| Summary: | Western hemlock (Tsuga heterophylla) is one of the most important tree species in
coastal British Columbia. Forest fertilization is a method used by foresters to enhance the
growth of forest trees, but results are inconsistent for western hemlock. The objective of
my research was to explore the use of carbon isotope analysis as a physiological tool to
diagnose the nutritional status and potential response of western hemlock to fertilization.
Normally cellulose is isolated from wood samples to be analyzed for carbon isotope
analysis (expressed as 813C values), but this is a tedious and likely unnecessary process.
Reaction wood (high lignin content) and adjacent normal wood in two western hemlock
saplings was analysed to evaluate the possible effects of wood composition on 813C. The
8 C values of the lignin and cellulose fractions differed by 3.43 %c ± 0.26 (mean ± SD;
n = 40). 813C values of lignin and cellulose from different disk positions were more
variable in one sapling than the other. The isotopic mass balance of whole wood was
conserved and therefore did not vary with lignin content indicating that use of whole
wood, rather than cellulose, is suitable for isotopic analysis.
Eight pure western hemlock stands selected and experimentally fertilized in an earlier
study were used as source for foliage and stemwood samples. Fertilization treatments
applied to these stands in mid to late May of 1995 were as follow: (1) control, (2) N (225
kg/ha), (3) N (225 kg/ha) + P (100 kg/ha), (4) N (225 kg/ha) + P (500 kg/ha), (5) N (225
kg/ha) + P (100 kg/ha) + blend (230 kg/ha), and (6) N (225 kg/ha) + P (500 kg/ha) +
blend (230 kg/ha). The blend included additions of S, K, Mg, Zn and Cu. 813C values
within foliage and stemwood were analysed after fertilization. At the end of first growing
season after fertilization, the effect of treatments on foliar 8 C was almost significant (P
= 0.0539) and there was an interaction between sites and treatments. At the end of second
growing season, no interaction between site and treatment was evident and the effect of
treatments on foliar 813C was not significant.
Foliar SO4-S (Sulfate) levels at the end of the first and second growing seasons following
fertilization were reduced by either N or N + P fertilization treatments.
The change in 813C values of tree rings from before to after nutrient additions was
significantly affected by treatment and site and there was an interaction between sites and
treatments. N applied alone had no significant effect on change in wood 813C. The
greatest change (0.33 %o) was in the NP100 (treatment 3 above) level of treatment.
Relative change in six-year basal area increment (BAI) was significantly affected by
treatments and sites and there was an interaction between sites and treatments. N applied
alone had no significant effect on relative change in basal area increment whereas
NP100B (treatment 5 above) had the greatest effect. The relative change in basal area
increment was also significantly affected by sites. === Forestry, Faculty of === Graduate
|
|---|
