Allometric equations for aboveground biomass estimation by size class for Pinus brutia Ten. trees growing in North and South Aegean Islands, Greece

Empirical allometric equations relating biomass of aboveground components to dendrometric variables for Pinus brutia Ten. trees are derived in this paper. They are based on data collected from Lesvos (North Aegean Sea) and Crete (South Aegean Sea) Islands. Comparisons to published equations for the same species growing in northwestern and southeastern Turkey, for Pinus nigra A. growing in Turkey and Pinus halepensis Mill. found in Western Aegean (island of Evia), are also presented. The biomass of branches from destructively sampled trees (twelve in Crete and six in Lesvos) was divided into four size classes (0?C0.63 cm, 0.64?C2.5 cm, 2.51?C7.61 cm, and 7.62?C22.8 cm). Tree crown biomass was calculated as the sum of the biomass in the four classes plus the fraction of stem above crown base. Over bark stem biomass was estimated through bole volume conversion based on wood density. The results showed clearly that, for a given diameter, the Cretan trees had more crown biomass and a higher share of small branches than trees on Lesvos, probably due to differences in environment and stand structure. Comparisons to published diameter versus crown biomass equations reveal a lower crown biomass for Turkish sites of Calabrian pine and Aleppo pine on Evia Island, while only Turkish Black pine seems to be comparable to the Calabrian pine on Crete. The derived allometries can be used for landscape fire behavior modeling, for ecophysiological studies and for the Kyoto protocol requirements of carbon changes in Pinus brutia Ten. forests located in northern and southern Greek sites.     

Predicting mean aboveground forest biomass and its associated variance

An approach to simplify the prediction of average aboveground forest biomass values and their associated variability is presented in this study. The advantage of the proposed approach is based on the fact that it can be applied to any form of equation describing tree size–shape relationships and to any tree species. The proposed approach was tested against a tree-level dataset comprising of 1211 pairs of aboveground tree biomass (M) and tree diameter (D) values. The compiled trees were grouped into several D classes and average M estimates (μ_M) with their associated variances (σ_M) were predicted for each class based on second-order Taylor expansion formulas. Nineteen beech (Fagus moesiaca Cz.) plots were also used to derive μ_M and σ_M estimates on an area basis in order to test the applicability of the approach on forest scale. The only assumption made was that the simple allometric model M = aD^b can accurately describe the M–D relationship. The results indicated that the mere recording of D distribution and appropriate selection of a and b values may provide very good estimates for μ_M and σ_M both at global and forest level. It is therefore concluded that biomass studies related to carbon sequestration, biofuel potential, ecophysiological processes and management practices are considerably simplified.     

Comparison between empirical and theoretical biomass allometric models and statistical implications for stem volume predictions

Comparisons between empirical and theoretical allometric modelsfor estimating tree biomass and the statistical caveats attachedto empirical stem volume equations are presented in this paper.First, the elastic and stress similarity models, derived fromfirst biomechanical principles, as well as predictions obtainedfrom geometric similitude, were validated against allometricequations that relate dry above-ground tree biomass M to stemdiameter D. In addition, a recent geometric model which predictsthat M D^8/3 was also validated against a pooled dataset whichconsisted of 764 M-D pairs compiled from empirical studies conductedthroughout the globe and for several tree species. Moreover,59 empirical equations which relate M to D were selected froma European database to validate the aforementioned theoreticalmodels. The analysis indicated that the biomechanical and thegeometric models failed to describe the shape in M-D allometryfor the empirical datasets. Finally, the multicollinearity problem,which is directly related to the reliability of the predictions,was analysed for stem volume equations (V). In total, 23 empiricalmodels based on the six-parameter formula V = a + bD + cD² +dD³ + eH + fD²H were used in order to pinpoint the dependencybetween the parameters. It is illustrated that parameters a,b and c are highly related to each other, and parameter e isalso related to parameter f. It is concluded that the interrelationshipbetween D and stem height (H) could be one of the reasons forthis dependency and scepticism should be placed in the reliabilityof V estimates derived from these models.     

Aboveground net primary productivity of a beech (Fagus moesiaca) forest: a case study of Naousa forest, northern Greece

Based on allometric relationships and information provided in forest management plans, we determined aboveground net primary productivity (ANPP) for a 10-year period in a Mediterranean beech forest (Fagus moesiaca Cz.) extending across an elevation gradient. The ANPP ranged from 1.87 to 15.71 Mg ha(-1) year(-1), and leaf area index (L*) ranged from 2.3 to 3.6. Although small trees (diameter at breast height < 10 cm) were not sampled, it was unlikely that this accounted for the low L* because there were very few small trees on a per-hectare basis. A weak positive relationship was found between ANPP and L*, and only ANPP was negatively related to elevation. Although L* did not vary with elevation, biomass growth efficiency (ANPP/L*) declined strongly with elevation. Leaf carbon isotope composition, leaf nitrogen content per unit area and specific leaf area of leaves collected from nine trees across an elevation gradient all varied significantly with elevation and were significantly related to one other, suggesting that water limitations at higher elevations may have driven the reduced growth efficiency at the stand level. Strong winds may also have negatively affected ANPP at higher elevations by altering belowground allocation. Further research is needed to test these hypotheses and to determine the belowground dynamics of phytomass in this ecosystem.