Assessing the relations between aquatic habitat indicators and forest harvesting in British Columbia

Selection of appropriate aquatic habitat indicators is important for supporting sustainable forest and watershed management.  We sampled 30 stream reaches in the interior of British Columbia, Canada. The selected reaches were similar with respect to gradient, watershed and topographic characteristics but with various levels of forest harvesting. Aquatic habitat indicators were derived based on the field survey, involving substrates, channel dimensions, pools, and large wood debris (LWD), together with some ratios and derivatives generated from them. Timber harvest disturbance was quantified by calculating historical forest clear-cut area based on the vegetation resources inventory database. Furthermore, to account for the subsequent forest recovery, equivalent clear-cut area (ECA) was calculated based on the dominant species of each stream watershed.  Pearson correlation showed that percent ECA and percent historical clear-cut area can effectively quantify the accumulative forest logging disturbance by eliminating the effect of watershed area and elevations which are considered as factors not related to forest logging activity. These two variables were then related to the aquatic habitat indicators using correlation analysis. Results showed that relative width (ratio of D to bankfull width), relative roughness (ratio of D to bankfull depth), pool frequency and per piece LWD volume are significantly correlated to percent ECA, while only three of these identified indicators excepting relative roughness, have significant correlations to percent historical clear-cut area.  In comparison, per piece LWD volume was considered as the best aquatic habitat indicator among the four due to its most significant correlation to percent ECA.