Geographic Variation in Wood Specific Gravity: Effects of Latitude, Temperature, and Precipitation

Abstract

Wood basic specific gravity (SG) was compared at sites located along a gradient from 52"N latitude to the equator.Mean SG increased by 0.0049 per "C mean annual temperature (MAT), and decreased by 0.00017 per cm of mean annual precipitation (MAP).Considered alone, MAT was a better predictor of mean SG across the temperate zone (3-22C MAT, latitude north of 29"N; r2 = 0.80) than it was across the entire MAT range (r2 = 0.62) or across warm tropical sites alone (MAT > 23C; r2 = 0.33, p = 0.67).In contrast, MAP considered alone was a better predictor of mean SG in the warm tropical sites (r' = 0.62) than across all sites (r' = 0.04, p = 0.39).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 Lone relative to the temperate zone, demonstrating that variability in SG in the warm tropics is much greater than would be predicted from greater species richness alone.