Management effects on carbon stocks and fluxes across the Orinoco Savannas

Across the physiognomic types of the Orinoco llanos, periodic inventories a nd changes in land-use between 1982-1992 are estimated. Results indicate th at the area under pastures and forest plantations is increased by 0.005337 x 10(6) km(2), whilts reducing the area of croplands by 0.000119 x 10(6) km (2). This is a net increase of 0.005218 x 10(6) km(2). The gross carbon rel ease is 174.66 Tg C per year to the atmosphere and transferring from cultiv ated and native vegetation to wood products (1.62 Tg C per year) and slash (1.18 Tg C per year). The processes of land preparation contribute 1.40 Tg C per year to the atmosphere. From the tree savannas, woodlands and forests 0.73 Tg C per year are estimated to have been transferred to the soil foll owing clearance and burning over this period, and 1.05 Tg C per year from h erbaceous savannas when were buried and decomposed at 0.84 Tg C per year. T he estimate of carbon balance here by inventories and changes in land-use a pproach indicates that the Orinoco llanos is a sink of -17.53 Tg C per year . The carbon turnover time in the Orinoco system is 68 years, which provide s a limited route for carbon sequestration. The calculated potential of the Orinoco Ilanos for storing carbon is 8300 Tg C. Ecological options to achi eve this potential value are addressed. However, nutrient deficiency and se asonal water supply are serious drawbacks to take into account for increasi ng carbon accretion. These results are particular for the Orinoco llanos, e ven though described processes could be similar to world-wide savannas, whe re a gradient of carbon heterogeneity exists. (C) 2001 Elsevier Science B.V . All rights reserved.