WIEMANN, MICHAEL C.1* and G. BRUCE WILLIAMSON2. 1Forestry Products Laboratory, USDA Forest Service, Madison, WI 53705; 2Department of Biological Sciences, Louisiana State University, Baton Rouge, LA 70803. - Geographic variation in wood specific gravity.
Wood basic specific gravity (SG) was compared along a gradient from 52
degrees north latitude to the equator. Mean SG increased with mean
annual temperature (MAT) and decreased with mean annual precipitation
(MAP). Considered alone, MAT was a better predictor of mean SG across
the temperate zone (MAT 3-22 degrees C; latitude north of 29 degrees)
than it was across the entire MAT range or across warm sites (MAT
greater than 23 degrees C). In contrast, MAP considered alone was a
significant predictor of mean SG only in the warm tropical sites.
Variability in SG among the sites was compared using two measures of
dispersion: range and standard deviation. As MAT increased across the
temperate zone, maximum SG increased and minimum SG remained constant,
resulting in an increase in SG range. SG standard deviation, however,
remained constant. Both SG range and SG standard deviation increased
dramatically in the warm tropical zone relative to the temperate zone,
demonstrating that variability in SG in the warm tropics is much
greater than would be expected from greater species richness alone.
Key words: climate, precipitation, specific gravity, temperate woods, temperature, tropical woods