CANOPY FEEDBACKS AND MICROTOPOGRAPHY REGULATE CONIFER SEEDLING DISTRIBUTION IN 2 MINNESOTA CONIFER-DECIDUOUS FORESTS

Successful regeneration of some species may be linked to microsite ava ilability, which in turn may be influenced by dominant canopy species. We investigated the relationship between canopy feedbacks and microsi te heterogeneity as they affect conifer regeneration in two Minnesotan mixed species forests: Abies balsamea (L.) Miller-Populus tremuloides Michx and Thuja occidentalis L.-Betula papyrifera Marshall, Objective s were to examine (i) microtopographic differences resulting from cano py feedbacks and (ii) conifer regeneration at three stages (seed dispe rsal, germination and establishment). We quantified seed rain and surv eyed microtopography and regeneration of T. occidentalis and A. balsam ea. Microtopographic features included pits, mounds, stumps, logs, and level ground. Differences in microtopography beneath deciduous and co nifer canopy types were generally minor. Conifer seeds fell in larger numbers under conifer canopy types than under adjacent hardwood canopy types in both forest types, but substantial seed rain occurred up to 20 m into hardwood canopy patches. In the Thuja-Betula stands, both ge rminants and seedlings of T. occidentalis occurred almost entirely und er the Thuja canopy type, and there predominantly on decayed wood (rot ting stumps and logs), which occupied only a small fraction of the for est floor. In the Abies-Populus stands, A. balsamea germinants and see dlings were relatively common beneath both canopy types and on all mic rotopographic features. The distribution of T. occidentalis was more r estricted than that of A. balsamea, indicating that A. balsamea may be more of a generalist.