|dc.description.abstract||The southern boreal forest environment in Saskatchewan
has been affected by the large-scale pulpwood harvesting operations
that commenced in 1968. The present study was undertaken to assess
the present environmental conditions on various terrain types with
the aim of predicting the likely future forests that will develop.
A biophysical inventory of approximately 5600 km2 of
forest terrain was undertaken to provide the frame of reference.
Forty-one land systems based on landform, topography, texture of
surficial deposits, drainage and vegetation were mapped at 1:125000
from air photos at 1:77500.
Standing crop and regeneration potential of each terrain
type provided a basis for predicting ecosystem development. Total
stand volumes decline in the following order: > 300m3 ha-l on fresh
sandy loam till; 250-300m3 ha-1 on fresh outwash or moderately fine
textured till; 200-250 m3 ha-l on dry sandy loam outwash and moist
to very moist moderately fine textured till; 150-200 m3 ha-l on dry
sands; < 150 m3 ha-l on very dry outwash sands. Advance regeneration,
primarily black spruce and balsam fir, does not play a major role in
Cumulative actual evapotranspiration (AE) on ten important
terrain types over the 1973 growing season was much higher than in
1972 due to -warmer and wetter conditions in 1973. Cumulative curves
were generally sigmoid in shape with the most rapid rise coinciding
with leaf expansion of broad-leaved vegetation. A plateau was attained
in early to mid-August which coincides with cessation of height and
diameter growth. Curve slopes in mid-summer were correlated with
soil moisture holding capacity and/or stage of vegetation development.
Recent cutovers and/or dry sandy sites had flatter curve slopes than
5-year-old cutovers or moist sandy loam till sites. Daily rates of AE
in 1973 (May 1 to August 31) ranged up to 5 mm. Semi-monthly estimates
of AE, which were calculated from the cumulative curves, indicate
moisture environemnts of significant length in determining regeneration
Water stress reduces germination and growth of regeneration.
Ratio of AE to potential evapotranspiration (PE) is one measure of
stress; the magnitude is influenced by growing season weather and
available soil water capacity. Ratios progressively decreased in
the following order: sandy clay loam till, washed sandy loam till
and sandy lacustrine or outwash terrain.
Comparative ecological studies of white spruce and jack
pine seedlings in greenhouse and field revealed morphological and
physiological differences. Pine had deeper taproots and greater
root mass than white spruce. Control of water loss and enhanced
drought avoidance are suggested by pine leaf water characteristic
curves. White spruce consistently developed higher stresses than
pine in the field under similar weather conditions. Stresses for both
species were highest on coarse textured soils. Pine strategy favours
drought avoidance and that of spruce favours growth.
July precipitation and temperature regimes of the previous
year correlate well with current-year height increments of jack pine,
white and black spruce seedlings. Wet to very wet conditions
(precipitation more than 2 cm above normal) appear most favourable
Integration of the various studies suggests that species
conversion and/or stand degradation is unlikely except under extreme
environments on moist sandy clay loam till supporting mixedwood
forests or in black spruce forests on wet, organic flats.
Specific silvicultural recommendations are made for major
terrain types. Greatest regeneration problems occur on moist lower ,
slopes and very moist to wet flats of till plains. Maximum size of
cutovers should be 50 and 25 ha respectively. Recommended site
preparation includes scalping or trenching on the former and scarification
followed by artificial reforestation on the latter.||en_US