Tropical Forest Plots Research Articles

Terrestrial vertebrates alter seedling composition and richness but not diversity in an Australian tropical rain forest

Although birds and mammals play important roles in several mechanisms hypothesized to maintain plant diversity in species-rich habitats, there have been few long-term, community-level tests of their importance. We excluded terrestrial birds and mammals from fourteen 6 x 7.5 m plots in Australian primary tropical rain forest and compared recruitment and survival of tree seedlings annually over the subsequent seven years to that on nearby open plots. We re-censused a subset of the plots after 13 years of vertebrate exclusion to test for longer-term effects. After two years of exclusion, seedling abundance was significantly higher (74%) on exclosure plots and remained so at each subsequent census. Richness was significantly higher on exclosure plots from 1998 to 2003, but in 2009 richness no longer differed, and rarefied species richness was higher in the presence of vertebrates. Shannon's diversity and Pielou's evenness did not differ in any year. Vertebrates marginally increased density-dependent mortality and recruitment limitation, but neither effect was great enough to increase richness or diversity on open plots relative to exclosure plots. Terrestrial vertebrates significantly altered seedling community composition, having particularly strong impacts on members of the Lauraceae. Overall, our results highlight that interactions between terrestrial vertebrates and tropical tree recruitment may not translate into strong community-level effects on diversity, especially over the short-term, despite significant impacts on individual species that result in altered species composition.

ForestPlots.net: a web application and research tool to manage and analyse tropical forest plot data

AbstractTropical forests are biologically diverse ecosystems that play important roles in the carbon cycle and maintenance of global biodiversity. Understanding how tropical forests respond to environmental changes is important, as changes in carbon storage can modulate the rate and magnitude of climate change. Applying an ecoinformatics approach for managing long‐term forest inventory plot data, where individual trees are tracked over time, facilitates regional and cross‐continental forest research to evaluate changes in taxonomic composition, growth, recruitment and mortality rates, and carbon and biomass stocks. We developed ForestPlots.net as a secure, online inventory data repository and to facilitate data management of long‐term tropical forest plots to promote scientific collaborations among independent researchers. The key novel features of the database are: (a) a design that efficiently deals with time‐series data; (b) data management tools to assess potential errors; and (c) a query library to generate outputs (e.g. biomass and carbon stock changes over time).

Macrohongos presentes en el bosque seco tropical de la región del Valle del Cauca, Colombia.

Los macrohongos son organismos importantes en los ecosistemas terrestres por su rol en los procesos de descomposición, reciclaje de nutrientes y gran potencial de uso. El Parque Natural Regional El Vínculo, en el Departamento del Valle del Cauca, es un área cubierta en su mayoría por bosque seco tropical (Bs-T). El objetivo de este estudio fue conocer y elaborar el primer listado de las especies de macrohongos presentes en este tipo de bosque, dada la carente información en este aspecto en Colombia. Se elaboraron parcelas de muestreo de 100 m2, en las cuales se colectaron los macrohongos presentes en la zona. En total se encontraron 199 especímenes, de las cuales el grupode los hongos Agaricales está representado en un 51% dentro del bosque y se encuentran distribuidos en 9 familias, 15 géneros, 60 morfoespecies y 19 especies. Algunas de las especies encontradas han sido reportadas como comestibles y de interés medicinal.

Deterministic tropical tree community turnover: evidence from patterns of functional beta diversity along an elevational gradient

Explaining the mechanisms that produce the enormous diversity within and between tropical tree communities is a pressing challenge for plant community ecologists. Mechanistic hypotheses range from niche-based deterministic to dispersal-based stochastic models. Strong tests of these hypotheses require detailed information regarding the functional strategies of species. A few tropical studies to date have examined trait dispersion within individual forest plots using species trait means in order to ask whether coexisting species tend to be more or less functionally similar than expected given a null model. The present work takes an alternative approach by: (i) explicitly incorporating population-level trait variability; and (ii) quantifying the functional beta diversity in a series of 15 tropical forest plots arrayed along an elevational gradient. The results show a strong pattern of decay in community functional similarity with elevation. These observed patterns of functional beta diversity are shown to be highly non-random and support a deterministic model of tropical tree community assembly and turnover.

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

ABSTRACTPapua 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 >10 cm diam. for 115 selectively harvested 1‐ha plots in lowland tropical forest was 66.3±3.5 Mg C/ha (95% CI) while for 10 primary forest plots the average was 106.3±16.2 Mg C/ha. We applied ratios based on field observations, in‐country studies, and the literature to estimate unmeasured pools of aboveground carbon (stems <10 cm diam., fine litter and coarse woody debris). Total aboveground carbon was estimated at 90.2 and 120.8 Mg C/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.

Microbial community shifts influence patterns in tropical forest nitrogen fixation

The role of biodiversity in ecosystem function receives substantial attention, yet despite the diversity and functional relevance of microorganisms, relationships between microbial community structure and ecosystem processes remain largely unknown. We used tropical rain forest fertilization plots to directly compare the relative abundance, composition and diversity of free-living nitrogen (N)-fixer communities to in situ leaf litter N fixation rates. N fixation rates varied greatly within the landscape, and 'hotspots' of high N fixation activity were observed in both control and phosphorus (P)-fertilized plots. Compared with zones of average activity, the N fixation 'hotspots' in unfertilized plots were characterized by marked differences in N-fixer community composition and had substantially higher overall diversity. P additions increased the efficiency of N-fixer communities, resulting in elevated rates of fixation per nifH gene. Furthermore, P fertilization increased N fixation rates and N-fixer abundance, eliminated a highly novel group of N-fixers, and increased N-fixer diversity. Yet the relationships between diversity and function were not simple, and coupling rate measurements to indicators of community structure revealed a biological dynamism not apparent from process measurements alone. Taken together, these data suggest that the rain forest litter layer maintains high N fixation rates and unique N-fixing organisms and that, as observed in plant community ecology, structural shifts in N-fixing communities may partially explain significant differences in system-scale N fixation rates.

A model-based method for estimating effective dispersal distance in tropical plant populations

Dispersal is a key mechanism to help populations propagate across space and thus is important in helping to understand spatial patterns. However, it is often difficult to quantify empirically as it requires intensive and detailed field study. Here we describe a method for estimating the effective dispersal distance of tropical plant populations. The method integrates a simple spatially explicit, individual-based dynamic model and spatial statistical analysis. The model is partly parameterized from spatial point pattern data as well as time series data from a 50 ha tropical forest plot in Barro Colorado Island (BCI) in Panama. Correlation between our estimated dispersal distances and those from inverse modeling based on field studies to date on BCI raises some questions about the match between our methods and those previously used. The method we propose can be generalized to any population for which spatial point pattern data are available. Additional field studies would be useful to further validate our method.

Effects of stochastic herbivory events on population maintenance of an understorey palm species (Geonoma schottiana) in riparian tropical forest

Abstract:Plant populations can respond to temporal environmental heterogeneity caused by natural disturbances, such as herbivory. Palm individuals of several species are preyed upon by mammals, but the effects of such herbivory events on population dynamics remain poorly known. To evaluate the effects of environmental stochasticity on aGeonoma schottiana(Arecaceae) population, we surveyed annually 40 permanent 20 × 10-m plots in a riparian tropical forest over 5 y (2000–2004) and results were analysed using matrix models. The population growth rate (λ) was in equilibrium during the study period and only one bad year was identified (2002–2003), which had a higher mortality of juvenile individuals due to herbivory. Additionally, the bad year had a higher mortality of reproductive individuals than the other periods. The stasis matrix elements of the later life stages were the vital rates with highest elasticities. The mortality of juvenile and reproductive individuals had a negative contribution to λ in the bad year. Conversely, the growth of infant and juvenile individuals and the clonal growth of juveniles were the vital rates with highest contribution to stability maintenance of λ in the bad year in a life-table response experiment. The palm population had a high individual density, high proportion of the initial life stages, clonal growth, high fertility, abundant seed bank and high seedling recruitment. Despite these traits, if stochastic herbivory events occur frequently over a long period of time, the population will have a negative growth rate and the probability of local extinction will be very high.

Functional trait variation and sampling strategies in species‐rich plant communities

Summary 1. Despite considerable interest in the application of plant functional traits to questions of community assembly and ecosystem structure and function, there is no consensus on the appropriateness of sampling designs to obtain plot‐level estimates in diverse plant communities. 2. We measured 10 plant functional traits describing leaf and stem morphology and ecophysiology for all trees in nine 1‐ha plots in terra firme lowland tropical rain forests of French Guiana (N = 4709). 3. We calculated, by simulation, the mean and variance in trait values for each plot and each trait expected under seven sampling methods and a range of sampling intensities. Simulated sampling methods included a variety of spatial designs, as well as the application of existing data base values to all individuals of a given species. 4. For each trait in each plot, we defined a performance index for each sampling design as the proportion of resampling events that resulted in observed means within 5% of the true plot mean, and observed variance within 20% of the true plot variance. 5. The relative performance of sampling designs was consistent for estimations of means and variances. Data base use had consistently poor performance for most traits across all plots, whereas sampling one individual per species per plot resulted in relatively high performance. We found few differences among different spatial sampling strategies; however, for a given strategy, increased intensity of sampling resulted in markedly improved accuracy in estimates of trait mean and variance. 6. We also calculated the financial cost of each sampling design based on data from our ‘every individual per plot’ strategy and estimated the sampling and botanical effort required. The relative performance of designs was strongly positively correlated with relative financial cost, suggesting that sampling investment returns are relatively constant. 7. Our results suggest that trait sampling for many objectives in species‐rich plant communities may require the considerable effort of sampling at least one individual of each species in each plot, and that investment in complete sampling, though great, may be worthwhile for at least some traits.

A new approach to trenching experiments for measuring root–rhizosphere respiration in a lowland tropical forest

Soil respiration in tropical forests is a major source of atmospheric CO 2. The ability to partition soil respiration into its individual components is becoming increasingly important to predict the effects of disturbance on CO 2 efflux from the soil as the responses of heterotrophic and autotrophic respiration to change are likely to differ. However, current field methods to partition respiration suffer from various methodological artefacts; root–rhizosphere respiration is particularly difficult to estimate. We used trenched subplots to estimate root–rhizosphere respiration in large-scale litter addition (L+), litter removal (L−) and control (CT) plots in a lowland tropical semi-evergreen forest in Panama. We took a new approach to trenching by making measurements immediately before-and-after trenching and comparing them to biweekly measurements made over one year. Root–rhizosphere respiration was estimated to be 38%, 17% and 27% in the CT, L+, and L− plots, respectively, from the measurements taken immediately before and one day after trenching in May–June 2007. Biweekly measurements over the following year provided no estimates of root–rhizosphere respiration for the first seven months due to decomposition of decaying roots. We were also unable to estimate root–rhizosphere respiration during the dry season due to differences in soil water content between trenched and untrenched soil. However, biweekly measurements taken during the early rainy season one year after trenching (May–June 2008) provided estimates of root–rhizosphere respiration of 39%, 24% and 36% in the CT, L+, and L− plots, respectively, which are very similar to those obtained during the first day after trenching. We suggest that measurements taken immediately before and one day after root excision are a viable method for a rapid estimation of root–rhizosphere respiration without the methodological artefacts usually associated with trenching experiments.

A new technique for inventory of permanent plots in tropical forests: a case study from lowland dipterocarp forest in Kuala Belalong, Brunei Darussalam

This paper describes a new technique for inventory of permanent plots in tropical forests and presents the results of its application in a 1 ha permanent plot in a lowland dipterocarp forest at Kuala Belalong, Ulu Temburong National Park, Brunei Darussalam. The technique is based on mapping of positions of tree individuals in three-dimensional space with a high accuracy. Measuring set consists of a distance measuring device (laser rangefinder) and a electronic compass supplying data to a field computer with specialized software (Field-Map®). This method is faster and more exact than methods based on Cartesian grids established in the field. As an example, inventories from 2000 and 2007 of the plot mentioned are compared concerning presence, taxonomical identity and diameter at breast height (dbh) of all tree individuals with dbh ≥ 5 cm. The structural and diversity properties of the forest show similar patterns to the other two permanent plots in Kuala Belalong. In 2007, 1 318 trees were found, out of which 116 were new individuals (i.e. exceeded the 5 cm dbh limit since 2000), 13 were dead individuals. 120 trees died since 2000 (9.2 % of the trees recorded in 2000). Total basal area was 39.18 m2 (0.2 m2 were dead individuals). Growth dynamics has distinct spatial patterns: about half of the plot shows fast dbh increment in 2000–2007 and appearance of numerous new trees; the other half displays stagnation. This is probably due to topographic conditions and partly to the gap dynamics (several dominant trees have fallen there since 2000). Concerning the taxonomic composition, 47 families were recorded, the dominant ones in terms of basal area being Dipterocarpaceae, Myrtaceae, Euphorbiaceae, Lauraceae, Sapotaceae and Burseraceae (sorted in decreasing order). The Dipterocarp family accounts for about 40 % of the total dbh. The most frequent ones were trees of Euphorbiaceae, Dipterocarpaceae, Myrtaceae, Burseraceae and Anacardiaceae. However, this census concerns mainly trees with dbh ≥ 10 cm, while the rest (dbh 5 –10 cm) remained partly undetermined until 2007.

Influence of soil, topography and substrates on differences in wood decomposition between one-hectare plots in lowland tropical moist forest in Central Amazonia

Abstract:Understanding how wood decomposition varies spatially at the mesoscale (between 1-ha plots) may improve carbon flux estimates in Amazonian forests. An experiment was carried out to test the influence of soil, slope, above-ground tree live biomass (biomass), fine-litter mass and characteristics of neighbouring trees on the variation of wood decomposition between 1-ha plots in four species of tropical trees that vary in wood density (Manilkara huberi – 0.86 g cm−3, Couratari guianensis – 0.54 g cm−3, Hura crepitans – 0.32 g cm−3 and Parkia pendula – 0.29 g cm−3). A wood sample from each species (30 × 5 × 2.5 cm) was placed in each of 71 plots within 64 km2 of terra firme tropical moist forest in Reserva Florestal Adolpho Ducke. One year later, samples were collected and weighed. The effects of specificity of decomposers was measured by the association of decomposition with the wood density and with the taxonomic group of the nearest tree with dbh ≥30 cm. Wood decomposition was independent of soil (texture and nutrients), slope, biomass and fine-litter mass at the mesoscale, except for C. guianensis, which showed greater decomposition in locations with greater biomass. Decomposition was also independent of wood density and taxonomic group of nearby large trees. In general, none of the variables was useful as a predictor of wood decomposition at the scale larger than 1 ha. Thus, the use of models that include soil and topography to improve estimates of carbon flux are limited because wood decomposition does not follow similar mesoscale patterns to that of biomass and fine-litter decomposition. Also, the results indicate that wood decomposition is more likely to be associated with generalist decomposers than with specialists associated with neighbouring trees.

Ecological Insights from Long‐term Research Plots in Tropical and Temperate Forests

This session was devoted to findings from an international network of long-term forest dynamics plots, providing some of the first comparisons between the tropical and temperate study areas. Whereas most ecologists recognize the importance of long-term research (Callahan 1984, Likens 1989, Magnuson 1990, Hobbie et al. 2003, and others), large-scale projects like this one are rare. The global network of forest dynamics plots has expanded since its origin in the early 1980s, yet research at the plots has remained integrated due to a combination of individual scientists’ efforts and institutional commitments from the Center for Tropical Forest Science (CTFS, ‹www.ctfs.si.edu› of the Smithsonian Tropical Research Institute and the Arnold Arboretum of Harvard University (Hubbell and Foster 1983, Condit 1995). Today, 26 large plots have been established in tropical or subtropical forests of Central and South America, Africa, Asia, and Oceania, along with 8 recently added temperate forest plots. A standard protocol (Condit 1998) is followed at all sites, including the marking, mapping, and measuring of all trees and shrubs with stem diameters ≥1 cm.

Tropical forest community ecology

Tropical forest community ecology

Multi‐stemmed trees in montane rain forests: their frequency and demography in relation to elevation, soil nutrients and disturbance

Summary Multi‐stemmed trees are a common component of tropical and temperate montane rain forests, where they co‐occur with single‐stemmed trees. We hypothesized that multi‐stemmed architecture should predominate in less productive sites (such as at high elevation or with low soil nutrient availability) and that, because it frequently results from sprouting, it should prevail in sites that are frequently disturbed. We also hypothesized that where multi‐stemmed architecture predominates, there should be lower rates of mortality and recruitment of individuals. We tested these hypotheses using data from permanent plots in tropical montane rain forests in Jamaica (14 years) and in temperate montane rain forests in New Zealand (19 years). The frequency of multi‐stemmed trees varied across plots in both forests (4–34% in Jamaica; 0–21% in New Zealand) along gradients of elevation and soil nutrients. Analyses examined the direct and indirect effects of the various environmental variables that are likely to drive site productivity and disturbance. We showed contrasting predictors of the frequency of multi‐stemmed trees in the tropical and temperate forests. Multi‐stemmed trees in Jamaican forests were most frequent on sites of low soil nutrient status (especially available soil phosphorus, P) whereas in New Zealand they were most frequent at high elevation sites, especially towards tree line. In both forests there was no relationship between multi‐stemmed tree frequency and slope. Turnover (the mean of mortality and recruitment rates) of multi‐stemmed trees in Jamaican forests was lowest on sites of low soil nutrient status (especially available P) but was unrelated to environmental predictors in New Zealand. In both forests, turnover rates of multi‐stemmed trees overall were 60% lower than those for co‐occurring single‐stemmed trees, offering support for the hypothesis that multi‐stemmed architecture favours persistence. Synthesis. Our study demonstrates that multi‐stemmed trees can predominate in low productivity sites in montane rain forests. Their low turnover compared with co‐occurring single‐stemmed trees confirms the importance of evaluating the persistence niche as a mechanism promoting woody species coexistence in forests.

Increasing carbon storage in intact African tropical forests

The response of terrestrial vegetation to a globally changing environment is central to predictions of future levels of atmospheric carbon dioxide. The role of tropical forests is critical because they are carbon-dense and highly productive. Inventory plots across Amazonia show that old-growth forests have increased in carbon storage over recent decades, but the response of one-third of the world's tropical forests in Africa is largely unknown owing to an absence of spatially extensive observation networks. Here we report data from a ten-country network of long-term monitoring plots in African tropical forests. We find that across 79 plots (163 ha) above-ground carbon storage in live trees increased by 0.63 Mg C ha(-1) yr(-1) between 1968 and 2007 (95% confidence interval (CI), 0.22-0.94; mean interval, 1987-96). Extrapolation to unmeasured forest components (live roots, small trees, necromass) and scaling to the continent implies a total increase in carbon storage in African tropical forest trees of 0.34 Pg C yr(-1) (CI, 0.15-0.43). These reported changes in carbon storage are similar to those reported for Amazonian forests per unit area, providing evidence that increasing carbon storage in old-growth forests is a pan-tropical phenomenon. Indeed, combining all standardized inventory data from this study and from tropical America and Asia together yields a comparable figure of 0.49 Mg C ha(-1) yr(-1) (n = 156; 562 ha; CI, 0.29-0.66; mean interval, 1987-97). This indicates a carbon sink of 1.3 Pg C yr(-1) (CI, 0.8-1.6) across all tropical forests during recent decades. Taxon-specific analyses of African inventory and other data suggest that widespread changes in resource availability, such as increasing atmospheric carbon dioxide concentrations, may be the cause of the increase in carbon stocks, as some theory and models predict.

The living library of The Cotapata National Park in Bolivia: an example of application of Bolivian law on the access to genetic resources

Developing countries with a rich biodiversity want to control the use of this natural patrimony, especially in the research of natural compounds of pharmaceutical interest. Here we present the organization of six permanent plots in a mountain tropical forest on the east side of the Andean Cordillera in Bolivia, and their role in the discovery of plants with antiplasmodial or antileishmanial activities. Permanent plots are widely used in ecological survey, but rarely in bioprospecting. This set-up allows Bolivian authorities to control the bioprospecting, and facilitates further chemical studies on the bioactive plants.

The role of gap phase processes in the biomass dynamics of tropical forests

The responses of tropical forests to global anthropogenic disturbances remain poorly understood. Above-ground woody biomass in some tropical forest plots has increased over the past several decades, potentially reflecting a widespread response to increased resource availability, for example, due to elevated atmospheric CO2 and/or nutrient deposition. However, previous studies of biomass dynamics have not accounted for natural patterns of disturbance and gap phase regeneration, making it difficult to quantify the importance of environmental changes. Using spatially explicit census data from large (50 ha) inventory plots, we investigated the influence of gap phase processes on the biomass dynamics of four 'old-growth' tropical forests (Barro Colorado Island (BCI), Panama; Pasoh and Lambir, Malaysia; and Huai Kha Khaeng (HKK), Thailand). We show that biomass increases were gradual and concentrated in earlier-phase forest patches, while biomass losses were generally of greater magnitude but concentrated in rarer later-phase patches. We then estimate the rate of biomass change at each site independent of gap phase dynamics using reduced major axis regressions and ANCOVA tests. Above-ground woody biomass increased significantly at Pasoh (+0.72% yr(-1)) and decreased at HKK (-0.56% yr(-1)) independent of changes in gap phase but remained stable at both BCI and Lambir. We conclude that gap phase processes play an important role in the biomass dynamics of tropical forests, and that quantifying the role of gap phase processes will help improve our understanding of the factors driving changes in forest biomass as well as their place in the global carbon budget.

Species Associations in a Heterogeneous Sri Lankan Dipterocarp Forest

We used point pattern analysis to examine the spatial distribution of 46 common tree species (diameter at breast height >10 cm) in a fully mapped 500x500-m tropical forest plot in Sinharaja, Sri Lanka. We aimed to disentangle the effect of species interactions (second-order effects) and environment (first-order effects) on the species' spatial distributions. To characterize first-order associations (segregation, overlap), we developed a classification scheme based on Ripley's K and nearest-neighbor statistics. We subsequently used heterogeneous Poisson null models, accounting for possible environmental heterogeneity, to reveal significant uni- and bivariate second-order interactions (regularity, aggregation and repulsion, attraction). First-order effects were strong; overall, 53% of all species pairs occupied largely disjoint areas (segregation), 40% showed partial overlap, and 6% overlapped. Only 5% of all species pairs showed significant second-order effects, but about half of the species showed significant intraspecific effects. Significant plant-plant interactions occurred mostly within 2-4 m and disappeared within 15-20 m of the focal plant. While lack of significant species interactions suggests support for the unified neutral theory, species' observed spatial segregation does not support the assumptions of the neutral theory. The strong observed tendency of species to segregate may have supplementary effects on other processes promoting species coexistence.

Impact of Research Trails on Seedling Dynamics in a Tropical Forest

ABSTRACTWe 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.