Climate change is threatening the growth and survival of natural forests (NF), while structurally simplified planted forests (PF) may face even greater risk. However, systematic comparisons of key ecological functions between PF and NF under climate change remain rare but are urgently needed. Here, we compared growth variability (quantified as the interannual coefficient of variation of leaf area index (LAI) as a proxy for productivity) between paired NF and PF across China during 2001-2020, using 836 paired 25 & times; 25 km windows where NF and PF co-occur under similar environmental conditions. We then investigated the main drivers of the differences in growth variability between the two forest types. Our results showed that PF exhibited higher growth variability compared to NF, with this divergence being most pronounced in subtropical broad-leaved evergreen forests. Growth variability of both NF and PF significantly decreased during 2011-2020 compared with 2001-2010, correlating with a regional shift towards reduced drought stress (higher water availability). Furthermore, analysis revealed that the higher growth variability in PF compared to NF was primarily associated with lower stand age and poorer soil nutrients conditions. These findings underscore that PF may have higher risk. To mitigate the impacts of future climate change on PF, our results indicate that future planting and management strategies for PF should prioritize multi-species composition, stand-level management (i.e., increase structural diversity), and forest restoration interventions, especially in regions with low nutrient and/or water availability, rather than focusing solely on expanding forests area.

Climate-warming induced lengthening of growing season has long been expected to promote tree growth, but this view has been increasingly challenged. How tree growth responds to shifts in early, late and total growing season length (GSL), especially the contrast between previous- vs. current-year GSL, and how these responses are jointly modulated by climatic gradients and species strategy, remain unclear. Here, we combined tree-ring chronologies with satellite-derived leaf phenology for early- (Betula platyphylla) and later-successional (Quercus mongolica) forests across seven sites spanning 39–51 °N in China, and examined the relationships of ring-width index (RWI) with early, late and total GSL in previous- and current-year, and how these relationships were affected by geographic climate gradients. We found that: 1) for both species, longer previous late (and total) growing-season had an overall promoting effect on radial growth; however, this benefit diminished into a null effect toward regions with unfavorable climate (higher latitude, lower heat-sum and radiation), probably because extended and warmer previous late growing-season under radiation limitation increases respiration that offset the limited photosynthesis, leaving little extra carbon to be stored for next-year growth. 2) In contrast, longer current early and total growing-season had an overall negative effect on growth because elongated current early growing-season leads to hotter drought. Further, this negative effect intensified toward unfavorable climate regions. 3) The growth of B. platyphylla was sensitive to shifts in both current- and previous-year GSL across latitudes, while that of Q. mongolica was largely decoupled from current-year GSL but mainly affected by previous late growing-season carbon storage. 4) Our results highlighted the lagged positive effect of elongated previous (late) GSL, likely through enhanced carbohydrate storage, but the negative effect of current (early) GSL on growth, likely because soil water constrains current-year cambial activity and xylem cell enlargement, which explains why a warming-induced longer growing season may not enhance, and can even reduce, radial growth toward continental high latitudes. These findings predict that future warming-induced elongated GSL may strongly threaten forests in continental high-latitudes, and have important implications for forest management to alleviate forest vulnerability.

Selective logging is a widely practiced afforestation management strategy aimed at promoting the sustainable utilization of disturbed forests. However, how nutrient allocation strategy between aboveground and belowground regulates community biomass accumulation dynamics after selective logging remains unclear, which becomes a research gap. This study selected six low-intensity selective logging sites and one unlogged site as a control in broad-leaved Korean pine forests located in Northeastern China, representing 6, 14, 25, 36, 45, 55, and 100 years after logging. The nutrient contents of leaf, root, and soil, and plant functional traits of 234 plant species were measured to quantify the nutrient allocation between aboveground and belowground of plants (bSMA) and the contributions of nutrient allocation to biomass accumulation. Results suggested more stable N utilization in leaves than in roots for trees (bSMA = 0.80 ± 0.02), shrubs (bSMA = 0.87 ± 0.03), and herbaceous plants (bSMA = 0.84 ± 0.02) in logged sites. With increased restoration years after logging, the bSMA of N increased for trees, shrubs, and herbaceous plants. The community biomass was positively correlated with nutrient bSMA, which was explained 45 % of the total variation in community biomass. The contribution of nutrient allocation to biomass accumulation was indirectly regulated by functional diversity (0.40) and species diversity (0.33) in selective logging forests. The results emphasize the importance of N allocation strategies of the trees and P allocation strategies of the understory species for biomass accumulation, which closely related with functional diversity. Therefore, this study suggests that forest management should appropriately expand the artificial cultivation of N-fixing plants, especially the understory species to promote the interspecific competition and nutrient cycling in maximizing the carbon stocks in the management of logged forests.

Deep water is essential for plant growth and survival during drought. However, the relationships between temporal and spatial variation of deep soil water utilization (DW) and their driving factors remain unclear. Here, we analyzed spatio-temporal DW variations of nine coexisting understory woody species across 29 subtropical coniferous plantations suffering frequent seasonal droughts. At the ecosystem scale, we assessed the soil properties and community structure drove spatio-temporal DW dynamics. At the species level, we linked the spatiotemporal DW variations to functional traits and isohydricity levels. The spatial and temporal DW variations showed significant positive correlations at both the ecosystem and species levels. At the ecosystem level, the spatial DW variation was predominantly shaped by soil pH and rock fragment content amongst soil factors, and the dominance and richness of herb layers amongst community index. Unexpectedly, the temporal DW variation is less susceptible to soil properties and community index at the ecosystem level. At the species level, species with larger DW variations typically employ 'fast' resource-acquisition and drought avoid strategies. In contrast, species with less DW variations show conservative growth strategies and mainly through strengthening their own resistance in response to environmental stress. Moreover, the spatio-temporal DW variations in the isohydric plants are larger than that in the anisohydric plants. By bridging ecosystem-scale drivers with species-level functional traits, our work advanced theoretical frameworks for predicting vegetation responses to drought and the role of isohydric species in driving hydrological cycles while offering practical insights for managing subtropical plantations under climate change.

1. Fine roots play a pivotal role in terrestrial carbon and nutrient cycling. However, our knowledge on drivers of fine-root biomass (FRB) and productivity (FRP) focus on functional traits, biodiversity and abiotic factors, while less attention on allometric constraints, an indispensable driver of organism carbon partitioning. 2. We measured FRB (FRP) for 24 plots using 216 soil cores (ingrowth cores) from four forest types (birch, oak, larch and pine) on a warm-temperate mountain of north China, and investigated leaf, stem and fine-root functional traits, stand factors, diversity and soil fertility. We tested the allometric relationships among FRB, FRP, aboveground (leaf) biomass and functional traits, and examined how allometry, size-dependent growth strategies, the mass-ratio and complementary effects affected FRB and FRP directly and indirectly. 3. There is stable allometric relationship between FRP and FRB at both the soil-core and plot levels, and the former supported the predicted exponent for leaves (=1) of the metabolic scaling theory. Contrary to common observations, plot-scale FRB and FRP showed negative (or non-significant) relationships with aboveground (leaves) biomass. Instead, higher aboveground biomass led to more conservative growth strategies, which led to lower FRB, and thus lower FRP due to allometric constraints. Root traits (mass-ratio effect) showed the strongest direct effect on FRB, while diversity (complementary effect) and soil fertility revealed weak effects. FRP was strongly driven by allometry (FRB) and soil nitrogen, while functional traits and diversity affected FRP via FRB instead of directly. 4. Our results do not conflict with the positive correlations of FRB (FRP) with aboveground (leaf) biomass reported by large-scale studies, but together suggest changes of growth strategies with tree size vs. climate, which may affect aboveground-root relationship simultaneously. Thus, we suggest to carefully test allometric relationships to better understand how biodiversity, traits and stand factors affect fine-root dynamics.

Tree growth and survival at alpine (arctic) treelines are generally limited by temperature, but it is increasingly observed that hotter drought is threatening tree growth at treelines. How treeline growth variability in response to climate change varies at broad scale, and how it is jointly modulated by functional traits, stand structure and climate factors remains unclear. We sampled tree-ring cores from 11 treeline sites along longitude (precipitation) gradients across northern China, and examined two new aspects of radial growth response to climate change: temporal growth variability and spatial growth synchrony. We explored how climate conditions, climate trends and temporal variability, functional traits [specific leaf area (SLA), leaf nitrogen concentration (LN)], and stand factors affect growth variability and synchrony, and assessed the major drivers with mixed-effects models. 1) Contrary to our expectation, growth variability decreased from humid to arid regions. This pattern was partly because water availability increased in the west (arid) while decreased in the east (humid) regions since 1950. 2) Hotter drought and higher climate variability led to higher growth variability and synchrony. 3) Species with fast-growing strategies (higher SLA and LN) showed higher growth variability and synchrony due to experiencing drastic hotter drought and having lower drought tolerance. 4) Taller and denser stands revealed higher growth variability and synchrony due to stronger hydraulic limitation and competition, respectively. 5) Functional traits and stand factors are indispensable modulators of growth spatiotemporal variability even at broad scales, because their variable importance was often higher than climate factors. These results caution against predicting forest vulnerability solely from climate factors. We conclude that forests at many treeline sites were threatened by hotter drought, especially in humid regions of northern China. But the importance of stand factors and functional traits found also suggests forest management as an effective way to alleviate climate change vulnerability.

Although numerous studies have proposed explanations for the specific and relative effects of stand structure, plant diversity, and environmental conditions on carbon (C) storage in forest ecosystems, understanding how these factors collectively affect C storage in different community layers (trees, shrubs, and herbs) and forest types (mixed, broad-leaved (E), broad-leaved (M), and coniferous forest) continues to pose challenges. To address this, we used structural equation models to quantify the influence of biotic factors (mean DBH, mean height, maximum height, stem density, and basal area) and abiotic factors (elevation and canopy openness), as well as metrics of species diversity (Shannon–Wiener index, Simpson index, and Pielou’s evenness) in various forest types. Our analysis revealed the critical roles of forest types and elevation in explaining a substantial portion of variability in C storage in the overstory layer, with a moderate influence of stand factors (mean DBH and basal area) and a slightly negative impact of tree species diversity (Shannon–Wiener index). Notably, forest height emerged as the primary predictor of C storage in the herb layer. Regression relationships further highlighted the significant contribution of tree species diversity to mean height, understory C storage, and branch biomass within the forest ecosystem. Our insights into tree species diversity, derived from structural equation modeling of C storage in the overstory, suggest that the effects of tree species diversity may be influenced by stem biomass in statistical reasoning within temperate forests. Further research should also integrate tree species diversity with tree components biomass, forest mean height, understory C, and canopy openness to understand complex relationships and maintain healthy and sustainable ecosystems in the face of global climate challenges.

Temporal growth variability is an important indicator of ecosystem function under climate change. However, we still lack a unified understanding of how climate conditions, climate change (trends and variability), nitrogen (N) deposition, functional traits and stand factors together affect radial growth variability. Using global conifer tree-ring records (123 species from 1780 sites) during 1970-2010 to calculate growth variability, we assessed how abiotic and stand factors affect growth variability directly and indirectly via functional traits with boosted regression tree and structural equation models, and examined the differences among continents (North America, Asia and Europe). We found: (a) growth variability was mainly affected by warm-induced drought and increased at lower latitudes. Climate warming in winter could decrease growth variability, but this effect is by far not enough to offset the threat of hotter drought; (b) there existed a trade-off between fast- and slow-growing (drought tolerance) strategies for global conifer species, and abiotic and stand factors affected growth variability via functional traits. Contrary to common conjecture, species with higher drought tolerance revealed higher growth variability due to their occupation of more xeric sites, and may also because higher investment in drought tolerance leads to less investment remaining for growth; (c) older trees revealed higher growth variability due to their more conservative growth strategy, while at large scales, taller trees showed lower growth variability due to occupying more productive sites; and (d) moderate N deposition could reduce growth variability by leading conifers to adopt a more fast-growing strategy (e.g. in Asia), but long-term and excessive N deposition led to increased growth variability (e.g. in North America and Europe). Synthesis. Our results suggest that coniferous forests in water-limited regions should be more vulnerable to hotter drought, and the 'fast-slow' growth strategies may be key in regulating the effects of various abiotic and stand factors on ecosystem stability. Moreover, future hotter drought and N deposition will severely threaten conifer growth, especially for old trees and conifers at lower latitudes. Temporal growth variability can provide new insights into forest response to climate change. Our results suggest warm-induced drought as a major driver of the temporal growth variability and found that the 'fast-slow' growth strategies may be key in regulating the effects of various abiotic and stand factors on the ecosystem stability of coniferous forests. Future hotter drought and N deposition will severely threaten conifer growth, especially for old trees and conifers at lower latitudes.image

As an essential part of the stoichiometric flexibility in regulating the relative tissue contents of nitrogen (N) or phosphorus (P), their homeostasis (H) could determine plant growth under changing nutrient environments, such as under wildfire disturbance. Although a growing number of studies have suggested a coupling relationship between plant nutrient H and species abundance, how leaf N and P homeostasis (HN and HP) regulates the accumulation of community biomass remains unclear, especially in nutrient-fluctuating burned areas. We measured leaf N and P concentrations and total biomass of all species and the soil N and P concentrations across 15 forest plots at four recovery periods (2, 10, 20, and 30 years after burning) with low-severity wildfire and one unburned treatment (>80 years after burning) in boreal forests and associated the community-level HN and HP with biomass accumulation in the Great Xing’an Mountains, China. We found that the HN of trees peaked 20 years after burning under N limitation conditions, and the HP of shrubs approached a maximum at 10 years after burning due to P limitation. It is worth noting that the biomass of trees and herbs was significantly positively correlated with HN, while negative relationships between HP and biomass were shown in trees. Nutrient H explained 59% of the total variation in community biomass, and the joint effect of HN and HP mainly contributed to the biomass accumulation of trees (43.5%) and shrubs (68.5%), respectively. These findings greatly improve the theoretical foundation for understanding how plant nutrient H is associated with biomass accumulation after wildfire. Flexible nutrient H in woody plants highlights the vital role of understory woody species in postfire forest management. Therefore, clearly understanding the relationship between nutrient H and carbon sequestration is essential for a thorough assessment of postfire forest sustainability.

Plant stoichiometry and nutrient allocation can reflect a plant’s adaptation to environmental nutrient changes. However, the allocation strategies of carbon (C), nitrogen (N), and phosphorus (P) between leaf and fine root in response to wildfire have been poorly studied. Our primary objective was to elucidate the trade-off of elemental allocation between above- and belowground parts in response to the soil nutrient changes after a wildfire. We explored the allocation sloping exponents of C, N, and P between leaf and fine root at the species and community levels at four recovery periods (year 2, 10, 20, and 30) after moderately severe wildfire and one unburned treatment in boreal forests in Great Xing’an Mountains, northeast China. Compared with the unburned treatment, leaf C concentration decreased and fine root C increased at year 2 after recovery. The leaf N concentration at year 10 after recovery was higher than that of unburned treatment. Plant growth tended to be limited by P concentration at year 10 after recovery. Nutrient allocation between leaf and fine root differed between species and community levels, especially in the early recovery periods (i.e., 2 and 10 years). At the community level, the nutrient concentrations of the leaf changed more as compared to that of the fine root at year 2 after recovery when the fine root nutrients changed more than those of the leaf. The different C, N, and P allocation strategies advanced the understanding of plant adaptation to soil nutrient changes during the postfire ecosystem restoration.

Biodiversity is found to have a significant promotion effect on ecosystem functions in manipulation experiments on grassland communities. However, its relative role compared with stand factors or functional identity is still controversial in natural forests. Here, we examined their relative effects on biomass and productivity during forest restoration. We investigated stand biomass and productivity for 24 plots (600 m(2)) across restoration stages in the subtropical forests of Mt. Shennongjia, Central China. We measured five key functional traits and calculated functional diversity (functional richness, evenness and dispersion) and community-weighted mean of traits. We used general linear models, variation partitioning methods to test the relative importance of stand factors (density, stand age, maximum height, etc.), functional identity, species and functional diversity on biomass and productivity. Our results illustrated that stand biomass and productivity increased significantly as forest restoration, and that community species richness increased, while functional dispersion decreased significantly. Variation partitioning analyses showed that diversity had no significant pure effects on biomass and productivity. However, diversity may affect biomass and productivity through the joint effect with stand factors and functional identity. Overall, we found that stand factors had the strongest effect on biomass and productivity, while functional identity significantly affects productivity but not biomass, suggesting that modulating stand structure and species identity are effective ways to enhance forest carbon storage and sequestrations potential in forest management.

Many studies have examined plant biomass allocation among leaf, stem and root organs in relation to environmental and ontogenetic factors. But the drivers for allocation of stand-level productivity across restoration stages, and the potential role of functional traits, are still poorly understood. Here we investigated 24 plots across four restoration stages in subtropical forests on Mt. Shennongjia, central China. We examined the relative effects of environment (slope, aspect and canopy openness), stand factors (forest height, total basal area, stand density and age), and community-weighted mean (CWM) of key functional traits (wood density and specific leaf area), on the allocation of forest productivity to stems, leaves and roots. The results showed that forest productivity, and the stem fraction of stand productivity, both increased during forest restoration; while leaf and root productivity fractions showed an overall decrease. A higher fraction of productivity was allocated to leaves and roots while lower fraction was allocated to stems towards harsher site condition. Stem fraction was positively related to stand age and forest height, whereas root fraction showed a converse pattern. None of the stem, leaf or root fraction was significantly correlated with the proxies of competition (stand density and total basal area). As for the effect of functional traits, stem productivity fraction was negatively related to the CWM of wood density, while leaf fraction was positively related, which can be explained by the optimal theory and growth strategy together. However, CWM of specific leaf area has no significant effect on productivity allocation. Multivariate analyses showed that topography (slope) and stand age were main drivers for the productivity allocation to woody organs (stem and root), and wood density was also important for stem productivity fraction. Meanwhile, leaf fraction is mainly affected by wood density and aspect. Our results suggest that, in addition to environmental and stand factors, functional traits (e.g. wood density) are also important in affecting the allocation of stand productivity. However, there are still many equivocal results about the influence of functional traits. Allocation of productivity among organs, and key functional traits (e.g. wood density and specific leaf area), are both indispensable parameters in ecosystem processes models. Further studies are needed to explore the mechanisms how functional traits and stand factors affect productivity allocation, to better predict forest carbon balance under future global change, and to better guide forest management to increase ecosystem services and carbon sink.

Increasing drought associated with climate warming (i.e., hotter drought) is seriously threatening tree growth and survival across the world. Previous studies have reported that tree growth response to climate change is affected by species. Nevertheless, how functional traits and stand factors affect radial growth are not well understood. North China has experienced severe hotter drought in recent decades. We sampled the tree-ring from four typical species with mean stand ages of 40 to 60 years at altitudes of 1100–1300 m, and examined two aspects of radial growth response to hotter drought: temporal growth variability [mean sensitivity (MS) and standard deviation (SD)], and the correlations of ring width indices (RWI) with historical temperature and water availability. We also explored the relative importance of functional traits and stand factors on radial growth response to hotter drought. We found that MS and SD were the highest in Betula platyphylla with the highest leaf nitrogen (N) concentration and specific leaf area (SLA) (acquisitive strategy), but decreased with lower leaf N concentration and SLA (conservative strategy), until MS and SD were the lowest in Pinus tabulaformis. Consistent with the hydraulic limitation hypothesis, the growth of taller stands was more limited by hotter drought. Meanwhile, stands with higher wood density and lower leaf N concentration showed stronger water sensitivity of radial growth. These evidences highlight the importance of functional traits and stand factors on radial growth response to climate change. Hotter drought has caused a significant negative influence on radial growth in our study region and thus may be a severe threat in the future. Further studies need to explore how functional traits and stand factors affect tree growth response to climate change, to better guide forest management in alleviating the threat of future hotter drought.

Exploring carbon allocation pattern and its influencing factors is of great significance for estimating the carbon sequestration rate and potential of forest ecosystems. Here, we investigate all carbon pool components (including above and belowground biomass of tree, shrub and herb layers, and dead biomass and soil carbon pools) in four successional stages of broad-leaved and Korean pine (Pinus koraiensis Siebold & Zucc.) mixed forests in Northeast China. We explore the change of allocation among carbon pools with succession and examine the relative importance of succession, stand age, and stand factors on carbon allocation pattern. Our results illustrate that above- and belowground vegetation carbon increase as maximum tree height increases. Below- to aboveground vegetation carbon ratio (R/S ratio) decreases significantly with succession and increases significantly as mean diameter at breast height (DBH) increases, but does not significantly correlate with stand age. With succession and increasing stand age, understory (shrub, herb) to tree carbon ratio (understory/tree ratio) and soil to vegetation carbon ratio (soil/vegetation ratio) decrease significantly. The joint effect of succession, stand age, and stand factors have the largest contribution on above- and belowground vegetation carbon and understory/tree ratio (26.83%, 27.93%, and 49.48% of variations explained, respectively). As for the pure effects, stand factors explain the largest proportion of variations in vegetation aboveground carbon (11.25%) and soil carbon (20.18%). Meanwhile, succession is the variable with the largest contribution to vegetation belowground carbon (12.64%), R/S ratio (21.83%), understory/tree ratio (25.84%), and soil/vegetation ratio (6.68%). Overall, these results suggest that species composition change during forest succession, instead of stand factors and stand age, is the main driver of forest vegetation carbon allocation. In contrast, stand factors play a major role in soil carbon allocation. Our findings suggest more studies to better understand the role of species composition (in addition to stand factors and age) on biomass allocation, and the influence of stand factors and litterfalls on soil carbon sequestration, which are critical to improve forest management strategies (e.g., adjustment of species composition and forest structure) to increase the future ability of forest carbon sequestration.

从文化传播的角度探讨如何在大学英语教学中通过多媒体网络技术引入文化的概念和内容,革新教学观念,促进和提高教学质量.

本文利用1987-2012年的数据，首先对北京市FDI的资本效应和技术溢出效应分别进行了分析，然后运用分布滞后模型对北京市产业结构和外商直接投资之间的关系进行了实证研究，并得出相关结论。

汉语句子中诸多动词如何翻译一直是英语学习者的难题,本文通过具体例句的翻译,总结了汉译英过程中汉语动词翻译的主要三个方法—介词法,现在分词法,过去分词法,本文是对汉语翻译的有益的补充,帮助语言学习者快速了解英汉差异,掌握正确的翻译技巧.

写作是检验学生语言综合应用能力的重要方法，因此如何提高学生的写作能力一直受到研究者的关注。在线评分系统的出现在一定程度上解决了教师需要大量批改作文的难题，同时教师也可根据系统提供的信息追踪学生的进步。通过在线评分系统，学生可以得到即时评分，根据系统提示不断修改自己的作文，并使用系统提供的题目进行更多的写作训练。在线评分系统的应用对教师的英语写作教学起到积极的辅助作用，并极大地促进学生自觉学习的积极性。

小班面授作为大学英语听说课的延伸和补充环节受到教师和学生的重视,它是当前各高校相应教育部号召充分利用计算机或互联网等现代科技开展学生自主学习的新形势下,为了弥补人机对话不足、确实保障和检测自主学习效果而设计的一种教学模式。本研究以交际教学理论和大学英语《课程要求》(2007年版)为依据,结合北京林业大学的大学英语教学实践,对小班面授这种教学模式的内容、方法和手段以及其在培养学生自主学习能力方面的作用进行了有益的探索和实践。

词汇是建筑语言大厦的混凝土。它和语音、语法共同构建了语言的三大要素。对于词汇学习和词汇教学,语言学家和教师都非常重视,在这方面做了很多研究和探索。其中对词块和语块的研究更为突出,本文通过对近年来国内发表的相关文章的研究,总结出国内词块语块研究的特点,并分析其在实际教学中的应用价值和意义,以促进更深刻的研究。