Effects of logging secondgrowth forests on headwater populations of coastal cutthroat trout: A 6-year, multistream, before-and-after field experiment

Abstract.—To understand how logging of second-growth forests affects populations of coastal cutthroat trout Oncorhynchus clarkii clarkii, we examined trout relative abundance, body condition (mass relative to length), and physical and thermal habitat in the summer and winter in four headwater streams (two treatment streams and two nonlogged control streams) over a 6-year period (2 years prelogging [1997–1998] and 4 years postlogging [1999–2002]). This is one of the first efforts to conduct a multiyear, replicated stream, before-and-after experiment on this scale to assess the effects of logging on fish and habitat. In the treatment streams, 21 % of the watershed area was logged by clear-cutting (no scarification or slash-burning). Careful logging approaches were employed to remove most of the riparian overstory (i.e., no machines were used within 5 m of stream, logs were felled and yarded away from riparian zones, all shrubs were left behind, and large wood was left in streams). Because a cooler summer climate occurred coincidentally with our postlogging period (the mean daily average summer air temperature was 1–28C cooler than the temperature during the prelogging period), the mean average and mean maximum daily stream temperatures declined after the logging period in the control streams and remained the same in the treatment streams. After accounting for the effects of climate, logging had warmed treatment streams by about 18C. We could not detect any logging treatment effects on summer or winter relative abundance or condition, nor were any changes evident t