Climate indices strongly influence old-growth forest carbon exchange

Abstract

We present a decade and a half (1998–2013) of carbon dioxide fluxes from an old-growth stand in the American Pacific Northwest to identify ecosystem-level responses to Pacific teleconnection patterns, including the El Niño/Southern Oscillation (ENSO). This study provides the longest, continuous record of old-growth eddy flux data to date from one of the longest running Fluxnet stations in the world. From 1998 to 2013, average annual net ecosystem exchange (F_NEE) at Wind River AmeriFlux was −32 ± 84 g Cm⁻²yr⁻¹ indicating that the late seral forest is on average a small net sink of atmospheric carbon. However, interannual variability is high (>300 g Cm⁻² yr⁻¹) and shows that the stand switches from net carbon sink to source in response to climate drivers associated with ENSO. The old-growth forest is a much stronger sink during La Niña years (mean F_NEE = −90 g Cm⁻² yr⁻¹) than during El Niño when the stand turns carbon neutral or into a small net carbon source (mean F_NEE = +17 g Cm⁻² yr⁻¹). Forest inventory data dating back to the 1930s show a similar correlation with the lower frequency Pacific North American (PNA) and Pacific Decadal Oscillation (PDO) whereby higher aboveground net primary productivity (F_ANPP) is associated with cool phases of both the PNA and PDO. These measurements add evidence that carbon exchange in old-growth stands may be more sensitive to climate variability across shorter time scales than once thought.

Citation

Wharton, Sonia; Falk, Matthias. 2016. Climate indices strongly influence old-growth forest carbon exchange. Environmental Research Letters. 11(4): 044016-. https://doi.org/10.1088/1748-9326/11/4/044016.