Biomass of coastal cutthroat trout in unlogged and previously clear-cut basins in the central coast range of Oregon

Populations of coastal cutthroat trout Oncorhpnchus cla,ki clarki were samp led in 16 Oregon headwater streams during 1991-1993. These streams were abo ve upstream migration barriers and distributed among basins that had been l ogged 20-30 and 40-60 years ago and basins that had not been logged but had burned 125-150 years ago. The objective of our study was to characterize t he populations and habitats of age-1 or older cutthroat trout within these three forest management types. Streams within unlogged basins had relativel y low levels and a small range of trout biomass (g/m(2)). Streams in basins logged 40-60 years ago supported low levels but an intermediate range of t rout biomass. Streams in basins logged 20-30 years ago supported the widest range of biomass, including the lowest and highest biomasses among all str eams sampled. The variable that best explained the variation of trout bioma ss among all 16 streams was the amount of large woody debris (LWD). All str eams were heavily shaded during at least part of the year by mostly closed tree canopies. Deciduous trees were more prominent in canopies over streams in logged basins, while conifers were more prominent in the stream canopie s of unlogged basins. Our results suggest that trout production in basins e xtensively clear-cut 20-60 years ago may generally decrease or remain low o ver the next 50 or more years because of decreasing loads of remnant LWD, p ersistent low recruitment potential for new LWD, and persistent heavy shadi ng by conifers. These logged basins are not likely to show an increase in t rout biomass over the next 50 years unless reset by favorable natural distu rbances or by habitat restoration efforts.