ALTERNATIVE SILVICULTURAL REGIMES IN THE PACIFIC-NORTHWEST - SIMULATIONS OF ECOLOGICAL AND ECONOMIC-EFFECTS

Citation
Aj. Hansen et al., ALTERNATIVE SILVICULTURAL REGIMES IN THE PACIFIC-NORTHWEST - SIMULATIONS OF ECOLOGICAL AND ECONOMIC-EFFECTS, Ecological applications, 5(3), 1995, pp. 535-554
Citations number
59
Categorie Soggetti
Ecology
Journal title
ISSN journal
10510761
Volume
5
Issue
3
Year of publication
1995
Pages
535 - 554
Database
ISI
SICI code
1051-0761(1995)5:3<535:ASRITP>2.0.ZU;2-1
Abstract
New silvicultural strategies to sustain both ecological and human comm unities are being developed and implemented on federal forest lands in the Pacific Northwest (PNW) United States. Two important stand-level components of the new silviculture regimes are rotation age and retent ion level of live trees in harvest units. Ecologists have suggested th at canopy tree retention and longer rotations will create patterns of stand structure in managed forest that are similar to those in natural forests, and promote long-term ecological productivity and biodiversi ty. Forest economists, however, are concerned that canopy tree retenti on and long rotations may reduce wood production, although the high va lue of large logs produced by these new silvicultural regimes may comp ensate for reduced growth rates. We used the forest model ZELIG to per form a factorial simulation experiment on long-term responses of ecolo gical and economic variables to nine retention levels and four rotatio n lengths. ZELIG output on forest structure and composition was input to a forest economics model that calculated net value of wood products in 1989 dollars. The simulated stand data were also linked with regre ssion equations to predict the densities of 17 bird species as a funct ion of tree size class distribution. Five replicates of each treatment were run for the 240-yr simulation period. Results indicated that sta nd structure under each of the canopy tree retention levels was more s imilar to the pre-treatment natural forest than following clear-cuttin g. Variation in tree size under intermediate levels of retention, howe ver, did not reach the level of the natural forest during the simulati on period. Tree species composition was strongly related to retention level and rotation age. Shade-intolerant Douglas-fir (Pseudotsuga menz iesii) lost dominance to shade-tolerant species under intermediate ret ention levels and longer rotations. Wood production decreased signific antly with increasing retention level and rotation age, with a notable threshold between retention levels of 0 and 5 trees per hectare. Net wood products value did not decrease as rapidly with retention level, and did not differ much among rotation ages, because of the high value of large logs. Bird species responded individualistically to retentio n level and rotation age. Some had peak densities under short-rotation clear-cutting, but most were associated with structurally complex, cl osed-canopy forest. Consequently, bird species richness increased sign ificantly with retention level and rotation age. Within the assumption s and limitations of our models, this application provided knowledge o n trends and thresholds that can help land managers to choose silvicul tural regimes that best balance their management objectives. We conclu ded that retention level and rotation age strongly influence ecologica l and economic responses in PNW forests; efforts are needed to reduce uncertainty about these effects.