Linking floristic patterns to edaphic gradients and remote sensing in Peruvian Amazonia
2005
Thesis
83
University of Missouri-St. Louis
St. Louis, USA
large spatial scales;trees;ferns;Melastomataceae;vegetation;ecology;distribution;Los Amigos;remote sensing
At present, an understanding of the floristic patterns and diversity of western Amazonian terra firme forests is still elusive. The most recent views present two perspectives: (1) habitat homogeneity (especially due to edaphic variation) is thought to be of primary importance in structuring the plant communities in the region, and (2) habitat homogeneity, where a group of generalist dominant species occur widespread in extended areas with weak or no signal of habitat specialization. The use of different methods to address these questions may be the reason for the contrasting results. Here, I present a comparative study of three plant groups that represent trees (standing trees more than 2.5 cm diameter), shrubs (Melastomataceae), and herbs (ferns) sampled in 12 0.1 ha plots in two regions of Peruvian Amazonia: Yurimaguas (northern Peruvian Amazonia) and Los Amigos (southern Peruvian Amazonia). I investigated the strength of the correlations between floristic, edaphic, pixel values from ASTER satellite images for the area, and between-plot geographical distances. Comparative studies of the Peruvian flora are scarce and this research provides and overview of the differences and similarities between floras in both regions, discusses several issues concerning their differences, and highlights the need to take into account regional differences in heterogeneity and diversity when taking conservation decisions and planning the land use in the area. Northern Peruvian Amazonia exhibited higher diversity (as measured by Fisher’s alpha index in the tree dataset) and abundance in the three groups of plants compared to southern Peruvian Amazonia. Different set of species dominated both regions. In southern plots the palm Iriartea deltoidea was the dominant tree and accounted also for the dominance of the Arecaceae family. In Yurimaguas most of the dominants were treelets, especially from families with explosive-dispersal mechanism like Violaceae, and Euphorbiaceae. Soil profiles in both regions were remarkable different. Whereas field observations and laboratory analysis identified more than three textural classes in northern plots, only one category was obtained in Los Amigos. Here, this predominant soil class (sandy loam) had up to 74% sand content. Northern plots were generally high in nutrient content and Cation Exchange Capacity (CEC). In Yurimaguas the floristic similarity between plots ranged from 6-26% (ferns), 0-50% (melastomes), and 9-34% (trees). In Los Amigos, the floristic similarity between plots ranged from 23-74% (ferns), 11-63% (melastomes), and 19-43% (trees). As deduced from the resemblance the
resemblance matrices, beta diversity (the change in species composition from one place to another) is higher in northern sites compared to southern sites. Plant groups showed differences in their correlations with the edaphic matrix that may be the result of their peculiar natural history (Melastomataceae), environmental determinism (ferns), or reflect a sampling bias (trees). Significant correlations between floristic and edaphic matrices were obtained for two groups of plants at northern sites: ferns and Melastomataceae. The floristic matrices of ferns vs. trees, and Melastomataceae vs. ferns showed significant correlation values. Trees were not correlated with any environmental or geographic matrix in both regions. Only Melastomataceae vs. trees was significantly correlated in southern Peru. Pixel values did not showed a significant correlation in both regions. Possible origins of the observed differences are discussed.