Plant diversity and tree responses following contrasting disturbances in boreal forest

We determined the abundance and diversity of vascular plants in seven types of disturbance in mixed-wood boreal forest. Disturbance treatments include d wildfire, natural regeneration after harvest and several methods of silvi cultural site preparation. Relative to undisturbed forest, all disturbance treatments increased plant diversity to about the same extent. The abundanc e of plant growth-forms differed significantly between disturbance treatmen ts. Silvicultural treatments involving soil disturbance (disk-trenching, dr um-chopping and blading) had higher cover of grasses and annual forbs; natu rally regenerated and Bracke-cultivated treatments contained more perennial forbs and shrubs. Thus, different post-disturbance plant communities estab lished following contrasting types of disturbance. Plant community biomass and tree growth varied among disturbance treatments. Shoot mass of aspen (P opulus tremuloides Michx.) and the root mass of all species declined signif icantly with increasing soil disturbance intensity. Aspen and white spruce (Picea glauca (Moench) Voss) differed in their response to disturbance. Asp en growth was similar among disturbance treatments. In contrast, aspen dens ity was significantly lower in disk-trenched and bladed treatments than in burned or naturally regenerated treatments, and aspen basal area was signif icantly lower only in drum-chopped treatments. White spruce grew fastest in drum-chopped sites. Burned treatments had the highest recruitment of volun teer spruce seedlings (up to 3200 ha(-1)), but not significantly higher tha n in other disturbance treatments. Taken together these results suggest tha t the most intensive silvicultural treatments had the expected effects of r educing aspen abundance and increasing the growth of spruce, but also conta ined more grasses and forbs and had lower total root mass than burned or na turally regenerating sites. Further work is needed to examine long-term pro ductivity and the persistence of both native and persistent weedy species f ollowing contrasting types of disturbance. (C) 2000 Elsevier Science B.V. A ll rights reserved.