Floristic patterns along a 43‐km long transect in an Amazonian rain forest

Abstract

Summary 1The floristic variation in Amazonian lowland forests is poorly understood, especially in the large areas of non-inundated (tierra firme) rain forest. Species composition may be either unpredictable as abundances fluctuate in a random walk, more-or-less uniform, or it may correspond to environmental heterogeneity. 2 We tested the three hypotheses by studying the floristic variation of two phylogenetically distant plant groups along a continuous 43-km long line transect that crossed tierra firme rain forest in northern Peru. 3 The observed floristic patterns were compared to patterns in the spectral reflectance characteristics of the forest as recorded in a Landsat TM satellite image. The topography of the transect was measured in the field, and surface soil samples were collected to document edaphic conditions. The two plant groups, pteridophytes and the Melastomataceae, were assessed in 2-m wide and 500-m long sampling units. 4 Floristic similarity (Jaccard index) between sampling units ranged from 0.01 to 0.71 (mean = 0.27), showing that some units were almost completely dissimilar while others were very alike. 5 Spatially constrained clustering produced very similar subdivisions of the transect when based separately on satellite image data, pteriophytes, and Melastomataceae, and the subdivisions were also related to topography and soil characteristics. Mantel tests showed that floristic similarity patterns of the two plant groups were highly correlated with each other and with similarities in reflectance patterns of the satellite image, and somewhat less correlated with geographical distance. 6 Our results lend no support to the uniformity hypothesis, but they partially support the random walk model, and are consistent with the hypothesis that species segregate edaphically at the landscape scale within the uniform-looking forest.

The Need for Large-Scale, Integrated Studies of Biodiversity - the Experience of the Program for Biodiversity Research in Brazilian Amazonia

“…Even with biased positioning, it would not be possible to locate a 10 ha or larger plot on homogeneous soil. Even within vegetation "types", such as terra firme forest, there is much small-scale (1-10 km) beta diversity in tropical forest vegetation (Clark et al 1999;Phillips et al 2003;Tuomisto and Ruokolainen 1994;Tuomisto et al 2003;Costa et al 2005). Therefore, large grid systems are essential to capture variation in environmental conditions that tend to manifest only at the landscape scale.…”

Distribution patterns of ferns and lycophytes in the Coastal Region of the state of Rio Grande do Sul, Brazil

“…At a local scale, climatic factors, such as temperature and humidity (Kessler 2001;Kessler et al 2011), variation in the chemical composition of the edaphic matrix (Tuomisto & Ruokolainen 1993;Tuomisto & Poulsen 1996;Tuomisto et al 2003a;Tuomisto et al 2003b;Tuomisto et al 2014), variation in pH (Ranal 1995a), environmental heterogeneity (Sylvestre & Windisch 2003;Dittrich et al 2005;Nettesheim et al 2014), and fragmentation and edge eff ect (Paciencia & Prado 2005) have been implicated in determining fern and lycophyte distribution.…”

Comunidades florestais como indicadores geobotânicos: o caso da mineralização aurífera do Grupo Serra do Itaberaba, Guarulhos, São Paulo

“…Aqueles autores consideram estar a similaridade florística nestas florestas relacionada com o logaritmo da distância geográfica, implicando em mudanças graduais e ausência de contatos bruscos e mosaicos de vegetação, a qual manteria independência das tênues variações ambientais presentes naquele bioma. Isto, entretanto, não encontra respaldo em trabalhos baseados em extensivos dados de campo, como em Poulsen & Balslev, (1991); Tuomisto et al (1995); Riaza et al (1998); Svenning (1999); Wright (2002); Schulze (2003) e Tuomisto et al (2003), autores que demonstram que diferenças nos solos ao longo das florestas de terra firme, no oeste da Amazônia, são suficientemente importantes para gerar numerosos mosaicos floristicamente diferentes, com estruturas bem definidas e contrastes bruscos. Tuomisto et al (2003), em transecto com 43 km de comprimento em Floresta de Terra-Firme no oeste da Amazônia, encontraram grande diversidade florística, com índices de Jaccard entre 0,01 e 0,71, com valor médio de 0,27.…”