Tree Species Community Spatial Structure in a Terra Firme Amazon Forest, Brazil
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BOSQUE 35(3): 347-355, 2014 DOI: 10.4067/S0717-92002014000300009 Tree species community spatial structure in a terra firme Amazon forest, Brazil Estructura espacial de la comunidad de especies arbóreas en el “terra firme”, selva amazónica, Brasil Kátia Emidio da Silva a*, Sebastião Venâncio Martins b, Marie-Josée Fortin c, Milton Cezar Ribeiro d, Celso Paulo de Azevedoa, Carlos Antonio Álvares Soares Ribeiro b, Nerilson Terra Santos e *Corresponding author: a EMBRAPA, Brazilian Agricultural Research Corporation, Embrapa Western Amazonia, Manaus, 69010-970, Amazonas, Brazil, [email protected], [email protected] b Universidade Federal de Viçosa, Departamento de Engenharia Florestal, Viçosa, 36570-900, Minas Gerais, Brazil, [email protected], [email protected] c University of Toronto, Department of Ecology and Evolutionary Biology, 25 Harbord St., Toronto, Ontario, M5S 3G5, Canada, [email protected] d Universidade Estadual Paulista-UNESP, Departamento de Ecologia, Rio Claro, Avenida 24 A, 1515, Bela Vista, São Paulo, Brazil. [email protected] e Universidade Federal de Viçosa, Departamento de Estatística, Viçosa, 36570-000, Minas Gerais, Brazil, [email protected] SUMMARY All trees with diameter at breast height dbh ≥ 10.0 cm were stem-mapped in a “terra firme” tropical rainforest in the Brazilian Amazon, at the EMBRAPA Experimental Site, Manaus, Brazil. Specifically, the relationships of tree species with soil properties were determined by using canonical correspondence analyses based on nine soil variables and 68 tree species. From the canonical correspondence analyses, the species were grouped into two groups: one where species occur mainly in sandy sites, presenting low organic matter content; and another one where species occur mainly in dry and clayey sites. Hence, we used Ripley`s K function to analyze the distribution of species in 32 plots ranging from 2,500 m2 to 20,000 m2 to determine whether each group presents some spatial aggregation as a soil variations result. Significant spatial aggregation for the two groups was found only at over 10,000 m2 sampling units, particularly for those species found in clayey soils and drier environments, where the sampling units investigated seemed to meet the species requirements. Soil variables, mediated by topographic positions had influenced species spatial aggregation, mainly in an intermediate to large distances varied range (≥ 20 m). Based on our findings, we conclude that environmental heterogeneity and 10,000 m2 minimum sample unit sizes should be considered in forest dynamic studies in order to understand the spatial processes structuring the “terra firme” tropical rainforest in Brazilian Amazon. Key words: canonical correspondence analysis, Ripley`s K, spatial point pattern, Amazon forest, soil nutrients. RESUMEN Fueron mapeados los árboles con diámetro a la altura del pecho ≥ 10,0 cm en un bosque tropical lluvioso “terra firme” de la amazonía brasileña, en el Sitio Experimental de EMBRAPA, Manaus, Brasil. Las relaciones de 68 especies arbóreas con las propiedades del suelo fueron determinadas mediante análisis de correspondencia canónica sobre la base de nueve variables del suelo. En este análisis, las especies fueron agrupadas en dos grupos: uno, donde estas crecen principalmente en arena, con suelos de bajo contenido de materia orgánica, y otro, con especies que se desarrollan principalmente en suelos secos y arcillosos. La función K de Ripley fue utilizada para analizar la distribución de las especies en 32 parcelas de 2.500 hasta 20.000 m2, con el fin de determinar si cada grupo presenta cierto grado de agregación espacial como resultado de variaciones del suelo. Una agregación espacial significativa para los dos grupos solo se encontró en unidades de muestreo > 10.000 m2, en particular, para especies en suelos arcillosos y ambientes más secos, en los que las unidades de muestreo parecían cumplir con los requisitos de las especies. Variables del suelo, mediadas por la posición topográfica, influyeron la agregación espacial de especies, principalmente en la gama de distancias intermedia a grande (≥ 20 m). Según los resultados, se concluye que la heterogeneidad ambiental y tamaños de unidades de muestreo de por lo menos 10.000 m2 se deben considerar en los estudios de dinámica de bosques con el fin de entender los procesos espaciales que estructuran la selva tropical “terra firme” en la amazonía brasileña. Palabras clave: análisis de correspondencia canónica, K Ripley’s, patrón punto espacial, los bosques del Amazonas, nutrientes del suelo. INTRODUCTION of plants in nature. Quantifying and relating the underlying generative processes that create these structures provide Identification of spatial structure is a key step in unders- crucial information to help us interpret the factors which tanding the ecological processes structuring the distribution structure and maintain ecological diversity (Rossi 1994, 347 BOSQUE 35(3): 347-355, 2014 Tree species community in a terra firme Illian et al. 2008). The interactions between living com- emergent trees (IBGE 1999), but with a degree of local va- munities and their environment, and among the organisms riation in topographic and edaphic conditions (Silva 2010). themselves, occur at definite spatial and temporal scales, and give rise to spatial patterns that must be assessed in Field sampling. Since topography may influence soil fer- order to better understand the processes structuring the- tility, generating gradients (Hofer et al. 2008, Quesada et se communities (Bocard et al. 2004, Jombart et al. 2009, al. 2009) we used a randomly stratified sampling of fifteen Amaral et al. 2013), which can also contribute to the se- 2,500 m2 plots aiming at collecting soil samples, which lection of minimum-sized areas for management purposes. were evenly distributed in each topographic category (top, In tropical Amazon forests, large numbers of species slope and base). These 15 plots were used to relate soil coexist, with high species diversity and low density of in- variables to species composition through canonical corres- dividuals per species (Condit et al. 2000). Indeed, several pondence analyses (CCA). Next, 32 random plots located studies have recorded 200-300 tree species co-occurring at different topographic positions, distributed in five sam- in a single hectare; including only over 10 cm dbh trees pling unit sizes throughout the study area were used, in (Amaral 1996, Ferreira and Prance 1998, Matos and Ama- order to identify in which sampling unit size the spatial ral 1999, Lima-Filho et al. 2001, Oliveira and Amaral dependence between soil variables and species community 2005). Rainforest plant species have been found to be as- could be detected: (1) fifteen, each measuring 2,500 m2, sociated with particular edaphic, topographic or successio- likewise the ones used in CCA; (2) six presenting irregular nal conditions due to their strong effects on niche or mi- shapes, ranging from 4,270 to 5,870 m2; (3) nine of 10,000 crosite diversity in landscapes which are topographically m2 each (100 x 100 m); (4) one measuring 14,300 m2 ; and heterogeneous (Tuomisto and Ruokolainen 1994, Clark et (5) one with 20,000 m2 (100 x 200 m). al. 1998, Valencia et al. 2004, Tuomisto 2006, Jones et al. In 2005, in the five sampling unit sizes, all dbh ≥ 10 cm 2007, Hofer et al. 2008, Quesada et al. 2009). trees were mapped (x-y coordinates) and identified to spe- Forest structure and dynamics vary across the Amazon cies level. Since the study area covers two Universal Trans- basin in an east-western gradient following a pattern coin- verse Mercator (UTM) zones, all trees were georeferenced ciding with soil fertility, physical properties and geomor- to the Local Transverse Mercator (zone 21 and central me- phological variation, showing that edaphic properties play ridian 60 W), placing the data into a single zone. an important role in accounting for forest biomass, species composition and diversity (Hofer et al. 2008, Quesada et Canonical correspondence analyses (CCA). A canonical al. 2009). While generalist species occur in all types of correspondence analysis was performed for identifying soils, other species have strong relationships to soil varia- tree species/soil properties relationship (Jongman et al. bles. Then, finding out how species are organized in space 1995, Legendre and Legendre 1998), by using soil va- according to environmental heterogeneity (spatial depen- riables sampled down to 20 cm deep at fifteen 2,500 2m dence) may reveal patterns that can help understand the plots. Each sample was a composite of three, at least 10 m biological processes generating such structures (Legendre apart, subsamples. Chemical (macro/micronutrients) and and Legendre 1998, Illian et al. 2008, Law et al. 2009). physical (texture) analyses were carried out for each soil Spatial structure quantification, however, is directly sample according to (EMBRAPA 1997); afterwards, nine related to and bounded by the study area (extent) and the soil variables were used at CCA: soil pH, organic matter sampling unit size (grain) (Wiens 1989, Fortin and Dale (MO), phosphorus, iron, zinc and manganese concentra- 2005, Massant et al. 2009). The present study was con- tion, aluminum toxicity (%m), sum of bases-SB (calcium, ducted in a “terra firme” tropical rain Forest near Manaus, magnesium, potassium, sodium) and sand percentage (S). Amazonas State Brazil and aimed at investigating in what We worked with species recorded at a minimum fre- plot size the spatial relationship among soil variables in- quency of 60 % (i.e. present in at least nine of the 15 fluence species spatial distribution in tree communities. sampled plots), having more than five individuals and removing the most frequent species (present in almost METHODS everywhere), remaining 68 species to CCA analyses, in order to identify some “species preferences” along the gra- Study area. The study area is located in a Western Bra- dient of soil variables. Our intent was to include species zilian Amazon “terra firme” dense forest, at EMBRAPA that could show some degree of dispersal along the soil Experimental site (Manaus, Amazonas state, Brazil); coor- variables gradient (selectivity).