i i Forest Forest Biogeosciences and Forestry Biogeosciences and Forestry Climatic factors defining the height growth curve of forest species Elvis Felipe Elli (1) , Braulio Otomar Caron (1) , Alexandre Behling (2) , Elder Eloy (1) , Velci Queiróz De Souza (1) , Felipe Schwerz (1) , John Robert Stolzle (1) The aim of this study was to modify several existing biological models by in- cluding several predictive variables that take into account the effect of cli- matic factors on tree height growth. Tree height was measured from 2007 to 2014 on 18 trees for each of the following species: Eucalyptus urophylla × Eucalyptus grandis, Parapiptadenia rigida, Peltophorum dubium, Mimosa scabrella and Schizolobium parahybae. Different existing nonlinear models were fitted to the observed data, and the best fitting models were selected. The inclusion of climatic variables into the selected models (mainly minimum temperature and rainfall) improved their predictions of tree height growth with age, and provided more accurate estimates than those obtained by tradi- tional nonlinear models. Simulations were carried out to explore the variation of tree height growth under different minimum temperature and precipitation regimes. The effects of frost and rainfall variation on height growth curves and their consequences for forest management are discussed. Keywords: Von Bertalanffy-Richards’ Model, Mean Minimum Temperature, Rain- fall, Frost Introduction Tree height is an important variable used in tree volume estimation, as well as in making decisions on cultivation, planning and management of tree stands (Zhang & Liu 2001). The height of trees in plantations is related to the level of intra-specific inter- action, planting arrangement (Armstrong & McGhee 1980, Jose et al. 2004), soil char- acteristics and availability of nutrients (Newman 1973), as well as the prevailing weather in the area (Fitter 1987, Lohmus et al. 1989). Tree height is commonly used in model- ing the growth of trees (Zhang et al. 2004, Uzoh & Oliver 2006, Jiang & Li 2010, Dia- mantopoulou & Ozçelik 2012, Rasche et al. 2012, Perin et al. 2013, David et al. 2015). Regression models have been widely ap- plied in several research areas. While re- gression linear models are easy to use, nonlinear models may be the most appro- priate choice in many cases. A common example of the application of non-linear re- gression models in biology is their use in modeling tree growth curves by fitting nonlinear functions. Biological growth models usually present the organism size or weight as the depen- dent variable, and the organism age as pre- dictor, without taking into account climatic factors. In regions where trees are sub- jected to harsh winters with absolute mini- mum temperatures below zero and frost occurrence, tree species sensitive to cold may incur damages to apical buds. Damage caused by winter conditions can potentially limit the growth of the upper third of the trees. To date, these and other variations in the growth curve due to climatic factors are not explained by biological models in the literature. Evidence of the importance of using cli- matic factors in forest modeling to explain the responses of tree species have been documented in several reports (Subedi & Sharma 2013, Prior & Bowman 2014, Rais et al. 2014, Trouvé et al. 2015). According to several authors (Hunter & Gibson 1984, Woollons et al. 1997, Snowdon et al. 1998, 1999), the predictive power of empirical models used to describe growth data can be improved by the incorporation of in- dices which account for climatic factors. In this study we tested the hypothesis that climatic factors, along with plant age, can be profitably used to define height growth curves of forest tree species. To this purpose, we modified several existing biological models by adding predictive vari- ables that take into account the effect of climatic factors on tree height growth. Material and methods Data source The study was conducted in the city of Frederico Westphalen, Rio Grande do Sul, Brazil, located at 27° 22′ S, 53° 25′ W at the altitude of 480 m a.s.l. (Fig. 1). The follow- ing tree species were used: Eucalyptus uro- phylla S.T. Blake × Eucalyptus grandis Hill ex Maiden, Mimosa scabrella Benth., Parapip- tadenia rigida, Peltophorum dubium (Spr.) Taubert and Schizolobium parahybae (Vell.) Blake. The experiment was established in Sep- tember 2007, through the manual planting of seedlings after ploughing and harrowing the area. The experimental design was a randomized complete block design and the variables measured were the tree species, tree age and height, with three replicates for each treatment. The determination of tree height began in March 2008, at the beginning of the au- tumn season, by selecting 18 trees of each species for the analysis. Since then, quar- terly evaluations were carried out on the selected trees at the beginning of each sea- © SISEF http://www.sisef.it/iforest/ 547 iForest 10: 547-553 (1) Federal University of Santa Maria, Frederico Westphalen Campus, Graduate Program in Agronomy - Agriculture and Environment. Linha Sete de Setembro n/a, Highway 386 km 40, CEP 98400-000, Frederico Westphalen, Rio Grande do Sul State (Brazil); (2) Federal Univer- sity of Paraná, Graduate Program in Forest Engineering. Av. Pref. Lothário Meissner, 900, Jardim Botânico, Campus III, CEP 80210-160, Curitiba, Paraná (Brazil) @ Elvis Felipe Elli (elvisfelipeelli@yahoo.com) Received: Aug 03, 2016 - Accepted: Feb 19, 2017 Citation: Elli EF, Caron BO, Behling A, Eloy E, Queiróz De Souza V, Schwerz F, Stolzle JR (2017). Climatic factors defining the height growth curve of forest species. iForest 10: 547- 553. – doi: 10.3832/ifor2189-010 [online 2017-05-05] Communicated by: Giustino Tonon Research Article Research Article doi: doi: 10.3832/ifor2189-010 10.3832/ifor2189-010 vol. 10, pp. 547-553 vol. 10, pp. 547-553