Patterns of Forest Disturbance in the Oregon Coast Range with Implications for Oregon Coast Coho Salmon

Forestry practices in the Oregon Coast Range are widely considered to be a threat to the viability of the Oregon Coast coho salmon Evolutionarily Significant Unit (ESU), yet there has been no way to uniformly evaluate patterns of forest disturbance over the range of the fish. Release of Landsat data to the public, along with recent advances in analysis, now enable us to map forest disturbance on an annual basis from 1986 to the present. Analysis shows that in some coastal river basins over forty percent of forest cover has been disturbed during this period. Prior to 1990, the highest disturbance rate was on Federal forests. After the implementation of the Northwest Forest Plan, harvest moved to private industrial lands, peaking in 2002 before falling off somewhat. We test the hypothesis that coho salmon spawners are less abundant in streams flowing through more highly disturbed forests. The relationship between disturbance and spatial patterns of coho spawning abundance are explored. Heterogeneous habitats within the ESU, the sensitivity of salmon usage to the timing of disturbance, time lags in effects, and primary control of abundance by marine survival all conspire to complicate the analysis. Nonetheless, improved information about patterns of disturbance will allow us to better understand the distribution of clear-cutting, thinning, and fire in space and time, and the implications of forest disturbance to the distribution, abundance, and productivity of coho salmon in the Oregon Coast ESU.