The ‘Returning Farmland to Forest Program’ (RFFP) in China has become an essential factor in land cover changes and forest transition, especially in terms of the ecological processes between two ...adjacent ecosystems. However, accurately delineating ecotones is still a big challenge for vegetation and landscape ecologists. Acquiring high spatial resolution imagery from a small, unmanned aircraft system (UAS) provides new opportunities for studying ecotones at a small scale. This study aims to extract forest-agriculture ecotones by RGB ultrahigh-resolution images from a small UAS and quantify the small biotopes in 3D space. To achieve these objectives, a canopy height model (CHM) is constructed based on a UAS-photogrammetric-derived point cloud, which is derived from the digital surface model (DSM) minus the digital terrain model (DTM). Afterward, according to the difference of plant community height between abandoned farmland ecosystem and forest ecosystem, the ecotones are delineated. A landscape pattern identified with ecotones and other small biotopes at the fine scale. Furthermore, we assess the accuracy of the ecotones’ delineation based on the transects method with the previous situ work we carried out and quantify the landscape structure using common landscape metrics to describe its spatial and geometric characteristics. Through transect-based analysis at three transects, the overall accuracy of the width of UAS-derived delineation is greater than 70%, and the detection accuracy for the occurrence location is 100%. Finally, we conclude that ecotones extraction from UAS images would also provide the possibility to gain a comprehensive understanding of the entire ecological process of agricultural abandoned land restoration through continuous investigation and monitoring.
Canopy height greatly affects the biomass stock, carbon dynamics, and maintenance of biodiversity in forests. Previous research reported that the maximum forest canopy height (Hmax) at global and ...regional scales could be explained by variations in water or energy availability, that is, the water- or energy-related hypothesis. However, fundamental gaps remain in our understanding of how different drivers (i.e., water and energy) contribute to the Hmax at the local scale. In this study, we selected eight dynamic forest plots (20–30 ha) across a latitudinal gradient (from 21.6° N to 48.1° N) in China and measured the canopy structure using airborne light detection and ranging (LiDAR) data. Based on the LiDAR point cloud data, we extracted the maximum tree height (Hmax) in a 20 × 20 m quadrat as a proxy for canopy height, and the topographic wetness index (TWI) and digital terrain model-derived insolation (DTMI) were calculated as proxies for water and energy conditions. We used a linear mixed model and spatial simultaneous autoregressive error model to quantify how TWI and DTMI contributed to variations in Hmax at the local scale. We found that the positive effect of TWI was stronger in subtropical and tropical forests, highlighting that water was the main factor that drives the canopy height pattern in these regions. In contrast, although the effects of DTMI can be both positive and negative, its relative contribution was higher in temperate forest plots than in other forest types, supporting the idea that energy input is more critical for Hmax in temperate forests. Overall, our study revealed the directional change from energy to water limitation from temperate to subtropical and tropical forests. Our findings can offer important insights into forest management, especially under global climate change in the Anthropocene.
Human-induced forest edges are common in many forest landscapes throughout the world. Forest management requires an understanding of their ecological consequences. This study addressed the responses ...of three ecological groups (non-forest species, secondary forest species and primary forest species) in edge soil seed banks and edge understory vegetation, and explored the relationship between the invasion of non-forest species in edge understory vegetation and the accumulation of their seeds in edge soil seed banks. The soil seed banks and understory vegetation were sampled along transects established at the edges of a continuous subtropical evergreen broad-leaved forest tract (
Lithocarpus xylocarpus forest) bordering anthropogenic grasslands and three tropical seasonal rain forest fragments (
Shorea wantianshuea forest) bordering fallows. Species composition in both soil seed banks and understory vegetation showed great difference among edge sites. In soil seed banks, the dominance (relative abundance and relative richness) of each ecological group did not change significantly along the edge to interior gradient. In understory vegetation, the invasion of non-forest species concentrated on the first several meters along the edge to interior gradient. The dominance of secondary forest species decreased with distance from the edge, while the dominance of primary forest species increased with distance from the edge. In forest edge zones, the invasion of a majority of non-forest species in understory vegetation lags behind the accumulation of their seeds in soil seed banks. Forest edges do not act as a good barrier for the penetration of non-forest species seeds. The lack of non-forest species in understory vegetation must then be due to conditions that are not appropriate for their establishment. Therefore, to prevent germination and survival of non-forest species further into the forest, management should focus on maintaining interior forest conditions.
Disturbances are crucial in determining forest biodiversity, dynamics, and ecosystem functions. Surface fire is a significant disturbance in tropical forests, but research on the effect of surface ...fire on structuring species and functional composition in a community through time remains scarce. Using a 20-year dataset of tree demography in a seasonal evergreen tropical forest in Thailand, we specifically addressed two essential questions: (1) What is the pattern of temporal turnover in species and functional composition in a community with frequent fire disturbance? (2) How did the temporal turnover vary with tree size?
We analyzed species compositional and functional temporal turnovers in four different tree size classes among five tree censuses. We quantified species turnover by calculating Bray-Curtis dissimilarity, and investigated its underlying mechanisms by comparing pairwise dissimilarity of functional traits with simulations from null models. If fire disturbances contribute more to a stochastic process, the functional composition would display a random pattern. However, if they contribute more towards a deterministic process, the functional composition should reveal a non-random pattern.
Over 20 years (1994-2014), we observed changes in species composition, whereas functional composition remained relatively stable. The temporal turnover patterns of species and functional compositions varied with tree sizes. In particular, temporal functional turnover shifted very little for large trees, suggesting that changes in species composition of larger trees are contributed by species with similar functional traits through time. The temporal functional composition turnovers of smaller trees (DBH ≤ 5 cm) were mostly at random. We detected a higher functional turnover than expected by null models in some quadrats throughout the 50-ha study plot, and their observed turnover varied with diameter classes.
Species compositional changes were caused by changes in the abundance of species with similar functional traits through time. Temporal functional turnover in small trees was random in most quadrats, suggesting that the recruits came from the equal proportions of surviving trees and new individuals of fast-growing species, which increased rapidly after fires. On the other hand, functional composition in big trees was more likely determined by surviving trees which maintained higher functional similarities than small trees through time. Fire disturbance is important for ecosystem functions, as changing forest fire frequency may alter forest turnover, particularly in functional composition in the new recruits of this forest.
Tropical forests are biologically diverse and structurally complex ecosystems that can store a large quantity of carbon and support a great variety of plant and animal species. However, tropical ...forest structure can vary dramatically within seemingly homogeneous landscapes due to subtle changes in topography, soil fertility, species composition and past disturbances. Although numerous studies have reported the effects of field-based stand structure attributes on aboveground biomass (AGB) in tropical forests, the relative effects and contributions of UAV LiDAR-based canopy structure and ground-based stand structural attributes in shaping AGB remain unclear. Here, we hypothesize that mean top-of-canopy height (TCH) enhances AGB directly and indirectly via species richness and horizontal stand structural attributes, but these positive relationships are stronger at a larger spatial scale. We used a combined approach of field inventory and LiDAR-based remote sensing to explore how stand structural attributes (stem abundance, size variation and TCH) and tree species richness affect AGB along an elevational gradient in tropical forests at two spatial scales, i.e., 20 m × 20 m (small scale), and 50 m × 50 m (large scale) in southwest China. Specifically, we used structural equation models to test the proposed hypothesis. We found that TCH, stem size variation and abundance were strongly positively associated with AGB at both spatial scales, in addition to which increasing TCH led to greater AGB indirectly through increased stem size variation. Species richness had negative to negligible influences on AGB, but species richness increased with increasing stem abundance at both spatial scales. Our results suggest that light capture and use, modulated by stand structure, are key to promoting high AGB stocks in tropical forests. Thus, we argue that both horizontal and vertical stand structures are important for shaping AGB, but the relative contributions vary across spatial scales in tropical forests. Importantly, our results highlight the importance of including vertical forest stand attributes for predicting AGB and carbon sequestration that underpins human wellbeing.
Frugivory and seed dispersal are key processes that shape both plant and animal communities, they are important in the maintenance and regeneration of forest ecosystems while threatened by ...environmental changes. This study investigated the frugivores and environmental factors affecting animal visitation and fruit consumption of the evergreen tree Baccaurea ramiflora (Lour.) in Chinese (Xishuangbanna) and Thai (Mo Singto) tropical forest plots. The two plots differ in their mammal faunas, with more large species (Asian elephant, white-handed gibbon, bears) surviving on the Mo Singto plot. We asked whether these differences could resulted in different seed dispersal patterns on the two plots. Nine individual trees were selected in each plot to record arboreal and ground frugivores of B. ramiflora using camera traps. A total of 27 frugivore species were captured from both forest plots, 15 species in Xishuangbanna and 22 in Mo Singto, with ten species shared in both plots. The major frugivores of B. ramiflora in Xishuangbanna were all pre-dispersal seed predators with little contribution to seed dispersal, including Palla’s squirrel (Callosciurus erythraeus), red-cheeked squirrel (Dremomys rufigenis) and black giant squirrel (Ratufa bicolor). Meanwhile, the major frugivores in Mo Singto were two effective seed dispersers pig-tailed macaque (Macaca leonina) and white-handed gibbon (Hylobates lar), and seed predator black giant squirrel (Ratufa bicolor). The diversity and body size of frugivores in the Xishuangbanna plot were relatively small compared with those in Mo Singto plot. Small-bodied frugivores showed higher activity in Xishuangbanna plot whereas relatively larger frugivores were most active in the Mo Singto plot. The environmental factor that consistently influenced frugivore activity (visitation and consumption of B. ramiflora fruits) was fruit abundance. Ground cover was also a predictor for average visit length and fruit consumption of frugivores. Frugivores visitation rate was higher in Xishuangbanna while average visit length and consumption rates were higher in Mo Singto. The defaunation of large body-size frugivores in Xishuangbanna could have been a result of habitat loss and higher hunting pressure. This may lead to shorter dispersal distances for large-seeded plants, restricting their ability to move across changing landscapes, and threatening their chances of survival over the long term.
The high uncertainty associated with the response of terrestrial carbon (C) cycle to climate is dominated by ecosystem C turnover time (τeco). Although the relationship between τeco and climate has ...been extensively studied, significant knowledge gaps remain regarding the differential climate sensitivities of turnover time in major biomass (τveg) and soil (τsoil) pools, and their effects on vegetation and soil C sequestration under climate change are poorly understood. Here, we collected multiple time series observations on soil and vegetation C from permanent plots in 10 Chinese forests and used model‐data fusion to retrieve key C cycle process parameters that regulate τsoil and τveg. Our analysis showed that τveg and τsoil both decreased with increasing temperature and precipitation, and τsoil was more than twice as sensitive (1.27 years/°C, 1.70 years/100 mm) than τveg (0.53 years/°C, 0.40 years/100 mm). The higher climate sensitivity of τsoil caused a more rapid decrease in τsoil than in τveg with increasing temperature and precipitation, thereby significantly reducing the difference between τsoil and τveg (τdiff) under warm and humid conditions. τdiff, an indicator of the balance between the soil C input and exit rate, was strongly responsible for the variation (more than 50%) in soil C sequestration. Therefore, a smaller τdiff under warm and humid conditions suggests a relatively lower contribution from soil C sequestration. This information has strong implications for understanding forest C‐climate feedback, predicting forest C sink distributions in soil and vegetation under climate change, and implementing C mitigation policies in forest plantations or soil conservation.
Plain Language Summary
Carbon turnover time is the average time that a carbon atom stays in an ecosystem from entrance to exit. Together, ecosystem carbon input via photosynthesis (i.e., productivity) and carbon turnover time determine ecosystem carbon sequestration. However, in contrast to the well‐studied ecosystem productivity, carbon turnover time was found to dominate the uncertainty in terrestrial carbon sequestration and its response to climate. However, the climate sensitivities of carbon turnover times in various plant and soil pools and their effects on carbon storage have not been well‐studied. Here, we quantified that carbon turnover time in soil (τsoil) was more sensitive to climate than that of vegetation (τveg). This finding indicated the difference between τveg and τsoil (τdiff) being shortened in warm and humid regions. We further found that τdiff, as an indicator of the balance between soil carbon input and the carbon exit rate, is closely associated with the capacity for soil carbon sequestration. Therefore, a decreasing τdiff with increasing temperature/precipitation indicates a smaller proportion of carbon sequestered by soil than vegetation. Our findings facilitate understanding of carbon‐climate feedback and the prediction of carbon sink distributions under climate change and could guide the implementation of carbon mitigation policies for vegetation/soil conservation.
Key Points
The carbon turnover time in soil (τsoil) has a higher climate sensitivity to temperature and precipitation than that of biomass (τveg)
The strong climate responses of woody allocation and soil decomposition in combination contribute to the higher climate sensitivity of τsoil than τveg
The higher climate sensitivity of τsoil than τveg led to a decreased soil carbon sequestration capacity under warm and humid conditions
Ecologists have historically used species-area relationships (SARs) as a tool to understand the spatial distribution of species. Recent work has extended SARs to focus on individual-level ...distributions to generate individual species area relationships (ISARs). The ISAR approach quantifies whether individuals of a species tend have more or less species richness surrounding them than expected by chance. By identifying richness 'accumulators' and 'repellers', respectively, the ISAR approach has been used to infer the relative importance of abiotic and biotic interactions and neutrality. A clear limitation of the SAR and ISAR approaches is that all species are treated as evolutionarily independent and that a large amount of work has now shown that local tree neighborhoods exhibit non-random phylogenetic structure given the species richness. Here, we use nine tropical and temperate forest dynamics plots to ask: (i) do ISARs change predictably across latitude?; (ii) is the phylogenetic diversity in the neighborhood of species accumulators and repellers higher or lower than that expected given the observed species richness?; and (iii) do species accumulators, repellers distributed non-randomly on the community phylogenetic tree? The results indicate no clear trend in ISARs from the temperate zone to the tropics and that the phylogenetic diversity surrounding the individuals of species is generally only non-random on very local scales. Interestingly the distribution of species accumulators and repellers was non-random on the community phylogenies suggesting the presence of phylogenetic signal in the ISAR across latitude.
The concept of microbial functional genes has added a new dimension to microbial ecology research by improving the model of microbial community-ecosystem functions relationship. However, our ...knowledge vis-à-vis fine-scale spatial distribution pattern of functional genes and their probable impact on plant community in the hyper-diverse tropical forest ecosystem is very limited. Here, we investigated the spatial pattern of functional genes abundance (NirK, AOA, AOB, and PhoD), identified key influencing factors, and distinguished the key functional group supporting the plant community in a tropical rainforest located in Xishuangbanna. In total, 200 soil samples and vegetation data of ~4800 individuals of plants across a 1 ha study area were collected. Our results detected higher spatial variability with a maximum magnitude of abundance for PhoD gene (4.53 × 107 copies) followed by NirK (2.71 × 106 copies), AOA (1.97 × 106 copies), and AOB (7.38 × 104 copies). A strong spatial dependence was observed for PhoD and NirK over the distance of 17 and 18 m, respectively. Interestingly, the N:P stoichiometry played a critical role in structuring the spatial pattern of the most abundant PhoD gene. The significant positive and negative relationship of PhoD with N:P ratio and available phosphorus, respectively, indicated that the P-limiting environment was a driving factor for recruitment of PhoD gene community. The structural equation modeling ascertained the direct positive impact of PhoD on plant biomass and high demand of available P by plants suggesting that the organic phosphorus mineralization process is essential to maintain plant productivity by re-establishing the availability of the most limiting P nutrient. Our preliminary study improves our understanding of how microbial functional genes-environment associations could be used for monitoring soil health and its overall impact on ecosystem multifunctionality. Finally, we intend to conduct the study at a large spatial scale for achieving a holistic view.
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•Spatial pattern of microbial functional genes was investigated in tropical forest.•PhoD gene abundance was higher than Nirk, AOA, and AOB.•PhoD gene abundance was positively correlated with soil N:P ratio.•Only PhoD gene showed a direct positive impact on the plant biomass.•Nutrient stoichiometry and plant community drive the spatial variability.
To understand soil biodiversity we need to know how soil communities are assembled. However, the relationship between soil community assembly and environmental factors, and the linkages between soil ...microbiota taxonomic groups and their body sizes, remain unexplored in tropical seasonal rainforests. Systematic and stratified random sampling was used to collect 243 soil and organism samples across a 20‐ha plot in a tropical seasonal rainforest in southwestern China. High‐throughput sequencing, variation analysis and principal coordinates of neighbourhood matrices were performed. Soil community composition, spatial distribution and assembly processes based on propagule size (including archaea, bacteria, fungi and nematodes) were investigated. The results showed that: (i) the community assembly of small soil microorganisms (bacteria, fungi) was mostly influenced by stochastic processes while that of larger soil organisms (nematodes) was more deterministic; (ii) the independent effects of habitat (including soil and topographic variables) and its interaction with plant attributes for community structure significantly decreased with increasing body size; and (iii) plant leaf phosphorus directly influenced the spatial distribution of soil‐available phosphorus, which indicates their indirect impact on the assembly of the soil communities. Our data suggest that the assembly of multitrophic soil communities can be explained to some extent by changes in above‐ground plant attributes. This highlights the importance of above‐ and below‐ground linkages in influencing multitrophic soil microbiota community assembly.
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