The relationship between seedling recruitment (under and away from parent trees) and the behaviour of seed dispersers and predators, was explored in a three-year study in Kibale National Park, Uganda. On the basis of 1261 hours of observation, the foraging activity of the diurnal frugivores which fed on fruit from six tree species was quantified. The fate of dispersed and non-dispersed seeds and seedlings was examined experimentally. The findings suggest that a trade-off exists between factors that promote seedling growth in areas with high seedling density and factors that promote dispersal by frugivores. For example, dispersal of Mimusops bagshawei increases both seed and seedling survival; seeds placed away from adult conspecifics had a 8% lower probability of disappearing than seeds placed under adults and seedlings away from adults had a 30% greater probability of surviving than seedlings grown under adults. In contrast, for Uvariopsis congensis, dispersed seeds had a 56% greater probability of disappearing than seeds directly under a parent tree, while the survival of dispersed and non-dispersed seedlings was similar. Non-dispersed seed and seedling disappearance were correlated with the percentage of the fruit crop removed from focal trees, suggesting that the ability to survive under an adult maybe related to other aspects of the tree's life history.

The Kibale Forest, western Uganda, is the only site where studies have compared the impact of elephants on rainforest regeneration in logged and unlogged control areas. Elephants used heavily logged areas more than lightly logged and unlogged areas. Forest gaps were used more by elephants than closed-canopy areas and large gaps more than small ones. Gaps were larger in logged than unlogged forest. There were lower densities of young trees (saplings and poles) and a higher incidence of elephant damage to them in heavily logged forest than in lightly logged and unlogged sites. Elephant use of an area and damage to young trees was inversely or unrelated to the density of young trees and directly related to the density of herbaceous tangle. Heavy logging resulted in large areas of herbaceous tangle, which attracted elephants who suppressed forest regeneration by damaging young trees and perpetuating the herbaceous tangle. The tangle directly competed with regeneration of young trees while also attracting elephants and rodents (seed and seedling predators) and facilitating increased windthrow of trees. Selective browsing of young trees by elephants affected rates of regeneration, growth form and species composition. Rather than remove elephants, a more effective and humane approach to long-term management of logging is to reduce logging offtake and incidental damage caused by timber extraction.

The abundance of all tree and shrub species has been monitored for eight years in a 50 ha census plot in tropical moist forest in central Panama. Here we examine population trends of the 219 most numerous species in the plot, assessing the impact of a long-term drying trend. Population change was calculated as the mean rate of increase (or decrease) over eight years, considering either all stems ≥10 mm diameter at breast height (dbh) or just stems ≥100 mm dbh. For stems ≥10 mm, 40% of the species had mean growth rates <1% per year (either increasing or decreasing) and 12% had changes ≥5% per year. For stems ≥100 mm, the figures were 38% and 8%.

Species that specialize on the slopes of the plot, a moist microhabitat relative to the plateau, suffered significantly more declines in abundance than species that did not prefer slopes (stems ≥10 mm dbh). This pattern was due entirely to species of small stature: 91% of treelets and shrubs that were slope-specialists declined in abundance, but just 19% of non-slope treelets and shrubs declined. Among larger trees, slope and non-slope species fared equally. For stems ≥100 mm dbh, the slope effect vanished because there were few shrubs and treelets with stems ≥100 mm dbh. Another edaphic guild of species, those occurring preferentially in a small swamp in the centre of the plot, were no more likely to decline in abundance than non-swamp species, regardless of growth form. Species that preferentially colonize canopy gaps in the plot were slightly more likely to decrease in abundance than non-colonizing species (only for stems ≥10 mm dbh, not ≥100 mm). Despite this overall trend, however, several colonizing species had the most rapidly increasing populations in the plot.

The impact of a 25-year drying trend and an associated increase in the severity of the 4-month dry season is having an obvious impact on the BCI forest. At least 16 species of shrubs and treelets with affinities for moist microhabitats are headed for extinction in the plot. Presumably, these species invaded the forest during a wetter period prior to 1966. A severe drought of 1983 that caused unusually high tree mortality contributed to this trend, and may also have been responsible for sharp increases in abundance of a few gap-colonizers because it temporarily opened the forest canopy. The BCI forest is remarkably sensitive to a subtle climatic shift, yet we do not know whether this is typical for tropical forests because no other large-scale censuses exist for comparison.

A comparative study of the damage caused by Hurricane Hugo on the three main types of forest in the lesser Antilles was carried out in the mangrove forest, the semi-evergreen forest and the rainforests of Guadeloupe. Hurricane impact on these forests showed at first that high canopy trees generally prevented understorey trees from heavy direct damage (shield effect). In the species-poor, structurally homogeneous stands, in the mangrove forest, species' susceptibility was the major determinant in both intensity and type of damage. Damage was heavy in places and showed a certain spatial uniformity. In the rainforest, the high structural complexity of the vegetation generally induced a great variability in the spatial distribution of damage even at a small scale. Due to the presence of tall trees, indirect damage was locally very heavy. Clumps of large trees formed resistant structures which diminished lethal damage below the main canopy (cluster effect). In such a highly structured, species-rich forest, species' susceptibility was concealed at the local scale by the prevailing influence of vertical structure. Because of its relatively rich flora but low stature, the semi-deciduous forest exhibited intermediate patterns of damage. It was concluded that floristic composition and forest structure help to explain, and to predict, hurricane damage to forest cover.

Ant species were sampled in three rainforest and 10 rehabilitated bauxite mine plots at Trombetas, in the tropical monsoonal region of Brazil. Rehabilitation ranged from 0 to 11 years in age and was mainly performed by planting mixed native forest tree species. One plot supported single-species blocks of Australian Eucalyptus and Acacia species. Two hundred and six ant species were recorded, of which 82 were exclusively found in the native vegetation, 54 were confined to the rehabilitation and 70 were found in both situations. In contrast with other studies, ant species richness in the Eucalyptus/Acacia plantation was as great as in the areas rehabilitated with native vegetation. The overall rate of return of ant species was considerably greater than in mines situated within subtropical regions of Brazil, Africa and Australia. However, if the greater richness of ants in the native vegetation at Trombetas was accounted for, the proportional return of the original ant fauna was not particularly rapid. The return of ant species slowed as the rehabilitated areas aged. In comparison with forest, the rehabilitation was characterized by proportionately more generalist species and fewer specialists, especially from the soil and litter layers. The full range of habitat requirements for the ant community has not been restored by the eleventh year of rehabilitation and further management may be required to enhance the degree of colonization. It is suggested that the findings for ants may apply to other components of the biota as well.

The effect of canopy species dominance on understorey light availability in secondary forests was examined for Pentaclethra macroloba and Goethalsia meiantha, two common tree species with contrasting canopy architecture at La Selva Biological Station in the Atlantic lowlands of Costa Rica. In each of six 12- to 16-year-old successional stands dominated by one of these species, relative abundance and basal area of the focal species were determined within a 20 m × 50 m plot. Light availability at 1 m height was measured within each plot using a Licor-2000 Plant Canopy Analyzer at 27 locations and by analysing hemispherical photographs taken at 10 locations. Across stands, mean LAI values were significantly negatively correlated with canopy openness. Understorey microsites beneath Pentaclethra had significantly higher light availability than microsites beneath Goethalsia. Across stands, however, light availability was not correlated with either total basal area or stem density of trees ≥10 cm DBH. These results indicate that basal area and stem density of trees in the upper levels of the forest canopy are poor predictors of light penetration to the understorey. One hypothesis suggested here is that dense subcanopy and understorey vegetation in tropical secondary forests can strongly influence understorey light levels. Alternatively, light transmittance characteristics of the upper forest canopy may be influenced by species-specific differences in canopy architecture or foliage density that vary independently from tree diameter and density.

The dispersal of African Acacia seeds in the presence and absence of large mammalian herbivores and ostriches was assessed in a savanna ecosystem in South Africa. In the absence of large herbivores, A. tortilis and A. nilotica pods were mainly dispersed in the shade, directly beneath the tree crown and seeds remained in pods for over 18 months. In the presence of large herbivores, A. tortilis, A. nilotica and A. karroo seeds were freed from pods and were dispersed into open, non-shaded habitats. Impala dispersed most A. tortilis seeds (18,900 ha−1), giraffe most A. nilotica seeds (1060 ha−1) and giraffe and kudu most A. karroo seeds (452 and 448 ha−1, respectively). Seedling survival in dung in open environments may exceed that of seedlings in soil shaded beneath the tree crown. It appears that seed dispersal by large herbivores may be advantageous to future seedling recruitment.

To examine the potential contribution of herbarium material to the description and analysis of tropical tree phenology, flowering times and geographical distribution were graphed for 1673 flowering collections from 18 species native to Neotropical dry forests and phenological differences between species were analysed. These include the timing and duration of flowering as well as morphological differences such as flowering on leafless twigs vs flowering on shoots bearing old or new foliage. Species-specific flowering periods of herbarium collections are similar to those observed in phenological field studies, but are often longer because of the larger geographical and temporal sampling range. Conspecific collections of different geographical origin show distinct differences in flowering periodicity, which are correlated with differences in the timing and intensity of the dry season. Interspecific differences in the timing of phenology relative to the dry season indicate differences in the control of phenology by seasonal drought. Herbaria thus represent a large potential source of phenological information which can either supplement and extend phenological field studies or provide phenological information for dry forest species not studied in the field but well represented in herbarium collections.

Evidence from southern African semi-arid savannas suggests that high elephant densities in nature reserves cause the over-utilization of woodlands. Northern Botswana, with its prolific elephant population, is expected to follow such a pattern unless the densities of elephants which could be sustained by indigenous woodlands are determined and maintained at carrying capacity. Above ground biomass production was estimated for mopane (Colophospermum mopane) woodlands, a principal food source for elephants, which grows over much of northern Botswana. Densities of trees and shrubs, dimensions of plants and elephant densities were recorded within stratified plots situated according to a regional rainfall gradient. Mean estimates of above ground biomass (foliage and twigs) were 9.41 and 7.83 t ha−1 for shrubs and trees respectively. A logistic model described the maximum levels of biomass removal from plants before over-utilization of mopane occurred. Variables incorporated in the model included above ground biomass of mopane shrubs and trees, growth rates of plants and expected off-take by elephants. The model predicted a complete biomass regain within 10 y if no elephant browsing occurs. Intensive elephant browsing in woodlands containing 15 elephants km−2, however, can suppress biomass production if growth rates of plants fall below 70% of the maximum annual rate. Nonetheless, there was no substantial evidence to suggest that elephants will reduce the biomass of mopane woodlands in northern Botswana below a sustainable level if their numbers are allowed to increase considerably beyond the current estimate.

Changes in structure of a Costa Rican upper montane Quercus forest were studied in twelve 0.1 ha plots along a chronosequence including 8- to 20-year-old Early Secondary Forest (ESF), 25- to 32-year-old Late Secondary Forest (LSF) and mature Primary Forest (PF). In 1.2 ha 2854 stems ≥ 3.0 cm dbh belonging to 42 tree species were recorded. Tree species richness per 0.1 ha ranged from 15 to 30. Diversity indices did not change significantly during succession. Stem density did not differ significantly among successional phases, while basal area was significantly higher in PF than in ESF and LSF. Maximum canopy height and basal area increased linearly during the first three decades of recovery. Height and dbh showed a significant, logarithmic regression for all forest phases. A period of 84 y was estimated as the theoretically minimum time needed for structural recovery. The maximum canopy height and basal area recovered two to five times slower in upper montane than in lower montane or lowland Neotropical forests.

A population of the tropical lizard Tropidurus hispidus, isolated on a granitic rock outcrop in tropical forest of northern Brazil, was studied during the 1993 wet season. Four types of observational studies revealed that lizards are active throughout most of the day. During 10-minute intervals, individual lizards moved five times for an average of 240 cm and tongue-flicked once. Habitat temperatures vary considerably during the day, with rock and air temperatures in sun exceeding body temperatures of lizards during much of the activity period. During most of the day, lizards thermoregulate by moving among shady, filtered sun, and sunny microhabitats maintaining body temperatures near 35°C. Temperatures of lizards active during cloudy periods were significantly lower than temperatures of lizards during sunny periods, indicating that clouds decrease the ability of lizards to effectively thermoregulate. Most feeding occurs in the afternoon at edges of rock outcrops with ants, insect larvae, termites and beetles dominating the diet. Comparisons with a near-by savanna population revealed differences in body size (males only), activity period (longer on rocks), body temperatures (higher on rocks), number of prey categories consumed (lower on rocks), mean size of prey (larger on rocks), number of prey eaten (fewer on rocks) and microhabitat use (more restricted on rocks).

The growth habits of five species of hemiepiphytic fig trees (Ficus subgenus Urostigma) were compared to see if any species occupied distinct canopy positions or showed unique host preferences in lowland rain forest in Gunung Palung National Park, Indonesian Borneo. Highly significant differences among species were found in the height of establishment on hosts, the level at which fig crowns were deployed, and the size and taxa of host trees. Ficus stupenda, F. dubia, and F. subtecta all had mean establishment heights between 29 and 31m above the ground, had their crowns in the upper canopy, and predominantly occupied large trees in the Dipterocarpaceae. F. consociata and F. xylophylla established at significantly lower mean heights of 24 and 18 m respectively, had their crowns predominantly in lower canopy layers, and disproportionately occupied smaller non-dipterocarp trees. These patterns were consistent both within lowland forest on alluvial terraces, which was most intensively sampled, and when data were combined from three other contiguous lowland forest habitats. Ficus species appear to be specialized to some extent for distinct microhabitats within the canopy.

Hurricane Gilbert caused disturbance to Jamaican montane rainforests in 1988. This study provides a detailed characterization of landscape-level changes in light below the canopy of these forests after the hurricane. Hemispherical photographs were taken below the forest canopy at four sites at permanent points 1 m above the ground between 7 and 33 mo after the hurricane. For each photograph photosynthetically active radiation (PAR) was computed. PAR declined exponentially in all sites during the period of measurement. During the first 24 mo after the hurricane, PAR beneath the canopy was significantly greater in sites that had been defoliated during the hurricane than in sites where few trees had been defoliated. By 28 mo after the hurricane there was no significant difference in PAR beneath the canopy among the four sites. By 33 mo after the hurricane canopy recovery was nearly complete and PAR was only slightly higher than measurements made before the hurricane. Our results were compared with studies of changes in light environment resulting from treefall gaps and under deciduous canopies. PAR during the first 18 mo after the hurricane was similar to that recorded in small canopy gaps in other forests. Widespread defoliation caused by hurricanes can thus increase PAR beneath the canopy over large areas and consequently opportunities may arise for widespread recruitment of tree species in response to increased light levels.

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.

Effects of irradiance, root competition and water availability on germination and seedling establishment of Swietenia macrophylla King were investigated in tropical secondary dry forests in the Guanacaste Conservation Area, Costa Rica. The fate of seeds sown in the beginning and the middle of the rainy season was studied in abandoned pasture, and in deciduous and semi-evergreen secondary forest. In the pasture, experimental treatments were mown and unmown grass. In the forest sites, thinning to increase light and trenching to reduce root competition were combined in a factorial design. Effects of moisture availability on germination were tested by supplementing natural rainfall in the initial rainy month. Germination at the beginning of the rainy season was not influenced by the supplementary water and was higher in the semi-evergreen forest than in the deciduous forest and pasture. In the forests, germination was little affected by irradiance or root competition. More seeds germinated in unmown than in mown pasture during the initial rains, but were not influenced by mowing when sown in the peak of the rainy season. Seedling mortality was low (>10%) during the initial months, but increased greatly in the dry season. Seedlings germinating early in the rainy season had a higher survival than those germinating later. The relatively slight effects of the different treatments and habitats on seedling establishment suggest that this species is rather insensitive to the large microsite variation in secondary vegetation.

The trophic ecology of Konaino Creek, a small mountain headwater stream draining rainforest in the aseasonal tropics on Bougainville Island, Papua New Guinea, was examined and a food web was constructed. The major source of energy in Konaiano Creek was allochthonous detritus, most of which had been terrestrially degraded to fine particulate organic matter rather than entering the stream as leaf litter. This fine detritus was collected by the filter-feeders (mostly Simuliidae and also Hydropsychidae) which formed the dominant functional feeding group (64.4% of the fauna). Thus filterers processed most of the allochthonous detritus and made the energy available to other trophic levels, rather than shredders (1.7% of the fauna) which perform this role in temperate headwater streams. Collector-gatherers made up 22.7% of the fauna, carnivorses, mostly Odonata, Decapoda (crabs) and Hydrobiosidae, comprised 2.8% of the fauna and grazer-scrapers made up 7.4%. The latter were inhibited by low instream production owing to heavy shading and the instability and abrasion of the substrate due to frequent spates. In comparison, the trophic ecology of the nearby, coastal, Bovo River (with a catchment mainly in rainforest but mostly cleared with introduced species at the study site) was quite different and it was dominated by collector-gatherers (74%) and grazer-scrapers (15%).

A bibliographical and herbarium investigation on the pollination syndrome of Mexican columnar cacti (tribe Pachycereeae) was conducted. Most Mexican species of columnar cacti show a chiropterophilic-pollination syndrome and they flower synchronously in March to May. The floral biology, reproductive system and visitors (to both fruits and flowers) of Neobuxbaumia tetetzo, the most abundant and dominant columnar cactus of succulent forest in the Tehuacan Valley, were studied. This species reached densities of c. 1200 individuals ha−1. The bats Leptonycteris curasoae and Choeronycteris mexicana were its only pollinators, whilst a more diverse array of visitors disperse seeds. Contrary to findings for multiple pollinators of columnar cacti in extratropical deserts in North America, the relationships between N. tetetzo and nectar-feeding bats was strong and tightly coupled in Mexico.