Summary
Deer browsing may encourage development of browse-tolerant vegetation at the expense of browse-sensitive species. This study evaluated the regeneration of eastern hemlock Tsuga canadensis (a shade-tolerant, browse-sensitive conifer) under different levels of intensive white-tailed deer Odocoileus virginianus browsing in northern Wisconsin, USA.
To examine regeneration patterns over time, data were compiled from earlier studies undertaken in three mixed deciduous-coniferous forest sites:
1) a site in Menominee County (sampled 1964) - year-round deer hunting permitted; deer density low (5-12/km²).
2) Flambeau River State Forest Scientific Area (Sawyer County) - data were from1967 in an area with intense deer browsing (deer density 50-100/km²). Additional data were collected from two deer exclosures (20 x 20 m) established in 1961 and sampled in 1973 (12 years of protection).
In sites 1 and 2, tree species were sampled in nested circular quadrats. Diameters of all trees (stems >9 cm diameter at breast height (dbh)) were measured in a 0.04 ha quadrat (in exclosures all trees measured). Stems >< 1.3 to 9 cm dbh (designated saplings) were counted in a 0.01 ha quadrat, and seedlings in a 0.004 ha quadrat.
3) Pike Lake exclosure (Price County) - a 0.37 ha (61 x 61 m) deer exclosure established in 1946 and sampled in 1973 (27 years protection). Deer density outside the exclosure was similar to that at Flambeau. Data were collected in quadrats within the exclosure; no sampling was undertaken outside it.
In the Menominee County forest an ‘all-aged’ hemlock population was present; deer densities were low so browsing had little effect on regeneration.
In the intensely browsed forest at Flambeau, although eastern hemlock was the dominant species of the tree stratum (indicating lower historical browsing pressure), seedlings and sapling density (41 saplings/ha) was very low. In the seedling and sapling strata, sugar maple Acer saccharum was dominant.
In the 12-year-old Flambeau exclosure, high densities of hemlock seedlings and saplings (7,362 saplings/ha) had established; no seedlings or saplings were present in adjacent areas open to deer. In the 27-year-old Pike Lake exclosure there was good regeneration of hemlock of all diameter classes.
Many woodlands throughout the mid-western USA are subject to intense deer browsing. The results of this study suggest that browsing levels need to be controlled to allow browse-sensitive trees to adequately regenerate.
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