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Therefore, caution should be given when using the dbh as a single estimator in the above-ground biomass equations (Chave et al. 2005).
We found the similar fluctuations between the independent variables for the needle biomass estimation with other studies (Grigal and Kernik, 1984; Miksys et al., 2007). On the other hand, the correlations between observed and predicted values of branches and needle biomass were relatively low. These differences were attributed to the nonstandard treatments of each forest stand throughout the entire study area.
The coefficient of determination and residual standard error values of this study and de Miguel et al. (2014) were depicted in Table 5 for model performance comparison. Our models were estimated the stem and total tree biomass better than that of de Miguel et al. (2014) models. On the other hand, de Miguel et al. (2014) models were better estimating branch and needle biomass than that of our models. It can be observed that the improved equations for Syria and Lebanon by de-Miguel et al. (2014) gave the two lowest estimations of the above ground biomass. The model developed in this study estimated lower biomass values than the equations improved by de-Miguel et al. (2014) for the Middle East.
As depicted in Figure 4, the total tree biomass estimation using dbh and tree height as double-entry estimators varied amongst the researchers studying the Calabrian pine tree growth in the Mediterranean region. Durkaya (2009) and de Miguel et al. (2014) for Syria and Lebanon were underestimated the total tree biomass comparing the estimation results from this study for dbh values less than 35 cm. Thus, de Miguel et al. (2014)’s model for estimating total tree biomass in the MiddleEast was better than any other models for the less than 35 cm dbh range. The diameter at breast height values that were more than 35 cm were overestimated by de Miguel et al. (2014) for the MiddleEast and Durkaya (2009) and were underestimated for Syria and Lebanon from our models. However, our above-ground biomass estimations were accurate and nonbiased.
We have shown that above-ground biomass equations for Calabrian pine trees could be used for estimating individual tree component biomasses. A system of five biomass equations (stem, bark, branch, needle and total biomass) was developed. The stem, bark and total biomass equations explained more than 90% of the variability of the observed data, while the branch and needle biomass equations accounted for 82% and 65%, respectively. In this study, bark and stem biomass were separately estimated so that their contribution to the total tree biomass could be explained more accurately. We can conclude that our above-ground and tree components biomass estimations were accurate and nonbiased. For more accurate estimation of branch and needle biomass, it would be advisable to add other tree parameters such as crown length and/or crown diameter to fit the data.
This study was carried out as part of a project financed by the Scientific and Technological Research Council of Turkey (TUBİTAK) (Project No. TOVAG-112O808). The authors wish to thank the other researchers and workers who contributed to this project. The authors declare that they have no conflict of interest.
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