The few studies that have examined effects of deer on size distributions of

The few studies that have examined effects of deer on

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The few studies that have examined effects of deer on size distributions of populations of herbaceous plants show that deer increase the proportion of the population in small size classes (Augustine and Frelich, 1998; Augustine et al., 1998). Under conditions of high deer density (>15 deer/km2) and low plant density (<0.1 stems/m2), deer prevented Laportea canadensis ramets from exceeding 40 cm in height, but in exclosures, more than 50% of ramets exceeded 40 cm in height (Augustine et al., 1998). Similarly, in forest fragments with high deer densities (>25 deer/km2), size distributions of Trillium cernuum and T flexipes populations shifted toward smaller size classes once deer began browsing plants in the spring, whereas no shift occurred in fragments with lower deer densities (<10 deer/ km2) (Augustine and Frelich, 1998). Lower proportional representation of large plants where deer are abundant may reflect the previously documented trend for browsing pres- sure to increase with plant size for plants below the browse line (Strauss, 1988; Campbell, 1993; Inouye et al., 1994). Other studies, although not describing size distributions, have shown the mean size of individuals in herbaceous plant populations to be significantly less where deer are present than where deer are absent (Rooney, 1997; Long et al., 1998). For example, the mean leaf area of shoots of Maianthemum canadensewas 23% less for shoots exposed to deer herbivory than for shoots that occurred in natural refugia (Rooney, 1997). Evidence of effects on mature or midsuccessional communities.-Exclosure experiments have demonstrated that deer can decrease tree regeneration (Tilghman, 1989; Healy, 1997), change the identity of the dominant tree species in the sapling layer (which could eventually change the species composition of the canopy) (Tilghman, 1989; Healy, 1997) and decrease species richness of tree seedlings, herbs and shrubs (Tilghman, 1989; Healy, 1997; Rooney and Dress, 1997; Augustine et al., 1998). The magnitude of deer effects on community composition may be very large. In old- growth hemlock-beech and hemlock forest in north- western Pennsylvania an increase in deer densities from near zero in the early 20th Century to 7-19 deer/km2 is correlated with 80.4% and 59% decreases in the number of understory herb and shrub species in hemlock-beech and hemlock forests, respectively (Rooney and Dress, 1997). Rare shrub and herbaceous species (<1% of cover in 1929) were significantly more likely to be eliminated during the 70 y of high deer densities than were abundant species (>1% of cover in 1929). Although large effects of deer on community composition have been demonstrated, whether these effects are widespread or restricted to habitats preferred by deer remains unclear. In northern hardwoods forests of the Allegheny Plateau deer reduced the species 2001 15 This content downloaded from 128.62.178.17 on Wed, 20 Mar 2013 20:36:49 PM All use subject to JSTOR Terms and Conditions
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THE AMERICAN MIDLAND NATURALIST richness of stems taller than 0.9 m and increased dominance of Prunus serotina only at experimentally elevated deer densities (26.8 deer/km2) that were more than twice the mean deer
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