Impact of forest type and management strategy on avian densities in the Mississippi Alluvial Valley, USA

摘要

Avian territory densities were determined from 20 breeding bird censuses in mature (>30 yr old) bottomland hardwood stands and 18 censuses in young (6-9 yr old) cottonwood (Populus deltoides) plantations in the Mississippi Alluvial Valley (USA) in 1994-97. Avian species richness, diversity, and territory density were greater in bottomland hardwood stands than in intensively-managed cottonwood stands but these parameters were not impacted by selective timber harvest within bottomland hardwood standsnor by method of regeneration within cottonwood plantations (from shoot cuttings or coppice from root sprouts). Even so, detrended correspondence analysis based on avian territory densities readily segregated forest types and silvicultural treatments. Timber harvest within bottomland hardwood stands resulted in a shift in bird communities toward those found in cottonwood stands by increasing the densities of early-successional species such as indigo bunting (Passerina cyanea), yellow-breasted Chat (Icteria virens), and common yellowthroat (Geothlypis trichas). Conversely, regenerating cottonwood stands from root sprouts, rather than planting cuttings, resulted in a shift in bird communities towards those found in bottomland hardwood stands by increasing densities of species such as white-eyed vireo (Vireo griseus) and wood thrush (Hylocichla mustelina [Catharus mustelinus]). Tree species diversity, angular canopy cover, and midstorey density were positively associated with bird species assemblages inbottomland hardwood stands, whereas vegetation density at ground level was positively associated with bird communities in cottonwood plantations. Conversion of agricultural fields to short-rotation cottonwood plantations results in increased breeding bird populations by adding up to 140 additional territories per 40 ha. Even so, relative conservation values, derived from indicator species analysis and Partners in Flight concern scores, suggest that mature bottomland hardwood forests are twice as 'valuable' for bird conservation as are cottonwood plantations.