RESOURCE CONGRUENCE AND FOREST REGENERATION FOLLOWING AN EXPERIMENTALHURRICANE BLOWDOWN

Catastrophic uprooting of forest canopy trees creates mounds, pits, an d other microsites that provide opportunities for regeneration of part icular species. We measured environmental factors on five types of mic rosites created by simulated blowdown of a mixed deciduous forest in c entral New England, United States. We then estimated spatial variation in resource levels and quantified congruence among different resource s at each site. Effects of simulated blowdown on light levels and CO2 concentrations were more pronounced after three years than effects on nitrogen availability and other soil resources. Spatial heterogeneity in light levels and net nitrification rates was greater in the blowdow n, but heterogeneities of soil organic matter concentration and net mi neralization rates were greater in the undisturbed forest. Availabilit y of nitrate, a limiting resource in most New England forests, was low on mounds and in pits, but high on the vertical portion of forest flo or resulting from uprooting of canopy trees. At a spatial scale releva nt to seedlings, resource congruence was greater in the undisturbed fo rest than in the experimental blowdown, primarily because of the effec ts of blowdown on light levels. Congruence in the blowdown increased w ith an increase in spatial scale, but congruence in the undisturbed fo rest was similar at both spatial scales. Seedling growth of two birch species was correlated with light levels and with congruence among soi l resources. This study shows that immediate disturbance effects on mi crotopography and light levels determine recruitment patterns of colon izing species, with changes in soil resource levels influencing later community development. Furthermore, some species appear to respond to resource congruence, which may provide an additional dimension to the regeneration niche.