This research is studying the biological communities of intermittent and perennial headwater streams in hemlock and hardwood forests in north-central Massachusetts, with particular focus on mosses and aquatic insects. The overall goal is to test the hypotheses that hemlock-dominated streams are more thermally stable, remain cooler in summer and warmer in winter, and are less susceptible to seasonal drying than hardwood-dominated streams, and that hemlock streams support a richer aquatic macroinvertebrate fauna, support a higher proportion of predatory fish species, and are more likely to sustain populations of native brook trout than hardwood streams.