Hydrogeological influences on forest community type along forest-peatland complexes in coastal British Columbia

The prospect of harvesting forest-peatland systems in the coastal western hemlock forest region of British Columbia has created the need for an understanding of the interrelationship between topography, groundwater flow, and site productivity. Detailed topographic mapping including the use of ground-penetrating radar coupled with point measurements of specific yield, bulk density, saturated hydraulic conductivity, and groundwater level were used to determine the characteristics of groundwater flow along forest-peatland complexes. A topographic index was then used to characterize the spatial distribution of groundwater flow and site conditions (as represented by water table depth and organic horizon thickness) influencing forest community type. Forest community type mean index decreased from open peatland to upland forest. Areas with high slope indices had thicker organic horizons (0.7-1.8 m), water tables closer to the surface (0-0.2 m), and higher soil moisture contents (46-92%). These conditions affect successional dynamics and favour the invasion of hydrophytic species such as Sphagnum mosses. Areas with low slope index values were associated with shallower organic horizons (<0.4 m), deeper water table (0.3 to >1.6 m), and drier soil moisture (35-76%), favouring more prolific timber growth.