PARENT SESSION
Poster Session 2: Forest Ecology
Monday, August 8, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal
The eastern hemlock-yellow birch association: Similar seedling requirements lead to tangled trees.
Marx, Laura*,1, Walters, Michael1, 1 Michigan State University, East Lansing, MI
ABSTRACT- In hemlock and northern hardwood forests of the Great Lakes region, Tsuga canadensis (eastern hemlock) and Betula alleghaniensis (yellow birch) are strongly associated. Kotar et al. (1999), among others, analyzed adult tree distributions and found that hemlock and yellow birch were more closely associated than 22 other species pairs in northern Wisconsin. We hypothesize that in old-growth forests, this association is maintained by the restriction of established hemlock and birch seedlings to hemlock and birch decaying wood. In a field study of four hemlock/northern hardwood forests in Upper Michigan, we surveyed tree seedlings (less than 30 cm tall) and aged a subset of these seedlings by counting growth rings. Seedlings of both hemlock and yellow birch are far more abundant on decaying wood than on soil, and more abundant on hemlock or birch wood than on sugar maple wood (one-way ANOVA p-values for each species < 0.05). Hemlock and yellow birch seedlings older than three years old are rarely found on sugar maple wood, even with intense oversampling of sugar maple. In contrast, older seedlings are common on hemlock wood and birch wood, where the oldest seedlings shorter than 30 cm were 13 and 12 years old, respectively. In addition, hemlock and birch roots remain physically attached to decaying wood well into the sapling stage. In a census of seedlings and saplings taller than 30 cm, 68.6% of hemlocks and birches on wood were found on hemlock logs, 28.5% on other conifer wood, and 2.9% on a single red oak log (N=70 individuals across four field sites, a total of 1.6 ha surveyed). Adult hemlock and yellow birch trees have very different life history strategies, but maintain their association by a strong affinity for hemlock and birch wood at the seedling stage combined with an inability to establish on the decaying wood of sugar maple, the other dominant species in these forests.
Key words: hemlock, yellow birch, forest association, woody debris