| The landscape of north coast British Columbia (BC), Canada is a mosaic of ecosystems comprising open peatland, forested peatand, lowland and upland forest systems. The proposed harvesting of the poorly drained lowland forests of the coastal western hemlock (CWH) forest region has created the need to better understand the hydrochemical processes contributing to forest community development. There is concern that harvesting will accelerate the advance of paludification into lowland forests, decreasing productivity and forest regeneration.; The analysis of topography, hydrophysical properties of the soil substrate and groundwater flow for the forest-peatland complexes demonstrated a systematic linkage between forest productivity and local hydrogeologic gradients. Organic soil that accumulates in areas of concave bedrock morphology favours the invasion of hydrophytic species such as Sphagnum mosses. In areas where bedrock topography is not conducive to peat accumulation, hard pan formation and paludification may account for the accumulation of peat. Low horizontal hydraulic gradients (0.01–0.06) impeded drainage and maintained near surface water table in the open peatland (11.6 ± 2.4 cm). Localized topographic highs within the peatland communities have scrubby tree stands. As horizontal hydraulic gradient increased (0.07–0.16) in the bog woodland, bog forest and swamp forest communities, the mean depth to water table increased (18.0 ± 4.7 cm, 34.4 ± 15.3 cm, 30.8 ± 9.3 cm; respectively) and less productive cedar stands with shrub and moss understories transition to larger western hemlock stands with fern and moss understories. The deepest water tables (101.2 ± 63.9 cm) occurred in the upland forest where large horizontal hydraulic gradients (0.11–0.30) increased drainage and favoured greater productivity.; The ln(a/tanβ) (a = upslope contributing area, tanβ = local slope angle) topographic index of TOPMODEL was modified to represent the downslope movement of water at the hillslope scale, i.e., along the forest-peatland transects for which concurrent stratigraphic and hydrologic data were measured. The index was used to characterize the spatial distribution of topographically controlled groundwater flow and site conditions (as represented by water table depth and organic horizon thickness) influencing forest community type. (Abstract shortened by UMI.)... |
