Effects of Model Choice and Forest Structure on Inventory-Based Estimations of Puerto Rican Forest Biomass

—Total aboveground live tree biomass in Puerto Rican lower montane wet, subtropical wet, subtropical moist and subtropical dry forests was estimated using data from two forest inventories and published regression equations. Multiple potentially-applicable published biomass models existed for some forested life zones, and their estimates tended to diverge with increasing tree diameter at breast height. Inventoried forests showed structural characteristics typical of secondary tropical forests and stand successional trends of increasing stem density from initial reversion to young closed forest, followed by a decrease in stem density and gradual increase in basal area and biomass as the stands developed. Stems with DBH < 10 cm contributed 9.9-50.9% of total aboveground biomass. When present, 50-90+ cm DBH trees greatly increased aboveground biomass values on individual plots, but these effects subsided when averaged over the forested landscape. Inherent variability in large-tree form combined with equations that extrapolate beyond the range of sampled trees impedes accurate aboveground biomass estimation for larger trees. Application of equations developed in areas that most closely match potential study sites should improve overall estimation accuracy of all forest stands, however, locally developed biomass equations are lacking for subtropical dry and perhaps subtropical moist forest life zones in Puerto Rico.