Background: Fire is important for the maintenance of African savanna ecosystems, particularly humid savanna. Despite the importance of fire behavior to our understanding of fire's ecological effects, few studies have documented fire behavior and its determinants in humid West African savannas and, in particular, whether fire behavior depends on season of the year. We analyzed fire behavior in the Guinean savanna of Lamto (Ivory Coast) during a 4-year field experiment. The fire regimes tested consisted of three different burning seasons: early-season fire, mid-season fire, and late-season fire. Nine 0.5 ha plots were burned annually to determine the rate of spread and fire intensity. Fuel characteristics and weather conditions were measured to assess their impact on fire behavior. Results: Understory grass height, total fresh fuel load, and moisture content had greater values in early-season fire than in mid-season and late-season fire. The rate of spread and intensity of both mid-season fire (0.14 ± 0.03 m s −1 and 3920 ± 740 kW m −1 , respectively) and of late-season fire (0.12 ± 0.02 m s −1 and 3134 ± 482 kW m −1 , respectively) were significantly greater than those of early-season fire (0.04 ± 0.01 m s −1 and 1416 ± 252 kW m −1 , respectively). The best predictors of fire behavior were fuel moisture content and air humidity; these two explanatory variables were the sole significant predictors for fire intensity, rate of fire spread, and flame height. Conclusions: Given that there is no difference between intensity of mid-season and late-season fire, we suggest that the generally reported higher impact of late-season fire on trees in the West African humid savannas is due not to fire intensity per se, but rather to a more sensitive phenological stage of trees (e.g., leafless in mid-season), and to a longer time of exposure to lethal temperatures (> 60°C) in the late dry season. These data provide important insights into fire behavior in the Guinean savanna−forest mosaic ecoregion, informing fire management.

Nous remercions l'IRD (Institut de Recherche pour le Développement) d'avoir financé cette étude à travers le programme JEAI (Jeune Equipe Associée). RESUME La mesure directe de l'intensité du feu n'étant pas toujours possible car fastidieuse et coûteuse, les indices post-feu substituent celle-ci et permettent de mieux comprendre les caractéristiques du feu et son impact sur la végétation. Cette étude a été menée dans la réserve de Lamto (Côte d'Ivoire) dans le but d'identifier les indices post-feu qui sont de bons indicateurs de l'intensité du feu. Trois régimes de feu ont été expérimentés de 2013 à 2017: le feu précoce, le feu de mi-saison, et le feu tardif. L'intensité du feu a été déterminée durant chaque feu. Ensuite, les indices post-feux que sont : la hauteur des flammes, l'efficacité de combustion, le volume d'eau évaporée, et les fractions de cendre fine et grossière ont été mesurés, et la surface couverte par le feu estimée. La hauteur des flammes est le meilleur indicateur de l'intensité du feu. Plus le feu est intense plus la zone d'action des flammes est haute, et plus il est susceptible de réduire le recrutement des jeunes ligneux. Cette étude propose en savane Guinéenne un indice facile à mesurer, qui permettrait aux gestionnaires des aires protégées en savane de mieux évaluer l'intensité du feu et son impact sur la végétation.

Biomass burning has become more frequent and widespread worldwide, with a significant proportion occurring in tropical Africa. Fire dynamics have been generally studied at global or regional scales. At local scale, however, fire impacts can be severe or catastrophic, suggesting local analyses are warranted. This study aimed to characterise the spatio-temporal variations of vegetation fires and identify the main fire hotspots in Côte d’Ivoire, a country of West Africa, one of the world’s burn centres. Using MODISderived fire data over a 10-year period (2007–2016), the number of fire days, active fires and fire density were assessed across the entire country. In the southern part dominated by forests, fire activity was low. Three main fire hotspots were identified between 2°30’–8°30’W and 7°00’–10°30’N in the North-West, North-East and Central areas all dominated by savannas. In these areas, Bafing, Bounkani and Hambol regions recorded the highest fire activity where fire density was 0.4±0.02, 0.28±0.02 and 0.18±0.01 fires/km²/year, respectively. At national scale, the annual fire period stretched from October to April with 91% of fires occurring between December and February, with a peak in January. Over the decade, there was a decreasing trend of fire activity. Fire density also was negatively correlated with rainfall >1000 mm for the synchronic analysis, whereas fire density was positively correlated with rainfall in the previous years. Results suggest that the positive relationship between the previous year’s rainfall and fire activity could operate on a cycle from 1 to 4 years.

Fire is a process of disturbance of natural ecosystems that can be used for land management and soil preparation for agricultural purposes, but can also drastically affect biodiversity and the distribution and abundance of species by changing land use and altering the microclimate. The analysis of data on thermal anomalies has become a valuable tool for the study of places with low monitoring of the occurrence of fires. In this study, information from the MODIS sensor was used to analyze the spatio-temporal distribution of fires in the five natural regions of Colombia (Caribbean, Andean, Pacific, Orinoquia, and Amazon) in the period of 2000–2020. Nevertheless, MODIS fire hotspots present some difficulties in estimating the magnitude of fire activity, due the relations between active fires and burned areas, which are not constant in space and time. The method used in this work consisted to performance an inter-annual and intra-annual analysis of thermal anomalies data and identifying the incidence of temperature in the occurrence of fires. The fire density (defined as the number of fires per unit area) and the fire trends over the study period were also analyzed. Inter-annual fire peaks were recorded in 2004 (8.21%) and 2007 (8.04%), and three main fire hotspots were identified in the Orinoquia, Andean, and Caribbean regions. Moreover, 87% of fire peaks were observed in the dry season (December–March). On the other hand, the highest incidence of thermal anomalies occurred in the Orinoquia region (83409 ± 185 fires), and the highest incidence of fires per unit area was recorded in the Andean region (0.162 ± 0.086 fires-km2-year). Fire activities varied strongly according to region and year over the study period. Significant correlations were observed between temperature and fire density in the Andean (Rho = 0.7506), Pacific (Rho = 0.7364), and Caribbean (Rho = 0.5571) regions. Thus, temperature seem to be a driver of fire density in these regions.

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