Windstorm disturbance effects on mountain stream ecosystems and the Plecoptera assemblages

Within the investigated river basins the deforestation ranged from 0-45.5%, dependent on the amount of windstorm damage. Our water temperature readings revealed that the canopy elimination above the streams in the areas damaged by the windstorm caused increase in daily and annual water temperature and also wider daily water temperature range, than those in the undisturbed reference stream, which caused the decline of cold stenotherm species abundance. The stream basins deforestation was collinear with FPOM and UFPOM concentrations, water temperature gradient and nitrate concentrations. Statistical analysis showed that size of stream, conductivity, catchment area and discharge were negatively correlated with the stonefly mesotherm ratio and nitrate contents. Higher average concentrations of nutrients ( like NO-3) in samples from some streams are a consequence of their mobilization from disturbed forest soils due to the windstorm. Most streams located in the deforested area were found by us in a higher trophic status, especially due the particulate organic matter (POM) content and biofilms amount, what caused increase in some functional feeding groups occurrence (collector-gatherers, scrapers and mainly predators). Stream degradation positively correlated with the percentage of deforested area, ratio of eurytherm taxa, transported organic matter, dissolved organic matter, and biofilms occurrence. The conductivity values measured in water samples were collinear with alkalinity and pH values and increased with watersheds areal extent. We established environmental variables influenced by the windstorm event along the catchment degradation gradient using measurable characteristics of stonefly assemblages and metrics. The proportion of the Leuctridae family and the Nemoura genus expressed as the LN index (1) shows a negative correlation with part undisturbed forested areas and channel stability, and positive correlation with stream erosion (expressed as the TAM quantity) in river basins. Proportion of shredders among the investigated streams was significantly higher in deforested streams, and shows lower stability of stonefly community in these habitats, where significantly fluctuate channel stability, water temperature and discharge of these streams.