Effects of non-native plant removal and fuels reduction on riparian breeding bird populations

Riparian cottonwood forests of the Middle Rio Grande valley, New Mexico have been invaded by exotic tree species, which, in combination with woody debris accumulation and flood control, make these forests vulnerable to frequent fires.  Land managers need effective methods to reduce fuel loads and invasive plants with minimal impacts on native flora and fauna.  We evaluated the effects of fuel reduction and invasive plant removal on riparian avifaunas.  Here we present late-breaking analyses of the first 6 years of this study.  In 2000, we established 12 study sties including non-native plant removal treatments and conrols.  Pre-treatment data were collected from 2000-2003, and post-treatment data were collected from 2003-2006.  We detected birds using point counts and converted count data to density estimates using Program Distance.  Total numbers of bird species was 132 but mean numbers of species fluctuated by year.  Results of GLMM Analysis revealed that numbers of bird species did not significantly differ between control and experimental sites or between pre- and post-treatment periods.  Nor was the interaction between treatment type and period significant, signifying that mean number of bird species did not change in response to removal of fuels and invasive plants. We evaluated treatment effects on common species and found that 3 mid-story nesting species and 1 ground-shrub nesting species showed declining abundance from treatments, whereas cavity nesting and canopy nesting species were not affected by treatments.  These effects likely result from the reduction in woody ground cover and vegetative material in the lower and middle understories.  Lower and middle understories are structurally important, and replanting with native shrubs will benefit species using this habitat.  Tree canopy and cavity nesting nesting species may benefit from restoration of cottonwood habitats because reducing fire risk will maintain nest trees that could otherwise be destroyed by fires or by conversion to invasive species.