Browsing by Subject "African drylands"

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    African dryland ecosystem changes controlled by soil water
    (Wiley, 2019-08) Wei, Fangli; Wang, Shuai; Fu, Bojie; Wang, Lixin; Liu, Yi Y.; Li, Yan; Earth Sciences, School of Science
    Monitoring long‐term vegetation dynamics in African drylands is of great importance for both ecosystem degradation studies and carbon‐cycle modelling. Here, we exploited the complementary use of optical and passive microwave satellite data— normalized difference vegetation index (NDVI) and vegetation optical depth (VOD)—to provide new insights of ecosystem changes in African drylands. During 1993–2012, 54% of African drylands experienced a significant increase of VOD, mainly located in southern Africa and west and central Africa, with an average rate of increase of (1.2 ± 2.7) × 10−3 yr−1. However, a significant decreasing NDVI was observed over 43% of the African drylands, in particular in western Niger and eastern Africa, with an average browning rate of (−0.13 ± 1.5) × 10−3 yr−1. The contrasting vegetation trends (increasing VOD and decreasing NDVI) were largely caused by an increase in the relative proportion of the woody component of the vegetation, as a result of the prevailing woody encroachment in African drylands during the study period. Soil water emerges as the dominant driver of ecosystem changes in African drylands, in particular in arid and semiarid areas. This is evidenced by a strong spatio‐temporal correlation between soil water and vegetation, where soil water changes explain about 48% of vegetation variations. This study emphasizes the potential of utilizing multiple satellite products with different strengths in monitoring different characteristics of ecosystems to evaluate ecosystem changes and reveal the underlying mechanisms of the observed changes.
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    Responses and feedbacks of African dryland ecosystems to environmental changes
    (Elsevier, 2021-02) Wei, Fangli; Wang, Shuai; Brandt, Martin; Fu, Bojie; Meadows, Michael E.; Wang, Lixin; Wang, Lanhui; Tong, Xiaowei; Fensholt, Rasmus; Earth Sciences, School of Science
    Drylands occupy 43% of the African continent and play an important role in the global carbon cycle and in supporting local livelihoods. Understanding how dryland ecosystems respond to environmental changes, both structurally and functionally, is of great significance for sustainable dryland management. In this article, we review the current remote sensing-based knowledge on African dryland ecosystem dynamics and the main drivers of changes. Global CO2 enrichment, changes in rainfall regimes, and a decline in fire activity have collectively driven vegetation greening, woody plant increase and carbon dynamics in African drylands over recent decades, challenging the long-held desertification narrative. Here we also highlight the importance of rainfall–vegetation–fire feedbacks in enhancing dryland ecosystem resilience and predicting future ecosystem responses.