Habitat patchiness, ecological connectivity and the uneven recovery of boreal stream ecosystems from an experimental drought. (29th March 2020) - Truchy, Amélie
Abstract: Ongoing climate change is increasing the occurrence and intensity of drought episodes worldwide, including in boreal regions not previously regarded as drought prone, and where the impacts of drought remain poorly understood. Ecological connectivity is one factor that might influence community structure and ecosystem functioning post‐drought, by facilitating the recovery of sensitive species via dispersal at both local (e.g. a nearby habitat patch) and regional (from other systems within the same region) scales. In an outdoor mesocosm experiment, we investigated how impacts of drought on boreal stream ecosystems are altered by the spatial arrangement of local habitat patches within stream channels, and variation in ecological connectivity with a regional species pool. We measured basal ecosystem processes underlying carbon and nutrient cycling: (a) algal biomass accrual; (b) microbial respiration; and (c) decomposition of organic matter, and sampled communities of aquatic fungi and benthic invertebrates. An 8‐day drought event had strong impacts on both community structure and ecosystem functioning, including algal accrual, leaf decomposition and microbial respiration, with many of these impacts persisting even after water levels had been restored for 3.5 weeks. Enhanced connectivity with the regional species pool and increased aggregation of habitat patches also affected multiple response variables, especially those associated with microbes, and in some cases reduced the effects of drought to a small extent. This indicates that spatial processes might play a role in the resilience of communities and ecosystem functioning, given enough time. These effects were however insufficient to facilitate significant recovery in algal growth before seasonal dieback began in autumn. The limited resilience of ecosystem functioning in our experiment suggests that even short‐term droughts can have extended consequences for stream ecosystems in the world's vast boreal region, and especially on the ecosystem processes and services mediated by algal biofilms. Abstract : Our experiment demonstrates that drought has impacts on multiple aspects of benthic structure and function in boreal stream ecosystems, including litter decomposition, autotrophic biomass accrual and microbial respiration. Some of those impacts persisted even after weeks of flow restoration. Spatial dynamics associated with habitat patchiness and connectivity with a regional species pool have potential to modestly enhance ecosystem recovery and stability. However, these effects were minor compared to the main effect of drought in our experiment, which overall demonstrates that the potential for functional recovery of boreal streams following late summer droughts is likely to be low.