Recovery of grassland plant communities after cessation of nutrient enrichment

Abstract

Diversity is declining in many ecosystems, resulting in rates of extinction much greater than what is expected based on the fossil record. Species declines can be attributed to human activities drastically changing ecosystems by increasing rates of nutrient inputs, altering precipitation and disturbance regimes, destroying habitat, and reducing landscape connectivity. If we are to preserve a considerable fraction of the species in our planet and our ability to enjoy the benefits we derive from them, direct and immediate action informed by science is necessary. My dissertation research investigates a small piece of this large puzzle. Here, I present results from three long-term nutrient addition and cessation experiments where I study barriers for the recovery of grassland plant diversity after cessation of long-term nutrient inputs, and explore strategies to prevent further species losses. First, I study the role of potential reinforcing feedbacks involving soil microbial communities and plant mutualists that could prevent the recovery of plant diversity after cessation of nutrient enrichment. I then explore the effectiveness of common restoration strategies that aim to further reduce nutrient inputs, increase light availability, and reduce recruitment limitation. Finally, I evaluate whether prescribed burning can slow rates of species loses and promote recovery of diversity after reducing nutrient inputs. While unassisted recovery of diversity might be impossible or slow, my dissertation provides experimental evidence that ecosystem management can help maintain local diversity. In particular, seed addition and prescribed burning are both useful strategies for promoting the recovery of grassland plant diversity following reductions in nutrient inputs.