© 2005 Heron Publishing—Victoria, Canada
Estimating leaf-level parameters for ecosystem process models: a study in mixed conifer canopies on complex terrain
Remko A. Duursma (1, 2, 3), John D. Marshall (1), Jesse B. Nippert (4), Chris C. Chambers (5) and Andrew P. Robinson (1)
1. Department of Forest Resources, University of Idaho, Moscow, ID 83844-1133, USA / 2. Department of Forest Ecology, University of Helsinki, P.O. Box 27, FIN-00014, Finland / 3. Corresponding author (remko.duursma@helsinki.fi) / 4. Department of Biology, Colorado State University, Fort Collins, CO 80523, USA / 5. Department of Biological Sciences, Washington State University, Pullman, WA 99164-4236, USA / Received January 10, 2005; accepted April 2, 2005; published online August 16, 2005
Summary
Ecosystem process models are often used to predict carbon flux on a landscape or on a global scale. Such models must be aggregate
and canopies are often treated as a uniform unit of foliage. Parameters that are known to vary within the canopy, e.g., nitrogen
content and leaf mass per area, are often estimated by a mean value for the canopy. Estimating appropriate means is complicated,
especially in mixed-species stands and in complex terrain.
We analyzed sources of variation in specific parameters with the goal of testing various simplifying assumptions. The measurements
came from mixed-species forests in the northern Rocky Mountains. We found that, for three important parameters (nitrogen concentration
and content, and leaf mass per area), a sample taken near the vertical center of the crown provided a good estimate of the
mean values for the crown. Altitude (700–1700 m), solar insolation (4200–5400 MJ m–2 year–1) and leaf area index (1–11) had negligible effects on the parameters; only species differences were consistently detected.
The correlation between mass-based photosynthetic rates and mass-based nitrogen concentrations was much weaker than the correlation
between area-based photosynthetic rates and area-based nitrogen concentration. Comparison of photosynthesis–nitrogen relationships
for a wide variety of conifer species and sites revealed a broad general trend that can be used in models.
These results suggest important potential simplifications in model parameterization, most notably that canopy means can be
estimated with ease, that complex terrain is a minor source of variation in these parameters and that use of one photosynthesis–nitrogen
relationship for conifer species does not result in large errors. Species-to-species variation, however, was large and needs
to be accounted for when parameterizing process models.
Keywords:
inter-species variation, leaf nitrogen concentration, light-saturated photosynthesis, model parameterization, photosynthetic
capacity, specific leaf area.
