Carbon production potential of different tree species plantations in north of Iran.
Forests are the primary source of terrestrial carbon uptake, storing approximately two-thirds of Earth's terrestrial carbon. One way to carry out carbon estimate would be to use the equations developed by other researchers for similar tree species from a few simple measurements of them. This research is based on published equations. Whereas four different allometric models (calculated model based on stem volume and wood density, IPCC model, Jenkins et al model and Chojnacky & Jenkins model) were used in order to estimate the total aboveground biomass and carbon productivity potential of per hectare plantations by Acer velutinum, Fraxinus exelsior, Tilia begonifolia, Quercus castanifolia, Alnus subcordata (native species), Pinus taeda and Pinus nigra (exotic species) based on age, species type and altitude. The data were collected in Astara zone located in north of Iran with area of 43791 ha. According to the accuracy required, site conditions, tree species and the stand age, 72 rectangular plots were chosen. The diameters of all trees on the plot were measured and height is determined usually by sampling in all diameter classes. As a primary result, the evaluation of ecological capability using Makhdoum model was done and the predicted area for each given species was specified. To compare different tested models, we used One-Way ANOVA (significance level=0.05). The result showed that, there wasn't significant difference between the amounts of aboveground biomass estimated by the four models in Acer velutinum, Quercus castanifolia, Tilia begonifolia and Fraxinus excelsior but these amounts differed significantly in Alnus subcordata, Pinus taeda and Pinus nigra. Also Pinus taeda as an exotic species produced the most carbon content (53-78 t/ha) that indicated carbon content in the biomass increased with the plantation age and then Alnus subcordata (47-65 t/ha), Acer velutinum (42-49 t/ha) Tilia begonifolia (35-59 t/ha), Quercus castanifolia (34-41 t/ha), Fraxinus excelsior (28-31 t/ha) and Pinus nigra (10-15 t/ha), respectively. This amount was remarkably small in Pinus nigra due to species age and short growth period in higher altitude. However, according to the predicted area for plantation of each species, Acer velutinum has the most carbon production and then Fraxinus excelsior, Alnus subcordata, Pinus taeda, Tilia begonifolia, Quercus castanifolia and Pinus nigra respectively. Totally Results showed that selected methods almost have the same accuracy for biomass estimation of the most species, however three ways were more similar to each other than IPCC default values, versus two exotic species that indicated the influence of being native or exotic species on accuracy and reliability.