DISTRIBUTION OF BLACK SPRUCE VERSUS EASTERN LARCH ALONG PEATLAND GRADIENTS - RELATIONSHIP TO RELATIVE STATURE, GROWTH-RATE, AND SHADE TOLERANCE

The relative abundance and performance of black spruce (Picea mariana) and eastern larch (Larix laricina) were quantified along fertility gr adients in two peatlands in northern Wisconsin. We hypothesized that: (i) the distribution of these two dominants should correspond to the p ortions of the gradient where each has an advantage in stature and (or ) rate of height growth relative to its principal competitor; that (ii ) larch should have a higher rate of height growth on wetter, more min erotrophic sites, based on the costs and benefits of its deciduous hab it; and that (iii) spruce should be more shade tolerant and increase i n abundance during succession. Our findings largely support these hypo theses, and (at the hydrologically stable site) provide the first circ umstantial evidence for the competitive sorting of woody species along a natural gradient. The incongruity of interspecific differences in h eight and growth at one of the two sites is evidence for an historic c hange in the environment there, involving a shift in hydrology around 1925.