Showing papers in "Biotropica in 2010"

Tree Diversity, Forest Structure and Productivity along Altitudinal and Topographical Gradients in a Species‐Rich Ecuadorian Montane Rain Forest

Abstract: We studied the spatial heterogeneity of tree diversity, and of forest structure and productivity in a highly diverse tropical mountain area in southern Ecuador with the aim of understanding the causes of the large variation in these parameters. Two major environmental gradients, elevation and topography, representing a broad range of climatic and edaphic site conditions, were analyzed. We found the highest species richness of trees in valleys <2100 m. Valleys showed highest values of basal area, leaf area index and tree basal area increment as well. Tree diversity also increased from ridges to valleys, while canopy openness decreased. Significant relationships existed between tree diversity and soil parameters (pH, total contents of Mg, K, Ca, N and P), and between diversity and the spatial variability of pH and Ca and Mg contents suggesting a dependence of tree diversity on both absolute levels and on the small-scale heterogeneity of soil nutrient availability. Tree diversity and basal area increment were positively correlated, partly because both are similarly affected by soil conditions. We conclude that the extraordinarily high tree species richness in the area is primarily caused by three factors: (1) the existence of steep altitudinal and topographic gradients in a rather limited area creating a small-scale mosaic of edaphically different habitats; (2) the intermingling of Amazonian lowland plant species, that reach their upper distribution limits, and of montane forest species; and (3) the geographical position of the study area between the humid eastern Andean slope and the dry interandean forests of South Ecuador.

The Importance of Defining ‘Forest’: Tropical Forest Degradation, Deforestation, Long‐term Phase Shifts, and Further Transitions

Abstract: While research continues on the causes, consequences, and rates of deforestation and forest degradation in the tropics, there is little agreement about what exactly is being lost, what we want back, and to whom the ‘we’ refers. Particularly unsettling is that many analyses and well-intended actions are implemented in fogs of ambiguity surrounding definitions of the term ‘forest’—a problem that is not solely semantic; with development of markets for biomass carbon, vegetation classification exercises take on new relevance. For example, according to the basic implementation guidelines of the Kyoto Protocol, closed canopy natural forest could be replaced by monoclonal plantations of genetically engineered exotic tree species and no deforestation would have occurred. Following these same guidelines, carbon credits for afforestation could be available for planting trees in species-rich savannas; these new plantations would count towards a country moving towards the ‘forest transition,’ the point at which there is no net ‘forest’ loss. Such obvious conflicts between biodiversity conservation and carbon sequestration might be avoided if ‘forest’ was clearly defined and if other vegetation types and other ecosystem values were explicitly recognized. While acknowledging that no one approach to vegetation classification is likely to satisfy all users at all scales, we present an approach that recognizes the importance of species composition, reflects the utility of land-cover characteristics that are identifiable via remote sensing, and acknowledges that many sorts of forest degradation do not reduce carbon stocks (e.g., defaunation) or canopy cover (e.g., over-harvesting of understory nontimber forest products).

Differential Use of Trails by Forest Mammals and the Implications for Camera-Trap Studies: A Case Study from Belize

Abstract: Relative abundance indices are often used to compare species abundance between sites. The indices assume that species have similar detection probabilities, or that differences between detection probabilities are known and can be corrected for. Indices often consist of encounter frequencies of footprints, burrows, markings or photo captures along trails or transect lines, but the assumption of equal detection probabilities is rarely validated. This study analyzes detection probabilities of a range of Neotropical mammals on trails in dense secondary forests, using camera-trap and track data. Photo captures of the two large cats, jaguars (Panthera onca) and pumas (Puma concolor), were correlated solely with trail variables, while photo captures of their potential prey species had no correlation or negative correlation with trail variables. The Neotropical mammals varied greatly in their tendency to follow or cross trails based on footprints surveys. This indicates that camera locations on trails will have varying detection probability for these Neotropical mammals. Even the two similar-sized jaguars and pumas, occupying relatively similar niches, differed subtly in their use of trails. Pumas followed trails more completely while jaguars were more likely to deviate from trails. The ecological significance of these findings is that jaguars seem to be more willing to use the forest matrix away from trails than do pumas. We conclude that trail-based indices, such as photographic captures or tracks along trails, are not appropriate for comparison between Neotropical species, and not even between relatively similar species like jaguars and pumas.

Saving slash-and-burn to save biodiversity.

Abstract: Several prominent articles have recently revived the debate on how to advance and reconcile two pressing global issues: conservation of biodiversity, and food production for an increasing human population. These discussions contrast a ‘land-sparing/intensive agriculture’ strategy with a ‘biodiversity-friendly’ agriculture approach. We propose that swidden or shifting cultivation should be an important component of the latter approach in the tropics because many swidden systems maintain very high levels of biodiversity while providing livelihood for populations in tropical forest areas worldwide. We suggest further that when many swidden systems are viewed without prejudice and in broader spatial and longer temporal perspectives, the conservationist aspects of the systems become evident.

Global mapping of ecosystem disservices: the unspoken reality that nature sometimes kills us

Abstract: Increasingly, we view nature through a utilitarian lens that leads us to attempt to measure and manage the services that species, habitats and ecosystems provide. Surprisingly, we have tended to consider only the positive values of ecosystems, their ecosystem services. In addition to providing our food and water, Nature also kills us, primarily through disease. If we are to effectively manage the terrestrial Earth, we need to also manage species, habitats and ecosystems so as to minimize such ‘ecosystem disservices’. I consider what we know about the spatial pattern of one disservice, pathogen prevalence and how changes in habitat influence it. I consider the effects of habitat changes on pathogen prevalence and, consequently, ecosystem disservices. In the end, we need to weigh both the costs and the benefits of particular ecosystems, habitats and species – to consider the bad with the good. Doing so requires that we learn much more about the biota than we currently know.

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

Abstract: 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.

Annual rainfall and seasonality predict pan-tropical patterns of liana density and basal area.

Abstract: We test the hypotheses proposed by Gentry and Schnitzer that liana density and basal area in tropical forests vary negatively with mean annual precipitation (MAP) and positively with seasonality. Previous studies correlating liana abundance with these climatic variables have produced conflicting results, warranting a new analysis of drivers of liana abundance based on a different dataset. We compiled a pan-tropical dataset containing 28,953 lianas (Z2.5cmdiam.) from studies conducted at 13 Neotropical and 11 Paleotropical dry to wet lowland tropical forests. The ranges in MAP and dry season length (DSL) (number of months with mean rainfall o100mm) represented by these datasets were 860‐7250mm/yr and 0‐7mo, respectively. Pan-tropically, liana density and basal area decreased significantly with increasing annual rainfall and increased with increasing DSL, supporting the hypotheses of Gentry and Schnitzer. Our results suggest that much of the variation in liana density and basal area in the tropics can be accounted for by the relatively simple metrics of MAP and DSL.

Game vertebrate densities in hunted and nonhunted forest sites in Manu National Park, Peru.

Abstract: Manu National Park of southern Peru is one of the most renowned protected areas in the world, yet large-bodied vertebrate surveys conducted to date have been restricted to Cocha Cashu Biological Station, a research station covering o 0.06 percent of the 1.7 Mha park. Manu Park is occupied by 4 460 settled Matsigenka Amerindians, 300–400 isolated Matsigenka, and several, little-known groups of isolated hunter–gatherers, yet the impact of these native Amazonians on game vertebrate populations within the park remains poorly understood. On the basis of 1495 km of standardized line-transect censuses, we present density and biomass estimates for 23 mammal, bird, and reptile species for seven lowland and upland forest sites in Manu Park, including Cocha Cashu. We compare these estimates between hunted and nonhunted sites within Manu Park, and with other Neotropical forest sites. Manu Park safeguards some of the most species-rich and highest biomass assemblages of arboreal and terrestrial mammals ever recorded in Neotropical forests, most likely because of its direct Andean influence and high levels of soil fertility. Relative to Barro Colorado Island, seed predators and arboreal folivores in Manu are rare, and generalist frugivores specializing on mature fruit pulp are abundant. The impact of such a qualitative shift in the vertebrate community on the dynamics of plant regeneration, and therefore, on our understanding of tropical plant ecology, must be profound. Despite a number of external threats, Manu Park continues to serve as a baseline against which other Neotropical forests can be gauged.

Bushmeat Hunting Alters Recruitment of Large‐seeded Plant Species in Central Africa

Abstract: We investigated the effect of local hunting on plant recruitment at the community level in the Ngotto Forest, Central African Republic. It is the first study of this kind in the afrotropics. To compare our results with previous studies conducted in the neotropics, we used the protocol proposed byNu˜ nez-Iturri and Howe. We compared animal relative abundances and seed length, density and diversity of seedlings at two sites with contrasting anthropogenic pressures: one with low hunting pressure (LH) and one with high hunting pressure (HH). Furthermore, we investigated how density and diversity of recruitment vary with seed length in the two sites. Both sites exhibit similar soil, climate and tree species composition, and have never been logged. Large mammals (frugivores and herbivores) were extirpated from HH and relative abundance of medium-sized frugivores drastically decreased in HH compared with LH. In HH, diversity of seedlings was reduced compared with LH, especially for large-seeded plant species dispersed by large game mammals. The approach used in this study shows promising perspectives to investigate the effects of human disturbances on the regeneration of tropical forests. Furthermore, in the afrotropical context of a lack of data on plant‐animal ecological relationships, seed length appears to be a good predictor of the strength of the deficit of plant recruitment due to large mammal extirpation because of hunting. Thus, more efforts are needed to study the ecological roles of large-seeded plants in order to better understand the effects of their disappearance on tropical forest resilience.

Mammalian Densities in a Neotropical Wetland Subject to Extreme Climatic Events

Abstract: Effective management and conservation of an ecosystem requires information on species assemblages as well as reliable estimates of population sizes to plan, implement and evaluate management strategies. The Brazilian Pantanal is one of the world's largest freshwater wetlands and considered a priority landscape for wildlife conservation. It is subject to pluri-annual extreme dry and wet periods, which cause extreme flood and drought events, which strongly affect wildlife. Using the line-transect method, this study examined the distribution of densities and metabolic biomass of medium- to large-sized nonvolant mammals in forest, cerrado and floodplain landscapes, in an area with low anthropogenic influence, in the central area of the Brazilian Pantanal during a prolonged drought. Comparisons with a previous survey conducted during years of average rainfall in part of the study area suggest that population fluctuations of certain species are closely associated with water due to the drought. Results from this study showed that mammal assemblages varied between landscapes. Forested landscapes have the highest densities of mammals and are the most important in terms of relative energy consumption. In addition, at the time of the study, frugivores were found to have higher energy consumption than browser/grazers across the three landscapes; most fruits are produced in forested areas stressing their importance. By converting forested landscapes into grasslands, the intensification of ranching practices seriously threatens biodiversity and ecological processes in the region. RESUMO O manejo efetivo e a conservacao de um determinado ecossistema requer a obtencao de informacoes sobre as comunidades de especies presentes bem como estimativas confiaveis de tamanhos populacionais de forma a permitir o planejamento, implementacao e avaliacao de estrategias de manejo. O Pantanal Brasileiro e uma das maiores areas alagadas do planeta e e considerado como paisagem prioritaria para a conservacao de vida silvestre. O Pantanal e caracterizado por periodos pluri-anuais de chuva e seca extrema os quais causam eventos extremos de cheia e seca que afetam a vida silvestre de maneira significativa. Atraves do uso do metodo de transectos lineares, este estudo examinou a distribuicao de densidades populacionais e biomassa metabolica de mamiferos nao-voadores de medio e grande porte em tres diferentes tipos de paisagem, em uma area com pequena influencia antropica, na regiao central do Pantanal Brasileiro durante um periodo de seca extrema. Comparacoes com um estudo previo realizado em parte da area de estudo e conduzido durante anos de chuva padrao para a regiao sugerem flutuacoes populacionais para determinadas especies estreitamente associadas aagua. Resultados deste estudo demonstraram que as comunidades de mamiferos variam entre paisagens. Paisagens florestadas apresentam maiores densidades de mamiferos and sao mais importantes em termos de consumo relativo de energia. Adicionalmente, os mamiferos frugivoros apresentaram maior consumo de energia do que pastador/folivoros nos tres tipos de paisagem, estressando a importância de areas de floresta, onde a maior parte dos frutos e produzida. A conversao de paisagens florestadas em areas de pastagens e a intensificacao das praticas de pecuaria ameaca seriamente a biodiversidade e os processos ecologicos ocorrentes no Pantanal.

Habitat Use by Sympatric Jaguars and Pumas Across a Gradient of Human Disturbance in Belize

Abstract: Jaguars (Panthera onca) and pumas (Puma concolor) are sympatric across the entire jaguar range, where they coexist in increasingly fragmented landscapes under threat of persecution mainly in response to livestock predation. Pumas are known to inhabit a greater variety of natural habitats than jaguars, but little is known about the influence of anthropogenic factors on the coexistence of these two similar-sized cats. This study compares habitat use of jaguars and pumas in Belize, Central America, using 1380 jaguar and puma photo captures from 3yr of camera trapping,comprising 64‐74 individual jaguars and an unknown number of pumas. Jaguars and pumas did not differ in their use of a large block of relatively homogenous secondary rain forest. However, pumas were scarce outside this forest block, whereas jaguars were detected throughout the human-influenced landscape. Reasons for this discrepancy may include differential tolerance to human disturbance, and resource limitation for pumas outside the forest block. Intra-specific variation in jaguar activity in the form of sex-dependent habitat use was detected across the landscape. Male jaguars were detected at more locations than female jaguars and more frequently at each location, with a declining difference from a 50-fold greater detection in the protected forest, through forest buffer, savannah, pastures, to negligible difference in the disturbed forest.

Patterns of Seed Dispersal and Dispersal Failure in a Hawaiian Dry Forest Having Only Introduced Birds

Abstract: Dry forests are among the most endangered natural communities in the Hawaiian Islands. Most have been reduced to isolated trees and small forest fragments in which native tree species reproduce poorly. The replacement of native birds by introduced generalists may be contributing to dry forest decline through modification of seed dispersal patterns. To document seed dispersal by introduced birds, we conducted foraging observations on fleshy-fruited trees and measured seed rain under trees and in adjacent open areas for 1 year in a dry forest dominated by native trees. Although trees covered only 15.2 percent of the study area, 96.9 percent of the bird-dispersed seeds were deposited beneath them. The Japanese white-eye (Zosterops japonicus) was the principal dispersal agent. Among bird-dispersed seeds, those of the invasive tree Bocconia frutescens accounted for 75 percent of all seeds collected beneath trees (14.8 seeds/m /yr) and the invasive shrub Lantana camara accounted for 17 percent. Although nearly 60 percent of the reserve's native woody species possess fleshy fruits, introduced birds rarely disperse their seeds. Native trees accounted for < 8 percent of all bird-dispersed seeds and are consequently experiencing dispersal failure by falling directly under parent trees. Smaller-seeded non-native plants, in contrast, may be benefiting from dispersal by introduced birds. Current dispersal patterns suggest that these readily disseminated non-native plants may eventually replace the remaining native flora.

Untangling a Decline in Tropical Forest Resilience: Constraints on the Sustainability of Shifting Cultivation Across the Globe

Abstract: Shifting cultivators depend on forest biomass inputs to nourish their crops. For them, forest resilience has an immediate impact: it affects crop productivity. A decline in the rate of recovery following shifting cultivation would ultimately affect local, regional and global carbon budgets, with feedbacks to climate. Yet the long-term impacts of shifting cultivation have been quantified in only six locations. In this study, we reanalyze data from these locations to determine whether the rate of biomass recovery is the same from cycle to cycle. Further, using case studies in Southern Yucatan, Mexico and West Kalimantan, Indonesia, we investigate the ecological and socioeconomic factors that affect forest resilience and thus determine whether or not shifting cultivation is sustainable. The reanalysis links aboveground biomass recovery following shifting cultivation to site productivity, forest age, fallow length, history of cultivation, and soil texture. Across locations, biomass accumulation rate declines by 9.3 percent with each cycle of shifting cultivation. Per cycle change in biomass accumulation rate is significantly more negative in younger forests and forests that experience a shorter fallow period. However, more detailed analyses for two case studies suggest that a purely ecological framework is of limited effectiveness in explaining variability in the effect of repeated shifting cultivation. Rather, socioeconomic factors such as migration, subsidies, roads, and settlement history can alter the outcome of shifting cultivation by limiting the accumulation and use of local knowledge.

Leaving the Oil Under the Amazon: Ecuador's Yasuní‐ITT Initiative

Abstract: Oil and gas concessions now cover vast swaths of the western Amazon, including protected areas and indigenous territories. The Yasuni-ITT Initiative, Ecuador's innovative proposal to leave nearly a billion barrels of oil locked beneath Yasuni National Park, is the first major effort to reverse this trend. We provide a concise overview of the initiative, including an in-depth look at its widely lauded goals of protecting biodiversity, respecting indigenous peoples' territory, and combating climate change. We also discuss the proposal's lingering caveats, such as technical questions regarding the generation of financial resources to replace the forgone oil revenue. We conclude that the Yasuni-ITT Initiative is a potentially precedent-setting advance towards avoiding damaging oil and gas development in sensitive areas.

Diversity of Interactions: A Metric for Studies of Biodiversity

Abstract: Multitrophic interactions play key roles in the origin and maintenance of species diversity, and the study of these interactions has contributed to important theoretical advances in ecology and evolutionary biology. Nevertheless, most biodiversity inventories focus on static species lists, and prominent theories of diversity still ignore trophic interactions. The lack of a simple interaction metric that is analogous to species richness is one reason why diversity of interactions is not examined as a response or predictor variable in diversity studies. Using plant–herbivore–enemy trophic chains as an example, we develop a simple metric of diversity in which richness, diversity indices (e.g., Simpson's 1/D), and rarefaction diversity are calculated with links as the basic unit rather than species. Interactions include all two-link (herbivore–plant and enemy–herbivore) and three-link (enemy–herbivore–plant) chains found in a study unit. This metric is different from other indices, such as traditional diversity measures, connectivity and interaction diversity in food-web studies, and the diversity of interaction index in behavioral studies, and it is easier to compute. Using this approach to studying diversity provides novel insight into debates about neutrality and correlations between diversity, stability, productivity, and ecosystem services. RESUMEN Las interacciones multitroficas son en gran parte responsables por el origen y el mantenimiento de la diversidad de especies, y las investigaciones de estas interacciones han contribuido a avances teoricos en ecologia y biologia evolutiva. Sin embargo, en la mayoria de los inventarios de biodiversidad se hacen listas estaticas de especies, y las teorias de la diversidad mas prominentes siguen ignorando las interacciones troficas. La falta de una metrica de interaccion sencilla y que sea analoga a la riqueza de especies es una de las razones para que no se examine la diversidad de interacciones como una respuesta o una variable dependiente en estudios de diversidad. Usamos las cadenas troficas de plantas-herbivoros-enemigos como un ejemplo y desarrollamos una variable simple de diversidad en la cual se puede calcular la riqueza de interacciones o los indices de diversidad (por ejemplo, 1 / D de Simpson) y la diversidad de rarefaccion; se usan los enlaces como la unidad basica en lugar de las especies. Las interacciones incluyen todas las interacciones de dos enlaces (planta-herbivoro y herbivoro-enemigo) y de tres enlaces (enemigo-herbivoro-planta) que se encuentra en muestreos o censos por transectos o por parcelas. Esta variable es diferente de otros indices de diversidad tradicionalmente usados como la conectividad de interaccion en estudios de cadenas troficas, y el indice de diversidad de interacciones que se usa en estudios comportamentales, ademas es mas facil de calcular. Usando esta aproximacion para estudiar la diversidad de interacciones creara nuevas perspectivas en debates sobre la teoria neutral y las correlaciones entre la diversidad, la estabilidad, la productividad, y servicios de los ecosistemas.

Effects of Agricultural Intensification on the Assemblage of Leaf‐Nosed Bats (Phyllostomidae) in a Coffee Landscape in Chiapas, Mexico

Abstract: The agricultural matrix surrounding forested areas serves critical functions as dispersal corridors and alternate habitat for wildlife. Agricultural intensification, however, can reduce the conservation value of these areas. To evaluate the effects of agroecosystem management on bat assemblages, we studied the abundance and diversity of leaf-nosed bats (family: Phyllostomidae) in southwestern Chiapas, Mexico, a landscape dominated by shade coffee agroforestry. During 2104 mist-net hour (MNH), we captured 3167 bats of 27 phyllostomid species. Total species richness in each land-use type varied from 24 species in forest fragments to 22 species in commercial shade polycultures. Although the cumulative observed species richness showed little change in response to management intensity, the number of bats captured per MNH declined significantly in the more intensively managed (i.e., low-shade monocultures) plantations. Intensively managed coffee plantations had lower phyllostomid diversity and species similarity, and had lower proportions of nectarivorous and animalivorous bats. Among frugivores, the proportion of large (> 25 g) frugivores captured increased with management intensity. Recapture frequency was significantly higher than expected in forest fragments, and lower than expected in more intensively managed coffee. Our results suggest that less intensively managed coffee agroforests can serve as valuable feeding and commuting areas for most leaf-nosed bats, and that maintaining forest fragments in agricultural landscapes contributes to bat diversity. Declines in populations of gleaning insectivores, however, could compromise natural suppression of insect pests in these agricultural areas.

Between a Pristine Myth and an Impoverished Future

Abstract: Early European naturalists saw Amazonian landscapes as pristine, but modern research has found a complex historical ecology, similar to that of other tropical and temperate regions. Although the pristine myth has been thoroughly debunked, too many biodiversity researchers fail to incorporate historical ecology into their analyses. For a world society out of balance with its natural resource base, careful interpretation is essential to understand trends, including impoverishment of planetary biodiversity. If world society avoids civilizational collapse, parts of Amazonia's historical ecology can contribute to future sustainability and improved survival of its biodiversity.

Tree Diversity Explains Variation in Ecosystem Function in a Neotropical Forest in Panama

Abstract: Many experimental studies show that a decline in species number has a negative effect on ecosystem function, however less is known about this pattern in natural communities. We examined the relative importance of environment, space, and diversity on ecosystem function, specifically tree carbon storage in four plant types (understory/canopy; trees/palms), in a tropical forest in central Panama. The objectives of this study were to detect the relationship between tree diversity and carbon storage given the environmental and spatial variation that occur in natural forests and to determine which species diversity measure is more important to tree carbon storage: richness or dominance. We used redundancy analyses to partition the effect of these sources of variation on tree carbon storage. We showed that together, environment, space, and diversity accounted for 43 percent of tree carbon storage, where diversity (19%) alone is the most important source of variation and explained more variation than space (13%) and environment (1%) together. Therefore, even in natural forests where substantial environment and spatial variation can be found, it is still possible to detect the effect of diversity on ecosystem function at scales relevant to conservation. Moreover, both richness and dominance are important to explain the variation on tree carbon storage in natural forests suggesting that these two diversity measures are complementary. Thus, tree diversity is important to predict tree carbon storage in hyperdiverse forests.

Effects of Plot Size and Census Interval on Descriptors of Forest Structure and Dynamics

Abstract: This study was designed to explicitly formulate the effect of census interval and plot size on the variability of descriptors of tropical forest structure (stand density, basal area, aboveground biomass [AGB]) and dynamic (tree growth, mortality and recruitment rates, biomass fluxes). A unique dataset from a broad plot network (37.5ha) surveyed every 2yr over a 16-yr period was used to develop and parameterize a new statistical model predicting the coefficients of variation for each forest descriptor. More than 90 percent of the inherent variability of these coefficients was predicted using a simple model including plot size and census interval in a Bayesian modeling framework. All descriptors of forest structure varied by o10 percent for plot sizes 42ha. Among the descriptors of forest dynamics, AGB loss was the most variable. The number of 6.25ha plots required to estimate its mean, over a 16-yr period, within a 20 percent error of the mean remains above four. This contrasts with a relative constant flux of biomass entering the plot through tree growth and tree recruitment. Tree growth was remarkably well estimated with o15 percent variability for a 2-yr census in a plot of 2ha. This study provides an easy method to assess dataset limitations in efforts to estimate descriptors of forest structure and dynamic, which is of primary importance to decipher any clear consequences of global change in tropical forests.

Variation in Susceptibility to Hurricane Damage as a Function of Storm Intensity in Puerto Rican Tree Species

Abstract: One of the most significant challenges in developing a predictive understanding of the long-term effects of hurricanes on tropical forests is the development of quantitative models of the relationships between variation in storm intensity and the resulting severity of tree damage and mortality. There have been many comparative studies of interspecific variation in resistance of trees to wind damage based on aggregate responses to individual storms. We use a new approach, based on ordinal logistic regression, tofit quantitativemodels of the susceptibility of a tree species to different levels of damage across an explicit rangeof hurricane intensity. Our approach simultaneously estimates both the local intensity of the storm within a plot and the susceptibility to storm damage of different tree species within plots. Using the spatial variation of storm intensity embedded in two hurricanes (Hugo in 1989 and Georges in 1998) that struck the 16ha Luquillo Forest Dynamics Plot in eastern Puerto Rico, we show that variationin susceptibility to storm damage is an important aspect of life history differentiation. Pioneers such as Cecropia schreberiana are highly susceptible to stem damage, while the late successional species Dacryodes excelsa suffered very little stem damage but significant crown damage. There was a surprisingly weak relationship between tree diameter and the susceptibility to damage for most of the 12 species examined. This may be due to the effects of repeated storms and trade winds on the architecture of trees and forest stands in this Puerto Rican subtropical wet forest.

Frugivory and seed dispersal by the lowland tapir Tapirus terrestris in the Peruvian Amazon.

Abstract: The lowland tapir Tapirus terrestris is the largest herbivore in the Neotropics and feeds on a large quantity of fruits, often ingesting the seeds and defecating them intact. Seed dispersal by the lowland tapir in the southwestern Amazon was studied by examining seeds from 135 dung samples collected between 2005 and 2007. Seeds of a total of 122 plant species were identified, representing 68 genera and 33 families. The species accumulation curve showed that more species can be expected with further sampling. Many species (45%) were only encountered once, and only 10 percent of all species were found in >10 samples, indicating that the lowland tapir is an opportunistic forager. Seed diversity showed a clear seasonal pattern and was highly correlated with fruit availability. Seed diameter ranged from <1 to 25 mm with 81 percent <10 mm diam. The size distribution of seeds found in lowland tapir dung generally followed that of seeds found in the forest, but had a lower proportion of seeds in the smallest size class (<2.5 mm) and a larger proportion found in the largest size class (20–25 mm). The diversity of seeds encountered in dung of the lowland tapir in this study was much higher than in previous studies. We conclude that the lowland tapir is a potential disperser for a large number of plant species, including many that previously have been thought to be dispersed only by large primates. RESUMEN El tapir (Tapirus terrestris) es el herbivoro mas grande en los Neotropicos y se alimenta de una gran cantidad de frutas, muchas veces ingiriendo las semillas y defecandolas intactas. La dispersion de semillas por el tapir en el Sureste del Amazonas Peruano se estudio mediante el analisis de semillas provenientes de 135 excretas colectadas entre 2005 y 2007. Se identificaron un total de 122 diferentes especies de semillas de diferentes plantas, representando 68 generos y 33 familias. La curva de acumulacion de especies mostro que se puede esperar un numero mayor de semillas con un muestreo mayor. Muchas especies (45%) se encontraron solo una vez y solo el 10% de todas las semillas se encontro en mas de 10 muestras, indicando que el tapir es un forrajero oportunista. El diametro de las semillas vario de < 1 mm a 25 mm. El 81% fue < 10 mm de diametro. La distribucion del tamano de las semillas encontrado en las excretas generalmente siguio al de las semillas encontradas en el bosque, pero tuvo una baja proporcion de semillas dentro de la clase mas pequena (< 2.5mm) y una mayor proporcion entrada en la clase mas grande (20–25mm). La diversidad de semillas encontrada en este estudio mostro tambien un claro patron estacional que se correlaciono grandemente con la diversidad de frutos y la variedad fue mucho mas diversa que la encontrada en otros estudios de este tipo. Concluimos que el tapir es un dispersador potencial para un gran numero de especies de plantas incluyendo muchas que se penso serian dispersadas solamente por primates.

Changes in structure, composition, and nutrients during 15 years of hurricane-induced succession in a subtropical wet forest in Puerto Rico.

Abstract: The trajectory of hurricane-induced succession was evaluated in a network of forest plots measured immediately before and 3mo, 5, 10, and 15yr after the direct impact of a Category 4 hurricane. Comparisons of forest structure, composition, and aboveground nutrients pools were made through time, and between species, lifehistory groups and geomorphic settings. The hurricane reduced aboveground biomass by 50 percent, causing an immediate decrease in stem density and diversity indices among all geomorphic settings. After 15yr, basal area and aboveground biomass returned to pre-hurricane levels, while species richness, diversity indices, and stem densities exceeded pre-hurricane levels. Differences in species composition among geomorphic settings had not returned after 15yr but differences in stem densities and structure were beginning to emerge. Significant differences were observed in the nutrient concentration of the three species that comprised the most aboveground biomass, and between species categorized as secondary high-light species and primary, low-light species. Species whose abundance was negatively correlated with the mature forest dominant also had distinct nutrient concentrations. When total aboveground nutrient pools were compared over time, differences in leaf nutrients among species were hidden by similarities in wood nutrient concentrations and the biomass dominance of a few species. The observed successional trajectory indicates that changes in species composition contributed to fast recovery of aboveground biomass and nutrient pools, while the influence of geomorphic setting on species composition occurs at time scales 415yr of succession.

Long‐distance Dispersal of Invasive Grasses by Logging Vehicles in a Tropical Dry Forest

Abstract: Predicting responses of vegetation to environmental factors in human-altered tropical ecosystems requires an understanding of the controls on plant population expansion across landscapes (i.e., long-distance dispersal) as well as of factors affecting recruitment at local scales (i.e., microsite conditions). We studied the roles of light availability, habitat type, soil disturbance, and seed dispersal in a selectively logged forest in lowland Bolivia where the exotic forage grass Urochloa (Panicum) maxima is abundant on roads and log landings but does not invade felling gaps or unlogged forest. Shade-house trials and seed addition experiments with U. maxima revealed that this C 4 grass thrives in high light but also grows in partial shade (10% full sun, but not 1% full sun), and that felling gaps, but not undisturbed forest, are suitable for grass establishment. To determine if seed dispersal by logging vehicles explains the discrepancy between actual and potential grass recruitment sites, we collected grass seeds that fell from trucks onto log landings located long distances (> 500 m) from established grass populations. Trucks dispersed an estimated 1800 alien grass seeds per log landing during the early dry season; automobiles also transported seeds of grass (135 seeds/vehicle). The seeds collected (and relative abundances) were the exotics U. (Panicum) maxima (97%) and Urocbloa (Brachiaria) brizantha (2%), and the pan-tropical weeds Sorghum halapense (1%) and Rottboellia cochinchinensis (0.2%). Grasses invade this forest where disturbance coincides with seed dispersal by motor vehicles, while dispersal limitation apparently prevents invasion of many sites otherwise suitable for grass recruitment (i.e., felling and natural gaps).

Canopy Herbivory and Insect Herbivore Diversity in a Dry Forest–Savanna Transition in Brazil

Abstract: This study aimed to compare canopy herbivore diversity and resultant insect damage to vegetation in two distinct and adjacent ecosystems, specifically a dry forest ecosystem and a cerrado (savanna) ecosystem that occur together in an abrupt transition zone in southeastern Brazil. In the dry forest, the canopy was reached using a single rope climbing technique, whereas the shorter canopy of the cerrado was assessed using a 7m ladder. Insect specimens were collected by beating the foliage, and 20 representative leaves were collected to calculate the specific leaf mass (SLM) and leaf area loss through herbivory. Also, we collected ten soil samples from each habitat to determine soil nutrient content. We sampled 118 herbivorous insects from ten families, mostly in dry forest trees (96 individuals belonging to 31 species). A higher abundance of chewing and sap-sucking insects were observed in dry forest trees than in cerrado trees. The same pattern was observed for the richness of chewers, with a higher degree of diversity of chewers found in dry forest trees than in cerrado trees. Herbivorous insects were not affected by SLM regardless of guild and habitat. However, we observed a negative correlation between the herbivory rate and the specific leaf mass (SLM). The cerrado trees showed a higher SLM and lower herbivory rates than trees occurring in the dry forest. These results suggest that herbivory rates in the transition dry forest‐cerrado may be driven by soil nutrient content, which is thought to influence leaf sclerophylly.

Giant Tortoises as Ecological Engineers: A Long‐term Quasi‐experiment in the Galápagos Islands

Abstract: Giant tortoises were once a megafaunal element widespread in tropical and subtropical ecosystems. The role of giant tortoises as herbivores and seed dispersers, however, is poorly known. We evaluated tortoise impacts on Opuntia cactus (Cactaceae) in the Galapagos Islands, one of the last areas where giant tortoises remain extant, where the cactus is a keystone resource for many animals. We contrasted cactus populations immediately inside and outside natural habitats where tortoises had been held captive for several decades. Through browsing primarily and trampling secondarily tortoises strongly reduced densities of small (0.5–1.5 m high) cacti, especially near adult cacti, and thereby reduced densities of cacti in larger size classes. Tortoises also caused a shift from vegetative to sexual modes of reproduction in cacti. We conclude that giant tortoises promote a sparse and scattered distribution in Opuntia cactus and its associated biota in the Galapagos Islands. RESUMEN Las tortugas gigantes fueron en un tiempo un elemento de mega-fauna ampliamente distribuido en ecosistemas tropicales, en los que parecen haber tenido un papel muy importante aunque aun no del todo comprendido, como herbivoros y dispersores de semillas. En las Islas Galapagos, una de los ultimos lugares donde las tortugas gigantes estan presentes, evaluamos el impacto de las tortugas en los cactos Opuntia (Cactaceae), que componen un recurso clave para muchas de las especies del archipielago. La comparacion de poblaciones de cactos inmediatamente dentro y fuera de habitats naturales en los que se han mantenido tortugas en cautividad por varias decadas indico que las tortugas reducen considerablemente las densidad de cactos pequenos (de entre 0.5 y 1.5 m de altura), y en consecuencia tambien las densidades de cactos en categorias de mayor tamano. Las tortugas redujeron la densidad de plantulas de cacto principalmente mediante ramoneo, y, en menor grado, mediante el pisoteo de las plantulas en las inmediaciones de los cactos adultos. Ademas, las tortugas ocasionaron un fuerte cambio en los metodos de reproduccion de los cactos, impulsando la reproduccion sexual en detrimento de las formas de reproduccion vegetativa. Concluimos que las tortugas gigantes probablemente promueven una distribucion dispersa y rala de cactos.

Species-specific growth responses to climate variations in understory trees of a Central African rain forest

Abstract: Basic knowledge of the relationships between tree growth and environmental variables is crucial for understanding forest dynamics and predicting vegetation responses to climate variations. Trees growing in tropical areas with a clear seasonality in rainfall often form annual growth rings. In the understory, however, tree growth is supposed to be mainly affected by interference for access to light and other resources. In the semi-deciduous Mayombe forest of the Democratic Republic of Congo, the evergreen species Aidia ochroleuca, Corynanthe paniculata and Xylopia wilwerthii dominate the understory. We studied their wood to determine whether they form annual growth rings in response to changing climate conditions. Distinct growth rings were proved to be annual and triggered by a common external factor for the three species. Species-specific site chronologies were thus constructed from the cross-dated individual growth-ring series. Correlation analysis with climatic variables revealed that annual radial stem growth is positively related to precipitation during the rainy season but at different months. The growth was found to associate with precipitation during the early rainy season for Aidia but at the end of the rainy season for Corynanthe and Xylopia. Our results suggest that a dendrochronological approach allows the understanding of climate–growth relationships in tropical forests, not only for canopy trees but also for evergreen understory species and thus arguably for the whole tree community. Global climate change influences climatic seasonality in tropical forest areas, which is likely to result in differential responses across species with a possible effect on forest composition over time

Assessment of Aboveground Carbon in Primary and Selectively Harvested Tropical Forest in Papua New Guinea

Abstract: Papua New Guinea (PNG) has become the focus of climate change mitigation initiatives such as reducing emissions from deforestation and forest degradation, but defensible estimates of forest carbon are lacking. Here we present a methodology for estimating aboveground forest carbon, and apply it to a large Permanent Sample Plot system maintained by Papua New Guinea Forest Research Institute. We report the first estimates of forest carbon in lowland tropical forest in PNG. Average aboveground carbon in stems 410cm diam. for 115 selectively harvested 1-ha plots in lowland tropical forest was 66.3 � 3.5MgC/ha (95% CI) while for 10 primary forest plots the average was 106.3 � 16.2MgC/ha. We applied ratios based on field observations, in-country studies, and the literature to estimate unmeasured pools of aboveground carbon (stems o10cm diam., fine litter and coarse woody debris). Total aboveground carbon was estimated at 90.2 and 120.8MgC/ha in selectively harvested and primary lowland forest, respectively. Our estimate for primary tropical forest is lower than biome averages for tropical equatorial forest, and we hypothesize that frequent disturbances from fire, frost, landslides, and agriculture are limiting carbon stock development. The methodology and estimates presented here will assist the PNG government in its preparedness for mitigation initiatives, are of interest to communities that are seeking to participate in voluntary carbon markets, and will encourage transparency and consistency in the estimation of forest carbon.

Twig-Nesting Ants: The Hidden Predators of the Coffee Berry Borer in Chiapas, Mexico

Abstract: Coffee is a globally important crop that is subject to numerous pest problems, many of which are partially controlled by predatory ants. Yet several studies have proposed that these ecosystem services may be reduced where agricultural systems are more intensively managed. Here we investigate the predatory ability of twignesting ants on the main pest of coffee, the coffee berry borer (Hypothenemus hampei) under different management systems in southwest Chiapas, Mexico. We conducted both laboratory and field experiments to examine which twig-nesting ant species, if any, can prey on free-living borers or can remove borers embedded in coffee fruits and whether the effects of the twig-nesting ant community differ with habitat type. Results indicate that several species of twig-nesting ants are effective predators of both free-living borers and those embedded in coffee fruits. In the lab, Pseudomyrmex ejectus, Pseudomyrmex simplex, and Pseudomyrmex PSW-53 effectively removed free-living and embedded borers. In the field, abundance, but not diversity, of twig-nesting ant colonies was influenced by shade management techniques, with the highest colony abundance present in the sites where shade trees were recently pruned. However, borer removal rates in the field were significant only in the shadiest site, but not in more intensively managed sites. This study provides evidence that twig-nesting ants can act as predators of the coffee berry borer and that the presence of twig-nesting ants may not be strongly linked to shade management intensity, as has been suggested for other arthropod predators of the borer.

Hurricane Disturbance Alters Secondary Forest Recovery in Puerto Rico

Abstract: Land-use history and large-scale disturbances interact to shape secondary forest structure and composition. How introduced species respond to disturbances such as hurricanes in post-agriculture forest recovery is of particular interest. To examine the effects of hurricane disturbance and previous land use on forest dynamics and composition, we revisited 37 secondary forest stands in former cattle pastures across Puerto Rico representing a range of exposure to the winds of Hurricane Georges in 1998. Stands ranged from 21 to>80 yr since agricultural abandonment and were measured 9 yr posthurricane. Stem density decreased as stands aged, while basal area and species richness tended to increase. Hurricane disturbance exerted contrasting effects on stand structure, contingent on stand age. In older stands, the basal area of large trees fell, shifting to a stand structure characteristic of younger stands, while the basal area of large trees tended to rise in younger stands with increasing hurricane disturbance. These results demonstrate that large-scale natural disturbances can alter the successional trajectory of secondary forest stands recovering from human land use, but stand age, precipitation and soil series were better predictors of changes in stand structure across all study sites. Species composition changed substantially between census intervals, but neither age nor hurricane disturbance consistently predicted species composition change. However, exposure to hurricane winds tended to decrease the abundance of the introduced tree Spathodea campanulata, particularly in smaller size classes. In all sites the abundance of the introduced tree Syzygium jambos showed a declining trend, again most strongly in smaller size classes, suggesting natural thinning through succession. RESUMEN Tanto la historia de uso de la tierra como los disturbios naturales pueden afectar la dinamica, estructura, y composicion de bosques secundarios. Su efecto sobre la dinamica de especies introducidas es de particular interes. En este estudio examinamos cambios en la estructura y composicion de 37 parcelas establecidas inicialmente en 1995–96 en una serie de bosques secundarios que crecieron en pastizales abandonados a traves de la isla de Puerto Rico. Estos bosques tienen de 21 a 80 anos y sufrieron danos variables durante el huracan Georges en 1998. El trabajo de campo para este estudio se llevo a cabo en 2007. La densidad de arboles aumento con la edad mientras que el area basal disminuyo. El efecto del huracan sobre la estructura de estos bosques dependio de su edad. En bosques mas maduros el huracan derrumbo los arboles de mayor tamano, creando una estructura semejante a bosques mas jovenes, mientras que en los bosques jovenes el huracan tendio a generar una estructura caracteristica de bosques mas maduros. Nuestros resultados demuestran que los disturbios naturales pueden alterar la trayectoria de recuperacion de bosques secundarios. Sin embargo tanto la edad como la precipitacion y calidad de suelos son mejores predictores de cambios en la estructura de estos bosques que el nivel de danos sufridos durante el huracan. La composicion de especies cambio de manera substancial entre los censos aunque ni el efecto del huracan ni la edad de las parcelas explica los cambios observados. La exposicion a los vientos de Georges tendio a aumentar la abundancia de la especie introducida Spathodea campanulata, particularmente en los pies de menos de 1 cm dap. La abundancia del arbol introducido Syzgium jambos tendio a disminuir con el tiempo, como resultado de la exclusion competitiva a lo largo de la sucesion.

Arthropod abundance and diversity in a lowland tropical forest floor in Panama: the role of habitat space vs. nutrient concentrations.

Abstract: Tropical forest floor characteristics such as depth and nutrient concentrations are highly heterogeneous even over small spatial scales and it is unclear how these differences contribute to patchiness in forest floor arthropod abundance and diversity. In a lowland tropical forest in Panama we experimentally increased litter standing crop by removing litter from five plots (L-) and adding it to five other plots (L+); we had five control plots. After 32 mo of treatments we investigated how arthropod abundance and diversity were related to differences in forest floor physical (mass, depth, water content) and chemical properties (pH, nutrient concentrations). Forest floor mass and total arthropod abundance were greater in L+ plots compared with controls. There were no treatment differences in nutrient concentrations, pH or water content of the organic horizons. Over all plots, the mass of the fermentation horizon (Oe) was greater than the litter horizon (Oi); arthropod diversity and biomass were also greater in the Oe horizon but nutrient concentrations tended to be higher in the Oi horizon. Arthropod abundance was best explained by forest floor mass, while arthropod diversity was best explained by phosphorus, calcium and sodium concentrations in the Oi horizon and by phosphorus concentrations in the Oe horizon. Differences in arthropod community composition between treatments and horizons correlated with phosphorus concentration and dry mass of the forest floor. We conclude that at a local scale, arthropod abundance is related to forest floor mass ( habitat space), while arthropod diversity is related to forest floor nutrient concentrations (habitat quality).