Environmental modulation of the seasonal cambial activity in Prosopis flexuosa DC trees from the Monte woodlands of Argentina M.A. Giantomasi a, * , F. Roig-Juñent a , D. Patón-Domínguez b , G. Massaccesi c a Laboratorio de Dendrocronología e Historia Ambiental, IANIGLA, CCT-CONICET-Mendoza, Avda. Ruiz Leal s/n, Parque Gral. San Martín, CC 330, 5500 Mendoza, Argentina b Departamento de Biología vegetal, Ecología y Ciencias de la Tierra, Facultad de Ciencias, Universidad de Extremadura, Avda. Elvas s/n, 06071 Badajoz, Spain c Área de Parques Nacionales, Parque Nacional Tierra del Fuego, Ushuaia, Argentina article info Article history: Received 13 October 2009 Received in revised form 20 May 2011 Accepted 24 August 2011 Available online 10 September 2011 Keywords: Arid woodland Cambium Dendroclimatology Growth-ring development abstract The rhythm of cambial activity and its relationship with precipitation, temperature and phenology was analyzed in Prosopis flexuosa trees from the xerophytic woodlands of western Argentina. Periodic tree growth measurements made in a P. flexuosa-dominated stand between 2005 and 2008 showed that earlywood tree-ring development starts in the early spring (October), when young vegetative buds begin expansion and completes its formation at the end of November when fruits are almost ripe. The development of the tree-ring latewood is completed in early January (the middle of summer). Redun- dancy Analysis suggests that cumulative daily rainfall 4e6 days prior to core sampling significantly influences cambial growth, while temperatures 0e3 days preceding core sampling show the most significant effect on growth. An Artificial Neural Network analysis suggests a positive, monotonic effect of rainfall on cambial growth, whereas temperature shows a modal effect on growth with a peak at 18 e20  C. The results provide important new information about the eco-physiology of P. flexuosa trees in the Monte region of Argentina, and indicate that this species responds rapidly to changes in rainfall and temperatures during the growing season. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction The arid and semi-arid ecosystems of the world experience strong seasonal variations in environmental conditions that induce growth rhythms of the vascular cambial tissue that can be seen in the annual rings formed in most woody species (Fahn and Sarnat, 1963). These ecosystems are sensitive to environmental changes, where most biological processes may be limited to the periods of occasional pulses of precipitation (Eriksson, 1989; Noy Meir, 1973). As a result, dendrochronological studies of several dryland tree species show the strong influence of climatic conditions on the anatomical characteristics of tree-rings and tree-ring width (Campelo et al., 2010; García González and Eckstein, 2003; Nicolini et al., 2010). Knowledge of the characteristics of the tree growth and wood structure are relevant for the construction of detailed models of those environmental factors that influence annual ring widths and other wood anatomical features. Moreover, the knowledge of the timing and circumstances in which seasonal cambial growth begins and ends is essential to explain the mechanisms involved in tree- ring formation during the growing season (Fritts, 1976). The different factors that regulate cambial activity may, through phys- iological processes, be responsible for morphological and wood anatomical plant adaptability strategies that occur in arid envi- ronments (Böcher and Lyshede, 1968; Carlquist, 1988; Simpson, 1977). The seasonal rhythm of cambial growth in woody plants is determined by hormonal factors (Little and Savidge, 1987), and is strongly influenced by environmental conditions (Deslauriers et al., 2008; Gri car et al., 2007; Pallardy, 2008; Rossi et al., 2006). The division of the cambial cells is activated during favorable conditions and becomes dormant when these conditions are adverse for growth (Lang et al., 1987). More than 60% of Argentina consists of arid and semi-arid environments: the shrub and woodlands of the Monte phytogeo- graphic region cover some 46 million hectares (Morello, 1958; Rundel et al., 2007). These mid-latitude drylands are character- ized by long and severe dry seasons, elevated air temperatures and high evaporation rates that produce water deficits which influence plant physiology and growth (Noy Meir, 1973). In these conditions trees display a seasonal growth behavior mainly related to soil water availability (Karlin and Díaz, 1984). Prosopis flexuosa DC is considered the most representative tree species in the Monte region due to its wide distribution, ecological * Corresponding author. Tel.: þ54 261 5244231; fax: þ54 261 5244201. E-mail address: mgiantomasi@lab.cricyt.edu.ar (M.A. Giantomasi). Contents lists available at SciVerse ScienceDirect Journal of Arid Environments journal homepage: www.elsevier.com/locate/jaridenv 0140-1963/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jaridenv.2011.08.010 Journal of Arid Environments 76 (2012) 17e22