The impact of non-native plants on bird communities in suburban forest fragments
Date
2011
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Publisher
University of Delaware
Abstract
Forest fragmentation has occurred across the Eastern United States, and an ecological effect linked to fragmentation is the invasion of non-native plants into forests. Few studies have examined the link between the density of native plants and avian habitat use in forest fragments. The objective of this project was to estimate the relationship between occupancy of eight songbird species and native plant density, forest structure, and invertebrate biomass. We collected data at ninety-eight 25 m radius forested plots in Delaware and Maryland. Avian point counts were conducted 3 times per season between 15 May-7 August, 2009-2010. Vegetation was analyzed by measuring understory coverage, canopy coverage, basal area, and proportion of native plants. Invertebrate biomass was measured by vacuum sampling. We used program PRESENCE to build occupancy models with invertebrate biomass and vegetation characteristics as covariates to explain candidate bird species presence, and evaluated the models using Akaike Information Criterion. The proportion of native plants was the best variable in predicting Wood Thrush occupancy. Forest structure variables were the strongest predictors of presence for American Robin, Carolina Chickadee, and Gray Catbird. Both forest structure and native plant proportion were important variables in predicting the occupancy of Eastern Towhee, Northern Cardinal, and Ovenbird. For Carolina Wren, invertebrate abundance was the most important variable in predicting occupancy. My results suggest that native plant proportion and vegetation structure may both be important factors to consider in conservation planning and habitat restoration for these songbirds.