James E. Panaccione
More than 2,000 species of exotic plants are established within the continental United States, with approximately 900 species occurring in New England. Many of these exotics are invading disturbance-generated habitats, including the shrublands and early-successional forests of the northeastern United States. Regionally, these habitats support a diverse assemblage of plants and animals. Because invasive vegetation can deleteriously alter community and ecosystem-level interactions, the spread of exotics may jeopardize the long-term viability of many wildlife species affiliated with these habitats. Specifically, recent research has found that sites invaded by nonnative vegetation had substantial reductions in insect biomass. As a result, species dependent on insects as a food resource (e.g., nesting songbirds) may be less abundant or have reduced fecundity in habitats dominated by exotic vegetation. During a preliminary inventory of early-successional habitats in southeastern New Hampshire, we found insects were approximately three times more abundant on native shrubs than exotics. Therefore, if exotic shrubs become the dominant vegetation within this landscape, large reductions in invertebrates may supervene, conceivably affecting organisms at higher trophic levels. Species that may be at the highest risk are avian shrubland obligates that forage via ―gleaning. Subsequently, we expanded our study to monitor birds nesting in early-successional sites that contained a range of exotic shrub coverages. Avian abundance and species richness were examined via point counts. We also examined fecundity and territory composition (especially coverage by exotic shrubs) of common yellowthroats (Geothlypis trichas) to determine if exotic shrubs reduce the productivity and density of this shrubland obligate.
Keywords: EARLY-SUCCESSIONAL HABITATS, SHURBLAND OBLIGATES, NESTING SONGBIRDS, EXOTIC SHRUBS, SEASONAL FECUNDITY
