scholarly journals Improved detection of abrupt change in vegetation reveals dominant fractional woody cover decline in Eastern Africa

2022 ◽  
Vol 271 ◽  
pp. 112897
Author(s):  
Temesgen Alemayehu Abera ◽  
Janne Heiskanen ◽  
Eduardo Eiji Maeda ◽  
Binyam Tesfaw Hailu ◽  
Petri K.E. Pellikka
Keyword(s):  
Abrupt Change ◽  
Eastern Africa ◽  
Woody Cover

Mid-holocene climate change in Lake Bosumtwi, Ghana

2003 ◽  
Vol 60 (2) ◽  
pp. 133-141 ◽  
Author(s):  
James Russell ◽  
Michael R. Talbot ◽  
Brian J. Haskell
Keyword(s):  
Late Holocene ◽  
Climate Changes ◽  
Abrupt Change ◽  
Congo Basin ◽  
Eastern Africa ◽  
Tropical Atlantic ◽  
Holocene Climate ◽  
Feedback Mechanisms ◽  
Equatorial Africa ◽  
Nitrogen Isotopic Composition

AbstractLake Bosumtwi is one of the most widely studied palaeoclimate archives in West Africa. Results from numerous AMS 14C dates of samples from four piston cores from Lake Bosumtwi show that an abrupt sedimentary transition from a mid-Holocene sapropel to calcareous laminated muds occurred at about 3200 cal yr B.P. High-resolution analyses of the nitrogen isotopic composition of organic matter across this transition confirm its abrupt nature, and suggest that the change may signal a step toward increased aridity and intensified surface winds that affected western equatorial Africa from Ghana to the Congo basin. Northern and Eastern Africa experienced a similar abrupt shift toward aridity during the late Holocene, but at about 5000 cal yr B.P., a difference in timing that illustrates the regional nature of climate changes during the Holocene and the importance of feedback mechanisms in regulating Holocene climate variability. Furthermore, an abrupt change at about 3000 cal yr B.P. occurs at several sites adjacent to the tropical and subtropical Atlantic, which may hint at major changes in the surface temperatures of the tropical Atlantic and/or Pacific at this time.

scholarly journals Woody Cover Fractions in African Savannas From Landsat and High-Resolution Imagery

2020 ◽  
Vol 12 (5) ◽  
pp. 813 ◽  
Author(s):  
Ryan L. Nagelkirk ◽  
Kyla M. Dahlin
Keyword(s):  
Landscape Heterogeneity ◽  
Reference Points ◽  
Eastern Africa ◽  
Landsat 8 ◽  
Wet Season ◽  
Savanna Vegetation ◽  
High Resolution Imagery ◽  
Woody Cover ◽  
Using Data ◽  
The Individual

The challenge of mapping savanna vegetation has limited our understanding of the factors that shape these ecosystems at large scales. We tested seven methods for mapping savanna woody cover (trees and shrubs; WC) across 12 protected areas (PAs) in eastern Africa using Landsat 8 imagery. Because we wanted a method viable for mapping across the often-limited Landsat historical archive, we limited ourselves to three images: one each from the wet, dry, and transition (halfway between wet and dry) seasons. Models were trained and tested using 1,330 WC reference points and the variance explained by cross validation (VEcv) accuracy metric. Of the methods we tested, RF significantly (p < 0.001) outperformed the others with the best models in nine PAs scoring over 75% (range of 34.5%–91.1%). RF models trained using data from all the PAs and tested in the individual PAs significantly (p < 0.001) outperformed their single-PA-derived counterparts (67.7 ± 23.3% versus 30.5 ± 27.4%). We also found that while the transition image appears to be critical to mapping WC and the wet season image should be avoided, no single season or seasonal combination significantly outperformed all the others, allowing some flexibility in image selection. Our findings show that with proper sampling of landscape heterogeneity, even with limited imagery, accurate maps of savanna WC are possible and could catalyze discoveries in this crucial biome.

Elastic Stress Singularities: Implications for the Attachment of Tendon to Bone

2011 ◽  
Author(s):  
Yanxin Liu ◽  
Victor Birman ◽  
Chanqing Chen ◽  
Stavros Thomopoulos ◽  
Guy M. Genin
Keyword(s):  
Stress Distribution ◽  
Abrupt Change ◽  
Elastic Stress ◽  
Insertion Site ◽  
Stress Singularities ◽  
Local Stresses ◽  
Material Mismatch ◽  
Moduli Of Elasticity

The material mismatch at the attachment of tendon to bone is amongst the most severe for any tensile connection in nature. This is related to the large difference between the stiffness of tendon and bone, whose moduli of elasticity vary by two orders of magnitude. Predictably, such an abrupt change in the stiffness realized over a very narrow insertion site results in high local stresses. One of the implications of the stress distribution is a potential for stress singularities at the junction of the insertion to the bone.

On the taxonomy of Afrotropical Coleophoridae (III). New or little known species from Central and Oriental Africa (Lepidoptera, Coleophoridae)

Zootaxa ◽  
2020 ◽  
Vol 4763 (2) ◽  
pp. 151-174
Author(s):  
GIORGIO BALDIZZONE ◽  
HUGO W. VAN DER WOLF
Keyword(s):  
New Species ◽  
Male Genitalia ◽  
Eastern Africa ◽  
First Time

This work presents a review of the Coleophoridae of Central and Eastern Africa. A lectotype is designated for Coleophora psychropa Meyrick, 1920, and the male genitalia of C. crossanthes Meyrick, 1938, are illustrated for the first time. Coleophora sabaea Baldizzone, 2007, previously known only from Yemen, is added to the African fauna. Nine new species of Coleophora Hübner, 1822 are described: C. schouteni sp. nov., C. giustii, sp. nov., C. centrafricana sp. nov., C. riftella sp. nov., C. camerunensis sp. nov., C. ensifera sp. nov., C. gilgilensis sp. nov., C. nyanzaensis sp. nov., C. silvestris sp. nov. 

scholarly journals The climatic imprint of bimodal distributions in vegetation cover for western Africa

2016 ◽  
Vol 13 (11) ◽  
pp. 3343-3357 ◽  
Author(s):  
Zun Yin ◽  
Stefan C. Dekker ◽  
Bart J. J. M. van den Hurk ◽  
Henk A. Dijkstra
Keyword(s):  
Land Cover ◽  
Congo Basin ◽  
Shortwave Radiation ◽  
Mean Annual Precipitation ◽  
Above Ground Biomass ◽  
Precipitation Regime ◽  
Ground Biomass ◽  
Western Africa ◽  
Precipitation Regimes ◽  
Woody Cover

Abstract. Observed bimodal distributions of woody cover in western Africa provide evidence that alternative ecosystem states may exist under the same precipitation regimes. In this study, we show that bimodality can also be observed in mean annual shortwave radiation and above-ground biomass, which might closely relate to woody cover due to vegetation–climate interactions. Thus we expect that use of radiation and above-ground biomass enables us to distinguish the two modes of woody cover. However, through conditional histogram analysis, we find that the bimodality of woody cover still can exist under conditions of low mean annual shortwave radiation and low above-ground biomass. It suggests that this specific condition might play a key role in critical transitions between the two modes, while under other conditions no bimodality was found. Based on a land cover map in which anthropogenic land use was removed, six climatic indicators that represent water, energy, climate seasonality and water–radiation coupling are analysed to investigate the coexistence of these indicators with specific land cover types. From this analysis we find that the mean annual precipitation is not sufficient to predict potential land cover change. Indicators of climate seasonality are strongly related to the observed land cover type. However, these indicators cannot predict a stable forest state under the observed climatic conditions, in contrast to observed forest states. A new indicator (the normalized difference of precipitation) successfully expresses the stability of the precipitation regime and can improve the prediction accuracy of forest states. Next we evaluate land cover predictions based on different combinations of climatic indicators. Regions with high potential of land cover transitions are revealed. The results suggest that the tropical forest in the Congo basin may be unstable and shows the possibility of decreasing significantly. An increase in the area covered by savanna and grass is possible, which coincides with the observed regreening of the Sahara.

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