Study finds wide-scale impacts from logging on stream biota

Chilliwack (aka Vedder) River at dawn. Image credit, Stephen Edwards.According to a new study in the Journal of Applied Ecology, forestry practices can cause wide reaching changes to the physical features and biological communities of rivers - impacts that are still evident even forty years later. 

Researchers looked at streams in forests subject to logging in the Chilliwack River basin of British Columbia and found that they had lower invertebrate diversity and abundance in the benthic zone compared to what was predicted from looking at reference streams in mature forests.  They also found that logging altered physical features, for example by reducing large wood accumulation and leaf litter input.

What is most interesting about the study, though, is that it looked at impacts to streams from forestry on a much wider scale than most previous research. Study authors Yixin Zhang, John Richardson and Xavier Pinto
write, 

"Most forestry-stream studies are performed at the reach scale to examine direct effects of local forest changes. Looking beyond reach-scale effects to impacts originating from upstream is rare, but crucial to better manage the impacts or mitigate the effects at catchment scales."

The authors hypothesize that the increased sedimentation from catchment-scale forestry practices may contribute to the decline of stream benthic communities. Forest cutting can cause soil exposure leading to Increased sediment load and downstream transport and deposition.

Based on the findings, the authors offer the following recommendation to managers:

"Our study demonstrates that there are persistent impacts measurable at catchment scales, which means that considerations for management at a broader scale for best management practices may be necessary, and not just at the local scale."

--Reviewed by Rob Goldstein

Zhang, Y., Richardson, J., & Pinto, X. (2009). Catchment-scale effects of forestry practices on benthic invertebrate communities in Pacific coastal streams Journal of Applied Ecology DOI: 10.1111/j.1365-2664.2009.01718.x