CANCELLED - Pine afforestation alters carbon cycling and pools along a precipitation gradient in Patagonia, Argentina

Background/Question/Methods

The balance between productivity and decomposition determines ecosystem carbon storage. Climate and vegetation are directly involved in the fate of carbon, and land-use change may directly impact carbon cycling though changes in pool sizes and ecosystem residence time. We took advantage of an unplanned natural experiment along a precipitation gradient (250-2300mm mean annual precipitation) in Patagonia, Argentina, where extensive areas of steppe and native forest have been converted to pine plantation of a single species (Pinus ponderosa). We established five paired sites, a natural vegetation site and a paired pine plantation of similar density and age. We explored how changes in the dominant vegetation, precipitation and its interaction simultaneously affected primary production, litter decomposition and soil carbon storage. Aboveground primary productivity (leaves and stems), litter decomposition using litterbags, and carbon stores in detritus and surface soil were evaluated over a two year period at all sites along the gradient.

Results/Conclusions

Productivity increased linearly with precipitation in both natural vegetation and in pine plantations (r²=0.95; 0.91), and was consistently higher in pine plantations primarily due to increased stem increment. Litter decomposition demonstrated a positive relationship with precipitation only in pine plantations (r²=0.94), but was substantially reduced when compared to decomposition in the natural vegetation counterparts. At the same time, total soil carbon in surface soils increased with precipitation but did not vary between natural vegetation and pine plantation sites. The net balance of litterfall inputs and litter decomposition demonstrated modeled detritus values with large accumulation of detritus carbon in pine plantations, mainly due to slower decomposition rates in these modified ecosystems. These results suggest that pine afforestation may be increasing carbon storage in some pools, such as stem biomass and detritus, but more stable soil carbon pools show no evidence of increased soil carbon sequestration after 30 years of afforestation.