In the tropics, conversion of woodland and forest into cropland and pasture has risen drastically during the last decade. Rapid population growth and poverty are believed to be the main factors of change in land use in these zones. Southern Burkina Faso experienced rapid population growth due to massive peasants' migration from the north and central regions of the Country, exacerbated by decreasing rainfall and arable land in the area of origin. This paper assessed the impact of such increased population on land use change in the attracting zones from 1986 to 2006. Satellite images were used to measure changes in land cover types over time and national population census data were used to examine the population dynamics over the same time. Results showed that the forest land was progressively converted to croplands at an annualized rate of 0Á96 per cent, while the population density shifted from 17 inhabitants per km 2 in 1986 to 30 inhabitants per km 2 in 2006. Pearson correlation analysis revealed the positive role of population size and distribution in explaining land cover change. Policy initiatives that will lead to better environmental management are recommended.

Assessing the recovery of species diversity and composition after major disturbance is key to understanding the resilience of tropical forests through successional processes, and its importance for biodiversity conservation. Despite the specifi c abiotic environment and ecological processes of tropical dry forests, secondary succession has received less attention in this biome than others and changes in species diversity and composition have never been synthesised in a systematic and quantitative review. Th is study aims to assess in tropical dry forests 1) the directionality of change in species richness and evenness during secondary succession, 2) the convergence of species composition towards that of old-growth forest and 3) the importance of the previous land use, precipitation regime and water availability in infl uencing the direction and rate of change. We conducted meta-analyses of the rate of change in species richness, evenness and composition indices with succession in 13 tropical dry forest chronosequences. Species richness increased with succession, showing a gradual accumulation of species, as did Shannon evenness index. Th e similarity in species composition of successional forests with old-growth forests increased with succession, yet at a low rate. Tropical dry forests therefore do show resilience of species composition but it may never reach that of old-growth forests. We found no signifi cant diff erences in rates of change between diff erent previous land uses, precipitation regimes or water availability. Our results show high resilience of tropical dry forests in term of species richness but a slow recovery of species composition. Th ey highlight the need for further research on secondary succession in this biome and better understanding of impacts of previous land-use and landscape-scale patterns.Succession has been a major focus of plant community ecology for more than a century (McIntosh 1999), yet the processes underlying assembly of secondary forests continue to be actively researched (Norden et al. 2015). Th e early view of Clements (1916) (monoclimax hypothesis) and initial fl oristic composition model of Egler (1954) were further formalized by the three models of Connell and Slatyer (1977). Th ese deterministic models are all based on the idea that tradeoff s between traits promote success in diff erent stages of succession (Huston and Smith 1987). However, none of these models accounts for stochastic events or historical contingencies (Young et al. 2005). Lawton (1987) proposed a model of succession based only on random survival of established species and colonization by new species, paving the way for the neutral theory of community assembly (Hubbell 2001). Although deterministic niche-based and neutral models of succession have often been treated as mutually exclusive explanations for empirical patterns, a growing body of literature evidences the importance of the integration of the two (Chave 2004, Gravel et al. 2006, Tilman 2004. A major focus of research is now to assess the res...

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There is growing evidence that population pressure on the land has become the most intractable problem in the developing countries where demand for food exceeds the food production capacity of the land. Southern Burkina Faso has experienced rapid population growth, mostly driven by immigration of farmers. This study was carried out in Sissili Province and used satellite images acquired over 31-year period, census and survey data to capture migration patterns and its impacts on land use change. Results showed that migrant population which accounted for only 3 per cent in the study area in 1976 shifted to 57 per cent in 2007. Migrant people were using improved technology to progressively convert forest land to cropland. Cropland increased at an annualized rate of 0Á46 per cent to the detriment of the dense forest and woodland which decreased at 0Á57 per cent per annum. Population growth was highly correlated with increasing area of cropland (r 2 ¼ 0Á95, p ¼ 0Á014) and declining dense forest (r 2 ¼ 0Á78) and woodland (r 2 ¼ 0Á95) covers. It can be concluded that rural migration, driven by the relatively good soil and rainfall conditions in the recipient area, is accounted for deforestation in the study area. If rural migration is not checked, it will seriously degrade the environment.

Fuel characteristics, fire behaviour and temperature were studied in relation to grazing, dominant grass type and wind direction in West African savanna-woodland by lighting 32 prescribed early fires. Grazing significantly reduced the vegetation height, total fuel load, and dead and live fuel fractions whereas plots dominated by perennial grasses had higher values for vegetation height, total fuel load and the quantity of live fuel load. Although fire intensity remained insensitive (P > 0.05) to any of these factors, fuel consumption was significantly (P = 0.021) reduced by grazing, rate of spread was faster in head fire (P = 0.012), and flame length was shorter in head fire than back fire (P = 0.044). The average maximum temperature was higher (P < 0.05) on non-grazed plots, on plots dominated by annual grasses, on plots subjected to head fire, and at the soil surface. Lethal temperature residence time showed a nearly similar trend to fire temperature. Wind speed and total fuel load were best predictors of fire behaviour parameters (R 2 ranging from 0.557 to 0.862). It can be concluded that grazing could be used as a management tool to modify fire behaviour, back fire should be carried out during prescribed burning to lower fire severity, and the fire behaviour models can be employed to guide prescribed early fire in the study area.