The abundance and diversity of lianas were examined along a tropical forest chronosequence at the Barro Colorado Nature Monument, Panama. Lianas ≥0.5 cm diameter were sampled along transects in two replicated stands in secondary (20, 40, 70 and 100 y after abandonment) and old-growth (>500 y) forests. Ordination of stands based on relative abundance, but not presence-absence, showed a significant separation of stands by age. Lianas were significantly more abundant and diverse (Fisher's α) in younger forests (20 and 40 y) than in older forests (70 and 100 y, and old-growth). The decline in liana abundance with stand age was offset by increased mean basal area per individual, resulting in a relatively constant total basal area and estimated biomass across stand age. The proportions of tendril climbers decreased and stem twiners increased over stand age. Decline in liana abundance and changes in liana composition may be related to changes in support and light availability. Although lianas are recognized as playing an important role in the early secondary sucession of many tropical forests, these results have shown that their important contribution to total basal area and biomass can continue as the forest matures, even as the numbers of established lianas declines.

The Atlantic forest of Brazil is considered to be a high priority for conservation in South America. Despite its importance, few phenological and ecophysiological data are available for plants of this area. In this study the seasonal changes in the water potentials (Ψ) and the phenological behaviour of three woody legumes are related to environmental conditions, particularly air vapour pressure deficit (VPD). The values of Ψ at predawn were greater than −0.75 MPa for all species even during the dry season (May–September). The minimal daily value of Ψ was −3.8 MPa. The maximum daily amplitude of Ψ (Δ parameter) was correlated with the air vapour pressure deficit, showing high correlation coefficients in linear equations. A high recovery rate of Ψ after rain (greater than 0.80) was registered for all species, suggesting a high hydraulic conductivity. The high values of Ψ at predawn during the year and the strong relationship between the daily amplitude of Ψ and VPD suggested that the changes in the canopy cover are related more to atmospheric drought than to soil water deficit.

ABSTRACT. Multi-species bird flocks in tropical forests are maintained throughout the annual cycle despite seasonal differences in resource availability, and the reproductive schedules and ecological requirements of individual species. This study examines the relationship between seasonal variation in flock structure and the availability of fruits and arthropods over a 12-mo period at a coastal Atlantic forest within the Juréia–Itatins Ecological Station, São Paulo, Brazil. Fruit abundance was estimated by a phenological survey of both canopy and understory trees, whereas arthropod abundance was quantified monthly on the basis of a nocturnal visual census technique. The seasonal variation in flock structure and composition was affected by both the breeding seasons of different core and attendant species, and the availability of food resources. The number of bird species attending flocks was greater during the dry season, declining thereafter during the breeding season. Understorey fruit availability exhibited a marked seasonal fluctuation with the lowest levels between the late dry and early wet season. Seasonal variation in canopy fruit availability, on the other hand, was far less demarcated than that of understorey plants. Arthropod abundance was greatest during the wettest months of the year, which apparently determined the timing of the main breeding season. Bird species richness attending flocks was, therefore, significantly correlated with the availability of understorey arthropods, but not with that of either understorey and canopy fruits. Arthropod abundance thus appears to affect profoundly the reproductive schedules of the understorey avifauna, which in turn influences the seasonal variation of flock size and composition.

RESUMO. Nas florestas tropicais a formação de bandos mistos de aves ocorre ao longo de todo o ano, porém existem variações sazonais na composição e estrutura destes bandos. Tais variações estão ligadas ao período reprodutivo das aves, à disponibilidade de recursos alimentares e a requisitos ecológicos inerentes a cada espécie. Este trabalho analisou a dinâmica sazonal destes bandos durante um ano, relacionando estes dados com a disponibilidade de recursos alimentares em uma área de Mata Atlântica na Estação Ecológica Juréia–Itatins. A disponibilidade de frutos foi estimada através de acompanhamento fenológico de espécies de dossel e de sub-bosque, enquanto a abundância de artrópodos foi feita através de censos noturnos mensais. A variação sazonal na estrutura e composição dos bandos foi afetada pela atividade reprodutiva das espécies mais freqüentes e pela disponibilidade de recursos alimentares. Nos meses mais secos ocorreu um aumento do número de espécies nos bandos, ocorrendo um declínio durante o período de reprodução das aves. A quantidade de frutos de sub-bosque apresentou maior escassez entre o final do período seco e o início do período chuvoso, variando de maneira muito mais drástica quando comparada aos frutos de dossel. A abundância de artrópodos foi maior durante os meses mais chuvosos do ano, coincidindo com a época reprodutiva das aves. A riqueza das espécies de aves associadas a bandos mistos foi significativamente correlacionada com a abundância de artrópodos, mas não com a disponibilidade de frutos de dossel e sub-bosque. A abundância de artrópodos deve ter influenciado o início das atividades reprodutivas das aves, que por sua vez, causou as variações sazonais na composição e tamanho dos bandos.

Swamp forest covers c. 2600 ha of coastal wetlands in Guadeloupe. An inventory of all vascular plants was conducted together with a characterization of the main abiotic descriptors within seventeen 10-m × 40-m plots, systematically sampled throughout the forest. Girth at breast height (GBH) was measured for all trees ≥10 cm GBH. Four forest types were discriminated according to pH, clay content and redox potential of the soils. Among the 107 species recorded, lianas and epiphytes were as much represented as tree species (28%). However, no epiphytes were encountered at the canopy level where Pterocarpus officinalis (Papilionaceae) was the evenly dominant tree. Local hummock-hollow topography was responsible for an aggregated distribution of P. officinalis. This species exhibits several adaptative traits which may explain its dominance over all of the lowland swamp forests subjected to permanent waterlogging in the hurricane-prone Caribbean islands.

Tepuis are uplifted mountains surrounded by forest or savannas in the Guayana Shield in northern South America. Large areas of the summits of these mountains are characterized by bare rock with vegetation isolates (‘islands’) that vary in size from less than 1 m2 to over 100 m2. The species composition, species–area relationships and the factors involved in the formation of these vegetation islands were quantified on Roraima Tepui, Canaima National Park, Venezuela. A total of 40 species were present on the islands, 35 of which were angiosperms. Orchidaceae was the family with the highest diversity, but Bonnetiaceae, Poaceae and Rapateaceae achieved higher coverage. A positive correlation between island size and species richness was found. This relationship was not linear and the best fit model between island size and richness was exponential. Of the environmental variables studied, the highest correlation was found between the log of soil volume and species richness. Soil nutrient availability, and not water, might be the limiting factor determining the species composition and diversity of these communities.

(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.

Leaf water and osmotic potentials and gas exchange were monitored during a prolonged El Niño drought in 1998 for saplings of seven species in a Bornean heath forest and compared with measurements taken during a subsequent wet period. The four dipterocarp species maintained reasonably good water status throughout the drought, especially Dipterocarpus borneensis which had thick and deep tap roots. In contrast, two of three non-dipterocarp species, Cleistanthus baramicus and Tristaniopsis obovata displayed predawn leaf water potentials approaching their turgor-loss points. During the drought, all species except D. borneensis displayed strongly reduced stomatal conductance after a brief exposure to sun, and all displayed lower maximum rates of stomatal conductance and net photosynthesis than during the wet period. Only Cotylelobium burckii displayed significant osmotic acclimation to the drought. T. obovata possessing a superficial root system suffered a high mortality due to the drought, but recovered faster after the first rains than the other species all of which had tap roots. Deep roots and strong stomatal control favour trees in tropical heath forests where water deficits probably occur regularly.

Patterns of dispersion and site fidelity were investigated in a tent-roosting population of the short-nosed fruit bat, Cynopterus sphinx (Megachiroptera), in southern India. A local population of C. sphinx occupied diurnal roosts in a variable subset of 45 stem tents constructed within the dense foliage of mast trees (Polyalthia longifolia). Individually marked tent-roosting bats were visually censused over the course of a 38-d interval spanning the postpartum oestrus period. On any given day, 33.3–85.7% (mean = 60.8%, SD = 14.2) of adult males roosted singly, with the remainder holding harems of 1–10 breeding females (mean = 3.01, SD = 0.79). Average harem sex ratio was 2.8-fold higher than the adult sex ratio of the total tent-roosting population within the study area, indicating the potential for a high variance in male mating success within a single breeding season. Bats of both sexes typically occupied one primary tent, interspersed with shorter periods of residency in alternate tents. Males exhibited a significantly higher degree of roost fidelity than females. Some females roosted sequentially with different males and with different combinations of females, whereas others remained continuously associated with a single male and/or particular female roostmates over the duration of the census period. There were no statistically significant relationships between physical characteristics of tents and rates of occupancy by males or females. Intermittent transfers by females between groups suggest that the defence of diurnal roosts by males represents a more profitable mating strategy than the direct defence of compositionally labile female groups.

Elephant populations have declined greatly in the rain forests of Upper Guinea (Africa, west of the Dahomey Gap). Elephants have a number of well-known influences on vegetation, both detrimental and beneficial to trees. They are dispersers of a large number of woody forest species, giving rise to concerns that without elephants the plant diversity of Upper Guinean forest plant communities will not be maintained. This prospect was examined with respect to four sources of inventory and research data from Ghana, covering nearly all (more than 2000) species of forest plant. Evidence supporting the hypothesis that plant populations are collapsing without elephants is conspicuously absent in these datasets, although Balanites wilsoniana is likely to suffer dramatically on a centennial scale in the absence of forest elephants. A few other species are likely to decline, although at an even slower rate. In the context of other processes current in these forests, loss of elephants is an insignificant concern for plant biodiversity. Elephant damage of forests can be very significant in Africa, but loss of this influence is more than compensated for by human disturbance. Elephants have played a significant part in the shaping of West African rain forest vegetation. However, it is the conservation of elephants that should be of primary concern. Tree populations should be managed to promote them, rather than vice versa.