Mosses play a crucial role in many stream ecosystems by providing habitat for insects and algae and contributing to instream nutrient cycling, however in contrast to algae and vascular plants, much less is known about the distribution and long-term dynamics of mosses. We mapped the stream moss cover across 15,000 meters in 10 different tributaries of the mainstem of Hubbard Brook within Hubbard Brook Experimental Forest (New Hampshire, USA) and compared moss distributions to previous observations.
Results/Conclusions
In 2019, stream moss cover varied widely across the landscape. Across streams, the proportion of the bed varied from a high average of 78% moss cover in watershed 2, to 23% average moss cover in watershed 1. A strong driver of present-day moss cover appears to be the presence of boulder and bedrock substrata and within each stream, moss cover was higher in reaches dominated by bedrock and boulders. In cases where moss cover was previously mapped, we measured significant increases in Bear Brook (from 5% to 21% 1997 to 2019), found a decrease from 2000 to 2019 in watershed 9, and had little change between 2000 and 2019 in repeated surveys of watershed 8. Moss are the dominant autotrophs in these shaded headwater streams, providing both stable habitat and autochthonous carbon. The variation we observe in moss cover over both space and time raises many questions about what drives this variation in moss cover (such as physical habitat, stream water chemistry, and winter scour) and how changes in moss cover affect stream ecosystem structure and function.