1. Landscape management practices that alter energetic linkages between aquatic and terrestrial habitats can affect associated ecosystem processes, and ultimately the provision of ecosystem services of importance to humanity. Such effects cannot always be inferred from current biomonitoring schemes, which are typically based on assessment of community structural parameters rather than functional attributes related to important ecosystem-level processes.
2. We investigated effects of forest clearcutting, a major landscape-level disturbance known to alter the energetic basis of aquatic food webs, on headwater streams in northern Sweden. The key ecosystem process of leaf decomposition was measured as an index of ecosystem functioning. The biomass of detritivorous shredders was also quantified, along with various community structural parameters associated with the diversity, composition and functional guild organisation of benthic macroinvertebrate assemblages.
3. No differences in macroinvertebrate abundance, diversity or assemblage composition were detected between forested and clearcut streams, and most functional guilds were similarly unaffected, though species density of scrapers was higher in forested than clearcut channels.
4. In contrast, mass loss of two leaf species was elevated in all clearcut streams, with evidence for increases in the efficiency per degree-day of both the microbial and detritivore mediated fractions of decomposition.
5. Increased rates of leaf mass loss in the clearcut streams were associated with greater phosphate concentrations and shredder biomass, and with an increased relative abundance of broadleaves in standing stocks of benthic litter. Together, these findings indicate a more rapid transfer of energy and nutrients through the detrital pathways of our clearcut streams.
6. These results demonstrate the utility of litter decomposition assays for monitoring effects of forest management on stream ecosystem functioning, and have implications for nutrient cycles in landscapes extensively influenced by forest management. The markedly different responses of our functional and structural measures to clearcutting highlight the value of incorporating methods for the functional assessment of ecosystems into biomonitoring schemes.