Scaling Uncertainties in Estimating Canopy Foliar Maintenance Respiration for Black Spruce Ecosystems in Alaska |
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| Authors: | Xinxian Zhang A David McGuire Roger W Ruess |
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| Institution: | (1) Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks, AK;(2) U.S. Geological Survey, Alaska Cooperative Fish and Wildlife Research Unit, University of Alaska Fairbanks, Fairbanks, AK;(3) Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK |
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| Abstract: | A major challenge confronting the scientific community is to understand both patterns of and controls over spatial and temporal
variability of carbon exchange between boreal forest ecosystems and the atmosphere. An understanding of the sources of variability
of carbon processes at fine scales and how these contribute to uncertainties in estimating carbon fluxes is relevant to representing
these processes at coarse scales. To explore some of the challenges and uncertainties in estimating carbon fluxes at fine
to coarse scales, we conducted a modeling analysis of canopy foliar maintenance respiration for black spruce ecosystems of
Alaska by scaling empirical hourly models of foliar maintenance respiration (Rm) to estimate canopy foliar Rm for individual stands. We used variation in foliar N concentration among stands to develop hourly stand-specific models and
then developed an hourly pooled model. An uncertainty analysis identified that the most important parameter affecting estimates
of canopy foliar Rm was one that describes Rm at 0 ∘C per g N, which explained more than 55% of variance in annual estimates of canopy foliar Rm. The comparison of simulated annual canopy foliar Rm identified significant differences between stand-specific and pooled models for each stand. This result indicates that control
over foliar N concentration should be considered in models that estimate canopy foliar Rm of black spruce stands across the landscape. In this study, we also temporally scaled the hourly stand-level models to estimate
canopy foliar Rm of black spruce stands using mean monthly temperature data. Comparisons of monthly Rm between the hourly and monthly versions of the models indicated that there was very little difference between the estimates
of hourly and monthly models, suggesting that hourly models can be aggregated to use monthly input data with little loss of
precision. We conclude that uncertainties in the use of a coarse-scale model for estimating canopy foliar Rm at regional scales depend on uncertainties in representing needle-level respiration and on uncertainties in representing
the spatial variability of canopy foliar N across a region. The development of spatial data sets of canopy foliar N represents
a major challenge in estimating canopy foliar maintenance respiration at regional scales. |
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| Keywords: | black spruce boreal forests canopy ecosystems maintenance respiration modeling spatial scaling temporal scaling |
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