THE EFFECTS OF DRAINAGE ON SUBSTRATE WATER-CONTENT AT SEVERAL FORESTED ALBERTA PEATLANDS

Hydrologic drainage criteria that describe the position of the water t able between adjacent ditches are commonly used to assess the initial effectiveness of peatland drainage projects for tree growth improvemen t. However, these criteria do not reflect the soil conditions that reg ulate tree growth and performance after drainage. The effect of three drainage ditch spacings (30, 40, and 50 m) on the spatial variability of soil water conditions at three drained boreal Alberta peatlands was studied. Soil water content (0-30 cm depth) was found to be insensiti ve (p = 0.686) to drainage ditch spacing several years after drainage. Greater variation was observed between different sampling locations ( p = 0.024) relative to the position of the ditch edge within similar d itch spacings. Spatial distribution of soil water in the unsaturated z one was found to be inversely related to the degree of water table low ering. Spatial patterns of soil water content were strongly associated with changes to substrate bulk density resulting from postdrainage pe atland subsidence.