The decomposition of coarse woody debris (CWD) plays a key role in forest carbon and nutrient cycling. Understanding this process has become increasingly important as rising tree mortality leads to substantial CWD production in forests locally and globally. As a low substrate quality plant residue with a high lignin:nitrogen (N) ratio, CWD decay may be more strongly influenced by N deposition than other types of forest litter. This study examined the five-year decomposition dynamics of five dominant tree species-including two broadleaved, two conifer species, and moso bamboo, under control (ambient as 25 kg N ha-1year-1) and N addition (50 kg N ha-1year-1added) conditions in a subtropical evergreen forest, southern China. Decomposition rates (k, year-1) were 1.14 and 1.28 times faster in broadleaved deadwood (0.247 and 0.278, respectively) than in bamboo (0.217), while conifers decomposed the slowest (0.016 and 0.062). After five years, mass loss was 41.4 % for broadleaves, 23.3 % for bamboo, and 8.9 % for conifers, with losses occurring mainly in cellulose and hemicellulose fractions. N addition only slightly stimulated the decay of Schima superba (broadleaved species) which had the lowest initial N and lignin content among the five species. After five years of decomposition, only bamboo logs significantly increased soil organic carbon (SOC), partly due to its relatively low CO2 emissions. Results of this study can help to better predict the ecological impact of tree mortality of different dominant species on the forest carbon balance. Despite the issue of low longevity and high levels of fallen bamboo culms accumulating in large-scale bamboo forest establishment, bamboo CWD-derived organic carbon will not result in additional pressure on carbon emissions, as the case of broadleaved species.

Gap fraction serves as a fundamental variable for quantifying forest light availability and deriving key canopy structural metrics. Hemispherical photography has been the standard method for gap fraction estimation, but has limited capacity to quantify three-dimensional stand architecture and light gradients. The advance of terrestrial laser scanning (TLS) overcomes these limitations by capturing complete 3D structural information. However, TLS-derived gap fraction is sensitive to acquisition and synthesis parameters, and wind-induced canopy movement during scanning may further compromise the reliability of these estimates. We evaluated how these parameters influence the accuracy and precision of TLS-derived gap fraction across a canopy density gradient. We generated 19,968 synthetic hemispherical images from eight TLS configurations, including angular resolution (ar12: 175 million points; ar14: 44 million points), scanning mode (single vs. multi-scan), scan quality (q1–q6, corresponding to 3–30 minutes per station), beam divergence (0.01–0.21°), and image resolution (2000–20000 pixels). We compared TLS estimates against reference hemispherical photography to quantify bias (accuracy) and variance (precision). Point cloud density of single-scan largely determined multi-scan effectiveness, with ar12 achieving significantly higher accuracy than ar14 (error: 0.12 vs. 0.20). Beam divergence dominated estimation accuracy, with 0.09° as optimal. High scan quality eliminated precision benefits due to wind-induced canopy movement. Multi-scan under moderate quality settings showed the strongest variance reductions, especially at high zenith angles. Our findings demonstrate that adequate single-scan point density amplifies multi-scan benefits rather than simply relying on multiple scan positions to compensate for sparse sampling. We recommend prioritizing angular resolution over scan duration and applying moderate beam divergence to optimize estimation accuracy, precision, and field efficiency. These results provide practical guidance for TLS data acquisition and highlight the necessity of parameter configuration.

Uncertainties in gross primary production (GPP) estimation by light-use efficiency (LUE) models are largely driven by fluctuations in photosynthetically active radiation inputs (PARin). To address this problem, the photosynthetic capacity model (PCM) reduces this sensitivity by replacing actual radiation with potential PAR, and estimates GPP from the MODIS-derived enhanced vegetation index (EVI), land surface water index (LSWI) and the ecological parameter, PCmax (maximum photosynthetic capacity). However, the PCM tends to underestimate GPP in cold temperate regions, primarily because it parameterizes PCmax using multi-year average nighttime land surface temperatures (LSTnight), which incorporate dormant-season extremes unrelated to photosynthesis. We developed an improved variant (PCMNF), which employs a quadratic function linking PCmax to growing-season LSTnight so as to better represent the nonlinear temperature-photosynthesis relationship. The PCMNF model was calibrated to forest ecosystems in Northeast China, with potential applicability to analogous temperate and cold-temperate forest biomes. When validated against eddy covariance observations from five ChinaFlux forest sites, PCMNF showed clear gains at multiple time scales over MODIS GPP products. Regional mean estimation error dropped from 21.8

Abstract Severe anthropogenic disturbances have caused significant forest degradation, making the exploration of community assembly mechanisms crucial for developing effective restoration strategies. These mechanisms may vary across size classes due to ontogenetic niche shifts in plants; however, this process remains insufficiently explored. In this study, we surveyed woody plants across five size classes within degraded forests and measured habitat conditions and neighborhood effects, aiming to investigate the size-class dependence of environmental filtering and biotic competition. The results showed that: (1) Due to ontogenetic niche shifts, the assembly mechanisms for seedlings and large trees differed, shifting from varying primarily by environmental filtering to a combination of filtering and competition. (2) These mechanistic differences resulted in the β-diversity among smaller size classes being primarily driven by species turnover and balanced variation in abundance, whereas nestedness and abundance gradients became the main drivers of structural dissimilarity among larger size classes. (3) At the family level, dominant families achieved intraspecific and interspecific coexistence through ontogenetic niche shifts and differentiated size structures. Overall, the relative importance of environmental filtering and biotic competition shifts significantly across size classes. These findings emphasize that forest restoration practices must account for the differentiated requirements of plants at different developmental stages. Based on these findings, we propose targeted forest restoration strategies to provide guidance for forest recovery efforts.

Prior research has demonstrated that the natural regeneration of Korean pine (Pinus koraiensis) in old-growth forests is quantitatively constrained by the composition of parent trees. To further explore the spatial relationships between regenerated and maternal Korean pine, we examined the spatial patterns of its regeneration across four ontogenetic stages (younger seedlings, older seedlings, smaller saplings, and taller saplings) in five old-growth mixed forest stands representing a gradient of Korean pine basal area proportion (33%-77%). Using spatial point pattern analysis with crown-projected coordinates, we quantified intra- and interspecific spatial associations. Results revealed that Korean pine natural regeneration is forest-type-specific, with the ribbed birch (Betula costata)-Korean pine forest being the most conducive to regeneration. Distribution patterns indicated a density-dependent ontogenetic shift: regenerated individuals exhibited strong aggregation at the early stage, which shifted to a random-dominated distribution in later stages, a trend amplified in stands with higher proportions of Korean pine. Associations between younger seedlings and parent trees transitioned from fine-scale facilitation to broad-scale repulsion (p < 0.05), but only where the Korean pine proportion was approximately 50%. Notably, most heterospecific associations were neutral, with facilitation being highly species- and context-specific. We conclude that high conspecific occupancy intensifies intraspecific competition, whereas neutral associations with broadleaved species suggest that niche partitioning governs coexistence. Conservation strategies should therefore focus on regulating parent tree density and maintaining stand diversity to ensure sustainable regeneration. Methodologically, we recommend that future point pattern analyses of large canopy trees, particularly those with severe crown asymmetry, using crown coordinates.

Understory afforestation is a key strategy in close-to-nature silviculture that can effectively transform monoculture plantations into mixed-species forests, and it is increasingly promoted for global forest restoration and biodiversity conservation. While most existing research has focused on seedlings, comparatively less is known about the light adaptation of young trees. In this study, we investigated survival, growth, biomass allocation, and leaf economic spectrum (LES) traits of 11-year-old Picea asperata trees underplanted across five canopy transmittance gradients (CTGs; CTG1: 10

Frequent low-intensity fires historically shaped forest composition and structure in the southeastern United States of America (USA). However, in modern times, fire suppression has inadvertently facilitated the recruitment of mesophytic trees and potentially the invasion of non-native woody plants. In this study, we selected twelve woody broadleaved plants from forested areas of South Carolina and categorized them into three groups: (1) non-native invasive species, (2) native pyrophytic species, and (3) native mesophytic species. We used these categories to examine bark thickness—one critical determinant of fire tolerance—across a spectrum of stem sizes (16.3 mm < DBH < 69.4 mm). Across all species, pyrophytic species consistently exhibited the thickest bark at all measurement heights, followed by invasive species, while mesophytic species had the thinnest bark. Invasive and mesophytic species displayed similar absolute and relative bark thickness values and demonstrated comparable trends in bark thickness variation with increasing stem size. Absolute bark thickness decreased with increasing height along the stem in all groups; however, pyrophytic species exhibited a more pronounced decline in bark thickness from the ground line to breast height compared to mesophytic and invasive species. For pyrophytic species, relative bark thickness at the ground line decreased sharply with increasing stem diameter, indicating a significant early-life investment in bark development. The congruence in absolute and relative bark thickness patterns between mesophytic and woody invasive plants along both horizontal (DBH) and vertical (height) gradients indicates that fire suppression may have helped to facilitate invasive species establishment and spread and that the restoration of historical fire regimes (e.g., repeated surface fire), suggested for reducing mesophytes, could aid in the management of woody invasive plants.

Larch (Larix spp.) monoculture plantations are widely used for timber production but often lead to reduced biodiversity and ecosystem functioning. Therefore, exploring strategies to transition these plantations into mixed-species forests while maintaining forest ecosystem sustainability is crucial. This study examines the tenyear impacts (2015-2024) of small-scale, low-intensity canopy manipulation on the growth performance of planted Manchurian walnut (Juglans mandshurica Maxim.) and Korean spruce (Picea koraiensis Nakai). Four canopy treatments were applied: control (no treatment), light thinning (25 % basal area reduction), smaller gaps (45 m2), and larger gaps (160 m2). We also compared artificial planting with existing natural regeneration under these treatments. Results indicated that both species primarily survived in gaps, with nearly all individuals in control and thinning treatments dying after 10 years. For Manchurian walnut, stems exhibited significantly greater height and root collar diameter (RCD) at gap centers, particularly in larger gaps, where height was 190 % greater than at gap edges. For Korean spruce, while RCD did not differ significantly between gap sizes, it was 16-21 % higher at gap centers compared to edges. Ecophysiological traits (i.e., specific leaf area, chlorophyll content, and non-structural carbohydrate concentration) were largely unaffected by gap size or within-gap position. Furthermore, the proportion of dominant species was higher in artificial planting plots (69 %) than in natural regeneration plots (57 %), while natural regeneration plots supported more common species (10 vs. 7). These findings highlight the efficacy of combining gap creation with artificial planting as a silvicultural approach to gradually transitioning larch monocultures into mixed-species forests.

The conversion of saline-alkali soils into paddy fields for long-term rice cultivation involves multiple disturbances, and as a result, soil microbial communities are altered to adapt to changing environmental conditions. However, a comprehensive understanding of the succession of soil bacterial communities that occurs during this process is still lacking. In the present study, we utilized data obtained from paddy fields of different rice cultivation years (0-23 years) to investigate the compositional and functional succession of soil bacterial communities. We focused on core bacterial taxa that were specifically enriched at different successional stages. Generalized joint attribute modeling (GJAM) was used to identify core bacterial taxa. Results indicated that the bare saline-alkali soil (0 year, prior to any rice cultivation) shared few core amplicon sequence variants (ASVs) with paddy fields. In the bare saline-alkali soil, Longimicrobiaceae from the phylum Gemmatimonadetes was dominant, while the dominance was subsequently replaced by Burkholderiaceae and Pedosphaeraceae phyla affiliated with Proteobacteria and Verrucomicrobia after 5 and 23 years of rice cultivation, respectively. The relative abundances of nitrogen metabolism functions in the core bacterial communities of the bare saline-alkali soil were higher than those at other successional stages, while sulfur metabolism functions exhibited the opposite trend. These indicated that the role of the core bacterial taxa in mediating nutrient cycling also evolved and adapted to changing soil conditions as rice cultivation was established. Redundancy analysis (RDA) indicated that the composition of the core bacterial community in paddy fields with rice cultivation for 0, 2 and 4, 6, 8, 10, and 12, and 20 and 23 years were driven by soil nitrate nitrogen content, pH, available phosphorus content, and the ratio of total carbon to total nitrogen, respectively. In summary, the present study provides insights into the succession of soil bacterial communities and core bacterial taxa that occurs during long-term rice cultivation.

Global change drivers, including drought and nitrogen (N) deposition, exert a wide-ranging influence on tree growth and fitness. However, our current understanding of their combined effects is still limited. Non-structural carbohydrate (NSC) storage is an important physiological trait for tree acclimation to drought. It acts as an important mobile carbon reserve to support tree function when carbon fixation or transport are reduced under drought. It is crucial to investigate how tree species with different NSC storage characteristics (e.g., storage level, partitioning) respond to drought events, and how N alters these patterns. We investigated the combined effects of drought (80% reduction in precipitation) and N addition (0, 30, and 120 kg/ha/year) on the growth and NSC storage of Pinus koraiensis and Fraxinus mandshurica (dominant species in the forests of Northeast China) saplings over two consecutive growing seasons. The results indicated that P. koraiensis exhibited high tolerance to drought, with growth unaffected by drought alone until the mid-growing season in the second year. However, N addition reversed its drought acclimation by impairing root development and exacerbating carbon shortage. In contrast, F. mandshurica was sensitive to drought, it had significantly reduced growth at harvest despite a large amount of NSC accumulation. The present study highlights the contrasting effects of N deposition on drought adaptation in coexisting conifer and temperate broadleaf species, the conifer showing a higher risk of carbon deficiency with increasing N deposition (i.e., a stronger reversal effect of N addition), whereas an earlier cessation of growth under drought defines a larger carbon safety margin for broadleaved species. These results have important implications for the development of adaptive forest management strategies such as to enhance the protection of conifers in the context of global change.

Nitrogen (N) deficiency is a critical factor limiting natural regeneration in coastal shelterbelt forests, but the influence of different N forms on seedling establishment under varying light conditions remains poorly understood. This study investigated the effects of N forms and N concentrations on Ligustrum compactum seedlings under simulated canopy gap conditions using a three-factor design: N form (NO3--N, NH4+-N, mixed N), N concentration (30 and 60 kg ha(-)1 a(-)1), and light intensity (30%, 60%, and 90% full sunlight). Results showed that N addition significantly promoted seedling growth, net photosynthesis rate, and water use efficiency; however, the effects varied among N forms and concentrations. Overall, NO3--N or mixed N were more favored by L. compactum seedlings; however, the N preference was altered by light intensity and N concentration. For instance, L. compactum showed greater NO3--N or mixed N preference under low and medium light intensities, while displaying more NH4+-N preference under high light intensity. N concentration also affected the growth and N preference of L. compactum seedlings, but the variance explained by N concentration was lower than that of light intensity. Leaf C, N, P stoichiometry exhibited stronger correlations with seedling's morphological trait plasticity than those of leaf gas exchange, and further analysis demonstrated that leaf C:P and N:P were the top two critical factors affecting seedling growth, indicating that the coordination and balance among C, N, P elements were more important in explaining the seedling growth under N addition. Therefore, our results clarified that the N preference of L. compactum seedlings could be altered by light intensity and revealed that leaf C, N, P ratios were stronger predictors than leaf gas exchange parameters for explaining the N effects on seedling performance. These findings demonstrated the mechanisms of light-N interactions affecting seedling performance, providing practical guidance for optimizing N fertilization and improving natural regeneration in canopy gaps of degraded coastal shelterbelt forests.

Forest gap dynamics drive succession processes; however, the long-term regeneration processes remain less understood due to the extended temporal scales of forest succession, particularly in temperate forests of Northeast China, limiting the application of gap-based silviculture. This study reconstructed 50-year gap-filling dynamics of tree species in primary broadleaved-Korean pine (Pinus koraiensis) forests using satellite images from six periods (1967-2017) combined with detailed field surveys. We analyzed medium and large forest gaps across different age classes (5-50 years) and compared their regeneration status with undisturbed forest stands serving as controls. Overall tree species richness remained relatively stable throughout gap closure, while species composition shifted from light-demanding to intermediate and shade-tolerant species. Intermediate species (particularly Acer spp.) dominated early gap stages due to their broad ecological niches. As gaps approached closure (>30 years after formation) by regeneration, dominant species stabilized with Quercus mongolica, Acer tegmentosum, and Tilia amurensis prevailing in both gap size categories. Notably, Korean pine regeneration was limited in primary forest gaps despite the presence of abundant seed trees, possibly due to human seed collection practices-suggesting complex interactions between anthropogenic factors and light conditions. Our study established a chronosequence of long-term gap filling and closure processes using space-for-time substitution methods, clarified compositional change patterns of dominant tree species during gap filling, and revealed the potential risk of Korean pine decline in broadleaved-Korean pine forests.

Under-canopy afforestation using different tree species is a key approach in close-to-nature management to improve the structural and functional stability of plantation forests. However, current research on understory afforestation mainly focuses on the seedling stage, with limited attention to saplings or young trees. In this study, we evaluated the growth characteristics and leaf traits of 14-year-old Pinus sylvestris var. Mongolica trees under four different upper forest density (UFD) treatments: 0 trees/hm2 (canopy openness 100%, CK), 150 trees/hm2 (canopy openness 51.9%, T1), 225 trees/hm2 (canopy openness 43.2%, T2), and 300 trees/hm2 (canopy openness 28.4%, T3). We found that the survival rate of P. sylvestris in the T3 was significantly lower than in the other treatments, with a decrease of 30.2%, 18.3%, and 19.5% compared to CK, T1, and T2, respectively. The growth of P. sylvestris in the T1 treatment exhibited superior performance. Specifically, T1 showed a significant increase of 18.8%, 5.5%, and 24.1% in tree height, diameter at breast height, and crown width, respectively, compared to the CK. The mean trunk biomass ratio in the understory was significantly higher than that in full light by 15.4%, whereas the mean leaf biomass ratio was significantly lower by 12.3%. Understory P. sylvestris trees tended to allocate more biomass to the trunk at the expense of decreasing leaf biomass, which would facilitate height growth to escape the shading environment, although the promotion was relatively limited. Leaf length, leaf width, leaf area, leaf thickness, mesophyll tissue thickness, epidermis thickness, and leaf carbon content were the highest in the CK and tended to decrease with increasing UFD, indicating that a high-light environment favored leaf growth and enhanced carbon accumulation. In summary, young P. sylvestris trees adapted to moderate shading conditions created by the upper canopy, and the T1 treatment was optimal for the growth of understory P. sylvestris. This study provides insights into different adaptive strategies of young P. sylvestris trees to changes in light environment, providing practical evidence for under-canopy afforestation using light-demanding trees during pure plantation transformation.

Clarifying gap patterns and dynamics on a regional scale is necessary to understand forest succession. However, few studies quantified the species composition influences except for geography and time effects. We examined the spatial and temporal gap patterns in an old-growth broadleaved-Korean pine (Pinus koraiensis) forest using two satellite image datasets with a ten-year interval and complementary field survey datasets. The forests were evenly divided into 121 plots with a plot size of 100 ha, and the crown projection area ratio of evergreen trees (RE/A) in each plot was quantified to represent simplified species composition (i.e., evergreen versus deciduous trees). We found that gap fraction and density reduced from 19.0% and 25.0 gaps ha-1 in 2007 to 16.8% and 17.6 gaps ha-1 in 2017, respectively, equivalent to a transformation of 213 ha from gaps to closed canopy. Generalized linear mixed models showed that the RE/A explained substantial variance in gap fraction, size, and number, much more than geography factors (slope and altitude). However, the gap size frequency distribution consistently followed a power-law distribution with weak geography, time, and species composition influences. Univariate analyses showed that the gap distribution patterns differed by gap size but tended to randomness over time, likely due to the randomness of gap formation and the differences in gap closure processes. The species composition of gap makers and fillers diverged along the RE/A gradient. In summary, our study proposed a novel factor (RE/A) to reveal the spatial and temporal gap patterns in the broadleaved-Korean pine forests, which provided insights into the necessity of refining species composition in conducting regional-scale gap studies with the development of airborne hyperspectral and LiDAR remote sensing technologies.

Background Understanding of the ratio of photosynthetic photon flux density (Q p ) to global solar radiation (R s ) (Q p /R s ) is crucial for applying R s to ecology-related studies. Previous studies reported Q p /R s and its variations based on measurements from a single observatory tower, instead of multi-site-based measurements over complex terrains. This may neglect spatial heterogeneity in the terrain, creating a gap in an understanding of how terrain affects Q p /R s and how this effect interacts with meteorological factors.Methods Here the Qingyuan Ker Towers (three towers in a valley with different terrains: T1, T2, and T3) were utilized to measure Q p and R s over mountainous forests of Northeast China. An airborne LiDAR system was used to generate a digital elevation model, and sky view factor of sectors (SVFs) divided from the field of view of tower's pyranometer was calculated as a topographic factor to explain the variations of Q p /R s .Results The results identified significant differences in Q p /R s of the three towers at both daily and half-hour scales, with larger differences on clear days than on overcast days. Q p /R s was positively correlated with SVFs of T1 and T3, while this correlation was negative with that of T2. The effect of SVFs on Q p /R s interacted with clearness index, water vapor pressure and solar zenith angle. Random forest-based importance assessment demonstrated that explanation (R 2) on Q p /R s was improved when SVFs was included in the predictor variable set, indicating that incorporating terrain effects enhances the prediction accuracy of Q p /R s . The improvement in the R 2 values was more pronounced on clear days than on overcast days, suggesting that the effect of terrain on Q p /R s depended on sky conditions.Conclusions All findings suggested that Q p /R s is affected by terrain, and integrating terrain information into existing Q p /R s models is a feasible solution to improve Q p /R s estimates in mountainous areas.

The widespread utilization of fossil fuels has emitted large amounts of CO2 into the atmosphere since the Industrial Revolution,leading to climate warming and frequent occurrence of extreme climate events.To effectively alleviate climate change,the international community has made various efforts to reduce carbon emissions and elim-inate CO2 from the atmosphere.In 2020,the Chinese government announced that carbon emission peaking and car-bon neutrality will be achieved by 2030 and 2060,respectively.According to the current forecast,by the time car-bon neutrality is achieved in 2060,even under the minimum conditions of fossil energy use,production,and living emissions,China will still have to emit about 1/4 of the current total emissions.These carbon must primarily be absorbed by ecosystems.Furthermore,approximately 140 ppm increase in CO2 in the atmosphere since the Industrial Revolution still needs to be removed by ecosystems.Forests are the main component of terrestrial ecosystems,con-tributing more than 80％of the carbon sequestration capacity of all terrestrial ecosystems.However,due to the long periodicity,complexity and dynamic variability of forests,the basic concepts of ecosystem carbon sink and its time effect are still unclear,leading to problems,such as lacking technologies for improving carbon sink capacity and disorganized rules in the carbon sink trading market.In this review,we introduced carbon sink concept according to the processes of absorbing and fixing CO2 by plant photosynthesis in forest ecosystems.Then,we analyzed the processes of time-scale-dependent carbon sinks of forest ecosystems,discussed the time effects of forest carbon sinks,and suggested using"t-year"as the unit of carbon sink(taking 3-6 months as the minimum measurement time,i.e.,the beginning of carbon sequestration).Third,we proposed the approaches to improve the carbon sink capacity of forest ecosystems.One way is to improve the carbon sink capacity(expanding forest area,improving for-est quality,and increasing forest soil carbon storage)of forest ecosystems.Another approach is to maintain the car-bon sink of forest ecosystems as long as possible,i.e.,to reduce temporary carbon sink(definition:carbon in the forest ecosystems emit into the atmosphere for a certain period)and to increase persistent carbon sink(definition:carbon in the forest ecosystems no longer emit into the atmosphere for a certain period;according to the relevant provisions of the Paris Agreement,the upper time limit for carbon sink measurement can be considered to be the year 2100.In order to maintain the persistent carbon sink,strateges such as efficient use of wood products(replace steel,cement,plastic with wood),control of forest fires or other disturbances-induced emissions,and turning for-est biomass into biochar should be taken.Finally,we proposed to develop climate-smart forestry driven by artificial intelligence(AI),which would provide new theoretical and technical support for improving the carbon sink of for-est ecosystems and facilitating sustainable forest management.

China's Three-North Protective Forest Program (TNP) is the world's most ambitious afforestation project (ongoing from 1978 to 2050), which aims to increase forest coverage through afforestation and reforestation, protect agriculture, reduce soil erosion, and control desertification. Although TNP has been ongoing for 45 years, its rationales and effects remain uncertain. Here, we conducted a range-wide assessment of TNP by analyzing data from >10,000 scenes of satellite images and >50,000 field survey plots. The TNP range and definitions of shelterbelts, arboreal forests, and shrublands were changed during the study period, but we used the initial TNP range (4.07 million km2) and the definitions in 1978 for keeping the consistency, comparability, and comprehensiveness. The TNP increased forest coverage from 5.05% in 1978 to 9.69% in 2022, with arboreal forests, shrublands, and shelterbelts increasing by 42.5%, 184.4%, and 53.6%, respectively. However, only 40.1% of the 471,113 km2 afforested area was established between 1978 and 2022. The well-established shelterbelts improved crop yield by 4.3%-9.5%, but only 10.2% of all the farmlands in TNP regions (TNR) were protected. The total area of soil erosion due to hydraulic forces was reduced by 447,363 km2, with 61% of this reduction attributed to TNP. TNP contributed to the reduction of desertification by 15%, largely due to the low rate of afforestation success and the largely decreased grasslands. The total carbon sequestration from TNP was 1.96 Pg C. Moreover, water storage in TNR showed a decreasing trend, but the contribution rate of TNP was only 7.8%. Our results illustrate that forestry eco-engineering projects are feasible in the management and restoration of arid and semi-arid degraded lands, but attention must be paid to fully considering the ecological carrying capacity of water resources, matching the species to sites, strengthening the post-afforestation management, as well as keeping the balances between composite ecosystems.

Climate change is the most severe ecological challenge faced by the world today. Forests, the dominant component of terrestrial ecosystems, play a critical role in mitigating climate change due to their powerful carbon sequestration capabilities. Meanwhile, climate change has also become a major factor affecting the sustainable management of forest ecosystems. Climate-Smart Forestry (CSF) is an emerging concept in sustainable forest management. By utilizing advanced technologies, such as information technology and artificial intelligence, CSF aims to develop innovative and proactive forest management methods and decision-making systems to address the challenges of climate change. CSF aims to enhance forest ecosystem resilience (i.e., maintain a condition where, even when the state of the ecosystem changes, the ecosystem functions do not deteriorate) through climate change adaptation, improve the mitigation capabilities of forest ecosystems to climate change, maintain high, stable, and sustainable forest productivity and ecosystem services, and ultimately achieve harmonious development between humans and nature. This concept paper: (1) discusses the emergence and development of CSF, which integrates Ecological Forestry, Carbon Forestry, and Smart Forestry, and proposes the concept of CSF; (2) analyzes the goals of CSF in improving forest ecosystem stability, enhancing forest ecosystem carbon sequestration capacity, and advocating the application and development of new technologies in CSF, including artificial intelligence, robotics, Light Detection and Ranging, and forest digital twin; (3) presents the latest practices of CSF based on prior research on forest structure and function using new generation information technologies at Qingyuan Forest, China. From these practices and reflections, we suggested the development direction of CSF, including the key research topics and technological advancement.

Forest gaps create environmental heterogeneity and drive forest dynamics through gap-phase regeneration. However, it is unclear when a forest gap can be considered closed, limiting a global synthesis of forest succession that integrates gap patterns and dynamics. We created twelve forest gaps (six large gaps, RD/H [ratio of gap diameter to gap border tree height] = 1.3; six small gaps, RD/H = 0.6) and monitored tree regeneration for seventeen years to establish an objective gap-closure standard for regeneration filling in a temperate secondary forest. Our results indicated that a forest gap could be considered closed or entering a gap-closure phase when the dominant gap regeneration layer (i.e., the top 10% gap-fillers) (1) reached the crown base height (8.9 m on average) of canopy trees and (2) entered a period of stability in density, richness, and evenness. Linear mixed-effects models found that these two conditions met each other in the same period (14.5 years) in the large gaps, with a mean density, richness, and evenness of 0.1 (stem m-2), 4.9 (species gap-1), and 0.9, respectively. However, if no repeated gap disturbance occurred, small gaps were closed by lateral extension rather than by height growth. Light-demanding species (e.g., Juglans mandshurica) mainly contributed to the closure of large gaps and played negligible roles in the small gaps, but intermediate or shade-tolerant species (e.g., Acer mono) in the small gaps had potential for successful gap filling following repeated gap disturbance. Our gap-closure standard links gap structure to species composition and provides a reference for large-scale research on gap patterns and dynamics, which helps to understand the ecological process during forest succession. The standard also provides a relatively clear boundary between forest gaps and closed forest stands, which is a premise to develop appropriate forest management and shorten the restoration period of degraded secondary forests.

Aims Nitrogen (N) enrichment from excessive fertilization influences the coupling of nutrients in terrestrial ecosystems, but whether it could alter the scaling relationships between multinutrients [including macronutrients: N, phosphorus (P), potassium, calcium (Ca), magnesium (Mg) and micronutrients: manganese (Mn), iron (Fe) and zinc] remains unclear. Methods We conducted an control experiment using two-year-old Chinese hickory ( Carya cathayensis ) saplings in hydroponics system, with six levels of N fertilization, to evaluate variations in scaling relationships of multinutrient concentrations in vegetative organs of Chinese hickory under consistent N fertilization. Results Correlational relationships between multinutrients concentrations were most significant in leaves, while stems and roots were less related. Micronutrients, in particular, were mostly negatively related to macronutrients. Significant allometric relationships were detected among multinutrients, but the response patterns were both organ- and nutrient-dependent. For example, positive allometric relationships were detected in N versus other macronutrients while negative allometric relationships were observed with N related to micronutrient response. Leaves generally presented more positive allometric relationships than negative relationships. Beyond expectation, increasing N fertilization minimally altered the scaling exponents between multinutrients, except stem N-Mg, root Mn-Fe, root P-Ca, and leaf P-Ca. Conclusions Chinese hickory saplings displayed relatively high nutrient homeostasis when excessive N fertilizer was applied. These results will enhance our understanding of organ-dependent allometric relationships between multinutrients in forest trees and may offer new insights into how plants develop adaptive functional traits to increasing N fertilization.