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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. [ABSTRACT FROM AUTHOR]

Abstract Stalagmite data from Anjohibe Cave in northwest Madagascar suggest six distinct climate periods from 9.1 to 0.94 ka. Periods I and II (9.1–4.9 ka) were wetter and punctuated by a series of prominent droughts. Periods IV-VI (4–0.94 ka) were much drier and less variable. Period III (4.9-4 ka) marks the transition between wetter and drier conditions and consists of two significant droughts: the first (4.8–4.6 ka) coincides approximately with the end of the African Humid Period and the second (4.3–4.0 ka) may be the expression of the Northern Hemisphere 4.2 ka dry event in northwest Madagascar. Strong positive correlations between δ13C and δ18O values in Periods I-IV (r = 0.63–0.91) suggest that both isotopes were influenced by natural climate changes indicating that humans may not have been present in the area. In contrast, during Periods V (r = 0.07) and VI (r = −0.12) the "decoupling" of δ13C and δ18O might signal an impact from human activities starting around 2.5 ka. Rapid changes in climate during the early and middle Holocene, with prominent droughts lasting up to 800 years, did not kill off Madagascar's megafauna, and neither did a human population, present since the early Holocene if evidence from south Madagascar is reliable. However, many extinctions occurred under the more stable climatic conditions of the late Holocene, despite an antiphase climate relationship between northern and southcentral Madagascar. This suggests that initial human colonization, or significant increase in human population, triggered the megafaunal extinctions by hunting and destruction of megafaunal habitats. Highlights • Massive droughts at 4.7 and 4.2 ka were followed by a permanently drier and less variable climate in NW Madagascar after 4 ka • Drought and human deforestation after 1.6 ka, indicated by higher stalagmite δ13C, may have triggered megafaunal extinctions • Decoupling of δ13C and δ18O values at 2.5 ka is the first evidence of humans in the 9-1 ka Anjohibe Cave stalagmite record • Holocene climate changes in NW Madagascar were in phase with N and E Africa but antiphase with S Madagascar and SE Africa [ABSTRACT FROM AUTHOR]

Abstract: Southern African savannas are mixed plant communities where C3 trees co-exist with C4 grasses. Here foliar δ 15N and δ 13C were used as indicators of nitrogen uptake and of water use efficiency to investigate the effect of the rainfall regime on the use of nitrogen and water by herbaceous and woody plants in both dry and wet seasons. Foliar δ 15N increased as aridity rose for both C3 and C4 plants for both seasons, although the magnitude of the increase was different for C3 and C4 plants and for two seasons. Soil δ 15N also significantly increased with aridity. Foliar δ 13C increased with aridity for C3 plants in the wet season but not in the dry season, whereas in C4 plants the relationship was more complex and non-linear. The consistently higher foliar δ 15N for C3 plants suggests that C4 plants may be a superior competitor for nitrogen. The different foliar δ 13C relationships with rainfall may indicate that the C3 plants have an advantage when competing for water resources. The differences in water and nitrogen use likely collectively contribute to the tree–grass coexistence in savannas. Such differences facilitate interpretations of palaeo-vegetation composition variations and help predictions of vegetation composition changes under future climatic scenarios. [Copyright &y& Elsevier]

Stable isotopes of O and H in water are meaningful indicators of hydrological and ecological patterns and processes. The Global Network of Isotopes in Precipitation (GNIP) and the Global Network of Isotopes in Rivers (GNIR) are the two most important global databases of isotopes in precipitation and rivers. While the data of GNIP is almost globally distributed, GNIR has an incomplete spatial coverage, which hinders the utilization of river isotopes to study global hydrological cycle. To fill this knowledge gap, this study supplements GNIR and provides a river isotope database with global-coverage by the meta-analysis method, i.e., collecting 17015 additional data points from 215 published articles. Based on the newly compiled database, we find that (1) the relationship between δ18O and δ2H in river waters exhibits an asymmetric imbricate feature, and bifurcation can be observed in Africa and North America, indicating the effect of evaporation on isotopes; (2) multiple regression analysis with geographical factors indicates that spatial patterns of river isotopes are quite different across regions; (3) multiple regression with geographical and meteorological factors can well predict the river isotopes, which provides regional regression models with r2 of 0.50 to 0.89, and the best predictors in different regions are different. This work presents a global map of river isotopes and establishes a benchmark for further research on isotopes in rivers. [ABSTRACT FROM AUTHOR]

Achieving food security is challenging in Africa, a continent beset by low crop yield and soil quality, climate adversities, pests, weed infestations, and crop disease outbreaks. In this context, it is important to re-visit the resource-use efficiency and ecosystem service values of intercropping of grain legumes and cereals, a practice that has long been used by small-scale producers to mitigate the risk of crop failure and to safeguard household food availability. Despite its historical use, there are significant knowledge gaps regarding multiple aspects of intercropping, including examination of the different crop combinations on ecosystem services from agriculture. Using meta-analysis approach of land equivalent ratio (LER), a widely-accepted index to assess the efficiency of intercropping production systems, we found that intercropping of cereals with legumes resulted in an elevated LER (i.e., 1.31), regardless of species combination. A significantly greater LER than the overall LER (P <.05) was observed with the combination of maize-pigeon pea (LER = 1.57) and maize-groundnut (LER = 1.52). Increasing LER with intercropping was constant across rainfall variability, as well as in the absence of nitrogen fertilizer, which are the hallmark properties of intercropping in resource-deprived Africa. Intercropping could also reduce soil erosion, pest/weed incidence, and increase carbon sequestration by about ~46%, ~20–30%, and ~15%, respectively, compared to its sole crop control. In this comprehensive quantitative assessment of intercropping benefits across the African continent, we highlighted the provision of different ecosystem services from agroecosystems, a crucial foundation to achieving sustainable agricultural production. • Different intercropping combinations resulted in different LER. • Maize-pigeon pea and maize-groundnut produced the highest LER. • Increasing LER with intercropping was consistent across rainfall variability. • Nitrogen fertilizer did not increase LER compared to the non-fertilized crops. • Intercropping was also associated with alleviation of multiple ecosystem services. [ABSTRACT FROM AUTHOR]