PARENT SESSION
Oral Session #44: Disturbance ecology of forests: Animals, wind, gaps, edges. Presiding: S. Archer.
Wednesday, August 8, 2001. 8:00 AM to 11:45 AM. Hall of Ideas G.
Vegetation responses along edge-to-interior gradients within green-tree retention patches in Douglas-fir forests.
NELSON, CARA1, HALPERN, CHARLES1, 1
ABSTRACT- Aggregated retention of overstory trees is now a standard component of harvest prescriptions on federal forests in the Pacific Northwest. Although patches of retained trees are thought to facilitate the maintenance of biological diversity in harvested areas, the extent to which they retain components of the original forest understory or ameliorate conditions in the surrounding disturbed matrix has not been tested. We are studying vegetation responses to disturbance and edge-to-interior gradients in and adjacent to 1-ha retention patches at two sites in the western Cascade Range of Washington. Pre- (1996) and post-harvest (1998, 1999) frequency and cover of vascular plants were measured along 16, 100-m long transects placed perpendicular to the edges of four retention patches. Over 2 yr, patches were relatively resistant to extirpation of forest species (mean loss of 1.0 species/patch) and to colonization by early-seral species (mean addition of 1.0 species/patch), and were relatively stable with respect to changes in total species richness (mean increase of 2.3 species/patch). By contrast, 3.0 forest understory species were lost, 9.0 species invaded, and mean richness increased by 9.0 species in the harvested matrix surrounding each patch. Cover of herbaceous and sub-shrub species were more strongly affected by proximity to edge than was cover of taller woody plants. Herbs associated with late-seral forests (in particular Achlys triphylla, Clintonia uniflora, and Listera caurina) were the most sensitive to creation of forest edges.
KEY WORDS: understory vegetation, edge effects, green-tree retention, late-seral herbs