Spatial Patterns and Succession in a Minnesota Southern‐Boreal Forest

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Abstract
Succession was studied in a cold—temperate forest in the Boundary Waters Canoe Area Wilderness (BWCAW) of northeastern Minnesota. The 13 x 18 km study area comprises a complex forest mixture of jack (Pinus banksiana) and other pines, quaking aspen (Populus tremuloides), paper birch (Betula papyrifera), black spruce (Picea mariana), balsam fir (Abies balsamea), and white cedar (Thuja occidentalis) on thin soils over the Canadian Shield bedrock. The main objectives of this study were to examine the relationship between spatial patchiness, spatial scale, and canopy succession in the southern—boreal forest of the BWCAW, and to evaluate under what conditions successional direction may remain stable, converge, or diverge. Knowledge of the successional direction of old forests in the BWCAW that are undergoing demographic transition from even—aged to uneven—aged is important because the landscape now has many old stands as a result of reduced fire frequency. Rotation periods for fires have changed from °50—100 yr in presettlement times to >1000 yr since 1910. Analyses were conducted at spatial scales ranging from the individual tree (0.01 ha) to the large stand (16 ha). Two permanent mapped plots (of area 0.53 and 0.56 ha) were established in stands of different age. Fine—scale age structure, successional change, transition from one species to another, and development of small patches (of area 2, maximum °0.1 ha) of black spruce, balsam fir, white cedar, and paper birch. Thus, at 1—16 ha spatial scales, succession leads to convergence on a mixture of species. At smaller spatial scales (e.g., 0.01—0.1 ha) successional pathways appear to diverge into four community types. The same successional pathways can be reconstructed from historical analysis of individual stands as from a chronosequence of stands; therefore, chronosequences in this area have been stable at least during the lifetime of the current generation of trees.

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