Water availability limits tree productivity, carbon stocks, and carbon residence time in mature forests across the western US

Abstract

Abstract. Water availability constrains the structure and function of terrestrial ecosystems and is projected to change in many parts of the world over the coming century. We quantified the response of tree net primary productivity (NPP), live biomass (BIO), and mean carbon residence time (CRT = BIO / NPP) to spatial variation in water availability in the western US. We used forest inventory measurements from 1953 mature stands (> 100 years) in Washington, Oregon, and California (WAORCA) along with satellite and climate data sets covering the western US. We summarized forest structure and function in both domains along a 400 cm yr −1 hydrologic gradient, quantified with a climate moisture index (CMI) based on the difference between precipitation and reference evapotranspiration summed over the water year (October-September) and then averaged annually from 1985 to 2014 (CMI wy ). Median NPP, BIO, and CRT computed at 10 cm yr −1 intervals along the CMI wy gradient increased monotonically with increasing CMI wy across both WAORCA (r s = 0.93-0.96, p < 0.001) and the western US (r s = 0.93-0.99, p < 0.001). Field measurements from WAORCA showed that median NPP increased from 2.2 to 5.6 Mg C ha −1 yr −1 between the driest and wettest 5 % of sites, while BIO increased from 26 to 281 Mg C ha −1 and CRT increased from 11 to 49 years. The satellite data sets revealed similar changes over the western US, though these data sets tended to plateau in the wettest areas, suggesting that additional efforts are needed to better quantify NPP and BIO from satellites in high-productivity, high-biomass forests. Our results illustrate that long-term average water availability is a key environmental constraint on tree productivity, carbon storage, and carbon residence time in mature forests across the western US, underscoring the need to assess potential ecosystem response to projected warming and drying over the coming century.

Carbon sequestration and biodiversity co‐benefits of preserving forests in the western United States

“…, ), and net primary productivity estimated from the MODIS satellites (Berner et al. ). We also compared modeled burned area with a burned area data set derived from the Landsat satellites (Eldenshenk et al.…”

Near‐future forest vulnerability to drought and fire varies across the western United States

“…The grid cells that were used in PFT parameter calibration were excluded from this evaluation. We evaluated simulated carbon fluxes with state-level net primary productivity (NPP) derived from MODIS sensors (Berner, Law, & Hudiburg, 2017), FIA-derived carbon fluxes over Oregon, Washington, and California (Hudiburg et al, 2009;Hudiburg, Law, Wirth, & Luyssaert, 2011) and observations from five AmeriFlux sites. We evaluated simulated area burned with observed area burned as recorded in the Monitoring Trends in Burn Severity (MTBS) database (Eldenshenk et al, 2007).…”

Seasonal variability of forest sensitivity to heat and drought stresses: A synthesis based on carbon fluxes from North American forest ecosystems

“…In 2012, a warmer spring and severe summer drought in the eastern temperate forests of North America caused a net reduction in carbon sequestration due to the rapid depletion of soil water content (Pan & Schimel, 2016;Wolf et al, 2016). An increasing frequency and severity of climate extremes highlight the need to quantitatively understand the response of forest carbon balance to climate extremes and its variability over time and space (Berner, Law, & Hudiburg, 2017;Frank et al, 2015).…”