MODELING THE EFFECTS OF FOREST HARVESTING ON LANDSCAPE STRUCTURE AND THE SPATIAL-DISTRIBUTION OF COWBIRD BROOD PARASITISM

Timber harvesting affects both composition and structure of the landsc ape and has important consequences for organisms using forest habitats . A timber harvest allocation model was constructed that allows the in put of specific rules to allocate forest stands for clearcutting to ge nerate landscape patterns reflecting the ''look and feel'' of managed landscapes. Various harvest strategies were simulated on four 237 km2 study areas in Indiana, USA. For each study area, the model was applie d to simulate 80 years of management activity. The resulting landscape spatial patterns were quantified using a suite of landscape pattern m etrics and plotted as a function of mean harvest size and total area o f forest harvested per decade to produce response surfaces. When the m ean clearcut size was 1 ha, the area of forest interior remaining on t he landscape was dramatically reduced and the amount of forest edge on the landscape increased dramatically. The potential consequences of t he patterns produced by the model were assessed for a generalized neot ropical migrant forest bird using a GIS model that generates maps show ing the spatial distribution of the relative vulnerability of forest b irds to brood parasitism by brown-headed cowbirds. The model incorpora tes the location and relative quality of cowbird feeding sites, and th e relation between parasitism rates and distance of forest from edge. The response surface relating mean harvest size and total area harvest ed to the mean value of vulnerability to cowbird brood parasitism had a shape similar to the response surfaces showing forest edge. The resu lts of our study suggest that it is more difficult to maintain large c ontiguous blocks of undisturbed forest interior when harvests are smal l and dispersed, especially when producing high timber volumes is a ma nagement goal. The application of the cowbird model to landscapes mana ged under different strategies could help managers in deciding where h arvest activity will produce the least negative impact on breeding for est birds.