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Evolution, Ecology, Soil fertility, Forest plants-Functional genomics, Plant communities-Ecology, Plant, Environmental gradient, Temperate forest, Functional traits, Forests and forestry-Northeastern states
The field of plant community ecology is increasingly seeking to integrate functional traits into theory and empirical research. Investigations of community structure that consider how species' functional traits vary within the context of environmental gradients are a powerful new approach to long-standing questions in community organization and diversity. Functional traits expected to affect species' potential range and abundance along major environmental gradients include seed mass and leaf area, plant height, specific leaf area (SLA), leaf form and herbaceous versus woody growth. These traits are thought to be indicators of plant competitiveness and establishment ability, and are predicted to vary along soil fertility gradients. In this study I investigated whether functional trait values were correlated with soil calcium content, a key indicator of soil nutrient availability and fertility in forests of the northeastern United States. I examined functional trait variation in forest vegetation at 27 forest sites with varying soil calcium levels in mature temperate deciduous forest vegetation across New York and New England. In a parallel analysis, I also tested variation in seed mass, leaf area and SLA among related species associated with different portions of the soil fertility gradient. Leaf area (p= 4.14e-5, R2= 0.647), plant height (p= 0.002, R2= 0.321), and SLA (p= 0.025, R2= 0.476) were all significantly positively correlated with soil calcium content. In addition, percent herbaceous growth (p < 7.71e-8) and percent compound leaf form (p < 1.62e-5) were both significantly positively correlated with soil calcium content. In the parallel specieslevel analysis, the mean seed mass, leaf area, and SLA of species found in calcium rich soils was significantly higher than the trait means of species associated with calcium poor soils (p=0.0034; p=0.0027; p=1.19e-07). Overall, my results support the hypothesis that plant functional species traits vary strongly along a major soil fertility gradient in forests of the Northeast. It may be that 4 species with higher trait values were able to establish in nutrient rich environments before their smaller counterparts. Nutrient rich areas rapidly became competitive, and selection for certain traits became stronger. Eventually, species became restricted to certain nutrient niches and suites of functional traits became associated with high and low zones of fertility. Interestingly, the trends toward larger, apparently more competitive plant growth forms on high calcium soils also coincide with increasing species richness in forest plant communities. This pattern may raise questions about the role of competition in limiting species diversity in plant communities.
Anderson, Grace Harper, "The evolution and ecology of functional traits along a soil fertility gradient" (2012). Honors Project, Smith College, Northampton, MA.
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