Abstract
Many studies have quantified uncertainty in forest carbon (C) storage estimation, but there is little work examining the degree of uncertainty in shrubland C storage estimates. We used field data to simulate uncertainty in carbon storage estimates from three error sources: (1) allometric biomass equations; (2) measurement errors of shrubs harvested for the allometry; and (3) measurement errors of shrubs in survey plots. We also assessed uncertainty for all possible combinations of these error sources. Allometric uncertainty had the greatest independent effect on C storage estimates for individual plots. The largest error arose when all three error sources were included in simulations (where the 95% confidence interval spanned a range equivalent to 40% of mean C storage). Mean C sequestration (1.73 Mg C ha–1 year–1) exceeded the margin of error produced by the simulated sources of uncertainty. This demonstrates that, even when the major sources of uncertainty were accounted for, we were able to detect relatively modest gains in shrubland C storage.
Highlights
Shrublands are one of the most widely distributed biomes globally [1], and make a significant contribution to terrestrial carbon (C) storage [2]
Our study aims to estimate the degree of uncertainty around shrubland C estimates, using a novel individual-level allometric approach, and tests whether observed changes in C storage between repeated plot surveys are beyond the margin of error produced by this uncertainty
Variability in the co-efficient values under bootstrapping arose because the few large shrubs harvested have a great deal of leverage in allometric equation fitting
Summary
Shrublands are one of the most widely distributed biomes globally [1], and make a significant contribution to terrestrial carbon (C) storage [2]. Accurate documentation of C gain during succession from shrubland to forest is vital for including abandoned agricultural land in afforestation-based emissions trading schemes. Accurate models of C gain during succession are needed for assessing potential C sequestration under different scenarios of land-use change [8,9], and these can, be used by landowners to assess economic viability of carbon farming as an alternative to traditional grazing [8]. Individual-level allometric approaches for shrublands are required for building mechanistic models of C sequestration (e.g., [10]) during succession from shrubland to forest, as these models require information on the establishment, growth, and mortality of individual plants. Use of an individual-level allometric approach in shrublands would allow these demographic processes to be documented from the very beginning of post-agricultural woody succession. This, in turn, would permit a unified modelling approach to be applied to all stages of succession, rather than a decoupled framework where shrublands and forests are modelled separately
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