Ecología de la altiplanicie de la Gran Sabana (Guayana Venezolana) II. Estructura, diversidad, crecimiento y adaptación en bosques de las subcuencas de los ríos Yuruaní y Alto Kukenán. Scientia Guayanae

SERBIULA (sistema Librum 2.0) 01/1999; 9.
Source: OAI

ABSTRACT Inlcuye bibliografáia

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    • "There is a general lack of knowledge about this palm species' biology and the communities it forms in the Gran Sabana (Ponce et al., 1999). Most GS forests are considered to fall within the category of lower montane forests (also called submesothermic forests, between 800 and 1500 m elevation), because of their intermediate position between lowland and highland forests (Hernández, 1999). Common genera include: "
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    ABSTRACT: The southern Gran Sabana (SE Venezuela) holds a particular type of neotropical savanna characterized by the local occurrence of morichales (Mauritia palm swamps), in a climate apparently more suitable for rain forests. We present a paleoecological analysis of the last millennia of Lake Chonita (4°39′N–61°0′W, 884 m elevation), based on biological and physico-chemical proxies. Savannas dominated the region during the last millennia, but a significant vegetation replacement occurred in recent times. The site was covered by a treeless savanna with nearby rainforests from 3640 to 2180 cal yr BP. Water levels were higher than today until about 2800 cal yr BP. Forests retreated since about 2180 cal yr BP onwards, likely influenced by a higher fire incidence that facilitated a dramatic expansion of morichales. The simultaneous appearance of charcoal particles and Mauritia pollen around 2000 cal yr BP supports the potential pyrophilous nature of this palm and the importance of fire for its recent expansion. The whole picture suggests human settlements similar to today – in which fire is an essential element – since around 2000 yr ago. Therefore, present-day southern Gran Sabana landscapes seem to have been the result of the synergy between biogeographical, climatic and anthropogenic factors, mostly fire.
    Quaternary Research 11/2011; 76(3):335-344. DOI:10.1016/j.yqres.2011.06.014 · 2.58 Impact Factor
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    ABSTRACT: This work consists of a key, descriptions and illustrations, to identify the most significant angiosperm pollen types (85 genera/ species, belonging to 36 families), from a paleoecological point of view, of the Gran Sabana and the 'tepui' (table mountains) summits from eastern Venezuelan Guayana. The pollen key and plates contain the most frequent and abundant pollen types found so far by the author in the Holocene sediments, as well as the significant medium and minor elements. This is enough to carry out a standard, successful palynological analysis in the area with a small percentage of unknown taxa, and can be considered a first step to be enhanced with future studies, especially from the 'tepui' summits of the western Venezuelan Guayana.
    Palynology 12/2003; 27(1). DOI:10.2113/27.1.99 · 0.95 Impact Factor
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    ABSTRACT: P fractions and sorption processes were studied in samples taken from the organic surface layer and in the underlying mineral soil of a forest-savanna sequence consisting of: (1) tall primary forest (TPF), (2) tall secondary forest (MSF), (3) low secondary forest (LSF), and (4) open savanna (S) in la Gran Sabana, South Venezuela. The organic surface layer in the TPF and MSF showed the highest P concentrations in all analysed P fractions. P in this organic layer was mainly associated with inorganic forms, suggesting that this layer is an important source of bio-available P. The organic surface layer was not present in LSF and S probably because of the occurrence of recurrent surface fires. The conversion of forest to savanna influenced the distribution of the different forms of P in the soil. While non-occluded (resin-+NaOH-P extractable) and organic (NaHCO3-+NaOH-+HCl-Po) P declined from the forest to savanna, occluded (concentrated HCl-extractable+residual P) forms increased. The correlation between sorption maxima and soil organic C was not significant; however, organically bound forms of Al were the main component that explained the adsorption capacity of these soils. The above findings suggest that the organic surface layer and the soil organic matter are important for maintaining P fertility in the undisturbed and little disturbed forests. However, when the system is heavily perturbed by fire the organic surface layer, the main P source, disappears and the patterns of P cycling change.
    Biology and Fertility of Soils 01/2004; 40(1):14-19. DOI:10.1007/s00374-004-0733-7 · 3.40 Impact Factor
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