The forest-bog complex of southeast Alaska

Major vegetational, environmental, and peat accumulation patterns were studied in the forest-bog complex of southeast Alaska. Attention was directed to three levels of vegetational pattern: (1) the community type level, with forest, bog, and intermediate types being recognized; (2) the community level, with investigation of major variations within forest, bog, and, to a lesser extent, the intermediate community types; and (3) the subcommunity level, with major patterns of the forest understory and the bog surface, being investigated. Both extensive survey and intensive sampling were carried out in a fairly widespread, but geographically even, array of sites. Chief attention was given to vegetational aspects and gross physical factors, with patterns of these then being used to suggest possible correlating features of habitat. Actual correspondence will be determined in subsequent studies. At the community type level, the three types blended into one another in a continually varying pattern, which, on a gross scale, conformed primarily to surface topography. Forests occurred chiefly on the steep mountain slopes, bogs on land of gentle repose, and intermediate communities on slopes in between these. That the correspondence was with drainage, rather than other microhabitat features related to topography, was shown by forest presence on land of little slope if it were near the ocean or large drainages, or on deep porous substrates, and by bog presence on steep slopes, if any local formations prevented runoff from being rapid the full length of the watershed. Major vegetational patterns on the peats conformed more with peat surface configuration than with peat depth, configuration of underlying topography, or major land slope. Species' patterns at this level included dominance of the upland forests byTsuga heterophylla andPicea sitchensis, withChamaecyparis nootkatensis, Thuja plicata, andTsuga Mertensiana of local importance. The first two species were increasingly sparse, and the last three increasingly conspicuous (within their geographic ranges), in intermediate communities. On the bogs proper, onlyPinus was consistent in occurrence, and the trees were widely scattered, small and slow growing. Major shrub, herbaceous vascular plant, bryophyte and lichen shifts and patterns along this major floristic gradient are described. Some species reached maximum importance in the forests, others in the intermediate type and others in the bogs. The majority of the species had overlapping, but largely independent, patterns of importance. At the community level, two major patterns were suggested by the forest data: (1) a shift from true upland forest, to forest showing increasingly poor drainage, and, finally, to bog forest; and (2) a shift from forests dominated by very large trees, with highPicea importance, an understory largely characterized by scattered small shrubs, herbaceous vascular plants, and mosses and liverworts indicative of moist oxygenated surfaces, to forests with lessPicea, smaller trees, a deep continuous moss cover, dense shrubs where the canopy was somewhat open and only mosses and sparse herbs where the canopy was closed. These patterns are postulated to correspond to specific combinations of slope angle, the possibility of receiving bog drainage waters, nearness to large streams or the ocean, substrate porosity, and varying mixtures of soil fertility, moisture, oxygenation, and depth. The two major patterns suggested for the bogs at the community level are: (1) a gradation from probably soligenous bogs to probably ombrogenous bogs; and (2) a gradation from actively growing bogs of various surface configurations to bogs with an apparently stagnant main surface. Possible recent rejuvenation of a few of these stagnant bogs was indicated. Various possible relationships among the bogs are discussed. The forest subcommunities were subjectively divided into those of (1) varying dominance by different life forms; and (2) variations in surface moisture conditions. Bog surface subcommunities were divided into (1) wet sites, including steep-sided pit ponds, shallow wet hollows, surface drainage systems, floating mats and eroding bare peats; and (2) dry subcommunities, including mounds, varyingSphagnum dominance, and varying importance of bog shrubs and the sedges. The postulated patterns at all levels are based on fairly extreme examples. Many groupings were found that exhibited varying mixtures of these more extreme conditions, either throughout “simple” communities, or as parts of “complex” communities. Whether the more extreme conditions are sufficiently numerous and distinct in the region to form a basis of classification, or whether no such limits can be set except by arbitrary decision, and the regional vegetation would be dealt with best on the basis of continuous variation, remains to be determined. The most pronounced impression gained from this vegetation is one of a continuous shifting of habitat patterns and species' occurrence, co-occurrence, and vigor at all levels in both time and space. Such has certainly been observed before with respect to vegetation, but may be particularly conspicuous in this region in which extensive land use and settlement has not occurred; and climate, topography and related features, and peat accumulation are such that a continuous tension exists at all levels between: (1) tendencies for better drainage, forest development, and raised bog humification; and (2) poorer drainage, bog development and raised bog growth. The actual vegetation at any one time and place would depend on the particular combination of the climate and surface physical features at that time and place, and the time lag of vegetational and substrate response to climatic fluctuation.