Historical and current forest landscapes of eastern Oregon and Washington. Part I: Vegetation pattern and insect and disease hazards. Prat 2.

We analyzed historical and current vegetation composition and structure in 49 sample watersheds， primarily on National Forests， within six river basins in eastern Oregon and Washington. Vegetation patterns were mapped from aerial photographs taken from 1932 to 1959， and from 1985 to 1992. We described vegetation attributes， landscape patterns， the range of historical variability， scales of change， and disturbance hazards. Forest cover increased eight percent in three river basins， but remained relatively unchanged in the other basins. Forests became more dense in vertical and horizontal canopy structure as understory cover increased with regeneration， of mostly shade-tolerant species. The distribution of forest age classes and structure has changed， with smaller area in early-seral and old forest stages and greater area in multiple-canopy young and mature stands. The percentage of visible dead trees increased in all river. basins. Landscape pattern has become more diverse and fragmented over time in five of the six river basins. Insect and disease hazards changed little， usually < 10 percent， at the river basin scale because there was considerable variation at the watershed scale， where large changes in hazards were common.(Richard L. Everett， assessment team leader; Eastside forest ecosystem health assessment; Paul F. Hessburg， science team leader and tech. ed.， Volume III: assessment.)