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The conversion of montane cloud forests into pastures for grazing cattle is the main cause of important impacts on rivers and streams in most of the Andes. In order to evaluate the effects of vegetation changes we need to understand water fluxes, particularly canopy interception. We measured net precipitation responses by the canopies of Pennisetum clandestinum Hochst. ex Chiov. and Melinis minutiflora Beauv. under simulated rainfall. The samples were taken from grazed pastures during 1 year, digging out round mats of grass, placing them on wire-mesh devices after eliminating soil and underground biomass, and irrigating with different water amounts. The resulting data allow us to present a validated model for each species that predicts percentage of interception at different precipitation intensities taking into account previous canopy wetness within determined biomass ranges. We use these models to estimate 2 years of interception values for pastures of both species in the upper watershed of El Canadon, Capaz River, Venezuelan Andes. Mean annual precipitation of El Canadon is 1244 mm and the estimate of pasture interception was 36.5% and 31.8% for P. clandestinum and M. minutiflora , respectively. Interception models, such as the ones derived in this study, provide a basis for quantifying interception rates as a function of previous wetness of canopies and grass species.

This comparative study of soil erosion considered different environments in an ecological unit of the Venezuelan Andes. The soils belong to an association of typic palehumults and humic dystrudepts. Soil losses were quantified by using erosion plots in areas covered by four types of vegetation, including both natural and cultivated environments. The highest soil erosion rate evaluated corresponded to horticultural crops in rotation: reaching a value of 22 Mg ha−1 per year. For apple tree (Malus sylvestris Miller) plots, soil losses reached values of 1.96 Mg ha−1 per year. Losses from pasture (Pennisetum clandestinum Hochst. ex Chiov.) plots, without livestock grazing, were as high as 1.11 Mg ha−1 during the second year of the experiment. The highest soil losses generated from plots under natural forest were equal to 0.54 Mg ha−1 per year. Environmental factors such as total and effective rainfall, runoff, and some soil characteristics as those related to soil losses by water erosion were evaluated. The type of management applied to each site under different land use type and the absence of conservation practices explain, to a large extent, the erosive processes and mechanisms.

Chamaedorea bartlingiana is a dioecious palm that grows in the cloud forest understories of the Venezuelan Andes. Age and sexual differences in phenology and reproductive patterns were studied in labelled individuals of all age categories. This species has long-lived leaves and low leaf production, both characteristic of understory plants. Growth rates are lower in juveniles than in adults and in females than in males, as in other palms. Male and female individuals show different reproductive patterns. Male inflorescences are always produced at the same rate and the probability of surviving until anthesis is constant. Females produce reproductive buds at the same rate as males, but these buds have a 35% probability of becoming a ripe infrutescence if the plant has infrutescences already growing, and 70% if it does not. This pattern and the slow growth of inflorescences (1 year for males from bud to flowers, 2 years for females from bud to ripe fruits) cause a pluriannual reproductive pattern at the population level. Field germination does not follow this pattern, but shows one annual peak probably related to environmental conditions.

Sweep samples of insects at 200, 1600, 3550, and 3600 m elevation in secondary vegetation in the Venezuelan Andes near Merida show that the greatest number of insect species and dry weight occurs at the intermediate elevation, that the species richness of Diptera and parasitic Hymenoptera is not as proportionately reduced by elevation as is the species richness of other insect groups, that at higher elevations there are a reduced number of species and an increasingly unequal distribution of the individuals among the species, and that large insects are much less abundant at high than low elevations. These results confirm trends first indicated in an earlier elevational transect of Costa Rican insects. WE REPORT the results of sweep sampling the insect community at 3600 m, 3550 m, 1600 m, and 200 m elevation in the Venezuelan Andes near Merida, and at 3380 m in Costa Rica. The study is a continuation of the examination of large scale heterogeneity in tropical insect community structure that was initiated by Janzen (1973a,b). Here, we ask how sweep samples of low secondary vegetation differ at elevations characterized by paramo, mid-elevation evergreen forest which is generally converted to coffee and sugar cane plantations in Venezuela, and lowland ("tierra caliente") evergreen forest, which is generally converted to cattle pasture and sugar cane in Venezuela.