Jennifer Fraterrigo

Advisor: Monica Turner

PhD 2005: Influence of land-use change on the long-term persistence of forest understory herbs in the southern Appalachian highlands.

Land-use change is recognized as an important factor for predicting the future status of forested landscapes. Changes in land use can lead to variation in the composition, structure, and function of modern forests. Land use may also impart persistent legacies that affect the suitability of sites for plant establishment and survival, yet this remains relatively unexplored. I compared cove-hardwood forests in the southern Appalachian Highlands differing in land-use history (farmed, logged, or reference) to examine how previous management influences the suitability of forest sites for herbaceous plant species. First, I used a multi-scale sampling design to determine long-term effects of past management on patterns of mineral soil nutrient and nitrogen (N) cycling heterogeneity. Second, I used geostatistics to determine how past land use, through its modification of nutrient heterogeneity, affected the spatial distribution of herbaceous species. Third, I examined herbaceous species biomass allocation and growth to determine whether plant performance varied with land-use history. Finally, I used phospholipids fatty acid analysis (PLFA) to investigate how past land use affected soil microbial community composition and whether community composition was related to N turnover.

Although comparisons of averaged values rarely indicated that historical land use had an enduring effect on mineral soil or N cycling, differences in variance suggested that former human activities continue to influence nutrient distributions by altering their spatial heterogeneity. Patterns differed by element, but generally variance of soil carbon, N and calcium decreased and variance of soil phosphorus, potassium and magnesium increased with past land use intensity. Geostatistical analysis showed that such differences in nutrient availability were an important factor in determining plant heterogeneity in reference stands, but not in previously altered stands. Species dispersal and reproductive syndromes also explained variability in the spatial heterogeneity of plants. Short-distance dispersal reduced plant heterogeneity regardless of past land use. In contrast, vegetative reproduction reduced heterogeneity only in reference stands. Plant biomass allocation patterns and growth rates varied considerably with past land use, but were associated only in historically unaltered stands. This suggested that competition for light and nutrients may be reduced in areas with a history of human activity. Soil microbial analyses showed that microbial communities in formerly farmed stands had a higher relative abundance of markers for Gram negative bacteria and a lower abundance of markers for fungi compared with previously logged and reference stands. Net N cycling rates were negatively correlated with fungi in both farmed and reference stands, suggesting that historic land use can alter microbial communities in ways that may influence the processes they mediate. This research demonstrates that land use imparts persistent legacies that may affect the long-term distribution of herbaceous species by altering habitat suitability.

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