SCHIRP
Trees, esp. Ss and Ba, grow poorly on
CH-salal cut blocks. Why? 4 hypotheses:
- DISTURBANCE
– areas frequently disturbed (major windthrow) are occupied by HB-blueberry
and not CH-salal. HB types are more productive. Therefore it must be the
disturbance improves the soil & dense HB stand shades out salal and is thus
linked to #2 below)
NO evidence that sudden disturbance (single windthrow event)
would sig. Improve nutrient conditions. MAYBE repeated disturbance events do.
- SALAL
–
Theory 1: a) allelopathic interference from salal inhibits tree root and/or
mycorrhizae growth/function. b) Further, these chemicals could also impede OM
decomposition and mineralization of N.
Theory 2: salal is just a better competitor.
YES, competition (lotsa salal biomass, ALSO salal able to
utilize organic N) & allelopathy on mycorrhizae. MAYBE phenolics &
tannins from salal interfere with N mineralization
- REDCEDAR
– wood of Cw has many toxins (thujaplycins & phenolics), therefore, sites with
lotsa Cw wood will have lower decomposition rates (bugs & fungus inhibited).
NO to wood being a factor. LIKELY Cw litter contributes to
problem – has little N (good internal recycling) and resists breakdown
(contain lignins, waxes & lipids).
- SITE DIFFERENCE
– HB on knolls & upper slopes that have more wind exposure and are better
drained. CH sites are on lower slopes (wetter, cooler, less wind).
YES, CH types were wetter (cooler) leading to incomplete
decomposition and low rates of N mineralization.
Note:
N & P were in low amounts in CH-salal
types before harvesting. After clearcut there is assart effect (temporary
increase in nutrient availability). But nutrients are quickly utilized by
seedlings (mod-good early growth) AND salal. Nutrients are then immobilized in
salal biomass.
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