Due to climate change, subtropical forests are increasingly exposed to severe disturbance, which may lead to increased tree mortality. To date, previous research has not sufficiently studied the ...deadwood biomass within forests over large study plots. To address this research gap, we calculated the deadwood biomass within a 20 hectare (ha) permanent old-growth forest plot in southern China during two censuses and assessed the factors contributing to it. The deadwood biomass was estimated by applying allometric regression equations. There was a total of 11,283 (22.4%) dead individuals in the study plot. Most of these dead trees had very small diameters (1–10 cm). The spatial distribution of the dead individuals differed across subplots and was determined by biotic and abiotic factors. The deadwood biomass storage was 142.5 ton (t) in our study plot. Small (DBH: 0–30 cm) and medium trees (DBH: 30–50 cm) were the largest contributors (54.9% and 30.7%) to deadwood biomass storage. Three dominant tree species contributed 64.8% of the deadwood biomass storage, and the deadwood biomass of 38 tree species was less than 1 t ha−1. Finally, the deadwood biomass was determined by breast diameter and the number of dead individuals, which was influenced by neighboring individuals and environmental factors. This study provides a detailed assessment of the patterns of the deadwood biomass in a subtropical forest and underscores the importance of including community characteristics and abiotic factors (e.g., topography) into research on forest ecosystem carbon. The results of this research provide valuable information that can deepen the understanding of the contribution of subtropical forests to the global carbon cycle and that can be used to improve forest protection and planning strategies.
Vertical stratification in trees may respond to selective pressures to enhance light interception and utilization; therefore, the vertical functional variation in leaf traits may indicate niche ...partitioning within forests. In this study, vertical variations in leaf and crown structure traits of seven common tree species were analysed with respect to differences between species in different height groups, within the same height range, in the same species across tree height, and different parts of the individual tree crown to reveal coexistence mechanisms in subtropical forest tree species. There were multiple levels of trait variation in the vertical dimension, validating the existence of vertical niche differentiation in subtropical forest species. The functional trait differences arose among different height groups, among species co-occurring within the same height range, in the same species across tree height, and among different parts of the individual tree crown. Variation in comparative advantages, which was characterised by those traits between species across different height ranges, was also one of the manifestations of niche differentiation in the vertical dimension. Moreover, contrasting results between lower height ranges and higher ranges in the relationship between species’ differences in functional traits and species’ difference of abundance were found, further confirming that there was obvious vertical niche separation in the community. This study emphasised the importance of vertical variation in species’ performances in elucidating the mechanisms of tree species coexistence in subtropical forests.
Associated endogenous hormones were affected by forest fragmentation and significantly correlated with aboveground biomass storage. Forest fragmentation threatens aboveground biomass (AGB) and ...affects biodiversity and ecosystem functioning in multiple ways. We ask whether and how forest fragmentation influences AGB in forest fragments. We investigated differences in AGB between forest edges and interiors, and how plant community characteristics and endogenous hormones influenced AGB. In six 40 m × 40 m plots spread across three forest fragments, AGB was significantly higher in plots in the forest interior than in those at the edge of forests. The proportion of individuals with a large diameter at breast height (DBH > 40 cm) in the forest edges is higher than that in the forest interiors. Further, trees within a 15–40 cm DBH range had the highest contribution to AGB in all plots. Trees in interior plots had higher abscisic acid (ABA) and lower indole-3-acetic acid (IAA) concentrations than those in edge plots. In addition, AGB was significantly positively and negatively correlated with ABA and IAA concentrations at the community scale. In this study, we provide an account of endogenous hormones’ role as an integrator of environmental signals and, in particular, we highlight the correlation of these endogenous hormone levels with vegetation patterns. Edge effects strongly influenced AGB. In the future, more endogenous hormones and complex interactions should be better explored and understood to support consistent forest conservation and management actions.
Tree mortality and recruitment are key factors influencing forest dynamics, but the driving mechanisms of these processes remain unclear. To better understand these driving mechanisms, we studied ...forest dynamics over a 5-year period in a 20-ha sub-tropical forest in the Dinghushan Nature Reserve, South China. The goal was to identify determinants of tree mortality/recruitment at the local scale using neighborhood analyses on some locally dominant tree species. Results show that the study plot was more dynamic than some temperate and tropical forests in a comparison to large, long-term forest dynamics plots. Over the 5-year period, mortality rates ranged from 1.67 to 12.33% per year while recruitment rates ranged from 0 to 20.26% per year. Tree size had the most consistent effect on mortality across species. Recruitment into the ≥1-cm size class consistently occurred where local con-specific density was high. This suggests that recruitment may be limited by seed dispersal. Hetero-specific individuals also influenced recruitment significantly for some species. Canopy species had low recruitment into the ≥1-cm size class over the 5-year period. In conclusion, tree mortality and recruitment for sixteen species in this plot was likely limited by seed dispersal and density-dependence.
The performance of asphalt mixtures greatly influences the long-term performance of bridge deck pavements. It is essential to optimise the asphalt mixtures with the best overall performance according ...to different regional conditions for use in engineering practice. This study proposes a comprehensive assessment method based on the Analytical Hierarchy Process (AHP) and Fuzzy Comprehensive Evaluation (FCE) to evaluate the serviceability of asphalt mixtures from different perspectives. It is used to optimise the best asphalt mixtures. The results show that the skeleton-dense structure asphalt mixture has better engineering applicability than the suspension-dense structure asphalt mixture, and the comprehensive performance of the asphalt mixture decreases with the increase of the nominal maximum particle size. The FCE determines that the total performance of the seven types of asphalt mixtures in the order of their superiority and inferiority are SMA-13 >asphalt mastic sand (AMS)>SMA-10 >AC-25 >AC-13 >AC-16 >AC-20. The study combines qualitative and quantitative factors, which makes the selection of engineering materials more scientific and rigorous and improves the rationality of material suitability evaluation.
We evaluated the degree to which relative growth rate (RGR) of saplings and large trees is related to seven functional traits that describe physiological behavior and soil environmental factors ...related to topography and fertility for 57 subtropical tree species in Dinghushan, China. The mean values of functional traits and soil environmental factors for each species that were related to RGR varied with ontogenetic stage. Sapling RGR showed greater relationships with functional traits than large-tree RGR, whereas large-tree RGR was more associated with soil environment than was sapling RGR. The strongest single predictors of RGR were wood density for saplings and slope aspect for large trees. The stepwise regression model for large trees accounted for a larger proportion of variability (R² = 0.95) in RGR than the model for saplings (R² = 0.55). Functional diversity analysis revealed that the process of habitat filtering likely contributes to the substantial changes in regulation of RGR as communities transition from saplings to large trees.
Eucalyptus is one of the fastest growing woody plants in the world, but few studies have reported the soil microbial community composition in Eucalyptus ecosystems. This study investigated the soil ...microbial communities in plantations of 3-, 7-, 10- and 13-year-old Eucalyptus in subtropical China based on phospholipid fatty acids (PLFA) analysis. The variation in soil microbial biomass and community compositions were influenced by sampling site and season and the interaction of both, which were consistent with the variation in soil total nitrogen (TN), soil organic carbon (SOC) and soil moisture. The number and abundances of PLFAs, and the amount of soil TN and SOC were higher in plantation of 13-year-old Eucalyptus than those in other younger plantations, suggesting that the soil properties and the soil microbial community composition is not negatively affected by the planting of Eucalyptus. The ratio of monounsaturated-to-branched fatty acids, the proportional abundance (mol%) of bacterial PLFA and fungal PLFA varied significantly with Eucalyptus plantations of different age, suggesting that the individual PLFA signatures might be sensitive indicators of soil properties associated with forest plantations.
The spatial dispersion of individuals in a species is an important pattern that is controlled by many mechanisms. In this study we analyzed spatial distributions of tree species in a large-scale (20 ...ha) stem-mapping plot in a species-rich subtropical forest of China. O-ring statistic was used to measure spatial patterns of species with abundance > 10. Qo_ io, the mean conspecific density within 10 m of a tree, was used as a measure of the intensity of aggregation of a species. Our results showed: (1) aggregated distribution was the dominant pattern in the plot. The percentage of aggregated species decreased with increased spatial scale. (2) The percentages of significantly aggregated species decreased from abundant to intermediate and to rare species. Rare species was more strongly aggregated than common species. Aggregation was weaker in larger diameter classes. (3) Seed traits determined the spatial patterns of trees. Seed dispersal mode can influence spatial patterns of species, with species dispersed by both modes being less clumped than species dispersed by animal or wind, respectively. Considering these results, we concluded that seed dispersal limitation, self-thinning and habitat heterogeneity primarily contributed to spatial patterns and species coexistence in the forest.
In response to stricter emission regulations, lean‐burn engines have attracted more and more attention. However, lean burn engines would inevitably lead to the increase in NOx emissions. The ...researchers combined Three‐Way Catalyst (TWC) and Selective Catalytic Reduction (SCR) to propose “passive SCR”, which makes the engine periodically switch between rich and lean burn. During rich combustion, ammonia is produced by the TWC catalyst, stored in the downstream SCR, and reacts with NOx during lean combustion, in which increasing the ammonia yield on the TWC catalyst is the key. In this study, the self‐propagating high‐temperature synthesis method was used to modify the catalyst by adding copper to improve the ammonia production efficiency. The conversion rate of catalysts with different copper doping ratios from NO to ammonia was measured. Through XRD, BET, H2‐TPR, TEM, HRTEM, XPS, in‐situ DRIFTS, etc., the improvement mechanism of copper doping was analysed. The results showed that Pt0.01Cu0.1Ce0.45Zr0.45Ox had the highest catalytic activity, the widest reaction temperature window (300–550 °C) with the conversion greater than 96 %. The characterization results showed that appropriate amount of copper doping can adjust the valence distribution, form more oxygen vacancies, and improve the distribution of active species. The in‐situ DRIFTS further demonstrated that the conversion from bridged to monodentate and bidentate nitrate may be the key factors on the catalyst surface.
Different proportions of Cu‐doped Pt0.01/Ce0.5Zr0.5Ox catalysts was synthesized to improve ammonia production activity of three‐way catalysts (TWC). Pt0.01Cu0.1Ce0.45Zr0.45Ox had the best activity. Appropriate amount of copper doping can adjust the valence distribution, form more oxygen vacancies, and improve the distribution of active species. The conversion from bridged to monodentate and bidentate nitrate may be the key factor on the catalyst.
Tree size distributions have long been of interest to ecologists and foresters because they reflect fundamental demographic processes. Previous studies have assumed that size distributions are often ...associated with population trends or with the degree of shade tolerance. We tested these associations for 31 tree species in a 20 ha plot in a Dinghushan south subtropical forest in China. These species varied widely in growth form and shade-tolerance. We used 2005 and 2010 census data from that plot. We found that 23 species had reversed J shaped size distributions, and eight species had unimodal size distributions in 2005. On average, modal species had lower recruitment rates than reversed J species, while showing no significant difference in mortality rates, per capita population growth rates or shade-tolerance. We compared the observed size distributions with the equilibrium distributions projected from observed size-dependent growth and mortality. We found that observed distributions generally had the same shape as predicted equilibrium distributions in both unimodal and reversed J species, but there were statistically significant, important quantitative differences between observed and projected equilibrium size distributions in most species, suggesting that these populations are not at equilibrium and that this forest is changing over time. Almost all modal species had U-shaped size-dependent mortality and/or growth functions, with turning points of both mortality and growth at intermediate size classes close to the peak in the size distribution. These results show that modal size distributions do not necessarily indicate either population decline or shade-intolerance. Instead, the modal species in our study were characterized by a life history strategy of relatively strong conservatism in an intermediate size class, leading to very low growth and mortality in that size class, and thus to a peak in the size distribution at intermediate sizes.
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