[Substitution of native savanna by Pinus caribaea (Pinaceae) plantations in Venezuela: effect on parameters that indicated changes in soil carbon content]

A great extension (615,000 ha) of native savannas of the eastern plains of Venezuela have been replaced by plantations of Pinus caribaea var. hondurensis; however, only scarce information exists about the impact of this land use on carbon dynamics in soils. We studied the effect of temporal variability and the substitution on the total organic carbon (TOC), water-soluble carbon (WSC), microbial biomass C (Cmic), basal respiration (BR), microbial metabolic quotient (qCO2) and Cmic/Corg ratio. Selected chemical properties and biological parameters of soils were measured under 3 and 29 year old forest plantations of P. caribaea and an adjacent native savanna which was considered the control. At each site, nine soil composite samples were collected (0-10 cm depth). The studied parameters did not show a defined pattern in relation to temporal variability. Higher carbon preservation occurs in soil microbial biomass under pine plantations. The basal respiration rate and qCO2 suggests that there is a more efficient microbial carbon utilization in the plantations. The Cmic/Corg ratio shows that the microbial biomass has an important stock of soil carbon in pine plantations. The conversion of savannas to pine plantations can increase soil carbon in the eastern plains of Venezuela, but this must be balanced with the ecological importance of natural savannas ecosystems.