckia laciniata). These seven species were germinated in a greenhouse and then transplanted into the field plots in April 2012.
Sun, et al., 2015, estimated the percentage cover of all native plants in September 2010, and compared that with cover in autumn 2012. They measured aboveground biomass by cuttings taken in autumn 2012, eight months after transplanting the target species. And they counted the number of seedlings that survived in each subplot, and collected, dried, and weighed them. They also measured the biomass of the target species grown in monocultures in the field.
In addition, Sun, et al., 2015, used field surveys to assess the “correlative relationship between the target alien invader or native biomass and resident native species richness.” They measured aboveground biomass of target species and resident species in natural field settings in Switzerland. They surveyed field settings in areas that included two of the target invasive alien species and/or dominant target native Swiss species. And they visited a few such sites in France. They collected density data of target species of each Swiss plot in 2012.
In the plant assemblages treatments, Sun, et al., 2015, found that, prior to the transplants, “resident [native plant] cover in subplots was generally higher than 75% and did not differ among the diversity treatments… At harvest, the biomass of the background native community in the uninvaded subplots… increased with increasing diversity…. The biomass of transplanted target invasive alien species and native [target] species in all native recipient subplots was significantly lower than in subplots in which the target species were grown in monocultures (on average, 97% lower).”
Sun, et al., 2015, found that, “The analysis of biomass and survival of target species revealed a significant species type x species richness interaction… Species richness had a strong negative effect on the biomass… and survival… of target invasive alien plants, whereas there were no significant effects of resident diversity on biomass… and survival… of target native plants. Biomass of the native community was, however, not correlated with the biomass and survival of target alien and native species… The biomass of Centaurea stoebe in native community subplots was remarkably lower than in the monoculture (on average, 99% lower)… However, neither resident species richness nor background native biomass affected the biomass… or survival… of C. stoebe. Total biomass of assemblages invaded by C. stoebe was similar to that of the paired uninvaded assemblages.”
In the field surveys, Sun, et al., 2015, found that, “Across all field sites monitored over the 2 years, biomass of invasive alien target species decreased significantly with increasing resident diversity… Biomass of the native dominant target species, however, was not correlated with the background species richness… We found that the total plot biomass of invasive target species was significantly higher than that of native target species… However, the density of invasive alien target species was not larger than that of the native target species… in the second-year survey.”
Sun, et al., 2015, stated that, “Our results suggest fundamental differences in competitive interactions between invasive alien species and resident species in the home versus invaded community. The results…indicate that local species richness is a good predictor of the performance of invasive alien species but not of native species.” Their results confirm prior studies that indicate that native species richness, or higher native plant diversity, can reduce invasion by alien species. But higher native plant diversity does not reduce the tendency of some native species to become dominant in an ecosystem.
Reference:
- Sun, Y., Müller-Scharer, H., Maron, J.L., & Schaffner, U. (June, 2015). Origin matters: Diversity affects the performance of alien invasive species but not of native species. The American Naturalist, 185 (6), 725-736.
Links to return to sections on the role of diversity in preventing invasions:
- How Ecosystems Maintain Diversity
- Fluctuation Dependent Mechanisms
- Competition-based coexistence mechanisms
- Niche Differences
Next Sections on the success of invasive species: