Riparian forests provide a wide variety of ecosystem functions to streams, including erosion control, a supply of leaf litter and wood, and shade. Tree harvest in riparian areas can diminish these functions for a period of time. We examined the effects of riparian logging at 12 sites after Best Management Practices were implemented during a timber harvest. The 12 sites were all within the Pokegama Creek system, a low-gradient headwater stream in north central Minnesota.  Treatments included control (no harvest), riparian control, cut-to-length riparian thin, and tree length riparian thin. Each site was 4.9 ha with 2.45 ha on each side of the stream; stream length through each site was 150-200 m. Data from 1997 (pre-harvest) through 2000 showed few local-scale effects but suggested that basin-scale effects may be present.  We collected additional data in 2006 and 2007 and used repeated measures ANOVAs to examine basin-scale year effects for variables characterizing instream habitat, geomorphology, and fish communities. 

Results/Conclusions

Some basin-scale effects documented in the first few years after harvest were still evident after ten years, whereas other variables had recovered. In 2006 and 2007, canopy coverage and unstable banks were no longer significantly different from pre-harvest levels.  However, sediment storage was significantly greater than pre-harvest levels, as evidenced by sand depths (i.e., depth of refusal) and residual pool depths. Surficial fine sediments were significantly more prevalent than pre-harvest levels in 2006 but not in 2007.  Although most other habitat and fish variables showed no trends, brook trout abundance estimates and fish Index of Biotic Integrity scores both showed evidence of long-term reductions. The basin-scale year effects described cannot be definitively attributed to forest harvest, however, the declines in brook trout and Index of Biotic Integrity are consistent with a chronic effect of fine sediments.