Succession of algal communities in headwaters: a comparison of pine afforested and natural grassland streams

Abstract

We evaluated changes in the succession process in benthic algal communities of an afforested stream by comparing them with those in a grassland stream through analysis of temporal changes in composition, structure and functional traits in a 3-month experiment. We hypothesized that sunlight intensity reduction as a result of streamside implanted tree shading reduces the succession rate and community physiognomic complexity. We selected two streams with different riparian cover (grassland and pine afforestation) for installation of unglazed tiles as artificial substrates. The tiles were collected from each stream after 23, 45 and 73 days of exposure. Afforestation produced changes in algal succession, with lower biomass, lower diversity at the beginning of the experiment, and an increase in the proportion of small, low-profile, tolerant, unicellular and stalked algae, coinciding with the predominance of Achnanthidium. However, the grassland stream contained a higher proportion of intermediate-size algae, as well as a larger proportion of high-profile algae, coinciding with the expected results. In the afforested stream, succession proceeded toward the dominance of low-profile species, that were tolerant of low-light conditions. However, in grassland streams with higher sunlight availability, high-profile algae prevailed without the displacement of tolerant forms. Overall, our results indicate that algal communities in afforested stream remain structurally simpler.