The Relationship Between Diversity and Ecological Functions
In recent decades, agricultural producers and conservation organizations have converted thousands of hectares of cropland to grassland in the Great Plains. This project investigated the relationship between species diversity in prairie restorations and ecological functions utilizing restoration plots along the Platte River in south central Nebraska. Both high diversity and low diversity seed mixes were used in the restoration plots. Although high diversity seed mixes can cost up to five to ten times as much as low diversity seed mixes, little information is available on the ecological functions that may result from the added diversity. Restorations that maintain critical ecological functions and services may help maintain functional and resilient working landscapes. This study is among the first to compare the ecological functions provided by grassland seed mixes commonly used by practitioners.
Increasing plant community diversity was found to be more important than increasing seeding density for enhancing resistance to invasion by unsown perennial forbs and legumes and in reducing inflorescence production by Bromus inermis. There was a significant positive relationship between plant community diversity and the abundance of coccinellid beetles, but the abundance of ants, carabid beetles, and spiders showed no significant response to diversity or seeding density. Seeding density had a positive effect on carabid beetle and spider species richness and Shannon-Weaver diversity. Year was the main significant effect for explaining levels of herbivory damage in Ratibida columnifera and Solidago Canadensis. Herbivory levels of each did not differ significantly among the treatments in 2010 and 2011. There was a significant negative relationship between diversity and levels of soil nitrate with low diversity plots containing higher amounts of nitrate and ammonium than the high diversity plots.
Overall, results indicate increasing diversity may be more important than increasing seeding density for provision of the ecological functions studied.