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Title: Ecosystem carbon dynamics from Andes to Amazon : investigating the effects of environmental parameters on productivity and carbon cycling of an Andean tropical montane forest
Author: Girardin, Cécile A. J.
Awarding Body: Oxford University
Current Institution: University of Oxford
Date of Award: 2011
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Abstract:
The productivity and carbon cycling 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 thesis examines spatial and temporal patterns of above- and below-ground forest ecosystem carbon cycling along a transect of study sites ranging from lowland Amazonia (194 m) to the high Andes in S.B. Peru (3025 m), with a mean annual temperature ranging from 26.4 QC (194 m) to 11.8 QC (3020 m) and an annual rainfall ranging from 3086 mm yr" (1000 m) to 1706 mm yr" (3025 m). Measurements of above-ground (stem, canopy litterfall) and below-ground (fine roots, soil respiration, soil organic matter) carbon stocks and CO2 fluxes were made at nine one-hectare forest plots along the elevational gradient extending from lowland forest, through pre-montane, lower montane and upper montane forest, with relatively homogeneous stand structure, geological substrate and topography. I began by documenting the spatial and temporal patterns of above-ground carbon allocation along the elevational gradient. In particular, I analysed net primary productivity allocation to canopy components (leaf, twigs, flowers, fruit, bromeliads, epiphytes) along the elevational gradient in detail and observe the effects of seasonal variation on each component of above-ground production. Consistently lower values of mean annual above-ground productivity were observed in the cloud immersion zone of the montane forest. Then, the below-ground components of the ecosystem were recorded through spatial and temporal measurements of soil CO2 efflux and fine root dynamics (carbon stocks, net primary productivity and residence time). CO2 efflux did not show a significant trend along the elevation gradient, with the range of soil C02 efflux values similar to that observed in lowland tropical forest sites, despite the large variation in mean annual temperatures. Below-ground, a step change in fine root productivity was recorded at the base of the mountain (~1 000 m) between most lowland plots and tropical montane forest plots, although there was no significant change in fine root productivity with elevation above 1000 m. These measurements allowed for a comparison of the allocation of net primary productivity above- and below-ground along the elevational gradient. I combined the data obtained in this D.Phil thesis with data from recent lowland studies to examine the spatial patterns of above- and below-ground carbon dynamics along the elevational transect. 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. Further, most processes driving the internal carbon cycle (net primary productivity, carbon stocks, autotrophic respiration) showed evidence of a step change at the base of the cloud immersion zone (1500 - 1855 m), and no significant change within the cloud immersion zone. These patterns imply that cloud forest characteristics (such as increased and year-long moisture resulting from frequent cloud cover immersion, a decrease in PAR incidence and slower soil nutrient uptake rates) combine with cooler temperatures to drive the internal carbon cycle.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.551278  DOI: Not available
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