Ecosystem dynamics of Amazonian Open Peatlands during the Late Holocene

Abstract

This project aims to improve the biogeographical understanding of the floristic character, formation and long-term development of 'open' peatlands in the Pastaza-Maranon Foreland Basin (PMFB), north-eastern Peru. A suite of ecological, palaeoecological and hydrological methods was adopted, and a specific focus was directed on two open peatland sites near the villages of Veinte de Enero and San Roque. Vegetation surveys revealed contrasts in the vegetation composition of the two open peatlands while showing that, compared to other peatland types, open peatlands have the lowest alpha diversity. Comparing vegetation abundance data to pollen rain collected using pollen traps (at Veinte de Enero) and surface samples (at San Roque) revealed that open peatlands receive a large quantity of pollen from wind-pollinated taxa, deposited from a large source area including the mosaic of vegetation communities surrounding the sites. Palaeoecological data was obtained from cores collected at Veinte de Enero and San Roque. Downcore palynology reveals that, in the area surrounding the coring sites, there were transitions from an open water scenario with aquatic vegetation and floating herbaceous mats, to a forested phase with flood-tolerant trees and palm taxa, and finally to a palm swamp dominated by Mauritia flexuosa. At the coring sites themselves, the records showed herbaceous scenarios since peat initiation, for the past 1,600 Cal yr BP (VEN_OP, the open peatland core at Veinte de Enero) and 3,500 Cal yr BP (SAR_T3_03_B, the open peatland core at San Roque). Vegetation change at the sites appears to be predominantly driven by autogenic processes associated with organic infilling of the basins, while links to possible climatic and anthropogenic drivers remain tentative. Frequent fluctuations in the flooding influence of sediment-laden rivers may have contributed to keeping the sites open, by raising flood levels and bringing mineral material to the site, which could have created limiting conditions that inhibited the expansion of palm swamp taxa. New insights into the current hydrological status are provided by the hydraulic conductivity (K) measurements carried out at Veinte de Enero, which show that K is consistent with measurements from other peatlands in the PMFB, and thus may be comparably sensitive to future climate change and human disturbance. Overall, this thesis has provided the first in-depth palaeoecological study targeting open peatlands in Amazonia, demonstrating that these ecosystems are ecologically valuable because of their unique taxonomic composition and that they represent an important phase of peatland development in the PMFB, evident in their palaeoecological records. This study ultimately improves our understanding of the ecology, functioning and sensitivity of open peatlands, and underscores the importance of the conservation and protection of intact peatlands in this region.

Date of Award	1 Aug 2022
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Peter Ryan (Supervisor) & William Fletcher (Supervisor)