Avaliação temporal da estrutura de um remanescente florestal ripário na planície de inundação do alto rio Paraná, Porto Rico, Paraná, Brasil.

Abstract

A phytosociological survey was accomplished encompassing an area of 1 ha (100 x 100 m), delimitated by the river bank, in the remnant riparian forest Mata do Araldo, located in the left bank from the Paraná River, in the Upper Paraná River floodplain (53º19'3'' W and 22º47'37'' S) inserted in the phytoecological region of Semi-deciduous Seasonal Forest. The procedures followed those adopted by Souza (1998) performed from 1993 to 1995. The area was divided in 50 contiguous plots (20 m parallels x 10 m perpendiculars to the river axis) for sampling the stratum 1, with perimeter at breast height (PBH) 15 cm. Within the 25 marginal plots, subplots (10 m x 5 m) were established for sampling the stratum 2 (PBH) < 15 cm and height >= 1 m) and, within those, other subplots (2 m x 1 m), for sampling the stratum 3 (height < 1 m). Preferably reproductive branch samples were collected, prepared and incorporated in the Special Collection Vegetação Ripária-Nupélia of the State University of Maringá (HUEM), from which we carried out the taxonomical identification. The following phytosociological parameters were measured: frequency, density and dominance, importance values (VI or RI), besides the Shannon diversity index (H'). The species distribution between wet and dry areas was analyzed for stratum 1. The species were classified considering the life forms and successional categories. The results were compared to a previous study, about 13 years ago, allowing the evaluation of vegetation structure in this time interval. Sørensen Similarity Index (ISs) was calculated between the surveys, current and previous, for each stratum. For stratum 1, the ISs was 75% and Lonchocarpus cultratus and Tabernaemontana catharinensis maintained their dominance, in VI, previously verified. Species from wet areas, as Cecropia pachystachya and Inga vera presented a decrease in the analyzed parameters; and Celtis iguanaea and Croton urucurana were not sampled again. The distinction between species from dry areas and those from areas subjected to floods was corroborated by DCA results. Evidences of succession were registered through the increase in density of species from more advanced successional stages (with emphasis on Trichilia pallida and Maclura tinctoria), and through the decrease of early stages (Cecropia pachystachya, Triplaris americana and Acrocomia aculeata). The reductions found in density of species from wet areas may compound an answer to the flood mitigation, which is occurring in the Upper Paraná River floodplain. For the stratum 2, the ISs was 64.46% and Petiveria alliacea, Psychotria carthagenensis and Piper tuberculatum maintained their dominance regarding the VI with change of placing for the first two. Arbustive and arborous presented equivalent dominance, considering the VI, of 49.13 and 48.61%, respectively. The structural analysis showed an increase in VI for arborous and a decrease for arbustive. Secondary and climacic species dominated, together, 76% of VI. The increase in VI for secondary species was 22% which is also evidence of succession. Reductions in density of species from wet areas (e.g. Psychotria carthagenensis and Piper tuberculatum), as well as the increase of species from dry areas (e.g. Petiveria alliacea) also suggest answers to the flood mitigation of Paraná River, in the Upper Paraná River floodplain. For stratum 3, the ISs was 39.28%. For dominant species, we observed changes in composition, ordination and RI values; however, Petiveria alliacea remained in the first place, regarding the RI. Arbustive and arborous composed 70% of importance value (RI), presenting elevations in relation to the previous study. The representativeness of climacic species among the dominants, as well as the decrease in RI for pioneer-arborous species, Tabernamontana catharinensis and Lonchocarpus cultratus, point out a successional advance in this remnant, which was enhanced by the occurrence of Gallesia integrifolia, Eugenia moraviana and Piper tuberculatum, arborous species of more advanced successional stages.