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Changes in the floristic and structure of a dry deciduous forest during a period of 4-years (1994-1998), southeastern Brazil
Abstract
Changes in the floristic and structure of a dry deciduous forest during a period of 4-years (1994-1998), southeastern Brazil). Changes in the structure and composition of a fragment of dry deciduous forest in southeastern Brazil were described for 4-year period (1994-1998). This fragment was quite disturbed by human activities up to 1993, but it has been protected since 1994. A survey of woody plants (≥ 3.2 cm dbh) was conducted in 26 transects of 50x6m (0.78ha) in1994. Four years later (1998) ,all the transects were revaluated In 1994, a total of 114 tree species from 46 families were identified. Species richness was almost identical in 1998. The values of the Shannon index (3.72) and the equability (0.79) did not differ significantly during the studied period (t test, p > 0.1). The species richness were greater than Neotropical dry forests due probably to the building sucessional phase of this fragment. Although tree density had declined by about 10.2%, total basal area had a small change, increasing 1.5%. Those alterations were reflected in the size class distribution, which had significant differences between 1994 and 1998 (Chi-square test, p < 0.01). Although overall forest
composition showed little change, several species showed significant imbalance between recruitment and mortality rates. The decline of pioneer species (Chi-square test, p < 0.001) and the growth in total basal area of the canopy species caused the changes observed during the four years. The preservation of the studied fragment has been important for its recovery in the last years
Changes in the floristic and structure of a dry deciduous forest during a period of 4-years (1994-1998), southeastern Brazil. Available from: https://www.researchgate.net/publication/262719742_Changes_in_the_floristic_and_structure_of_a_dry_deciduous_forest_during_a_period_of_4-years_1994-1998_southeastern_Brazil [accessed May 23, 2017].
... In studies carried out in Brazilian SDTF, temporal changes in vegetation composition and structure are mainly related to the history of the evaluated area. Changes in quantitative parameters such as richness, H' , J, basal area and/or coverage, density and phytosociological indexes by species, and qualitative, such as species and family composition, were influenced by factors such as presence and anthropization level and the regeneration time (Cavalcanti et al., 2009;Fernandes et al., 2015;Werneck & Franceschinelli, 2004;Werneck et al., 2000). ...
The comparison of vegetation at two different moments allows for recognizing the stability of plant communities. The structure and floristic composition of a Caatinga fragment in the municipality of Poço Verde, state of Sergipe, were evaluated after four years (2011-2015). Sampling was performed through 30 plots of 20 m × 20 m, considering individuals with circumference at breast height ≥ 6 cm. Despite the increase in density (0.79%) and basal area (4.82%), changes in floristic composition, in Shannon-Wiener diversity (from 3.33 nats.ind-1 to 3.30 nats.ind-1) and in Pielou equability (from 0.78 to 0.80) were small. None of the structural parameters evaluated (richness, density, basal area, importance value and Shannon-Wiener diversity) significantly differed between evaluation periods. The vegetation remained stable over time, tolerating current anthropization levels and enabling the use of its natural resources through planned management.
O presente trabalho teve como finalidade determinar a composição florística e os índices de agregação das espécies da regeneração natural de uma floresta tropical úmida da região de Manaus, sob quatro níveis de exploração. Pelos resultados observou-se a influência dos tratamentos no número total de indivíduos e no número de indivíduos por classe de tamanho. A floresta estudada compreendeu 291 espécies, 169 gêneros e 56 famílias botânicas. A testemunha aprensetou o menor número de espécies. Os valores do grau de homogeinidade e Quociente de mistura de Jentsch também evidenciaram uma alta heterogeneidade, sendo a testemunha mais heterogênea. As famílias predominantes foram: Burserapeae, Annonaceae, Violaceae, Melastomataceae e Rubiaceae. As famílias mais ricas em espécies foram: Caesalpiniaceae, Sapotaceae, Lauraceae e Mimosaceae. O ìndice de Fracher & Brischle apresentou maior número de espeécies agrupadas nos 4 tratametnos, já o índice de Payandeh apresentou maior número de espécies não agrupadas.
Neotropical forest dynamics are reviewed by focusing on four questions: (1) What is a mature neotropical forest? (2) How long does it take to attain maturity? (3) How important are gaps to species regeneration? and (4) What are the important equilibrium processes in neotropical forest dynamics? The absence of regeneration of dominants has often been used as a distinguishing feature of late secondary forest; however, the abundance of shade-intolerant species in mature forest suggests that local absence of regeneration is an inadequate criterion for distinguishing between late secondary and mature forest. Recent studies estimate forest turnover rates of 75-150 years, indicating tropical forests are much more dynamic than thought previously. The dependence on gaps by almost half of the 320 tree species in a Costa Rican wet forest for successful regeneration illustrates the importance of gaps in tropical forest dynamics. Factors important in determining which species successfully colonize a gap are: time of gap occurrence; proximity and dispersal of seeds; size of gap; substrate conditions; and plant-herbivore interactions.
The smaller stature of canopy trees growing on or near ridge-crests of montane rain forests is a consequence of higher turnover rates, not slower growth rates. The annual canopy tree turnover area of c1.7% in the upslope section of the sample area was two times greater than in the downslope section. DBH growth increments in the upslope and downslope sections also were significantly different, but it was the upslope trees that grew at the faster rate (upslope 3.1 mm yr-1; downslope 2.4 mm yr-1). The mean DBH growth increment of 2.7 mm yr-1 for the entire plot is relatively high compared to other montane tropical rain forests. Interspecific variation among the 23 tree species also was notable, with mean DBH increments ranging from 0.4-7.8 mm yr-1. Ceratopetalum virchowii and Elaeocarpus ferruginiflorus were the most dominant species in 1982: C. virchowii increased its dominance over the 10-yr period with a higher rate of recruitment than mortality and a change in relative importance for 22.7% in 1982 to 28.4% in 1992; E. ferruginiflorus experienced the most significant change of all the species examined, with a decrease in relative importance from 14.1% in 1982 to 5.3% in 1992 as a result of its high mortality, its slow growth rates, and its failure to recruit any individuals into the ≥30 cm DBH size-class; the local demise of this species may be part of a shifting floristic mosaic associated with natural disturbance events or perhaps part of an irreversible trend. -from Authors
The upland rainforests of the Amazon Basin are being fragmented by deforestation brought on by planned and unplanned small-scale agricultural colonization, cattle ranching, tree plantations, and the expanding road networks that bring such activities to previously inaccessible regions. Evaluation of the impact of forest fragmentation and forest isolation by clear-cutting depends on detailed knowledge of the intact continuous forest community. The study described in this chapter was undertaken to determine tree mortality and recruitment for trees 10 cm DBH (diameter at breast height= 1.3 m) or more in undisturbed upland rain forest of the Central Amazon. The conditions of dead trees and the probable causes of death, the number of dead trees per treefall or other mortality-related event, the changes in mortality with tree size, stand turnover time, and the relation between family abundance and mortality and recruitment were also examined.
1. A review of the literature shows that in nearly all cases tropical rain forest fragmentation has led to a local loss of species. Isolated fragments suffer reductions in species richness with time after excision from continuous forest, and small fragments often have fewer species recorded for the same effort of observation than large fragments or areas of continuous forest. 2. Birds have been the most frequently studied taxonomic group with respect to the effects of tropical forest fragmentation. 3. The mechanisms of fragmentation-related extinction include the deleterious effects of human disturbance during and after deforestation, the reduction of population sizes, the reduction of immigration rates, forest edge effects, changes in community structure (second- and higher-order effects) and the immigration of exotic species. 4. The relative importance of these mechanisms remains obscure. 5. Animals that are large, sparsely or patchily distributed, or very specialized and intolerant of the vegetation surrounding fragments, are particularly prone to local extinction. 6. The large number of indigenous species that are very sparsely distributed and intolerant of conditions outside the forest make evergreen tropical rain forest particularly susceptible to species loss through fragmentation. 7. Much more research is needed to study what is probably the major threat to global biodiversity.