Seasonal hydrology explains interannual and seasonal variation in carbon and water exchange in a semiarid mature ponderosa pine forest in central Oregon

Abstract

[1] We analyzed 7 years (2002)(2003)(2004)(2005)(2006)(2007)(2008) of micrometeorological and concurrent biological observations of carbon and water fluxes at a mature ponderosa pine forest in central Oregon in a semiarid climate. We sought to evaluate the extent that gross primary productivity, net ecosystem exchange, ecosystem respiration, net primary productivity, net ecosystem productivity, tree transpiration, and evapotranspiration varied seasonally and interannually in this ecosystem subjected to varying periods and severity of droughts. To explain variation, we found it necessary to define seasons functionally within a hydroecological year rather than by fixed calendar dates. The interannual variability in growing season length was large (45 days), and the end date was more variable than the onset. Plant-available soil water was the main determinant of carbon fluxes. Spring evapotranspiration primarily used shallow water, whereas summer and fall evapotranspiration drew water from deeper in the soil profile. A multiyear drought (2001)(2002)(2003) had a more severe and fundamentally different impact on carbon and water cycles than a single-year (2005) drought because of carryover effects in soil water and carbohydrate reserves in plant tissue. Calendar year-based analysis was inadequate to diagnose drought years in precipitation and ecosystem drought response. Extension of meteorological records back to 1982 showed that anomalies were coherent across the region and that the observations represented below-average precipitation and above-average temperatures coherent with a warm-phase Pacific Decadal Oscillation. The carbon sink of this seasonally water-limited ecosystem is anticipated to increase with increasing available soil water during the growing season.Citation: Thomas, C. K., B. E. Law, J. Irvine, J. G. Martin, J. C. Pettijohn, and K. J. Davis (2009), Seasonal hydrology explains interannual and seasonal variation in carbon and water exchange in a semiarid mature ponderosa pine forest in central Oregon,

Covariation between gross primary production and ecosystem respiration across space and the underlying mechanisms: A global synthesis

“…RE is strongly coupled with GPP across timescales (Dunn et al, 2007;Migliavacca et al, 2011). For example, RE follows the same dynamic patterns as GPP from daily to seasonal scales (Krishnan et al, 2009; et al, 2011; Thomas et al, 2009). Annually, GPP and RE are both enhanced in humid years, but repressed in dry years (Hussain et al, 2011;Rodrigues et al, 2011); especially, both of them are remarkably reduced in extreme drought years Reichstein et al, 2007a).…”

Evaluation and improvement of the Community Land Model (CLM4) in Oregon forests

“…We utilized annual carbon stocks and net primary production (NPP) computed from over 3000 forest inventory plots that had been scaled to the study region with remote sensing data to produce a spatial dataset (Hudiburg et al, 2011;, and the seasonal data were gross photosynthesis from two FLUXNET sites in the region (Krishnan et al, 2009;Thomas et al, 2009). Model evaluation with an observationbased spatially representative dataset such as federal forest inventory (FIA) data is critical in order to constrain model estimates, facilitate model development and ultimately reduce model uncertainty.…”

Bamboo Forest Water Use Efficiency in the Yangtze River Delta Region, China

“…With a projected increase in the frequency and severity of droughts in the mid and high latitudes (Thomas et al 2009), more attention has been paid to research into the seasonal drought effect on WUE. Previous studies showed inconsistent results.…”