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The pa Âramo is a high-altitude ecosystem of the northern Andes. The vegetation is continuous, with grasses as the dominant groundcover. Because of their high water retention, pa Âramos play a fundamental role in water availability for all the population of the inter-Andean valleys. There are many studies of this speci®c ecosystem, but very few are focussed on overgrazing and its effect on vegetation and soil properties.Intensive grazing started less than 20 years ago and was studied in a representative area in the western Cordillera of central Ecuador covered by recent volcanic ash deposits. Intensive sheep grazing has led to a strong decline in the number of plant species, the replacement of the tussock grass vegetation by a short carpet grass vegetation, and an increase of bare land. In that area, the upper 50 cm of Andisols are deeply affected by a convergent decrease of Al and Fe oxalate and pyrophosphate in soil extracts, carbon contents decrease from 100 g kg ±1 to less than 50 g kg ±1 in the humid zone, from 70 to 40 g kg ±1 in the dry zone and a reduction of water-retention capacity at ±33 kPa matrix potential from 800 g kg ±1 to 200 g kg ±1 in humid zones, from 350 to less than 100 g kg ±1 in drier areas. They showed also a decrease in the macrostructure and the development of a highly water repellent microstructure. All these important transformations favour the development of aeolian erosion in dry areas, runoff on bare surfaces, and gully erosion on slopes. The role of the pa Âramo in water-regulation of this ecosystem seems to have been adversely affected for the future.

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The impact of extensive livestock farming on the physical and chemical characteristics of the volcanic soils and on the nutrient status of green plant tissues of neotropical alpine grasslands (p~amo) is studied. Soil and plant samples were taken over a one-year period at five sites with different agricultural (grazing and burning) management. In the undisturbed pAramo ecosystem, soil moisture (50-250%) and organic matter content are high (7-27%) and decomposition (11-35% yr -1) and element concentrations are low. Low temperatures (max < 10°C) and phosphorus fixation by the soil (5 mg P g-1 soil) determine the low mineralization and turn-over rates.Multivariate analysis of laboratory results indicates that the season of sampling and the agricultural practice are the most important explanatory factors for variation of soil characteristics. After long-term heavy grazing, soils have a higher bulk density and a lower moisture content. The outcome of a litterbag experiment confirms the hypothesis of higher decomposition rates at grazed sites. In the intermediate (wet-dry) season, conditions were somewhat better for plant growth but the system remained nutrient limited. Surprisingly, no relation between soil density, moisture or carbon content and concentrations of available nutrients in the soil is found. This is supported by the rather uniform nutrient concentrations in green plant tissue among the sites. It is concluded therefore that the effect of burning and grazing on p~amo soils is principally restricted to physical characteristics, and that differences in chemical characteristics of the soil do not cause differences in vegetation structure between grazed, burned and undisturbed sites.

Aim In tropical rain forests, epiphytes can contribute signi®cantly to species diversity and biomass, a feature not generally associated with temperate forest systems. This study investigates epiphyte-liane diversity and biomass on three host trees (two Dacrycarpus dacrydioides [Podocarpaceae] and one Nothofagus menziesii [Fagaceae]).Location These trees were of varying architecture on different sites in a New Zealand lowland temperate rain forest at 45°43¢ S.Methods Cover of epiphytic and lianoid species (vascular and non-vascular) was recorded in 5 m vertical height segments (trunk), on four aspects (north, south, east and west); and in four sections (inner, middle, outer branches and branch extremes) on four branch faces (positions: topside, both sides, underside) on each tree. Inclination, branch face, and diameter of branch/trunk substrate, height above ground, duff thickness, and location on tree (trunkfoot, main trunk, inner branches, middle branches, outer branches, branch extremes) were all recorded in 359 samples. Epiphytic biomass was derived for one tree.Results Sixty-one vascular and ninety-four non-vascular taxa were recorded. Eight communities associated with the highly vegetated inner branches and main trunk, and seven indicative of the less vegetated middle to outer branches and branch extremes were recognized. Thirteen of the ®fteen communities were present on a forest interior D. dacrydioides tree, nine on a riverside D. dacrydioides tree and seven on a N. menziesii tree. Most of the seven measured environmental variables were statistically signi®cant in relation to ordination analyses of the samples. Dry mass per unit area and dry bulk density recorded were 350 AE 125 and 118 AE 13 g dm ±2 , respectively (trunkbase), and 206 AE 21 and 91 AE 4 g dm ±2 , respectively (inner and middle branches combined).Main conclusions Epiphytic community analyses that do not include non-vascular¯ora either as generalized categories or as individual taxa are incomplete. Values for epiphytic dry weight for the trunkfoot of one tree appear to exceed comparable ®gures recorded from tropical rain forest systems. Epiphytic communities and biomass within at least some temperate rain forests can be validly compared with those of tropical rain forests.

Pollen analysis of a 150-cm-long core from Pantano de Pecho (0°20′S, 78°37′W) at 3870 m altitude in the Ecuadorian páramo documents altitudinal migrations and the composition of the upper forest line prior to deforestation. Four successive radiocarbon dates of 293 ± 41 14C y BP, 498 ± 40 14C y BP, 626 ± 33 14C y BP, and 729 ± 44 14C y BP show that the record includes the last c. 730 radiocarbon y, corresponding to the last c. 660 calendar years (cal y BP). The natural upper forest line was at a minimum altitude of 3400-3500 m between c. AD 1290 to 1315 (zone 1), from c. AD 1315 to 1350 at 3500-3600 m (zone 2), from c. AD 1350 to 1640 at 3600-3700 m (zone 3), from c. AD 1640 to c. 1765 at 3750 m (zone 4), and from c. AD 1765 to the present at 3700-3650 m (zone 5). The most important taxa were Alnus, Hedyosmum, Miconia, other Melastomataceae, Gunnera and Solanaceae. Since c. AD 1350 Podocarpus was continuously present with low abundance, but possibly not close to the upper forest line. Rarer elements of the upper montane forest were Dodonaea, Myrsine, Weinmannia, Myrica, Myrtaceae, Sapium, Juglans, Piper, Euphorbiaceae and Rubiaceae. Human disturbance and deforestation are shown by the presence of Rumex, Spermacoce pollen and charcoal particles. We surveyed the vegetation composition from isolated forest patches located between 3650 m and 4300 m. TWINSPAN analysis indicates forest patches up to 3950 m have a similar floristic composition to closed forest below the upper forest line. We argue that this apparent similarity does not necessarily mean that the slopes between 3750 and 3950 m were covered by closed forest in the past.