Fog interception and rainfall were measured at 14 stations across the Central Cordillera in western Panamá. Fog interception and rainfall were measured monthly during 1988–1989 with artificial fog catchers and rain gauges, respectively. Fog interception was highest on ridges and increased with increasing altitude. Fog interception contributed between 2.4 and 60.6% of the total water input, depending on altitude and exposure to the prevailing winds. Absolute amounts of annual fog interception ranged from 142 to 2295 mm. Although low clouds were more frequent in montane forests, clouds close to the ground also occurred in the lowlands. During the study period, there was a gradient of increasing total rainfall from the Caribbean (3355 mm) to the Pacific side (5759 mm) of the Central Cordillera. Nevertheless, rainfall was more seasonal on the leeward side of the mountain range. Seasonal variation in fog intereption was different from rainfall patterns and no correlation was found between monthly (or annual) rainfall and fog interception. The results of this study showed the importance of montane forests for the preservation of water sources, particularly along ridges of the Fortuna drainage basin that provides more than 50% of the electricity of the Republic of Panamá.

Fog interception and rainfall were measured during one year in three elfin cloud forests on small mountains along the Caribbean coast of South America and one in the Venezuelan Andes. (1) While rainfall increases from west to east in the small mountains along the coast, fog interception decreases. In 1985, the total annual rainfall and fog interception were 853 mm and 796 mm in the cloud forest of Serrania de Macuira, 1630 mm and 518 mm in Cerro Santa Ana and, 4461 mm and 480 mm in Cerro Copey. In the Andean forest of El Zum-bador, the 1985 rainfall was 1983 mm and the annual fog interception was only 72 mm. (2) Fog interception seems to be an important source of water to the elfin cloud forests of the small mountains which are surrounded by dry vegetation types and where the rainfall regime is highly seasonal. (3) Fog interception increases with altitude (in the same mountain), exposure (windward slopes) and leaf inclination. These variations of fog interception could partially explain the observed distribution of epiphytic flora in some of these cloud forests.

Distribution patterns of vascular plants with diameter at breast height (dbh) ≥ 2.5 cm were studied on the basis of compositional data from 30 small plots located in a rain-forest area in Colombian Amazonia. The research questions were: How are distribution patterns of species in relation to local abundance in plots? Do understorey species (defined as species with individuals that never attained dbh ≥ 10 cm anywhere) show better correlations with soils and environment than canopy species (defined as species with individuals that attained dbh ≥ 10 cm)? Are patterns found in the entire range of landscape units comparable to those found in well-drained uplands alone? Species that occurred in more than one plot showed higher local abundances. This pattern was consistent among environmental generalists and specialists. Locally rare species (with only one individual in a plot) occurred mostly in well-drained uplands. Considering all landscape units, Mantel tests showed substantial correlations between environmental data (soil chemical data, drainage and flooding) and species composition. Canopy species were only slightly less correlated with environmental data than understorey species. Elimination of the spatial component in the data did not reduce these correlations. In well-drained uplands, understorey species were better correlated with soils than canopy species. Here, however, the spatial configuration of the plots became more important in explaining species patterns.

Daily and seasonal activity of the mountain tapir Tapirus pinchaque was measured along trails and at two salt licks in mature and secondary montane forests of the Central Andes of Colombia using active and passive infrared monitors. Daily activity of the mountain tapir showed a clear bimodal pattern, with maxima during the early hours of the day (5:00–7:00) and early hours of the evening (18:00–20:00). This bimodal activity pattern has also been found in radio-tracking studies of T. terrestris and T. bairdii. Overall, there was more activity in mature than in secondary forest and at lower (3100 m) than higher altitudes (3600 m). Night-time activity was higher during full moon than during quarter and new moons. There was no correlation between monthly rainfall and seasonal activity. The time the mountain tapir was at the salt licks varied between 1 and 190 min. Daily activity at Quebrada Paraiso salt lick (3400 m) showed a clear bimodal pattern with maxima around midnight (0:00–2:00) and midday (11:00–14:00). These patterns of diurnal and nocturnal activity of the mountain tapir could be used in combination with future radio-tracking studies to better understand habitat use by this species.

(Accepted 31st July 1999)

In the ‘elfin’ cloud forest of Serrania de Macuira, exchangeable ammonium and nitrate, and the rates of soil nitrogen mineralization and nitrification were measured in soil samples under different water, temperature and mineral nutrient additions. The effects of nitrogen, phosphorus and nitrogen plus phosphorus fertilization on radial trunk growth were measured in three tree species. In the cloud forest soils, concentrations of ammonium were much higher than those of nitrate. Nitrate was higher in samples collected during the afternoon than during the morning, probably as a result of leaching during the night or nitrification during the day. When samples were incubated under different water and temperature treatments, rates of nitrogen mineralization and nitrification increased more with changes in soil water content than with changes in temperature. Nitrification was significantly increased in soils amended with ammonium or with ammonium plus phosphorus, suggesting that nitrification is substrate-limited. Fertilization with nitrogen and phosphorus resulted in significantly increased girth increments in Guapira fragrans (Dum. -Cours.) Little and Rapanea guianensis Aublet. Myrcianthes fragrans (Sw.) D.C. did not respond to the fertilization. The results of this study support the hypothesis that the characteristics of montane rain forest in small and large tropical mountains (the ‘Massenerhebung’ effect) are greatly controlled by soil water conditions and related soil nitrogen availability.

Information is presented on the phenology, herbivory, phytochemistry and production of the tree species Polylepis quadrijuga. Leaf production was lower during the dry season than during the wet season, when minimum temperatures also occurred. Flower and fruit phenology were also seasonal. Herbivory was significantly higher for leaves expanded during the wet season (20%) than during the dry season (1%), and was also higher for younger leaves. Flavonoids, compounds known as UV-B protectors, were found in high concentration in leaves of P. quadrijuga. There was a significant positive relationship between monthly rainfall, monthly minimum temperatures and flavonoid concentration, but no relationship was found with leaf age. The annual fine litterfall for the Polylepis forest was estimated to be 3.9 t ha−1 y−1, a high value when compared to other paramo and upper montane rain forests in tropical mountains. High production was associated with high leaf nitrogen concentration (3.0–3.5%), high rates of nitrogen retranslocation (80% dry weight), and relatively low leaf longevity (8.4 mo). High production in P. quadrijuga is probably a key factor in explaining the existence of this large woody species in a paramo environment otherwise dominated by bunch grasses, cushion plants and giant rosettes of the genus Espeletia.