| Summary: | Conifer plantations established on cutovers in the CWHb1
zone on Northern Vancouver Island grow well initially, but
coincident with the reinvasion of salal (Gaultheria shallon
Pursh.) on sites formerly dominated by western red cedar and
western hemlock (CH phase) the trees become chiorotic and
growth stagnates. These symptoms are not seen on sites
dominated by western hemlock and amabalis fir (HA phase).
This study examined some site and soil chemical factors which
could be responsible for differences in forest productivity
by: 1) documenting physical differences between the CH and HA
phases; 2) documenting morphological and chemical differences
between the organic horizons found in forest floors of CH and
HA phases using classical wet chemistry techniques and 13C
nuclear magnetic resonance (NMR) spectroscopy; 3) determining
seasonal trends in free phenolic acid concentrations of soils
under salal on CH cutovers by high speed centrifugation and
High Performance Liquid Chromatography, and 4) determining if
solutions of phenolic acids at field concentrations or of
salal leachates have a negative effect on conifer seed
germination, growth and short term 32phosphorus uptake.
The HA phase was found to occur on higher topographic
positions making them drier and more susceptible to windthrow
events than the CH phase which occur on adjacent, lower slope
positions. This windthrow process appears to rejuvenate the
site by mixing organic horizons with mineral soil, increasing
aeration, breaking hardpans, and generally improving site
conditions.
Six distinct humus horizons were identified on the basis
of origin and on degree of decomposition. The proportion of
humus horizon types on the CH reflected ecosystem maturity and
lack of disturbance; that of the HA indicated repetitive
windthrow events. The CH humus horizons tended to have higher
concentrations of K, Ca, Mn, available S, lipids, and total
and labile polysaccharides, as well as a higher pH. The HA
humus horizons were found to be higher in available N and P
and tended to have a lower C/N ratio for the more well—
humified horizons. Tannin signals from 13C NMR spectroscopy
were found in the Fm horizons of both CH and HA, but the
intensity was greater for the CH. The source of tannins
appears to be salal, as strong tannin peaks were identified in
salal roots, leaves, flowers, berries and litter. Tannins are
known to inhibit decomposition and mineralization processes.
Concentrations of phenolic acids originating from
angiosperms (presumably salal) were significantly higher in
summer months, coincident with greater physiological activity
of salal. Phenolic acids are known to cause root membrane
dysfunctioning in some situations. The germination values of
seeds and the biomass of seedlings of Sitka spruce, western
hemlock and western red cedar tended to be lower given
treatments of either a phenolic acid solution at field
concentrations or a salal leachate solution compared to a
control of distilled water. The uptake of 32P by the excised
roots of Sitka spruce and western hemlock were higher for the
phenolic acid and salal leachate solutions than for the
control, indicating P was probably limiting even after only 12
weeks. Uptake of 32P by fine roots of mature western red cedar
and western hemlock was significantly reduced by the phenolic
acid and salal leachate solutions.
In conclusion, this study provides evidence to suggest
that the growth-check of conifer regeneration involves a
number of interacting factors. These include: 1) the presence
of hardpans and compacted mineral soils which contribute to
annual periods of anaerobic soil conditions; 2) the presence
of large pockets of nutrient poor woody humus, and 3) the
presence of tannins, lipids and phenolic acids in active humus
horizons which may be contributing to decreased decomposition,
mineralization and nutrient uptake in trees. === Forestry, Faculty of === Graduate
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