Composition and aboveground tree biomass of a dry semi-evergreen forest on Mexico's Yucatan Peninsula

Forest biomass estimates are used to help quantify pools and flux of greenhouse gases (e.g., CO2-C) from the terrestrial biosphere to the atmosphere associated with land-use and land cover changes. Such estimates based on direct measurements are quite limited for tropical dry forests. The goal of this study was to assess the species composition and biomass density in an intact Mexican forest representative of the tropical dry forest biome. We then compared our measured biomass with biomass estimates computed with a published model in current use. A total of 72 species were found in a 0.5 ha stand with a basal area of 31.3 m(2) ha(-1). The dominant species, in terms of biomass, were Brosimum alicastrum Sw., Manilkara zapota (L.) Royen, Luehea speciosa Wildl., Pouteria unilocularis (Donn. Sm.) Baehni, Trichilia minutiflora Standl., and Spondias mombin Linn. Tree heights ranged up to 30 m and dbh to 82.1 cm. Species-specific biomass regression models were developed for the six most common species of large (>10 cm dbh) trees and for the nine most common species of small (<10 cm dbh) trees from the destructive harvest of 698 trees. Mass of large trees (n = 195) were used to derive the regression model Y = exp{-2.173 + 0.868 ln((DTH)-T-2) + 0.0939/2}, where Y is the total dry weight (kg), D the dbh (cm), and TH the total height (m). Total above ground tree biomass was estimated to be 225 Mg ha(-1), and was dominated (85%) by the biomass of the large trees. The actual biomass of each of the 195 large trees was compared to individual tree biomass calculated with a published regression model [Estimating biomass and biomass change of tropical forests. A primer. FAO Forestry Paper 134. Food and Agriculture Organization of the United Nations, Rome, Italy, 1997] that is based on measurements of 29 trees. We found that the published model underestimated biomass of these trees by 31% (37.6 versus 54.4 Mg). Calculated biomass was less than measured biomass for 29 of 33 species. The current study points to the value of site-specific assessment of above ground biomass and may contribute to more accurate estimates of dry tropical forest biomass densities currently used to estimate greenhouse gas flux from land management activity. Published by Elsevier B.V.