Abstract
In Canada, climate change and forest harvesting may both threaten the ecological integrity of boreal lakes. To disentangle the effects of natural variation in climate and lake environments from those of logging, we evaluated long-term variation (1991–2003) in zooplankton communities of six boreal lakes in Ontario. We monitored concomitantly changes in zooplankton abundance and composition in three undisturbed and three harvested lakes, five years prior and eight years after watershed clearcut logging. We tested the hypothesis that long-term natural variation in climate and lake environments will be more important drivers of zooplankton community changes than short-term impacts of logging. We used space/time interaction tests and asymmetric eigenvector maps to model zooplankton responses to environmental changes and logging. Year-to-year variation in zooplankton abundance and composition were almost an order of magnitude whereas among-lake variation was stable through time. Breakpoints in time series of zooplankton in each lake were not directly related to logging. Climatic and limnological features were the most important drivers of long-term variation in the zooplankton community, shading the effect of logging. These results highlight the need to better understand the pressures exerted by climate change on boreal lake ecosystems in the context of anthropogenic pressure, such as logging.
Highlights
lake variation (Lake) are the major landscape features of the boreal ecoregion in Canada
There were significant long-term changes in zooplankton abundance which were not, consistently associated with the changes in zooplankton abundance which were not, consistently associated with the occurrence and intensity of logging disturbances, confirming our hypothesis that variations in occurrence and intensity of logging disturbances, confirming our hypothesis that variations limnological features and climate exert a stronger effect on zooplankton community changes than in limnological features and climate exert a stronger effect on zooplankton community changes short-term impacts of logging disturbance
There is a considerable potential for interactions climate change and human perturbations affecting boreal lakes, including overharvesting by clearcut between climate change and human perturbations affecting boreal lakes, including overharvesting by logging of watersheds
Summary
Lakes are the major landscape features of the boreal ecoregion in Canada. Climate change and watershed clearcut logging are two major disturbances in Canadian forests and represent important threats for the ecological integrity of boreal lakes [1,2]. As zooplankton organisms respond both to bottom-up and top-down forces (multiple force hypothesis [31]), it is very difficult to disentangle the effects of natural variation in abiotic (climate, water quality, nutrients) and biotic (algal resources, grazing, and predation) factors from the direct and indirect effects of logging disturbances These difficulties arise from the confounding effects of natural variation at regional scale in climate, limnological features, and trophic interactions. To investigate long-term impacts of watershed forest harvesting on Boreal Shield lakes in regards to natural environmental variation in climate and limnological features, we monitored changes in zooplankton communities of three harvested lakes five years before and eight years after logging, concomitantly with three neighbouring undisturbed lakes. The final aim should beconsiderable, to test if the change in lake community structure community [34], impact assessment of watershed disturbances must be replicated at the scale of the and function is beyond what one may expect from natural variation in unperturbed ecosystems. Is beyond what one may expect from natural variation in unperturbed ecosystems [14,35,36]
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