Stream biota under shade: pine plantations alter macroinvertebrate assemblages and habitat structure in upland grassland catchments

Abstract

Assessing forestry impacts on aquatic communities is crucial for effective water resource management and cost-efficient monitoring. This study evaluates the effects of converting grassland catchments to pine plantations on stream macroinvertebrate assemblages across three distinct habitats: riffles, pools, and macrophyte patches. We investigated spatial and temporal dynamics in taxonomic composition, abundance, and functional feeding groups in three headwater streams draining natural grasslands and three draining pine plantations in a mountain watershed of central Argentina. Our results revealed that the conversion to pine plantations leads to significant alterations in stream biota. Assemblage composition was notably different in macrophyte patches and pools, with EPT metrics (richness and abundance) consistently reduced across all habitats in pine plantations. Furthermore, a decline in indicator taxa—particularly in riffles and macrophyte patches—and the predominance of dipterans typically associated with degraded conditions underscore the negative ecological impacts of pine plantations. Functionally, gathering collectors, the dominant group in the region, exhibited marked reductions in both richness and abundance within macrophyte patches. The loss of macrophyte diversity, likely driven by reduced light levels from dense pine canopies, compromises habitat complexity and resource availability, posing broader risks to stream biodiversity. These findings underscore the need for improved management practices to mitigate the adverse effects of pine afforestation on freshwater ecosystems.