PARENT SESSION
Oral Session # 1: Ecological Theory I: Theory; Scaling.
Presiding: M Pascual
Monday, August 4. 8:00 AM to 11:30 AM, SITCC Meeting Room 100.
Biophysical scaling relationships for tree structure and stand patterns: Extensions to semiarid ecosystems.
Breshears, David*,1, West, Geoffrey1, Brown, James2, Allen, Craig3, Enquist, Brian4, 1 Los Alamos National Laboratory, Los Alamos, NM2 University of New Mexico, Albuquerque, NM3 US Geological Survey, Midcontinent Ecological Science Center, Los Alamos, NM4 University of Arizona, Tucson, AZ
ABSTRACT- Recently developed theory on biophysical scaling relationships quantitatively predicts how many biological attributes of size and energy are related. The theory has been applied from molecular through biosphere scales. There are four critical hypotheses relative to the theory: (1) The flow of biological energy at all scales is limited by a hierarchical resource distribution network. (2) A constant amount of energy is required to produce unit biomass at all size scales ("energy equivalence"). (3) Metabolic power scales as a fractional power function of mass at all levels of biological organization. (4) Variations from predicted behavior result from niche-related adaptations driven by evolution (species-dependent variation) or dynamic responses to recent perturbations (environmentally dependent variation). Here we test several aspects of theory using data on plant community structure in a semiarid pinyon-juniper woodland. Our findings indicate that for both of the co-dominant woody species, Pinus edulis and Juniperus monosperma, large trees exhibit a trend similar to the predicted scaling relationship that the number of tress of a given size is proportional to the inverse diameter squared. These relationships did not differ between species. Small trees, however, violate the predicted relationships, thereby providing insight into ongoing ecosystem processes. Both species exhibit scaling trends within individuals relating basal diameter and height that are similar to those predicted by theory. These results extend the predicted scaling relationships, which have thus far been tested primarily in tropical species to semiarid ecosystems with a more patchy structure. Further, the results highlight how deviations from the theory can provide a diagnostic for patterns and processes in biology.
Key words: pinyon juniper woodland, theoretical ecology, biophysical scaling theory, population and community structure