A comparative study of resource allocation in Pteridium in different Brazilian ecosystems and its relationship with European studies (original) (raw)
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Acta botânica …, 2009
This paper describes the variation of the above-ground biomass, necromass, and net above-ground primary production (NAGPP) of two weed species, Panicum maximum Jacquin (Poaceae) and Pteridium arachnoideum (Kaulf.) Maxon. (Dennstaedtiaceae), at two sites in the Poço das Antas Biological Reserve, southeast Brazil. Both species form mono-dominant stands in the matrix surrounding forest fragments. The organic matter was sampled monthly from each site, separated into biomass and necromass, and net above-ground primary production (NAGPP) was calculated. There was marked intra-seasonal fluctuation for both species; Pa. maximum generally had the largest values for necromass, total mass and NAGPP (NAGPP, Pa. maximum = 3953 g.m-2.y-1, Pt. arachnoideum = 2667 g.m-2.y-1). NAGPP did not vary between the two growth periods for Pa. maximum, but marked differences were found for Pt. arachnoideum (2% compared to 44% variation around the mean). The second growth year was drier and Pa. maximum produced much greater necromass in that year; Pt. arachnoideum showed little variation in biomass but much greater productivity in the drier second season. Pteridium arachnoideum appears to be more sensitive to climate, and especially rainfall.
Fuel and Energy Abstracts, 2011
Biological invasion is one of the major components of global change. In the Brazilian Cerrado, the fern Pteridium arachnoideum (neotropical bracken) is a potentially invasive species which is expected to change the vegetation structure of savannas. We assessed effects of the dominance of P. arachnoideum on the diversity of woody Cerrado species. We compared three sites dominated by neotropical bracken with three sites without neotropical bracken. We used multivariate analyses of variance and rarefaction curves with confidence limits to test whether the groups of species found in invaded areas were different from those found in non-invaded ones. We also analyzed the density of individuals and species and the mean area at breast height per plot. We found significant floristic differences between the areas. The diversity and the densities in the invaded areas were lower than in non-invaded ones. However, we did not observe differences in the mean area at breast height of woody plants. Thus, the P. arachnoideum invasion is a potential threat to Cerrado biodiversity. Management efforts should be made to control the bracken, since its dominance in the plant community may lead to impoverishment and simplification of the savanna vegetation.
PeerJ
The role of invasive species in ecosystem functioning represents one of the main challenges in ecology. Pteridium aquilinum is a successful cosmopolitan invasive species with negative effects on the ecological mechanisms that allow secondary succession. In this study, we evaluated the influence of P. aquilinumon secondary succession under different disturbances in a seasonal dry forest of the Yucatán Peninsula. We determined species richness, composition and the relative importance value in four sampling units. Fabaceae followed by Asteraceae, Meliaceae, Rubiaceae, Sapindaceae and Verbenaceae were the most species rich families. A dissimilarity analysis determined significant differences in beta diversity between sampling units. With a generalized linear model we found that species richness was best explained by site conditions, followed by calcium and soil organic matter. Also, the generalized linear model showed that abundance resulted in a strong correlation with site conditions ...
The aim of this study was to test the hypothesis that the monodominant nonpioneer Peltogyne gracilipes, which was once observed to suffer massive defoliation of young leaves on adult trees, typically does not suffer density-dependent herbivory (Janzen-Connell model). Two components of intraspecific variation in leaf herbivory were measured: 1) the variation between individuals in the population at the same time and 2) the temporal variation in rates of damage to each individual. The study was carried out on Maracá Island, Roraima, Brazil in three plots (50 m x 50 m) in each of three forest types: Peltogyne-rich forest (PRF), Peltogynepoor forest (PPF), and forest without Peltogyne (FWP). Two other non-pioneer species (Ecclinusa guianensis and Pradosia surinamensis) were chosen for comparison because they were fairly abundant and their seedlings could be readily identified. The values of leaf area removed by herbivores of trees and seedlings of the three study species were in the range reported for other tropical tree species (2-16%, standing damage). There were no differences within species between forests. However, there was a significant difference among species but this was not correlated with seedling density. Peltogyne seedlings showed no evidence of density-dependent herbivory as predicted by the Janzen-Connell model despite the fact that adult trees were observed to suffer a mass defoliation in April 1992. This result can be consider a strong suggestion that Peltogyne may partly be dominant due to escape from herbivory.
Distribution of pteridophyte communities along environmental gradients in Central Amazonia, Brazil
Biodiversity and Conservation, 2009
Extrapolation of local abundance–environment relationships to broader scales provides species distribution models used for conservation planning. We investigated the importance of environmental heterogeneity and geographic distance on pteridophyte species spatial distribution on 38 plots of 250 × 2.5 m distributed over 90 km2 in Central Amazon. Inclusion of canopy openness in our models increased the capacity of predicting community composition even under the narrow range of canopy openness found in our plots. Nevertheless, there was still a large amount of unexplained variance (55–65%). The response of the community to the light gradient was hierarchical and we did not find evidences of light partitioning. Most species were concentrated in low light plots but a few common and abundant occurred along the entire gradient. Soil properties were the major determinants of community composition. Contrary to similar studies, slope was not a good predictor of pteridophyte community composition, indicating that this relationship may be site-specific. There was no correlation between floristic distances and geographic distances. We concluded that mesoscale turnover is low, although locally environmental variation determines high turnover of species. Studies among different Amazonian physiognomies tend to find high levels of beta-diversity. However, coarse comparisons can not reveal subtle patterns that are relevant for biodiversity conservation planning. This study found some important changes on pteridophyte community within the same type of forest, mainly related to environmental heterogeneity, even in narrow ranges of environmental variation.
Neotropical bracken fern invades disturbed forests and burned and abandoned pastures in Latin America, inhibiting the growth of associated vegetation and altering community structure. Cutting of all aboveground vegetation every 6 to 12 mo has proven to be inefficient as a control method. We studied the impact of selective cutting of bracken every 2 mo, shading, and a combination of cutting + shading during 14 mo in a bracken-dominated, abandoned pasture in Veracruz, Mexico. At the end of the experiment, cutting with or without shading drastically reduced bracken cover from .90% to less than 1%, decreased leaf number from 18 to fewer than two leaves per m 2 , and depleted bracken leaf biomass. The significant reduction of bracken was correlated with a significant 3.9-to 5.7-fold increase in richness of other plant species. Cutting without shading was the only treatment that significantly reduced rhizome biomass to less than 62% of control plots, whereas cutting + shading was the only treatment to promote a significant increase in both cover and shoot biomass of successional plant species. Selective cutting of P. arachnoideum repeated every 2 mo was more successful than nonselective cuttings repeated at longer intervals, because it removed newly emerging leaves before their complete expansion and supported the recovery and reestablishment of other plant species, which may help to control bracken. Although costs for the first year of selective cutting were twice as much as for nonselective cutting, it may prove less expensive and more efficient than nonselective cutting in the long term. Nomenclature: Bracken, Pteridium spp.; Neotropical bracken fern, Pteridium arachnoideum (Kaulf.) Maxon.
Biotropica, 2002
We documented the floristic composition of pteridophytes (ferns and fern allies) and Melastomataceae in Yasuní National Park, Amazonian Ecuador. Our main questions were: (1) Are the density of individuals, species richness, and/or species diversity (measured with Shannon's H′) of the two plant groups related to edaphic differences? and (2) How many of the pteridophyte and Melastomataceae species are non–randomly distributed in relation to a soil base content gradient within terra firme (non–inundated forest). To answer these questions, we sampled 27 line transects of 500 × 5 m distributed in an area of ca 20 × 25 km. The study area included a permanent 50 ha plot established to monitor forest dynamics; thus, our results also provide information on landscape–scale floristic variability to which results from within the plot can be compared. A total of 45,608 individuals and 140 species of pteridophytes, and 4893 individuals and 89 species of the Melastomataceae, were counted in the transects. Both with pteridophytes and with Melastomataceae, a clear negative correlation was found between the amount of extractable bases in the soil and the number of plant individuals encountered in a transect. With Melastomataceae, species richness and species diversity also were negatively correlated with soil base content, but with pteridophytes they were not. More than 50 percent of the common species of both pteridophytes and Melastomataceae were nonrandomly distributed along the soil cation content gradient within terra firme. We conclude that while the species richness patterns observed in one plant group are not indicative of similar patterns in other plant groups, it seems likely that a substantial (but unknown) proportion of species belonging to other plant groups will be found to show distribution patterns that reflect edaphic preferences within terra firme forests.Se estudió la composición florística de pteridofitas (helechos y plantas afines) y Melastomataceas en el Parque Nacional Yasuní, Amazonía ecuatoriana. Nuestras preguntas principales fueron: (1) están relacionadas la densidad de individuos, la riqueza de especies y/o la diversidad (medida con la H' de Shannon) de los dos grupos de plantas con las diferencias edáficas? y (2) cuántas de las especies de pteridofitas y Melastomataceas están distribuidas en tierra firme de una manera que no sea al azar, sino en relación a un gradiente de concentración de cationes en el suelo? Para desarrollar estas preguntas, muestreamos 27 transectos de 500 por 5 m distribuidos en una área de 20 por 25 km. El área de estudio incluye una parcela permanente de 50 ha, establecida para estudiar la dinámica del bosque; por lo tanto, nuestros resultados proveen información sobre la variabilidad florística en una escala del paisaje que puede compararse con la de la parcela. En total se encontraron en los transectos 45,608 individuos y 140 especies de pteridofitas, y 4893 individuos y 89 especies de Melastomataceas. Tanto las pteridofitas como las Melastomataceas, mostraron una correlación negativa significativa entre la cantidad de cationes en el suelo y el número de individuos de plantas dentro de un transecto. En las Melastomataceas, la riqueza de especies y la diversidad estuvieron negativamente correlacionadas con el contenido de cationes en el suelo, pero en las pteridofitas, no existio tal correlacion. Más de 50 por ciento de las especies comunes de pteridófitas y Melastomataceas estuvieron distribuidas dentro de la tierra firme de una manera no aleatoria en relación con el gradiente de cationes en el suelo. Concluimos que aunque los patrones de diversidad de las especies observadas en un grupo de plantas no son indicatives de patrones similares en otros grupos, es probable que una proporción apreciable (pero desconocida) de especies pertenecientes a otros grupos de plantas pueda mostrar patrones de distribución que reflejen preferencias edáficas dentro de los bosques de tierra firme.
The bracken fern (Pteridium arachnoideum (Kaulf.) Maxon) dilemma in the Andes of Southern Ecuador
Ecotropica, 2003
Bracken fern (Pteridium aquilinum (L.) Kuhn) is one of the world's most powerful weeds, especially in agricultural areas. Its vigor and resistance to any kind of non-polluting pest control result from its extensive rhizome system. Growth of this rhizome system is strongly promoted by fire. As elsewhere in the tropics, farmers in the Andes of southern Ecuador make extensive use of fire to convert primary forest into arable land and to maintain their pastures. This communication addresses, from a phytosociological viewpoint, the ecological problems arising from the use of fire as an agricultural tool in the presence of the extremely aggressive and fire-tolerant bracken fern Pteridium arachnoideum. Repeated burning of the pastureland weakens the competitive strength of the most important pasture grass Setaria sphacelata, while the competitive strength of bracken increases. Pastures are finally abandoned when Pteridium has become completely predominant. Wind-dispersed seeds of several weedy Asteraceae and Melastomataceae species germinate under the canopy of the bracken leaves and, due to the steepness of the slopes, the seedlings receive sufficient light for further growth. The majority of these species are bushes that finally overtop the bracken leaves and can successfully compete with the shade intolerant fern. A vegetation composed of dense patches of Pteridium interspersed with individual bushes develops, which, because of the immense seed production of the bushes and the vigor of the bracken, is very stable and appears to be a longlasting and even at times the final successional stage. Since natural regeneration of the indigenous forest is very unlikely in these areas, reforestation may be the only way out of the dilemma caused by the extensive use of fire and the fire-tolerance of bracken.