Are vegetation-soil systems drivers of ecosystem carbon contents along an elevational gradient in a highland temperate forest?

Vegetation-soil systems differentially influence the ecosystem processes related to the carbon cycle, particularly when one tree species is dominant over wide geographic regions that are undergoing climate change. The objective of this study was to quantify the stocks of ecosystem carbon in three vegetation-soil systems along a highland elevational gradient in central Mexico. The vegetation-soil systems, from lower to higher elevation, were dominated by Alnus jorullensis Kunth, Abies religiosa (Kunth) Schltdl. & Cham., and Pinus hartwegii Lindl., respectively. Above-and below-ground tree biomass was determined in each system, along with the litter, coarse woody material, roots, and litterfall. The A. religiosa system had the greatest stock of aboveground biomass carbon (216 +/- 31 Mg C.ha(-1)). The A. jorullensis system had the greatest production of litterfall (3.1 +/- 0.08 Mg.ha(-1).year(-1)); however, the carbon content of this litter layer (1.2 +/- 0.32 Mg C.ha(-1)) was lower than that of P. hartwegii (10.1 +/- 0.28 Mg C.ha(-1)). Thus, the litter layer in the A. jorullensis system had markedly the shortest residence time (8 years), suggesting high rates of litter decomposition. The soil carbon stock (at soil depth of 1m) was greater in A. jorullensis (189 Mg C.ha(-1)) and P. hartwegii (137 Mg C.ha(-1)) than in A. religiosa (68 Mg C.ha(-1)). The A. religiosa and A. jorullensis systems had the highest and lowest total ecosystem C content (301 and 228 Mg C.ha(-1), respectively). Upward migration of the A. religiosa system in response to global climate change, however, could cause losses by 2030 of 187 Mg C.ha(-1) associated with aboveground biomass.