Effect of Two Native Invasive Tree Species on Upland Pine Breeding Bird Communities in Georgia

摘要

Georgia land lottery maps from the 1820s reveal two tree species, water oak {Quercus ni-gra) and sweetgum {Liquidambar styraciflua), were formerly limited to major floodplains in the Piedmont and Coastal Plain. These species are now common in upland sites as a result of past land use and disruption of fire regimes. We investigated the effect this invasion had on breeding bird diversity in upland mixed pine (Pinus spp.) stands based on 90 point counts conducted in spring 2005. Half of these stands had no water oak or sweetgum (open stands) and half had a minimum of 25% of their basal area as water oak and/or sweetgum (invaded stands). Bird species richness and abundance were 42 and 41% lower, respectively, in invaded stands. Thirty-five bird species had more than 20 records and were tested for an association with invaded stands. No species were positively associated with invaded stands while 10 were negatively associated with invaded stands; these were mostly grassland pine savanna and shrubland bird species of high conservation value. Invasion of upland pine forest by these native tree species is similar to invasion by exotic species, and appears to disrupt ecosystem function causing declines in bird diversity.