The recovery of taxonomic, functional, or phylogenetic diversity in plant communities is often a primary goal of restoration. In tallgrass prairies, restoration practitioners may use a combination of grazing and/or prescribed fire to promote a diverse native plant community. While these actions often increase plant taxonomic diversity, we know less about their effects on plant functional and phylogenetic diversity. Furthermore, the primacy of plant community restoration is based on the implicit assumption that building a diverse habitat leads to establishment of diverse animal communities.
We used a structural equation framework to test a series of causal pathways depicting the relationship between management (time since restoration, time since prescribed burning, and presence of bison) and the taxonomic, functional, and phylogenetic diversity of plants and animals (small mammals, snakes, ground beetles, dung beetles). We tested the relationships between management, plant communities, and animal communities using data collected at Nachusa Grasslands, a restored eastern tallgrass prairie in northern Illinois. Data were collected from permanent monitoring plots in 17 restored prairies between 2016 and 2019 that vary in restoration age (range: 3-33 years), time since burn (range: 3-50 months), and presence of bison, which were reintroduced in 2013.
Results/Conclusions
Prescribed fire typically had a strong positive effect on plant taxonomic diversity, whereas restoration age had a strong positive effect on plant functional diversity. Management explained little variation in plant phylogenetic diversity. We found little evidence that plant diversity was an important predictor of animal diversity; rather, variation in animal diversity was more often explained directly by response to management. For example, small mammal taxonomic diversity increased with time since prescribed fire, and dung beetle phylogenetic diversity was lower in the presence of bison. Only ground beetles showed little to no direct response to management.
These analyses challenge the assumption that restoring diverse plant communities will necessarily lead to diverse animal communities. Rather, restoration ecologists and land managers should consider how animal species respond directly to actions such as grazing or prescribed fire. Additionally, our analyses highlight that understanding the effect of restoration on diversity of either plants or animals may require multiple measures of diversity. Measuring only plant taxonomic diversity or functional diversity would have underestimated the importance of restoration age or prescribed fire, respectively. Ecosystem-wide restoration will require understanding how management actions simultaneously affect multiple trophic levels along multiple dimensions of diversity.