Mapping Tropical Forest Trees Using High‐Resolution Aerial Digital Photographs

The spatial arrangement of tree species is a key aspect of community ecology. Because tree species in tropical forests occur at low densities, it is logistically challenging to measure distributions across large areas. In this study, we evaluated the potential use of canopy tree crown maps, derived from high‐resolution aerial digital photographs, as a relatively simple method for measuring large‐scale tree distributions. At Barro Colorado Island, Panama, we used high‐resolution aerial digital photographs (~0.129 m/pixel) to identify tree species and map crown distributions of four target tree species. We determined crown mapping accuracy by comparing aerial and ground‐mapped distributions and tested whether the spatial characteristics of the crown maps reflect those of the ground‐mapped trees. Nearly a quarter (22%) of the common canopy species had sufficiently distinctive crowns to be good candidates for reliable mapping. The errors of commission (crowns misidentified as a target species) were relatively low, but the errors of omission (missed canopy trees of the target species) were high. Only 40 percent of canopy individuals were mapped on the air photographs. Despite failing to accurately predict exact abundances of canopy trees, crown distributions accurately reproduced the clumping patterns and spatial autocorrelation features of three of four tree species and predicted areas of high and low abundance. We discuss a range of ecological and forest management applications for which this method can be useful.     

Age‐related Crown Thinning in Tropical Forest Trees

Gap dynamics theory proposes that treefall gaps provide high light levels needed for regeneration in the understory, and by increasing heterogeneity in the light environment allow light‐demanding tree species to persist in the community. Recent studies have demonstrated age‐related declines in leaf area index of individual temperate trees, highlighting a mechanism for gradual changes in the forest canopy that may also be an important, but less obvious, driver of forest dynamics. We assessed the prevalence of age‐related crown thinning among 12 tropical canopy tree species sampled in lowland forests in Panama and Puerto Rico (total N = 881). Canopy gap fraction of individual canopy tree crowns was positively related to stem diameter at 1.3 m (diameter at breast height) in a pooled analysis, with 10 of 12 species showing a positive trend. Considered individually, a positive correlation between stem diameter and canopy gap fraction was statistically significant in 4 of 12 species, all of which were large‐statured canopy to emergent species: Beilschmiedia pendula, Ceiba pentandra, Jacaranda copaia, and Prioria copaifera. Pooled analyses also showed a negative relationship between liana abundance and canopy gap fraction, suggesting that lianas could be partially obscuring age‐related crown thinning. We conclude that age‐related crown thinning occurs in tropical forests, and could thus influence patterns of tree regeneration and tropical forest community dynamics.     

Impact of Research Trails on Seedling Dynamics in a Tropical Forest

We evaluated the impact of research access trails on adjacent seedling density, survival, and recruitment in a permanent tropical forest plot in Panama. Significant differences were detected up to 20 m from trails, indicating that data collected close to trails may be biased. However, observed effects were not substantial enough to affect plot-wide estimates of seedling dynamics, suggesting that research trail impacts are negligible when affected areas constitute only a small fraction of the total area sampled.     

Poachers and Forest Fragmentation Alter Seed Dispersal,Seed Survival,and Seedling Recruitment in the Palm Attalea butyraceae,with Implications for Tropical Tree Diversity1

We examined the interaction between a palm and two bruchid beetles along with several mammal species to explore how poachers and habitat fragmentation may indirectly alter the spatial pattern of seed dispersal, seed predation, and seedling recruitment in central Panama. The large, stony endocarps of Attalea butyraceae decay slowly and bear distinctive scars when opened by rodents or beetles. We determined the final distance between endocarps and reproductive trees (which we call an ecologically effective dispersal distance), the predation status of each endocarp, and the distance between seedlings and reproductive trees. The 68 focal trees were divided among 14 sites and four levels of anthropogenic disturbance. Levels of disturbance included full protection from poachers, light and heavy pressure from poachers, and small island habitat fragments. Ecologically effective seed dispersal distances were greatest for protected sites, intermediate for lightly poached sites, and shortest for heavily poached sites and habitat fragments. Seed predation by rodents increased with distance to the nearest reproductive Attalea and was greatest for fully protected sites, intermediate for lightly poached sites, and least for heavily poached sites and habitat fragments. Seed predation by beetles reversed the patterns described for seed predation by rodents. Total seed predation by beetles and rodents combined was independent of distance, greatest for fully protected sites, and lower for poached sites and habitat fragments. Seedling densities were always greatest close to reproductive trees; however, the increase in seedling densities close to reproductive trees was minimal for fully protected sites, clearly evident for poached sites, and pronounced for habitat fragments. Increased seedling recruitment near conspecific trees may in time reduce tree diversity where humans disrupt mammal communities.     

Hyper‐abundance of Native Wild Pigs (Sus scrofa) in a Lowland Dipterocarp Rain Forest of Peninsular Malaysia1

This study reports extraordinarily high density estimates for the wild pig (Sus scrofa) from an aseasonal tropical forest site within the species'native range. At Pasoh Forest Reserve, a 2500 ha area of lowland dipterocarp rain forest in Peninsular Malaysia, line transects were used to estimate pig density from May to October in 1996 and 1998. In 1996, 44 sightings of S. scrofa consisting of 166 individuals were recorded along 81 km of transects. In 1998, 39 sightings documented 129 individuals along 79.9 km of transects. Estimated population density was 47.0 pigs/km² in 1996 and 27.0 pigs/km²‐ in 1998. Sus scrofa biomass in this forest was estimated at 1837 kg/km² and 1346 kg/ km² in 1996 and 1998, respectively. Differences between years were attributed to changes in the density of young pigs, coincident with a mast‐seeding year of dipterocarp trees in 1996. Pig densities at Pasoh Forest Reserve were much higher than at other forest locations within the species' native range in Europe and Asia. Because Pasoh Forest Reserve is a forest fragment, two factors likely account for the extremely high pig densities: (1) local extinction of natural predators (mainly tigers and leopards) and (2) an abundant year‐round food supply of African oil palm fruits from extensive plantations bordering the reserve.     

Incidence of Fungal Necrotrophic and Biotrophic Pathogens in Pioneer and Shade‐tolerant Tropical Rain Forest Trees

This study assessed the hypothesis that plant life history traits determine the incidence of fungal biotrophic and necrotrophic pathogens in pioneer vs. shade‐tolerant tropical plant species. Considering that pioneer species mainly invest in induced defenses, we expected a negative relationship between the incidence of biotrophic and necrotrophic pathogens; in contrast, as shade‐tolerant species invest heavily in constitutive defenses, we expected to find no correlation between the incidence of biotrophic and necrotrophic pathogens. These ideas were evaluated by assessing standing levels of fungal damage in a set of pioneer and shade‐tolerant species from the Lacandona tropical rain forest (Mexico). The results showed that among pioneer plant species, leaves with biotrophic lesions were between 34 and 44 percent more abundant than those with necrotic lesions. In contrast, among shade‐tolerant species, the proportions of leaves with necrotic lesions were 17–23 percent higher than those of leaves with injuries caused by biotrophic pathogens. Our study suggests that tropical tree species might present different defense strategies depending on the life‐style of the pathogens that attack them, and the life history strategy of the attacked host plant species. Thus, the host constitutive and induced defenses, as well as the mechanisms used by different types of pathogens to circumvent those defenses maybe responsible for the patterns of attack observed in perennial tropical plants. Abstract in Spanish is available at http://www.blackwell‐synergy.com/loi/btp .     

Tropical Understory Piper Shrubs Maintain High Levels of Genotypic Diversity Despite Frequent Asexual Recruitment

Many plant species have the capacity to regenerate asexually by resprouting from stem and leaf fragments. In the pan‐tropical shrub genus Piper, this tendency is thought to be higher in shade‐tolerant than light‐demanding species, and to represent a trade‐off with annual seed production. Here we use molecular markers to identify clones in five Piper species varying in light requirements. We test predictions that (i) asexual recruitment success is highest in shade‐tolerant species, and (ii) that consequently, shade‐tolerant species are characterized by lower genotypic diversity than light‐demanding Piper. We found that two shade‐tolerant Piper species recruited asexually more frequently (36–42% of sampled shoots were of asexual origin) than, two light‐demanding and one shade‐tolerant species (0–26%). Furthermore, as predicted, genotypic diversity was negatively correlated with the frequency of asexual recruitment in the population. Nonetheless, genotypic diversity of Piper was high compared with other clonal plants. The proportion of unique genotypes found per population ranged from 0.58 to 1.0 and the genotypic Simpson's diversity ranged from 0.93 to 1.0 for all five species. Our results suggest that even though asexual reproduction plays an important role in maintaining local populations of Piper in the understory, it does not seem to reduce genotypic diversity to levels that will threaten these species ability to respond to environmental change. Abstract in Spanish is available in the online version of this article.     

Herbivory Rate of Leaf-Cutting Ants in a Tropical Moist Forest in Panama at the Population and Ecosystem Scales

Leaf-cutting ants are frequently characterized as the major herbivores in the Neotropics, but quantitative data to back up this assumption are scarce. In this study, the consumption and herbivory rates for the entire leaf-cutting ant ( Atta colombica , Formicidae) population in an old secondary forest on Barro Colorado Island (BCI) in Panama were determined over 15 mo (on average 49 colonies). The number of harvested leaf fragments was calculated from monthly refuse deposition rates of the colonies and the regression between refuse deposition and harvesting rates. The inclusion of fragment characteristics (proportion of leaf fragments in the harvest, average fragment weight, and area) allowed us to calculate consumption and herbivory rates at colony, population, and ecosystem levels. The A. colombica population harvested 13.2 tons of biomass/yr and 13.1 ha of leaf area/yr, and deposited 9.4 tons of refuse material/yr. Rates varied considerably among colonies. At the ecosystem level, i.e. , per forest area, herbivory rates were 132 kg biomass/ha/yr and 1310 m² foliage/ha/yr. For the area on BCI where A. colombica occurs (100 ha), this is equivalent to 2.1 percent of the foliage area in the forest or 1.7 percent of the annual leaf-area production. This value is considerably lower than previously published estimates of leaf-cutting ant herbivory rates in tropical forests.     

Heterogeneity of Light Availability and its Effects on Simulated Carbon Gain of Tree Leaves in a Small Gap and the Understory in a Tropical Rain Forest1

To clarify the small-scale heterogeneity of light regimes in a rain forest, photosynthetic photon flux density (PFD) was measured at 1-min intervals during six days at 12 microsites in each of two plots, a small gap and an understory in Pasoh Forest Reserve, Peninsular Malaysia. Frequency distribution of microsite PFD was unimodal with the peak value between 16 and 32 μmol/m²/sec in the small gap, but between 8 and 16 μmol/m²/sec in the understory. In the small gap, PFD was more variable among microsites; total daily PFD and daily sunfleck PFD exceeding 10 μmol/ m²/sec tended to be higher (P <0.05; t-test) compared to those in the understory. Sunfleck PFD exceeding 50 μmol/ m²/sec, however, showed no difference between the two plots. Diffuse PFD transmittance, defined as the ratio of PFD in the forest to that measured at 43 m above ground during the periods 0800-0810 and 1750-1800 h, was significantly higher in the small gap than in the understory plot. Diffuse PFD transmittance was also positively correlated with microsite total daily PFD. To examine the effects of the subtle heterogeneity of light regimes on leaf carbon gain, we simulated carbon gain by sun and shade leaves in a typical shade-tolerant species, Brosimum aticastrum Sw. (Moraceae). Despite the similarity in total daily PFD, total daily carbon gain was considerably higher in the gap than in the understory for both sun and shade leaves. This study suggests that frequency distribution of PFD is critical in describing microsite PFD regimes and determining leaf carbon gain in the tropical forest floor.     

Edaphic and Floristic Variation within a 1‐ha Plot of Lowland Amazonian Rain Forest1

Several studies in lowland tropical rain forests have documented effects of local‐scale topographic variation on plant species distribution and abundance patterns. Few studies have compared the distribution patterns of more than one plant group, however, and even fewer have related these to measured physical and chemical soil characteristics. Here, we document such soil characteristics within a square 1‐ha plot in Amazonian Ecuador, and compare them to the distribution patterns of terrestrial pteridophytes, angiosperm ground herbs, and palms. Substantial variation in soil properties was found within the plot. The three plant groups showed highly correlated floristic patterns within the 1‐ha plot even after the effect of geographical distances had been taken into account. Mantel tests yielded significant correlations between edaphic patterns, as measured by distances in various soil and topographic characteristics, and floristic patterns. For all three plant groups, differences in elevation within the plot were highly correlated with floristic distances, and for terrestrial pteridophytes and palms, distances in soil calcium content and sand content were also important. Our results resembled those obtained at wider spatial scales with the same plant groups, which indicates that soil factors may play an important role for distribution and beta diversity of plants, even at the local scale.     

Susceptibility of Tree Seedlings to Biotic and Abiotic Hazards in the Understory of a Moist Tropical Forest in Panama

We evaluated temporal patterns of seedling survival of eight Neotropical tree species generated under multiple abiotic and biotic hazards (vertebrates, disease, litterfall) in the forest understory on Barro Colorado Island, Panama. Seedlings were transplanted at first leaf expansion in low densities along a 6-km transect and damage and mortality were recorded for 1 yr. We also planted and monitored small and large artificial seedlings to estimate physical disturbance regimes. During 0–2 mo after transplant, vertebrate consumers of reserve cotyledons caused high mortality of real seedlings, but little damage to artificial seedlings. On real seedlings after 2 mo, disease became an important agent of mortality, despite a decrease in overall mortality rates. Damage by litterfall remained relatively low during the 1-yr study period. Survival ranks among species showed ontogenetic shifts over time, as species changed susceptibility to the mortality agents. Survival after 2 mo was positively correlated with stem toughness, not because species with tough stems were less likely to receive mechanical damage, but because they survived better after receiving mechanical damage. Within each transplant station, artificial seedlings were not good predictors of litterfall damage experienced by real seedlings. Forest-wide litterfall damage level, however, was similar for both real and artificial seedlings ( ca 10%/yr), a moderate level compared to other tropical forests. In conclusion, species traits including biomechanical traits interact to create complex temporal patterns of first year seedling survival, resulting in ontogenetic shifts that largely reflect changes in the relative importance of vertebrate consumers relative to other hazards.     

Bushmeat and the Fate of Trees with Seeds Dispersed by Large Primates in a Lowland Rain Forest in Western Amazonia

In Neotropical forests, large fruit-eating primates play important ecological roles as dispersal agents of large seeds. Bushmeat hunting threatens to disrupt populations of primates and large-seeded trees. We test the hypothesis that otherwise intact Neotropical forests with depressed populations of large primates experience decline in recruitment of large-seeded trees. We quantify the proportion of small juveniles (> 0.5 m tall–1 cm diameter at breast height, DBH) of large primate-dispersed tree species found underneath heterospecifc trees that are also dispersed by large primates at two protected sites in Manu National Park and one hunted site outside Manu N.P. in southeastern Peru. The forests are comparable in edaphic and climatic qualities, successional stage, and adult tree species composition. We found that hunting locally exterminates populations of large primates, and reduced primates of intermediate body size (hereafter "medium primates") by 80 percent. Moreover, tree species richness was 55 percent lower and density of species dispersed by large and medium-bodied primates 60 percent lower in hunted than in protected sites. In addition, richness and density of abiotically dispersed species and plants dispersed by non-game animals are greater in hunted sites. Overhunting threatens to disrupt the ecological interactions between primates and the plants that rely on them for seed dispersal and recruitment. Sustainable wildlife management plans are urgently needed, because protected areas are at risk of becoming "island" parks if buffer zones become empty of animals and have impoverished flora.     

The Influence of Topography on Tree Growth,Mortality, and Recruitment in a Tropical Montane Forest1

To determine if there were consistent differences in growth, mortality, and recruitment on slopes and ridge crests in tropical montane forests, which could explain the (frequent but not universal) low stature of trees in the ridgetop forests, we analyzed data from long‐term plots in Jamaica (1990–1994; sixteen 200‐m² plots, six on ridge crests and five each on north and south slopes). Mortality was higher on north slopes, while growth and recruitment rates were not significantly different among positions. Soil pH and effects of recent disturbance by Hurricane Gilbert were positively correlated with growth and recruitment, while slope angle and disturbance effects were the best predictors of mortality. The patterns we found in Jamaica, that growth and recruitment were not higher on ridge crests than slopes, are different than those found by Herwitz and Young in Australia where growth and turnover were greater on a ridge crest. Therefore, it is not possible at present to make simple generalizations about dynamics of ridge crest versus slope forests in the montane tropics.     

海南尖峰岭热带林土壤动物群落——群落的组成及其特征

以海南尖峰岭自然保护区热带山地雨林为标准样地,研究热带土壤动物在原始生境中的群落结构。样地设５个固定取样点,每月固定时间用３种方法,对原生动物、线虫和其它大、中型土壤动物分别取样。调查结果显示：（１）以风干土培养法获得的原生动物共有１８目７２种,种类以纤毛虫类为主,数量则以肉足虫类为主。本调查点与以北各地带相比,其分布的种类较少,这与热带林枯枝落叶层薄有关。（２）以湿漏斗法获得的线虫有７目７６种,为国内各地带之首。其中矛线目种类及个体数量均占多数。（３）以手拣和大、小于漏斗法获得的土壤动物共有３２个类群（以目为主）,其多样性指数（Ｈ′）高于本区以北各地带调查点。类群的重要性,按平均数量及其稳定性来排序,排在最前的几个类群有蚂蚁、鞘翅目、蚯蚓、及等翅目等。比西双版纳热带沟谷雨林的土壤动物群落结构更具热带性。     

The Relationship between Local Abundance and Distribution of Rain Forest Trees across Environmental Gradients in India

We tested whether local abundance of rain forest trees in the medium elevation wet forests of the southern Western Ghats (WG) was related to environmental tolerance, life form, and geographical range. We selected trees in medium elevation wet forests (750–1700 m asl) of the southern WG, using two data bases: a small plot (30 × 30 m) data base of 288 species of trees (≥ 3 cm dbh) in 33 plots totaling 2.97 ha, and a data base of 135 species of tree (≥ 10 cm dbh) in larger plots of 1 ha each, totaling 4.84 ha. The species density per hectare and number of records in the plot network was used in a factor analysis to give a measure of the local abundance of each species. The altitude and seasonality ranges of these species in the WG was assessed from independent data bases and used to generate an environmental tolerance score. Results indicated that as a species became locally more abundant, it occurred across a wider range of environmental gradients, but regional distribution was not related to geographical distribution. Understory species tended to be rarer with smaller range sizes and lower environmental tolerances than overstory species. Climate change is predicted to have drastic effects on restricted range species with limited environmental tolerances.     

Effects of Elevated CO2 and Defoliation on Compensatory Growth and Photosynthesis of Seedlings in a Tropical Tree,Copaifera aromatica1

After defoliation by herbivores, some plants exhibit enhanced rates of photosynthesis and growth that enable them to compensate for lost tissue, thus maintaining their fitness relative to competing, undefoliated plants. Our aim was to determine whether compensatory photosynthesis and growth would be altered by increasing concentrations of atmospheric CO₂. Defoliation of developing leaflets on seedlings of a tropical tree, Copaifera aromatica, caused increases in photosynthesis under ambient CO₂, but not under elevated CO₂. An enhancement in the development of buds in the leaf axils followed defoliation at ambient levels of CO₂. In contrast, under elevated CO₂, enhanced development of buds occurred in undefoliated plants with no further enhancement in bud development due to exposure to elevated CO₂. Growth of leaf area after defoliation was increased, particularly under elevated CO₂. Despite this increase, defoliated plants grown under elevated CO₂ were further from compensating for tissue lost during defoliation after 5¹/₂ weeks than those grown under ambient CO₂ concentrations.     

Composition and Dynamics of Functional Groups of Trees During Tropical Forest Succession in Northeastern Costa Rica

We compared the functional type composition of trees ≥10 cm dbh in eight secondary forest monitoring plots with logged and unlogged mature forest plots in lowland wet forests of Northeastern Costa Rica. Five plant functional types were delimited based on diameter growth rates and canopy height of 293 tree species. Mature forests had significantly higher relative abundance of understory trees and slow-growing canopy/emergent trees, but lower relative abundance of fast-growing canopy/emergent trees than secondary forests. Fast-growing subcanopy and canopy trees reached peak densities early in succession. Density of fast-growing canopy/emergent trees increased during the first 20 yr of succession, whereas basal area continued to increase beyond 40 yr. We also assigned canopy tree species to one of three colonization groups, based on the presence of seedlings, saplings, and trees in four secondary forest plots. Among 93 species evaluated, 68 percent were classified as regenerating pioneers (both trees and regeneration present), whereas only 6 percent were classified as nonregenerating pioneers (trees only) and 26 percent as forest colonizers (regeneration only). Slow-growing trees composed 72 percent of the seedling and sapling regeneration for forest colonizers, whereas fast-growing trees composed 63 percent of the seedlings and saplings of regenerating pioneers. Tree stature and growth rates capture much of the functional variation that appears to drive successional dynamics. Results further suggest strong linkages between functional types defined based on adult height and growth rates of large trees and abundance of seedling and sapling regeneration during secondary succession.
Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp