In Ethiopia, plantation forestry for soil conservation and wood supply is mainly based on exotic tree species harvested at 12–25-y rotation age. To evaluate if these forests truly represent ecological rehabilitation of degraded areas through the build-up of soil organic matter before harvest, relative abundances of C3 vs. C4 carbon in soils under a 25-y-old forest on Mt. Yegof have been studied based on changes in soil δ13C values due to vegetation cover changes by afforestation. At Yegof, shrub and tree leaves had δ13C value of −28.7 ± 0.4‰. The grasses showed a value of −30.7 ± 0.6‰ at 2700–3000 m asl (typical C3) and of −13.6 ± 0.3‰ at 2520 m asl (typical C4). Soil δ13C values were −21.7 ± 0.9‰ in soil at 0–5 cm and −20.7 ± 0.6‰ in soil at 30–50 cm indicating a long history of C4-dominated grass or cropland over the elevations sampled. The shifts towards lower δ13C values in soil at 0–5 cm coincide with 25 y of C3 vegetation. Carbon content in topsoil was 3.4–9.2% and in tree leaves was 45–56%. However, an estimate of new C3 carbon (54%) in 0–5 cm soil was low as compared with tropical rain-forest and savanna ecosystems suggesting a slow rate of carbon turnover at Yegof. The results suggest that degraded sites at Yegof may need further duration of forest cover longer than current rotation times of the forests to improve soil conditions and restore soil organic matter and carbon, which have been lost during the past land use. It is encouraging from the perspectives of ecological rehabilitation and soil conservation that a shift in the dominance from C4 vegetation types of agricultural and grassland ecosystems to C3 forest ecosystems could be established in less than 25 y on these highly degraded slopes of Mt. Yegof.

The aim of this work was to analyse the phenological variation of a residual invasive semi-evergreen shrub in Sahelian fallows in Niger. This species, Guiera senegalensis (Combretaceae), has benefited from the elimination of other species thanks to its high resistance to the increasing cutting pressure for cultivation. We sought to identify traits of its life cycle that could contribute to its persistence and widespread dominance under such a disturbance regime. Leafing, flowering and fruiting were monitored on seven fallows differing in topographic location, age, shrub density and degradation state, during two rainy seasons and one dry season. Phenological spectra showed similar timing of the three phenophases of the seven populations. Differences were observed mainly in magnitude of the phases. However, there were both a high intra-fallow variability (64.6% of the whole variability) and a statistically significant inter-fallow variability, despite only 35.4% of the total variability being due to differences between fallows. A statistical classification of the fallows was proposed based on shrub phenological course over the two cycles monitored. This classification corresponds to a gradient of life-cycle achievement primarily linked to the topographic situation of the stations, and then to a combination of other factors. The flexibility of the phenology at the individual, population and metapopulation scales, inherent to its specific semi-evergreenness property, appeared as an essential phenological attribute contributing to successful widespread persistence of G. senegalensis in the study area.

To examine the influence of seasonality on the abundance and composition of species in the community, we studied the seed rain and the seed bank in a seasonal, semi-deciduous forest in south-eastern Brazil. Soil samples (depth 3 cm, 0.25 m2) were collected within a 1-ha plot in the dry seasons of 1996 and 1997 and the rainy season of 1997 (84 samples per collection). Thirty-five seed traps (0.25 m2 each) were placed randomly in the forest from March 1997 to February 1998. The greatest density of seeds in the soil occurred in samples collected during the rainy season, the period which coincides with the main fruiting period in this forest. The Sørensen similarity index values for the seed bank composition among the three periods were high (> 0.50). The fallout of propagules was strongly seasonal, with more than half of the annual total number of seeds being caught in the two months around the end of the dry season and beginning of the rainy season. The mean density of seeds in the soil bank was nearly 86% lower than the seed rain density. There was no clear evidence of seasonal effects on species density and richness in this forest.

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).

We analysed the selection of tree species consumed by an isolated troop of Mexican howler monkeys (Alouatta palliata mexicana) released in a translocation programme on Agaltepec Island, in Catemaco Lake, Veracruz, Mexico. During November 1989–December 1996, howlers used 36 of the 63 tree species present on the island as food. Selection ratios indicated that six Ficus species (particularly F. pertusa) were among the seven most important food species. Data on time spent feeding showed that the six Ficus species were among the eight most important food species for the monkeys. Howlers spent 64.2% of their feeding time on Ficus products with F. pertusa being consumed significantly more often than foods from other Ficus species. However, monkeys fed on only one third of the 81 adult Ficus trees on the island. No significant differences were found in various food constituents (water, ash, fibre, protein, carbohydrates, lipids) of the six Ficus and two other abundant species in the habitat, whether across species, plant parts (young leaves, mature leaves, fruits), or between seasons (wet, dry). Monkeys consumed Ficus fruits rather the leaves. Fruits showed a much higher energy content per g dry weight than leaves. We also estimated the average daily biomass of leaves and fruits of Ficus spp. consumed by howlers and their energetic contribution to the daily diet of these monkeys. We suggest that some of these tendencies to frugivory reflect the abundance of Ficus trees within the home ranges of the howlers; when few fig trees are present, folivory is the dominant tendency, whereas when many fig trees are present, frugivory is dominant.

Palm seeds of the genus Astrocaryum are known to attract a wide range of seed predators, including insects, rodents and peccaries. We investigated the removal of seeds of Astrocaryum murumuru var. macrocalyx in dense groves and under solitary palms, both within and outside of peccary exclosures. We set out arrays of 40 seeds at each of 40 sites representing four treatments: in the open and in peccary exclosures, in groves and under solitary palms. Seed removal from each site was monitored daily for 55 d. Infra-red-triggered cameras were installed to identify the species that removed seeds. From the known and hypothesized behaviour of vertebrate seed predators under various circumstances, we predicted that (1) overall seed loss should be higher under solitary trees, (2) peccaries should forage preferentially in groves, (3) the variance in the rate of seed removal should be higher in groves, (4) a greater fraction of the seeds removed from solitary palms should be scatterhoarded, and consequently, (5) greater numbers of seedlings should recruit near solitary palms than in groves. The first four of these predictions were confirmed and the last was rejected by the results. Peccaries preferred to forage in groves, and small rodents preferred to forage under solitary palms. Whether in groves or under solitary palms, peccaries preferentially removed seeds from large arrays (21–40 seeds), and mostly ignored small arrays (≤ 20 seeds). Camera trapping demonstrated that the most frequent visitors to seed arrays were Myoprocta pratti and Proechimys spp. There was no significant difference in the numbers of seedlings around trees in groves versus solitary trees.

Fire is the most prevalent form of disturbance in the cerrado savannas of south-central Brazil, commonly occurring at 2-to 3-y intervals (Coutinho 1990). Frequent fires are known to increase tree mortality (Sato & Miranda 1996), but it is unclear how they affect the growth of the surviving trees. Damage to the crown from scorching is likely to have a direct negative effect on plant growth, however the reduction in tree density due to repeated burning could indirectly stimulate growth because of release from competition. Understanding the relative strength of these contrasting direct and indirect effects of fire on tree growth is important for predicting human impacts on the cerrado vegetation.

The fact that certain climatic variables are similar in high-latitude temperate zones and at high-altitude sites in the tropics, has led to assumptions about ecologically equivalent situations. The altitudinal differences between two data sets obtained in forests in temperate Denmark at sea level and in tropical Ecuador at 3000–3350 m above sea level provided a comparison suitable for examining whether high-altitude Andean forests are temperate or tropical from the standpoint of avian richness, abundance and trophic organization. Sampling methods at the two locations were similar. The Ecuadorian high-altitude sites were found to be significantly more species-rich than Danish temperate sites at all spatial scales studied (from point census to 10 km2). Additionally, species–area curves from the two countries displayed positive correlations, as expected, but with different rates of increase. The high-altitude Andean curve demonstrated a higher rate of increase causing the two curves to separate widely as more area was added. This means that when increasing areas are considered, proportionately more species squeeze into the Ecuadorian high-altitude forest landscape than do into the temperate Danish forest landscape. Corresponding to the data on richness, bird abundance was significantly higher at the Ecuadorian sites than at the Danish ones. The analysis of rank–abundance plots from Denmark and Ecuador throws light on the organization of bird species and abundance. The majority of communities in both countries fitted both the log-series and the log-normal models, making statistical distinction impossible. However, a visual inspection of the rank-ordered abundance distributions demonstrated that the Danish communities, in contrast to the Ecuadorian ones, had dominant species with relatively higher abundance, had more species with intermediate abundance, and had fewer species ‘rare by abundance’. Some major food resources (especially fruit and nectar) exploited in high-altitude sites of Ecuador were not reliably available in temperate Denmark leading also to differences in the distribution of bird species within six major trophic categories. In conclusion, the ecological characteristics of birds of the high Andes apparently are similar to those of the tropical and tropical lower montane sites (increased richness and abundance, similar organization of richness and abundance, similar additional trophic categories, similar clutch sizes), and not to those of the high- and low-latitude temperate sites.

The high predation pressure in aquatic environments is generally assumed to be the ultimate cause of terrestrial breeding in anurans (Downie 1993, Magnusson & Hero 1991, Poynton 1964, Yorke 1983). It has evolved multiple times and is presently found in most anuran families (Bogart 1981, Duellman 1992). It is often associated with higher humidity and thus lower desiccation risk in tropical forests (Duellman & Trueb 1986). Most clutches that are oviposited terrestrially are either hidden in subterranean refuges or attached more or less exposed to vegetation (Duellman & Trueb 1986, Lamotte & Lescure 1977). Exposed clutches however, face the risk of desiccation, even in rain-forest environments (Rödel pers. obs.) and are still vulnerable to predation. Such disparate groups as various arthropods (Villa 1977, 1980; Villa & Townsend 1983, Vonesh 2000), frogs (Crump 1974), snakes (Roberts 1994, Scott & Starrett 1974, Warkentin 1995) and birds (Brosset 1967), have been reported to feed on these clutches. The foam nests,which occur in at least six tropical anuran families, seem to provide better protection. Their drying surface and their more or less liquid interior offers the tadpoles an aquatic environment that is well protected against desiccation and predation (Duellman & Trueb 1986, Seymour & Loveridge 1994). In addition the bubbles of the foam facilitate oxygen diffusion within the nest and may even provide a capacious oxygen store for eggs and hatched tadpoles (Seymour & Loveridge 1994). Few predators have been reported to feed on foam nests, one of which,paradoxically, is a frog (Drewes & Altig 1996). In the Taï National Park, Ivory Coast, we discovered a quite unexpected group of predators preying on foam nests and frog clutches exposed on leaves: monkeys.

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.

Because of its position on the northern margin of the tropics (22° 17′N) and the southern coast of a huge continent, Hong Kong has a climate in which both temperature and rainfall are highly seasonal. Although summer temperatures are equatorial, the January mean is only 15.8 °C,and the absolute minimum recorded at sea level is 0 °C (Dudgeon & Corlett 1994). As a result, all aspects of the ecology of Hong Kong show seasonal changes. The most dramatic changes occur in the bird fauna, with the majority of species migratory (Carey et al. 2001). The winter fruiting peak in secondary shrublands and the forest understorey coincides with the arrival of partially frugivorous migrant robins and thrushes (Corlett 1993). However, while resident insectivore-frugivores consume almost entirely fruit during this period (Corlett 1998), all the winter visitors continue to eat insects and some (e.g. Phylloscopus warblers) are entirely insectivorous. The study of insect seasonality reported here formed part of a 30-mo study of the seasonality of a forest bird community in Hong Kong (Kwok & Corlett 1999, 2000). Plant names follow Corlett et al. (2000).

Four structural types of cerrado vegetation were examined to test the following hypotheses: (1) there are predictable changes in woody plant density, species richness and life-history strategies from one structural type to another; and (2) plant species composition in the less-rich structural types represent particular and impoverished subsets of those found in the richer ones. The study was conducted at Fazenda Palmares (5°33′S, 42°37′W) Piauí State, Brazil. A 47% decrease in woody plant density between cerradão (forest) and the least-dense type of cerrado sensu stricto (scrub) was associated with a 40% decrease in species richness. The percentage of lower-layer species was reduced by 29% in the least dense type of cerrado sensu stricto compared to cerradão. The proportion of species that flower and fruit during the rainy season was also reduced by one third. Species were not distributed as impoverished subsets along the cerradão–cerrado sensu stricto gradient. It is argued that the reduction in woody plant density and richness is partly due to factors limiting the occurrence of species with particular life-history strategies. The species composition of structural types is affected by the ‘mass effect’ and also by surrounding biotas, which provide species that colonize particular types of cerrado vegetation. Both these processes reduce the likelihood that the species composition in the poorer structural types are simple subsets of those present in the richer types.

Euglossine bees (Hymenoptera: Apidae: Euglossini) are considered keystone species in the neotropics because of their role as pollinators of several plant species, particularly orchids (Dodson et al.1969, Roubik 1992). Pollination by male euglossine bees occurs when they visit flowers to collect fragrances, which may be used for courtship (Eltz et al. 1999) or attraction of other males and females (Peruquetti 2000). Synthetic products that mimic those fragrances have been used frequently in studies of euglossine bee ecology and population structure (Armbruster & McCormick 1990, Powell & Powell 1987, Roubik & Ackerman 1987). The ability of euglossine bees to disperse and find isolated flowers and distant baits (Dressler 1968, Janzen 1971) has led Janzen (1981) and Janzen et al. (1982) to suggest that bees attracted to fragrances come from a wide area that may include different habitats. According to this hypothesis, individuals collected at baiting stations are part of the same pool of bees. However, Armbruster (1993) found significant variation in the number of bees collected at nearby baiting stations, and he considered these differences as demonstration of within-habitat heterogeneity of the euglossine bee community. In Armbruster's model, results of bait collections are strongly affected by the concentration of resources in ‘hot spots’, therefore a sampling station would not necessarily represent the habitat, but only particular microhabitats.

Fruit-eating birds play an important role in the seed dispersal of many tropical plants (e.g. Herrera 1984), and the foraging behaviour of avian frugivores may affect their seed-dispersal capabilities (Loiselle & Blake 1999,Schupp 1993, Traveset 1994). For instance,shorter visits tend to produce less clumped seed distributions (Graham et al. 1995). Also,avian frugivores often feed on the fruits of several plant species over short periods of time (Herrera 1984, 1988a; Levey et al. 1994) in some non-random pattern (Herrera 1998). This potentially produces a predictable spatial pattern of the dispersed seeds (White & Stiles 1990). Forest destruction leads to fragmentation and degradation of the remaining habitats, which may influence patterns of adult tree distribution if the production, predation, dispersal, and/or regeneration of tree seeds is affected (Harrington et al. 1997). If dispersal of avian frugivores is disrupted by habitat fragmentation, plant species might face reduced regeneration, or even local extinction if they depend on a single, locally extinct disperser (Kellman et al. 1996). Increased predation of seeds and regenerating plants in the edges and gaps may also directly reduce regeneration rates (Corlett & Turner 1997, Harrington et al. 1997, Schupp 1988).

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.

The Amazonian rain forests form one of the largest areas of continuous forest in the world, and they harbour a substantial part of the world's biodiversity (World Conservation Monitoring Centre 1992). The extravagant species richness of Amazonia makes collecting information on species distribution patterns there a formidable challenge. Relatively few studies have been able to provide data that cover both a large enough number of species and wide enough geographical areas to allow relevant biogeographical and ecological generalizations (such studies concerning plants include Balslev 1988, de Oliveira & Daly 1999, Pitman et al. 1999, Prance 1973, ter Steege et al. 2000, Terborgh & Andresen 1998, Tuomisto & Poulsen 1996). The scarcity of field observations is undoubtedly one of the reasons why very different ideas exist about the mechanisms that control plant distributions and patterns of species richness in Amazonia (Balslev 1988, Condit 1996, Gentry 1988, Nelson et al 1990, Pitman et al. 1999, Prance 1973, 1982; ter Steege et al. 2000, Tuomisto et al. 1995).

An important property of plant communities is the Leaf Area Index (LAI), which is the vertically integrated surface of leaves per unit of ground area. Leaves are the primary sites of photosynthesis and transpiration, thus the LAI, which conditions the light interception by the canopy, is directly related to carbon and water exchange with the atmosphere at the stand scale (McNaughton & Jarvis 1983). LAI also has an impact on tree growth through the interception of light. Light availability below canopies is the principal limiting factor of tree recruitment and growth in forests (Denslow et al. 1990). Several methodologies have been used for measuring LAI in the field. These can be classiffed in four categories (Marshall & Waring 1986): (1) direct measurements by litterfall collection or destructive sampling, (2) allometric correlations with variables such as tree height or tree diameter, (3) gap-fraction assessment (e.g. with hemispherical photographs), (4) measurement of light transmittance with optical sensors.

The influence of herbivory on dipterocarp seedling growth and survival in Bornean primary lowland forest understorey during and after the 1997–8 El Niño-Southern Oscillation was investigated. During the drought, a coleopteran (Scolytidae) root borer attacked dipterocarp seedlings, primarily of the genus Parashorea. Infestation was spatially heterogeneous on a large (c. 100 m) scale. Attack rate decreased with plant vigour within infested areas. Experiments showed that root damage was fatal under drought conditions, but not after rain. Defoliation and apical meristem removal did not increase mortality. The spatio-temporal heterogeneity of herbivore outbreaks and difficulties involved in experimenting with root herbivores limit the power of such short-term investigations. However, the study shows that herbivores can cause differential mortality between species, and can therefore influence dipterocarp regeneration dynamics. The effect of herbivory depends on the plant organ attacked and interactions with other stresses such as drought. El Niño-related droughts are increasing in frequency in South-East Asian rain forests, which may lead to increased numbers of herbivore outbreaks and greater seedling mortality due to these factors.

Despite the progress made in understanding the ecophysiology of tropical plants during the past two decades (Lüttge 1997, Mulkey et al. 1996), questions regarding relationships between the environment and physiological diversity remain. It is now recognized that tropical climate can be quite variable (see Coen 1983) which could lead to significant functional diversity (increased variation in life history traits) among species due to the tight association between gas exchange physiology and the environment (see Enquist & Leffler 2001, Guehl et al. 1998, Huc et al. 1994, Martinelli et al. 1998, Sobrado 1993). It remains unclear, however, how the subtleties of variation in tropical climate and tree life history traits are related to the functional diversity of tropical communities (Borchert 1994, 1998).

The integrity of ecological interactions, such as pollination and seed dispersal, has been recognized as important for long-term conservation of biodiversity (Asquith et al. 1999, Buchmann & Nabhan 1997, Howe 1984, Pizo 1997). This is illustrated by the fact that the loss of large-bodied animals like birds and mammals after habitat fragmentation can result in population changes or even extinction of many plant species (Silva & Tabarelli 2000). In the absence of primary seed dispersers (vertebrates), the importance of invertebrates such as ants, that can carry or clean seeds, probably increases.