Kerdraon-Byrne, Deirdre and Sayer, Emma and Drewer, Julia and Slade, Eleanor (2019) The effects of forest degradation on soil carbon dynamics in the tropics. PhD thesis, Lancaster University.
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Abstract
Plant-soil interactions and soil carbon dynamics are an essential part of soil function. Land-use change can affect the soil’s ability to accumulate and store carbon. Deforestation and conversion to croplands has decreased tree species cover and diversity in the tropics resulting in degraded and secondary forests becoming the dominant forested habitat. Understanding the effects of forest degradation on soil carbon dynamics is vital if we are to remediate these ecosystems under climate change. The overarching aim of this thesis was understanding how changes in tree and plant species composition at different levels of degradation affect soil carbon dynamics and litter decomposition in the old and neo-tropics using litter transplant experiments in the field. Malaysia is one of the two biggest producers of palm oil in the world with Indonesia. Borneo is a biodiversity hotspot, but this ecosystem is decreasing at an alarming rate. Sabah, in norther Malaysian Borneo is converting its tropical forest to oil palm plantations resulting in vast expanses of oil palm monocultures containing secondary forest fragments at various degrees of degradation. In Central America, the tree cover is also dominated by secondary forests and timber plantations; in Panama, only 21 % of the tree cover classified as intact forest and there are remediation projects in place to encourage reforestation of degraded landscapes into plantations using native timber species. The level of degradation in the habitats changed the microclimate which affected soil properties, microbial activity and litter decomposition. Litter properties also had an effect on the rate of litter decomposition and microbial activity. The loss of tree cover in the deforested habitats and monocultures resulted in lower microbial activity and decomposition rates whereas the secondary forests has similar microbial activity and decomposition rates as the old growth forests. Overall, my results suggest that mixed litter inputs are crucial for maintaining soil function and that tropical forest soils might be more resilient to change than expected.