Site preparation effects on growing season soil water regimes were
investigated on three clearcut, grass-dominated sites in the Interior
Douglas-fir (IDFdk), Montane Spruce (MSxk) and Engelmann spruce-Subalpine
fir (ESSFxc) Biogeoclimatic Subzones, near Kamloops, British Columbia. The
response of newly planted Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco)
and lodgepole pine (Pinus contorta Dougl.) to these treatments was
determined at the IDFdk site.
Soil water regimes were measured in scalped, ripped and herbicide site
preparation treatments and in an untreated control using a neutron moisture
meter, a two-probe gamma-density gauge, tensiometers and thermocouple
psychrometers. At the IDFdk, seedlings were spring planted in each of the
treatments and control to determine whether microclimate modification by
site preparation would improve seedling water relations, growth and survival
during the first growing season.
Root zone soil water content was most limited at the low-elevation site
(IDFdk) and least limited at the high-elevation site (ESSFxc). The different
site preparation treatments provided similar increases in root zone soil
water content, profile water storage and drainage at each site. This
resulted in substantial increases in soil water supply at the lowest two
sites.
Site preparation resulted in increased Douglas-fir and lodgepole pine
stomatal conductance (gs), transpiration (E), leaf area, root egress, root collar basal area and dry matter production. Survival of both species was
high in the control and in all site preparation treatments.
Both species had similar seasonal patterns of gs and E in the control. In
the site preparation treatments, lodgepole pine had greater gs, and by late
summer, greater E than Douglas-fir. Although lodgepole pine had
substantially higher twig xylem pressure potentials and lower soil-plant
liquid flow resistances than Douglas-fir, both species appeared well adapted
to survive drought.
First growing season stomatal responses of both species to environmental
conditions, including normalized vapor pressure deficit at seedling height
(Ds/P), solar irradiance (Rs) and root zone extractable water (Φe), were
similar when normalized against annual maximum conductance (gsmax ).
A multiplicative model with non-linear least squares optimization (NLLS)
of response functions to Rs, Ds/P and Φe provided a simple, reasonably
accurate description of gs/gsmax for both species, and accounted for differences in gs between the control and ripped treatment. In most cases,
the NLLS models developed for a given species and year resulted in
relatively precise (R²>0.60) and unbiased estimates of gs /gsmax, and yielded
estimates of mean daily stomatal conductance (Gs ) and total daily
transpiration (T) within 20% of measured values, for the same species in
other years. / Land and Food Systems, Faculty of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/41652 |
| Date | January 1993 |
| Creators | Fleming, Robert LeSueur |
| Publisher | University of British Columbia |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
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