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Individual Highlight

Is the relationship between tree height and diameter consistent across species and ranges?

Photo of Longleaf pine trees growing on sandy uplands.Longleaf pine trees growing on sandy uplands.Snapshot : Scaling exponents reveal differences in longleaf pine height-diameter relationships across its range, possibly due to water availability. Tree species adapted to swampy conditions have developed growth forms that result in deviations from expected relationships.

Principal Investigators(s) :
Brockway, Dale 
Research Location : Tuskegee National Forest, AL; Bankhead National Forest, AL; Goethe State Forest, FL; Blackwater River State Forest, FL; Wheeler Wildlife Refuge, AL; AAMU Agricultural Experimental Station, AL
Research Station : Southern Research Station (SRS)
Year : 2017
Highlight ID : 1323


The relationship between tree height and diameter is important for understanding patterns of tree growth and estimating tree biomass. Metabolic ecology predicts that forest tree growth will have an allometric coefficient of two-thirds, such that trees should increase in diameter faster than they grow taller. But does this relationship change when trees are stressed, such as at the edges of their natural range? Forest Service scientists compared field data for longleaf pine and four swamp tree species across their ranges. The scaling exponents of height and diameter for longleaf pine varied at four locations across its natural range. These differences appeared related to differing amounts of rainfall in the locations. The scaling exponents for red maple and river birch were consistent with those predicted by metabolic ecology but those for water tupelo and bald cypress were not. These two species can live in flooded conditions and have swollen trunks, or "knees." This growth form affected the scaling exponents for these swampy species. As managers work to restore longleaf pine and other coastal plain species, high plasticity and variation in allometric scaling of the tree height and diameter relationship may very well be the rule, rather than the exception.

Forest Service Partners

External Partners

  • Alabama A&M University, AL
  • Blackwater River State Forest, FL
  • Goethe State Forest, FL
  • Wheeler Wildlife Refuge, AL