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Floristic Variation (floristic + variation)
Selected AbstractsEffects of mesoscale environmental heterogeneity and dispersal limitation on floristic variation in rain forest fernsJOURNAL OF ECOLOGY, Issue 1 2006MIRKKA M. JONES Summary 1Field studies to evaluate the roles of environmental variation and random dispersal in explaining variation in the floristic composition of rain forest plants at landscape to regional scales have yet to reach a consensus. Moreover, only one study has focused on scales below 10 km2, where the effects of dispersal limitation are expected to be easiest to observe. 2In the present study, we estimate the importance of differences in some key environmental variables (describing canopy openness, soils and topography) relative to the geographical distances between sample plots as determinants of differences in pteridophyte (ferns and fern allies) species composition between plots within a c. 5.7 km2 lowland rain forest site in Costa Rica. 3To assess the relative importance of environmental vs. geographical distances in relation to the length of environmental gradient covered, we compared the results obtained over the full range of soil types, including swamps, with those for upland soils alone. 4Environmental variability was found to be a far stronger predictor of changes in floristic differences than the geographical distance between sample plots. In particular, differences in soil nutrient content, drainage and canopy openness correlated with floristic differences. 5The decline in mean floristic similarity with increasing geographical distance was stronger than proposed by the random dispersal model over short distances (up to c. 100 m), which is probably attributable to both dispersal limitation and environmental changes. The scatter around the mean was large at all distances. 6Our initial expectation was that the effects of dispersal limitation (represented by geographical distance) on observed patterns of floristic similarity would be stronger, and those of environmental differences weaker, than at broader spatial scales. Instead, these results suggest that the niche assembly view is a more accurate representation of pteridophyte communities at local to mesoscales than the dispersal assembly view. [source] Ecological gradients, subdivisions and terminology of north-west European miresJOURNAL OF ECOLOGY, Issue 2 2000B. D. Wheeler Summary 1,The historical development of mire ecology and terminology is reviewed in relation to evolving concepts and perceptions, and the diverse schools and traditions of vegetation and habitat description and research. 2,Most ecological and floristic variation within north-west European mire vegetation is accounted for by three ecological gradients: the acid base-poor vs. neutral, base- and bicarbonate-rich gradient; the gradient in fertility related to availability of the limiting nutrient elements N and P; and the water level gradient. Effects of salinity and the spring,flush,fen gradients are of more local significance, usually easily recognized. Land use is an important additional factor. 3,The mineral-soil-water limit between ombrotrophic and minerotrophically influenced sites is not sharp, and cannot be related to consistent differences in either vegetation or water chemistry. It should be abandoned as a general main division within mires. 4,The most important natural division is between ,bog', with pH generally < 5.0, low Ca2+, and Cl, and SO42, as the main inorganic anions, typically dominated by sphagna, ericoids and calcifuge Cyperaceae, and ,fen', with pH generally > 6.0, high Ca2+ and HCO3,, vegetation rich in dicotyledonous herbs and ,brown mosses'. This division is reflected in a bimodal distribution of pH. 5,The terms oligotrophic, mesotrophic and eutrophic should refer only to nutrient richness (fertility, mainly N and P), not to base richness (metallic cations and pH). 6,It is recommended that ,mire' should embrace both wetlands on peat and related communities on mineral soils, that ,bog' (unqualified) should encompass both ombrotrophic and weakly minerotrophic mires, including ,bog woodland', and that ,fen' should be restricted to base-rich mires but include both herbaceous and wooded vegetation (,fen carr'). 7,Definitions are given for a range of broadly defined categories that should cover most vegetation types commonly encountered. The relation of these to British national vegetation classification types and to major units in European phytosociology is outlined. [source] Vegetation patterns and environmental gradients in tropical dry forests of the northern Yucatan PeninsulaJOURNAL OF VEGETATION SCIENCE, Issue 2 2004D.A. White Patterns of plant species composition and their relationships to soil and topographic variables were investigated in tropical dry forests across the north central Yucatan, Mexico. Seven sites were studied in the oldest accessible forests along a 200,km transect oriented northwest to southeast; an eighth site was located in a little-disturbed area located 75 km northeast of the transect. Two of the sites were on Mayan ruins. All sites were sampled using 9,24, 10m × 20m plots ( Effects of fire intensity on plant species composition of sandstone communities in the Sydney regionAUSTRAL ECOLOGY, Issue 4 2002DAVID A. MORRISON Abstract Fire intensity measures the heat output of a fire, and variation in fire intensity has been shown to have many effects on the demography of plant species, although the consequent effects on the floristic composition of communities have rarely been quantified. The effects of variation in fire intensity on the floristic composition of dry sclerophyll vegetation with different fire histories near Sydney was estimated. In particular, differences in species abundance of woodland and shrubland communities subjected to four fire-intensity classes: unburnt, low intensity (<500 kW m -1), medium intensity (500-2500 kW m -1) and high intensity (>2500 kW m -1) were examined. The samples had a standardized previous fire frequency and season, thus minimizing the effects of other aspects of the fire regime. There was a clear effect of fire intensity on the relative abundances of the vascular plant species, with increasing intensity of the fire producing vegetation that was increasingly different from the unburnt vegetation. This pattern was repeated in both the woodland and shrubland vegetation types, suggesting that it was not an artefact of the experimental conditions. However, the effects of fire intensity on floristic composition were no greater than were the differences between these two similar vegetation types, with variation in fire intensity accounting for only approximately 10% of the floristic variation. Nevertheless, the effects of fire intensity on the abundance of individual species were consistent across taxonomic groups, with the monocotyledon and Fabaceae species being more abundant at higher than lower intensities, the Proteaceae and Rutaceae more abundant at intermediate intensities, and the Epacridaceae more abundant at lower rather than higher intensities. The number of fire-tolerant species increased with increasing fire intensity, and those fire-tolerant species present were most abundant in the areas burnt with medium intensity. The number of fire-sensitive species did not respond to fire intensity, and those species present were most abundant in the areas burnt with low intensity. This suggests that either fire-sensitive species respond poorly to higher fire intensities or fire-tolerant species respond poorly to lower fire intensities, perhaps because of differences in seed germination, seedling survival or competition among adults. [source] Distance Decay of Tree Species Similarity in Protected Areas on Terra Firme Forests in Colombian AmazoniaBIOTROPICA, Issue 5 2009Álvaro Duque ABSTRACT In this study, we investigated the pattern of floristic similarity as a function of geographical distances and environmental variability in well-drained uplands (terra firme) in Colombian Amazonia. The study site comprised three National Natural Parks, Tinigua, Chiribiquete, and Amacayacu, located in different geological units that represent a soil fertility gradient linked to parental materials. Differences in species richness between sites were compared using rarefaction analysis. A clear floristic transition appeared in the east,west direction following a soil fertility gradient along the first PCoA axis. In multiple regression analyses based on distance matrices, both geographical distances and geology explained 64 percent of the total floristic variation. Geographical distances alone accounted for 12 percent of variation in floristic similarities among plots, while geology alone accounted for 1 percent, and the joint effect of both explained 51 percent of the floristic variation. The species richness trend supports the existence of a latitudinal corridor southward of the geographical Equator in the Amazon basin, where tree diversity reaches the maximum expected values. A coupled effect of stochastic dispersal limitation and habitat specialization would certainly appear to be an appropriate explanation for tree species turnover in terra firme forests in Colombian Amazonia, strongly emphasizing that competition and neutrality must be supplementary rather than mutually exclusive processes. This result pinpoints the effect of dispersal on floral mixing as an ongoing active process for structuring tree communities in NW Amazonia, and the size of the reserves as a relevant issue to protect rare species from extinction by chance. [source] Tree Community Change across 700 km of Lowland Amazonian Forest from the Andean Foothills to BrazilBIOTROPICA, Issue 5 2008Nigel C. A. Pitman ABSTRACT We describe patterns of tree community change along a 700-km transect through terra firme forests of western Amazonia, running from the base of the Andes in Ecuador to the Peru,Brazil border. Our primary question is whether floristic variation at large scales arises from many gradual changes or a few abrupt ones. Data from 54 1-ha tree plots along the transect support the latter model, showing two sharp discontinuities in community structure at the genus level. One is located near the Ecuador,Peru border, where the suite of species that dominates large areas of Ecuadorean forest declines abruptly in importance to the east. This discontinuity is underlain by a subterranean paleoarch and congruent with a change in soil texture. A second discontinuity is associated with the shift from clay to white sand soils near Iquitos. We hypothesize that the first discontinuity is part of an edaphic boundary that runs along the Andean piedmont and causes a transition from tree communities preferring richer, younger soils near the base of the Andes to those preferring poorer, older soils farther east. Because the floristic changes observed at this discontinuity are conserved for large distances to the east and west of it, the discontinuity is potentially key for understanding floristic variation in western Amazonia. The significant floristic turnover at the Ecuador,Peru border suggests that the only large protected area in the region,Ecuador's Yasuní National Park,is not adequate protection for the very diverse tree communities that cover vast areas of northern Peru. RESUMEN Describimos cambios en la comunidad de árboles a lo largo de un transecto de 700 km que atraviesa los bosques de tierra firme de la Amazonía occidental, desde la base de los Andes en Ecuador hasta la frontera Perú-Brasil. Nuestra pregunta principal es si la variación florística a grandes escalas es generada a base de muchos cambios graduales o en unos pocos cambios abruptos. Datos de 54 parcelas de árboles de 1 ha a lo largo del transecto apoyan el segundo modelo, mostrando dos discontinuidades bien definidas en la estructura de la comunidad a nivel de género. Una discontinuidad está localizada cerca de la frontera Ecuador-Perú, donde el grupo de especies que domina grandes áreas de la Amazonía ecuatoriana declina abruptamente en importancia hacia el este. Esta discontinuidad está asociada con un paleoarco subterráneo y es congruente con cambios en la textura del suelo. Una segunda discontinuidad está asociada con un cambio de suelos arcillosos a suelos de arena blanca cerca de Iquitos. Sugerimos que la primera discontinuidad es parte de un limite edáfico que corre a lo largo del piedemonte andino y causa una transición de comunidades de árboles que prefieren suelos más fértiles y jóvenes cerca de los Andes, a aquellos que prefieren suelos más pobres y antiguos hacia el este. Ya que los cambios florísticos observados en esta discontinuidad se conservan por grandes distancias hacia el este y oeste, la discontinuidad es potencialmente clave para entender la variación florística en la Amazonía occidental. El importante recambio florístico en la frontera Ecuador-Perú sugiere que la única gran área protegida en la región,el Parque Nacional Yasuní en Ecuador,no presta protección adecuada a las muy diversas comunidades de árboles en el norte del Perú. [source] Plant Community Structure in Tropical Rain Forest Fragments of the Western Ghats, India,BIOTROPICA, Issue 2 2006S. Muthuramkumar ABSTRACT Changes in tree, liana, and understory plant diversity and community composition in five tropical rain forest fragments varying in area (18,2600 ha) and disturbance levels were studied on the Valparai plateau, Western Ghats. Systematic sampling using small quadrats (totaling 4 ha for trees and lianas, 0.16 ha for understory plants) enumerated 312 species in 103 families: 1968 trees (144 species), 2250 lianas (60 species), and 6123 understory plants (108 species). Tree species density, stem density, and basal area were higher in the three larger (> 100 ha) rain forest fragments but were negatively correlated with disturbance scores rather than area per se. Liana species density, stem density, and basal area were higher in moderately disturbed and lower in heavily disturbed fragments than in the three larger fragments. Understory species density was highest in the highly disturbed 18-ha fragment, due to weedy invasive species occurring with rain forest plants. Nonmetric multidimensional scaling and Mantel tests revealed significant and similar patterns of floristic variation suggesting similar effects of disturbance on community compositional change for the three life-forms. The five fragments encompassed substantial plant diversity in the regional landscape, harbored at least 70 endemic species (3.21% of the endemic flora of the Western Ghats,Sri Lanka biodiversity hotspot), and supported many endemic and threatened animals. The study indicates the significant conservation value of rain forest fragments in the Western Ghats, signals the need to protect them from further disturbances, and provides useful benchmarks for restoration and monitoring efforts. [source]
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