Moving away from the native forest edge: Changes in ecosystem processes towards the interior of Pinus taeda plantations

Abstract

Tree plantations are considered as strategic systems for climate change mitigation and economic development. However, their establishment in subtropical areas frequently involves the replacement of a species-rich forest by a tree monoculture with exotic species, which may be functionally different from native species. The impact of this change on ecosystem processes is still widely unknown. In Argentina, large portions of the Semideciduous Atlantic Forest were replaced by non-native Pinus taeda monocultures. The P. taeda litter has lower quality and a slower decomposition rate than native plant litter. Therefore, this replacement would change the characteristic of the litter that reaches the ground. Litter quality is one of the major drivers of decomposition. In the transitional area between two different environments, the edge effect influences populations and communities and could affect ecosystem processes due to changes in its drivers. We wonder how ecosystem processes, as litter decomposition and litterfall production, will respond from the forest edge into the exotic pine monocultures. In five P. taeda plantations and five sites in native forest, we established litter traps to estimate litterfall and litterbags to estimate pine litter decay rate. Litter layer thickness and necromass were also estimated. The change of these variables along a distance gradient from the forest edge into the pine plantation was studied in 10 points at different distances from the edge (0?300 m). Comparisons of these variables between P. taeda plantations and native forest were also done. Native forest replacement by P. taeda monocultures changed the litter identity that reached the ground and decreased the pine litter decomposition rate. The litter layer necromass increased towards the interior of P. taeda plantations, consistently with the increase in pine litterfall. Within the pine plantation, the distance to the native forest edge had no effect on the litterfall neither on pine litter decomposition rates. However, the increase in litter layer necromass towards the interior of plantations suggests that the presence of native forest contiguous to pine plantations in the Semideciduous Atlantic Forest favors litter layer decomposition. Litter from native species, with higher quality than pine litter, decomposes faster in the litter layer and would drive to a more efficient stabilization of soil organic matter. Accordingly, management techniques promoting the increase in the abundance of native species inside pine plantations would improve nutrient cycling and monoculture sustainability.