Grassland invasion, management, and multifunctionality

• Main Author: Pasari, Jae R
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01.01.2011
• Subjects: Biogeochemistry; Conservation; Conservation biology; Ecology
• ISBN: 1124966862; 9781124966861

Society values biodiversity and landscapes that reliably provide many ecosystem functions. I investigated how multiple scales of diversity influenced the provision of landscape-level ecosystem multifunctionality in an experimental Minnesota tall grass prairie ecosystem over ten years. I found that local species richness (α diversity) had strong positive effects on most individual functions and multifunctionality, while positive effects of community (3) diversity and regional species richness (γ diversity) emerged only when multiple functions were considered simultaneously. I also used both observational and experimental approaches to investigate native plant conservation and exotic plant management strategies in native-rich, nitrogen-limited serpentine grasslands in the San Francisco Bay Area. Here, the most widely cited threat to natives is the stimulatory effect of nitrogen deposition on the growth of exotic grasses, and the most widely recommended exotic management strategy is cattle grazing. However, a large number of other biophysical factors are known to influence native and exotic species. In an observational study, I used path analysis to determine the relative strengths of nine biophysical factors on native richness and exotic cover in from 1991 to 2005. Significant effects of nitrogen deposition, serpentine patch size, longitude, and precipitation in ungrazed grasslands demonstrated the importance of reducing or mitigating against nitrogen deposition effects, and the need to conserve a diversity of serpentine habitats to maintain native richness. In another study, I simulated realistic nitrogen deposition increases and manipulated grazing using low-level fertilization and fencing in a four-year factorial experiment. Observed trends in this study suggested a positive interaction effect of fertilization and grazing on native richness, and a negative fertilization effect in ungrazed plots. Grazing limited exotic grass cover and the native richness-reducing competitive effects of litter accumulation. Grazing also buffered community composition patterns against a large resource pulse. However, grazing reduced native grass cover and showed no clear ability to mitigate against the possibility of exotic cover gains under accumulating nitrogen. Finally, I found that grazing intensity was not a simple function of cattle stocking rates, suggesting that more intensive grazing management may be required to ensure that conservation benefits of grazing occur throughout the landscape.