Broadleaf Tree Species Research Articles

Potential Trees Species of North-East India for Dendroclimatological Studies

Many tropical trees show distinct annual ring formation as in temperate conifers, and the growth of these annual rings is used as bio-indicators of environmental changes. Dendroclimatology is the science dealing with the reconstruction of a history of past climate through dendrochronological (tree ring) analysis and assessing the effect of climatic change on tree growth. Trees are living natural archives and their growth is largely impacted by various climatic and non-climatic events occurring in the surrounding environments. In Northeast India, several conifers and broad-leaf tree species such as Abies densa, Larix griffithii, Pinus merkusii, Pinus kesiya, Pinus wallichiana, Quercus serrata, Toona ciliata and Tectona grandis have been used for tree ring-based studies. Dendrochronological studies mainly focused on the reconstruction of climate history, climate-tree growth relationship, river flow history reconstruction, inter-annual density fluctuation, and for development of climate proxies. Among these, the oldest tree ring chronology of Abies densa of 490 years (1504 to 1994) was reported from Yumthang of Sikkim. Whereas the youngest chronology of Toona ciliata of 35 years (1984 to 2018) was from Chandel district of Manipur. The knowledge derived from the detailed study of these species will help forest managers and conservationists to manage the forest in a changing environment. This paper presented dendrochronological information of different trees of northeast India based on the published literature and their possible impact on climate reconstruction through dendroclimatology. However, further potential tree species forming tree rings need to be worked out for possible climate mitigation measures of tropical trees in northeast India.

Evaluation of the effect of leaf spatial aggregation on chlorophyll content retrieval in open-canopy apple orchards

The real-world crowns of broadleaf tree species feature green leaves surrounding branches, resulting in leaf spatial aggregation effect in the crown. However, the impact of such leaf spatial aggregation on chlorophyll content retrieval has not yet been determined. This study investigated the effect of leaf spatial aggregation on chlorophyll content retrieval in two distinct apple orchards with open canopies. The “PROSPECT + LESS” model was used for canopy reflectance simulation, and 25 hyperspectral vegetation indices (VIs) were analyzed to identify universal VIs for various leaf aggregations. Sensitivity analysis was conducted to evaluate the impact of leaf aggregation on the relationships between VIs and chlorophyll content. An artificial neural network regression algorithm was used to retrieve chlorophyll content by reversing the radiative transfer model (RTMs). The results show that leaf aggregation significantly affects the relationships between VIs and chlorophyll content as a result of the variability in the ratio of photosynthetic vegetation pixels to background pixels captured by the sensor at the top of the canopy. TCARI/OSAVI was found to be resistant to confounding factors (e.g., leaf area index and dry matter content) and maintained stable relationships with chlorophyll content. Leaf spatial aggregation had a significant impact on chlorophyll content retrieval, especially when leaves were highly aggregated. In such cases, the spectral variation driven by the photosynthetic vegetation was masked by the background, leading to a large divergence between simulated and observed spectra. Low to moderate levels of leaf aggregation, on the other hand, provided accurate chlorophyll content retrieval in both apple orchards (R2 = 0.49 to 0.67). In conclusion, when using 3D RTMs to retrieve chlorophyll content, it is recommended to configure low to moderate levels of leaf aggregation to ensure high accuracy and efficiency.

Exploring the potential of machine learning for leaf angle distribution type identification from leveled digital photography: A case study for broadleaf tree and shrub species

Leaf angle distribution (LAD) is an important plant structural trait that determines radiation interception, biomass production, rainfall interception, and evapotranspiration. LAD has remained one of the most poorly constrained parameters and a major source of uncertainty in ecological models due to difficulty in quantification. In this study, we look for a simple, affordable way to estimate leaf angle distribution type by anyone, anywhere. For the first time, we test the possibility of determining LAD type from photographs (816 in total) of single plants from various broadleaf tree and shrub species taken from field works. We used Google's TensorFlow and built models using a convolutional neural network to classify these images by LAD type. The best results, training accuracy of 95% and validation accuracy of 91%, were acquired using the two most distinct LAD types – planophile and erectophile. The accuracy decreased with the addition of categories, as expected. However, our results indicate that the involvement of machine learning may indeed hold the potential to remove the current bottleneck in retrieving the information on LAD.

Broadleaf tree phenology and springtime wildfire occurrence in boreal Canada.

Although broadleaf tree species of the boreal biome have a lower flammability compared to conifers, there is a period following snow melt and prior to leaf flush (i.e., greenup), termed the "spring window" by fire managers, when these forests are relatively conducive to wildfire ignition and spread. The goal of this study was to characterize the duration, timing, and fire proneness of the spring window across boreal Canada and assess the link between these phenologicalvariables and the incidence of springtime wildfires. We used remotely sensed snow cover and greenup data to identify the annual spring window for five boreal ecozones from 2001 to 2021 and then compared seasonality of wildfire starts (by cause) and fire-conducive weather in relation to this window, averaged over the 21-year period. We conducted a path analysis to concomitantly evaluate the influence of the spring window's duration, the timing of greenup, and fire-conducive weather on the annual number and the seasonality of spring wildfires. Results show that the characteristics of spring windows vary substantially from year to year and among geographic zones, with the interior west of Canada having the longest and most fire-conducive spread window and, accordingly, the greatest springtime wildfire activity. We also provide support for the belief that springtime weather generally promotes wind-driven, rather than drought-driven wildfires. The path analyses show idiosyncratic behavior among ecozones, but, in general, the seasonality of the wildfire season is mainly driven by the timing of the greenup, whereas the number of spring wildfires mostly responds to the duration of the spring window and the frequency of fire-conducive weather. The results of this study allows us to better understand and anticipate the biome-wide changes projected for the northern forests of North America.

Evaluating retention forestry 10 years after its introduction in temperate forests regarding the provision of tree-related microhabitats and dead wood

The individual or grouped retention of habitat trees in managed multiple-use forests has become an approach used to protect biodiversity-related structural attributes typically found in old close-to-nature forests. This study focuses on the effect of one such retention approach in the managed forests of Baden-Württemberg, Germany, ten years after its introduction. Specifically, we asked: (1) How effective are habitat tree groups (HTGs) at providing large living trees (LLTs > 80 cm DBH), tree-related microhabitats (TreMs), and dead wood?, and (2) which tree and stand variables have the greatest influence on the occurrence of TreMs? For this purpose, we inventoried 326 HTGs and 94 reference plots in forests dominated by the most widely occurring native conifer and broadleaf tree species, silver fir (Abies alba) and European beech (Fagus sylvatica). In accordance with our hypotheses, LLTs and TreMs were significantly more abundant in HTGs than in reference plots in both forest types. More importantly, when retaining 5% of the forest area as HTGs (a common retention level), old forest attributes such as woodpecker cavities, rot-holes or exposed heartwood increased significantly at the stand level while the volume of LLTs almost tripled, and volume of snags increased by 25%. However, quantities of these two attributes remain below minimum thresholds recommended in the scientific literature. A conversion of 15–25% of the stand area into HTGs is needed to increase the stand level abundance of TreMs such as concavities, exposed sapwood, or crown dead wood significantly in the short term. At the single-tree level, tree diameter (DBH), tree species, vitality and neighborhood competition had a significant influence on modeled TreM abundance. At the stand level, TreM occurrence increased with stand age and amount of snags, whereas TreM richness declined with stand density. Ten years after introducing the retention approach, forest stands with HTGs comprised significantly more important structural attributes than those without. Selecting HTGs with high stand volume or low tree density that also include snags, a mix of tree species, LLTs, and some low-vitality habitat trees could further improve this practice.

Lamina-specific localization of silicon accumulation in two broadleaf tree species.

Silicon (Si) accumulation differs greatly among plant species, as revealed by an increasing number of studies reporting whole-leaf Si concentration for a wide range of land plants. Yet, we have limited knowledge about Si distribution across leaf parts (e.g., lamina vs. veins) within a leaf of eudicots. Here, we report how Si accumulation with leaf age differs among petiole, midrib, and lamina in two broad-leaved trees, Acer rufinerve and Ficus erecta. We marked a pair of neighboring leaves in each marked shoot and harvested one in May and the other in October to measure Si concentration. In both species, the lamina showed much higher Si concentration than the petiole and vein in both young and old leaves, and only the lamina showed clear increases in Si concentration from young to old leaves. Si accumulation rate correlated positively with shoot size and leaf production in F. erecta but not in A. rufinerve. These results strongly suggest that, in eudicot species, Si is deposited mostly in leaf lamina but in only a negligible amount in petioles and veins through which Si dissolved in water is transported. Future research on physiological regulations of Si accumulation in eudicot species should consider which specific cells in leaf lamina are responsible for such highly localized Si deposition.

Interactions within the climate-vegetation-fire nexus may transform 21st century boreal forests in northwestern Canada

Dry and warm conditions have exacerbated the occurrence of large and severe wildfires over the past decade in Canada's Northwest Territories (NT). Although temperatures are expected to increase during the 21st century, we lack understanding of how the climate-vegetation-fire nexus might respond. We used a dynamic global vegetation model to project annual burn rates, as well as tree species composition and biomass in the NT during the 21st century using the IPCC's climate scenarios. Burn rates will decrease in most of the NT by the mid-21st century, concomitant with biomass loss of fire-prone evergreen needleleaf tree species, and biomass increase of broadleaf tree species. The southeastern NT is projected to experience enhanced fire activity by the late 21st century according to scenario RCP4.5, supported by a higher production of flammable evergreen needleleaf biomass. The results underlie the potential for major impacts of climate change on the NT's terrestrial ecosystems.

A simple concept for estimating deadwood carbon in forests

Deadwood in forests is becoming an important topic globally for forest management and carbon markets. While deadwood volume is now routinely assessed by forest inventories and can be even monitored using remote sensing, data about deadwood carbon and density depending on the extent of decay is scarce. We propose a simple concept for estimating deadwood carbon using data from a pilot study in selected coniferous and broadleaf forests covering different climate zones in Austria. We measured deadwood volume and decay classes and calculated deadwood density and carbon fraction from destructive field samples. We found that decay reduces deadwood density significantly, while carbon fraction increases moderately with decay. Partitioning the explained variation confirmed that size and site parameters are more important for explaining deadwood carbon fraction than for deadwood density. These patterns were consistent for coniferous and broadleaf tree species. We also show how to estimate deadwood carbon stocks using standard forest inventory measurements or country statistics, without information on decay classes. We found differences in decay classes of standing versus lying deadwood, and our proposed method allows considering this in large-scale deadwood carbon assessments. We highlight research gaps and missing deadwood information, to provide more accurate carbon assessments of deadwood.

Responses of soil microbial communities to vegetation restoration on the Loess Plateau of China: A meta-analysis

Vegetation restoration has been implemented to prevent ecosystem degradation worldwide. However, the general response of soil microbial communities to vegetation restoration remains highly controversial. Herein, 417 paired observations from 74 studies on the Loess Plateau of China were selected to investigate the effects of vegetation restoration on the soil microbial community and to determine the factors that affected their variation. The results showed that vegetation restoration significantly increased microbial biomass (phospholipid fatty acid and microbial biomass C, N, and P) and enzyme activities (invertase, urease, phosphatase, catalase and glucosidase) but decreased the fungi to bacteria ratio (F:B). Specifically, microbial biomass was mainly affected by slope gradient, pH, and available nitrogen. Enzyme activities were mainly affected by available nitrogen, pH, and soil water content. F:B was mainly affected by available phosphorus. However, the variations in Oligotroph:Copiotroph ratio, gram-positive bacteria to gram-negative bacteria ratio, microbial diversity (Shannon index and OTU richness), and microbial activity (microbial respiration, metabolic quotient, and microbial entropy carbon) were nonsignificant. Our study also showed that the effects of vegetation restoration on the soil microbial community were substantially dependent on vegetation type (restoration type, leaf form, mycorrhizal type) and restoration year. For example, greater microbial biomass was found in soils of trees (sites that had been restored to forest), higher enzyme activity was found in soils of broadleaf tree species, and a lower F:B was found in soils of arbuscular mycorrhizal species.

Mixed with Broadleaf Tree Species Improved Soil Aggregate Stability in Chinese Fir (Cunninghamia lanceolata) Plantations: Based on the Le Bissonnais Method

Mixed with Broadleaf Tree Species Improved Soil Aggregate Stability in Chinese Fir (Cunninghamia lanceolata) Plantations: Based on the Le Bissonnais Method

Determination on Tree Species Selection for Lingzhi or Reishi Medicinal Mushroom Ganoderma lucidum (Agaricomycetes) Cultivation by Fourier Transform Infrared and Two-Dimensional Infrared Correlation Spectroscopy

As a wood-degrading Agaricomycetes mushroom, Ganoderma lucidum can be cultivated on broad-leaf hardwoods. Generally, producers care about the yield, but not the quality of G. lucidum cultivated by different tree species. In this study, five broad-leaf hardwood tree species-Quercus variabilis Bl. (Qv), Castanea mollissima Bl. (Cm), Liquidambar formosana Hance (Lf), Dalbergia hupeana Hance (Dh), and Platycarya strobilacea Sieb. et Zucc. (Ps)-were selected for cultivating of G. lucidum. The chemical compositions of G. lucidum fruiting bodies produced by these tree species were determined by Fourier transform infrared and two-dimensional infrared correlation spectroscopy in order to select the most suitable tree species for cultivation. The overall spectra showed less discrimination of each peak variation detected and properly kept most of the primary metabolites. The second derivative unfolded the stagnation of the first spectrum and more base peaks were detected especially in the range of the first two sections. The protein content contained in G. lucidum cultivated on Ps was 92%, like that on Dh. On the other hand, only 27% similarity was determined in G. lucidum cultivated on Ps and Qv. Therefore, the correlation of this range for the protein content can help in tree species selection. The active sequence of 2DIR spectral could be determined by the active bonding of the component reacted to the perturbation. The result could provide a scientific basis for the selection of tree species and the comprehensive utilization of broad-leaf tree resources on G. lucidum cultivation.

Genetic diversity and paternity analysis of Mytilaria laosensis hybrids using microsatellite markers provide insight into the breeding system

Mytilaria laosensis is an important evergreen broadleaf tree species in Southeast Asia and can provide excellent raw materials for pulp and fiberboard industrial production due to its fast growth and desirable wood properties. It produces hundreds of hermaphrodite flowers in a single inflorescence and controlled pollination through emasculation is difficult. In this study, we adopted hand-assisted pollination to investigate the seed set ratio and hybrid efficiency. A total of 65 cross combinations including 723 inflorescences were performed by using five female and eight male trees. The fruit-set rate varied greatly from 6.67% to 84.62% among different groups with an average of 23.68%. Moreover, new microsatellite markers were developed through transcriptome sequencing and ten polymorphic markers were screened out to examine the genetic variation and hybrid purity of 742 progeny. An average of 14.7 alleles was detected per locus. The parent population showed the highest expected heterozygosity of 0.77, while other hybrid populations exhibited different heterozygosity values from 0.46 to 0.71. Both principal coordinate analysis and phylogenetic tree revealed that these groups could be divided into five clusters and each cluster represented progeny which shared the same female parent. Paternity test showed that 18 offspring were sired by the designated pollen parents, while all other offspring were all heterozygous with pollens from non-target father. The results implied that outcrossing might be the predominant breeding system and self-incompatibility might exist in M. laosensis . This study provides useful reference for molecular-assisted hybrid breeding research and a practicable approach for new cultivar development in tree species. • The fruit-set rate varied greatly in different cross combinations of M. laosensis . • Ten highly efficient SSR markers were developed through transcriptome sequencing. • High genetic diversity level was detected among 52 hybrid groups. • The 18 offspring were sired by the designated parents and others were all heterozygous. • Self-incompatibility might exist in M. laosensis.

Effect of stem rot on wood basic density, carbon, and nitrogen content of living deciduous trees in hemiboreal forests

While numerous studies have focused on analyzing various aspects of the carbon (C) budget in forests, there appears to be a lack of comprehensive assessments specifically addressing the impact of stem rot on the C budget of broadleaf tree species, especially in old-growth forests where stem rot is prevalent. One of the main challenges in accurately quantifying C losses caused by stem rot is the lack of precise data on the basic density and C content of decayed wood, which are crucial for converting decayed wood volume into biomass and C stocks. Using linear mixed-effects models, we examine the variability of wood basic density, C content, and nitrogen (N) content. Discolored and decomposed wood was collected from the stems of 136 living deciduous trees common in hemiboreal forests in Latvia. Our research indicates a noticeable reduction in the wood basic density, coupled with an increase in the N content within the stem wood throughout the decomposition process in birch (Betula spp.), European aspen (Populus tremula L.), grey alder (Alnus incana (L.) Moench), and common alder (Alnus glutinosa (L.) Gaertn.). While aspen wood showed a decreasing trend in C content as decay progressed, a pairwise comparison test revealed no significant differences in C content between discolored and decomposed wood for the studied species, unlike the findings for basic density and N content. This study emphasizes the need to account for stem rot in old-growth forest carbon budgets, especially in broadleaf species, and calls for more research on stem rot-induced carbon losses.

Examining the Cultivation, Degradation Characteristics and Health Effects of the Golden Oyster Mushroom Pleurotus citrinopileatus (Agaricomycetes): A Review

Pleurotus citrinopileatus, also known as golden oyster mushroom, is a newly industrialized edible mushroom mainly distributed in East Asia. It is a kind of saprophytic edible fungus with strong degradation characteristics, commonly found on fallen trees and stumps of broad-leaf tree species. So far, abundant kinds of bioactive compounds such as polysaccharides, ergothioneine, sesquiterpenes, and glycoprotein have been isolated from P. citrinopileatus and studied. Studies have confirmed that these compounds are beneficial to human health. In this paper, the recent studies on the cultivation, degradation characteristics application, and health effects of P. citrinopileatus are reviewed, and their development trends are discussed.

Convolutional neural network tree species identification based on tree-ring radial section image features.

Convolutional neural networks can automatically identify tree species based on the images of structural features of tree-rings samples. In this study, we used a tree-ring image dataset for different species to achieve tree-ring based species automatic identification with high accuracy by four convolutional neural network models (LeNet, AlexNet, GoogLeNet, and VGGNet), aiming to determine the identification accuracy of the models, clarify the species misidentification during the automatic processes, and explore the identification differences among the models. The results showed that tree species identification derived from the trained convolutional neural network models was reliable, with the GoogLeNet and LeNet showed the highest (96.7%) and lowest (66.4%) identification accuracy. The tree species identifications using different models were highly consistent. Quercus mongolica and Abies nephrolepis showed the highest (100% for AlexNet) and lowest identification accuracy, respectively. Misidentification could occur among tree species with similar tree-ring structure. The identification accuracy of the models was higher at family and genus levels than that at the species level. The identification accuracy of broadleaf tree species was higher than that of coniferous trees due to distinct radial structure among broadleaf species. Overall, our method achieved a high accuracy for tree species identification, and provided a fast, convenient, and automatic tree species identification by detecting specific tree-ring properties with convolutional neural network.

Tree species composition alters the decomposition of mixed litter and the associated microbial community composition and function in subtropical plantations in China

Converting coniferous plantations to mixed plantations influences the microbial community composition and potential functions during litter decomposition. However, it is unclear how litter decomposition and associated microbial communities are interactively affected by litter mixing and environmental factors. Here, an in situ litter decomposition experiment was conducted to investigate the dynamics of microbial diversity in mixed litter (at a mass ratio of 1:1) from coniferous (Pinus massoniana) and broadleaf tree, including Bretschneidera sinensis, Manglietia chingii, Cercidiphyllum japonicum, Michelia maudiae, and Camellia oleifera. We found that the mass loss from mixed litter was higher than that of monospecific litter. The chemical characteristics of the broadleaf tree species included in the mixed litter significantly affected the microbial community composition and diversity, and those effects increased over time. Compared to the monospecific litter, the mixed litter had a higher relative abundance of saprotrophs and microbial functional groups related to carbon and nitrogen cycling. Moreover, litter chemistry (i.e., pH, lignin and cellulose content) and environmental factors (i.e., air temperature and soil moisture content) were the most crucial factors affecting the microbial decomposer community. Our results suggest that introducing broadleaf tree species with high litter quality to coniferous plantations changes the composition and function of microbial communities related to litter decomposition, which is conducive to accelerating litter decomposition in subtropical plantations.

Root Development in Cunninghamia lanceolata and Schima superba Seedlings Expresses Contrasting Preferences to Nitrogen Forms

The inorganic nitrogen (N) that can be absorbed and utilized by plants is mainly ammonium N (NH4+-N) and nitrate N (NO3−-N), which may affect seedlings’ root morphology and growth through its heterogeneous distribution. Root morphology and seedling growth were investigated in a subtropical major conifer (Cunninghamia lanceolata) and a broadleaf tree species (Schima superba) under five different NH4+-N to NO3−-N ratios (10:0, 0:10, 7:3, 3:7, 5:5). Results: (1) While both species developed thinner roots under the treatment with a high NO3−-N concentration, the roots of C. lanceolata were longer than those of S. superba. In contrast, the roots of both species were thicker under the treatment with a high NH4+-N concentration, with those in S. superba being much longer than those in C. lanceolata. (2) The mixed NH4+-N and NO3−-N treatments were more conducive to the aboveground growth and biomass accumulation of both tree species and the underground growth of S. superba. N sources with high NO3−-N concentrations were more suitable for underground growth in C. lanceolata seedlings and aboveground growth in S. superba seedlings. Under the N sources with high NH4+-N concentrations, C. lanceolata tended to develop aboveground parts and S. superba tended to develop underground parts. (3) The roots of the two tree species adopted the expansion strategy of increasing the specific root length and reducing the root tissue density under the N sources with high NO3−-N concentrations but the opposite with high NH4+-N concentrations. The root-to-shoot ratio of C. lanceolata increased under high NO3−-N concentrations, while that of S. superba increased under high NO3−-N concentrations. These results indicate that the responses of root morphology to different N forms are species-specific. Furthermore, according to the soil’s N status, NH4+-N can be appropriately applied to C. lanceolata and NO3−-N to S. superba for cultivating seedlings.

AngleCam: Predicting the temporal variation of leaf angle distributions from image series with deep learning

AbstractVertical leaf angles and their variation through time are directly related to several ecophysiological processes and properties. However, there is no efficient method for tracking leaf angles of plant canopies under field conditions.Here, we present AngleCam, a deep learning‐based approach to predict leaf angle distributions from horizontal photographs acquired with low‐cost timelapse cameras. AngleCam is based on pattern recognition with convolutional neural networks and trained with leaf angle distributions obtained from visual interpretation of more than 2500 plant photographs across different species and scene conditions.Leaf angle predictions were evaluated over a wide range of species and scene conditions using independent samples from visual interpretation (R2 = 0.84) and compared to leaf angle estimates obtained from terrestrial laser scanning (R2 = 0.75). AngleCam was tested for the long‐term monitoring of leaf angles for two broadleaf tree species in a temperate forest. The plausibility of the predicted leaf angle time series was underlined by its close relationship with environmental variables related to transpiration.The evaluations confirm that AngleCam is a robust and efficient method to track leaf angles under field conditions. The output of AngleCam is compatible with a range of applications, including functional‐structural plant modelling, Earth system modelling or radiative transfer modelling of plant canopies. AngleCam may also be used to predict leaf angle distributions for existing data, for instance from PhenoCam networks citizen science projects.

Variations of rhizosphere and bulk soil microbial community in successive planting of Chinese fir (Cunninghamia lanceolata).

Successive planting and monoculture, as common forest management methods, are widely used globally, especially in Chinese fir plantations in the subtropical areas of southern China. Although soil fertility depletion and productivity decline caused by successive planting have been widely reported, the underlying mechanism is still ambiguous. In this study, the composition and diversity of soil microorganisms (rhizosphere and bulk soils) in Chinese fir seedlings exposed to successive planting soils (first-generation Chinese fir seedings, FCP. second-generation Chinese fir seedings, SCP. third-generation Chinese fir seedings, TCP) and broadleaf tree species soil (Phoebe zhennan S. Lee et F. N. Wei, CK) were examined with high-throughput sequencing technology. Our findings revealed that the diversity and richness of bacterial and fungal communities were remarkably reduced in TCP than FCP and SCP, and were remarkably different between FCP and SCP. At the phylum level, the fungi with greatest relative abundance were Basidiomycota (5.74–32.88%) and Ascomycota (57.63–87.38%), while the bacteria with the greatest relative abundance were Acidobacteria (23.16–31.17%) and Proteobacteria (24.71–29.32%) for all treatments in both soil types. Additionally, the relative abundance of some pathogens (Penicillium and Burkholderia) was significantly higher in TCP than in FCP and SCP, suggesting that the presence of pathogens is an important factor in increasing the incidence of soil-borne sickness. Moreover, changes in fungal and bacterial communities were predominantly driven by soil dissolved organic carbon (DOC), DOC/DON ratio (DOCN), NO3–-N, microbial biomass carbon (MBC), and MBC/MBN ratio (MBCN). Overall, the long-term monoculture of Chinese fir promotes the microecological imbalance of rhizosphere and bulk soil, and remarkably reduced soil microbial community diversity. These results can provide a scientific support for the implementation of future management measures for fir plantations (e.g., fertilization, addition of microbial fungicides, and construction of mixed forests).

Encroachment order and spatial patterns of broad-leaf tree species in the naturalization of a Cunninghamia lanceolata plantation

The aim of this study was to understand the encroachment order, spatial patterns, interspecific associations, and species diversity of a Cunninghamia lanceolata plantation and to provide context for how to improve the spatial structure of C. lanceolata plantations. We investigated a Guanshan (C. lanceolata) Plantation in the Jiangxi Province. The C. lanceolata plantation was divided into three developmental stages (early, middle and late), with a space-for-time substitution method, according to their diameter at breast height (DBH) measurements. Across these plots, we analyzed encroachment patterns of the species and their interspecific associations with C. lanceolata according to the coordinates of trees in the plot, as well as the variation of species diversity after the encroachment of broad-leaf tree species. Our results show that the encroachment of broad-leaf trees into the C. lanceolata plantation followed a clear successional sequence of tree community assembly: intolerant tree species encroachment first, such as Alniphyllum fortunei and Liquidambar formosana, encroached; neutral tree species then encroachment, such as Daphniphyllum oldhamii and Schima superba, and shade-tolerant tree species encroachment last, such as Castanopsis eyrei and Castanopsis tibetana. Further, the spatial pattern of species establishment differed based upon when they encroached on the plantation. Intolerant and neutral tree species of early and middle developmental stages were distributed randomly. However, intolerant and some shade-tolerant tree species of the late developmental stage were aggregated on a scale of about 0–3 m. In addition, the interspecific associations between broad-leaf species encroachment into the C. lanceolata plantation were mainly negative, among which the most competitive ones were A. fortunei, D. oldhamii and Machilus thunbergii. However, with the development of the community, some species with negative correlations changed to having no correlation with C. lanceolata. We found that species diversity in the plantation gradually increased by nearly-five times from the early to the late developmental stage. Based on our collective results, we conclude that the encroachment and assembly of tree species show obvious order and pattern, which has a strong competitive effect with C. lanceolata in the naturalized plantation. Additionally, the community biodiversity has been significantly improved. Therefore, this successional process is important in the transformation of the C lanceolata plantation and different tree species should be replanted according to C. lanceolata plantation developmental stages with priority given to competitive species, such as A. fortunei, D. oldhamii, and M. thunbergii, so as to promote the C. lanceolata plantation change to C. lanceolata and broadleaf mixed forest.