PARENT SESSION
Poster Session 37: Forest Ecology.
Thursday, August 5 Presentations from 5:00 PM to 6:30 PM, Exhibit Hall A 1.
Vegetation responses to varying levels and patterns of overstory retention: Early results of the DEMO experiment.
Halpern, Charles *,1, McKenzie, Donald2, Evans, Shelley1, Saracco, James3, Maguire, Douglas 4, Halaj, Juraj5, 1 University of Washington, Seattle, WA2 United States Forest Service, Seattle, WA3 The Institute for Bird Populations, Pt. Reyes Station, CA4 Oregon State University, Corvallis, OR5 Cascadien, Inc., Corvallis, OR
ABSTRACT- The practice of retaining overstory trees through timber harvest has become increasingly common in both temperate and boreal ecosystems as land managers seek to balance the commodity and ecological values of managed forests. We used a randomized block design in mature coniferous forests at six locations in the Pacific Northwest to examine vegetation responses to overstory retention at two levels (15% vs. 40% of initial basal area) and spatial patterns (dispersed vs. aggregated). Post-harvest mortality of residual trees declined over the 3-yr measurement period; cumulative mortality was 2.1-2.4 times greater at 15% than at 40% retention and 2 times greater in dispersed than in aggregated treatments due to windsnap or windthrow of newly exposed trees. Declines in the abundance and richness of vascular understory plants and changes in species composition were significantly greater at 15% than at 40% retention, yet pattern of retention had little effect on understory response. Within aggregated treatments, changes in abundance and richness were small within the 1-ha forest patches, but declines in adjacent harvest areas were large and generally greater than those in dispersed treatments. Late-seral herbs were particularly sensitive to these effects, experiencing more frequent extirpation from harvested portions of aggregated treatments than from dispersed treatments. Ground-layer bryophytes showed large, but comparable declines in abundance and richness among all harvest treatments. Initial understory responses may be explained, in large part, by variation in the amount and distribution of ground disturbance and logging slash, but as effects of disturbance diminish with time, overstory structure will increasingly shape patterns of understory development.
Key words: plant diversity, disturbance, forest, tree mortality