The purpose of this research was to evaluate the effects of forest drainage and subsequent subsidence on peat pore properties that govern soil moisture and aeration conditions important to tree growth. Changes to soil moisture and aeration conditions resulting from post-drainage subsidence were investigated at two peatlands drained for forestry near Saulteaux River, and Wolf Creek, Alberta.

Subsidence was associated with increased peat bulk density and degree of decomposition after drainage of both peatlands. These changes corresponded to a loss of pore sizes greater than 600 $\mu$m dia., and a concurrent increase in pore sizes between 3-30 $\mu$m dia. Mean soil water retention at soil water potentials spanning $-$5 to $-$15000 cm head was increased in drained areas by 20-300% over that of undrained areas. Relative differences in water retention were proportional to differences in bulk density between drainage conditions. Mean saturated hydraulic conductivity in drained areas was 1.69 cm/h compared to 14.46 cm/h in undrained areas. Conversely, unsaturated hydraulic conductivity in drained areas was greater than that in undrained areas at water potentials between $-$5 and $-$15000 cm head. Subsidence increased both the volume and transport rate of soil water in the range of soil water potentials available for use by trees.

Increased water retention in drained areas decreased the air-filled pore space important in soil aeration by 30-200% over that of undrained areas at Saulteaux River and Wolf Creek. However, this reduction in air-filled pore space did not result in decreased aeration of surface peat in drained areas of either peatland. Oxygen transport rates and O$\sb2$ concentrations were consistently greater, and the aerated zone extended 10-40 cm deeper in drained areas due to much lower water table levels compared to undrained areas. However, subsidence reduced aeration response of deeper soil layers to water table fluctuation by increasing the thickness of the capillary zone above the water table by 10-20 cm over that evident in undrained areas. Consistent with spatial patterns for water table drawdown, oxygen transport rates and depth of the aerated zone did not vary among different ditch spacings, but were affected by proximity to drainage ditch edges. Overall, both soil moisture conditions and aeration were improved for tree growth by drainage and subsequent subsidence.