© 2002 Heron Publishing—Victoria Canada
Structural differences and functional similarities between two sugar maple (Acer saccharum) stands
1 Natural Resources Canada, Canadian Forest Service, Laurentian Forestry Centre #1055 du P.E.P.S., P.O. Box 3800, Sainte-Foy, Quebec, G1V 4C7, Canada
2 Author to whom correspondence should be addressedfraulier{at}cfl.forestry.ca
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Abstract |
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The spatially inexplicit or functional multilayer models used to predict canopy transpiration or photosynthesis are based on the assumption that closed stands show less functional variability than structural variability, because foliage tends to arrange itself in space to optimize the capture of light. To validate this assumption, we compared the structural and functional properties, and the measured and modeled transpiration fluxes of two sugar maple (Acer saccharum Marsh.) stands of comparable leaf mass but differing in height and diameter distributions. One stand was characterized by a well-developed single-layer canopy, whereas the other stand had a multilayered canopy and a stem diameter distribution of the classical inverse-J shape. Stand differences in height and diameter distribution, and canopy gap fraction, were highly significant. There were minor but significant differences in leaf mass and leaf mass per unit leaf area (LMA) distributions. We found no differences in tree-level relationships between basal area and either transpiration flux or sapwood area. We compared measurements of stand transpiration with transpiration estimates obtained from a multilayer gas exchange model, in which only the nonspatial inputs, leaf area index and LMA frequency distribution described stand structure. For both stands, modeled values of daily transpiration closely followed measured values (r2 = 0.94). These results support use of the nonspatially explicit approach to estimating canopy gas exchange, especially if the intent is to scale-up to larger portions of the landscape.
Keywords: canopy transpiration, leaf mass per area, sapwood area, scaling, stand structure
Received November 30, 2001; Accepted March 28, 2002