Reproductive Success of Columbian Black-Tailed Deer in a Sewage-Fertilized Forest in Western Washington

Abstract

Disposal of municipal sewage sludge is a problem of national importance (U.S. Environmental Protection Agency 1972, Cairns 1978, Stearns and Ross 1978). Commonly used disposal methods (incineration, wetland filling, freshwater dumping, and ocean dumping) have widely recognized negative environmental impacts. Because sludges contain high levels of nitrogen and plant macronutrients, it may be possible to defray disposal costs by fertilizing agricultural, range, and forest lands with sludge. In 1973 the College of Forest Resources, University of Washington, began a cooperative effort with metropolitan Seattle to examine the feasibility of fertilizing soils of the Tsuga heterophylla Zone of western Washington with sludge for silvicultural purposes. Because glacial soils of this region are typically nitrogen-poor, the growth rate of economically important conifers can be substantially increased by sludge amendment (Edmonds and Cole 1977). This increased wood yield may defray disposal costs (Taggart and Schroeder 1980). Incidental to the impact of sludge fertilization on wood yield is the potential for altering wildlife habitat through the fertilization of understory vegetation. The game animal of particular interest in western Washington is the Columbian black-tailed deer (Odocoileus hemionus columbianus). Because diet quality has frequently been associated with reproductive success in Odocoileus (Cheatum and Severinghaus 1950, Taber 1956, Forbes 963, Verme 1965, Murphy and Coates 1966, Dechert 1968), it was hypothesized that forest fertilization with sewage sludge would increase herd productivity. The objective of this paper is to document that sludge application increased the crude protein content of key deer forage items and that female deer exploiting sludge-amended areas recruited more fawns to the 6-month age-class than did controls.