Abstract
Forests constitute a key component of the Earth system but the sustainability of the forest reserves in the semi-arid zone is a real concern since its vegetation is very sensitive to the climate fluctuation. The understanding of the mechanisms for the vegetation–climate interaction is poorly studied in the context of African Sahel. In this study, the characteristics of the vegetation response to the fluctuations of precipitation and temperature is determined for the forest reserve of Fina. Rainfall estimates, air temperature and NDVI were re-gridded to a same spatial resolution and standardized with respect to their respective long-term mean. Lag-correlations analysis was used to estimate lag times between changes of climate variables and vegetation response at both seasonal and interannual bases. Results show increasing tendency of NDVI started from the 1990s coinciding the recovery of the rainfall from the 1980s drought, and the obtained correlation (r = 0.66) is statistically significant (p value < 0.01). The strongest responses of vegetation to rainfall and temperature fluctuations were found after 30 and 15 days, respectively. Moreover, at a shorter time lag (e.g., 15 days), more pronounced vegetation responses to both rainfall and temperature were found in agriculturally dominated land while at a longer time lag (e.g., 30 days), a stronger response was observed in Bare-dominated land. The vegetation response to the climate fluctuation is modulated by the land-use/cover dynamics.
Highlights
The Sahel is a sub-region of sub-Saharan Africa stretching between about 12◦ and latitude north and characterized by the transition from the arid conditions of the Sahara-desert and the humid climate from the Guinea coast
Results regarding the negative correlation between Normalized Difference Vegetation Index (NDVI) and air temperature are arguable since previous study [19] in similar semi-arid climatic condition revealed that temperature anomalies were negatively correlated to NDVI in the lower river basin of Colorado and positively correlated in the upper river basin of Colorado. These results corroborate with the study on the response of vegetation to changes in air temperature, and precipitation was investigated in a semi-arid zone of Northern China where the lag length of vegetation growth in response to temperature and precipitation was shorter in agriculture areas (~2 months) than the forest-dominant area (3–4 months lag length) [18]
Applying a lag-correlation approach between fluctuations of vegetation and climate variables at both seasonal and inter-annual bases, the present study has determined the characteristics of the vegetation response to the fluctuations of precipitation and temperature for the forest reserve of Fina, and the results are examined in the context of the existing land-use/-cover classification of the forest reserve
Summary
The Sahel is a sub-region of sub-Saharan Africa stretching between about 12◦ and latitude north and characterized by the transition from the arid conditions of the Sahara-desert and the humid climate from the Guinea coast. The sub-region is undergoing serious impacts of climate variability with high fluctuations in the vegetation [1]. The vegetation–climate interaction is very strong in semi-arid zone as the Sahel. Since 1950, the population in Africa had quadrupled and is projected to quadruple again until the end of the twenty-first century [2]. Enormous population growth and urbanization contribute as factors to alter the ecosystems specially forest [3]. The understanding of the mechanisms of the vegetation–climate interaction remains a challenge, and it is poorly studied in the context of African Sahel
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