Wildfires are a principal force shaping ecological patterns and processes across diverse terrestrial ecosystems. The complex interactions of ignition sources with vegetation, climate, and topography give rise to fire regimes, an ecological concept describing the range of fire characteristics occurring at a given geographic location and time period [1
]. Fire regimes can be characterized by various metrics, including fire size, seasonality, frequency, intensity, and severity. Examining multiple components of the fire regime is therefore necessary for understanding the geographic patterns, drivers, and ecological effects of fire [3
]. This knowledge is essential for projecting how fire regimes will respond to future changes in climate and land use, and for developing strategies to adapt to these changes. West Africa, in particular, is a region where fire has a significant impact on terrestrial ecosystems [4
]. The region also exhibits strong geographic variation in land use, climate, vegetation types, and human population, all of which influence spatial heterogeneity of fire regimes. The main goal of this study was to explore the influences of climate, vegetation, and land use on multiple fire regime components across the forest and woody savanna zones of West Africa.
Over the past four decades West Africa has lost a substantial portion of its natural vegetation, including savannas, woodlands, and forests, to expanding croplands and human settlements. As a result, the remaining natural vegetation is highly fragmented [5
]. A recent analysis of satellite remote sensing data indicated a decreasing trend of woody vegetation cover across the savanna ecoregions along with widespread degradation of the humid forests [7
]. The tropical humid forest (also known as the Upper Guinean forest, UGF), a globally significant biodiversity hotspot [8
], is estimated to have lost over 80% of its original forest cover, with the remainder distributed in a fragmented agriculture-forest mosaic [9
]. Moreover, West Africa’s population almost doubled between 1990 and 2015 (180 to 353 million), and it is projected to nearly double again by 2050, from 353 million to 797 million [11
]. The region has also been experiencing climate change in recent decades. Temperatures have become warmer, and precipitation has either not changed or declined for many locations below the Sahel, especially along the Guinea Coast [12
In the rapidly changing environment of West Africa, fire regimes are affected by changes that alter fuel conditions and ignitions, but fire also serves as a driver of vegetation and land use change. As a result, fire and vegetation change are linked via strong positive and negative feedbacks [4
]. Yet, studies of fire regimes in this region are rare. Quite recently, Prichard et al. [13
] reviewed fire regimes across the world’s major bioregions and pointed out the relative scarcity of literature on African savannas. Surprisingly this review did not include any examples of research on tropical forest fires in Africa.
Much of our knowledge of fire regimes in West Africa has been gleaned from studies conducted at broader continental to global extents. In a global characterization of fire regimes, Archibald et al. [14
] found that most of the region was dominated by relatively frequent, small-sized fires with low intensity. Additionally, the West African fire regime was largely controlled by human impacts [2
]. Another global analysis of burned areas also indicated that human activities strongly influence fire size distribution in West Africa through land cover changes, fire ignitions, landscape fragmentation, and fire management [15
]. Multiple studies have found evidence of decreasing fire activity in the dry, savanna-dominated regions across Africa [17
]. Most regional to continental scale fire studies have not explicitly addressed the tropical forest regions of West Africa, where fire is relatively rare. However, there is evidence that fires have encroached into the northern portions of the dry tropical forest zone in recent decades, leading to degradation and eventual loss of forest vegetation [4
Although studies of fire have been conducted in other tropical regions, the distinctive physical and social environments of West Africa suggest that knowledge from such studies is not directly transferable. For example, land use pressure in the forested zone is dominated by selective logging, small-scale slash-and-burn farming and bush meat hunting, in contrast to the agro-industrial pressures that are prevalent in the tropical Americas [20
]. Disproportionate dependence on forest resources, high levels of poverty, and recent history of wars and political instability are all important socio-economic characteristics of the Upper Guinean region. Given these unique features, better regional information about the patterns and drivers of fire regime is needed to support projections of future fire regime changes and aid in the development of adaptation strategies. To help meet these needs, we conducted a regional study of fire regimes in the forest and woody savanna dominated portions of West Africa and addressed the following research questions:
What are the spatial patterns and interrelationships of multiple fire regime components in the Upper Guinean region?
What are the overall trends in fire activity and how do they differ amongst the humid forest and the savanna-dominated ecoregions?
How do the relative influences of climate, topography, vegetation type, and human activity vary across different fire regime components?
In the Upper Guinean Region of West Africa, different components of the fire regime were influenced by different environmental drivers. As a result, the various combinations of these environmental factors create distinctive fire regimes throughout the region. The strong gradient of increasing fire activity from the wetter coastal regions to the drier regions in the north was related primarily to the shift from forest to savanna vegetation types rather than direct climatic effects. Within the savanna zone, there was a distinction between fire regimes with high active fire density, low burned area, long fire seasons, and late peak fire months compared to fire regimes with fewer active fires, higher burned area, shorter fire seasons, and earlier peak fire months. There was also an area of particularly high fire intensity located in the westernmost coastal regions of the study area. These differences were attributable to the combined effects of vegetation cover, recent land use changes, topography, and climate. Increasing trends in active fire detections in parts of the forested zone and decreasing trends in both active fire detections and burned area in the savanna zone were likely associated with differential impacts of land use change in these distinctive ecoregions. We conclude that while ongoing climate change will continue to influence fire regimes throughout the region, land use change and the resulting feedbacks between fire and vegetation will have a major impact as well. Efforts to project future fire regimes and develop regional strategies for adaptation will therefore need to encompass multiple components of the fire regime and consider multiple drivers, including land use as well as climate. It will also be essential to develop a stronger understanding of how these drivers affect the timing and spatial pattern of ignitions, the abundance and spatial connectivity of available fuels, and the amount of biomass consumed by fire.