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Earth Observations; Essential Ecosystem Variables
Abstract:
How forest growth responds to climate change will impact the global carbon cycle. The sensitivity of tree
growth and thus forest productivity to climate can be inferred
from tree-ring increments, but individual tree responses may
differ from the overall forest response. Tree-ring data have
also been used to estimate interannual variability in aboveground
biomass, but a shortage of robust uncertainty estimates
often limits comparisons with other measurements of
the carbon cycle across variable ecological settings. Here we
identify and quantify four important sources of uncertainty
that affect tree-ring-based aboveground biomass estimates:
subsampling, allometry, forest density (sampling), and mortality.
In addition, we investigate whether transforming rings
widths into biomass affects the underlying growth-climate
relationships at two coniferous forests located in the Valles sources of uncertainty contributed most (34–57 and 24–42%,
respectively) and subsampling uncertainty least (7–8%) to
the total uncertainty for cumulative biomass estimates.
Subsampling uncertainty, however, was the largest source
of uncertainty for year-to-year variations in biomass estimates,
and its large contribution indicates that between-tree
growth variability remains influential to changes in year-toyear
biomass estimates for a stand. The effect of the large
contribution of the subsampling uncertainty is reflected
by the different climate responses of large and small trees.
Yet, the average influence of climate on tree growth persisted
through the biomass transformation, and the biomass
growth-climate relationship is comparable to that found in
traditional climate reconstruction-oriented tree-ring chronologies.
Including the uncertainties in estimates of aboveground
biomass will aid comparisons of biomass increment
across disparate forests, as well as further the use of these data in vegetation modeling frameworks.
