Changes from pasture to a native tree plantation affect soil organic matter in a tropical soil, Panamá.

Background and aims: We examined changes in soil organic matter arising from conversion of a 45-year old pasture to a 10 yr. old native tree plantation in Panamá, to evaluate the effect of monoculture and mixtures.Methods: We intensively sampled the soil 0-10 cm depth in the pasture in 2001 and in 22 plantation plots in 2011, ranging from 5 monocultures to 3- and 6-species treatments; samples were also taken from an undisturbed forest site. Soil analyses included organic carbon (SOC) and δ13C.Results: Conversion of the pasture to tree plantation resulted in an overall loss of SOC of 0.6 kg m−2 (18%) in the top 10 cm, but neither tree species nor diversity had a significant effect. End-member δ13C values suggested that the contribution of C3 plants to SOC was increased from 26% in the pasture to 55% after 10 years of plantation and SOC turnover times were calculated to be 21-36 yr.Conclusions: The magnitude of the loss in soil SOC is smaller than the increases in tree biomass (~3 kg C m−2) and litter (~0.3 kg C m−2) in the plantation, but still a significant part of the ecosystem C balance. [ABSTRACT FROM AUTHOR]