Vertical variation in canopy structure and CO2 exchange of oak-maple forests: influence of ozone, nitrogen, and other factors on simulated canopy carbon gain
1990
Reich, P.B. | Ellsworth, D.S. | Kloeppel, B.D. | Fownes, J.H. | Gower, S.T.
Stand-level and physiological measurement were made for oak and maple species common in Wisconsin forest. Scaling relationships were identified to allow the development of a model for estimating net carbon exchange at the levels of a leaf, canopy stratum, and whole canopy. Functional relationships were determined between tissue gas exchange rates and perceived controlling variables. Vertical variation in leaf properties and in the distribution of foliage by weight, area, and species were characterized for several closed canopy forests. Forest canopies were divided into four horizontal strata to develop predictive models for canopy gas exchange. Leaf and canopy layer carbon dioxide exchange rates were predicted using leaf nitrogen concentration, leaf mass per area, ozone exposure, predawn leaf water potential, photosynthetically active radiation, and vapor pressure deficit as driving variables. Direct measurements of leaf gas exchange were used to validate the components (subroutines) of the model. Net carbon dioxide exchange was simulated for canopy layer at 5-min intervals over a diurnal time course. Simulations of canopy CO2 exchange were made for a 30-m tall, mixed oak-maple forest under hypothetical ambient and greater-than-ambient ozone pollution regimes. Daily canopy net CO2 exchange was predicted for seven forest stands and compared with estimates of aboveground net primary production, N availability, leaf area index, and canopy N.
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