Experimental Study of Fire Behavior in Annually Burned Humid Savanna of West Africa in the Context of Bush Encroachment

Abstract

AbstractPrescribed yearly mid-dry season fire is generally used in the Guinean savanna (a humid savanna of West Africa) as a vegetation management tool. Despite this fire, bush encroachment can be observed due to climate change and high sapling recovery rates with increasing CO2 emissions. There is therefore a need to analyze other fire seasons. We analyzed fire behavior during a 5-year field fire in the Guinean savanna of Lamto reserve in Ivory Coast. Early (EDS), mid (MDS), and late (LDS) dry season fires were tested. Nine 0.5 ha plots were burnt annually to determine the rate of spread, fire intensity and the residence time above 60 °C. Fuel characteristics and weather conditions were measured to assess their impact on fire behavior. Recruitment from resprout to adult tree stage were assessed for an estimation of these fires’ severity. Understory grass height, fuel load, and moisture content had greater values in EDS than in MDS and LDS. The rate of spread and intensity of both MDS and of LDS were greater than those of EDS fires. The best predictors for fire behavior were fuel moisture content and air humidity. In dry conditions, fires were faster and more intense. With climate change predicting increasingly longer and drier periods, we expect more and more intense fires. A longer time of exposure to lethal temperatures (>60 °C) and the phenological state of trees in the late dry season explains the higher severity of this fire (there was no recruitment to adult stage under LDS fire). In some years, LDS helped to reduce bush encroachment in the subject region. This data provides important insights into fire behavior and its severity in the Guinean savanna, informing fire management policies and procedures.KeywordsBurning seasonClimate changeFire behaviorFire severityGuinean savanna