Fire in the Amazon forest amidst selective logging and climatic variation

Fires in tropical forests are strongly associated with climate, but also contingent on anthropogenic ignition sources. Tropical forests are facing increasing pressure of deforestation for agriculture, and further degradation, such as through fire and selective logging, thereby triggering detrimental
impacts on biodiversity and ecosystem services. This is likely to intensify with climate change and increasing demands for agricultural goods. In this
thesis, I examine how anthropogenic pressures and climatic variations relate to fire in the Brazilian Amazon. I first focused on selective logging, which
is the most widespread pattern of forest degradation and has been identified as a facilitator of fire for altering microclimates through disrupting the canopy and increasing fuel loads from operational residual damage. I explored how long is required for the thermal environment of logging gaps and roads to recover, through relating canopy structure with temperature of understorey ambient and forest floor. I also investigated the extent to which damages caused to the forest structure from selective logging can alter the thermal environment of gaps and remaining surrounding forest, and how such impacts can affect forest flammability. Selective logging increases forest fire proneness through creating hotter and drier thermal environments, which accelerates desiccation of fuel loads, as well as increasing exposure to anthropogenic ignition sources. Selectively logged forests can, however, recover their thermal environment to baseline levels of a primary forest fairly rapidly (less than 5 years), and thus decrease their fire proneness as forest regenerates. In addition to smart and strategic planning of selective logging operations, it is critical that logging companies impose strong post-logging management regulations to control ignition sources during at least the first five years after harvest to prevent fires. This thesis then tackles this issue at a broader scale, where I disentangled climatic variation and anthropogenic pressures, and quantified their relative contribution in driving fire across the Brazilian Amazon. Put together, my findings demonstrate that fire is driven by a synergy between climate and anthropogenic pressures. Regulating human activities and fire use in the Amazon forest is crucial to preventing fires and preserving biodiversity and ecosystem services, especially under climate change.