Resilience and response:Unveiling the impacts of extreme droughts on forests through integrated dendrochronological and remote sensing analyses

Extreme droughts are anticipated to have detrimental impacts on forest ecosystems,especially in water-limited regions,due to the influence of climate change.However,considerable uncertainty remains regarding the patterns in species-specific responses to extreme droughts.Here,we conducted a study integrating dendrochronology and remote sensing methods to investigate the mosaic-distributed maple-oak(native)natural forests and poplar plantations(introduced)in the Horqin Sandy Land,Northeast China.We assessed the impacts of extreme droughts on tree performances by measuring interannual variations in radial growth and vegetation index.The results showed that precipitation and self-calibrated palmer drought severity index(scPDSI)are the major factors influencing tree-ring width index(RWI)and normalized difference vegetation index(NDVI).The severe droughts between 2000 and 2004 resulted in reduced RWI in the three studied tree species as well as led to NDVI reductions in both the maple-oak natural forests and the poplar plantations.The RWI reached the nadir during the2000-2004 severe droughts and remained at low levels two years after the severe drought,creating a legacy effect.In contrast to the lack of significant correlation between RWI and scPDSI,NDVI exhibited a significant positive correlation with scPDSI indicating the greater sensitivity of canopy performance to droughts than radial growth.Furthermore,interspecific differences in RWI and NDVI responses were observed,with the fast-growing poplar species experiencing a more significant RWI decrease and more negative NDVI anomaly during severe droughts than native species,highlighting the species-specific trade-offs between drought resilience and growth rate.This study emphasizes the importance of combining tree-level radial growth with landscape-scale canopy remote sensing to understand forest resilience and response.Our study improves our understanding of forest responses to extreme drought and highlights species differences in climate responses,offering crucial insights for optimizing species selection in sustainable afforestation and forest management in water-limited regions under the influence of climate change.

Natural forests exhibit higher organic carbon concentrations and recalcitrant carbon proportions in soil than plantations:a global data synthesis

Different chemical compositions of soil organic carbon(SOC)affect its persistence and whether it signifi-cantly differs between natural forests and plantations remains unclear.By synthesizing 234 observations of SOC chemical compositions,we evaluated global patterns of concentra-tion,individual chemical composition(alkyl C,O-alkyl C,aromatic C,and carbonyl C),and their distribution even-ness.Our results indicate a notably higher SOC,a markedly larger proportion of recalcitrant alkyl C,and lower easily decomposed carbonyl C proportion in natural forests.How-ever,SOC chemical compositions were appreciably more evenly distributed in plantations.Based on the assumed con-ceptual index of SOC chemical composition evenness,we deduced that,compared to natural forests,plantations may have higher possible resistance to SOC decomposition under disturbances.In tropical regions,SOC levels,recalcitrant SOC chemical composition,and their distributed evenness were significantly higher in natural forests,indicating that SOC has higher chemical stability and possible resistance to decomposition.Climate factors had minor effects on alkyl C in forests globally,while they notably affected SOC chemi-cal composition in tropical forests.This could contribute to the differences in chemical compositions and their distrib-uted evenness between plantations and natural stands.

Seedling dynamics differ between canopy species and understory species in a tropical seasonal rainforest,SW China

We used 11 years of census data from 450 seedling quadrats established in a 20-ha forest dynamics plot to study seedling dynamics in tree species of a tropical seasonal rainforest in Xishuangbanna,southwestern China.We found that overall seedling recruitment rate and relative growth rate were higher in the rainy season than in the dry season.Both the recruitment rate of seedlings from canopy tree species(two species)and the relative growth rate of seedlings from understory species(nine species)were higher in the rainy season than in the dry season.However,in the rainy season,the recruitment rate of seedlings was higher for canopy tree species than for understory tree species.In addition,relative growth rate of seedlings was higher in the canopy species than in understory seedlings in the dry season.We also observed that,in both rainy and dry seasons,mortality rate of seedlings was higher for canopy species than for understory species.Overall,canopy tree species appear to have evolved a flexible strategy to adapt to the seasonal changes of a monsoon climate.In contrast,understory tree species seem to have adopted a conservative strategy.Specifically,these species mainly release seedlings in the rainy season and maintain relatively stable populations with a lower mortality rate and recruitment rate in both dry and rainy seasons.Our study suggests that canopy and understory seedling populations growing in forest understory may respond to future climate change scenarios with distinct regeneration strategies.

Lipid concentration and composition in xylem sap of woody angiosperms from a tropical savanna and a seasonal rainforest

Lipids may play an important role in preventing gas embolisms by coating nanobubbles in xylem sap.Few studies on xylem sap lipids have been reported for temperate plants,and it remain unclear whether sap lipids have adaptational significance in tropical plants.In this study,we quantify the lipid composition of xylem sap for angiosperm species from a tropical savanna(seven species)and a seasonal rainforest(five species)using mass spectrometry.We found that all twelve species studied contained lipids in their xylem sap,including galactolipids,phospholipids and triacylglycerol,with a total lipid concentration ranging from 0.09 to 0.26 nmol/L.There was no difference in lipid concentration or composition between plants from the two sites,and the lipid concentration was negatively related to species’open vessel volume.Furthermore,savanna species showed little variation in lipid composition between the dry and the rainy season.These results support the hypothesis that xylem sap lipids are derived from the cytoplasm of individual conduit cells,remain trapped inside individual conduits,and undergo few changes in composition over consecutive seasons.A xylem sap lipidomic data set,which includes 12 tropical tree species from this study and 11 temperate tree species from literature,revealed no phylogenetic signals in lipid composition for these species.This study fills a knowledge gap in the lipid content of xylem sap in tropical trees and provides additional support for their common distribution in xylem sap of woody angiosperms.It appears that xylem sap lipids have no adaptive significance.

Stable reverse J-shaped diameter distribution occurs in an old-growth karst forest

The reverse J-shaped diameter distribution is considered an inherent attribute of natural forests,cru-cial for forest resource utilization and community stabil-ity.However,in karst regions,intense habitat heterogene-ity might alter species composition,spatial distribution,growth,biomass allocation,and mortality processes,yet its impact on diameter structure remains unclear.A fixed plot of 200 m×110 m was established in the Nanpan River Basin,Southwest China,within an old-growth oak forest(>300 years old),and the influence of site substrates(i.e.,rock and soil),topographic factors,sample area,and ori-entation on diameter distribution was analyzed.Trees on both rock and soil exhibited a reverse-J shape,quantifiable Project funding:This work was supported by the National Natural Science Foundation of China(32060340 and 31400542),the Scientific Research Capacity Building Project for Laibin Jinxiu Dayaoshan Forest Ecosystem Observation and Research Station of Guangxi(22-035-130-01).through the Weibull function.The substrates had a similar density,approximately 2100 plants/ha.However,the aver-age and range of diameter of trees on rock were smaller than those on soil,suggesting that rock constrains tree growth.The diameter distribution of trees across microtopography also displayed a reverse-J shape.Yet,higher elevations and sunny slopes showed a greater curvature of diameter classes compared to lower elevations and shady slopes,indicating habitat preferences in karst trees.Sample area and orienta-tion had minimal effects on diameter class curve that reached stability when the plot size was 6000 m2.These results sug-gest that the reverse J-shaped diameter distribution prevails at small scales in karst old-growth forests,encompassing multiple curvatures and spanning forest ecosystems.

Grouping tree species to estimate basal area increment in temperate multispecies forests in Durango,Mexico

Multispecies forests have received increased scientific attention,driven by the hypothesis that biodiversity improves ecological resilience.However,a greater species diversity presents challenges for forest management and research.Our study aims to develop basal area growth models for tree species cohorts.The analysis is based on a dataset of 423 permanent plots(2,500 m^(2))located in temperate forests in Durango,Mexico.First,we define tree species cohorts based on individual and neighborhood-based variables using a combination of principal component and cluster analyses.Then,we estimate the basal area increment of each cohort through the generalized additive model to describe the effect of tree size,competition,stand density and site quality.The principal component and cluster analyses assign a total of 37 tree species to eight cohorts that differed primarily with regard to the distribution of tree size and vertical position within the community.The generalized additive models provide satisfactory estimates of tree growth for the species cohorts,explaining between 19 and 53 percent of the total variation of basal area increment,and highlight the following results:i)most cohorts show a"rise-and-fall"effect of tree size on tree growth;ii)surprisingly,the competition index"basal area of larger trees"had showed a positive effect in four of the eight cohorts;iii)stand density had a negative effect on basal area increment,though the effect was minor in medium-and high-density stands,and iv)basal area growth was positively correlated with site quality except for an oak cohort.The developed species cohorts and growth models provide insight into their particular ecological features and growth patterns that may support the development of sustainable management strategies for temperate multispecies forests.

Tree mycorrhizal associations determine how biodiversity,large trees,and environmental factors drive aboveground carbon stock in temperate forests

Biodiversity,large trees,and environmental conditions such as climate and soil have important effects on forest carbon stocks.However,recent studies in temperate forests suggest that the relative importance of these factors depends on tree mycorrhizal associations,whereby large-tree effects may be driven by ectomycorrhizal(EM)trees,diversity effects may be driven by arbuscular mycorrhizal(AM)trees,and environment effects may depend on differential climate and soil preferences of AM and EM trees.To test this hypothesis,we used forest-inventory data consisting of over 80,000 trees from 631 temperate-forest plots(30 m×30 m)across Northeast China to examine how biodiversity(species diversity and ecological uniqueness),large trees(top 1%of tree diameters),and environmental factors(climate and soil nutrients)differently regulate aboveground carbon stocks of AM trees,EM trees,and AM and EM trees combined(i.e.total aboveground carbon stock).We found that large trees had a positive effect on both AM and EM tree carbon stocks.However,biodiversity and environmental factors had opposite effects on AM vs.EM tree carbon stocks.Specifically,the two components of biodiversity had positive effects on AM tree carbon stocks,but negative effects on EM tree carbon stocks.Environmental heterogeneity(mean annual temperature and soil nutrients)also exhibited contrasting effects on AM and EM tree carbon stocks.Consequently,for the total carbon stock,the positive large-tree effect far surpasses the diversity and environment effect.This is mainly because when integrating AM and EM tree carbon stock into total carbon stock,the opposite diversity-effect(also environment-effect)on AM vs.EM tree carbon stock counteracts each other while the consistent positive large-tree effect on AM and EM tree carbon stock is amplified.In summary,this study emphasized a mycorrhizal viewpoint to better understand the determinants of overarching aboveground carbon profile across regional forests.

The changes in soil organic carbon stock and quality across a subalpine forest successional series

Soil organic carbon(SOC)affects the function of terrestrial ecosystem and plays a vital role in global carbon cycle.Yet,large uncertainty still existed regarding the changes in SOC stock and quality with forest succession.Here,the stock and quality of SOC at 1-m soil profile were investigated across a subalpine forest series,including shrub,deciduous broad-leaved forest,broadleaf-conifer mixed forest,middle-age coniferous forest and mature coniferous forest,which located at southeast of Tibetan Plateau.The results showed that SOC stock ranged from 9.8 to29.9 kg·m^(-2),and exhibited a hump-shaped response pattern across the forest successional series.The highest and lowest SOC stock was observed in the mixed forest and shrub forest,respectively.The SOC stock had no significant relationships with soil temperature and litter stock,but was positively correlated with wood debris stock.Meanwhile,the average percentages of polysaccharides,lignins,aromatics and aliphatics based on FTIR spectroscopy were 79.89%,0.94%,18.87%and 0.29%,respectively.Furthermore,the percentage of polysaccharides exhibited an increasing pattern across the forest successional series except for the sudden decreasing in the mixed forest,while the proportions of lignins,aromatics and aliphatics exhibited a decreasing pattern across the forest successional series except for the sudden increasing in the mixed forest.Consequently,the humification indices(HIs)were highest in the mixed forest compared to the other four successional stages,which means that the SOC quality in mixed forest was worse than other successional stages.In addition,the SOC stock,recalcitrant fractions and HIs decreased with increasing soil depth,while the polysaccharides exhibited an increasing pattern.These findings demonstrate that the mixed forest had higher SOC stock and worse SOC quality than other successional stages.The high proportion of SOC stock(66%at depth of 20-100 cm)and better SOC quality(lower HIs)indicate that deep soil have tremendous potential to store SOC and needs more attention under global chan ge.

Differential roles of seed and sprout regeneration in forest diversity and productivity after disturbance

Natural regeneration after disturbances is a key phase of forest development,which determines the trajectory of successional changes in tree species composition and diversity.Regenerating trees can originate from either seeds or sprouts produced by disturbed trees with sprouting ability.Although both regeneration strategies often develop and co-occur after a disturbance,they tend to affect forest development differently due to significant functional differences.However,the origin of tree regeneration is rarely distinguished in post-disturbance forest surveys and ecological studies,and the differential roles of seed and sprout regeneration in forest productivity and diversity remain poorly understood.To address these research gaps,we explored the role of sprout and seed regeneration in the formation of woody species diversity and above-ground biomass(AGB)productivity in early-stage forest development.Data were collected in two experimental forest stands in the Czech Republic,where trees were cut with varying intensities with the density of residual(uncut)trees ranging from 0 to 275 trees per hectare.All trees were mapped and their sizes were measured before cutting and then,either as a stump with sprouts or a residual tree,remeasured 11 years later.In addition,all tree saplings were mapped and measured 11 years after logging,and their origin(sprout or seed)was identified.To assess abundances and productivity,we estimated AGB of all2,685 sprouting stumps of 19 woody species and 504 generative(i.e.,seed origin)individuals of 16 woody species,using allometric equations.Mixed-effects models were used to analyze the effects of each regeneration strategy on woody species diversity and the total AGB under varying densities of residual trees.Nonmetric multidimensional scaling was used to evaluate the effect of regeneration strategies on species composition.AGB and diversity of sprouts were significantly higher than those of seed regeneration.Sprouts formed on average97.1%of the total regeneration AGB in H ady and 98.6%in Sobe s ice.The average species richness of sprouts was4.7 in H ady and 2.2 in Sob e sice,while the species richness of seed regeneration averaged 2.1 and 1.1 in H ady and Sob e sice,respectively.Increasing density of residual trees reduced AGB and diversity of both sprouts and seed regeneration,but seed regeneration was affected to a greater extent.Residual trees had an especially strong inhibitory effect on the establishment of seed regeneration.Consequently,seed-originated saplings were nearly absent in plots with high residual tree density,and abundant sprouts accounted for most of the AGB and diversity.However,unlike sprouts whose species composition resembled that of the original stand,seed regeneration brought in new species,enriching the stand?s overall species pool and beta diversity.Our results demonstrated differential roles of sprout and seed regeneration in the early stage of forest succession.Sprout regeneration was the main source of woody AGB productivity as well as species diversity,and its importance increased with the increasing density of standing mature trees.The results indicate the crucial yet previously underestimated role of sprout regeneration in post-disturbance forest dynamics.They suggest that the presence of residual mature trees,whether retained after partial cutting or undisturbed,can substantially suppress seed regeneration while the role of sprout regeneration in early succession becomes more distinctly evident.

Pitfalls in forest carbon sink projection

Global forests are increasingly crucial for achiev-ing net-zero carbon emissions,with a quarter of the miti-gation efforts under the Paris Climate Agreement directed towards forests.In China,forests currently contribute to 13%of the global land’s carbon sink,but their stability and per-sistence remain uncertain.We examined and identified that published studies suffered from oversimplifications of eco-system succession and tree demographic dynamics,as well as poor constraints on land quality.Consequently,substan-tial estimations might have been suffered from underrepre-sented or ignored crucial factors,including tree demographic dynamics,and disturbances and habitat shifts caused by global climate change.We argue that these essential factors should be considered to enhance the reliability and accuracy of assessments of the potential for forest carbon sinks.

Aboveground biomass stocks of species-rich natural forests in southern China are influenced by stand structural attributes,species richness and precipitation

Forests,the largest terrestrial carbon sinks,play an important role in carbon sequestration and climate change mitigation.Although forest attributes and environmental factors have been shown to impact aboveground biomass,their influence on biomass stocks in species-rich forests in southern China,a biodiversity hotspot,has rarely been investigated.In this study,we characterized the effects of environmental factors,forest structure,and species diversity on aboveground biomass stocks of 30 plots(1 ha each) in natural forests located within seven nature reserves distributed across subtropical and marginal tropical zones in Guangxi,China.Our results indicate that forest aboveground biomass stocks in this region are lower than those in mature tropical and subtropical forests in other regions.Furthermore,we found that aboveground biomass was positively correlated with stand age,mean annual precipitation,elevation,structural attributes and species richness,although not with species evenness.When we compared stands with the same basal area,we found that aboveground biomass stock was higher in communities with a higher coefficient of variation of diameter at breast height.These findings highlight the importance of maintaining forest structural diversity and species richness to promote aboveground biomass accumulation and reveal the potential impacts of precipitation changes resulting from climate warming on the ecosystem services of subtropical and northern tropical forests in China.Notably,many natural forests in southern China are not fully stocked.Therefore,their continued growth will increase their carbon storage over time.

Aging Mongolian pine plantations face high risks of drought-induced growth decline:evidence from both individual tree and forest stand measurements

Discerning vulnerability differences among different aged trees to drought-driven growth decline or to mortality is critical to implement age-specific countermeasures for forest management in water-limited areas.An important species for afforestation in dry environments of northern China,Mongolian pine(Pinus sylvestris var.mongolica Litv.)has recently exhibited growth decline and dieback on many sites,particularly pronounced in old-growth plantations.However,changes in response to drought stress by this species with age as well as the underlying mechanisms are poorly understood.In this study,tree-ring data and remotely sensed vegetation data were combined to investigate variations in growth at individual tree and stand scales for young(9-13 years)and aging(35-52 years)plantations of Mongolian pine in a water-limited area of northern China.A recent decline in tree-ring width in the older plantation also had lower values in satellited-derived normalized difference vegetation indices and normalized difference water indices relative to the younger plantations.In addition,all measured growth-related metrics were strongly correlated with the self-calibrating Palmer drought severity index during the growing season in the older plantation.Sensitivity of growth to drought of the older plantation might be attributed to more severe hydraulic limitations,as reflected by their lower sapwood-and leaf-specific hydraulic conductivities.Our study presents a comprehensive view on changes of growth with age by integrating multiple methods and provides an explanation from the perspective of plant hydraulics for growth decline with age.The results indicate that old-growth Mongolian pine plantations in water-limited environments may face increased growth declines under the context of climate warming and drying.

Overstory functional groups indicate the legacy of land use in a secondary tropical forest in southwestern China

Anthropogenic disturbances are widespread in tropical forests and influence the species composition in the overstory.However,the impacts of historical disturbance on tropical forest overstory recovery are unclear due to a lack of disturbance data,and previous studies have focused on understory species.In this study,the purpose was to deter-mine the influence of historical disturbance on the diver-sity,composition and regeneration of overstory species in present forests.In the 20-ha Xishuangbanna tropical sea-sonal rainforest dynamics plot in southwestern China,the historical disturbance boundaries were delineated based on panchromatic photographs from 1965.Factors that drove species clustering in the overstory layer(DBH≥40 cm)were analyzed and the abundance,richness and composition of these species were compared among different tree groups based on multiple regression tree analysis.The coefficient of variation of the brightness value in historical panchro-matic photographs from 1965 was the primary driver of spe-cies clustering in the overstory layer.The abundance and richness of overstory species throughout the regeneration process were similar,but species composition was always different.Although the proportion of large-seeded and vigorous-sprouting species showed no significant differ-ence between disturbed and undisturbed forests in the tree-let layer(DBH<20 cm),the difference became significant when DBH increased.The findings highlight that historical disturbances have strong legacy effects on functional group composition in the overstory and the recovery of overstory species was multidimensional.Functional group composi-tion can better indicate the dynamics of overstory species replacement during secondary succession.

Sustaining forest biodiversity:Exploring the effect of long-term natural disturbance dynamics on contemporary lichen communities in primary forest ecosystems

In this era of biodiversity loss and climate change,quantifying the impacts of natural disturbance on forest communities is imperative to improve biodiversity conservation efforts.Epiphytic and epixylic lichens are effective forest quality bioindicators,as they are generally long-lived organisms supported by continuity of specific forest structures and their associated microclimatic features.However,how lichen communities respond to the effects of fluctuating historical disturbances remains unclear.Using a dendrochronological approach,this study investigates how natural disturbance dynamics indirectly influence various lichen community metrics in some of Europe's best-preserved primary mixed-beech forests.Mixed modelling revealed that natural historical disturbance processes have decades-long effects on forest structural attributes,which had both congruent and divergent impacts on lichen community richness and composition.Total species richness indirectly benefited from both historical and recent higher-severity disturbances via increased standing dead tree basal area and canopy openness respectively-likely through the presence of both pioneer and late-successional species associated with these conditions.Red-listed species richness showed a dependence on habitat continuity(old trees),and increased with disturbance-related structures(standing dead trees)whilst simultaneously benefiting from periods without severe disturbance events(old trees and reduced deadwood volume).However,if the disturbance occurred over a century in the past,no substantial effect on forest structure was detected.Therefore,while disturbance-mediated forest structures can promote overall richness,threatened species appear vulnerable to more severe disturbance events-a concern,as disturbances are predicted to intensify with climate change.Additionally,the high number of threatened species found reinforce the critical role of primary forest structural attributes for biodiversity maintenance.Hence,we recommend a landscape-scale conservation approach encompassing forest patches in different successional stages to support diverse lichen communities,and the consideration of long-term disturbance dynamics in forest conservation efforts,as they provide critical insights for safeguarding biodiversity in our changing world.

Nest-site selection and breeding ecology of Streaked Wren-Babbler(Napothera brevicaudata)in a tropical limestone forest of southern China

Background: The breeding information of most birds in Asian tropical areas,especially in limestone forests,is still poorly known.The Streaked Wren-Babbler(Napothera brevicaudata) is an uncommon tropical limestone bird with a small range.We studied its nest-site selection and breeding ecology,in order to understand the adaptations of birds to the conditions of tropical limestone forest in southern China.Methods: We used methods of systematical searching and parent-following to locate the nests of the Streaked Wren-Babbler.We measured characteristics of nest sites and rock cavities.Data loggers and video cameras were used to monitor the breeding behavior.Results: All the observed nests of the Streaked Wren-Babbler were placed in natural shallow cavities or deep holes in large boulders or limestone cliffs.The great majority(96.6%) of Streaked Wren-Babbler nests had three eggs with an average fresh weight of 3.46-± 0.43 g(n = 36,range 2.52-4.20 g).Most(80.4%) females laid their first eggs between March and April(n = 46).The average incubation and nestling period of the Streaked Wren-Babbler was 10.2 range 9-11 days),respectively.Most(87.9%) nests h± 0.4 days(n = 5,range 1011 days) and 10.5 ± 0.8 days(n = 6,ad at least one nestling fledge between 2011 and 2013(n = 33).Conclusions: Our study suggests that several features of the breeding ecology of the Streaked Wren-Babbler,including building nests in rocky cavities,commencing breeding earlier than most species,and reducing foraging times during the incubation period,are well-adapted to the unique habitat of tropical limestone forest.

Forest landscape ecology and its applications in China

Landscape ecology is playing an increasingly important role in resources management and landuse planning in recent decades and attracting much attention from resource managers and scientists in China as well as in the world. Reviews of landscape ecology development in China have been well documented, whereas forest landscape ecology and its applications receive relatively fewer reviews. In this paper, we first present a brief review of the historical development and current advances of landscape ecology in China and then introduce the applications of landscape ecology to forest park designs, urban greenspace planning, ecological restoration, biodiversity conservation and forest eco-hydrology. Finally, the problems with the application of forest landscape ecology in China, such as inadequate synthesis and integration, lack of basic research on patterns and processes, basic data shortage and model usage problem are discussed on the basis of which we suggest a future direction of forest landscape ecology in China.

Multi-year throughfall reduction enhanced the growth and non-structural carbohydrate storage of roots at the expenses of above-ground growth in a warm-temperate natural oak forest

The more frequent occurrence and severer drought events resulting from climate change are increasingly affecting the physiological performance of trees and ecosystem carbon sequestration in many regions of the world.However,our understanding of the mechanisms underlying the responses and adaption of forest trees to prolonged and multi-year drought is still limited.To address this problem,we conducted a long-term manipulative throughfall reduction(TFR,reduction of natural throughfall by 50%–70%during growing seasons)experiment in a natural oriental white oak(Quercus aliena var.acuteserrata Maxim.)forest under warm-temperate climate.After seven years of continuous TFR treatment,the aboveground growth in Q.aliena var.acuteserrata started to decline.Compared with the control plots,trees in the TFR treatment significantly reduced growth increments of stems(14.2%)and leaf area index(6.8%).The rate of net photosynthesis appeared to be more susceptible to changes in soil water in trees subjected to the TFR than in the control.The TFR-treated trees allocated significantly more photosynthates to belowground,leading to enhanced growth and nonstructural carbohydrates(NSC)storage in roots.The 7-year continuous TFR treatment increased the biomass,the production and the NSC concentration in the fine roots by 53.6%,153.6%and 9.6%,respectively.There were clear trade-offs between the aboveground growth and the fine root biomass and NSC storage in Q.aliena var.acuteserrata trees in response to the multi-year TFR treatment.A negative correlation between the fine root NSC concentration and soil water suggested a strategy of preferential C storage over growth when soil water became deficient;the stored NSC during water limitation would then help promote root growth when drought stress is released.Our findings demonstrate the warm-temperate oak forest adopted a more conservative NSC use strategy in response to long-term drought stress,with enhanced root growth and NSC storage at the expenses of above-ground growth to mitigate climate changeinduced drought.

Ecology,growth and management of black locust(Robinia pseudoacacia L.),a non-native species integrated into European forests

Black locust(Robinia pseudoacacia L.),a species native to the eastern North America,was introduced to Europe probably in 1601 and currently extends over2.3×10~6 ha.It has become naturalized in all sub-Mediterranean and temperate regions rivaling Populus spp.as the second most planted broadleaved tree species worldwide after Eucalyptus spp.This wide-spreading planting is because black locust is an important multipurpose species,producing wood,fodder,and a source of honey as well as bio-oil and biomass.It is also important for carbon sequestration,soil stabilization and re-vegetation of landfills,mining areas and wastelands,in biotherapy and landscaping.In Europe,black locust is drought tolerant so grows in areas with annual precipitation as low as 500-550 mm.It tolerates dry,nutrient poor soils but grows best on deep,nutrient-rich,well-drained soils.It is a fast-growing tree and the height,diameter and volume growth peak before the age of 20.It mostly regenerates vegetatively by root suckers under a simple coppice system,which is considered the most cost-effective management system.It also regenerates,but less frequently,by stool sprouts.Its early silviculture in production forests includes release cutting to promote root suckers rather than stool shoots,and cleaning-respacing to remove low-quality stems,reduce the number of shoots per stool,and adjust spacing between root suckers.In addition,early,moderate and frequent thinning as well as limited pruning are carried out focusing on crop trees.The species is regarded as invasive in several European countries and its range here is expected to expand under predicted climate changes.

Demographic changes in China’s forests from 1998 to 2018

Background: Tree demography is an essential indicator of various forest ecosystem services, and understanding its changes is critical for the sustainable management of forests. During the past four decades, China implemented unprecedented forest restoration projects, which altered tree demography by increasing the number of trees and introducing new species. However, it remains unclear how species composition has changed in China in response to the past forest restoration and demographical processes.Methods: We applied Forest Stability Index(FSI) and the relative change of FSI(%FSI) to describe the population dynamics of tree species and structure in China since 1998, using field-survey data collected from over 200,000plot-records from the 6th to 9th National Forest Inventories(NFIs).Results: The overall populations of both natural and planted forests have grown rapidly from 1998 to 2018, while the range of changes in the relative tree density was more variable for natural forests(ranging from-8.53% to42.46%) than for planted forests(ranging from-1.01% to 13.31%). The populations declined only in some of the tree species, including Betula platyphylla, Ulmus pumila, and Robinia pseudoacacia. In contrast, the populations of trees in the largest size-class either remained stable or expanded.Conclusions: Tree density of China?s forests(both natural and planted forests) generally expanded and the overall populations increased in most size classes, with greater increases occurred in planted forests. In contrasting to the global decline trends of large diameter trees, here we found no apparent decline for trees in the largest size-class in China, highlighting China?s success in improving forest health and forest adaptations to climate change. We advocate for more studies to reveal the mechanisms of the changes in tree demography, which will help to improve forest ecosystem services such as the carbon sequestration capacity.

Leaf nitrogen resorption is more important than litter nitrogen mineralization in mediating the diversity–productivity relationship along a nitrogen-limited temperate forest succession chronosequence

The resorption of nutrients by plants before litter fall and the mineralization of nutrients from plant litter by soil processes are both important pathways supporting primary productivity. While the positive relationship between plant biodiversity and primary productivity is widely accepted for natural ecosystems, the roles of nutrient resorption and mineralization in mediating that relationship remains largely unknown. Here, we quantified the relative importance of nitrogen(N) resorption and N mineralization in driving plant community N investment and the correlation between species diversity and community productivity along an N-limited successional chronosequence of the mixed broadleaved–Korean pine(Pinus koraiensis) forest in northeastern China. Leaf N resorption efficiency(NRE) at the community level increased significantly along the successional chronosequence,whereas litter N mineralization rate decreased significantly. Leaf NRE was more important than litter N mineralization rate in driving the diversity–productivity relationship. However, higher leaf NRE led to less N mineralization as succession progressed along the chronosequence. Our results highlight the importance of the N resorption pathway rather than the N mineralization pathway for forest N acquisition with community succession,and they provide mechanistic insights into the positive effects of biodiversity on ecosystem functioning. In future forest management practices, we recommend appropriate application of N fertilizer to mitigate the adverse effects of N-poor soil on seedling regeneration during late succession and thus maintain the sustainable development of temperate forest ecosystems.