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R.H. Waring and W.E. Winner
much of the western United States (Running, 1994; Running & Coughlan,
1988; Running & Gower, 1991). We extracted basic relationships from
this model that couple photosynthesis and growth to the availability of
light, water, and nutrients and tested the ability of a simplified model to
predict forest growth across a steep climatic gradient in Oregon (Runyon,
Waring, Goward, & Welles, 1994; Waring et al., 1993).
In this chapter, we present the logic behind the simplified model and
summarize the results of field comparisons. Extrapolation of some components of the simplified growth model provides insights into how a
changing climate associated with continued accumulation of CO 2 and
other greenhouse gases in the earth's atmosphere might alter forest
productivity in the Pacific Northwest and in the temperate forest region of
Chile .
General Model Principles
The forest-growth component of the FOREST-BGC ecosystem model
accumulates daily estimates of photosynthesis and subtracts the cost of
maintenance respiration accumulated throughout a year. The remaining
carbon resource is distributed above and below ground, based on the
relative availability of nitrogen for leaf growth and an integrated measure
of drought stress (Running & Gower, 1991).
Photosynthesis
The absorption of visible light by leaves, branches, and whole canopies
has received much study in the last two decades. A number of models
estimate light interception and maximum rates of photosynthesis for
individual strata of leaves in canopies (Wang & Jarvis, 1990). In mild
climates, photosynthesis is a linear function of light absorption by the
canopy (Wang, McMurtrie, & Landsberg, 1992).
More complex simulation models allow for variation in the rates of
photosynthesis as a function of leaf nitrogen content (or the primary
photosynthetic enzyme), soil-water availability, humidity deficits, ambient
temperature, and carbon dioxide concentrations (McMurtrie, Comins,
Kirschbaum, & Warg , 1992; Raupach, 1989). The data requirements for
such models, however, are rather demanding and thus limit their application. We sought a simplified model that generalized responses for whole
canopies and assumed thresholds common for a wide range of species
(Running & Coughlan, 1988).
Water Relations
Water relations of plants are a function of the supply of water in the soil
and the demand from transpiration, balanced against limitations in the
R.H. Waring and W.E. Winner
much of the western United States (Running, 1994; Running & Coughlan,
1988; Running & Gower, 1991). We extracted basic relationships from
this model that couple photosynthesis and growth to the availability of
light, water, and nutrients and tested the ability of a simplified model to
predict forest growth across a steep climatic gradient in Oregon (Runyon,
Waring, Goward, & Welles, 1994; Waring et al., 1993).
In this chapter, we present the logic behind the simplified model and
summarize the results of field comparisons. Extrapolation of some components of the simplified growth model provides insights into how a
changing climate associated with continued accumulation of CO 2 and
other greenhouse gases in the earth's atmosphere might alter forest
productivity in the Pacific Northwest and in the temperate forest region of
Chile .
General Model Principles
The forest-growth component of the FOREST-BGC ecosystem model
accumulates daily estimates of photosynthesis and subtracts the cost of
maintenance respiration accumulated throughout a year. The remaining
carbon resource is distributed above and below ground, based on the
relative availability of nitrogen for leaf growth and an integrated measure
of drought stress (Running & Gower, 1991).
Photosynthesis
The absorption of visible light by leaves, branches, and whole canopies
has received much study in the last two decades. A number of models
estimate light interception and maximum rates of photosynthesis for
individual strata of leaves in canopies (Wang & Jarvis, 1990). In mild
climates, photosynthesis is a linear function of light absorption by the
canopy (Wang, McMurtrie, & Landsberg, 1992).
More complex simulation models allow for variation in the rates of
photosynthesis as a function of leaf nitrogen content (or the primary
photosynthetic enzyme), soil-water availability, humidity deficits, ambient
temperature, and carbon dioxide concentrations (McMurtrie, Comins,
Kirschbaum, & Warg , 1992; Raupach, 1989). The data requirements for
such models, however, are rather demanding and thus limit their application. We sought a simplified model that generalized responses for whole
canopies and assumed thresholds common for a wide range of species
(Running & Coughlan, 1988).
Water Relations
Water relations of plants are a function of the supply of water in the soil
and the demand from transpiration, balanced against limitations in the