Deciduous Broadleaf Research Articles

The Impact of Bamboo (Phyllostachys edulis) Expansion on the Water Use Patterns of Broadleaf Trees

The expansion of bamboo (Phyllostachys edulis) affects the growth status of trees in colonized forests, but there has been insufficient research on changes in tree water physiology. In this study, we used stable δ2H, δ18O, and 13C isotope ratios to analyze the water sources and water use efficiency (WUE) of bamboo, deciduous broadleaf trees (Alniphyllum fortunei), and evergreen broadleaf trees (Machilus pauhoi and Castanopsis eyrei) in a bamboo-expended broadleaf forest (BEBF), a bamboo-absent broadleaf forest (BABF), and a bamboo forest (BF). We found that the expansion of bamboo had no significant effect on the water sources and WUE of deciduous broadleaf trees, but altered the water sources of evergreen broadleaf trees. During the growing season, evergreen broadleaf trees decrease their uptake fractions of surface soil water by 7.1% to 9.6% and increased their uptake fractions of middle soil water by 5.8%~9.4%. Conversely, during the non-growing season, they increased their uptake fractions of surface soil water by 11.9% and decreased their uptake fractions of deeper soil water by 5.6%~12.9%. Additionally, after expanding into broadleaf forests, bamboo increased its uptake proportion of surface and shallow soil water by 20.0% and 9.4% during the growing season. Its WUE also improved, increasing by 20.0 μmol/mol and 13.0 μmol/mol during the growing and non-growing seasons, respectively. These results indicate that as bamboo expands into broadleaf forests, it enhances its competitiveness for water resources by changing its water use strategy. Compared to deciduous broadleaf trees, evergreen broadleaf trees exhibit more flexible water use strategies under the conditions of bamboo expansion. Our research reveals, for the first time, how broadleaf trees adjust their water use strategies in response to bamboo expansion, and uncovers the mechanisms behind bamboo expansion into evergreen broadleaf forests from the perspective of water use strategies. This will aid future forest management under the conditions of bamboo expansion.

Relationship Between Evolutionary Diversity and Aboveground Biomass During 150 Years of Natural Vegetation Regeneration in Temperate China.

While the link between plant species diversity and biomass has been well-studied, the impact of evolutionary diversity on community biomass across long timescales or ongoing change remains a subject of debate. We elucidated the association between evolutionary diversity and community aboveground biomass (AGB) using an ideal experimental system with over 150-year history of natural vegetation regeneration. Higher phylogenetic diversity facilitated the sampling effect under the influence of environmental filtering, and caused an increase in AGB. Phylogenetic structure varied from aggregation to dispersion during the later period of vegetation recovery (70-150 years), which was correlated with increases in niche complementarity and increasing AGB. Woody plant evolutionary diversity was used as a key to predict the relationship between vegetation recovery and AGB, with a total explanatory power of ~84.7%. Mixed forests composed of evergreen conifers and deciduous broadleaf forests had higher carbon sequestration potential than that of pure forests, which is advantageous for increasing top-stage AGB. This research expands our knowledge of the causes and effects of biodiversity and ecosystem function dynamics over time and space, which is important for accurately predicting future climate change effects.

Analysis of changes before and after forest fires with LAI, NDVI and ET time series: Focusing on major forest fires in Korea

This study investigates the changes caused by forest fires and the following recovery processes, targeting four forest fire sites in Korea. The time series of two vegetation indices, leaf area index (LAI) and normalized difference vegetation index (NDVI) are investigated along with evapotranspiration (ET) time series for the study objectives. The analysis results show that LAI is most sensitive to burn severity and burned area with its change ranging from 40 % to 70 %, while the changes of NDVI and ET remain 30 % and 20 %, respectively, regardless of forest fire sites. The recovery time from forest fire also varies according to indices: the recovery time is estimated to be about 15 years when considering LAI and NDVI, while just 5 years when considering ET. Overall, LAI seems better to analyze the change in vegetation before and after forest fires. Different vegetation shift patterns after the forest fire are also noticed, mostly from evergreen needleleaf trees to deciduous broadleaf trees. However, it is also found that bad soil fertility condition and artificial afforestation help to maintain the evergreen needleleaf trees after the forest fire.

Spatiotemporal variability of leaf critical senescence age across northern lands and its key drivers

Leaf senescence, a pivotal phenological event, signifies the aging of vegetation canopies and triggers abrupt shifts in various biogeochemical processes. However, the spatiotemporal pattern of leaf senescence age and its primary driving factors across northern lands remains unclear. In this study, we introduced a concept termed leaf critical senescence age (CSA) to characterize the initiation of senescence stage, which quantifies the time span between the onset dates of vegetation growth and senescence. Then, utilizing long-term remote sensing vegetation index data, we investigated the spatiotemporal variations of leaf CSA over northern lands (>30°N). Spatially, leaf CSA displayed extensive variability (ranging from 42 to 263 days), with an average of 146 ± 32 days. Deciduous broadleaf forests exhibited the longest CSA (177 ± 28 days), while shrublands demonstrated the shortest (121 ± 22 days). Temporally, most plant functional types experienced a reversal in leaf CSA trends around 2010, leading to the contrasting trends between 1982–2010 (+0.21 days/year) and 2010–2015 (−2.36 days/year) across northern lands. Further random-forest regression and partial correlation analysis together indicated that temperature was the dominant factor driving spatiotemporal variations in leaf CSA. These findings suggest that climate warming is reshaping the geographical pattern of leaf senescence age, posing great uncertainty to future projections of terrestrial feedback to climate change.

Canopy temperature dynamics are closely aligned with ecosystem water availability across a water- to energy-limited gradient

Canopy temperature (Tc) plays an important role in regulating the rates of mass and energy fluxes at the leaf surface. Better understanding of the relationship between Tc and water availability may enable more accurate monitoring of ecosystem functioning in a changing climate. Here, we used high spatiotemporal resolution thermal infrared cameras deployed at three eddy covariance flux tower sites along a water- to energy-limited gradient – including a predominately water-limited grassland/shrubland site, a seasonally water-limited evergreen needleleaf forest, and a predominantly energy-limited deciduous broadleaf forest – to determine Tc seasonality and its relationship with gross primary productivity (GPP) and environmental drivers. We found midday Tc was generally warmer than air temperature (Tair) during the growing season (Tc:Tair slope: 1.14–1.27) for all sites. Water-limited sites exhibited higher positive Tc deviations from Tair (2.30 ± 0.06 °C) compared to the energy-limited site (1.29 ± 0.09 °C) partly due to their reduced latent heat fluxes during water-limited periods. We further found that the Tc:Tair slope increased with site aridity, namely for 1.14 slope for the grassland, 1.15 for the evergreen forest, and 1.27 for the broadleaf forest. Peak GPP occurred when Tc was higher than Tair across all sites, with peak GPP at the grassland site occurring at +1.1 °C (Tc-Tair) and peak GPP at the broadleaf evergreen site occurring at +2.2 °C (Tc-Tair). Tc-Tair dynamics were mostly associated with soil water content at water-limited sites where canopies undergo a substantial cooling during the transition from dormancy to the peak GPP, while net radiation played a crucial role at the energy-limited site where the canopy heats up compared to Tair over the same phenological transition. Our findings provide novel insights into Tc-ecosystem water availability links, highlighting the drivers of Tc-Tair across diverse ecosystems in various phenological stages, which has implications for ecosystem management in a changing climate.

Spatial Pattern of Living Woody and Coarse Woody Debris in Warm-Temperate Broad-Leaved Secondary Forest in North China.

The investigation into the spatial distribution of living woody (LWD) and coarse woody debris (CWD) within forests represents a fundamental methodology for probing the inherent mechanisms governing coexistence and mortality within forest ecosystems. Here, a complete spatial randomness (CSR) null model was employed to scrutinize the spatial pattern, while canonical correspondence analysis (CCA) and the Torus-translation test (TTT) were utilized to elucidate the distribution patterns of LWD and CWD within warm-temperate deciduous broadleaf secondary forests in Dongling Mountains plot, northern China. The results reveal that both LWD and CWD exhibit an aggregated distribution as the predominant pattern in the Dongling Mountains plot, with the proportion and intensity of aggregation diminishing as spatial scale increases. Specifically, the aggregation intensity g0-10 demonstrates a significant negative correlation with abundance and maximum diameter at breast height (DBH). Notably, the g0-10 of LWD manifests a stronger correlation with the maximum DBH, whereas the g0-10 of CWD exhibits a greater association with the mortality rate. CCA outcomes suggest that elevation, convexity, and aspect significantly impact LWD distribution, whereas CWD distribution shows substantial negative correlations with elevation, convexity, slope, and aspect. TTT findings indicate that ecosystems characterized by a substantial presence of LWD also display a notable prevalence of CWD. Additionally, the majority of species exhibit no habitat preference, displaying neutral habitat connections and low ecological niche differentiation within the sampled plot.

Investigating the temporal lag and accumulation effect of climatic factors on vegetation photosynthetic activity over subtropical China

Monitoring vegetation photosynthesis in China’s subtropical regions using remote sensing is challenging because of the complex ecosystems and climate variability. Previous studies often pay less attention on the influence of multiple climatic factors on the temporal effects (lag and accumulation) of vegetation photosynthesis, thereby underestimating their impact. This study utilizes a dataset comprising Solar-induced chlorophyll fluorescence (SIF) data (GOSIF product), MODIS Land Cover product (MCD12C1), and various climatic variables. Analytical methods including Theil-Sen Median trend analysis, the Mann-Kendall test, partial correlation analysis, and the optimal parameter-based geographical detector (OPGD) model were employed to explore the temporal dynamics of subtropical vegetation SIF responses to climatic factors and to identify their climate drivers in subtropical China. The study findings indicate that (1) vegetation photosynthesis, as indicated by SIF, exhibited an increasing trend in the majority of Chinese subtropical regions, which constitute over 80 % of the study area, with particularly pronounced enhancements in the southern and central western parts of the Chinese subtropics. (2) Soil moisture primarily exhibits lag effects on SIF, particularly in evergreen needleleaf forests, deciduous broadleaf forests, and mixed forests, whereas temperature does not exhibit significant temporal effects. Solar radiation and vapor pressure deficits impact SIF through both lag and accumulation effects. Under the lag and accumulation effects, the proportion of significant correlations between climatic factors and vegetation SIF increases by 36.71 % ∼ 43.8 %, excluding temperature. (3) Temperature is the dominant factor affecting vegetation SIF, particularly in the evergreen needleleaf forest. Interactions between climatic factors have a significantly stronger influence on SIF than individual factors. Notably, the explanatory power of the vapor pressure deficit increases substantially when it interacts with other factors. Studying the lag and accumulation effects of climatic factors on photosynthesis aids in accurately predicting vegetation responses to climate change, thereby improving the accuracy of global carbon cycle models and guiding the development of carbon sequestration management strategies.

Wood decay and Norway spruce vulnerability to wind-inflicted mortality in monospecific and mixed stands in hemiboreal forests

Pathogen-caused stem and root decay are becoming increasingly common in Norway spruce (Picea abies (L.) H. Karst) which is believed to contribute to greater stand instability and susceptibility to wind-inflicted damage. Thus, this study aims to assess the effect of root and stem decay on Norway spruce vulnerability to wind-inflicted mortality in monospecific and mixed stands, to widen our base of knowledge on potentially more resilient spruce forest management approaches in hemiboreal forest zone. In this study we used data from: i) the National Forest inventory (NFI), ii) 34 observation plots established in wind-affected stands, iii) two transects (9200 m long, 36.8 ha inspection area combined), iv) and monospecific spruce plantation thinning experiment (five thinning intensities with two repetitions of each) affected by wind. We found that the total mortality of spruce during the NFI four five-year re-measurement cycles (2003–2007, 2008–2012, 2013–2017, 2018–2022) was 2.28 %, during which the main disturbance-causing agents were wind at 0.86 %, pests at 0.41 %, intra/interspecific competition at 0.37 %, and diseases at 0.36 %. NFI data-based multinomial logistic regression model revealed that the probability of wind-inflicted spruce mortality is dictated by soil moisture regime, stand age, stand stocking level, and tree decay presence. Results from the 34 established observation plots show that wood decay is a potential risk factor associated with wind damage occurrence in spruce stands. In a spruce stand, when a group of trees are damaged by wind the proportion of undecayed trees increases. Whereas a single tree is more likely to be attributed to decay caused wind damage.Results point towards deciduous broadleaf admixture having a positive effect on mitigating wind damage among non-decayed spruce trees: however, decayed trees, are more likely to be affected in such stands. The thinning experiment portion of this study suggests that increasingly intensive thinning in monospecific spruce stands will lead to an increasing spread of root and stem decay and thus the risk of wind damage. Therefore, from this perspective, the main goal is to reduce the root and stem decay presence in the stand and thus increase wind stability. We suggest further research to be directed into finding the optimal initial spruce seedlings density with a combination of coniferous and deciduous broadleaf species in order to mitigate root and stem decay presence and wind-inflicted spruce mortality in the forest stands.

Coordination of water use strategies and leaf economic traits in coexisting exotic and native woody species from evergreen and deciduous broadleaf forests

The leaf economics spectrum (LES) describes the covariation of traits relevant for carbon and nutrient economy in different plant species. However, much less is known about the correlation of LES with leaf water economy, not only because some woody species do not follow the rules, but also because they are rarely tested on the widespread, non-native, fast-growing trees. We hypothesized that fast-growing exotic species that spread on the fast side of the LES coordinate their water-use strategies (WUS) to maintain rapid growth, and that the pattern of coordination differs between evergreen and deciduous forests. Using 4 exotic and 4 native species from evergreen and deciduous broadleaf forests in China, we measured 17 traits of LES and WUS and analyzed their functional roles in different species groups. Our results suggest that LES plays a more important role in the coexistence of species within a community, while WUS contributes more to the distribution of species across different regions. The multidimensional coordination of LES and WUS could better explain the growth and distribution of different plant species and shed light on the coexistence of species from different forest types, especially fast-growing woody exotics.

Understory bamboo removal impacts on woody seedling regeneration in forest ecosystems: a meta-analysis

BackgroundTree seedling regeneration in forests is often hindered by the competitive influence of dense understory bamboo competition. While localized studies have investigated the ecological effects of understory bamboo removal on tree seedlings, a comprehensive analysis at a global scale is lacking. In this meta-analysis, we synthesized 497 observations from 32 experimental studies to assess the overall effects of understory bamboo removal on tree seedling regeneration.ResultsThe results showed that understory bamboo removal enhanced tree seedling survival, emergence, and height growth. However, the response of tree seedlings to bamboo removal varied depending on regeneration characteristics, forest types, and bamboo removal methods. Specifically, understory bamboo removal increased the survival rate of deciduous seedlings but had no significant effect on evergreen seedlings. For regeneration stages, bamboo removal had a significant positive effect on the survival rate of saplings but not on seedlings. Regarding differences across forest types, bamboo removal significantly increased the emergence density of seedlings in deciduous broadleaf forests but had a significant negative influence in evergreen and mixed evergreen-deciduous forests. Additionally, natural removal of bamboo showed a greater positive effect on seedlings than bamboo removal by artificial or animal gnawing methods. Furthermore, we found that the duration of bamboo removal, mean annual temperature, precipitation of seasonality, and soil pH strongly influenced the response ratios of tree seedling regeneration.ConclusionsOur meta-analysis demonstrates the significant effects of understory bamboo removal on multiple facets of tree seedling dynamics across different regeneration characteristics, forest types, and bamboo removal methods. In addition, our study emphasizes that the duration of bamboo removal, climate, and soil pH have a critical effect on tree seedling regeneration. Our findings elucidate the effects of understory bamboo removal on seedling regeneration, offering robust scientific insights for sustainable forest management.

Hyperspectral Leaf Area Index and Chlorophyll Retrieval over Forest and Row-Structured Vineyard Canopies

As an unprecedented stream of decametric hyperspectral observations becomes available from recent and upcoming spaceborne missions, effective algorithms are required to retrieve vegetation biophysical and biochemical variables such as leaf area index (LAI) and canopy chlorophyll content (CCC). In the context of missions such as the Environmental Mapping and Analysis Program (EnMAP), Precursore Iperspettrale della Missione Applicativa (PRISMA), Copernicus Hyperspectral Imaging Mission for the Environment (CHIME), and Surface Biology Geology (SBG), several retrieval algorithms have been developed based upon the turbid medium Scattering by Arbitrarily Inclined Leaves (SAIL) radiative transfer model. Whilst well suited to cereal crops, SAIL is known to perform comparatively poorly over more heterogeneous canopies (including forests and row-structured crops). In this paper, we investigate the application of hybrid radiative transfer models, including a modified version of SAIL (rowSAIL) and the Invertible Forest Reflectance Model (INFORM), to such canopies. Unlike SAIL, which assumes a horizontally homogeneous canopy, such models partition the canopy into geometric objects, which are themselves treated as turbid media. By enabling crown transmittance, foliage clumping, and shadowing to be represented, they provide a more realistic representation of heterogeneous vegetation. Using airborne hyperspectral data to simulate EnMAP observations over vineyard and deciduous broadleaf forest sites, we demonstrate that SAIL-based algorithms provide moderate retrieval accuracy for LAI (RMSD = 0.92–2.15, NRMSD = 40–67%, bias = −0.64–0.96) and CCC (RMSD = 0.27–1.27 g m−2, NRMSD = 64–84%, bias = −0.17–0.89 g m−2). The use of hybrid radiative transfer models (rowSAIL and INFORM) reduces bias in LAI (RMSD = 0.88–1.64, NRMSD = 27–64%, bias = −0.78–−0.13) and CCC (RMSD = 0.30–0.87 g m−2, NRMSD = 52–73%, bias = 0.03–0.42 g m−2) retrievals. Based on our results, at the canopy level, we recommend that hybrid radiative transfer models such as rowSAIL and INFORM are further adopted for hyperspectral biophysical and biochemical variable retrieval over heterogeneous vegetation.

Central China as LGM plant refugia: Insights from biome reconstruction for palaeoclimate information

The demonstration of survival of forest stands in relatively stable refugia during cold glacial stages has offered an increased understanding of the response of vegetation to climate change, but also provides insight into considerations for the conversation of biodiversity hotspots. However, refugia studies in China remain in question due to the lack of plant macrofossils, especially those of endemic and relict species. Palynology, while more broad brush, provides a method for exploring whether refugia occur, and can provide some details of palaeovegetation composition and temporal dynamics. Here, three pollen records derived from subalpine wetlands in central China, spanning the Last Glacial Maximum (LGM), have been coupled with biome and mean annual precipitation (MAP) reconstructions to identify the presence of trees that endured cold climate. The results indicated that some forest, including temperate deciduous broadleaf forest and cool mixed forest, survived the LGM at the three locations, and was thus at odds with the hypothesis that forests were replaced by herbs and grasses in central China at that time. Refugia favored by protection from cold air drainage and the availability of adequate water can explain the survival of the trees during otherwise harsh episodes. Our findings are consistent with other records from central China that argue for tree dominated refugia during the LGM.

Temperature variations impacting leaf senescence initiation pathways alter leaf fall timing patterns in northern deciduous forests

Simulating the timing of leaf fall in large scale is crucial for accurate estimation of ecosystem carbon sequestration. However, the limited understanding of leaf senescence mechanisms often impedes the accuracy of simulation and prediction. In this study, we employed the advanced process-based models to fit remote sensing-derived end dates of the growing season (EOS) across deciduous broadleaf forests in the Northern Hemisphere, and revealed the spatial pattern associated with two leaf senescence pathways (i.e., either photoperiod- or temperature- initiated leaf senescence) and their potential effects on EOS prediction. The results show that the pixel-specific optimum models effectively fitted all EOS time series. Leaf senescence in 67.6 % and 32.4 % of pixels was initiated by shortening daylength and declining temperature, respectively. Shortening daylength triggered leaf senescence occurs mainly in areas with shorter summer daylength and/or warmer autumns, whereas declining temperature induced leaf senescence appears primarily in areas with longer summer daylength and/or colder autumns. The strong dependence of leaf senescence initiation cues on local temperature conditions implies that the ongoing increase in autumn temperature has the potential to alter the leaf senescence initiation, shifting from temperature cues to photoperiod signals. This shift would occur in 26.2–49.6 % of the areas where leaf senescence is initiated by declining temperature under RCP 4.5 and 8.5 scenarios, while forest areas where leaf senescence is induced by shortening daylength may expand northward. The overall delaying of the currently predicted EOS would therefore slow down by 4.5–10.3 % under the two warming scenarios. This implies that the adaptive nature of plants will reduce the overestimation of changes in carbon exchange capacity between ecosystems and atmosphere. Our study offers novel insights into understanding the mechanism of leaf senescence and improving the estimation of autumn phenology and ecosystem carbon balance in the deciduous broadleaf forests.

Spatiotemporal characteristics of Net Ecosystem Exchange in the Beijing-Tianjin sand source region and its response to drought

In the context of global change, the carbon budget in arid and semi-arid regions have changed significantly. Understanding these dynamic features and their response to climate change is essential for regional carbon cycle assessments. The Beijing-Tianjin Sand Source Region (BTSSR), a significant ecological project in China, is central to studies on carbon budget dynamics. While global change intensifies, understanding its carbon budget response to drought is crucial. By integrating data from the Net Ecosystem Exchange (NEE) and the Standardized Precipitation Evapotranspiration Index (SPEI), we analyzed the spatiotemporal attributes of NEE in this region and its response to drought. The BTSSR is currently in a carbon sink state, with the mean NEE being −45.13 gCm−2 and a rate of change at −0.005 gCm−2a-1. The maximum carbon sink occurs during the summer, whereas the winter is characterized by a net release of carbon to the atmosphere. In terms of spatial variation, the NEE shifts from positive to negative from southeast to northwest across the region. The impact of drought on summer NEE is notably significant, with the correlation and sensitivity being −0.717 (p < 0.05) and −3.911, respectively. As drought intensity increases, NEE changes from negative to positive, transforming BTSSR into a carbon source. NEE responded most significantly to strong drought and was less affected by light drought. The NEE of BTSSR showed a significant short-term response to drought, with a lag of 1–4 months. Considering different vegetation types, the temperate desert’s NEE is most significantly affected by drought and is the most sensitive, with correlation and sensitivity values of −0.841 (p < 0.05) and −12.570, respectively. In contrast, the warm temperate deciduous broadleaf forest shows stronger resistance to drought. This study elucidates how the carbon budget of different vegetation types in a typical ecological engineering area changes under the background of climate change and human activities, and contributes to the understanding of the impacts of drought events on the carbon cycle of different vegetation types, as well as the response of the latter to the former, especially the lagged response. It provides different perspectives for the subsequent ecological engineering construction.

Disparities in tree mortality among plant functional types (PFTs) in a temperate forest: Insights into size-dependent and PFT-specific patterns

Tree mortality significantly influences forest structure and function, yet our understanding of its dynamic patterns among a range of tree sizes and among different plant functional types (PFTs) remains incomplete. This study analysed size-dependent tree mortality in a temperate forest, encompassing 46 tree species and 32,565 individuals across different PFTs (i.e., evergreen conifer vs. deciduous broadleaf species, shade-tolerant vs. shade-intolerant species). By employing all-subset regression procedures and logistic generalized linear mixed-effects models, we identified distinct mortality patterns influenced by biotic and abiotic factors. Our results showed a stable mortality pattern in evergreen conifer species, contrasted by a declining pattern in deciduous broadleaf and shade-tolerant, as well as shade-intolerant species, across size classes. The contribution to tree mortality of evergreen conifer species shifted from abiotic to biotic factors with increasing size, while the mortality of deciduous broadleaf species was mainly influenced by biotic factors, such as initial diameter at breast height (DBH) and conspecific negative density. For shade-tolerant species, the mortality of small individuals was mainly determined by initial DBH and conspecific negative density dependence, whereas the mortality of large individuals was subjected to the combined effect of biotic (competition from neighbours) and abiotic factors (i.e., convexity and pH). As for shade-intolerant species, competition from neighbours was found to be the main driver of tree mortality throughout their growth stages. Thus, these insights enhance our understanding of forest dynamics by revealing the size-dependent and PFT-specific tree mortality patterns, which may inform strategies for maintaining forest diversity and resilience in temperate forest ecosystems.

A new computationally efficient algorithm to generate global fractional vegetation cover from Sentinel-2 imagery at 10 m resolution

ABSTRACT The multi-angle method in the pixel dichotomy model (PDM) is used to produce fine spatial resolution (FSR) products of fractional vegetation cover (FVC), which involves numerous iterative computations. This phenomenon causes a low computational efficiency for global FVC. Here, we established the multi-angle equations, and simplified the two-stream approximation method to obtain multi-angle reflectance, which calculated the KDM parameters possible. Moreover, to accelerate the calculation of parameters in the multi-angle equations, land cover data were utilized as priority knowledge, which aims to decrease iterative computations to speed up the computational speed. Finally, we proposed an accelerated pixel dichotomy coupled linear kernel-driven model (PDKDM-A). By validating PDKDM-A using field measurements and FVC products, we found that the global FVC computed for various land covers exhibited strong agreement with the field measurements. The root mean square errors (RMSEs) were consistently below 0.150, except for grasslands, croplands, and cropland/natural vegetation mosaics. When comparing FVC products on the same scale, we discovered that the RMSE was less than 0.103, except for deciduous broadleaf forests. Our study demonstrates that PDKDM-A is an efficient algorithm, with the potential to quickly generate accurate global FVC products with fine spatial resolution.

Phenology of Photosynthesis in Winter‐Dormant Temperate and Boreal Forests: Long‐Term Observations From Flux Towers and Quantitative Evaluation of Phenology Models

AbstractWe examined the seasonality of photosynthesis in 46 evergreen needleleaf (evergreen needleleaf forests (ENF)) and deciduous broadleaf (deciduous broadleaf forests (DBF)) forests across North America and Eurasia. We quantified the onset and end (StartGPP and EndGPP) of photosynthesis in spring and autumn based on the response of net ecosystem exchange of CO2 to sunlight. To test the hypothesis that snowmelt is required for photosynthesis to begin, these were compared with end of snowmelt derived from soil temperature. ENF forests achieved 10% of summer photosynthetic capacity ∼3 weeks before end of snowmelt, while DBF forests achieved that capacity ∼4 weeks afterward. DBF forests increased photosynthetic capacity in spring faster (1.95% d−1) than ENF (1.10% d−1), and their active season length (EndGPP–StartGPP) was ∼50 days shorter. We hypothesized that warming has influenced timing of the photosynthesis season. We found minimal evidence for long‐term change in StartGPP, EndGPP, or air temperature, but their interannual anomalies were significantly correlated. Warmer weather was associated with earlier StartGPP (1.3–2.5 days °C−1) or later EndGPP (1.5–1.8 days °C−1, depending on forest type and month). Finally, we tested whether existing phenological models could predict StartGPP and EndGPP. For ENF forests, air temperature‐ and daylength‐based models provided best predictions for StartGPP, while a chilling‐degree‐day model was best for EndGPP. The root mean square errors (RMSE) between predicted and observed StartGPP and EndGPP were 11.7 and 11.3 days, respectively. For DBF forests, temperature‐ and daylength‐based models yielded the best results (RMSE 6.3 and 10.5 days).

Characteristics of Bacterial Communities under Different Tree Species and Their Response to Soil Physicochemical Properties

This study investigates the structure of soil bacterial communities in the brown mountain soils beneath the deciduous broadleaf forests of Dongling Mountain and their response to soil physicochemical properties. Aiming to provide a scientific basis for soil conservation and sustainable forest development under deciduous broadleaf forests, this research utilized high-throughput sequencing technology to examine the diversity and community structure of bacteria in soil under different tree species, alongside assessing soil physicochemical properties. The results revealed significant differences in nutrient content between the 0–20 cm and 20–40 cm soil layers. Additionally, the N:P in the brown mountain soils of Dongling Mountain was found to be below the national average, indicating potential nitrogen limitation. Dominant bacterial phylum included Actinobacteria, Proteobacteria, and Acidobacteria. The study also found that soil bacterial community structure was similar under different tree species at the same depth but varied significantly with soil depth. Furthermore, redundancy analysis (RDA) showed that the available potassium (AK), total nitrogen (TN), and ammonium nitrogen (NH4+-N) significantly influenced the structural changes in the soil bacterial community. This research highlights the characteristics of soil bacterial community structure beneath deciduous broadleaf forests and its relationship with soil physicochemical properties, offering valuable insights for regional soil ecosystem conservation and forest management.

Understanding vegetation phenology responses to easily ignored climate factors in china's mid-high latitudes

Previous studies have primarily focused on the influence of temperature and precipitation on phenology. It is unclear if the easily ignored climate factors with drivers of vegetation growth can effect on vegetation phenology. In this research, we conducted an analysis of the start (SOS) and end (EOS) of the growing seasons in the northern region of China above 30°N from 1982 to 2014, focusing on two-season vegetation phenology. We examined the response of vegetation phenology of different vegetation types to preseason climatic factors, including relative humidity (RH), shortwave radiation (SR), maximum temperature (Tmax), and minimum temperature (Tmin). Our findings reveal that the optimal preseason influencing vegetation phenology length fell within the range of 0–60 days in most areas. Specifically, SOS exhibited a significant negative correlation with Tmax and Tmin in 44.15% and 42.25% of the areas, respectively, while EOS displayed a significant negative correlation with SR in 49.03% of the areas. Additionally, we identified that RH emerged as the dominant climatic factor influencing the phenology of savanna (SA), whereas temperature strongly controlled the SOS of deciduous needleleaf forest (DNF) and deciduous broadleaf forest (DBF). Meanwhile, the EOS of DNF was primarily influenced by Tmax. In conclusion, this study provides valuable insights into how various vegetation types adapt to climate change, offering a scientific basis for implementing effective vegetation adaptation measures.

Seasonal patterns of nonstructural carbohydrate storage and mobilization in two tree species with distinct life-history traits.

Nonstructural carbohydrates (NSC) are essential for tree growth and adaptation, yet our understanding of the seasonal storage and mobilization dynamics of whole-tree NSC is still limited, especially when tree functional types are involved. Here, Quercus acutissima Carruth. and Pinus massoniana Lamb, with distinct life-history traits (i.e. a deciduous broadleaf species vs an evergreen coniferous species), were studied to assess the size and seasonal fluctuations of organ and whole-tree NSC pools with a focus on comparing differences in carbon resource mobilization patterns between the two species. We sampled the organs (leaf, branch, stem and root) of the target trees repeatedly over four seasons of the year. Then, NSC concentrations in each organ were paired with biomass estimates from the allometric model to generate whole-tree NSC pools. The seasonal dynamics of the whole-tree NSC of Q. acutissima and P. massoniana reached the peak in autumn and summer, respectively. The starch pools of the two species were supplemented in the growing season while the soluble sugar pools were the largest in the dormant season. Seasonal dynamics of organ-level NSC concentrations and pools were affected by organ type and tree species, with above-ground organs generally increasing during the growing season and P. massoniana roots decreasing during the growing season. In addition, the whole-tree NSC pools of P. massoniana were larger but Q. acutissima showed larger seasonal fluctuations, indicating that larger storage was not associated with more pronounced seasonal fluctuations. We also found that the branch and root were the most dynamic organs of Q. acutissima and P. massoniana, respectively, and were the major suppliers of NSC to support tree growth activities. These results provide fundamental insights into the dynamics and mobilization patterns of NSC at the whole-tree level, and have important implications for investigating environmental adaptions of different tree functional types.