Amazonian forests are being rapidly cleared, and the remaining forest fragments appear unusually vulnerable to fire. This occurs because forest remnants have dry, fire-prone edges, are juxtaposed with frequently burned pastures, and are often degraded by selective logging, which increases forest desiccation and fuel loading. Here we demonstrate that in eastern Amazonia, fires are operating as a large-scale edge effect in the sense that most fires originate outside fragments and penetrate considerable distances into forest interiors. Multi-temporal analyses of satellite imagery from two frontier areas reveal that fire frequency over 12-14-y periods was substantially elevated within at least 2400 m of forest margins. Application of these data with a mathematical core-area model suggests that even large forest remnants (up to several hundred thousand ha in area) could be vulnerable to edge-related fires. The synergistic interactions of forest fragmentation, logging and human-ignited fires pose critical threats to Amazonian forests, particularly in more seasonal areas of the basin.

We tested the hypothesis that tree species in a subtropical rain forest in south-east Queensland are ecologically equivalent and therefore have identical environmental requirements for their regeneration. We assessed the evidence that juveniles of species differed in their distributions in treefall gap microsites and along gradients of light availability, soil pH, soil PO4-P availability and soil NO3-N availability. Pairwise comparisons were made on a subset of the common species selected on the basis that they showed a relatively high level of positive association, and would therefore, a priori, be expected to have similar regeneration requirements. Detailed comparisons between the species failed to demonstrate evidence for species differentiation with respect to their tolerance of the disturbance associated with gap microsites or to the gradient of NO3-N availability. However, species differed markedly in their distributions along the soil pH gradient and along the gradients of light availability and soil PO4-P availability. The overall level of ecological differentiation between the species is high: seven out of the 10 possible species pairings showed evidence for ecological differentiation. Such niche differentiation amongst the juveniles of tree species may play an important role in maintaining the species richness of rain-forest communities.

On clearing fields, Ntumu farmers in southern Cameroon leave some large trees. The seed rain beneath 30 such remnant trees (12 species) was compared with that 10 m away from the edges of their crowns. Of a total of 39 765 seeds recorded in 90 seed traps over 2 y, 73.6% were of species different from the tree associated with each set of traps (‘foreign seed rain’). Seed rain included 100 morphospecies, two-thirds of which possessed endozoochorous seeds. Seeds of the pioneer tree Musanga cecropioides accounted for 71.4% of total foreign seed rain; seeds of this and other animal-dispersed species accounted for 94.5% of the total. Seed rain was 25 times higher beneath remnant trees than 10 m away. Mean species richness of monthly seed rain was three times higher beneath remnant trees than 10 m away. Both fleshy-fruited and wind-dispersed species of remnant trees attracted seed-dispersing animals which greatly enhanced the seed rain; attraction thus did not depend solely on presence of fleshy fruits. Seed rain was lower when human activity in fields was intense and increased during the period of growth of the last crops, which were not usually weeded. Heavy seed rain just before fallow may contribute significantly to regeneration, as does the presence of remnant trees.

Remnant trees in fields may facilitate regeneration in fallows by attracting seed dispersers and creating favourable sites for plant establishment. Ntumu shifting cultivators in Cameroon clearing rain forest spare some trees to provide shade for crops. This study examines their effects on regeneration by comparing vegetation in quadrats beneath and away from their crowns, in fallows of varying age (3-20 y). For fallows of all age classes, plant diversity was not significantly different between positions. Trees accounted for larger proportions of species and stems beneath remnant trees. Herbs, principally large monocots, accounted for larger proportions away from trees. Basal area was much higher in quadrats beneath trees. In all quadrats, the majority of individuals belonged to species with animal-dispersed seeds. These accounted for a larger proportion of individuals beneath trees (75%) than away (64%). Wind-dispersed species accounted for a larger proportion of stems away from trees (23.6%) than beneath (11.7%). These data suggest that enhanced seed rain by attraction of perching animals, demonstrated in a companion study, nfluenced regeneration patterns. Effects on regeneration were similar beneath trees of an animal-dispersed (Pycnanthus angolensis, Myristicaceae) and a wind-dispersed (Triplochiton scleroxylon, Sterculiaceae) species. Remnant trees in fallows may facilitate succession by nucleation, resulting in more rapid restoration of forest and conservation of nutrients in plant biomass.

Throughfall volume and interception of bulk precipitation events were measured during individual rain events of differing magnitudes in a primary wet tropical forest at La Selva Biological Station, Costa Rica. The relationship between canopy structure and throughfall were examined to identify key sources of spatial variation. Geostatistical analyses were also used to examine the spatial variation in throughfall, spatial autocorrelation and to determine minimum distances for independence of collectors. Throughfall volume was collected from 56 ground-based (funnel-style) collectors. Throughfall was collected for 26 separate precipitation events during July and August 1998. Per cent cover, distance to nearest tree, distance to nearest leaf were also estimated for each collection point. A weak relationship was found with per cent cover (r2 = 0.11). No relationship was found between throughfall and distance to the nearest leaf above the collector. Estimated interception was 1.88 mm (r2 = 0.94) with increased variance as bulk precipitation increased. A range distance of 45 m was estimated from variograms, strongly suggesting that large tree canopies and gaps are the source of much of the spatial variance in throughfall volume. Interception was reduced by 19% if only spatially independent collectors were used.

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.

Bactrocera Macquart (Diptera: Tephritidae) is a genus of nearly 500 species, the majority of which are endemic to tropical South-East Asia and Australasia (Drew 1989). Nearly all Bactrocera have frugivorous larvae that feed on the fleshy fruit of tropical trees, shrubs, and vines, and some species are major horticultural pests (White & Elson-Harris 1992). In this paper,where the term ‘fruit fly’ is used, we are referring explicitly to species of Bactrocera.

The analysis of litter quantity, litter decomposition and its pattern of nutrient release is important for understanding nutrient cycling in forest ecosystems. Plant growth and maintenance are partly met through nutrient cycling (O'Connell & Sankaran 1997) which is dominated by litter production and decomposition. Litter fall is a major process for transferring nutrients from above-ground vegetation to soils (Vitousek & Sanford 1986), while decomposition of litter releases nutrients (Maclean & Wein 1978). The rate at which nutrients are recycled influences the net primary productivity of a forest. Knowledge of these processes from tropical rain forests is relatively poor (O'Connell & Sankaran 1997), and in particular there are no known published studies on nutrient cycling from lowland tropical forests in Papua New Guinea. The few studies from Papua New Guinea are confined to the mid-montane forest zone (Edwards 1977, Edwards & Grubb 1982, Enright 1979, Lawong et al. 1993).

In abandoned pastures where the seed bank of forest species has been depleted and a seedling bank does not exist, dispersal events are the only source of forest seeds for natural regeneration (Gómez-Pompa & Vázquez-Yanes 1981). Lack of dispersal has been reported as an important limitation for rain-forest regeneration in pastures (Hardwick et al. 1997 in Thailand; Holl 1999 in Costa Rica; Nepstad et al. 1990 in Brazil) or colonization of fallow land (Kollmann 1995). A high percentage of tropical plant species have fleshy fruits that are dispersed by birds and flying and terrestrial mammals (Howe & Smallwood 1982, Snow 1981). In this study we report the spatial distribution of fleshy-fruited species dispersed to tropical pastures at different distances from the vegetation border in 12 tropical pastures as a measure of the instant regenerative potential of these sites.

There are seven species of skunk (Mustelidae) in Mexico which belong to the genera Mephitis, Conepatus and Spilogale (Ramírez-Pulido et al. 1996). They may be found all over the country and live in a wide variety of habitats. Some species occur sympatrically, particularly in tropical and subtropical ranges (Cervantes & Yépez 1995). However, their biology is relatively unknown.