Contents lists available at ScienceDirect Dendrochronologia journal homepage: www.elsevier.com/locate/dendro Growth dynamics and disturbances along the last four centuries in the Prosopis caldenia woodlands of the Argentinean pampas Teresa Velasco Sastre a, ⁎ , Marta Vergarechea b , Alicia Tapia c , Esteban Dussart d , Jorge Leporati a , Stella Bogino a a Departamento de Ciencias Agropecuarias, Universidad Nacional de San Luis, Avenida 25 de Mayo 384, 5730, Villa Mercedes, San Luis, Argentina b Forest Research Center – National Institute of Agricultural and Food Research and Technology, INIA-CIFOR, Carretera A Coruña km 7.5, 28040, Madrid, Spain c Instituto de Arqueología, Universidad Nacional de Buenos Aires, 25 de mayo 217, CP 1002, Ciudad de Buenos Aires, Argentina d Facultad de Agronomía, Universidad Nacional de La Pampa, Ruta 35, km 334, CP 6300, Santa Rosa, La Pampa, Argentina ARTICLE INFO Keywords: Dendrochronology Fire Semiarid Woodland dynamics Disturbance ABSTRACT Semiarid woodlands of the Argentinean pampas are dominated by Prosopis caldenia Burkart (caldén)(Fabaceae). This area has experimented severe changes over the last centuries, and fire events, overexploitation and land use changes have shaped the landscape. A sound knowledge of these disturbances and their effects on woodland dynamics is essential to plan a management and wise use of caldén woodlands. The objective of this study is to analyse the relation between growth dynamics and disturbances of P. caldenia woodlands in the last four cen- turies in the Argentinean pampas. Fire frequency and growth releases were analysed using dendrochronological techniques in three sampling sites (n = 86). Mean radial growth varied between 1.88 and 2.49 mm year -1 , according to the site. One chronology covered the 1738–2011 period, the largest one for the Argentinean pampas. Fire frequency was higher during the aboriginal period (18th–19th centuries) and mid-twentieth cen- tury. Growth releases were consistent at all sampling sites and they all had a positive association with sheep introduction after the aboriginal settlement. These results demonstrated that the use of fire by aborigines challenged the widespread concept of an idyllic relation between them and forests. Growth releases were linked to sheep introduction, consistent with records of massive deforestation which took place at the end of the 19th century, resulting in a savannah forest physiognomy. The concept of caldén forests being open to semi-open should be reconsidered in the light of these new insights. 1. Introduction Prosopis species grow in arid and semiarid areas of Asia, Africa, and America with the centre of polymorphism in Argentina (Burkart, 1976). Throughout the world, Prosopis forests provide diverse and valuable ecosystem services including shade, food, fire, building materials, bee food, basin protection, carbon storage, and medical substances (Bovey, 2016). The semiarid part of the Argentinean pampas is covered by caldén (Prosopis caldenia Burkart) woodlands, around 2.5 million ha, and it is the only place in the world where this species grows (SAyDS, 2007). Social and political changes have affected these forests over the last four centuries, e.g. aborigines from Chile (known as ranqueles) occupied the area between the middle of the 18th up to the end of the 19th centuries, and they were exterminated by the army to favour massive European immigration at the end of the 19th century (Dussart et al., 2015). Usually, it is assumed that the caldenales had been affected severely by human activities, including the use of fire as a management tool only along the 20th century. Massive deforestation during the First and the Second World Wars, named “the big first and second cut down”, are considered the most relevant impact on this ecosystem (SAyDS, 2007). At present, these woodlands are one of the most deforested in Argentina (with a mean deforestation rate of 0.86% per year (MinAgri, 2013)) resulting from the introduction of new agricultural technologies, in- cluding genetically modified organisms that favour land use changes from cattle to crop production, mainly soybean (Gasparri and de Waroux, 2015). Historically, it is accepted that ancient or mature forests of P. cal- denia are open to semi-open, similar to the African savannah, the ty- pical landscape during the aboriginal occupation period (Monticelli, 1938; Anderson et al., 1970). However, the scarce existing historical chronicles described the caldenales as thick and inaccessible before https://doi.org/10.1016/j.dendro.2017.12.005 Received 15 June 2017; Received in revised form 15 December 2017; Accepted 28 December 2017 ⁎ Corresponding author. E-mail addresses: teresvs13@hotmail.com (T. Velasco Sastre), vergarechea.marta@gmail.com (M. Vergarechea), aliciahtapia@yahoo.com.ar (A. Tapia), estebangdussart@yahoo.fr (E. Dussart), jorgeleporati@yahoo.com.ar (J. Leporati), stellabogino@gmail.com (S. Bogino). Dendrochronologia 47 (2018) 58–66 Available online 03 January 2018 1125-7865/ © 2018 Elsevier GmbH. All rights reserved. T