Forest History and Meadow Invasion at the Rigdon Meadows Archaeological Site, Western Cascades, Oregon

Combining stand structure and fire-scar data with historical records, aerial photographs, and soil descriptions, the forest history of the Rigdon Meadows Archaeological Site in the western Cascades of Oregon is reconstructed. Results indicate that forest composition and meadow persistence are determined primarily by disturbance, soil properties, and topography. Before the arrival of Europeans, south-facing slopes and seasonally saturated sites near the meadow were dominated by an open, fire-maintained, ponderosa pine forest with scattered Douglas-fir. Mesic sites were dominated by Douglas-fir intermixed with incense-cedar and ponderosa pine. Dramatic changes in forest structure beginning in the mid-1800s resulted from fire, fire exclusion, grazing, road building, clearing, and selective logging. Currently, Douglas-fir and incense-cedar co-dominate all but the wettest forest sites surrounding the meadow. Seasonally saturated sites are occupied by ponderosa pine and include those areas experiencing rapid tree invasion. Soil morphology, lack of tree regeneration success, and a high natural fire frequency suggest the core portion of Rigdon Meadows has persisted since the mid-Holocene. [Key words: forest history, tree invasion, disturbance, Oregon Cascades.]