Understanding local variation in forest biomass allows for a better evaluation of broad-scale patterns and interpretation of forest ecosystems’role in carbon dynamics.This study focuses on patterns of aboveground tre...Understanding local variation in forest biomass allows for a better evaluation of broad-scale patterns and interpretation of forest ecosystems’role in carbon dynamics.This study focuses on patterns of aboveground tree biomass within a fully censused 20 ha forest plot in a temperate forest of northern Alabama,USA.We evaluated the relationship between biomass and topography using ridge and valley landforms along with digitally derived moisture and solar radiation indices.Every live woody stem over 1 cm diameter at breast height within this plot was mapped,measured,and identified to species in 2019-2022,and diameter data were used along with speciesspecific wood density to map the aboveground biomass at the scale of 20 m×20 m quadrats.The aboveground tree biomass was 211 Mg·ha^(-1).Other than small stream areas that experienced recent natural disturbances,the total stand biomass was not associated with landform or topographic indices.Dominant species,in contrast,had strong associations with topography.American beech(Fagus grandifolia)and yellow-poplar(Liriodendron tulipfera)dominated the valley landform,with 37% and 54% greater biomass in the valley than their plot average,respectively.Three other dominant species,white oak(Quercus alba),southern shagbark hickory(Carya carolinaeseptentrionalis),and white ash(Fraxinus americana),were more abundant on slopes and benches,thus partitioning the site.Of the six dominant species,only sugar maple(Acer saccharum)was not associated with landform.Moreover,both topographic wetness and potential radiation indices were significant predictors of dominant species biomass within each of the landforms.The study highlights the need to consider species when examining forest productivity in a range of site conditions.展开更多
The composition of animal species and interactions among them are widely known to shape ecological communities and fine-scale(e.g.,<1 km)monitoring of animal communities is essential for understanding the relations...The composition of animal species and interactions among them are widely known to shape ecological communities and fine-scale(e.g.,<1 km)monitoring of animal communities is essential for understanding the relationships among animals and plants.Although the co-existence of large-and medium-sized species has been studied across different scales,research on fine-scale interactions of herbivores in deciduous broadleaf forests is limited.Camera trapping of large-and medium-sized mammals was carried out over a 1 year period within a 25 ha deciduous broadleaf forest dynamics plot in the Qinling Mountains,China.Fourteen species of large-and medium-sized mammals,including six carnivores,six ungulates,one primate and one rodent species were found.Kernel density estimations were used to analyse the diel or 24 h activity patterns of all species with more than 40 independent detections and general linear models were developed to explore the spatial relationships among the species.The combination of overlapping diel activity patterns and spatial associations showed obvious niche separation among six species:giant panda(Ailuropoda melanoleuca David),takin(Budorcas taxicolor Hodgson),Reeves’s muntjac(Muntiacus reevesi Ogilby),tufted deer(Elaphodus cephalophus Milne-Edwards),Chinese serow(Capricornis milneedwardsii David)and wild boar(Sus scrofa Linnaeus).Long-term fine-scale monitoring is useful for providing information about the co-existence of species and their interactions.The results demonstrate the importance for fine-scale monitoring of animals and plants for improving understanding of species interactions and community dynamics.展开更多
Stocking and structural composition of a deciduous broad-leaved forest were determined to predict coarse woody debris quantity by quantifying the empirical relationships between these two attributes.The most ecologica...Stocking and structural composition of a deciduous broad-leaved forest were determined to predict coarse woody debris quantity by quantifying the empirical relationships between these two attributes.The most ecologically significant families by stem density were Salicaceae,Betulaceae,Fagaceae,and Aceraceae.P opulus davidiana was the most dominant species followed by B etula dahurica,Quercus mongolica,and Acer mono.The four species accounted for 69.5%of total stems.Numerous small-diameter species characterized the coarse woody debris showing a reversed J-shaped distribution.The coarse debris of P.davidiana,B.dahurica,and Q.mongolica mainly comprised the 10–20 cm size class,whereas A.mono debris was mainly in the 5–10 cm size class.The spatial patterns of different size classes of coarse woody debris were analyzed using the g-function to determine the size of the tree at its death.The results indicate that the spatial patterns at the 0–50 m scale shifted gradually from an aggregated to a random pattern.For some species,the larger coarse debris might change from an aggregated to a random distribution more easily.Given the importance of coarse woody debris in forest ecosystems,its composition and patterns can improve understanding of community structure and dynamics.The aggregation pattern might be due to density dependence and self-thinning effects,as well as by succession and mortality.The four dominant species across the different size classes showed distinct aggregated distribution features at different spatial scales.This suggests a correlation between the dominant species population,size class,and aggregated distribution of coarse woody debris.展开更多
In eastern Asian subtropical forests,leaf habit shifts from evergreen to deciduous broad-leaved woody plants toward higher latitudes.This shift has been largely explained by the greater capacity of deciduous broad-lea...In eastern Asian subtropical forests,leaf habit shifts from evergreen to deciduous broad-leaved woody plants toward higher latitudes.This shift has been largely explained by the greater capacity of deciduous broad-leaved plants to respond to harsh climatic conditions(e.g.,greater seasonality).The advantages of deciduous leaf habit over evergreen leaf habit in more seasonal climates have led us to hypothesize that leaf habits would shift in response to climate changes more conspicuously in forest canopy trees than in forest understory shrubs.Furthermore,we hypothesize that in the forests of the subtropics,plants at higher latitudes,regardless of growth form,would better tolerate seasonal harsh climates,and hence show less differentiation in leaf habit shift,compared to those at lower latitudes.To test these two hypotheses,we modelled the proportion of deciduous broad-leaved species and the incidence of deciduous and evergreen broad-leaved species in woody angiosperm species compositions of ten largesized forest plots distributed in the Chinese subtropics.We found that the rate of leaf habit shift along a latitudinal gradient was higher in forest trees than in forest shrubs.We also found that the differentiation in leaf habit shift between trees and shrubs is greater at lower latitudes(i.e.,warmer climates)than at higher latitudes(i.e.,colder climates).These findings indicate that specialized forest plants are differentially affected by climate in distinct forest strata in a manner dependent on latitudinal distribution.These differences in forest plant response to changes in climate suggest that global climate warming will alter growth forms and geographical distributions and ranges of forests.展开更多
The spatial-temporal variation of understory light availability has important influences on species diversity and community assembly.However,the distribution characteristics and influencing factors of understory light...The spatial-temporal variation of understory light availability has important influences on species diversity and community assembly.However,the distribution characteristics and influencing factors of understory light availability have not been fully elucidated,especially in temperate deciduous,broad-leaved forests.In this study,the understory light availability was monitored monthly(May–October)in a temperate deciduous,broad-leaved forest in Henan Province,China.Differences in the light availability among different months and habitat types were statistically analyzed using Kruskal–Wallis method,respectively.Partial least squares path modeling(PLS-PM)was used to explore the direct and/or indirect effects of stand structure,dominant species and topographic factors on the light environment.Results showed that there were differences in light environments among the four habitat types and during the studied six months.The PLS-PM results showed that the stand structure and the dominant species were negatively correlated with the light environment,and the path coefficient values were−0.089(P=0.042)and−0.130(P=0.004),respectively.Our result indicated that the understory light availability exhibit a distinct spatial and temporal heterogeneity in temperate deciduous,broad-leaved forest of north China.The characteristics of woody plant community,especially the abundance of one of the dominant plant species,were the important factors affecting the understory light availability.展开更多
Background The full lifespan of long-lived trees includes a seedling phase,during which a seed germinates and grows to a size large enough to be measured in forest inventories.Seedling populations are usually studied ...Background The full lifespan of long-lived trees includes a seedling phase,during which a seed germinates and grows to a size large enough to be measured in forest inventories.Seedling populations are usually studied separately from adult trees,and the seedling lifespan,from seed to sapling,is poorly known.In the 50-ha Barro Colorado forest plot,we started intensive censuses of seeds and seedlings in 1994 in order to merge seedling and adult demography and document complete lifespans.Methods In 17 species abundant in seedling censuses,we subdivided populations into six size classes from seed to 1cm dbh,including seeds plus five seedling stages.The smallest seedling class was subdivided by age.Censuses in two consecutive years provided transition matrices describing the probability that a seedling in one stage moved to another one year later.For each species,we averaged the transition matrix across 25 censuses and used it to project the seedling lifespan,from seed until 1cm dbh or death.Results The predicted mean survival rate of seeds to 1cm dbh varied 1000-fold across species,from 2.9×10^(−6)to 4.4×10^(−3);the median was 2.0×10^(−4).The seedling lifespan,or the average time it takes a seed to grow to 1cm dbh,varied across species from 5.1 to 53.1 years,with a median of 20.3 years.In the median species,the 10%fastest-growing seeds would reach 1cm dbh in 9.0 years,and the slowest 10%in 34.6 years.Conclusions Combining seedling results with our previous study of lifespan after 1cm dbh,we estimate that the focal species have full lifespans varying from 41 years in a gap-demanding pioneer to 320 years in one shade-tolerant species.Lifetime demography can contribute precise survival rates and lifespans to forestry models.展开更多
BACKGROUND Patients with chronic obstructive pulmonary disease(COPD)frequently experience exacerbations requiring multiple hospitalizations over prolonged disease courses,which predispose them to generalized anxiety d...BACKGROUND Patients with chronic obstructive pulmonary disease(COPD)frequently experience exacerbations requiring multiple hospitalizations over prolonged disease courses,which predispose them to generalized anxiety disorder(GAD).This comorbidity exacerbates breathing difficulties,activity limitations,and social isolation.While previous studies predominantly employed the GAD 7-item scale for screening,this approach is somewhat subjective.The current literature on predictive models for GAD risk in patients with COPD is limited.AIM To construct and validate a GAD risk prediction model to aid healthcare professionals in preventing the onset of GAD.METHODS This retrospective analysis encompassed patients with COPD treated at our institution from July 2021 to February 2024.The patients were categorized into a modeling(MO)group and a validation(VA)group in a 7:3 ratio on the basis of the occurrence of GAD.Univariate and multivariate logistic regression analyses were utilized to construct the risk prediction model,which was visualized using forest plots.The model’s performance was evaluated using Hosmer-Lemeshow(H-L)goodness-of-fit test and receiver operating characteristic(ROC)curve analysis.RESULTS A total of 271 subjects were included,with 190 in the MO group and 81 in the VA group.GAD was identified in 67 patients with COPD,resulting in a prevalence rate of 24.72%(67/271),with 49 cases(18.08%)in the MO group and 18 cases(22.22%)in the VA group.Significant differences were observed between patients with and without GAD in terms of educational level,average household income,smoking history,smoking index,number of exacerbations in the past year,cardiovascular comorbidities,disease knowledge,and personality traits(P<0.05).Multivariate logistic regression analysis revealed that lower education levels,household income<3000 China yuan,smoking history,smoking index≥400 cigarettes/year,≥two exacerbations in the past year,cardiovascular comorbidities,complete lack of disease information,and introverted personality were significant risk factors for GAD in the MO group(P<0.05).ROC analysis indicated that the area under the curve for predicting GAD in the MO and VA groups was 0.978 and 0.960.The H-L test yieldedχ^(2) values of 6.511 and 5.179,with P=0.275 and 0.274.Calibration curves demonstrated good agreement between predicted and actual GAD occurrence risks.CONCLUSION The developed predictive model includes eight independent risk factors:Educational level,household income,smoking history,smoking index,number of exacerbations in the past year,presence of cardiovascular comorbidities,level of disease knowledge,and personality traits.This model effectively predicts the onset of GAD in patients with COPD,enabling early identification of high-risk individuals and providing a basis for early preventive interventions by nursing staff.展开更多
Aims While using phylogenetic and functional approaches to test the mechanisms of community assembly,functional traits often act as the proxy of niches.However,there is little detailed knowledge regarding the correlat...Aims While using phylogenetic and functional approaches to test the mechanisms of community assembly,functional traits often act as the proxy of niches.However,there is little detailed knowledge regarding the correlation between functional traits of tree species and their niches in local communities.We suggest that the co-varying correlation between functional traits and niches should be the premise for using phylogenetic and functional approaches to test mechanisms of community assembly.Using functional traits,phylogenetic and environmental data,this study aims to answer the questions:(i)within local communities,do functional traits of co-occurring species covary with their environmental niches at the species level?and(ii)what is the key ecological process underlying community assembly in Xishuangbanna and Ailaoshan forest dynamic plots(FDPs)?Methods We measured seven functional traits of 229 and 36 common species in Xishuangbanna and Ailaoshan FDPs in tropical and subtropical China,respectively.We also quantified the environmental niches for these species based on conditional probability.We then analyzed the correlations between functional traits and environmental niches using phylogenetic independent contrasts.After examining phylogenetic signals of functional traits using Pagel’sλ,we quantified the phylogenetic and functional dispersion along environmental gradients within local tree communities.Important Findings For target species,functional traits do co-vary with environmental niches at the species level in both of the FDPs,supporting that functional traits can be used as a proxy for local-scale environmental niches.Functional traits show significant phylogenetic signals in both of the FDPs.We found that the phylogenetic and functional dispersion were significantly clustered along topographical gradients in the Ailaoshan FDP but overdispersion in the Xishuangbanna FDP.These patterns of phylogenetic and functional dispersion suggest that environmental filtering plays a key role in structuring local tree assemblages in Ailaoshan FDP,while competition exclusion plays a key role in Xishuangbanna FDP.展开更多
Aims Understanding the controls influencing tree growth is central to forest ecology.Although many factors such as tree size,neighborhood competition and environmental variables,have been proposed as being important i...Aims Understanding the controls influencing tree growth is central to forest ecology.Although many factors such as tree size,neighborhood competition and environmental variables,have been proposed as being important in explaining patterns of tree growth,but their relative contributions are still subject to debate.We aimed to examine the relative importance of tree size,local abiotic conditions and the density and identity of neighbors on tree growth in an old-growth temperate forest in northeast china.Methods We used linear mixed models with data from a 25 ha(500×500 m)broad-leaved Korean pine(Pinus koraiensis)mixed forest perma-nent plot to examine the relative importance of these local drivers on tree growth at three organizational levels(community,guild and species).Subplot was included as a random effect to account for spatial autocorrelation in growth of trees located within the same subplot,and species was included as a random effect to account for variation among species in growth.Important Findings Tree size was typically the most important predictor of growth,followed by neighborhood competition and then soil nutrients.The correlation of tree size to growth varied from strongly positive for large trees and medium trees to slightly positive for small trees.The effect of neighbor-hood competition on growth showed weak negative density dependence as indicated by slightly negative effect of total basal area of neighbors and the proportion of conspecific neighbors.Environmental factors influenced growth of very common species,smaller tree-size classes and shade-tolerant species.We concluded that the relative importance of variables driving patterns of tree growth varied greatly among tree size classes,shade tolerance and abundance classes in this temperate for-est.These results provide critical information for future studies of forest dynamics and offer insight into forest management in this region.展开更多
An important mechanism promoting species coexistence is conspecific negative density dependence(CNDD),which inhibits conspecific neighbors by accumulating host-specific enemies near adult trees.Natural enemies may be ...An important mechanism promoting species coexistence is conspecific negative density dependence(CNDD),which inhibits conspecific neighbors by accumulating host-specific enemies near adult trees.Natural enemies may be genotype-specific and regulate offspring dynamics more strongly than non-offspring,which is often neglected due to the difficulty in ascertaining genetic relatedness.Here,we investigated whether offspring and non-offspring of a dominant species,Castanopsis eyrei,suffered from different strength of CNDD based on parentage assignment in a subtropical forest.We found decreased recruitment efficiency(proxy of survival probability)of offspring compared with non-offspring near adult trees during the seedling-sapling transition,suggesting genotype-dependent interactions drive tree demographic dynamics.Furthermore,the genetic similarity between individuals of same cohort decreased in late life history stages,indicating genetic-relatedness-dependent tree mortality throughout ontogeny.Our results demonstrate that within-species genetic relatedness significantly affects the strength of CNDD,implying genotype-specific natural enemies may contribute to population dynamics in natural forests.展开更多
Aims Relationships between local habitat heterogeneity and tree commu-nities in miombo woodlands have been very little studied.While some studies have addressed this topic at broad scales and based on few environmenta...Aims Relationships between local habitat heterogeneity and tree commu-nities in miombo woodlands have been very little studied.While some studies have addressed this topic at broad scales and based on few environmental parameters,this study aims at(i)detecting fine-scale habitats(≤10 ha)on the basis of a detailed characterisation of soil explicitly considering past anthropogenic disturbances,and an exhaustive census of the tree community,and at(ii)searching for indicator tree species corresponding to the resulting habitats.Methods The study was carried out in the miombo woodland of Mikembo Forest Reserve,Upper Katanga,The Democratic Republic of the congo.A complete census of the tree community was conducted in a 10-ha forest dynamics plot comprising 160 adjacent quadrats of 25×25 m,with a total of 4604 trees(diameter at breast height>10 cm).Thirty-six physicochemical soil parameters were measured.Studying the frequency distribution of soil charcoal content allowed identifying local signature of past human agriculture in the soil.Two strategies were used to define habitats:(i)a combination of principal component analysis(PcA)on soil variables and Ward clustering and(ii)multivariate regression trees(MRT)to search for key soil parameters allowing the best prediction of species composition.Tree-habitat associations were tested by means of a robust statistical framework combining the IndVal index and torus randomisations.Important Findings The forest contained 82 tree species and a significant proportion of wet miombo species(e.g.Marquesia macroura).We detected a strong east-west edaphic gradient driven by soil texture;most chemical soil parameters followed this pattern.Five habitats were identified based on soil factors and floristic composition.Nine indicator species of these habitats were found.The key soil fac-tors discriminating habitats were total calcium,available forms of phosphorus and clay content.Even though past agricultural practices were successfully detected in soils,they did not display any significant influence neither on habitat differentiation nor on the associated tree communities.Based on an unprecedented large number of soil parameters,fine-scale soil heterogeneity and niche partitioning were shown to contribute to the variabil-ity of the floristic composition in this forest.Our results indicated that considering the most variable environmental parameters,as in PcA,is a poor manner for defining habitats.In contrast,combining MRT with the IndVal index and torus randomisation has proved to be a much more robust and sensitive approach to highlight tree-habitat associations at this scale.The common dichotomous viewpoint of considering deterministic and neutral effects as acting at broad and fine scales,respectively,is not confirmed when measuring suitable environmental variables,even in a case where the physical environment does not exhibit strong heterogeneity.展开更多
Objective To study the variational trend in disease characteristics of patients with hepatitis B-related primary liver cancer(HBV-HCC)in the past fiveyears.Methods A single-center retrospective cross-sectional analysi...Objective To study the variational trend in disease characteristics of patients with hepatitis B-related primary liver cancer(HBV-HCC)in the past fiveyears.Methods A single-center retrospective cross-sectional analysis was performed to compare patients diagnosed with HBV-HCC from January 2012 to December 2016(control group)and from January 2017 to December 2021(observation group).The data of the study variables were extracted from the electronic medical record system of the hospital information system of the Second Hospital of Lanzhou University.The 1:2 propensity score matching was used to adjust potential confounding factors such as gender and age.Multivariate logistic regression analysis was used to study the factors affecting changes in disease characteristics of the HBVHCC population in the observation group.GraphPad Prism 8.0 software was used to draw forest plots to intuitively display the effect size of the study variables in the logistic regression analysis.The t-test was used to compare normally distributed data between groups.The X^(2)test was used for inter-group comparison.Results A total of 1717 eligible cases were collected,including 510 in the control group and 1207 in the observation group.Compared with the control group,the number of newly diagnosed cases in the observation group increased by 2.36 times,and males were still the main onset population(83.3%vs.82.7%).The median age of onset increased(51.9 vs.53.5 years,P<0.001).79.4%of HBV-HCC patients had not received antiviral therapy,and the proportion of HBeAg-negative patients increased(56.4%).The factors affecting HBV-HCC patients included family history of HBV(OR=1.626,95%CI:1.181-2.238),family history of hepatocellular carcinoma(OR=1.388,95%CI:1.013-1.901),hypoviremia(OR=1.322,95%CI:1.046-1.671),abnormal alanine aminotransferase(0R=1.545,95%CI:1.231-1.940),liver fibrosis(0R=1.478,95%CI:1.153-1.894),liver cirrhosis(OR=1.431,95%Cl 1.128-1.815),and metabolic-related fatty liver disease(0R=1.438,95%Cl:1.116-1.815)after propensityy score matching adjustment.The factors affecting HBeAg-positive patients were decreased(OR=0.390,95%Cl:0.389-0.617);however,the number of early HBV-HCC diagnoses was increased(12.7%vs.19.3%,P=0.001).Conclusion The characteristics of patient disease and occurrence of HBVHCC are changing over the past five years.The risk of developing hepatocellular carcinoma in middle to older male patients with chronic hepatitis B is increasing with familial history of HBV and hepatocellular carcinoma,HBeAg negativity,hypoviremia,abnormal alanine aminotransferase,liver fibrosis,cirrhosis,and metabolicrelated fatty liver disease.展开更多
Background Recent increases in tree mortality are often attributed to climate, but climate extremes may just be the last of many stressors that have unfolded over many years resulting in tree death. Potentially it is ...Background Recent increases in tree mortality are often attributed to climate, but climate extremes may just be the last of many stressors that have unfolded over many years resulting in tree death. Potentially it is only those trees weakened by mechanical damage or attacks by insects or fungi that are susceptible to climate-mediated mortality, whereas vigorous trees resist periods of unfavorable climate. Although previous studies have explored immediate and catastrophic effects of mechanical damage via blowdowns and stem breakage, few have investigated the delayed effects of mechanical damage on mortality. Taxus is a shade-tolerant genus of subcanopy trees or shrubs distributed throughout the northern hemisphere. Populations of Taxus are in decline worldwide but owing to the tenacity of Taxus in the face of stressors, this decline is poorly understood. Here, we provide spatial evidence that cumulative stress interactions, particularly mechanical damage, contribute to Taxus mortality.Methods We examined 14 years of annual demographic data from the 27.2 ha Wind River Forest Dynamics Plot(WFDP), where woody stems, snags, and deadwood have been tagged, mapped and identified to species. We analyzed the multiple factors associated with tree death, including mechanical damage, pathogens, suppression, beetles, animal damage, and their combinations. We performed spatial pattern analyses with the pair correlation function to investigate the prevalence of density-dependent mortality, effects of neighboring large-diameter trees, and effects of nearby snag fall and deadwood.Results In 2011, there were 29,827 trees within the WFDP of which 2119 were Taxus. Between 2011 and 2024, Taxus declined to 1523 trees(mean annual mortality of 2.79% yr^(-1)). Taxus mortality was not influenced by intraspecific density dependence or the presence of snags but was mainly driven by mechanical damage, pathogens, and suppression. Dead Taxus were strongly associated with deadwood within 2 m of the bole. Structural equation modeling showed that mechanical damage likely increased the vulnerability of Taxus to pathogen infection and exposure to drier gap areas.Conclusions These results suggest that Taxus mortality is rarely due to a single event, but a cumulative process of interacting stressors initiated by falling wood and often culminating in death by other stressors—potentially many years later. The association of newly dead trees with deadwood suggests that falling snags likely contributed to past crown damage, initiating or accelerating a decline spiral. The results emphasize that previous mechanical damage—evidenced by mapped and persistent deadwood—can disproportionately affect tree species, influencing successional dynamics.展开更多
Background:Baseline levels of tree mortality can,over time,contribute to high snag densities and high levels of deadwood(down woody debris)if fire is infrequent and decomposition is slow.Deadwood can be important for ...Background:Baseline levels of tree mortality can,over time,contribute to high snag densities and high levels of deadwood(down woody debris)if fire is infrequent and decomposition is slow.Deadwood can be important for tree recruitment,and it plays a major role in terrestrial carbon cycling,but deadwood is rarely examined in a spatially explicit context.Methods:Between 2011 and 2019,we annually tracked all trees and snags≥1 cm in diameter and mapped all pieces of deadwood≥10 cm diameter and≥1 m in length in 25.6 ha of Tsuga heterophylla/Pseudotsuga menziesii forest.We analyzed the amount,biomass,and spatial distribution of deadwood,and we assessed how various causes of mortality that contributed uniquely to deadwood creation.Results:Compared to aboveground woody live biomass of 481 Mg ha^(−1)(from trees≥10 cm diameter),snag biomass was 74 Mg ha^(−1) and deadwood biomass was 109 Mg ha^(−1)(from boles≥10 cm diameter).Biomass from large-diameter trees(≥60 cm)accounted for 85%,88%,and 58%,of trees,snags,and deadwood,respectively.Total aboveground woody live and dead biomass was 668 Mg ha^(−1).The annual production of downed wood(≥10 cm diameter)from tree boles averaged 4 Mg ha^(−1) yr^(−1).Woody debris was spatially heterogeneous,varying more than two orders of magnitude from 4 to 587 Mg ha^(−1) at the scale of 20 m×20 m quadrats.Almost all causes of deadwood creation varied in importance between large-diameter trees and small-diameter trees.Biomass of standing stems and deadwood had weak inverse distributions,reflecting the long period of time required for trees to reach large diameters following antecedent tree mortalities and the centennial scale time required for deadwood decomposition.Conclusion:Old-growth forests contain large stores of biomass in living trees,as well as in snag and deadwood biomass pools that are stable long after tree death.Ignoring biomass(or carbon)in deadwood pools can lead to substantial underestimations of sequestration and stability.展开更多
The reintroduction of fire to landscapes where it was once common is considered a priority to restore historical forest dynamics,including reducing tree density and decreasing levels of woody biomass on the forest flo...The reintroduction of fire to landscapes where it was once common is considered a priority to restore historical forest dynamics,including reducing tree density and decreasing levels of woody biomass on the forest floor.However,reintroducing fire causes tree mortality that can have unintended ecological outcomes related to woody biomass,with potential impacts to fuel accumulation,carbon sequestration,subsequent fire severity,and forest management.In this study,we examine the interplay between fire and carbon dynamics by asking how reintroduced fire impacts fuel accumulation,carbon sequestration,and subsequent fire severity potential.Beginning pre-fire,and continuing 6 years post-fire,we tracked all live,dead,and fallen trees≥1 cm in diameter and mapped all pieces of deadwood(downed woody debris)originating from tree boles≥10 cm diameter and≥1 m in length in 25.6 ha of an Abies concolor/Pinus lambertiana forest in the central Sierra Nevada,California,USA.We also tracked surface fuels along 2240 m of planar transects pre-fire,immediately post-fire,and 6 years post-fire.Six years after moderate-severity fire,deadwood≥10 cm diameter was 73 Mg ha^(−1),comprised of 32 Mg ha^(−1) that persisted through fire and 41 Mg ha^(−1) of newly fallen wood(compared to 72 Mg ha^(−1) pre-fire).Woody surface fuel loading was spatially heterogeneous,with mass varying almost four orders of magnitude at the scale of 20 m×20 m quadrats(minimum,0.1 Mg ha^(−1);mean,73 Mg ha^(−1);maximum,497 Mg ha^(−1)).Wood from large-diameter trees(≥60 cm diameter)comprised 57%of surface fuel in 2019,but was 75%of snag biomass,indicating high contributions to current and future fuel loading.Reintroduction of fire does not consume all large-diameter fuel and generates high levels of surface fuels≥10 cm diameter within 6 years.Repeated fires are needed to reduce surface fuel loading.展开更多
Background:The epidemic Dendroctonus rufipennis(spruce beetle)outbreak in the subalpine forests of the Colorado Plateau in the 1990s killed most larger Picea engelmannii(Engelmann spruce)trees.One quarter century late...Background:The epidemic Dendroctonus rufipennis(spruce beetle)outbreak in the subalpine forests of the Colorado Plateau in the 1990s killed most larger Picea engelmannii(Engelmann spruce)trees.One quarter century later,the larger snags are beginning to fall,transitioning to deadwood(down woody debris)where they may influence fire behavior,regeneration,and habitat structure.Methods:We tracked all fallen trees≥1 cm in diameter at breast height(1.37-m high)and mapped all pieces of deadwood≥10-cm diameter and≥1 m in length within 13.64 ha of a high-elevation mixed-species forest in the Picea–Abies zone annually for 5 years from 2015 through 2019.We examined the relative contribution of Picea engelmannii to snag and deadwood pools relative to other species and the relative contributions of large-diameter trees(≥33.2 cm at this subalpine site).We compared spatially explicit mapping of deadwood to traditional measures of surface fuels and introduce a new method for approximating vertical distribution of deadwood.Results:In this mixed-species forest,there was relatively high density and basal area of live Picea engelmannii 20 years after the beetle outbreak(36 trees ha^(−1) and 1.94 m^(2) ha^(−1)≥10-cm diameter)contrasting with the near total mortality of mature Picea in forests nearby.Wood from tree boles≥10-cm diameter on the ground had biomass of 42 Mg ha^(−1),7 Mg ha^(−1) of Picea engelmannii,and 35 Mg ha^(−1) of other species.Total live aboveground biomass was 119 Mg ha^(−1),while snag biomass was 36 Mg ha^(−1).Mean total fuel loading measured with planar transects was 63 Mg ha^(−1) but varied more than three orders of magnitude(0.1 to 257 Mg ha^(−1)).Planar transects recorded 32 Mg ha^(−1) of wood≥7.62-cm diameter compared to the 42 Mg ha^(−1) of wood≥10-cm diameter recorded by explicit mapping.Multiple pieces of deadwood were often stacked,forming a vertical structure likely to contribute to active fire behavior.Conclusion:Bark beetle mortality in the 1990s has made Picea an important local constituent of deadwood at 20-m scales,but other species dominate total deadwood due to slow decomposition rates and the multi-centennial intervals between fires.Explicit measurements of deadwood and surface fuels improve ecological insights into biomass heterogeneity and potential fire behavior.展开更多
Background: Large-diameter trees have an outsized influence on aboveground forest dynamics, composition, and structure. Although their influence on aboveground processes is well studied, their role in shaping belowgro...Background: Large-diameter trees have an outsized influence on aboveground forest dynamics, composition, and structure. Although their influence on aboveground processes is well studied, their role in shaping belowground fungal communities is largely unknown. We sought to test if (i) fungal community spatial structure matched aboveground forest structure;(ii) fungal functional guilds exhibited differential associations to aboveground trees, snags, and deadwood;and (iii) that large-diameter trees and snags have a larger influence on fungal community richness than smaller-diameter trees. We used MiSeq sequencing of fungal communities collected from soils in a spatially intensive survey in a portion of Cedar Breaks National Monument, Utah, USA. We used random forest models to explore the spatial structure of fungal communities as they relate to explicitly mapped trees and deadwood distributed across 1.15 ha of a 15.32-ha mapped subalpine forest. Results: We found 6,177 fungal amplicon sequence variants across 117 sequenced samples. Tree diameter, dead-wood presence, and tree species identity explained more than twice as much variation (38.7% vs. 10.4%) for ectomy-corrhizal composition and diversity than for the total or saprotrophic fungal communities. Species identity and dis-tance to the nearest large-diameter tree (≥ 40.2 cm) were better predictors of fungal richness than were the identity and distance to the nearest tree. Soil nutrients, topography, and tree species differentially influenced the composition and diversity of each fungal guild. Locally rare tree species had an outsized influence on fungal community richness. Conclusions: These results highlight that fungal guilds are differentially associated with the location, size, and species of aboveground trees. Large-diameter trees are implicated as drivers of belowground fungal diversity, particularly for ectomycorrhizal fungi.展开更多
基金supported in part by the intramural research program of the US Department of Agriculture,National Institute of Food and Agriculture,Evans-Allen#1024525,and Capacity Building Grant#006531supported in part by the US National Science Foundation RII Track 2 FEC:Leveraging Intelligent Informatics and Smart Data for Improved Understanding of Northern Forest Ecosystem Resiliency(INSPIRES)#1920908by The Lyndhurst Foundation.
文摘Understanding local variation in forest biomass allows for a better evaluation of broad-scale patterns and interpretation of forest ecosystems’role in carbon dynamics.This study focuses on patterns of aboveground tree biomass within a fully censused 20 ha forest plot in a temperate forest of northern Alabama,USA.We evaluated the relationship between biomass and topography using ridge and valley landforms along with digitally derived moisture and solar radiation indices.Every live woody stem over 1 cm diameter at breast height within this plot was mapped,measured,and identified to species in 2019-2022,and diameter data were used along with speciesspecific wood density to map the aboveground biomass at the scale of 20 m×20 m quadrats.The aboveground tree biomass was 211 Mg·ha^(-1).Other than small stream areas that experienced recent natural disturbances,the total stand biomass was not associated with landform or topographic indices.Dominant species,in contrast,had strong associations with topography.American beech(Fagus grandifolia)and yellow-poplar(Liriodendron tulipfera)dominated the valley landform,with 37% and 54% greater biomass in the valley than their plot average,respectively.Three other dominant species,white oak(Quercus alba),southern shagbark hickory(Carya carolinaeseptentrionalis),and white ash(Fraxinus americana),were more abundant on slopes and benches,thus partitioning the site.Of the six dominant species,only sugar maple(Acer saccharum)was not associated with landform.Moreover,both topographic wetness and potential radiation indices were significant predictors of dominant species biomass within each of the landforms.The study highlights the need to consider species when examining forest productivity in a range of site conditions.
基金This work was supported by the National Natural Science Foundation of China project(No 41671183).
文摘The composition of animal species and interactions among them are widely known to shape ecological communities and fine-scale(e.g.,<1 km)monitoring of animal communities is essential for understanding the relationships among animals and plants.Although the co-existence of large-and medium-sized species has been studied across different scales,research on fine-scale interactions of herbivores in deciduous broadleaf forests is limited.Camera trapping of large-and medium-sized mammals was carried out over a 1 year period within a 25 ha deciduous broadleaf forest dynamics plot in the Qinling Mountains,China.Fourteen species of large-and medium-sized mammals,including six carnivores,six ungulates,one primate and one rodent species were found.Kernel density estimations were used to analyse the diel or 24 h activity patterns of all species with more than 40 independent detections and general linear models were developed to explore the spatial relationships among the species.The combination of overlapping diel activity patterns and spatial associations showed obvious niche separation among six species:giant panda(Ailuropoda melanoleuca David),takin(Budorcas taxicolor Hodgson),Reeves’s muntjac(Muntiacus reevesi Ogilby),tufted deer(Elaphodus cephalophus Milne-Edwards),Chinese serow(Capricornis milneedwardsii David)and wild boar(Sus scrofa Linnaeus).Long-term fine-scale monitoring is useful for providing information about the co-existence of species and their interactions.The results demonstrate the importance for fine-scale monitoring of animals and plants for improving understanding of species interactions and community dynamics.
基金supported by The National Science Foundation of China(31770567,31570630)。
文摘Stocking and structural composition of a deciduous broad-leaved forest were determined to predict coarse woody debris quantity by quantifying the empirical relationships between these two attributes.The most ecologically significant families by stem density were Salicaceae,Betulaceae,Fagaceae,and Aceraceae.P opulus davidiana was the most dominant species followed by B etula dahurica,Quercus mongolica,and Acer mono.The four species accounted for 69.5%of total stems.Numerous small-diameter species characterized the coarse woody debris showing a reversed J-shaped distribution.The coarse debris of P.davidiana,B.dahurica,and Q.mongolica mainly comprised the 10–20 cm size class,whereas A.mono debris was mainly in the 5–10 cm size class.The spatial patterns of different size classes of coarse woody debris were analyzed using the g-function to determine the size of the tree at its death.The results indicate that the spatial patterns at the 0–50 m scale shifted gradually from an aggregated to a random pattern.For some species,the larger coarse debris might change from an aggregated to a random distribution more easily.Given the importance of coarse woody debris in forest ecosystems,its composition and patterns can improve understanding of community structure and dynamics.The aggregation pattern might be due to density dependence and self-thinning effects,as well as by succession and mortality.The four dominant species across the different size classes showed distinct aggregated distribution features at different spatial scales.This suggests a correlation between the dominant species population,size class,and aggregated distribution of coarse woody debris.
基金supported by the Natural Science and Technology Foundation of Guizhou Province[[2020]1Z013]the Joint Fund of the National Natural Science Foundation of Chinathe Karst Science Research Center of Guizhou Province[U1812401]。
文摘In eastern Asian subtropical forests,leaf habit shifts from evergreen to deciduous broad-leaved woody plants toward higher latitudes.This shift has been largely explained by the greater capacity of deciduous broad-leaved plants to respond to harsh climatic conditions(e.g.,greater seasonality).The advantages of deciduous leaf habit over evergreen leaf habit in more seasonal climates have led us to hypothesize that leaf habits would shift in response to climate changes more conspicuously in forest canopy trees than in forest understory shrubs.Furthermore,we hypothesize that in the forests of the subtropics,plants at higher latitudes,regardless of growth form,would better tolerate seasonal harsh climates,and hence show less differentiation in leaf habit shift,compared to those at lower latitudes.To test these two hypotheses,we modelled the proportion of deciduous broad-leaved species and the incidence of deciduous and evergreen broad-leaved species in woody angiosperm species compositions of ten largesized forest plots distributed in the Chinese subtropics.We found that the rate of leaf habit shift along a latitudinal gradient was higher in forest trees than in forest shrubs.We also found that the differentiation in leaf habit shift between trees and shrubs is greater at lower latitudes(i.e.,warmer climates)than at higher latitudes(i.e.,colder climates).These findings indicate that specialized forest plants are differentially affected by climate in distinct forest strata in a manner dependent on latitudinal distribution.These differences in forest plant response to changes in climate suggest that global climate warming will alter growth forms and geographical distributions and ranges of forests.
基金This work a contribution to Youth Foundation of Natural Science Foundation of Henan Province(212300410153)The Young Talents Promotion Project of Henan Province(2020HYTP037)+1 种基金Science and Technology Project of Henan Provincial Department of Natural Resources(No.2021-178-9)Basic scientific research expenses of Henan Province(2021JB02014).
文摘The spatial-temporal variation of understory light availability has important influences on species diversity and community assembly.However,the distribution characteristics and influencing factors of understory light availability have not been fully elucidated,especially in temperate deciduous,broad-leaved forests.In this study,the understory light availability was monitored monthly(May–October)in a temperate deciduous,broad-leaved forest in Henan Province,China.Differences in the light availability among different months and habitat types were statistically analyzed using Kruskal–Wallis method,respectively.Partial least squares path modeling(PLS-PM)was used to explore the direct and/or indirect effects of stand structure,dominant species and topographic factors on the light environment.Results showed that there were differences in light environments among the four habitat types and during the studied six months.The PLS-PM results showed that the stand structure and the dominant species were negatively correlated with the light environment,and the path coefficient values were−0.089(P=0.042)and−0.130(P=0.004),respectively.Our result indicated that the understory light availability exhibit a distinct spatial and temporal heterogeneity in temperate deciduous,broad-leaved forest of north China.The characteristics of woody plant community,especially the abundance of one of the dominant plant species,were the important factors affecting the understory light availability.
基金funded by the Environmental Seed Arrival and Interspecific Associations in Seedling Sciences Program of the Smithsonian Institutionthe National Science Foundation (DEB-0075102,DEB-0823728,DEB-0640386,DEB-1242622,DEB-1464389)the Andrew Mellon Foundation,The Ohio State University,and Yale University
文摘Background The full lifespan of long-lived trees includes a seedling phase,during which a seed germinates and grows to a size large enough to be measured in forest inventories.Seedling populations are usually studied separately from adult trees,and the seedling lifespan,from seed to sapling,is poorly known.In the 50-ha Barro Colorado forest plot,we started intensive censuses of seeds and seedlings in 1994 in order to merge seedling and adult demography and document complete lifespans.Methods In 17 species abundant in seedling censuses,we subdivided populations into six size classes from seed to 1cm dbh,including seeds plus five seedling stages.The smallest seedling class was subdivided by age.Censuses in two consecutive years provided transition matrices describing the probability that a seedling in one stage moved to another one year later.For each species,we averaged the transition matrix across 25 censuses and used it to project the seedling lifespan,from seed until 1cm dbh or death.Results The predicted mean survival rate of seeds to 1cm dbh varied 1000-fold across species,from 2.9×10^(−6)to 4.4×10^(−3);the median was 2.0×10^(−4).The seedling lifespan,or the average time it takes a seed to grow to 1cm dbh,varied across species from 5.1 to 53.1 years,with a median of 20.3 years.In the median species,the 10%fastest-growing seeds would reach 1cm dbh in 9.0 years,and the slowest 10%in 34.6 years.Conclusions Combining seedling results with our previous study of lifespan after 1cm dbh,we estimate that the focal species have full lifespans varying from 41 years in a gap-demanding pioneer to 320 years in one shade-tolerant species.Lifetime demography can contribute precise survival rates and lifespans to forestry models.
基金Supported by the Henan Provincial Health Commission,No.232102310145.
文摘BACKGROUND Patients with chronic obstructive pulmonary disease(COPD)frequently experience exacerbations requiring multiple hospitalizations over prolonged disease courses,which predispose them to generalized anxiety disorder(GAD).This comorbidity exacerbates breathing difficulties,activity limitations,and social isolation.While previous studies predominantly employed the GAD 7-item scale for screening,this approach is somewhat subjective.The current literature on predictive models for GAD risk in patients with COPD is limited.AIM To construct and validate a GAD risk prediction model to aid healthcare professionals in preventing the onset of GAD.METHODS This retrospective analysis encompassed patients with COPD treated at our institution from July 2021 to February 2024.The patients were categorized into a modeling(MO)group and a validation(VA)group in a 7:3 ratio on the basis of the occurrence of GAD.Univariate and multivariate logistic regression analyses were utilized to construct the risk prediction model,which was visualized using forest plots.The model’s performance was evaluated using Hosmer-Lemeshow(H-L)goodness-of-fit test and receiver operating characteristic(ROC)curve analysis.RESULTS A total of 271 subjects were included,with 190 in the MO group and 81 in the VA group.GAD was identified in 67 patients with COPD,resulting in a prevalence rate of 24.72%(67/271),with 49 cases(18.08%)in the MO group and 18 cases(22.22%)in the VA group.Significant differences were observed between patients with and without GAD in terms of educational level,average household income,smoking history,smoking index,number of exacerbations in the past year,cardiovascular comorbidities,disease knowledge,and personality traits(P<0.05).Multivariate logistic regression analysis revealed that lower education levels,household income<3000 China yuan,smoking history,smoking index≥400 cigarettes/year,≥two exacerbations in the past year,cardiovascular comorbidities,complete lack of disease information,and introverted personality were significant risk factors for GAD in the MO group(P<0.05).ROC analysis indicated that the area under the curve for predicting GAD in the MO and VA groups was 0.978 and 0.960.The H-L test yieldedχ^(2) values of 6.511 and 5.179,with P=0.275 and 0.274.Calibration curves demonstrated good agreement between predicted and actual GAD occurrence risks.CONCLUSION The developed predictive model includes eight independent risk factors:Educational level,household income,smoking history,smoking index,number of exacerbations in the past year,presence of cardiovascular comorbidities,level of disease knowledge,and personality traits.This model effectively predicts the onset of GAD in patients with COPD,enabling early identification of high-risk individuals and providing a basis for early preventive interventions by nursing staff.
基金National Natural Science Foundation of China(31000201,31370445,31061160188)National Key Basic Research Program of China(2014CB954104)the West Light Foundation of Chinese Academy of Sciences and the Special Program for Basic Research of the Ministry of Science and Technology of China(2012FY10400,2011FY120200).
文摘Aims While using phylogenetic and functional approaches to test the mechanisms of community assembly,functional traits often act as the proxy of niches.However,there is little detailed knowledge regarding the correlation between functional traits of tree species and their niches in local communities.We suggest that the co-varying correlation between functional traits and niches should be the premise for using phylogenetic and functional approaches to test mechanisms of community assembly.Using functional traits,phylogenetic and environmental data,this study aims to answer the questions:(i)within local communities,do functional traits of co-occurring species covary with their environmental niches at the species level?and(ii)what is the key ecological process underlying community assembly in Xishuangbanna and Ailaoshan forest dynamic plots(FDPs)?Methods We measured seven functional traits of 229 and 36 common species in Xishuangbanna and Ailaoshan FDPs in tropical and subtropical China,respectively.We also quantified the environmental niches for these species based on conditional probability.We then analyzed the correlations between functional traits and environmental niches using phylogenetic independent contrasts.After examining phylogenetic signals of functional traits using Pagel’sλ,we quantified the phylogenetic and functional dispersion along environmental gradients within local tree communities.Important Findings For target species,functional traits do co-vary with environmental niches at the species level in both of the FDPs,supporting that functional traits can be used as a proxy for local-scale environmental niches.Functional traits show significant phylogenetic signals in both of the FDPs.We found that the phylogenetic and functional dispersion were significantly clustered along topographical gradients in the Ailaoshan FDP but overdispersion in the Xishuangbanna FDP.These patterns of phylogenetic and functional dispersion suggest that environmental filtering plays a key role in structuring local tree assemblages in Ailaoshan FDP,while competition exclusion plays a key role in Xishuangbanna FDP.
基金We particularly appreciate the CBS plot census and data management teams.This work was supported by Ministry of Sciences and Technology of China(2016YFC0500300)National Natural Science Foundation of China(31570432 and 31370444)Key Research Program of Frontier Sciences,CAS(QYZDB-SSW-DQC002).
文摘Aims Understanding the controls influencing tree growth is central to forest ecology.Although many factors such as tree size,neighborhood competition and environmental variables,have been proposed as being important in explaining patterns of tree growth,but their relative contributions are still subject to debate.We aimed to examine the relative importance of tree size,local abiotic conditions and the density and identity of neighbors on tree growth in an old-growth temperate forest in northeast china.Methods We used linear mixed models with data from a 25 ha(500×500 m)broad-leaved Korean pine(Pinus koraiensis)mixed forest perma-nent plot to examine the relative importance of these local drivers on tree growth at three organizational levels(community,guild and species).Subplot was included as a random effect to account for spatial autocorrelation in growth of trees located within the same subplot,and species was included as a random effect to account for variation among species in growth.Important Findings Tree size was typically the most important predictor of growth,followed by neighborhood competition and then soil nutrients.The correlation of tree size to growth varied from strongly positive for large trees and medium trees to slightly positive for small trees.The effect of neighbor-hood competition on growth showed weak negative density dependence as indicated by slightly negative effect of total basal area of neighbors and the proportion of conspecific neighbors.Environmental factors influenced growth of very common species,smaller tree-size classes and shade-tolerant species.We concluded that the relative importance of variables driving patterns of tree growth varied greatly among tree size classes,shade tolerance and abundance classes in this temperate for-est.These results provide critical information for future studies of forest dynamics and offer insight into forest management in this region.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB31000000)the National Key Research and Development Program of China(2017YFA0605103)funded by the US National Science Foundation(NSF DEB-2029997)。
文摘An important mechanism promoting species coexistence is conspecific negative density dependence(CNDD),which inhibits conspecific neighbors by accumulating host-specific enemies near adult trees.Natural enemies may be genotype-specific and regulate offspring dynamics more strongly than non-offspring,which is often neglected due to the difficulty in ascertaining genetic relatedness.Here,we investigated whether offspring and non-offspring of a dominant species,Castanopsis eyrei,suffered from different strength of CNDD based on parentage assignment in a subtropical forest.We found decreased recruitment efficiency(proxy of survival probability)of offspring compared with non-offspring near adult trees during the seedling-sapling transition,suggesting genotype-dependent interactions drive tree demographic dynamics.Furthermore,the genetic similarity between individuals of same cohort decreased in late life history stages,indicating genetic-relatedness-dependent tree mortality throughout ontogeny.Our results demonstrate that within-species genetic relatedness significantly affects the strength of CNDD,implying genotype-specific natural enemies may contribute to population dynamics in natural forests.
文摘Aims Relationships between local habitat heterogeneity and tree commu-nities in miombo woodlands have been very little studied.While some studies have addressed this topic at broad scales and based on few environmental parameters,this study aims at(i)detecting fine-scale habitats(≤10 ha)on the basis of a detailed characterisation of soil explicitly considering past anthropogenic disturbances,and an exhaustive census of the tree community,and at(ii)searching for indicator tree species corresponding to the resulting habitats.Methods The study was carried out in the miombo woodland of Mikembo Forest Reserve,Upper Katanga,The Democratic Republic of the congo.A complete census of the tree community was conducted in a 10-ha forest dynamics plot comprising 160 adjacent quadrats of 25×25 m,with a total of 4604 trees(diameter at breast height>10 cm).Thirty-six physicochemical soil parameters were measured.Studying the frequency distribution of soil charcoal content allowed identifying local signature of past human agriculture in the soil.Two strategies were used to define habitats:(i)a combination of principal component analysis(PcA)on soil variables and Ward clustering and(ii)multivariate regression trees(MRT)to search for key soil parameters allowing the best prediction of species composition.Tree-habitat associations were tested by means of a robust statistical framework combining the IndVal index and torus randomisations.Important Findings The forest contained 82 tree species and a significant proportion of wet miombo species(e.g.Marquesia macroura).We detected a strong east-west edaphic gradient driven by soil texture;most chemical soil parameters followed this pattern.Five habitats were identified based on soil factors and floristic composition.Nine indicator species of these habitats were found.The key soil fac-tors discriminating habitats were total calcium,available forms of phosphorus and clay content.Even though past agricultural practices were successfully detected in soils,they did not display any significant influence neither on habitat differentiation nor on the associated tree communities.Based on an unprecedented large number of soil parameters,fine-scale soil heterogeneity and niche partitioning were shown to contribute to the variabil-ity of the floristic composition in this forest.Our results indicated that considering the most variable environmental parameters,as in PcA,is a poor manner for defining habitats.In contrast,combining MRT with the IndVal index and torus randomisation has proved to be a much more robust and sensitive approach to highlight tree-habitat associations at this scale.The common dichotomous viewpoint of considering deterministic and neutral effects as acting at broad and fine scales,respectively,is not confirmed when measuring suitable environmental variables,even in a case where the physical environment does not exhibit strong heterogeneity.
文摘Objective To study the variational trend in disease characteristics of patients with hepatitis B-related primary liver cancer(HBV-HCC)in the past fiveyears.Methods A single-center retrospective cross-sectional analysis was performed to compare patients diagnosed with HBV-HCC from January 2012 to December 2016(control group)and from January 2017 to December 2021(observation group).The data of the study variables were extracted from the electronic medical record system of the hospital information system of the Second Hospital of Lanzhou University.The 1:2 propensity score matching was used to adjust potential confounding factors such as gender and age.Multivariate logistic regression analysis was used to study the factors affecting changes in disease characteristics of the HBVHCC population in the observation group.GraphPad Prism 8.0 software was used to draw forest plots to intuitively display the effect size of the study variables in the logistic regression analysis.The t-test was used to compare normally distributed data between groups.The X^(2)test was used for inter-group comparison.Results A total of 1717 eligible cases were collected,including 510 in the control group and 1207 in the observation group.Compared with the control group,the number of newly diagnosed cases in the observation group increased by 2.36 times,and males were still the main onset population(83.3%vs.82.7%).The median age of onset increased(51.9 vs.53.5 years,P<0.001).79.4%of HBV-HCC patients had not received antiviral therapy,and the proportion of HBeAg-negative patients increased(56.4%).The factors affecting HBV-HCC patients included family history of HBV(OR=1.626,95%CI:1.181-2.238),family history of hepatocellular carcinoma(OR=1.388,95%CI:1.013-1.901),hypoviremia(OR=1.322,95%CI:1.046-1.671),abnormal alanine aminotransferase(0R=1.545,95%CI:1.231-1.940),liver fibrosis(0R=1.478,95%CI:1.153-1.894),liver cirrhosis(OR=1.431,95%Cl 1.128-1.815),and metabolic-related fatty liver disease(0R=1.438,95%Cl:1.116-1.815)after propensityy score matching adjustment.The factors affecting HBeAg-positive patients were decreased(OR=0.390,95%Cl:0.389-0.617);however,the number of early HBV-HCC diagnoses was increased(12.7%vs.19.3%,P=0.001).Conclusion The characteristics of patient disease and occurrence of HBVHCC are changing over the past five years.The risk of developing hepatocellular carcinoma in middle to older male patients with chronic hepatitis B is increasing with familial history of HBV and hepatocellular carcinoma,HBeAg negativity,hypoviremia,abnormal alanine aminotransferase,liver fibrosis,cirrhosis,and metabolicrelated fatty liver disease.
基金Utah State University and the Utah Agricultural Experiment Station(Project 1711)
文摘Background Recent increases in tree mortality are often attributed to climate, but climate extremes may just be the last of many stressors that have unfolded over many years resulting in tree death. Potentially it is only those trees weakened by mechanical damage or attacks by insects or fungi that are susceptible to climate-mediated mortality, whereas vigorous trees resist periods of unfavorable climate. Although previous studies have explored immediate and catastrophic effects of mechanical damage via blowdowns and stem breakage, few have investigated the delayed effects of mechanical damage on mortality. Taxus is a shade-tolerant genus of subcanopy trees or shrubs distributed throughout the northern hemisphere. Populations of Taxus are in decline worldwide but owing to the tenacity of Taxus in the face of stressors, this decline is poorly understood. Here, we provide spatial evidence that cumulative stress interactions, particularly mechanical damage, contribute to Taxus mortality.Methods We examined 14 years of annual demographic data from the 27.2 ha Wind River Forest Dynamics Plot(WFDP), where woody stems, snags, and deadwood have been tagged, mapped and identified to species. We analyzed the multiple factors associated with tree death, including mechanical damage, pathogens, suppression, beetles, animal damage, and their combinations. We performed spatial pattern analyses with the pair correlation function to investigate the prevalence of density-dependent mortality, effects of neighboring large-diameter trees, and effects of nearby snag fall and deadwood.Results In 2011, there were 29,827 trees within the WFDP of which 2119 were Taxus. Between 2011 and 2024, Taxus declined to 1523 trees(mean annual mortality of 2.79% yr^(-1)). Taxus mortality was not influenced by intraspecific density dependence or the presence of snags but was mainly driven by mechanical damage, pathogens, and suppression. Dead Taxus were strongly associated with deadwood within 2 m of the bole. Structural equation modeling showed that mechanical damage likely increased the vulnerability of Taxus to pathogen infection and exposure to drier gap areas.Conclusions These results suggest that Taxus mortality is rarely due to a single event, but a cumulative process of interacting stressors initiated by falling wood and often culminating in death by other stressors—potentially many years later. The association of newly dead trees with deadwood suggests that falling snags likely contributed to past crown damage, initiating or accelerating a decline spiral. The results emphasize that previous mechanical damage—evidenced by mapped and persistent deadwood—can disproportionately affect tree species, influencing successional dynamics.
基金Funding was received from the Utah Agricultural Experiment Station(projects 1153,1398,and 1423 to JAL)the National Science Foundation(DEB#1542681 to JAL and colleagues)the Smithsonian Institution ForestGEO.Research was performed under a 5-year permit(2016–2020)from the USDA Forest Service Pacific Northwest Research Station.
文摘Background:Baseline levels of tree mortality can,over time,contribute to high snag densities and high levels of deadwood(down woody debris)if fire is infrequent and decomposition is slow.Deadwood can be important for tree recruitment,and it plays a major role in terrestrial carbon cycling,but deadwood is rarely examined in a spatially explicit context.Methods:Between 2011 and 2019,we annually tracked all trees and snags≥1 cm in diameter and mapped all pieces of deadwood≥10 cm diameter and≥1 m in length in 25.6 ha of Tsuga heterophylla/Pseudotsuga menziesii forest.We analyzed the amount,biomass,and spatial distribution of deadwood,and we assessed how various causes of mortality that contributed uniquely to deadwood creation.Results:Compared to aboveground woody live biomass of 481 Mg ha^(−1)(from trees≥10 cm diameter),snag biomass was 74 Mg ha^(−1) and deadwood biomass was 109 Mg ha^(−1)(from boles≥10 cm diameter).Biomass from large-diameter trees(≥60 cm)accounted for 85%,88%,and 58%,of trees,snags,and deadwood,respectively.Total aboveground woody live and dead biomass was 668 Mg ha^(−1).The annual production of downed wood(≥10 cm diameter)from tree boles averaged 4 Mg ha^(−1) yr^(−1).Woody debris was spatially heterogeneous,varying more than two orders of magnitude from 4 to 587 Mg ha^(−1) at the scale of 20 m×20 m quadrats.Almost all causes of deadwood creation varied in importance between large-diameter trees and small-diameter trees.Biomass of standing stems and deadwood had weak inverse distributions,reflecting the long period of time required for trees to reach large diameters following antecedent tree mortalities and the centennial scale time required for deadwood decomposition.Conclusion:Old-growth forests contain large stores of biomass in living trees,as well as in snag and deadwood biomass pools that are stable long after tree death.Ignoring biomass(or carbon)in deadwood pools can lead to substantial underestimations of sequestration and stability.
基金Funding was received from the Utah Agricultural Experiment Station(projects 1153,1398,and 1423 to JAL)the Joint Fire Science Program(award 16-1-04-02 to JAL and AJL)+1 种基金the National Park Service(Awards P14AC00122 and P14AC00197 to JAL)the Smithsonian Institution ForestGEO.Re-search was performed under National Park Service research permits YOSE-2013-SCI-0012,YOSE-2014-SCI-0005,YOSE-2015-SCI-0014,YOSE-2016-SCI-0006,YOSE-2017-SCI-0008,YOSE-2018-SCI-0006,and YOSE-2019-SCI-0009 for study YOSE-0051.
文摘The reintroduction of fire to landscapes where it was once common is considered a priority to restore historical forest dynamics,including reducing tree density and decreasing levels of woody biomass on the forest floor.However,reintroducing fire causes tree mortality that can have unintended ecological outcomes related to woody biomass,with potential impacts to fuel accumulation,carbon sequestration,subsequent fire severity,and forest management.In this study,we examine the interplay between fire and carbon dynamics by asking how reintroduced fire impacts fuel accumulation,carbon sequestration,and subsequent fire severity potential.Beginning pre-fire,and continuing 6 years post-fire,we tracked all live,dead,and fallen trees≥1 cm in diameter and mapped all pieces of deadwood(downed woody debris)originating from tree boles≥10 cm diameter and≥1 m in length in 25.6 ha of an Abies concolor/Pinus lambertiana forest in the central Sierra Nevada,California,USA.We also tracked surface fuels along 2240 m of planar transects pre-fire,immediately post-fire,and 6 years post-fire.Six years after moderate-severity fire,deadwood≥10 cm diameter was 73 Mg ha^(−1),comprised of 32 Mg ha^(−1) that persisted through fire and 41 Mg ha^(−1) of newly fallen wood(compared to 72 Mg ha^(−1) pre-fire).Woody surface fuel loading was spatially heterogeneous,with mass varying almost four orders of magnitude at the scale of 20 m×20 m quadrats(minimum,0.1 Mg ha^(−1);mean,73 Mg ha^(−1);maximum,497 Mg ha^(−1)).Wood from large-diameter trees(≥60 cm diameter)comprised 57%of surface fuel in 2019,but was 75%of snag biomass,indicating high contributions to current and future fuel loading.Reintroduction of fire does not consume all large-diameter fuel and generates high levels of surface fuels≥10 cm diameter within 6 years.Repeated fires are needed to reduce surface fuel loading.
基金Funding was received from the Utah Agricultural Experiment Station(projects 1153 and 1398 to JAL and 1423 to JAL,LLY,and DJM)and the Smithsonian Institution ForestGEO.Research was performed under the National Park Service research permits CEBR-2014-SCI-0001,CEBR-2015-SCI0001,CEBR-2016-SCI-0001,CEBR-2017-SCI-0001,CEBR-2018-SCI-0001,and CEBR-2019-SCI-0001 for study CEBR-00016.
文摘Background:The epidemic Dendroctonus rufipennis(spruce beetle)outbreak in the subalpine forests of the Colorado Plateau in the 1990s killed most larger Picea engelmannii(Engelmann spruce)trees.One quarter century later,the larger snags are beginning to fall,transitioning to deadwood(down woody debris)where they may influence fire behavior,regeneration,and habitat structure.Methods:We tracked all fallen trees≥1 cm in diameter at breast height(1.37-m high)and mapped all pieces of deadwood≥10-cm diameter and≥1 m in length within 13.64 ha of a high-elevation mixed-species forest in the Picea–Abies zone annually for 5 years from 2015 through 2019.We examined the relative contribution of Picea engelmannii to snag and deadwood pools relative to other species and the relative contributions of large-diameter trees(≥33.2 cm at this subalpine site).We compared spatially explicit mapping of deadwood to traditional measures of surface fuels and introduce a new method for approximating vertical distribution of deadwood.Results:In this mixed-species forest,there was relatively high density and basal area of live Picea engelmannii 20 years after the beetle outbreak(36 trees ha^(−1) and 1.94 m^(2) ha^(−1)≥10-cm diameter)contrasting with the near total mortality of mature Picea in forests nearby.Wood from tree boles≥10-cm diameter on the ground had biomass of 42 Mg ha^(−1),7 Mg ha^(−1) of Picea engelmannii,and 35 Mg ha^(−1) of other species.Total live aboveground biomass was 119 Mg ha^(−1),while snag biomass was 36 Mg ha^(−1).Mean total fuel loading measured with planar transects was 63 Mg ha^(−1) but varied more than three orders of magnitude(0.1 to 257 Mg ha^(−1)).Planar transects recorded 32 Mg ha^(−1) of wood≥7.62-cm diameter compared to the 42 Mg ha^(−1) of wood≥10-cm diameter recorded by explicit mapping.Multiple pieces of deadwood were often stacked,forming a vertical structure likely to contribute to active fire behavior.Conclusion:Bark beetle mortality in the 1990s has made Picea an important local constituent of deadwood at 20-m scales,but other species dominate total deadwood due to slow decomposition rates and the multi-centennial intervals between fires.Explicit measurements of deadwood and surface fuels improve ecological insights into biomass heterogeneity and potential fire behavior.
基金Funding was received from the Natural Science and Engineering Council of Canada to JK and the Utah Agricultural Experiment Station(Projects 1153,1398 and 1423 to JAL)which has designated this as Journal Paper 9626.
文摘Background: Large-diameter trees have an outsized influence on aboveground forest dynamics, composition, and structure. Although their influence on aboveground processes is well studied, their role in shaping belowground fungal communities is largely unknown. We sought to test if (i) fungal community spatial structure matched aboveground forest structure;(ii) fungal functional guilds exhibited differential associations to aboveground trees, snags, and deadwood;and (iii) that large-diameter trees and snags have a larger influence on fungal community richness than smaller-diameter trees. We used MiSeq sequencing of fungal communities collected from soils in a spatially intensive survey in a portion of Cedar Breaks National Monument, Utah, USA. We used random forest models to explore the spatial structure of fungal communities as they relate to explicitly mapped trees and deadwood distributed across 1.15 ha of a 15.32-ha mapped subalpine forest. Results: We found 6,177 fungal amplicon sequence variants across 117 sequenced samples. Tree diameter, dead-wood presence, and tree species identity explained more than twice as much variation (38.7% vs. 10.4%) for ectomy-corrhizal composition and diversity than for the total or saprotrophic fungal communities. Species identity and dis-tance to the nearest large-diameter tree (≥ 40.2 cm) were better predictors of fungal richness than were the identity and distance to the nearest tree. Soil nutrients, topography, and tree species differentially influenced the composition and diversity of each fungal guild. Locally rare tree species had an outsized influence on fungal community richness. Conclusions: These results highlight that fungal guilds are differentially associated with the location, size, and species of aboveground trees. Large-diameter trees are implicated as drivers of belowground fungal diversity, particularly for ectomycorrhizal fungi.
