Ministry of Forests

Cariboo Region Research Section

Forage Litterfall in Douglas-fir Forests int the Centeral interior of Britsh Columbia

Douglas-fir and arboreal lichen litterfall are important components of mule deer winter diet in the Cariboo Forest Region, central British Columbia. Trees that produce the most litterfall per hectare are highly valuable and require special consideration in management plans for winter ranges.

Over a 3-year period at Tree Farm Licence (TFL) 5, we found that a 198-year-old stand produced more lichen litter than either a 60- or an 87-year-old stand. Also, a high volume 1 74-year-old stand growing on a mesic bench site produced more lichen litterfall than the 198-year-old stand on a subxeric steep slope. On Fox Mountain (near Williams Lake), trees in age classes over 100 years produced significantly (p = .0~) more lichen litterfall than did younger classes. On TFL 5, more Douglas-fir litterfall fell in the 87- and 198-year-old stands than in the 60-year-old stand in 2 of 3 years. Rates did not vary between the two over-mature stands of similar age but different volume. On Fox Mountain, the mean Douglas-fir litterfall rates increased with class age but, because of high variability, were not significantly different. Both arboreal lichen and Douglas-fir litterfall rates vary greatly among and within years.

These results and additional observations led us to the following conclusions of interest to forest managers:

1. Trees beyond 100 years old supply the greatest potential amount of litterfall forage.

2. The natural clumpy arrangement of trees within dry-belt Douglas-fir stands should promote maximum litterfall as a result of breakage from crown contact. The clumpy structure of these stands can be maintained by the small group selection system described by Armleder et al. (1986).

3. Uneven-aged stand management will provide a continuous source of litterfall and a source of lichen fragments to inoculate the young trees.

4. Low volume partial cutting will not disrupt the microclimate necessary for lichen production. Low volume removal may be especially important on warm, dry aspects.

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