COS 98-6 - CANCELLED - Upland forest construction promotes evaporative losses in integrated watershed reclamation projects in the Boreal Plains of Canada
Landscape-scale construction in the Athabasca Oil Sand Region (AOSR) is driving new questions about ecosystem interconnectivity and on ecosystem-scale metrics to evaluate landscape scale processes. Here we present a network of eddy covariance systems to anlayze productivity and water use efficiency. The network consists of 9 sites (55 site years) of constructed upland forests in the Athabasca Oil Sands, 3 sites post-harvest disturbance (18 site years) as well as drawing on 3 nearby mature FLUXNET reference sites (38 site years). We contrast the various disturbance types and recovery with regard to the mature reference sites to highlight how emphasis on forest recovery may impact hydraulic fluxes downgradient. The constructed forests are in different watersheds being constructed in the AOSR and are constructed to be resilient to cyclically dry climate regime of the Boreal Plains. The ASOR forests are upgradient of constructed lakes and wetlands built to accumulate organic matter (i.e. peat). The harvested sites are more typical disturbance as they are naturally regenerating within an unmodified landscape post-harvest.
Results/Conclusions
The harvest sites showed a return to seasonal productivity rates similar to the mature sites within 5 to 10 years of harvest. Progress was much slower in the constructed landscapes and productivity remained below the mature sites even in the oldest stands (17 years since planting). We demonstrate the resilience to climate variability was achieved with little change in productivity associated with extreme dry, hot, wet or cold years. We argue this resilience is a direct result of soils designed to maintain high soil moisture. This explains the high evapotranspiration rates observed in the constructed forests when compared to either the mature sites or the post-harvest sites. Furthermore, despite continued increases in productivity with age, the water use efficiency in the constructed sites plateaued after the first 10 years. This highlights a potential trade-off in designing future watersheds between prioritizing climate resilience in reclaimed forests (current ecosystem scale emphasis) by limiting downgradient hydraulic fluxes which are needed to promote wet lowland ecosystems (landscape scale) in this peat rich ecozone. This study uses a unique dataset to evaluate ecosystem-atmosphere interactions and contributes to a gap in our assumptions about large-scale watershed reclamation.
