Effects of canopy cover and embeddedness on macroinvertebrate communities in California's Northern Coast Range streams

Background/Question/Methods Logging is well known to decrease canopy cover and increases the amount of sediment entering into local stream systems. Very little is known about how each of these factors influence stream communities. The increase in sediment, in particular, changes the amount of cobble buried by sediment (embeddedness). The effects and possible interactions of embeddedness and canopy cover on macroinvertebrate community structure (abundance, richness, and percentages of functional feeding groups) were examined in four streams in California, USA. Using a block design, in-bed trays were manipulated to contain high and low levels of embeddedness and high and low levels of shade. The high shade treatment (80%) was chosen to reflect current California standards for the degree of canopy closure left in logged forests. Replicate blocks were placed in logged streams with open canopy, warm water and historic anadromous (steelhead and coho) salmon runs and less degraded, closed canopy cold water streams with current salmon runs. Results/Conclusions Using ANOVA, we found that canopy and embeddedness affected feeding group abundance and richness and that individual families had varying responses to the treatments. There was also a trend toward an interaction effect of the two treatments. These results help identify the mechanisms underlying the effects of logging on stream invertebrate communities and suggests ways to focus restoration efforts.