PS 3-37 - Seed bank and plant community composition of an early successional grassland

Abstract: Human activity often results in physical disturbances that have impacts on natural systems, including habitat loss and species extinction. Grassland biodiversity in particular is susceptible to land use change, with disturbances affecting community assembly and dynamics within ecosystems. Disturbances such as mowing have been shown to increase species diversity, while actions such as addition of multiple nutrients decreases species diversity. Given that grasslands are important for ecosystem services, including grazing, soil formation, and regulation of greenhouse gases, it is important to determine the effects of human activity on these systems. The Disturbance and Resources Across Global Grasslands Network (DRAGNet) focuses on ascertaining the effects of disturbances and nutrient addition on grasslands. The goal of our study is to determine how disturbance, nutrient addition, or both affect plant community dynamics in an early successional grassland. The study also aims to determine what species’ seeds are introduced through natural dispersal and were already present in the seed bank. Our approach to addressing these questions was to establish a research site at the Blandy Experimental Farm in northern Virginia. Measurements of light availability, aboveground biomass, percent cover, seed dispersal, and soil nutrients were taken. Soil samples were germinated in a greenhouse to determine the seed bank. Disturbance and nutrient treatments were implemented after two years of baseline measurements. Pre-treatment results from Spearman correlations show that only some species have a positive correlation in their percent cover when comparing consecutive years, such as Linaria vulgaris (yellow toadflax) and Solanum carolinense (Carolina horsenettle). Other species, such as Nepeta cataria (catnip), do not show this correlation, indicating a lack of influence from the percent cover of the previous year. Further Spearman correlations also indicate a lack of significant relationships between the existing percent cover and the abundance of that species in the seed bank. The exception to this is L. vulgaris, which shows a strong positive correlation between the existing percent cover and its abundance in the seed bank. This implies that many species are storing their seeds within the seed bank for a long period of time and only germinate when certain conditions, such as those resulting from a disturbance, are met. It is likely that disturbance events will result in a shift in community composition due to the seed bank composition, and future results from the disturbance and nutrient addition treatments will hopefully reflect this and provide further knowledge for grassland conservation efforts.