Tree rings and growth trajectories of tree species from seasonally dry tropical forest Ana Carolina Maioli Barbosa A , Gabriel Assis Pereira A , Daniela Granato-Souza A,B , Rubens Manoel Santos A and Marcos Aurélio Leite Fontes A A Federal University of Lavras (UFLA), Forest Sciences Department, C.P. 3037, 37200-000, Lavras, Brazil. B Corresponding author. Email: danigsbio@gmail.com Abstract. The presence of distinct growth rings in a large number of tropical tree species has allowed a range of studies involving the growth history during the life span of the tree. This work aimed to examine the presence of tree rings and study growth patterns of tree species from five seasonally dry tropical forest fragments. Wood cores were extracted using 5-mm increment borer. The macroscopic structure of growth rings from 24 deciduous tree species was observed under stereomicroscope and classified according to anatomical features and visibility of the ring boundary. Distinct growth rings were detected for 19 species (79%). Seven species were submitted to tree-ring analyses, including cross-dating and dating quality control using the COFECHA program. Dated ring-series were analysed by comparing increment rates and accumulated diameter at breast height fitted curves to detect growth patterns. The variations among growth curves indicated different strategies of establishment and development for each studied species, and allowed the identification of different ecological groups. The results show the potential of tree rings to study populations and communities of seasonally dry tropical forest. Additional keywords: dendroecology, radial growth, seasonal deciduous forest, tree growth. Received 27 October 2017, accepted 27 August 2018, published online 13 September 2018 Introduction The theory that tropical trees do not show periodic growth, recorded through distinguishable growth rings, has prevailed for almost a century (Jacoby 1989; Dünisch et al. 2002). However, dendrochronological studies have confirmed that this is not necessarily true for many tropical species in the world (Stahle et al. 1999; López and Villalba 2016; López et al. 2017). The studies conducted in this context have indicated the existence of two main mechanisms capable of inducing the seasonal formation of visible rings in tropical species: annual flood pulses in floodplains (Worbes 1989; Schöngart et al. 2002) and well defined seasonality of the precipitation (Stahle et al. 1999; Locosselli et al. 2016). In Brazil, a considerable number of species were listed as having seasonal growth in the Amazonian floodplains (Schöngart 2008; Rosa et al. 2016), semideciduous seasonal forest (Lisi et al. 2008; Pitsch et al. 2017) and areas of high water stress, such as Cerrado and Caatinga (Locosselli et al. 2016; Pagotto et al. 2017). The seasonally dry tropical forests (SDTF) in particular are promising areas for the development of growth-ring studies because in these forest formations the trees respond to a clear rainfall seasonality. The complete deciduous habit of these forests, with a clear seasonal segregation of leaf flush and leaf fall constitutes a strong indicator that cambial dormancy is induced during the annual dry phase and, therefore, the formation of growth bands in some species is annual (Worbes 1995; Stahle 1999). The SDTF areas occur as isolated patches, encircles the Amazon basin, extends from Argentina to Mexico (Pennington et al. 2009; Linares-Palomino et al. 2011). The Caatinga in north-eastern Brazil is the second richest group of SDTF, with 1112 species (Banda-R et al. 2016), but this forest formation is highly threatened by the advance of agriculture and livestock (Blackie et al. 2014) and only 1.2% of its area is protected (Ministério do Meio Ambiente 2017). In the north of Minas Gerais, SDTF occur in a transition zone of the Mata Atlântica, Cerrado and Caatinga domains, presenting great heterogeneity of the floristic units (Santos et al. 2012). Knowing the mechanisms involved in the dynamics of these formations has profound implications for the conservation of these increasingly threatened ecosystems. The study of tree rings can provide reliable estimates of age and annual growth rates, constituting an important tool for understanding the successional structure and dynamics of tropical forests (Baker et al. 2005; Brienen and Zuidema 2006a; Schöngart 2010). Growth rings of known periodicity can be used to study species replacement patterns at different stages of succession, as they contains retrospective information on growth history and approximate recruitment dates (Brienen et al. 2009). Although the presence of annual rings is less CSIRO PUBLISHING Australian Journal of Botany https://doi.org/10.1071/BT17212 Journal compilation Ó CSIRO 2018 www.publish.csiro.au/journals/ajb