for southern region of Costa Rica on acid soils (Eco-region 1 and 2) were the two introduced species Gmelina arborea and Pinus caribaea followed by the two native Vochysias. In volcanic soils (Eco-region 3) and alluvial soils (Eco-region 4) the Hieronyma alchorneoides and Terminalia amazonia resulted in comparable adaptability and productivity indices as the two Vochysia species, a clear indication that these two native species prefer more fertile soils (Andisols and alluvial Inceptisols) with a shorter dry season.
3.2. Aboveground biomass
Fig. 1 shows the distribution of aboveground biomass by tree compartment and the variations according to tree dimensions (DBH, tree height and total dry weight) for each species (n¼ 4). A common tendency for all the species is the increase in stem biomass as tree dimensions increase. This pattern is particularly evident in Terminalia amazonia whose trees of smaller dimensions the stem represents only 40% of the total aboveground biomass, while for treesof larger dimensions, the stem represents up to 80% of the total biomass. An inverse tendency in this same species is shown for foliage, branch and bark biomass, their percentages decrease as tree dimensions increase. Looking at the differences between species, the largest portion of above ground biomass is concentrated in the stems of Hieronyma alchorneoides and Gmelina arborea. These two species distribute between 70% and 80% of their above ground biomass in the stems regardless of tree dimensions.
The percentage of bark in Pinus caribaea is also notable, representing approximately 14% of the total biomass, while for the rest of the species it does not surpass 7%.
Table 2 shows the means multiple comparisons for above ground biomass content according to tree compartments at 6 years of age. The species with the highest stem biomass is G. arborea which is an expected result due to the larger dimensions of sampled trees. P. caribaea by far has the highest bark biomass followed by G. arborea, while T. amazonia is the species with the least bark biomass. V. ferruginea has the highest branch biomass followed by the group of V. guatemalensis, P. caribae and G. arborea. Foliage biomass is the highest for G. arborea followed by P. caribaea and V. ferrugenia.
Table 3 includes a set of allometric equations used to estimated biomass by tree compartment and whole tree for each study species or group of species. These equations were developed using the 24 sampled trees for the biomass analysis. Fig. 1 provides extra information that provides the range of DBH values for which these equations should be applied.
3.3. Nutrient concentrations in above ground tree compartments
Table 4 shows the means multiple comparisons for above ground biomass nutrient concentrations according to tree compartments and species. On average, the distribution of nutrients contained in the above ground biomass shows the following pattern for N,P, K and Mg:Foliage>Bark>Branches>Stem,and for Ca:Bark>