Topography is a key driver of tropical forest structure and composition, as it constrains local nutrient and hydraulic conditions within which trees grow. Yet, we do not fully understand how changes ...in forest physiognomy driven by topography impact other emergent properties of forests, such as their aboveground carbon density (ACD). Working in Borneo – at a site where 70‐m‐tall forests in alluvial valleys rapidly transition to stunted heath forests on nutrient‐depleted dip slopes – we combined field data with airborne laser scanning and hyperspectral imaging to characterise how topography shapes the vertical structure, wood density, diversity and ACD of nearly 15 km2 of old‐growth forest. We found that subtle differences in elevation – which control soil chemistry and hydrology – profoundly influenced the structure, composition and diversity of the canopy. Capturing these processes was critical to explaining landscape‐scale heterogeneity in ACD, highlighting how emerging remote sensing technologies can provide new insights into long‐standing ecological questions.
Developing a robust algorithm for automatic individual tree crown (ITC) detection from airborne laser scanning (ALS) data sets is important for tracking the responses of trees to anthropogenic ...change. Such approaches allow the size, growth, and mortality of individual trees to be measured, enabling forest carbon stocks and dynamics to be tracked and understood. Many algorithms exist for structurally simple forests, including coniferous forests and plantations. Finding a robust solution for structurally complex, species-rich tropical forests remains a challenge; existing segmentation algorithms often perform less well than simple area-based approaches when estimating plot-level biomass. Here, we describe a multiclass graph cut (MCGC) approach to tree crown delineation. This uses local 3D geometry and density information, alongside knowledge of crown allometries, to segment ITCs from airborne light detection and ranging point clouds. Our approach robustly identifies trees in the top and intermediate layers of the canopy, but cannot recognize small trees. From these 3D crowns, we are able to measure individual tree biomass. Comparing these estimates with those from permanent inventory plots, our algorithm can produce robust estimates of hectare-scale carbon density, demonstrating the power of ITC approaches in monitoring forests. The flexibility of our method to add additional dimensions of information, such as spectral reflectance, make this approach an obvious avenue for future development and extension to other sources of 3D data, such as structure from motion data sets.
Tropical forests are a key component of the global carbon cycle, and mapping their carbon density is essential for understanding human influences on climate and for ecosystem-service-based payments ...for forest protection. Discrete-return airborne laser scanning (ALS) is increasingly recognised as a high-quality technology for mapping tropical forest carbon, because it generates 3D point clouds of forest structure from which aboveground carbon density (ACD) can be estimated. Area-based models are state of the art when it comes to estimating ACD from ALS data, but discard tree-level information contained within the ALS point cloud. This paper compares area-based and tree-centric models for estimating ACD in lowland old-growth forests in Sabah, Malaysia. These forests are challenging to map because of their immense height. We compare the performance of (a) an area-based model developed by Asner and Mascaro (2014), and used primarily in the neotropics hitherto, with (b) a tree-centric approach that uses a new algorithm (itcSegment) to locate trees within the ALS canopy height model, measures their heights and crown widths, and calculates biomass from these dimensions. We find that Asner and Mascaro's model needed regional calibration, reflecting the distinctive structure of Southeast Asian forests. We also discover that forest basal area is closely related to canopy gap fraction measured by ALS, and use this finding to refine Asner and Mascaro's model. Finally, we show that our tree-centric approach is less accurate at estimating ACD than the best-performing area-based model (RMSE 18% vs 13%). Tree-centric modelling is appealing because it is based on summing the biomass of individual trees, but until algorithms can detect understory trees reliably and estimate biomass from crown dimensions precisely, areas-based modelling will remain the method of choice.
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•Compared tree- vs area-based models for mapping forest carbon from airborne LiDAR•Tree crown allometry used to search for individual stems in tropical rainforest•Biomass of tall tropical trees were predicted without bias but with high uncertainty.•Consequently, area-based models proved more effective than tree-based models.•A power-law model including top-of-canopy height and gap fraction was selected.
Borneo contains some of the world's most biodiverse and carbon-dense tropical
forest, but this 750 000 km2 island has lost 62 % of its
old-growth forests within the last 40 years. Efforts to protect ...and restore
the remaining forests of Borneo hinge on recognizing the ecosystem services
they provide, including their ability to store and sequester carbon. Airborne
laser scanning (ALS) is a remote sensing technology that allows forest
structural properties to be captured in great detail across vast geographic
areas. In recent years ALS has been integrated into statewide assessments of
forest carbon in Neotropical and African regions, but not yet in Asia. For
this to happen new regional models need to be developed for estimating carbon
stocks from ALS in tropical Asia, as the forests of this region are
structurally and compositionally distinct from those found elsewhere in the
tropics. By combining ALS imagery with data from 173 permanent forest plots
spanning the lowland rainforests of Sabah on the island of Borneo, we
develop a simple yet general model for estimating forest carbon stocks using
ALS-derived canopy height and canopy cover as input metrics. An advanced
feature of this new model is the propagation of uncertainty in both ALS- and
ground-based data, allowing uncertainty in hectare-scale estimates of carbon
stocks to be quantified robustly. We show that the model effectively captures
variation in aboveground carbon stocks across extreme disturbance gradients
spanning tall dipterocarp forests and heavily logged regions and clearly
outperforms existing ALS-based models calibrated for the tropics, as well as
currently available satellite-derived products. Our model provides a simple,
generalized and effective approach for mapping forest carbon stocks in
Borneo and underpins ongoing efforts to safeguard and facilitate the
restoration of its unique tropical forests.
Logged tropical forests represent a major opportunity for preserving biodiversity and sequestering carbon, playing a large role in meeting global forest restoration targets. Left alone, these ...ecosystems have been expected to undergo natural regeneration and succession towards old growth forests, but extreme drought events may challenge this process. While old growth forests possess a certain level of resilience, we lack understanding as to how logging may affect forest responses to drought. This study examines the drought-logging interaction in seedling dynamics within a landscape of logged and unlogged forests in Sabah Malaysia, based on 73 plots monitored before and after the 2015-16 El Niño drought. Drought increased seedling mortality in all forests, but the magnitude of this impact was modulated by logging intensity, with forests with lower canopy leaf area index and above-ground biomass experiencing greater drought induced mortality. Moreover, community traits in more heavily logged forests shifted towards being more ruderal after drought, suggesting that the trajectory of forest succession had been reversed. These results indicate that with reoccurring strong droughts under a changing climate, logged forests that have had over half of their biomass removed may suffer permanently arrested succession. Targeted management interventions may therefore be necessary to lift the vulnerable forests above the biomass threshold.
Aim Using dung beetles (Coleoptera: Scarabaeidae: Scarabaeinae) in a tropical land-bridge island system, we test for the small island effect (SIE) in the species-area relationship and evaluate its ...effects on species richness and community composition. We also examine the determinants of species richness across island size and investigate the traits of dung beetle species in relation to their local extinction vulnerability following forest fragmentation. Location Lake Kenyir, a hydroelectric reservoir in north-eastern Peninsular Malaysia. Methods We sampled dung beetles using human dung baited pitfall traps on 24 land-bridge islands and three mainland sites. We used regression tree analyses to test for the SIE, as well as species traits related to local rarity, as an indication of extinction vulnerability. We employed generalized linear models (GLMs) to examine determinants for species richness at different scales and compared the results with those from conventional linear and breakpoint regressions. Community analyses included non-metric multidimensional scaling, partial Mantel tests, nestedness analysis and abundance spectra. Results Regression tree analysis revealed an area threshold at 35.8 ha indicating an SIE. Tree basal area was the most important predictor of species richness on small islands (<35.8 ha). Results from GLMs supported these findings, with isolation and edge index also being important for small islands. The SIE also manifested in patterns of dung beetle community composition where communities on small islands (<35.8 ha) departed from those on the mainland and larger islands, and were highly variable with no significant nestedness, probably as a result of unexpected species occurrences on several small islands. The communities exhibited a low degree of spatial autocorrelation, suggesting that dispersal limitation plays a part in structuring dung beetle assemblages. Species with lower baseline density and an inability to forage on the forest edge were found to be rarer among sites and hence more prone to local extinction. Main conclusions We highlight the stochastic nature of dung beetle community composition on small islands and argue that this results in reduced ecosystem functionality. A better understanding of the minimum fragment size required for retaining functional ecological communities will be important for effective conservation management and the maintenance of tropical forest ecosystem stability.
Previous studies have revealed that quantitative hepatitis B surface antigen (HBsAg) or hepatitis B core antibody (qAnti-HBc) levels can be used as predictors of treatment response in both ...interferon-α and nucleoside analogue therapies. Few data have been published regarding the relationship between quantitative HBsAg or Anti-HBc levels and liver fibrosis stages in patients with chronic hepatitis B (CHB).
We conducted a cross-sectional study of treatment-naïve CHB patients. A total of 624 CHB patients were recruited. We assessed the serum HBsAg and qAnti-HBc levels, HBV DNA levels, HBV genotypes, BCP/PC mutations, histological fibrosis staging by Scheuer classification.
In HBeAg (+) patients, the S0-1 subjects had significantly higher serum HBsAg and lower qAnti-HBc levels than the S2-4 subjects (both p < 0.001). A moderate inverse correlation was present between serum HBsAg levels and fibrosis scores (r = −0.381, p < 0.001), and a moderate positive correlation was found between qAnti-HBc levels and fibrosis scores (r = 0.408, p < 0.001). In the HBeAg (−) patients, the S0-1 subjects also had significantly lower qAnti-HBc levels than the S2-4 subjects (p < 0.001); however, no significant difference in the HBsAg levels was observed between the S0-1 and S2-4 subjects (p > 0.05). Serum qAnti-HBc levels showed a moderate positive correlation with fibrosis scores (r = 0.383, p < 0.001), while serum HBsAg levels exhibited a low inverse correlation with fibrosis scores (r = −0.171, p < 0.001). Multiple logistic regression analysis showed that the parameters for predicting significant fibrosis (S ≥ 2) included age, PLT, qAnti-HBc levels, HBV genotype and BCP/PC mutations in HBeAg (+) group, and age, PLT, qAnti-HBc levels in HBeAg (−) group (all p < 0.05). The AUC of qAnti-HBc levels associated with the diagnosis of significant fibrosis abnormalities in HBeAg (+) and HBeAg (−) patients were 0.734 (95%CI 0.689 to 0.778) and 0.707 (95%CI 0.612 to 0.801), respectively.
Our study found an association between high serum qAnti-HBc levels and significant fibrosis in both HBeAg (+) and HBeAg (−) treatment-naïve CHB patients. However, low serum HBsAg levels were correlated with moderate to severe fibrosis in HBeAg (+) subjects only.
Abstract
Although tropical forests differ substantially in form and function, they are often represented as a single biome in global change models, hindering understanding of how different tropical ...forests will respond to environmental change. The response of the tropical forest biome to environmental change is strongly influenced by forest type. Forest types differ based on functional traits and forest structure, which are readily derived from high resolution airborne remotely sensed data. Whether the spatial resolution of emerging satellite-derived hyperspectral data is sufficient to identify different tropical forest types is unclear. Here, we resample airborne remotely sensed forest data at spatial resolutions relevant to satellite remote sensing (30 m) across two sites in Malaysian Borneo. Using principal component and cluster analysis, we derive and map seven forest types. We find ecologically relevant variations in forest type that correspond to substantial differences in carbon stock, growth, and mortality rate. We find leaf mass per area and canopy phosphorus are critical traits for distinguishing forest type. Our findings highlight the importance of these parameters for accurately mapping tropical forest types using space borne observations.
Habitat loss and fragmentation can have severe negative and irreversible effects on biodiversity. We investigated the effects of forest fragmentation on frog diversity in Singapore because of its ...high rates of deforestation and the demonstration that frogs are some of the most sensitive species to habitat degradation. We surveyed frog species in 12 forest fragments varying from 11 to 935 ha. We compared differences in species richness, abundance, and Shannon's index in relation to forest fragment size, connectivity (distance between fragments), and breeding habitat heterogeneity. A total of 20 species from 12 genera and five families were encountered in 12 fragments. Larger fragments and those closer to larger fragments had higher species richness. Abundance, however, was not correlated with forest area or connectivity, but we found fewer individual frogs in the larger fragments. We also found that breeding habitat heterogeneity best explained frog species diversity and abundance in forest fragments. Fragments with a high diversity of breeding habitats had more species. We found no evidence to suggest that abundance and diversity are strongly correlated, particularly in disturbed areas, but that breeding habitat heterogeneity is an under-appreciated factor that should be considered when prioritizing areas for anuran conservation. Enriching breeding habitat heterogeneity, creating corridors between fragments, and reforesting degraded areas are some of the most beneficial strategies for preserving urban frog biodiversity.
The regeneration of many climax species in tropical forest critically depends on adequate seed dispersal and seedling establishment. Here, we report the decreased abundance and increased spatial ...aggregation of younger trees of the Borneo ironwood (Eusideroxylon zwageri) in a protected forest in Sabah Malaysia. We observed a high level of seedling herbivory with strong density dependence, likely exacerbated by local aggregation and contributing to the progressively shrinking size distribution. We also note the largely undocumented selective herbivory by sambar deer on E. zwageri seedlings. This study highlights the combined impact of altered megafauna community on a tree population through interlinked ecological processes and the need for targeted conservation intervention for this iconic tropical tree species.
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