A generalized, lumped-parameter model of photosynthesis, evapotranspiration and net primary production in temperate and boreal forest ecosystems

Abstract

PnET is a simple, lumped-parameter, monthlytime-step model of carbon and water balances of forests built on two principal relationships: 1) maximum photosynthetic rate is a function of foliar nitrogen concentration, and 2) stomatal conductance is a function of realized photosynthetic rate. Monthyly leaf area display and carbon and water balances are predicted by combining these with standard equations describing light attenuation in canopies and photosynthetic response to diminishing radiation intensity, along with effects of soil water stress and vapor pressure deficit (VPD). PnET has been validated against field data from 10 well-studied temperate and boreal forest ecosystems, supporting our central hypothesis that aggregation of climatic data to the monthly scale and biological data such as foliar characteristics to the ecosystem level does not cause a significant loss of information relative to long-term, mean ecosystem responses. Sensitivity analyses reveal a diversity of responses among systems to identical alterations in climatic drivers. This suggests that great care should be used in developing generalizations as to how forests will respond to a changing climate. Also critical is the degree to which the temperature responses of photosynthesis and respiration might acclimate to changes in mean temperatures at decadal time scales. An extreme climate change simulation (+3° C maximum temperature, -25% precipitation with no change in minimum temperature or radiation, direct effects of increased atmospheric CO ignored) suggests that major increases in water stress, and reductions in biomass production (net carbon gain) and water yield would follow such a change.

A satellite‐based biosphere parameterization for net ecosystem CO2 exchange: Vegetation Photosynthesis and Respiration Model (VPRM)

“…where T min , T max , and T opt are minimum, maximum, and optimal temperatures ( 0 C) for photosynthesis, respectively [Aber and Federer, 1992;Raich et al, 1991]. If air temperature falls below T min , T scale is set to be zero [Xiao et al, 2004a[Xiao et al, , 2004b.…”

TRIPLEX: a generic hybrid model for predicting forest growth and carbon and nitrogen dynamics

“…Many current process-based models, such as FOEST-BGC (Running and Coughlan, 1988), TEM (Melillo et al, 1993), CENTURY (Parton et al, 1987(Parton et al, , 1993, PnET (Aber and Federer, 1992), TREGROW (Weinstein et al, 1991), and Hybrid v3.0 (Friend et al, 1997), are not appropriate for management applications because they are not designed to predict stand characteristic such as basal area, mean tree diameter, height, and annual mortality, and thus the outputs are not directly useful in management planning (Landsberg and Waring, 1997); Most process-based models are too complex and require a large amount of information (the number of parameter and input variables) beyond what is readily available to forest managers, making them of minimal interest to practicing foresters and forest managers (Sands, 1988;Landsberg and Coops, 1999); Most models lack a user-friendly modeling interface and their documentation is insufficient, making them difficult for forest managers to use (Peng, 2000b). Forest managers are increasingly interested in using C balance process-based approaches for assessing the sustainability of forest ecosystem productivity under short-rotation forestry and the potential effects of projected global warming and increasing atmospheric CO 2 concentration.…”

Predictions and Projections of Pine Productivity and Hydrology in Response to Climate Change Across the Southern United States

“…A derivation of the PnET-H model developed by Aber et al, (1995) to predict forest hydrology and productivity in the northeastern United States (McNulty et al, 1994;McNulty et al, 1996bMcNulty et al, , 1997, PnET-HS utilizes site-specific soilwater-holding capacity (SWHC), four monthly climate parameters (i.e., minimum and maximum air temperature, total precipitation, and solar radiation) and species-specific process coefficients to predict evapotranspiration (ET), water drainage and net primary productivity (NPP) from the stand level (< one hectare (ha)) to a 0.5° * 0.5° grid cell resolution (approximately 50 x 75 km) across the southern United States (Aber et al, 1992(Aber et al, , 1995McNulty et al, 1994McNulty et al, , 1996aMcNulty et al, , 1997. The model calculated the maximum amount of leaf area that could be supported on a site based on the soil, the climate, and the parameters specified for the vegetative type.…”

“…Instead, loblolly pine-specific vegetation coefficients were used (Table 22.1). These coefficients were largely derived from the published literature (Aber and Federer, 1992;Aber et al, 1995;McNulty et al, 1994McNulty et al, , 1996b.…”