Tropical Forest Dynamics Research Articles

Canopy area of large trees explains aboveground biomass variations across neotropical forest landscapes

Abstract. Large tropical trees store significant amounts of carbon in woody components and their distribution plays an important role in forest carbon stocks and dynamics. Here, we explore the properties of a new lidar-derived index, the large tree canopy area (LCA) defined as the area occupied by canopy above a reference height. We hypothesize that this simple measure of forest structure representing the crown area of large canopy trees could consistently explain the landscape variations in forest volume and aboveground biomass (AGB) across a range of climate and edaphic conditions. To test this hypothesis, we assembled a unique dataset of high-resolution airborne light detection and ranging (lidar) and ground inventory data in nine undisturbed old-growth Neotropical forests, of which four had plots large enough (1 ha) to calibrate our model. We found that the LCA for trees greater than 27 m (∼ 25–30 m) in height and at least 100 m2 crown size in a unit area (1 ha), explains more than 75 % of total forest volume variations, irrespective of the forest biogeographic conditions. When weighted by average wood density of the stand, LCA can be used as an unbiased estimator of AGB across sites (R2 = 0.78, RMSE = 46.02 Mg ha−1, bias = −0.63 Mg ha−1). Unlike other lidar-derived metrics with complex nonlinear relations to biomass, the relationship between LCA and AGB is linear and remains unique across forest types. A comparison with tree inventories across the study sites indicates that LCA correlates best with the crown area (or basal area) of trees with diameter greater than 50 cm. The spatial invariance of the LCA–AGB relationship across the Neotropics suggests a remarkable regularity of forest structure across the landscape and a new technique for systematic monitoring of large trees for their contribution to AGB and changes associated with selective logging, tree mortality and other types of tropical forest disturbance and dynamics.

Effects of long-term inter-annual rainfall variation on the dynamics of regenerative communities during the old-field succession of a neotropical dry forest

Effects of long-term rainfall inter-annual variation on regeneration dynamics of tropical dry forests (TDF) are still poorly understood. Such understanding is particularly important to assess the regeneration potential of TDF in landscapes subjected to slash-and-burn farming management. Here, we studied from 2004 to 2016 the effects of inter-annual rainfall variation on the dynamics of regenerative communities of woody species during the old-field succession of a TDF in Western Mexico. Over the study period a severe drought, caused by an El Niño Southern Oscillation (ENSO) event in 2005, and two hurricanes (Jova, 2011, magnitude 2; Patricia, 2015, magnitude 4) were experienced. In 2004, we established a chronosequence of abandoned cattle pastures and old-growth forest sites, which were assigned to four successional categories, each one with three sites: Pasture (0–3 years fallow age), Early (3–5 years), Intermediate (8–12 years), and Old-Growth Forest (without any human disturbance). At each site, seedlings, saplings and resprouts 10–100 cm height of shrub and tree species were tagged, taxonomically identified, measured in height and monitored over 12 continuous year intervals. At each year, all new plants reaching 10 cm height were recorded and considered as recruits. Community rates (recruitment, relative growth rate in height, mortality, species gain and species loss) were calculated per year, considering all plants combined and separating shrub from tree species. All community rates varied notoriously in response to temporal rainfall variability, with almost null interaction with successional category. As expected, mortality and species loss rates declined as the amount of rainfall increased, especially when precipitation of the current and the previous year were taken into account; these rates peaked in the ENSO year and were still high in the following year. Unexpectedly, recruitment and species gain rates also declined with the increase in rainfall, especially with the amount of rainfall in the current year. Overall, community rates of tree species were more responsive than those of shrub species to temporal rainfall variation. The ENSO-related drought event produced a short and transient instability in the plant density and species density of regenerative communities. However, ENSO effects were smoothed out by subsequent rainy years, leading to a net increase in plant density and species density in all successional categories, especially in the younger one. Overall, our study shows that global (e.g. ENSO) and regional (e.g. storms, hurricanes) climate factors play a key role on forest succession, modulating the speed of the TDF regeneration dynamics. We conclude that low impact agricultural land use and the presence of good levels of remnant forest cover in the landscape confers a high potential for regeneration in abandoned agricultural fields, even under the impact of severe droughts and severe hurricanes.

Assessing the role of megafauna in tropical forest ecosystems and biogeochemical cycles – the potential of vegetation models

Megafauna (terrestrial vertebrate herbivores > 5 kg) can have disproportionate direct and indirect effects on forest structure, function, and biogeochemical cycles. We reviewed the literature investigating these effects on tropical forest dynamics and biogeochemical cycles in relation to ecology, paleoecology, and vegetation modelling. We highlight the limitations of field‐based studies in evaluating the long‐term consequences of loss of megafauna. These limitations are due to inherent space‐time restrictions of field‐studies and a research focus on seed dispersal services provided by large animals. We further present evidence of a research gap concerning the role of megafauna in carbon cycling in tropical ecosystems. Specifically, changes in aboveground biomass might not be noticeable in short‐term studies because of slow vegetation dynamics requiring decades to respond to disturbance (i.e. defaunation). Nutrient cycling has received even less attention in relation to the role of megafauna in tropical forests. We present an approach to investigate the effects of megafauna from new perspectives and with various tools (notably, vegetation models), which can simulate long‐term dynamics in different environmental and megafauna density scenarios. Vegetation models could facilitate interaction between plant–animal ecology and biogeochemistry research. We present practical examples on how to integrate plant–animal interactions in vegetation models to further our understanding of the role of large herbivores in tropical forests.

Tropical forest dynamics in unstable terrain: a case study from New Guinea

Abstract:Long-term forest dynamics plots in the tropics tend to be situated on stable terrain. This study investigated forest dynamics on the north coast of New Guinea where active subduction zones are uplifting lowland basins and exposing relatively young sediments to rapid weathering. We examined forest dynamics in relation to disturbance history, topography and soil nutrients based on partial re-census of the 50-ha Wanang Forest Dynamics Plot in Papua New Guinea. The plot is relatively high in cations and phosphorus but low in nitrogen. Soil nutrients and topography accounted for 29% of variation in species composition but only 4% of variation in basal area. There were few areas of high biomass and most of the forest was comprised of small-diameter stems. Approximately 18% of the forest was less than 30 y old and the annual tree mortality rate of nearly 4% was higher than in other tropical forests in South-East Asia and the neotropics. These results support the reputation of New Guinea's forests as highly dynamic, with frequent natural disturbance. Empirical documentation of this hypothesis expands our understanding of tropical forest dynamics and suggests that geomorphology might be incorporated in models of global carbon storage especially in regions of unstable terrain.

Tropical Peatland Vegetation Structure and Biomass: Optimal Exploitation of Airborne Laser Scanning

Accurate estimation of above ground biomass (AGB) is required to better understand the variability and dynamics of tropical peat swamp forest (PSF) ecosystem function and resilience to disturbance events. The objective of this work is to examine the relationship between tropical PSF AGB and small-footprint airborne Light Detection and Ranging (LiDAR) discrete return (DR) and full waveform (FW) derived metrics, with a view to establishing the optimal use of this technology in this environment. The study was undertaken in North Selangor peat swamp forest (NSPSF) reserve, Peninsular Malaysia. Plot-based multiple regression analysis was performed to established the strongest predictive models of PSF AGB using DR metrics (only), FW metrics (only), and a combination of DR and FW metrics. Overall, the results demonstrate that a Combination-model, coupling the benefits derived from both DR and FW metrics, had the best performance in modelling AGB for tropical PSF (R2 = 0.77, RMSE = 36.4, rRMSE = 10.8%); however, no statistical difference was found between the rRMSE of this model and the best models using only DR and FW metrics. We conclude that the optimal approach to using airborne LiDAR for the estimation of PSF AGB is to use LiDAR metrics that relate to the description of the mid-canopy. This should inform the use of remote sensing in this ecosystem and how innovation in LiDAR-based technology could be usefully deployed.

Cranial Geometric Morphometric Analysis of the Genus Tapirus (Mammalia, Perissodactyla)

Tapirs are perissodactyl ungulates of the genus Tapirus. The family Tapiridae was more diverse in the past. Genus Tapirus include five living species: T. indicus, T. pinchaque, T. bairdii, T. terrestris, and T. kabomani. Despite all the information available about tapirs, evolutionary relationships among species within the genus are still uncertain. Recent works suggest that T. terrestris may be a species complex. A better understanding of the evolutionary history of this clade is essential to better support conservation strategies for the species of this genus, which are keys in the dynamics of tropical forests in Southeast Asia and Central and South America. Geometric morphometry has been proved to be a useful tool for the study of morphological evolution in mammals, but studies involving cranial geometric morphometry of tapiroids have never been done. We hereby propose landmarks for the study of tapir cranial shape through 2D geometric morphometric technique, including 20 in lateral cranial view (n = 71), 14 in dorsal cranial view (n = 51), and 21 in ventral cranial view (n = 44), followed by PCA multivariate statistical analysis that ordinated specimens from each of the three data groups along the major axis of shape variation. Lateral and dorsal view landmarks proved to be the most diagnostic for the species studied, providing interesting insights and trends on tapiroid cranial evolution. Ventrally, the species analyzed do not differentiate significantly. In this paper, we add new information to the current cranial morphometric database of tapirs, which can help elucidate questions about their evolutionary history.

Mapping Forest and Their Spatial–Temporal Changes From 2007 to 2015 in Tropical Hainan Island by Integrating ALOS/ALOS-2 L-Band SAR and Landsat Optical Images

Accurately monitoring forest dynamics in the tropical regions is essential for ecological studies and forest management. In this study, images from phase-array L-band synthetic aperture radar (PALSAR), PALSAR-2, and Landsat in 2006–2010 and 2015 were combined to identify tropical forest dynamics on Hainan Island, China. Annual forest maps were first mapped from PALSAR and PALSAR-2 images using structural metrics. Those pixels with a high biomass of sugarcane or banana, which are widely distributed in the tropics and subtropics and have similar structural metrics as forests, were excluded from the SAR-based forest maps by using phenological metrics from time series Landsat imagery. The optical–SAR-based forest maps in 2010 and 2015 had high overall accuracies (OA) of 92–97% when validated with ground reference data. The resultant forest map in 2010 shows good spatial agreement with public optical-based forest maps (OA = 88–90%), and the annual forest maps (2007–2010) were spatiotemporally consistent and more accurate than the PALSAR-based forest map from the Japan Aerospace Exploration Agency (OA = 82% in 2010). The areas of forest gain, loss, and net change on Hainan Island from 2007 to 2015 were 415 000 ha (+2.17% yr–1), 179 000 ha (–0.94% yr –1), and 236 000 ha (+1.23% yr–1), respectively. About 95% of forest gain and loss occurred in those areas with an elevation less than 400 m, where deciduous rubber, eucalyptus plantations, and urbanization expanded rapidly. This study demonstrates the potential of PALSAR/PALSAR-2/Landsat image fusion for monitoring annual forest dynamics in the tropical regions.

Shock and stabilisation following long‐term drought in tropical forest from 15 years of litterfall dynamics

Abstract Litterfall dynamics in tropical forests are a good indicator of overall tropical forest function, indicative of carbon invested in both photosynthesising tissues and reproductive organs such as flowers and fruits. These dynamics are sensitive to changes in climate, such as drought, but little is known about the long‐term responses of tropical forest litterfall dynamics to extended drought stress. We present a 15‐year dataset of litterfall (leaf, flower and fruit, and twigs) from the world's only long‐running drought experiment in tropical forest. This dataset comprises one of the longest published litterfall time series in natural forest, which allows the long‐term effects of drought on forest reproduction and canopy investment to be explored. Over the first 4 years of the experiment, the experimental soil moisture deficit created only a small decline in total litterfall and leaf fall (12% and 13%, respectively), but a very strong initial decline in reproductive litterfall (flowers and fruits) of 54%. This loss of flowering and fruiting was accompanied by a de‐coupling of all litterfall patterns from seasonal climate variables. However, following >10 years of the experimental drought, flower and fruiting re‐stabilised at levels greater than in the control plot, despite high tree mortality in the drought plot. Litterfall relationships with atmospheric drivers were re‐established alongside a strong new apparent trade‐off between litterfall and tree growth. Synthesis. We demonstrate that this tropical forest went through an initial shock response during the first 4 years of intense drought, where reproductive effort was arrested and seasonal litterfall patterns were lost. However, following >10 years of experimental drought, this system appears to be re‐stabilising at a new functional state where reproduction is substantially elevated on a per tree basis; and there is a new strong trade‐off between investment in canopy production and wood production.

Disentangling the long-term effects of disturbance on soil biogeochemistry in a wet tropical forest ecosystem.

Climate change is increasing the intensity of severe tropical storms and cyclones (also referred to as hurricanes or typhoons), with major implications for tropical forest structure and function. These changes in disturbance regime are likely to play an important role in regulating ecosystem carbon (C) and nutrient dynamics in tropical and subtropical forests. Canopy opening and debris deposition resulting from severe storms have complex and interacting effects on ecosystem biogeochemistry. Disentangling these complex effects will be critical to better understand the long-term implications of climate change on ecosystem C and nutrient dynamics. In this study, we used a well-replicated, long-term (10years) canopy and debris manipulation experiment in a wet tropical forest to determine the separate and combined effects of canopy opening and debris deposition on soil C and nutrients throughout the soil profile (1m). Debris deposition alone resulted in higher soil C and N concentrations, both at the surface (0-10cm) and at depth (50-80cm). Concentrations of NaOH-organic P also increased significantly in the debris deposition only treatment (20-90cm depth), as did NaOH-total P (20-50cm depth). Canopy opening, both with and without debris deposition, significantly increased NaOH-inorganic P concentrations from 70 to 90cm depth. Soil iron concentrations were a strong predictor of both C and P patterns throughout the soil profile. Our results demonstrate that both surface- and subsoils have the potential to significantly increase C and nutrient storage a decade after the sudden deposition of disturbance-related organic debris. Our results also show that these effects may be partially offset by rapid decomposition and decreases in litterfall associated with canopy opening. The significant effects of debris deposition on soil C and nutrient concentrations at depth (>50cm), suggest that deep soils are more dynamic than previously believed, and can serve as sinks of C and nutrients derived from disturbance-induced pulses of organic matter inputs.

Effects of large aboveground biomass loss events on the deadwood and litter mass dynamics of seasonal tropical forests in Cambodia

Effects of large aboveground biomass loss events on the deadwood and litter mass dynamics of seasonal tropical forests in Cambodia

Shift in Abundance From Seedling to Juvenile Gives Lianas Advantage Over Trees: A Case Study in the Atlantic Forest Hotspot

The Atlantic Forest has been threatened by frequent human disturbances that affect its ecological processes. Lianas are an important component of tropical forest dynamics and, under chronic disturbance, may proliferate vigorously, potentially arresting secondary succession and hindering forest recovery. Our study aims to analyze abundance and diversity of liana and trees in different life stages in a disturbed semidecidual seasonal tropical forest fragment in southeast Brazil. We sampled the species richness and relative abundance in the following life stages of lianas and trees: I—seed (as seed arrival and seed bank processes), II—seedling, III—juvenile, and IV—adult. Lianas are more abundant than trees after the seedling stage, while trees showed more rarefied species richness only at the seed rain stage. Our results show that dispersal does not seem to be a bottleneck for either liana or tree community in disturbed fragments, but competition at the seedling stage may give lianas advantage over trees. Lianas may proliferate abundantly in forest fragments, even decades after disturbance. We recommend interventions for the management and restoration of disturbed forest fragments dominated by lianas to target this life form in life stages where they suppress the forest community, such as after the seedling stage.

Recovery of species composition over 46 years in a logged Australian tropical forest following different intensity silvicultural treatments

Currently, more than 400 million hectares of tropical forests worldwide are now being managed for timber production. Understanding the long-term responses of tropical forests to management practices is critical for managing tropical forests sustainably. To investigate the responses of tropical forest dynamics to different silvicultural treatment intensities, permanent plots were established in 1967 in an Australian tropical forest with four treatments: selective logging only as a control and selective logging followed by three differing intensity silvicultural treatments in 1969. We investigated changes in the number of species, species dominance, and species composition of trees (DBH ≥ 10 cm) from 1967 to 2015. Before selective logging, the number of tree species did not differ between the treatments, ranging from 70 to 75. Selective logging alone had small immediate effects on the number of species and species abundance distributions. After silvicultural treatment, the number of species in the low-intensity treatment, medium-intensity treatment and high-intensity treatment were reduced to 48, 42, and 18 respectively. The number of species in the control, low-intensity, and medium-intensity treatments recovered to their pre-logging levels within 46 years, but recovery in the high-intensity treatment was incomplete due to much greater initial species loss through silvicultural treatment. Silvicultural treatments increased species dominance, with the differences being progressively more marked as the level of treatment intensity increased. Over 46 years, tree species abundance distribution in the silvicultural treatments became more even and largely returned to pre-logging conditions, with more rapid recovery after low and intermediate silvicultural treatments. Following silvicultural treatments, species composition in the logging only, low-intensity and medium-intensity silvicultural treatments did not change markedly, whereas species composition was substantially altered by high-intensity silvicultural treatment and was subsequently distinct from the other treatments. Within 46 years following treatments, species composition in the high intensity treatment showed a recovery trajectory towards pre-logging conditions, leading to increased species compositional similarity among the four treatments. Increasing the intensity of silviculture treatment led to greater time required for recovery of species diversity, composition and compositional similarity. We recommend that high-intensity silvicultural treatments should be avoided if rapid recovery of species diversity and composition is the desired management outcome in tropical rainforests similar to those in our study area.

Biodiversity Monitoring in Changing Tropical Forests: A Review of Approaches and New Opportunities

Tropical forests host at least two-thirds of the world’s flora and fauna diversity and store 25% of the terrestrial above and belowground carbon. However, biodiversity decline due to deforestation and forest degradation of tropical forest is increasing at an alarming rate. Biodiversity dynamics due to natural and anthropogenic disturbances are mainly monitored using established field survey approaches. However, such approaches appear to fall short at addressing complex disturbance factors and responses. We argue that the integration of state-of-the-art monitoring approaches can improve the detection of subtle biodiversity disturbances and responses in changing tropical forests, which are often data-poor. We assess the state-of-the-art technologies used to monitor biodiversity dynamics of changing tropical forests, and how their potential integration can increase the detail and accuracy of biodiversity monitoring. Moreover, the relevance of these biodiversity monitoring techniques in support of the UNCBD Aichi targets was explored using the Essential Biodiversity Variables (EBVs) as a framework. Our review indicates that although established field surveys were generally the dominant monitoring systems employed, the temporal trend of monitoring approaches indicates the increasing application of remote sensing and in -situ sensors in detecting disturbances related to agricultural activities, logging, hunting and infrastructure. The relevance of new technologies (i.e., remote sensing, in situ sensors, and DNA barcoding) in operationalising EBVs (especially towards the ecosystem structure, ecosystem function, and species population classes) and the Aichi targets has been assessed. Remote sensing application is limited for EBV classes such as genetic composition and species traits but was found most suitable for ecosystem structure class. The complementarity of remote sensing and emerging technologies were shown in relation to EBV candidates such as species distribution, net primary productivity, and habitat structure. We also developed a framework based on the primary biodiversity attributes, which indicated the potential of integration between monitoring approaches. In situ sensors are suitable to help measure biodiversity composition, while approaches based on remote sensing are powerful for addressing structural and functional biodiversity attributes. We conclude that, synergy between the recent biodiversity monitoring approaches is important and possible. However, testing the suitability of monitoring methods across scales, integrating heterogeneous monitoring technologies, setting up metadata standards, and making interpolation and/or extrapolation from observation at different scales is still required to design a robust biodiversity monitoring system that can contribute to effective conservation measures.

Multidecadal stability in tropical rain forest structure and dynamics across an old-growth landscape.

Have tropical rain forest landscapes changed directionally through recent decades? To answer this question requires tracking forest structure and dynamics through time and across within-forest environmental heterogeneity. While the impacts of major environmental gradients in soil nutrients, climate and topography on lowland tropical rain forest (TRF) structure and function have been extensively analyzed, the effects of the shorter environmental gradients typical of mesoscale TRF landscapes remain poorly understood. To evaluate multi-decadal performance of an old-growth TRF at the La Selva Biological Station, Costa Rica, we established 18 0.5-ha annually-censused forest inventory plots in a stratified-random design across major landscape edaphic gradients. Over the 17-year study period, there were moderate differences in stand dynamics and structure across these gradients but no detectable difference in woody productivity. We found large effects on forest structure and dynamics from the mega-Niño event at the outset of the study, with subdecadal recovery and subsequent stabilization. To extend the timeline to >40 years, we combined our findings with those from earlier studies at this site. While there were annual to multiannual variations in the structure and dynamics, particularly in relation to local disturbances and the mega-Niño event, at the longer temporal scale and broader spatial scale this landscape was remarkably stable. This stability contrasts notably with a current hypothesis of increasing biomass and dynamics of TRF, which we term the Bigger and Faster Hypothesis (B&FHo). We consider possible reasons for the contradiction and conclude that it is currently not possible to independently assess the vast majority of previously published B&FHo evidence due to restricted data access.

Patterns, drivers and implications of dissolved oxygen dynamics in tropical mangrove forests

Estuarine mangrove forests regulate and facilitate many ecological processes, and provide nursery ground for many commercially important species. However, mangroves grow in sediments with high carbon loading and high respiration rates which can potentially influencing the dissolved oxygen (DO) dynamics of tidal water flowing into mangrove forests, as bacteria strip DO from the incoming water to carry out metabolic functions. In turn this is likely to influence the way nekton and other aquatic organisms utilize mangrove forests. Despite these possibilities, previous work has focused on looking at DO dynamics within mangrove creeks, with little research focusing on understanding DO dynamics within the mangrove forests themselves during tidal inundation or of DO levels of pools within the forest remaining once the tide has ebbed. The present study investigates the pattern in DO at various distances within an estuarine Rhizophora stylosa forest in tropical north Queensland. DO levels were recorded at 5 min interval over 2 days and multiple tidal cycles, data were collected between 2013 and 2014 for a total of 32 tidal cycles encompassing multiples seasons and tidal amplitudes. There were substantial fluctuations in DO, often varying from normoxic to hypoxic within the same tidal cycle. A range of factors influenced DO dynamics, in particular: tidal height, amount of sunlight, tidal phase, and distance from the outer edge of the mangrove forest. In fact, spring tides tend to have high DO saturation, particularly during the flooding phase, however as the tide starts ebbing, DO depletes rapidly especially in areas further inside the forest. Moreover during tidal disconnection the remnant pools within the forest quickly became anoxic. These variations in DO suggest that the use of mangrove forests by animals is likely to be constrained by their ability to withstand low DO levels, and provides a plausible explanation for the apparent paucity of benthic organism observed inside similar mangrove forest in previous studies of South Pacific mangroves. Low DO levels coupled with low densities of benthic prey also provides a likely explanation for the limited utilisation of landwards areas of these forests by fish and other nekton.

The understory bat community in a fragmented landscape in the lowlands of the Los Tuxtlas, Veracruz, Mexico

Bat species in Neotropical regions are known to reach a high diversity. The Chiropteran fauna contributes significantly to the ecological dynamics of tropical forests and are excellent indicators of the state of conservation. The Los Tuxtlas, Veracruz has suffered severe habitat degradation and forest fragmentation in the last four decades, mostly due to anthropogenic activities. The main objective of the present study was to describe in terms of species richness, feeding guild, biomass, and dominance, the little known bat community of the Parque de Flora and Fauna Silvestre Tropical (PAFFASIT) in the municipality of Catemaco, Veracruz. We expected that after nearly 30 years of ambient protection that this study site would maintain its functional diversity, as well as complexity in the bat understory assemblage. Since the relationship between richness and abundance is regulated by area size and the structural complexity of the vegetation, we hypothesize that in the PAFFASIT, a small number of species in the understory are dominant in terms of abundance and biomass. Fieldwork was conducted from November 2007 to November 2008. Sixteen mist nets were operated on four consecutive nights monthly from dusk until 0300 hours. All bats captured were processed and released in the field. We estimate the overall species diversity. A species accumulation curve over time was constructed. All species were assigned a feeding guild. Sampling effort totaled 1344 net/hours. We captured a total of 509 individuals, which represented 22 species. The Phyllostomidae family accounted for 98% of the total captures. Four species of this family, Sturnira parvidens, Carollia sowelli, Artibeus jamaicensis and Glossophaga soricina, alone accounted for 79 % of the total captures. The frugivore guild had the highest number of species (68 % of total captures). Two species, S. parvidens and C. sowelli, represented 57 % of the total gross biomass of the sample. The Shannon-Wiener Index value was 1.97 for the overall sample. New species were added slowly each month, but after nine months the accumulation curve tended to reach an asymptote. Nine species were added to the bat inventory for this site. In PAFFASIT due to the slow accumulation of species the number of bat species may increase as more surveys are carried out. In our study, we initially hypothesized a dominance by a few species. Our results concur with our prediction; as we found four species, S. parvidens, C. sowelli, A. jamaicensis and G. soricina that dominated the bat assemblage. In agreement with our hypothesis, results revealed the presence of a rich understory assemblage of bat species, which is similar to other findings in neotropical forests, but with a different species composition. The four species, belonging to the Phyllostomidae family accounted for 79 % of all captures, as well as 68 % of the total captures of the frugivore guild. The PAFFASIT forest reserve probably serves as an important link between two large areas of relatively well-preserved rainforest immersed in an anthropogenic landscape. The bat community, we observed at the PAFFASIT seems to be a simplification of that of mature rainforests in Los Tuxtlas, and it is noteworthy the absence of rare or sensitive animalivorous bat species such a as Chrotopterus auritus, Lophostoma evotis, Trachops cirrhosus and Vampyrum spectrum.

The phenology of leaf quality and its within-canopy variation is essential for accurate modeling of photosynthesis in tropical evergreen forests.

Leaf quantity (i.e., canopy leaf area index, LAI), quality (i.e., per-area photosynthetic capacity), and longevity all influence the photosynthetic seasonality of tropical evergreen forests. However, these components of tropical leaf phenology are poorly represented in most terrestrial biosphere models (TBMs). Here, we explored alternative options for the representation of leaf phenology effects in TBMs that employ the Farquahar, von Caemmerer & Berry (FvCB) representation of CO2 assimilation. We developed a two-fraction leaf (sun and shade), two-layer canopy (upper and lower) photosynthesis model to evaluate different modeling approaches andassessed three components of phenological variations (i.e., leaf quantity, quality, and within-canopy variation in leaf longevity). Our model was driven by the prescribed seasonality of leaf quantity and quality derived from ground-based measurements within an Amazonian evergreen forest. Modeled photosynthetic seasonality was not sensitive to leaf quantity, but was highly sensitive to leaf quality and its vertical distribution within the canopy, with markedly more sensitivity to upper canopy leaf quality. This is because light absorption in tropical canopies is near maximal for the entire year, implying that seasonal changes in LAI have little impact on total canopy light absorption; and because leaf quality has a greater effect on photosynthesis of sunlit leaves than light limited, shade leaves and sunlit foliage are more abundant in the upper canopy. Our two-fraction leaf, two-layer canopy model, which accounted for all three phenological components, was able to simulate photosynthetic seasonality, explaining ~90% of the average seasonal variation in eddy covariance-derived CO2 assimilation. This work identifies a parsimonious approach for representing tropical evergreen forest photosynthetic seasonality in TBMs that utilize the FvCB model of CO2 assimilation and highlights the importance of incorporating more realistic phenological mechanisms in models that seek to improve the projection of future carbon dynamics in tropical evergreen forests.

The carbon fluxes in different successional stages: modelling the dynamics of tropical montane forests in South Ecuador

BackgroundTropical forests play an important role in the global carbon (C) cycle. However, tropical montane forests have been studied less than tropical lowland forests, and their role in carbon storage is not well understood. Montane forests are highly endangered due to logging, land-use and climate change. Our objective was to analyse how the carbon balance changes during forest succession.MethodsIn this study, we used a method to estimate local carbon balances that combined forest inventory data with process-based forest models. We utilised such a forest model to study the carbon balance of a tropical montane forest in South Ecuador, comparing two topographical slope positions (ravines and lower slopes vs upper slopes and ridges).ResultsThe simulation results showed that the forest acts as a carbon sink with a maximum net ecosystem exchange (NEE) of 9.3 Mg C∙(ha∙yr)−1 during its early successional stage (0–100 years). In the late successional stage, the simulated NEE fluctuated around zero and had a variation of 0.77 Mg C∙(ha∙yr) –1. The simulated variability of the NEE was within the range of the field data. We discovered several forest attributes (e.g., basal area or the relative amount of pioneer trees) that can serve as predictors for NEE for young forest stands (0–100 years) but not for those in the late successional stage (500–1,000 years). In case of young forest stands these correlations are high, especially between stand basal area and NEE.ConclusionIn this study, we used an Ecuadorian study site as an example of how to successfully link a forest model with forest inventory data, for estimating stem-diameter distributions, biomass and aboveground net primary productivity. To conclude, this study shows that process-based forest models can be used to investigate the carbon balance of tropical montane forests. With this model it is possible to find hidden relationships between forest attributes and forest carbon fluxes. These relationships promote a better understanding of the role of tropical montane forests in the context of global carbon cycle, which in future will become more relevant to a society under global change.

Growth and reproduction respond differently to climate in three Neotropical tree species.

The response of tropical forests to anthropogenic climate change is critically important to future global carbon budgets, yet remains highly uncertain. Here, we investigate how precipitation, temperature, solar radiation and dry- and wet-season lengths are related to annual tree growth, flower production, and fruit production in three moist tropical forest tree species using long-term datasets from tree rings and litter traps in central Panama. We also evaluated how growth, flower, and fruit production were interrelated. We found that growth was positively correlated with wet-season precipitation in all three species: Jacaranda copaia (r=0.63), Tetragastris panamensis (r=0.39) and Trichilia tuberculata (r=0.39). Flowering and fruiting in Jacaranda were negatively related to current-year dry-season rainfall and positively related to prior-year dry-season rainfall. Flowering in Tetragastris was negatively related to current-year annual mean temperature while Trichilia showed no significant relationships of reproduction with climate. Growth was significantly related to reproduction only in Tetragastris, where it was positively related to previous year fruiting. Our results suggest that tree growth in moist tropical forest tree species is generally reduced by drought events such as those associated with strong El Niño events. In contrast, interannual variation in reproduction is not generally associated with growth and has distinct and species-specific climate responses, with positive effects of El Niño events in some species. Understanding these contrasting climate effects on tree growth and reproduction is critical to predicting changes in tropical forest dynamics and species composition under climate change.

Long-term variation in abundance of terrestrial mammals and birds in eastern Ecuador as measured by photographic rates and occupancy estimates

Long-term studies from undisturbed forests provide a baseline by which to assess impacts of human activities, including climate change, on vertebrate population dynamics in lowland tropical forests. We use cameratrap data from January to March, 2005 to 2015, to examine patterns of variation in numbers of images and occupancy (proportion of cameras where images of a species were obtained), variables that may reflect changes in abundance or activity patterns of terrestrial mammals and birds in an undisturbed lowland forest of eastern Ecuador. We accumulated 1,961 independent records of 31 mammal species and 427 images of 17 bird species during 5,547 trap-days. Number of mammal species ranged from 15 to 25 per year (107 to 466 images), whereas birds ranged from 3 to 11 species per year (10 to 122 images). Capture rates varied both among species and among years but showed no evidence of declines; populations of several species appeared to increase (Priodontes maximus, Dasypus novemcinctus, Pecari tajacu, and Dasyprocta fuliginosa). Similarly, occupancy rates provided no indication of consistent declines; occupancy rates increased significantly for D. fuliginosa, D. novemcinctus, and P. maximus. There was no indication that variation in either capture rates or occupancy was related to variation in large-scale climate trends as represented by the Southern Oscillation Index. Results suggest that populations of most species that are well sampled by camera traps have remained relatively stable over 11 years. Long-term studies from other regions in the tropics are needed to evaluate the generality of this pattern.