Effect of alternative silvicultural systems on vegetation and bird communities in coastal montane forests of British Columbia, Canada

Abstract

The montane alternative silvicultural systems (MASS) study was established to test the feasibility and ecological consequences of alternative silvicultural systems in montane old-growth forests of coastal British Columbia. The experiment includes replicated treatments representing a range of overstory removal (shelterwood, patch clearcut and green tree retention), adjacent old-growth and clearcut `control' areas and pre- and post-harvest measurement of a variety of ecological attributes. In this paper, we report results from vegetation and bird studies. Forest trees and understory vegetation were sampled on a series of permanent plots. Forest birds were monitored using transect methods during winter and point-counts during the breeding season. The cover, frequency and number of species of understory plants decreased after all harvesting treatments. Three years after harvest, cover increased in the harvested areas primarily due to herbaceous colonizers. The shelterwood, where understory vegetation was protected in undisturbed groups of leave trees, retained the greatest diversity of understory trees, shrubs and bryophytes compared to the other systems. Shelterwood species richness and abundance were greater 3 years after harvesting than before harvesting, but changes in species composition were quite variable. Presence of bryophytes and herbs that prefer moist, shaded habitats generally decreased after harvesting. Pre-harvest breeding bird communities were dominated by a few abundant species. Of 26 species detected, 4 species accounted for 64% of all bird detections, and 10 species accounted for 96%. Different levels of canopy retention produced dramatic effects on breeding birds. Species richness and bird abundance were reduced 3 years after harvesting. Most common species (9 species) showed evidence of population decline, 2 species showed significant increase, and 3 species showed unchanged abundance. Few species were completely lost or added to the avifauna. Only 17 species were recorded during winter surveys, of which 2 species accounted for the majority (68%) of detections. The vast majority (85%) of winter resident birds were concentrated in the old growth and the unlogged portions of patch-cut blocks.