Carbono em vegetação lenhosa da caatinga e viabilidade econômica de manejo

Abstract

The best alternative to reduce carbon dioxide (CO2) emissions, one of the responsible gases for the increase of the greenhouse effect, is the arboreal vegetation, which has the capacity to store carbon during the biomass production process. The objective of the present study is to analyze carbon stocks and dynamics and CO2eq removal potential in above-ground biomass, evaluating the economic viability of implementing carbon projects as an alternative to land use in a Caatinga. For this, the present study was divided into four chapters with specific objectives. The first chapter quantifies stocks and describes equations of dry above-ground biomass for the species of highest absolute density and importance value in the study area. The second chapter determines the carbon contents (C) in the stem, leaf and branch compartments and checks the statistical differences between the values. The third chapter analyzes the dynamics of the structure, biomass and carbon stocks in the in above-ground biomass between the years 2008 and 2013. The fourth chapter to evaluate the economic viability between the implementation of payment for the environmental service projects the of carbon sink and the production of firewood. Data collection was made in an area of Caatinga in the municipality of Floresta, Pernambuco, where, since 2008, 40 permanent plots were established and monitored, all tree individuals with CAP ≥ 6 cm were measured annually. The species evaluated are: Anadenanthera colubrina, Aspidosperma pyrifolium, Bauhinia cheilantha, Cnidoscolus quercifolius, Croton heliotropiifolius, Mimosa ophthalmocentra, Mimosa tenuiflora and Poincianella bracteosa, representing 91.6% of the total of the study area. Trees representative of these species were cut, weighed and cubed, with the separation in the following compartments: stem, leaves, thin branches (CAP <6 cm) and thick branches (CAP ≥ 6 cm). Samples were collected for the determination of the dry biomass and for the analyzes of the carbon contents using the CHNS/O elemental analyzer. For the adjustment of the linear and non-linear mathematical models tested, the data of total dry above-ground biomass as dependent variable were used and the independent variables were the diameter at breast height and the total height of individuals per species. For the analysis of the dynamics of the carbon stock in the area, the adjusted equations and the carbon contents obtained for each species were used, as well as the dendrometric data obtained in the years 2008 and 2013 during the measurements of the permanent plots. Factor 3.67 was used to convert carbon stock (C) to equivalent carbon dioxide (CO2eq). The economic viability analysis was based on two scenarios: (1) Caatinga for the production of firewood to provide the energy demand of the region, through a regulated management plan and (2) Caatinga preserved as a possible source of payment for the environmental service by the generation of credits of carbon. The planning of the projects was 15 years and the economic evaluation criterion adopted was the Net Present Value (NPV). The results showed that the dry above-ground biomass stocks of the eight species vary from 0.5 kg to 99.4 kg per individual and that equations were developed for each species and for all species together with good precision statistics. The carbon contents were determined and it was possible to obtain a single value of 46.4% for A. colubrina, A. pyrifolium, B. cheilantha, C. quercifolius, M. ophthalmocentra and M. tenuiflora without distinguishing between stem, branches and leaves. But for C. heliotropiifolius and P. bracteosa it is necessary to use distinct values per compartment, so that there are no bias in the estimates of carbon stocks. In the analysis of the dynamics it was observed that the mortality rate was three times higher than the recruitment rate and this behavior was influenced by the water deficit occurred between the years of 2012 and 2013, as a consequence there were significant changes in the structure and growth of the species, mainly M. ophthalmocentra, which affected the decrease of density, dominance, basal area, biomass and carbon stocks during the five years analyzed. In years with a good incidence of rainfall and low mortality, the area was able to fix carbon, but in periods with water deficit and high mortality, it was carbon source. The economic analysis showed that the payment for the environmental service by carbon projects are more economically attractive than the production of firewood in small areas, but in larger areas due to the low remuneration of the firewood exploitation the forest management plans are better. Nevertheless, there is great potential carbon sink in the Caatinga and should be appropriate into small and medium scale projects at the state, national, and global levels, helping to mitigate global climate change.