Forest In Venezuela Research Articles

New Mochlozetidae (Acari, Oribatida) from the Merida State, Western Venezuela

Two new species of Mochlozetidae (Oribatida)—Dynatozetes asetosus n. sp. and Uracrobates (Uracrobates) paramasneri n. sp.—are described, based on materials collected from sweep sample in cloud forest in Venezuela. Dynatozetes asetosus n. sp. differs from all representatives of the genus in the presence of the prolamella and the morphology of the bothridial seta; Uracrobates (Uracrobates) paramasneri n. sp. differs from all representatives of the genus by the morphology of the notogastral porose area Aa. The genus Uracrobates is recorded in the Venezuelan fauna for the first time. Identification keys, distribution and habitat to the known species of Dynatozetes and Uracrobates are provided. The generic diagnosis of Dynatozetes is partially revised.

Distribution of juveniles of tree species along a canopy closure gradient in a tropical cloud forest of the Venezuelan Andes

Abstract: Cloud forests represent a minor portion of the world forests, though outstanding in terms of biodiversity, endemisms, and environmental services provided. Understanding the factors that drive the regeneration and species composition of these forests, and in particular how light availability affects the patterns of juvenile tree distribution in the understory, is critical for conservation and restoration programs. In this study, we determined the range-size and overlap of the abundance distribution of juveniles for 20 tree species in an Andean tropical cloud forest in Venezuela along a gradient of percentage canopy openness (%CO) used as a surrogate of light availability. The observed distribution of %CO was then compared with a bounded null model of community structure in order to test light partitioning as a driver of tree species’ coexistence. We measured %CO using hemispherical photography and the abundance and size of juvenile trees in 280 plots of 1-m radius spread over a 32 ha forest area. The distribution of sites was skewed towards the lower end of the %CO gradient (0.5 to 12.8%), while species abundance sharply diminished at both ends of the gradient. Nevertheless, 15 out of 20 species had a non-random distribution in relation to %CO, with many species concentrated near the lower side of the gradient. The observed pattern of species’ overlap was within the 95% confidence limits for the average overlap expected under the bounded null model. These patterns indicate that low canopy openness is the rule in this forest, in spite of the scattered tree-fall gaps, and suggest that light partitioning does not determine the tree community structure at the juvenile stage. High redundancy in light requirements among juveniles of tree species may have a positive effect on species coexistence in cloud forests, thus maintaining a high species diversity. However, other factors such as recruitment limitation and differential growth/carbon-gain among species at the juvenile stage along the light gradient could contribute to the high diversity of these ecosystems.

Breeding biology of the Spotted Barbtail (Premnoplex brunnescens)

The Spotted Barbtail (Furnariidae) is poorly studied but shows some extreme traits for a tropical passerine. We located and monitored 155 nests to study this species for 7 years in an Andean cloud forest in Venezuela. Spotted Barbtails have an unusually long incubation period of 27.2 ± 0.16 days, as a result of very long (3–6 hr) off-bouts even though both adults incubate. The long off-bouts yield low incubation temperatures for embryos and are associated with proportionally large eggs (21% of adult mass). They also have a long nestling period of 21.67 ± 0.33 days, and a typical tropical brood size of two. The slow growth rate of the typical broods of two is even slower in broods artificially reduced to one young. Nonetheless, the young stay in the nest long enough to achieve wing lengths that approach adult size.

Scolecobeltrania, an interesting new microfungus from Venezuela

A new microfungus collected on dead plant material from the “Cerro El Ávila” mountain range and “Parque Nacional Canaima” tropical forest in Venezuela is described and illustrated. Scolecobeltrania vermispora gen. & sp. nov. is characterized by macronematous branched conidiophores, polyblastic conidiogenous cells, and unicellular vermiform to sigmoid pale brown conidia with up to 11 hyaline transverse bands.

Leaf Spectra and Weight of Species in Canopy, Subcanopy, and Understory Layers in a Venezuelan Andean Cloud Forest

We characterize the leaf spectra of tree species of an Andean cloud forest in Venezuela, grouped according to position in canopy, subcanopy and understory. We measured leaf reflectance and transmittance spectra in the 400–750 nm range using a high-resolution spectrometer. Both signals were subtracted from unity to calculate the absorbance signal. Nine spectral variables were calculated for each signal, three based on wide-bands and six based on features. We measured leaf mass per unit area of all species, and calculated efficiency of absorbance, as ratio of absorbance in photosynthetic range over leaf mass. Differences among groups were significant for several absorbance and transmittance variables, leaf mass, and efficiency of absorbance. The clearest differences are between canopy and understory species. There is strong correlation for at least one pair of band variables for each signal, and each band variable is strongly correlated with at least one feature variable for most signals. High canonical correlations are obtained between pairs of the three canonical axes for bands and the first three canonical axes for features. Absorbance variables produce species clusters having the closest correspondence to the species groups. Linear discriminant analysis shows that species groups can be sorted by all signals, particularly absorbance.

Diversity and substrate partitioning of Discomycetes in a cloud forest in Venezuela

Diversity and substrate partitioning of Discomycetes in a cloud forest in Venezuela

Asymmetrical legitimate pollination in distylous Palicourea demissa (Rubiaceae): the role of nectar production and pollinator visitation

Abstract:We investigated morph differences in attributes that contribute to rewarding floral visitors of the distylous shrub Palicourea demissa at La Mucuy cloud forest in Venezuela. In both morphs, we measured nectar production from flowers subjected to repeated removals at 2-h intervals (10 plants per morph) and flowers that accumulated nectar for 24 h (10 plants per morph). In both cases, floral visitors were excluded. In addition, we quantified nectar availability (30 plants per morph), floral visitation (10–12 plants per morph) and legitimate pollination (30 plants per morph) throughout the day. We explored morph differences in the variables mentioned above using analyses of variance, and the effects of nectar variation on floral visitation and legitimate pollination using regression models. We observed 1205 floral visits, grouped into six hummingbird (94.7%) and three insect species (5.3%), across observations (264 h). Coeligena torquata was the most frequent floral visitor (34%) in both morphs (1.4–1.7 visits per plant h−1). Nectar production and availability, and visitation rate were similar between morphs. Visitation rate and legitimate pollen deposition increased with the nectar production in both morphs, but levels of legitimate pollination were higher on short-styled flowers than long-styled flowers. These results show that short-styled and long-styled flowers reward floral visitors equally, but frequency and foraging behaviour of long-billed pollinators can promote asymmetrical legitimate pollination.

Diversidad de líquenes Cortícolas en el bosque Subandino de la finca Zíngara (Cali, Valle del Cauca)

El presente trabajo tuvo como objetivo contribuir al conocimiento de la diversidad de los líquenes del Valle del Cauca mediante un registro preliminar de estos organismos en el Bosque Subandino de la Finca Zíngara. Para esto, se seleccionaron cinco individuos de cinco especies de árboles (forófitos) y se identificaron las especies de líquenes presentes en un cuadrante de 0,50 x 0,20 m2 ubicado en el tronco de cada árbol a 1,3 m de altura. Se encontraron 69 morfoespecies de líquenes, de los cuales 37 fueron determinados hasta especie, 18 hasta género y 14 no fueron determinados debido a que estaban estériles o no presentaban esporas. La mayoría de las especies de líquenes (59 especies) fueron crustáceos, 6 fueron foliosos, 1 escuamuloso, 1 dimórfico, 1 gelatinoso y 1 filamentoso. Se hallaron 27 géneros agrupados en 16 familias. Los géneros con el mayor número de especies fueron Herpothallon (12 especies), Pyrenula (4 ), Graphis (4), Arthonia, Coenogonium y Phaeographis (3). La familia Arthoniaceae fue la mejor representada (15 especies), seguida de Graphidaceae (12), Thelotremataceae (7) y Pyrenulaceae (4). Por otro lado, las familiasCladoniaceae, Collemataceae, Pilocarpaceae, Porinaceae, Ramalinaceae y Roccelaceae presentaron una especie. Teniendo en cuenta las diferencias en el área y el tipo de muestreo (25.000 cm2), la diversidad del sitio es muy alta comparada con otros lugares como la cordillera central de Colombia (173 especies), en un bosque húmedo bajo de Venezuela (250 especies), en Ecuador (45 especies), en un bosque montano en Costa Rica, en un bosque húmedo bajo en Guyana (114 especies) y en un bosque húmedo tropical en el norte de Brasil (150 especies).

Ant-plant associations in different forests in Venezuela

We evaluated the hypothesis that the abundance and species distribution of two different kinds of myrmecophilous plants is influenced differently by the ant diversity and abundance. In eight different natural forests in Venezuela we estimated the species richness and abundance of plants, ants on the soil and on the canopy, the leaf damage of plants and soil nutrients. The main results of the study show that plants with domatia (PD) and plants with extrafloral nectaries (PEFN) have different relationships with ants and suffer from different ecological constraints. PD attract a more specific group of ants than PEFN. Our results are consistent with the hypothesis that domatia are adaptations that help plants to increase rare nutrient uptake rather than for herbivore defense. We found that PEFN attract a larger variety of ant species than PD, and ant abundance seems to limit the ecological range of PEFN. The attraction of ants as a mechanism to reduce herbivory, as done by PEFN, does not seem to be superior to alternative anti-herbivore mechanisms used by other plants. Contrary to many former studies, we found that ants are generally more diverse on the soil compared to canopies.

Tropical dry forests in Venezuela: assessing status, threats and future prospects

Tropical dry forests may be among the world's most threatened ecosystems, but few studies have objectively quantified their status and threats. This study analysed Venezuelan dry forests at multiple scales, assessing status, present threats and the policy context shaping their future. Historical and current dry forest cover at both national and local scales were contrasted, and a set of quantitative risk assessment criteria applied. While dry forests were vulnerable nationally, in northern-central locations they were endangered. Clearing for cattle ranching and for intensive and subsistence agriculture were the principal factors driving dry forest loss at the national scale, while at a local level, urbanization and fire seemed to be the primary threats. The analysis emphasized the separation of risk assessment from the very different task of establishing conservation priorities; high risk areas may not necessarily be the highest priority for investment, and policy makers may become explicitly aware of the spatial scale at which their policies are implemented, as well as how these policies may affect or be affected by the status of ecosystems beyond their area of influence. The main challenge to future dry forest conservation is a paucity of explicit policies for management and use. However, scientifically-based management can support positive dry forest policies in many ways, including identifying locations and protocols for ecological restoration, maintaining seed banks, quantifying baseline conditions, and monitoring genetic diversity and other indicators.

Tropical Dry Forests of Venezuela: Characterization and Current Conservation Status1

ABSTRACTTropical dry forests are located predominantly in the northern portion of Venezuela, above 6°N. Although their potential extent covers ca 400,000 km2 (44% of the land), they currently occupy about 10 percent of this area. The diversity and complexity of Venezuelan dry forests increases from north to south along a gradient of decreasing severity of the dry season. A typical dry forest in Venezuela presents ca 110–170 species of plants from ca 40 to 50 families within an area of approximately 10 ha. Species composition and forest structure, however, are dependent on local landscape conditions (e.g., soil type, topography), and nearby forest types can be very different. Our analysis of five dry forest variants showed a maximum family similarity of 67 percent, although most values fell in the 50–60 percent interval. They are currently considered as one of Venezuela's most threatened ecosystems, but only 5 percent of extant dry forests are included in protected areas; this represents 0.5 percent of their potential extent. It is fundamental to promote the creation of at least 3 or 4 more large protected areas (ca 5000 ha), with different climatic and orographic characteristics, in combination with the recovery of threatened species, the restoration of degraded systems, and the implementation of sustainable development projects. Their apparent high resilience suggests that with the proper management we can restore and maintain the integrity of Venezuelan dry forests.

Frugivorous butterfly species in tropical forest fragments: correlates of vulnerability to extinction

Insects exhibit a variety of population-level responses to forest fragmentation, ranging from population increase to extinction. However, the biological attributes that underlie differences in extinction vulnerability among insects have been little-studied. Using the frugivorous butterfly community of tropical dry forest in Venezuela, we studied body size, population density and colonization ability as attributes that might underlie the range of responses of insects to forest fragmentation. The study was carried out in a set of forest fragments in the reservoir Lago Guri, formed by the damming of the Caroni River in eastern Venezuela. Results show that larger butterfly species were more vulnerable to extinction from habitat fragments than smaller ones. Rarer species were not more vulnerable to extinction, showing that rarity may not be an important correlate of vulnerability to extinction amongst insects. Contrary to expectation, faster-flying species were more and not less vulnerable to extinction from small habitat fragments. We speculate on the possible reasons for the observed patterns in extinction vulnerability using additional observations on behavioural patterns and larval host plant distributions of some of the butterfly species.

Latin American Center Symposium on Environment and Health: Exploring Natural Products

This will be an interdisciplinary one-day symposium that should be of great interest to biologists, especially botanists, biomedical researchers, practitioners of complementary and alternative medicine, and public health workers. What do the forests in Venezuela and Brazil and plants from California yield as natural products that can be exploited as alternative therapies for the benefit of health? The popular press (e.g. every Monday, the LA Times health section gives an example of some kind of `cure') is a good source of information. Thus there is an ever-growing awareness of the possibility of using such natural products in place of other drugs. Most important, there is an attempt to place these products within the realm of solid science through the publication of evidence-based reports. The symposium will be organized around three international experts who will give formal presentations from 9:00 to 12:00 h. After a no-host two-hour lunch, we will reconvene from 14:00 to 17:00 h for a roundtable discussion. There is no charge for participation and everyone is welcome.

Phenology and stem-growth periodicity of tree species in Amazonian floodplain forests

To study the impact of the annual long-term flooding (flood-pulse) on seasonal tree development in Amazonian floodplains, the phenology and growth in stem diameter of various tree species with different leaf-change patterns were observed over a period of 2 y. The trees of the functional ecotypes, evergreen, brevi-deciduous, deciduous and stem-succulent showed a periodic behaviour mainly triggered by the flood-pulse. Trees have high increment during the terrestrial phase. Flooding causes a shedding of some or all leaves leading to a cambial dormancy of about 2 mo and the formation of an annual ring. Studies carried out in tropical dry forests verify a strong relationship between the phenological development and the water status of the trees, strongly affected by seasonal drought. The comparison of the phenology and the diameter growth of the corresponding ecotypes in floodplain forest and a semi-deciduous forest in Venezuela shows a displacement of at least 2 mo in the periodicity, except for stem-succulent tree species. For stem-succulent trees it remains unclear which factors influence phenology and stem diameter growth.

The genus Menisporopsis in Venezuela with the addition of M. anisospora anam. sp. nov. from a palm tree

Menisporopsis anisospora anam. sp. nov., found on decaying petiole of fallen leaves of Wettinia praemosa in a cloud forest in Venezuela, is described and illustrated. This is characterized by having heterosporous conidia (allantoid, fusiform, subsigmoid, sublunate, vermiform to irregular) with unequal sides, subtruncate or truncated at base, attenuate at apex, one-celled, hyaline with 2–4-setulae. Two other Menisporopsis species are recorded for the first time from Venezuela and a key to the described species is provided.

Sustainable timber harvesting in Venezuela: a modelling approach

Summary Reliable data on the growth and yield of logged‐over forest, to determine sustainable cutting cycles, are widely missing for the tropics. We used the process‐based model formind2.0 to analyse the growth and yield of logged‐over forest in Venezuela under different logging scenarios over a period of 240 years, and compared results with unlogged stands. The performance of the model was evaluated with a detailed stability and sensitivity analysis. In the absence of further logging, the logged‐over stand approached the stand structure of mature forest in terms of bole volume and basal area after about 50–100 years. Thirty‐year cutting cycles with conventional logging methods and net extraction volumes of 45 and 60 m3 ha−1 cycle−1 did not provide sustainable yields under either of two minimum felling diameters (35 and 50 cm) that were applied. Only the 60‐year cutting cycle provided sustainable yields under conventional and reduced‐impact logging, with the different minimum felling diameters and a range of net volumes extracted (30–60 m3 ha−1 cycle−1). With the longest cutting cycle (60 years), bole volume recovered to levels similar to the mature unlogged stand, but the species composition was very different. Scenarios with reduced‐impact logging provided a significantly higher timber volume than under conventional logging. The conservation of forest resources will only be possible with long cutting cycles (at least 60 years) in combination with reduced‐impact logging.

Bird communities of dry forests and oak woodland of western Mexico

Bird species‐richness and densities were studied in spring and autumn of 1991 and 1992 in dry forest and oak woodland in western Mexico. Classification of the vegetation resulted in the identification of six dry forest types: from thorn forests, dominated byAcacia, through broad‐leaved tree forest (typical dry forest of western Mexico) and small‐leaved tree forest toIpomoeaforest. Oak woodland and mixed woodland, which are a transition between dry forest and the more mesic oak woodland, formed two further forest types. In the study area as a whole, bird densities were higher in autumn, following the rainy season, than in spring, which is the dry season, and the beginning of the breeding season. Densities in the two autumns were very similar (mean 93 ± 7.8 birds per 2.8 ha) but differed significantly between spring 1991 (57 ± 2.2 per 2.8 ha) and spring 1992 (70 ± 3.2 per 2.8 ha), possibly due to unseasonal rain in 1992. In autumn, bird densities were highest in thorn forests and lowest in broad‐leaved tree forests and oak woodland. In spring 1991, bird densities were highest inProsopisthorn forest and mixed woodland, and lowest in oak woodland. Bird species‐richness was low in oak woodland, in both seasons, and high in mixed woodland andIpomoeaforest in spring. Bird species composition between forest types was more similar in the spring than autumn. The spring similarity in species composition is explained by the presence of generalist species in times of food scarcity during the dry season, and by the homogeneity of the predominantly leafless vegetation. Comparison with the bird species composition of a dry forest in Venezuela and the Pacific coast of Mexico indicates that the sites in the present study have an intermediate number of species. Although the present study recorded a smaller number of bird species than on the Pacific coast, 16 were different, expanding the total for Mexican dry forest by 14% from 118 to 134.

Breeding systems in a secondary deciduous forest in Venezuela: The importance of life form, habitat, and pollination specificity

Breeding systems and mating systems of plants in a previously studied secondary deciduous forest were reanalysed in the context of new data. In this analysis, we increased the number of plant species (up to approximately 25% of the plant species in the community), included other life forms (23 annual and perennial species, plus habitat disturbance categories), and considered information about pollinator specificity. The frequencies of species with different sexual systems in a sample of 51 species were 82% hermaphrodite, 14% monoecious, and 4% dioecious. The frequencies of breeding systems in the sample of 49 hermaphroditic and monoecious species were 53% self-incompatible and 47% self-compatible. Self-compatible species included seven partially self-compatible, three self-compatible non-autogamous, and 13 self-compatible autogamous species. None of the species evaluated proved to be agamospermous. Fifty-five percent of the species tested were obligate outbreeders. The proportion of self-incompatible species was higher among trees and shrubs than among annual herbs. The proportion of self-compatible species for perennial herbs and lianas was not different. The association between annual herbs and autogamy was not strong: seven of 13 species were autogamous, five were partially self-compatible, and one was self-incompatible. The main characteristics or factors associated with breeding system were life cycle and successional stage. Short-lived species were mostly self-compatible, and xenogamy tended to be associated with forest and forest-border. In contrast, pollination specificity and life form were not consistently related to breeding system (self-compatibility or self-incompatibility) and mating system (xenogamy or autogamy).

A test for the adequacy of bioindicator taxa: Are tiger beetles (Coleoptera: Cicindelidae) appropriate indicators for monitoring the degradation of tropical forests in Venezuela?

Indicator species can be a valuable tool for conservation research. Their use has been divided in two categories: inventory studies and monitoring studies. Tiger beetles (Coleoptera: Cicindelidae) have been identified as appropriate indicators for inventory studies. Here we test their value as potential bioindicators for monitoring habitat degradation in Venezuela. We analyze the general habitat associations of 47 of the 51 species of this insect family known to occur in Venezuela. We also analyze the assemblage patterns of forest-floor dwelling species associated with contiguous forest patches of primary and secondary forest in two sites. At the family level, tiger beetles occupy most of the major habitat types of Venezuela, but individual species tend to be restricted to one or two habitats. Forest-floor species assemblages change significantly with the degree of forest disturbance, and each stage of disturbance is characterized by a particular subset of species. Species associated with intermediate levels of disturbance show larger habitat breadth than those located at the extremes of the spectrum. The results of this study provide evidence that supports the use of tiger beetles as bioindicators for monitoring the degradation and regeneration of tropical forests.

Hydraulic Conductance and Water Potential Differences Inside Leaves of Tropical Evergreen and Deciduous Species

Several pieces of research suggest that leaf liquid-path conductance (K1) may be smaller in evergreen species (EG) than in deciduous species (DC), coexisting in tropical dry forests. This was investigated in four DC and two EG in a tropical dry forest in Venezuela. The K1 (kg m-2 MPa-1 s-1) were consistently lower in EG (8.4 × 10-5) than in DC (12 to 20 × 10-5). Differences in water potential (ΔΨW) inside the leaves were calculated using K1 values in connection with maximum transpiration rates measured in the field. It was found that ΔΨW was about 1.9 MPa in EG, intermediate for one DC (Pithecellobium dulce, 1.7 MPa) and minimum for other DC (1.0 to 1.3 MPa).