Change in Extent of Meadows and Shrub Fields in the Central Western Cascade Range, Oregon*

Abstract

We examined change in areal extent of mountain meadows and fields of deciduous shrubs and conifer saplings in the central western Cascade Range of Oregon, based on analysis of aerial photographs taken in 1946 and 2000. These nonforest vegetation patches are distinctive habitats in dominantly forested landscapes, such as the Cascades, and change in extent of these habitats is of interest to scientists and land managers. We mapped and dated even-aged forest stands of probable postfire origin around the nonforest patches, using tree-ring analysis and interpretation of aerial photographs. We used these and archival data to interpret possible influences of past wildfire and sheep grazing on the extent of nonforest patches. The total area of nonforest vegetation patches decreased from 5.5 percent of the study area in 1946 to 2.5 percent in 2000. Significantly more cases of contracted patches were observed for mesic and xeric meadows which have adjacent forest established after wildfire in the approximately 150 years preceding 1946. A higher proportion of mesic (47 percent, n = 47) than xeric (17 percent, n= 115) meadows contracted between 1946 and 2000. Broad-leaved shrub fields were unchanged, probably because of topo-edaphic controls, dense cover of shrubs, and snow effects; but all fields of conifer saplings underwent succession to forest. We observed no strong influences of sheep grazing on the extent of meadows.