Large-scale patterns of understory biomass and its allocation across China's forests

Dynamic patterns and drivers of carbon accrual under different forest restoration approaches

Forest restoration represents a critical nature-based solution for climate change mitigation through enhanced carbon accumulation. While recognized for its ecological potential, the temporal trajectories of carbon accumulation across restoration approaches and their underlying mechanisms remain poorly quantified. This study analyzes multi-decadal (26 years) of carbon storage dynamics within a chronosequence framework to elucidate the mechanisms linking carbon accumulation patterns with drivers and management legacies. Restoration strategies diverged markedly: old-growth forests (OF; ≥40 years old in 1990; n = 25) sustained persistent carbon accumulation, whereas secondary forests (SF; <40 years old in 1990; n = 30) protection exhibited marked temporal variability in carbon gain and loss. Reforestation (RF, n = 30) yields 2.2-13.5 times higher carbon gains (1.3-2.7 vs 0.2-0.6 Mg C ha-1 yr-1) than natural recovery (NR, n = 50) in regions in which forests have been removed. Structural equation modeling (SEM) revealed initial C stocks emerged as the most important regulators of changes in carbon stocks (ΔC stocks) when considering direct and indirect effects (p < 0.001). Tree diversity (species richness) and stand structure attributes (stand density in terms of tree per ha, age and tree size) (p < 0.05) exhibited temporal divergence in both effect size and relevance on carbon accumulation. Notably, tree size effects displayed context-dependent reversals: correlations with ΔC stocks shifted from positive to negative when baseline stocks exceeded 23.05 Mg C ha-1. These results underscore the optimization of carbon accumulation requires targeted strategies aligned with conservation priorities and restoration objectives.

Biomass allocation between reproductive and vegetative organs of Artemisia along a large environmental gradient

BACKGROUND

Biomass allocation reflects functional tradeoffs among plant organs and thus represents life history strategies. However, little is known about the patterns and drivers of biomass allocation between reproductive and vegetative organs along large environmental gradients. Here, we examined how environmental gradients affect biomass and the allocation between reproductive and vegetative organs. We also tested whether the allocation patterns conform optimal or allometric partitioning theory.

METHODS

We collected 22 Artemisia species along a large environmental gradient in China and measured reproductive (infructescences including seeds) and vegetative (leaves, stems and roots) mass for each plant. We then used standardized major axes regressions to quantify the relationships between reproductive and vegetative organs and linear mixed-effect models to examine the effect of environmental gradients (climate and soil) on biomass allocation patterns.

RESULTS

We found significant negative correlations between total biomass of Artemisia and the first principal component of climate, an axis that was negatively correlated with temperature and precipitation. Overall, there were significant isometric relationships between reproductive and vegetative mass. In addition, the ratio of reproductive to vegetative mass increased with the second principal component of climate (representing climate variability), but decreased with the second principal component of soil (representing bulk density and available water capacity). These patterns were consistent at the individual and interspecific levels, but were mixed at the intraspecific level.

CONCLUSIONS

Our findings of the plastic responses of biomass allocation to environmental gradients support the optimal partitioning theory (OPT). The isometric relationships between reproductive and vegetative organs indicate that plant growth and reproduction are intricately linked. Furthermore, the plasticity of biomass ratios of reproductive to vegetative organs to climate variability and soil physical properties suggests that the flexible allocation between growth and reproduction is crucial for successful adaptation to diverse habitats.

Biomass Allocation in Gentianella turkestanorum is Driven by Environmental Factors and Functional Traits

Exploring the elevation distribution characteristics, biomass allocation strategies, and the effects of elevation, soil factors, and functional traits on the biomass of Gentianella turkestanorum (Gand.) Holub is of great significance for the production, development, utilization, and protection of the medicinal material resources. In this study, we investigated the biomass and functional traits of the root, stem, leaf, and flower of G. turkestanorum, analyzing their elevation distribution patterns, allometric growth trajectories, and their correlations. The results showed that the biomass of different organs of G. turkestanorum decreases with increasing elevation, and the belowground biomass/aboveground biomass increases with elevation. The flower biomass accounts for 59.24% of the total biomass, which was significantly higher than that of other organs. G. turkestanorum biomass follows the optimal allocation theory, adopting a 'pioneering' growth strategy at low elevations and a 'conservative' strategy at high elevations. Chlorophyll content and leaf thickness of G. turkestanorum were positively correlated with elevation, but leaf dry matter content and the number of flowers were negatively correlated with elevation. Compared to functional traits, elevation and soil factors have a stronger explanatory power regarding the biomass of G. turkestanorum. Elevation, soil moisture content, pH, available phosphorus, total nitrogen, and ammonium nitrogen significantly affect the biomass of G. turkestanorum, with only pH showing a positive correlation with biomass. Among these factors, elevation, soil moisture content, and pH significantly impact the accurate prediction of G. turkestanorum biomass. The number of flowers, crown width, root length, root diameter, and leaf dry matter content all have a significantly positive correlation with the biomass of G. turkestanorum, with the number of flowers and root diameter making significant contributions to the accurate prediction of biomass. Elevation can directly affect the biomass of G. turkestanorum and can also indirectly affect it through other pathways, with the direct effect being greater than the indirect effect.

Optimization of vegetation carbon content parameters and their application in carbon storage estimation in China

As a key parameter for C pool and flux assessments, vegetation carbon (C) content can be used in ecological models to predict climate-induced changes in the C sequestration capacity of vegetation. However, the differences in methods for upscaling C content from the organ to the community scale and their impact on regional C stock estimates have been ignored. Based on a comprehensive community structure survey of 72 typical natural ecosystems in China and 27,905 measured samples of plant organs (leaves, twigs, trunks, and roots), we first quantified the differences among scaling-up methods for vegetation C content. These methods included the community or dominant species-weighted mean, geometric mean, arithmetic mean, and traditional empirical coefficients (45 % and 50 %), and their impact on C storage estimation at the regional scale. Comparing the accuracy, variability, and response patterns of the different scaling-up methods, the dominant C species biomass-weighted mean (CDWM) method had the highest similarity to the community-weighted C mean (CCWM) method. Concerning vegetation C storage estimation in China's natural terrestrial ecosystems, the relative errors of the other methods ranged from -2.6 % to 8.22 % compared with that of the CCWM method (18.39 Pg C). The empirical coefficients had the highest uncertainty, with a 45 % empirical coefficient underestimating the vegetation C stock by 2.60 %, and a 50 % empirical coefficient overestimating it by 8.22 %. The CDWM method proposed here has high reliability for C storage estimation (overestimated by only 0.44 %), making it a preferable sampling and scaling-up method for regional C content and stock assessment. Additionally, our study provided the C content of plant organs for China's provinces and typical vegetation types based on the CCWM, which could be used for regional C stock assessment and C cycle models.

Understory vegetation diversity patterns of Platycladus orientalis and Pinus elliottii communities in Central and Southern China

As a vital component of arbor forests, understory vegetation serves as an essential buffer zone for storing carbon due to its strong capacity for community regeneration. This study aimed to identify the diversity pattern and construction mechanism of Platycladus orientalis and Pinus elliottii understory vegetation based on large-scale sample surveys. The Bayesian Information Criterion value of species abundance distribution (SAD) indicated that the Zipf and Zipf-Mandelbrot models were the best-fitting models. The SAD and gambin fitting results suggested that the Pi. elliottii community had a more balanced structure, with most species being relatively abundant. The multiple regression tree model detected four and six indicator species in P. orientalis and Pi. elliottii communities, respectively. The α-diversity index increased with a rise in altitude and showed a wavy curve with latitude. Linear regression between the β diversity and environmental and geographic distance indicated that the P. orientalis and Pi. elliottii understory communities tended to be dominated by different ecological processes. The partition of β diversity indicated that both communities were dominated by turnover processes, which were caused by environmental classification or spatial constraints. This study helped to understand the diversity maintenance in the P. orientalis and Pi. elliottii understory vegetation communities, and will benefit for diversity restoration and conservation of pure conifer forests.

Precipitation Dominates the Allocation Strategy of Above- and Belowground Biomass in Plants on Macro Scales

The allocation of biomass reflects a plant's resource utilization strategy and is significantly influenced by climatic factors. However, it remains unclear how climate factors affect the aboveground and belowground biomass allocation patterns on macro scales. To address this, a study was conducted using aboveground and belowground biomass data for 486 species across 294 sites in China, investigating the effects of climate change on biomass allocation patterns. The results show that the proportion of belowground biomass in the total biomass (BGBP) or root-to-shoot ratio (R/S) in the northwest region of China is significantly higher than that in the southeast region. Significant differences (p < 0.05) were found in BGBP or R/S among different types of plants (trees, shrubs, and herbs plants), with values for herb plants being significantly higher than shrubs and tree species. On macro scales, precipitation and soil nutrient factors (i.e., soil nitrogen and phosphorus content) are positively correlated with BGBP or R/S, while temperature and functional traits are negatively correlated. Climate factors contribute more to driving plant biomass allocation strategies than soil and functional trait factors. Climate factors determine BGBP by changing other functional traits of plants. However, climate factors influence R/S mainly by affecting the availability of soil nutrients. The results quantify the productivity and carbon sequestration capacity of terrestrial ecosystems and provide important theoretical guidance for the management of forests, shrubs, and herbaceous plants.

Prediction of the potentially suitable areas of Ligularia virgaurea and Ligularia sagitta on the Qinghai-Tibet Plateau based on future climate change using the MaxEnt model

Ligularia virgaurea and Ligularia sagitta are two species of poisonous plants with strong invasiveness in natural grasslands in China that have caused considerable harm to animal husbandry and the ecological environment. However, little is known about their suitable habitats and the key environmental factors affecting their distribution. Although some studies have reported the distributions of poisonous plants on the Qinghai-Tibet Plateau (QTP) and predicted their potential distributions at local scales in some regions under climate change, there have been few studies on the widespread distributions of L. virgaurea and L. sagitta. In this study, we recorded 276 and 118 occurrence points of L. virgaurea and L. sagitta on the QTP using GPS, and then used the MaxEnt model to predict the distribution of suitable habitats. Results showed that (1) under current climate conditions, L. virgaurea and L. sagitta are mainly distributed in southern Gansu, eastern Qinghai, northwestern Sichuan, eastern Tibet, and southwestern Yunnan, accounting for approximately 34.9% and 39.8% of the total area of the QTP, respectively; (2) the main environmental variables affecting the distribution of suitable habitats for L. virgaurea and L. sagitta are the Human Footprint Index (52.8%, 42.2%), elevation (11%, 4.4%), soil total nitrogen (18.9%, 4.2%), and precipitation seasonality (5.1%, 7.3%); and (3) in the future, in the 2050s and 2070s, the area of habitat of intermediate suitability for L. virgaurea will spread considerably in northwest Sichuan, while that of high suitability for L. sagitta will spread to eastern Tibet and western Sichuan.

Forest understory vegetation study: current status and future trends

Understory vegetation accounts for a large proportion of floral diversity. It provides various ecosystem functions and services, such as productivity, nutrient cycling, organic matter decomposition and ecosystem self-regeneration. This review summarizes the available literature on the current status and progress of the ten most studied branches of understory vegetation on both its structural and functional aspects based on global climate change and forest management practices. Future research directions and priorities for each branch is suggested, where understory vegetation in response to the interplay of multiple environmental factors and its long-term monitoring using ground-based surveys combined with more efficient modern techniques is highlighted, although the critical role of understory vegetation in ecosystem processes individually verified in the context of management practices or climate changes have been extensively investigated. In summary, this review provides insights into the effective management of the regeneration and restoration of forest ecosystems, as well as the maintenance of ecosystem multilevel structures, spatial patterns, and ecological functions.