Diminishing the climate footprint with afforestation in Patagonia, Argentina

AUSTIN A.T; ARAUJO P.I.; GONZALEZ ARZAC, ADELIA; MARTINEZ, L; MÉNDEZ, S

Conferencia; XXVIII Reunión Argentina de Ecología; 2018

Land-use change, and in particular the conversion of natural ecosystems for the productionof tangible products such as food or wood, is one of the most prominent manifestationsof global change in terrestrial ecosystems. In particular, the planting of tree speciesin previously non-forested ecosystems to achieve rapid growth and potential carbon sequestrationhas become an attractive option proposed for long-term carbon (C) storageand climate change mitigation. Nevertheless, there are many open questions regardinghow ecosystem processes are modified as a function of this land-use change. We tookadvantage of an unplanned natural experiment involving a 40-year-old forestation project,where a single conifer species (Pinus ponderosa), was planted between the years197 4 - 197 8 regionally in Patagonia, Argentina, replacing natural ecosystems rangingfrom semi-arid steppe to broadleaf forest along a broad range of precipitation (250 -2200 mm). We explored how ecosystem processes were altered by comparing the naturalvegetation with paired pine plantations at six sites along this regional precipitation gradient.We evaluated ecosystem C and nitrogen cycling, net primary production (NPP)and decomposition, and biotic modification of the soil fauna. Although NPP was greaterin most afforested sites, C-sequestration was only observed in the woody increment, withdramatic increases in litter detritus at the soil surface. This coincided with a significantreduction in C and N in surface soil pools in afforested sites. Dramatic changes in the soilfauna in arid plantation sites resulted in a ?forestation? effect, meaning that the abundanceand composition of the macrofaunal community become increasingly indistinguishablefrom the mesic forests. Taken together, our results suggest that a change in the speciescomposition of the dominant vegetation was sufficient to modify the major drivers of Cand N cycling in these sites independently of climate constraints. Alterations of ecosystemprocesses due to afforestation were sufficient to significantly diminish, if not erase,the climate footprint along this broad precipitation gradient.