No abstract

FAO guidelines on water requirements for plant growth in the absence of irrigation, stipulate that cultivation is not viable in areas with less than 450mm of annual rainfall. Indeed, in all maps of agricultural land use, most hyper-arid, arid, and semi-arid drylands are considered unproductive. Yet, modern societies in arid and semi-arid drylands still practice rainfed cultivation under regimes of much lower annual rainfall. This paper presents the results of ethnographic and cross-cultural investigations in the cultivation of Pearl millet, Finger millet and Sorghum, with a global perspective. We use published ethnographic material and novel data collected on the field to build and test models that display the interaction of ecological and geographic variables in explaining agricultural practices. The aim of this research is to show how rainfed agriculture is practised much more often, and in much more suitable areas, than normally reported. This holds the potential for the understanding of how these practices can play a pivotal role for long-term resilience and future sustainability of agricultural systems in drylands.

Taxonomical results: anatomical descriptions and ecological features. Taxonomic classifications were proposed by following Höhn and Neumann (2018) methodology for charcoal identification in species-rich environments. Descriptions of the wood anatomy are accompanied by a list of the main diagnostic characters of each charcoal type, a discussion of each identification and photos of the transverse (TS), tangential longitudinal (TLS) and radial longitudinal (RLS) sections, as well as brief summaries of the ecological distributions and economic features of the taxa in each case.The description of charcoal types follows the standard terminology of the International Association of Wood Anatomists (IAWA) (Wheeler et al. 1989;Ritcher et al. 2004) with minor adaptations for characters not listed by IAWA (e.g. intervessel pits coalescent). Note that not all IAWA characters could be evaluated as some are usually difficult to identify in archaeological charcoal (e.g. length of parenchyma strands). The only quantitative feature included is mean diameter of vessel lumina, which was calculated by measuring a minimum of 10 vessels in 5 different charcoal fragments when possible. Microscopic photographs were taken using the Olympus Stream Basic commercial software and a Olympus BX51 reflected light microscope -available at the laboratory of Environmental Archaeological of Universitat Pompeu Fabra (UPF) -with incident light and magnifications 50x, 100x, 400x and 1000x, which are indicated in each photograph by the scales -200 µm, 100 µm, 50 µm and 20 µm respectively . The allocation to northern Ethiopian taxa is done in relation to available wood and charcoal reference materials from Ethiopia at the Muséum National d'Histoire Naturelle (MNHN) deposits, but also using pre-existing literature and collections from other areas of the world since the available reference samples of Ethiopian taxa are still very limited. As a general rule, the naming of the different taxa follows Friis et al. (2010), who does not mention authorship. However, authorship is included for reference collection samples when available, as well as when quoting botanical synonyms. Botanical synonyms accepted by the International Plant Names Index database (IPNI 2020) are considered to refer to the same taxa when comparing their wood anatomies (e.g. Dodonaea angustifolia, and D. viscosa, see below). Vernacular names in Tigrinya (November et al. 2002, Bekele-Tessema 2007 are transcribed without phonetic characters following the example of Bekele-Tesemma (2007; but see November et al. 2002: 2). The ecological distributions of the species related to each charcoal type are assigned according to Friis et al. (2010) classification into the following vegetational units: i) Desert and semi-desert scrubland (DSS); ii) Acacia-Commiphora woodland and bushland proper (ACB); iii) Acacia wooded grassland of the Rift Valley (ACB/RV); iv) Combretum-Terminalia woodland and wooded grassland (CTW); v) Afromontane woodlands, wooded grasslands and grasslands (DAF/WG); vi) Undifferentia...