Relaciones suelo-vegetación en una toposecuencia del Escudo Guayanés, Venezuela

Abstract

Soil-vegetation relationships in a toposequence of the Guayana Shield, Venezuela. The Guayana Shield is one of the oldest territories in the planet and has millions of years subjected to leaching and erosion processes that produce oligotrophic soils. This scarcity of nutrients has not avoided the development of high, diverse and magnificent forests, where plants have adaptations to survive these difficult conditions. The aim of this work was to characterize the physical and chemical parameters of the soils in different forest communities of the imataca Forest Reserve (iFR), to establish some interpretations on their origin, and some relationships between the edaphic components and the inhabitant species. Terrestrial journeys were carried out and two pathways were traced for the interpretation of forest communities. in each community, three plots (100m x 100m) for the ecological survey were established. In each plot, all trees, palms, and lianas were measured (dbh≥10cm; dbh: diameter at breast height); four 10m x 10m understory sub-plots were evaluated, and a census of all the spermatophyta species (dbh<10cm) was made. Soils were evaluated by means of a trial pit in each community, and a bore in each one understory sub-plot. The obtained data were analyzed by both a detrended and a canonical correspondence analysis. Results from a total of 15 plots allowed us to identify three communities: a forest dominated by Mora excelsa located in a narrow valley with high content of silt; a swamp forest dominated by Catostemma commune in a sandy broad valley, and a forest in clay hills dominated by Alexa imperatricis. Most of the soils had a pH between 3.1 and 4.5. Nutrients were in very low concentrations (N: 0-0.2%; P: 0-14ppm; K: 0-0.3Cmol/kg) and Al in toxicity quantities. We observed that Ca/Al relationship greater than 1 meant a neutralization of the toxic effect of Al. Besides, basal area ranged from 20.4 to 32.3m 2 /ha; the highest level (top local forest development) corresponded with the C. commune community with a Ca/Al value of 2.5. This research found an adequate relationship between soil and vegetation, as it was able to identify three communities into three distinct soil conditions. Nevertheless, edaphic constraints indicated that high forest cover must be maintained as an essential element for the conservation of these communities. Rev. Biol. Trop. 62 (1): 385-401. Epub 2014 March 01.Key words: oligotrophic soils, soil toxicity, imataca, tropical forests, ecosystem susceptibility.Desde hace poco más de un siglo, el trabajo de Flahault & Schöter (citados por Biondi, 2011) reconoce que una asociación es una agrupación vegetal con una determinada composición florística, que presenta una fisionomía uniforme y que se desarrolla en condiciones invariables del sitio. Esta es la base de Teoría Organísmica (Clements, 1916) y de la rama ecológica denominada Fitosociología (Braun-Blanquet, 1979), donde se considera que las comunidades vegetales pueden ser identificadas y clasificadas en un sistema jerár-quico....

Soil-vegetation relationships and community structure in a "terra-firme"-white-sand vegetation gradient in Viruá National Park, northern Amazon, Brazil

“…The community structure is mainly characterized by the species Tetragastris panamensis and Astrocaryum gynacanthum, with the second and third highest importance value (IV), but with higher density and absolute and relative frequency. The T. panamensis was also found in clayey soils in Peruvian, Venezuelan and Colombian Amazon, and also in State of Acre in Brazil (Duque and Cavelier 2003, Trivede et al 2004, Fine et al 2005, Rockwell et al 2007, Lozada et al 2014, showing a widespread distribution in Amazon forest. The same occurs with A. gynacanthum with distribution throughout the Amazon basin and the Guianas, found in Bolivia, Brazil (Acre, Amapá, Amazonas, Pará, Rondônia, Roraima), Colombia, French Guiana, Guyana, Peru, Suriname, Venezuela (Kahn 2008).…”

Efecto de mezclas de fibra semicomposteada con suelo en el crecimiento y la tolerancia de enfermedades en vivero de palma aceitera

“…Es probable que las características químicas de las fibras semicomposteadas no beneficiaron en la nutrición de las plantas en vivero. Aunque posee relaciones C:N ideales > 20% (Lozada et al 2014), las plantas con dosis crecientes de fibra no presentaron incrementos en las fechas evaluadas. Sin embargo, se encontró que por arriba de un 25% de compost en mezcla con el suelo tuvieron reducciones con el vigor de las plantas precisamente con el diámetro de bulbo.…”

The biogeographical kingdoms and regions of the world

“…In the tepuis, due to their elevation, the mists often condense on the slopes at intermediate altitudes, and this causes very humid mountain forests almost always shrouded in mist. The existence of numerous reliefs of this type, specific climatic conditions with increased humidity and cooler temperatures due to altitude, and the extremely acid substrates result in a distinct flora that sharply differs from the surrounding Amazonian and Antillean-Mesoamerican regions (Maguire, 1979;Berry et al, 1995Berry et al, -1997Lozada et al, 2014). There is a high number of endemic species, close to 50% of the estimated 8,000 species believed to inhabit this region.…”