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The extent of forest in dryland biomes

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Science  12 May 2017:
Vol. 356, Issue 6338, pp. 635-638
DOI: 10.1126/science.aam6527

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  • RE: The extent of forest in dryland biomes
    • Christine B. Schmitt, Center for Development Research (ZEF), University of Bonn, Germany
    • Other Contributors:
      • Thomas W. Crowther, Global Forest Biodiversity Initiative (GFBI), Morgantown, USA
      • Sebsebe Demissew, Department of Plant Biology & Biodiversity Management, College of Natural Sciences, Addis Ababa University, Ethiopia
      • Kennedy Matheka, East African Herbarium (EA), Botany Department, National Museums of Kenya, Kenya
      • Feyera Senbeta, Center for Environment and Sustainable Development, College of Development Studies, Addis Ababa University, Ethiopia

    In their report “The extent of forest in dryland biomes” (12 May 2017, p. 635), J.-F. Bastin and colleagues identified 1079 million hectares of forest in global dryland biomes based on very high spatial resolution (VHR) images. Forest was defined as “land spanning an area of more than 0.5 hectares with a tree cover over 10% that is not predominantly used for agriculture or urban land use (…)” [1]. Scope and spatial resolution of the data are impressive. However, further ecosystem information is required for them to fulfill their potential to inform global carbon stock estimates, biodiversity conservation and land restoration. In fact, the present report does not mention the stunning variety of wooded ecosystems in dryland biomes that meet the 10% tree cover threshold [2]. These include different types of forest and wooded grassland, also called savanna [3, 4]. For instance, tropical and subtropical dry forests and savannas may exist under similar climatic conditions but are adapted to different regimes of soil fertility, fire frequency and grazing intensity [3]. In contrast to forests, savannas are mixed tree-C4 grass systems with a significant grass layer and may store more carbon below ground than above [5, 6]. They are characterized by fire tolerant and shade intolerant plant species and often support mammalian megafauna [2, 5]. Hence, variations in carbon allocation mechanism, fire regime and species diversity need to be considered when drafting carbon budgets and mana...

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    Competing Interests: None declared.