Abstract
The net primary productivity, carbon stocks and turnover rates (i.e. carbon dynamics) of tropical forests are an important aspect of the global carbon cycle. These variables have been investigated in lowland tropical forests, but they have rarely been studied in tropical montane forests. This study examines spatial patterns of above- and below-ground carbon dynamics along a transect ranging from lowland Amazonia to the high Andes in S.E. Peru. Fine root biomass values increased from 1.50 Mg C ha-1 at 194m to 4.95±0.62 Mg C ha-1 at 3020 m, reaching a maximum of 6.83±1.13 Mg C ha-1 at the 2020 m elevation site. Above-ground biomass values decreased from 123.50 Mg C ha-1 at 194 m to 47.03 Mg C ha-1 at 3020 m. Mean annual below-ground productivity was highest in the most fertile lowland plots (7.40±1.00 Mg C ha-1 yr-1) and ranged between 3.43±0.73 Mg C ha-1 yr-1 and 1.48±0.40 Mg C ha-1 yr-1 in the pre-montane and montane plots. Mean annual above-ground productivity was estimated to vary between 9.50±1.08 Mg C ha-1 yr-1 (210 m) and 2.59±0.40 Mg C ha-1 yr-1 (2020 m), with consistently lower values observed in the cloud immersion zone of the montane forest. Fine root carbon residence time increased from 0.31 years in lowland Amazonia to 3.78±0.81 years at 3020 m and stem carbon residence time remained constant along the elevational transect, with a mean of 54±4 years. The ratio of fine root biomass to stem biomass increased significantly with increasing elevation, whereas the allocation of net primary productivity above- and below-ground remained approximately constant at all elevations. Although net primary productivity declined in the tropical montane forest, the partitioning of productivity between the ecosystem sub-components remained the same in lowland, pre-montane and montane forests.
