Environmental determinism and forest structure and composition: a naturally replicated experiment

Ecological theory states that forest succession is largely environmentally determined. Many investigators have suggested, however, that stochastic processes can frequently alter successional pathways. In particular, the colonization phase is thought to be very stochastic. This study utilizes a unique series of 6 naturally replicated sites on Brush Mountain (Montgomery Co., VA) to determine whether forest structure and species composition is primarily deterministic or stochastic in nature. Although the canopy stratum of the mature forest at these environmentally similar sites was very Similar in structure and species composition (p>0.05), the composition of the subcanopy strata vegetation differed Significantly among sites (p<0.05). This indicated that stochastic events (e.g. low intensity ground fires, deer browsing, cattle grazing) were were important factors during the development of understory and ground layer vegetation.

Site-to-site differences in subcanopy species composition remained apparent during the first 2 years following disturbance (removal of canopy cover) of 4 sites. Brush Mountain lacked a significant seed bank (< 1 seed/m²), and the dominant sub canopy species reproduced largely by vegetative sprouting. Post-disturbance colonization of the sites was very stochastic, but had relatively little immediate effect on vegetation structure and composition. In the future, however, as colonist species reproduce and increase in density, stochastic colonization events may become an important aspect of forest development at some of the sites.