Contents lists available at ScienceDirect Dendrochronologia journal homepage: www.elsevier.com/locate/dendro Anatomy and dendrochronological potential of Moringa peregrina from the hyper-arid desert in Egypt Emad Farahat a, ⁎ , Holger Gärtner b a Botany and Microbiology Department, Faculty of Science, Helwan University, P.O. 11790, Cairo, Egypt b Swiss Federal Research Institute for Forest, Snow and Landscape Research (WSL), Zürcherstrasse 111, CH-8903, Birmensdorf, Switzerland ARTICLE INFO Keywords: Moringa peregrina Drought Tree-rings Ray parenchyma Xylem vessels Dendrochronology ABSTRACT The annual growth and wood characteristics of tree species at southern Mediterranean countries, and its re- lationship with climate variables are recently two important topics for the researchers in this region. Although Moringa peregrina (Forssk.) Fiori is a key species in Africa due to its medicinal and economic values (e.g. as fuel, food and water purifier), little is known about its annual growth or its response to climate variables. In this study, we analyze its dendrochronological potential, macroscopic and microscopic wood structure, and corre- lation with climate. Wood discs were collected from two desert sites in Egypt: Saint Catherine (SC) and Hurghada (HG). Wood discs and micro-slides were prepared, and the distinctness and pattern of rings, vessels, and ray structure were examined microscopically. The ring boundaries of M. peregrina were distinct and marked by thick- walled and flattened fibers. For the HG site, the resulting ring-width chronology spans 16 years, from 2001 to 2016. A significant positive relationship was found between tree growth at HG and precipitation prior to the vegetation period (January-March). April temperature of the year prior to growth had a significant positive relationship with M. peregrina growth. In contrast, April and May-August temperatures of the current growing season had a significant negative relationship with tree growth. We could not develop a chronology for M. peregrina at SC site due to the presence of growth anomalies in the collected wood discs from the site. Consequently, we did not get a clear picture on the climate- annual growth relationship for M. peregrina trees at this site. At SC, M. peregrina trees respond to stressful environmental conditions by adjusting their anatomical structure to produce a high number of small vessels. Moreover, there was spatial variability in the architecture of ray parenchyma that reflected the degree of stress in both sites. The results of this study improve our under- standing of the growth-climate relationship in sub-tropical trees and the potential role of ray parenchyma in stressed environments. 1. Introduction The southern Mediterranean basin and tropics are one of the most sensitive regions in the world, showing the effects of climate change. The expected increase in mean annual temperature and decrease in mean annual precipitation will likely affect the region in a negative way (IPCC, 2007; Giorgi and Lionello, 2008). Risks of droughts and pre- cipitation deficits are projected to be higher at 2 °C compared to those at 1.5 °C of global warming in some regions of the world, including southern Mediterranean countries. The number of hot days is projected to increase in most land regions, with the greatest increases in the tropics (IPCC, 2018). According to these scenarios, the Middle East and Northern Africa have the highest risk of drought. These changes in climate will not only exacerbate the severity and recurrence of drought events, but also the occurrence of heavy rainfall events that will make climatic seasonality of this area more pronounced (Copenheaver et al., 2010; IPCC, 2018). This could have negative consequences for the survival and distribution of tree and shrub species (Matesanz and Valladares, 2014). Studies have already reported reductions in tree growth and an increasing number of mortality events as a result of drought stress in the northern Mediterranean basin (e.g. Lloret et al., 2004; Sarris et al., 2007; Doblas-Miranda et al., 2017; Gouveia et al., 2017; O’Brien et al., 2017; Gauquelin et al., 2018). In the southern Mediterranean basin, less attention has been paid to the desert trees and shrubs that represent key species in arid and semi- arid habitats. Information regarding the population growth dynamics, annual productivity, and age of such species are essential to any con- servation and sustainable management plan. In this region, only a few https://doi.org/10.1016/j.dendro.2019.125606 Received 20 April 2019; Received in revised form 19 June 2019; Accepted 21 June 2019 ⁎ Corresponding author. E-mail address: emad23_1999@yahoo.com (E. Farahat). Dendrochronologia 56 (2019) 125606 Available online 21 June 2019 1125-7865/ © 2019 Elsevier GmbH. All rights reserved. T