Impact of forestry practices on ecology of algal communities in small brooks in the Nurmes experimental forest area, Finland

The effects of clear felling, ditching and site preparation on the species composition, biomass and production of algae in forest brooks have been studied in 1982–93 as a part of the Nurmes Project in Finland. After clear felling and site preparation the primary factors causing change in species composition of algae were the increased nutrient content and colour of water. As the effects of site preparation started to wear off the nutrient content and temperature of the water returned towards the original level, a new response was seen in species of algae. Immediately after ditching and clear felling the biomasses of Volvocales and Cryptophyceae rose and reached their maximum in the following open water season, while the proportion of diatoms in the biomass decreased. A protective forest zone between the brook and the area affected by the intervention appeared to be highly effective in preventing changes in the water quality.