Detrimental effects of white-tailed deer browsing on balsam fir growth and recruitment in a second-growth stand on Anticosti Island, Québec

Abstract

White-tailed deer (Odocoileus virginianus Zimmermann) was introduced on Anticosti Island in the late 1890s. The current population, estimated at 120 000 (15 animals/km2), jeopardizes balsam fir (Abies balsamea [L.] Mill.) growth and recruitment to the canopy. Balsam fir is a preferred browsed species of white-tailed deer during winter. In a second-growth stand resulting from a clearcut and a fire in 1959, we investigated the stand structure and developmental patterns of fir stems using dendroecological methods. White spruce (Picea glauca [Moench] Voss), a less palatable, occasionally browsed species, was used as a control to evaluate the influence of repeated browsing on fir and to differentiate it from the possible effects of other factors. Our data showed that deer browsing delayed vertical and radial growth and altered the stand structure in favor of white spruce. Browsing resulted in a semi-open stand with a tree layer dominated by white spruce and a scattered understory of predominantly small balsam fir (< 3 m) of approximately the same age as spruce. Stem analysis showed that growth patterns varied among the fir sampled. The few stems that had escaped deer browsing showed faster stem development, punctuated by short periods of minimal growth. Above the mean maximum level of browsing (ca. 110 cm from ground level), mean vertical growth was twice (17 cm year-1) that calculated for the lower part (9.3 cm year-1). The fir tree-ring series showed a major growth depression between 1985 and 1989, possibly associated with increased deer browsing pressure and spruce budworm activity. Incomplete rings were also frequent after 1984. Browsing intensity on fir may increase in years to come because of an expected higher site attendance. This could favor white spruce at the expense of balsam fir.