Historical Savanna Structure And Succession At Jim’s Creek, Willamette National Forest, Oregon

Description

Oak savanna was once a major ecosystem of Oregon’s Willamette Valley. Changing land-use patterns, urbanization and fire suppression have contributed to the loss of oak savanna throughout its former range, and it is estimated that less than 1% remains. Using tree distribution, tree-age and environmental data, historical savanna structure and recent forest succession at Jim’s Creek, Willamette National Forest were investigated. Data were collected at 38 30 m x 30 m study plots representing five different community types. Monte Carlo methods were utilized to simulate community-wide tree age class and species distributions. Results indicate that the area was once an open savanna with 17 trees/ha composed of Oregon white oak, ponderosa pine and Douglas-fir. Beginning 125-150 years ago, dramatic changes took place and the area is now principally a Douglas-fir forest with up to 566 trees/ha. Oak comprised 35% of former savanna trees, but only 2% of current trees.