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Canopy Stratification in Tropical Seasonal Forests: How the Functional Traits of Community Change Among the Layers

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Canopy Stratification in Tropical Seasonal Forests: How the Functional Traits of Community Change Among the Layers 1551 Original Article CANOPY STRATIFICATION IN TROPICAL SEASONAL FORESTS: HOW THE FUNCTIONAL TRAITS OF COMMUNITY CHANGE AMONG THE LAYERS ESTRATIFICAÇÃO DE DOSSEL EM FLORESTAS ESTACIONAIS TROPICAIS: COMO OS TRAÇOS FUNCIONAIS DA COMUNIDADE MUDAM AO LONGO DOS ESTRATOS VERTICAIS Sérgio F. LOPES 1; Vagner S. VALE 2; Ivan SCHIAVINI 2, Jamir A. PRADO JÚNIOR 2, Ana Paula OLIVEIRA 2; Carolina S. ARANTES 2 1. Paraiba State University, Laboratory of Plant Ecology, Campina Grande, Paraiba, Brazil. [email protected]; 2. Uberlandia Federal University, Laboratory of Plant Ecology. Uberlandia, Minas Gerais, Brazil. ABSTRACT . The discussion of the existence and measurement of layers in forests refers to one of the earliest and most controversial concepts of forest ecology, the stratification. Since there is no consensus on the most appropriate methodology to describe the vertical structure of forest communities, we chose for this paper to develop a methodology that was adequate to represent the stratification observed on site. The objective was to determine the species and functional traits characteristic of each vertical layer in the semideciduous seasonal forests (SSF). The study was conducted in ten fragments (10 ha) located in southeastern Brazil. Stratification was performed according to species using the median and the 3 rd quartile (non-parametric statistical analysis) of tree heights were used for canopy stratification the (understory, midstory and canopy). This result shows the small range of the midstorey layer, highlighting the dichotomy between the canopy and understory. The variations found for the quartile and median values represent the history of successional stage of each fragment, allowing variations in the vertical occupation by species of certain layers. The analysis of SSF vertical structure allowed a visualization of the division of species and their respective functional traits performing different ecosystem functions in each layers. KEYWORDS: Ecosystem functions. Forest ecology. Functional groups. Semideciduous seasonal forests. Successional stage. INTRODUCTION mean height of the canopy for each species, Pagano and Leitão Filho (1987) established the existence of The discussion of the existence and two layers in tropical forests. The identification of measurement of layers in forests refers to one of the layers was also performed by preparing frequency oldest and most controversial concepts of forest histograms of height classes (MARTINS, 1993). ecology, called canopy stratification (WHITMORE, However, formulas that take into account the mean 1975; RICHARDS, 1996). This discussion occurs height and standard deviation for the identification firstly due to the variety of ways in which the of layers have also been used (PAULA et al. 2004), canopy structure can be conceived, measured, and as well as multivariate analysis techniques (DCA) described, and also due to the multitude of like the one used by Guilherme et al. (2004). parameters used to describe the canopy and the Nowadays, a new methodology based on profile various levels of integration that can be used as the diagrams and individual tree crown was proposed to basis for such descriptions. the identification of canopy stratification in tropical Studies of vertical structure began with the and temperate forests (BAKER; WILSON, 2000). elaboration of profile diagrams, aiming to clarify Thus, the vertical distribution is not always controversies about the canopy stratification in evident in tropical forests and recognition of the tropical rainforest (DAVIS; RICHARDS, 1933). layers in a woody community is, sometimes, The method developed by these authors was imperceptible and/or proceeds from subjective subsequently used by Richards (1939), Whitmore judgments (LATHAM et al. 1998). However, layers (1975), and others. However, this method has some have been sampled (ASHTON; HALL, 1992) and problems because it represents only part of the normally, for descriptive purposes in tropical studied community (VALE et al. 2009). Over time, forests, one should consider the existence of two or studies about canopy stratification have used three layers (RICHARDS, 1996; BAKER; different methodologies according to the different WILSON, 2000). questions and focuses of these studies. Based on the Received: 13/03/13 Biosci. J., Uberlandia, v. 30, n. 5, p. 1551-1562, Sept./Oct. 2014 Accepted: 05/05/14 1552 Canopy stratification in tropical… LOPES, S. F. et al. Few studies have used the same standard Thus, tested hypotheses are just applicable to the procedure for describing and analyzing forest tree community in the understory. More details on stratification. In part this is due to the different the sampling methodology description of the ten questions and focuses of these studies, but also due sites can be found in Lopes (2012a). the difficulty of standardizing the definition. The Seasonal semideciduous forest occurs in a term “stratification” has been used to characterize climate characterized by the seasonality, with forest in distinct ways, vertical stratification of annual rainfall lower than 1,600 mm and with phytomass, vertical stratification of individual regular drought in five to six months of each year, crowns, and vertical stratification of species when the monthly total rainfall is less than 10 mm (BAKER; WILSON, 2000). Furthermore, local (GENTRY, 1995). The seasonal climate intensity is characteristics and disturbance history which each related to local variations, such as characteristics of studied fragment presents, as well as the the relief, water retention and soil depth, which successional stage in which the forest is classified determine the trees’ level of deciduousness during (CHAZDON et al. 2010), are also factors that the dry season (OLIVEIRA-FILHO; RATTER, contribute for the difficulty of standardization of 2002). The dominant species lose their leaves during methodology. the dry period as an adaptation to water stress. The Studies about the vertical structure in average height of the tree layer ranged among 15 forests, which so far has been less investigated, and 35 m. The majority of the trees is upright, with should be as important as those related to the some individuals emerging (LOPES et al. 2012a; horizontal structure, and such studies would allow LOPES et al. 2012b). higher correlations between vegetation and The tropical savanna climate (megathermal functional traits (CHAZDON et al. 2010), especially Aw) prevails in the region, which is characterized, those related to successional, dispersion, and leaf according to the adaptation of Köeppen-Geiger deciduousness groups, which may be the result of classification (PEEL et al. 2007) as having dry ecological mechanisms (VALE et al. 2009). winters and rainy summers. The average This paper aims to identify patterns in the temperature and rainfall are 18ºC and 12.1 mm, structure of Semideciduous Seasonal Forests (SSF) respectively. During the rainy season (October to through a study of vertical stratification of tree February), the temperature ranges among 20.9ºC components in ten fragments. The aim of this study and 23.1ºC, and the average rainfall is 228 mm. Half was to determine the species and the functional of the annual rainfall (1500 to 1600 mm) are traits (successional groups, dispersal mechanism and concentrated in the months of December and leaf deciduousness) from each layer found in SSF, February. The dry season normally lasts to April attempting to answer the following questions: 1) Is and September, and presents a notable decrease in the vertical structure homogeneous among the rainfall (average of 35.5 mm per month) (PRADO fragments? 2) How the functional traits are JÚNIOR et al. 2010). distributed in each vertical layer? 3) Is there a pattern of distribution of functional traits in the Vertical structure layers among the studied SSF? 4) Is it possible, We assume the evident existence of a based on the canopy stratification and functional canopy (higher layer) and, consequently, an traits, to better sort the forest fragments according to understory (lower layer). The midstorey layer would their stage of conservation? be formed by a set of species that are part of a continuum among the shaded understory and the MATERIAL AND METHODS canopy layer (BAKER; WILSON, 2000). Since there is no consensus on the most appropriate Database and geographic and climatic factors methodology to describe the vertical structure of This study departed from previous forest communities, we try a characterization of the phytosociological tree community studies (DBH ≥ 5 strata able to differentiate clearly, at least, the forest cm) in ten sites of SSF in southeastern Brazil, canopy and the understory. In this way, this totaling a sample of 10 ha (Lopes et al., 2012a). The classification does not focus on the midstorey layer, height measurements were taken with the help of a due the difficult to evaluate it using a simple meter stick. Since this paper aimed to study the tree method. This analysis of the vertical structure has community, with DBH ≥ 5 cm standardized for segmented forest communities in two main layers Seasonal Semidecidual Forests (FELFILI et al. and the continuum of midstorey. We used only 2011), herbaceous and shrubby species that occured those species that had a minimum of 10 individuals, in the understory “ lato sensu ” were not samped. Biosci. J., Uberlandia, v. 30, n. 5, p. 1551-1562, Sept./Oct. 2014 1553 Canopy stratification in tropical… LOPES, S. F. et al. excluding from the analysis the
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