Effects of landscape pattern and vegetation type on the fire regime of a mesic savanna in Mali

摘要

Savanna fires are a critical earth-system process that alter vegetation regionally and contribute to changes in atmospheric composition globally. The fire regime in savannas has shifted over time resulting in a large reduction in burned area. Savanna fires, which are human caused and set for a plethora of reasons, produce complex mosaic burned area patterns that tend to result in lower overall burned area. Mosaic fire regimes are difficult to detect and map accurately using available satellite data. Imagery-induced low-resolution bias makes it difficult to link fires with relevant environmental and anthropogenic factors, while higher resolution imagery is temporally less frequent. We explore how landscape pattern affects the fire regime in a mesic savanna by quantifying relationships between the spatial patterns of vegetation, which are shaped by natural and human factors, widely used ecological indices, and the seasonality and frequency of fires. The study finds that landscape pattern influences the fire regime; fire seasonality and frequency varied by landscape index at both the vegetation class and landscape scales. Percent cover, shape index and largest patch landscape ecological indices demonstrated the most consistency in burn date trends across scales. The study finds that landscape fragmentation-specifically a reduction in the size of patches and an increase in their number-results in an earlier fire regime. We conclude that fire intensity and severity will continue to decline as agriculture expands and landscapes fragment from agriculture in savannas. Our methods also demonstrate the ability to integrate landscape indices with coarse-resolution fire data.