Climatic versus biotic constraints on carbon and water fluxes in seasonally drought‐affected ponderosa pine ecosystems

Abstract

[1] We investigated the relative importance of climatic versus biotic controls on gross primary production (GPP) and water vapor fluxes in seasonally drought-affected ponderosa pine forests. The study was conducted in young (YS), mature (MS), and old stands (OS) over 4 years at the AmeriFlux Metolius sites. Model simulations showed that interannual variation of GPP did not follow the same trends as precipitation, and effects of climatic variation were smallest at the OS (<10%), largest at the MS (>50%), and intermediate at the YS (<20%). In the young, developing stand, interannual variation in leaf area has larger effects on fluxes than climate, although leaf area is a function of climate in that climate can interact with age-related shifts in carbon allocation and affect whole-tree hydraulic conductance. Older forests, with well-established root systems, appear to be better buffered from effects of seasonal drought and interannual climatic variation. Interannual variation of net ecosystem exchange (NEE) was also lowest at the OS, where NEE is controlled more by interannual variation of ecosystem respiration, 70% of which is from soil, than by the variation of GPP, whereas variation in GPP is the primary reason for interannual changes in NEE at the YS and MS. Across spatially heterogeneous landscapes with high frequency of younger stands resulting from natural and anthropogenic disturbances, interannual climatic variation and change in leaf area are likely to result in large interannual variation in GPP and NEE.

Modeling stomatal conductance in the earth system: linking leaf water-use efficiency and water transport along the soil–plant–atmosphere continuum

“…We used ψ l min = −2 MPa, which reflects values typically found in closed forest canopies. This is similar to values used in previous SPA simulations for arctic ecosystems and black spruce boreal forest (−1.5 MPa; Williams et al, 2000;Hill et al, 2011), ponderosa pine (−1.7 to −2.0 MPa; Williams et al, 2001a, b;Schwarz et al, 2004), deciduous forest (−2.5 MPa; Williams et al, 1996), tropical rainforest (−2.5 MPa; Williams et al, 1998;Fisher et al, 2007), and Australian woodland (−2.8 MPa; Zeppel et al, 2008). …”

An analysis of soil moisture dynamics using multi-year data from a network of micrometeorological observation sites

“…The Metolius site is an intermediate age ponderosa pine forest located in the eastern Cascade Mountains near Sisters, OR. It has a temperate climate, with a mean annual precipitation of approximately 360 mm y −1 and a mean annual temperature of 7 to 8 o C [18]. It is the only one of the four sites that receives a substantial amount of snow, which affects soil infiltration patterns during the winter.…”

Heat Flux in the Strong-Wind Nocturnal Boundary Layer

“…(Table 1) based on CSAT-3 sonic anemometers deployed at 6.1 m above a 15-m mature ponderosa pine forest, 11 m above the surface of a 3-m sparse juniper forest and 10 m over a largely burned area (Table 1). These sites are described in Schwarz et al (2004).…”