White – tailed deer population increase and response by understory saplings and shrubs in the Apostle Islands National Lakeshore: Final Report

Smith, Douglas

Increasing populations of white-tailed deer (Odocoileus virginiana) have reached the point of overabundance in many regions of the eastern United States and have triggered great concern by ecologists and resource managers (Côté, Rooney, Trembley, Dussault, and Waller 2004, Stromayer and Warren 1997). In the last 100 years, deer populations have increased due to regulated deer harvests, deer reintroductions (McShea et al 1997), and habitat alteration that increased forage quality for white-tailed deer year-round (Alverson et al. 1988, Fuller and Gill 2001, Porter and Underwood 1999). Land use changes from forest cover to agriculture as well as silvicultural conversions from later to early successional forest types have created ideal interspersion of habitats that benefit deer. Thus with high interspersion of habitats (e.g., smaller patch size) in the landscape deer carrying capacities increased (Diefenbach et al. 1997).Cultural norms have also contributed to the overabundance of white-tailed deer. Regulated hunting has traditionally been the primary tool of wildlife management to control populations of white-tailed deer (Woolf and Roseberry 1998). However, in many regions of the USA hunting regulations have historically protected female deer, because of their greater contribution to population increase. Where goals of white-tailed deer management have shifted from population increase to population maintenance or reduction, cultural reluctance to harvest a greater proportion of female deer has prevented the achievement of population goals. Additionally, cultural acceptance of hunting may have caused the population of deer hunters to stabilize or decrease (Brown et al. 2000). And lastly, the contribution of winter severity in regulating white-tailed deer populations has declined with low winter severity indices in northern regions for the past 10 years (WDNR unpubl. data). White-tailed deer have been present in the Apostle Islands since before it was designated a National Lakeshore. Some islands maintained high populations of white-tailed deer (e.g., Rocky), but liberal hunting regulations and severe winters reduced the populations (Brander and Bailey 1983). Harvest histories on individual islands suggest that densities of white-tailed deer varied greatly among islands (Brander and Bailey 1983). In recent years deer have been absent or undetectable from all but Basswood and Oak islands. However, white-tailed deer were detected in high densities on Sand Island in 2002 and on York Island in 2004. From 2003 to the present my students and I have monitored white-tailed deer density and its impact on Canada yew (Taxus Canadensis) and regenerating hardwoods and conifers on Sand Island (Smith 2003, 2004, 2005). The evidence of an overabundant deer population on Sand Island is dramatic. All plots that contained Canada yew were browsed and 80% of the plots contained white-tailed deer pellets (Smith 2005). Average deer browse/plot was 33% meaning that one third of the meristematic ends of Canada yew had been removed by white tailed deer. I concluded that much of the island as been heavily impacted by deer and the intensity of browse was greater than annual growth by Canada yew (Smith 2006). Under this grant, we expanded the deer population estimation and deer browse impacts study to York, Basswood, Oak, and Raspberry Islands, as well as the mainland portion of APIS. Our objectives were to determine whether deer were present, estimate deer density using pellet surveys, and determine the impact of deer on a suite of sub-canopy shrubs and regenerating woody plants.