Conifer-broadleaf Forest Research Articles

Functional traits explain growth–mortality trade-offs in a mixed broadleaf-conifer forest in northeastern China

Functional traits explain growth–mortality trade-offs in a mixed broadleaf-conifer forest in northeastern China

Estimation of the Conifer-Broadleaf Ratio in Mixed Forests Based on Time-Series Data

Most natural forests are mixed forests, a mixed broadleaf-conifer forest is essentially a heterogeneously mixed pixel in remote sensing images. Satellite missions rely on modeling to acquire regional or global vegetation parameter products. However, these retrieval models often assume homogeneous conditions at the pixel level, resulting in a decrease in the inversion accuracy, which is an issue for heterogeneous forests. Therefore, information on the canopy composition of a mixed forest is the basis for accurately retrieving vegetation parameters using remote sensing. Medium and high spatial resolution multispectral time-series data are important sources for canopy conifer-broadleaf ratio estimation because these data have a high frequency and wide coverage. This paper highlights a successful method for estimating the conifer-broadleaf ratio in a mixed forest with diverse tree species and complex canopy structures. Experiments were conducted in the Purple Mountain, Nanjing, Jiangsu Province of China, where we collected leaf area index (LAI) time-series and forest sample plot inventory data. Based on the Invertible Forest Reflectance Model (INFORM), we simulated the normalized difference vegetation index (NDVI) time-series of different conifer-broadleaf ratios. A time-series similarity analysis was performed to determine the typical separable conifer-broadleaf ratios. Fifteen Gaofen-1 (GF-1) satellite images of 2015 were acquired. The conifer-broadleaf ratio estimation was based on the GF-1 NDVI time-series and semi-supervised k-means cluster method, which yielded a high overall accuracy of 83.75%. This study demonstrates the feasibility of accurately estimating separable conifer-broadleaf ratios using field measurement data and GF-1 time series in mixed broadleaf-conifer forests.

Increase of litterfall mercury input and sequestration during decomposition with a montane elevation in Southwest China

Litterfall mercury (Hg) input has been regarded as the dominant Hg source in montane forest floor. To depict combining effects of vegetation, climate and topography on accumulation of Hg in montane forests, we comprehensively quantified litterfall Hg deposition and decomposition in a serial of subtropical forests along an elevation gradient on both leeward and windward slopes of Mt. Ailao, Southwest China. Results showed that the average litterfall Hg deposition increased from 12.0 ± 4.2 μg m−2 yr−1 in dry-hot valley shrub at 850–1000 m, 14.9 ± 6.8 μg m−2 yr−1 in mixed conifer-broadleaf forest at 1250–2400 m, to 23.1 ± 8.3 μg m−2 yr−1 in evergreen broadleaf forest at 2500–2650 m. Additionally, the windward slope forests had a significantly higher litterfall Hg depositions at the same altitude because the larger precipitation promoted the greater litterfall biomass production. The one-year litter Hg decomposition showed that the Hg mass of litter in dry-hot valley shrub decreased by 29%, while in mixed conifer-broadleaf and evergreen broadleaf forests increased by 22–48%. The dynamics of Hg in decomposing litter was controlled by the temperature mediated litter decomposition rate and the additional adsorption of environmental Hg during decomposition. Overall, our study highlights the litterfall mediated atmospheric mercury inputs and sequestration increase with the montane elevation, thus driving a Hg enhanced accumulation in the high montane forest.

Changes in Long-Term Light Properties of a Mixed Conifer—Broadleaf Forest in Southwestern Europe

Natural and anthropogenic factors affect forest structure worldwide, primarily affecting forest canopy and its light properties. However, not only stand-replacing events modify canopy structure, but disturbances of lower intensity can also have important ecological implications. To study such effects, we analyzed long-term changes in light properties of a conifer–broadleaf mixed forest in the Southwestern Pyrenees, placed in the fringe between the Mediterranean and Eurosiberian biogeographical regions. At this site, a thinning trial with different intensities (0%, 20%, and 30–40% basal area removed) took place in 1999 and 2009, windstorms affected some plots in 2009 and droughts were recurrent during the sampling period (2003, 2005, 2011). We monitored light properties during 14 years (2005–2019) with hemispherical photographs. We applied partial autocorrelation functions to determine if changes between years could be attributed to internal canopy changes or to external disturbances. In addition, we mapped the broadleaf canopy in 2003, 2008, and 2016 to calculate broadleaf canopy cover and richness at the sampling points with different buffer areas of increasing surface. We applied generalized linear mixed models to evaluate the effects of light variables on canopy richness and cover. We found that light variables had the most important changes during the period 2008 to 2010, reacting to the changes caused that year by the combined effects of wind and forest management. In addition, we found that an area of 4.0 m radius around the sampling points was the best to explain the relationship between light properties and species richness, whereas a radius of 1.0 m was enough to estimate the relationship between light and canopy cover. In addition, light-related variables such as diffuse light and leaf area index were related to species richness, whereas structural variables such as canopy openness were related to canopy cover. In summary, our study demonstrates that non stand-replacing disturbances such as windstorms, thinning, or droughts can have an important role in modifying structural and light-related canopy properties, which in turn may influence natural processes of stand development and ecological succession.

Linking Vegetation, Soil Carbon Stocks, and Earthworms in Upland Coniferous–Broadleaf Forests

Linking vegetation, soil biota, and soil carbon stocks in forests has a high predictive value. The specific aim of this study was to identify the relationships between vegetation, earthworms, and soil carbon stocks in nine types of forests dominating autonomous landscape positions in a coniferous–broadleaf forest zone of the European part of Russia. Mountain forests were selected in the Northwest Caucasus, while plain forests were selected in Bryansk Polesie and on the Moskva-Oka plain. One-way analysis of variance (ANOVA) and v-tests were used to assess the impact of different factors on soil C stocks. To assess the contribution of vegetation, litter quality, and earthworms to variation of carbon stocks in organic (FH-layer) and mineral layer (0–50 cm), the method of hierarchical partitioning was performed. The highest C stocks in the organic horizons were associated with the low-quality litter, i.e., with a low base saturation, high acidity, and wide C/N ratio. The highest soil C stocks in the mineral layers were found in mixed forests with the highest richness of plant species, producing litterfall of different quality. The C stock in the organic horizon was negatively related to the biomass of worms that process the litter, while the carbon stock in the mineral layers was positively related to the biomass of worms whose life activity is related to the mineral layers. These findings demonstrated the substantial influence of plants producing a litter of different quality, and of earthworms, belonging to different functional groups, on soil C stocks in coniferous–broadleaf forests.

Stand Volume Growth Modeling with Mixed-Effects Models and Quantile Regressions for Major Forest Types in the Eastern Daxing’an Mountains, Northeast China

The relative growth rate (RGRnv) is the standardized measurement of forest growth, whereby excluding the size differences between individuals allows their performance to be compared equally. The RGRnv model was developed using the National Forest Inventory (NFI) data on the Daxing’an Mountains, in Northeast China, which contain Dahurian larch (Larix gmelinii Rupr.), white birch (Betula platyphylla Suk.), and mixed coniferous–broadleaf forests. Four predictor variables—i.e., quadratic mean diameter (Dq), stand basal area (G), average tree height (Ha), and altitude (A)—and four different methods—i.e., the nonlinear mixed-effects models (NLME), three nonlinear quantile regression (NQR3), five nonlinear quantile regression (NQR5), and nine nonlinear quantile regression (NQR9) models—were used in this study. All the models were validated using the leave-one-out method. The results showed that (1) the mixed coniferous–broadleaf forest presented the highest RGRnv; (2) the RGRnv was negatively correlated with the four predictors, and the heteroscedasticity reduced significantly after the weighting function was integrated into the models; and (3) the quantile regression models performed better than NLME, and NQR9 outperformed both NQR3 and NQR5. To make more accurate predictions, parameters of the adjusted mixed-effects and quantile regression models should be recalculated and localized using sampled RGRnv in each region and then applied to predict all the other RGRnv of plots. MAPE% indicates the mean absolute percentage error. The values were stable when the sample numbers were greater than or equal to six across the three forest types, which showed relatively accurate and lowest-cost prediction results.

Belowground consequences of converting broadleaf to conifer forest: Comparing the fine root systems of European beech and Scots pine

Planted forests of Scots pine (P. sylvestris L.) and other Pinus species extend over >1.7 million hectares in the Pleistocene lowlands of northern Germany, replacing former broadleaf forests (primarily European beech, Fagus sylvatica L.). This transformation belongs to the world’s largest broadleaf-conifer forest conversions; yet, the belowground consequences of this species shift are poorly studied. Based on root coring, an ingrowth core study and root morphological analyses, we compared (i) the bio- and necromass, productivity and morphology of fine roots in pairs of beech and pine stands and (ii) analyzed the species’ fine root system response to variation in soil properties and climatic conditions across a climate continentality gradient. Fine root biomass was on average 6.5 times higher (237 vs. 37 g m−2) and fine root productivity 1.9 times greater (147 vs. 77 g m−2 yr−1, difference not significant) in beech than pine stands. Beech responded with considerable plasticity in fine root system size and fine root morphology to variation in soil acidity and soil fertility and to the contrasting growing conditions in organic layer and mineral soil, but was not responsive to the climatic gradient. In contrast, pine modified fine root biomass and root morphology in response to precipitation and temperature, but did not respond to soil chemistry and fertility. Pine had a somewhat higher mean fine root diameter and also higher specific fine root surface area than beech, while its fine root tip abundance and mean fine root lifespan were lower than in beech (4 vs. 13 months). We conclude that the conversion of broadleaf (beech) to coniferous (pine) forest is accompanied by marked root system changes, notably the reduction of standing fine root biomass and productivity and an apparently contrasting belowground responsiveness to climatic and edaphic changes, with possible consequences for the trees’ susceptibility to climate-warming and drought.

Reconstruction of local-scale plant community characteristics using phytolith: A case study of a forested region in Northeast China

Understanding local-scale paleoecological processes and their driving mechanisms is a major challenge in plant community ecology. However, phytolith records have the potential to retrieve localized signals of the evolution and patterns of past ecosystems. As a case study, we selected a forested region in Northeast China. We first established a modern phytolith reference dataset which enabled numerical estimates to be made of various aspects of the plant community. We then apply the dataset to a phytolith record from a sedimentary profile (HN) from the Changbai mountain region in order to quantitatively reconstruct the evolution of the vegetation since the last deglaciation. The results of partial least squares regression were used demonstrate that modern phytoliths can quantitatively estimate plant community coverage, species diversity and dry weight ratio; three numerical estimates respectively explained 62.3%, 50.3% and 49.5% of the variance. These quantitative relationships can provide reliable modern phytolith analogues for paleoecological reconstructions. The modern phytolith-based vegetation reconstruction indicates that the Changbai mountain region was dominated by forest communities since the late glacial period. The temporal development of the vegetation can be summarized as follows: boreal or coniferous forest, sparse and species-poor → mixed broadleaf-conifer forest, relatively dense and species-rich → mixed broadleaf-conifer forest, dense and species-rich. The phytolith-inferred changes in plant community coverage, dry weight ratio and species diversity correspond well with climatic changes. This supports the view that the environmental background mainly dominates ecosystem evolution, and it also confirms the utility of phytolith records to resolve local paleovegetation patterns and evolution.

IMPACT OF EARTHWORMS OF DIFFERENT MORPHO-ECOLOGICAL GROUPS ON CARBON ACCUMULATION IN FOREST SOILS

To date, forest ecology has not made any clear conclusions regarding the impact of large saprophagous invertebrates such as earthworms on soil carbon dynamics. Some authors claim that earthworm activities result in decreased carbon accumulation. Other studies show that earthworms contribute to soil carbon accumulation. At the same time, many studies do not take into account the differences between trophic and digging activity of different morpho-ecological groups of earthworms in different soil horizons. The objective of this study was to carry out differentiated assessment of the impact of different morpho-ecological groups of earthworms on carbon accumulation and correspondent soil parameters (nitrogen content and С/N ratio) throughout the change in forest succession status. Field operations were performed in the spring and summer of 2016 and 2018 in three regions: Bryansk Oblast (Bryansk Forest reserve), Moscow Oblast (Moskva–Oka plain, Valuyevsky urban forest) and Northwest Caucasus (Krasnodar Krai, Apsheron forestry; Republic of Adygeya, Caucasian Biosphere Reserve). Three main stages of coniferous-broadleaf forest restoration after clear cuttings were identified in each region. Three test plots 50х50 m were allocated for each stage; geobotanical and soil descriptions as well as earthworm registration were carried out on each plot. It was found out that during the change in forest succession status the species composition and the set of morpho-ecological groups of earthworms became more complicated, but there was no successive replacement of any groups with others. Ambiguous effects of different morpho-ecological groups of earthworms on carbon accumulation in forest soils were revealed. Negative correlation was found between the total biomass of earthworms feeding on the soil surface (epigeic, epi-endogeic and anecic species) and litter store. In the humus horizon, the biomass of epi-endogeic species was positively correlated with the content of carbon. C/N ratio and nitrogen content are unidirectionally correlated with the biomass of earthworms in the horizons of their activity: with an increase in the biomass of earthworms of different morpho-ecological groups, the C/N ratio decreases, and the nitrogen content increases.

Analysis of complete mitochondrial genome sequence of bar-tailed Treecreeper certhia himalayana (psittaciformes: Certhiidae)

Bar-tailed Treecreeper Certhia himalayana usually lives in coniferous or mixed broadleaf-conifer forests, often crawling along the trunk. In this study, we first sequenced and described the complete mitochondrial genome and phylogeny of C. himalayana. The whole genome of C. himalayana was 16,852 bp in length, and contained 13 protein-coding genes, 22 transfer RNA genes, 2 ribosome RNA genes, and 1 non-coding control regions. The overall base composition of the mitochondrial DNA was 25.1% for A, 29.2% for T, 14.5% for C, 31.2% for G, with a GC content of 45.7%. A phylogenetic tree strongly supported that C. himalayana closely related with Family Troglodytidae by highly probability.

不同生态修复措施和环境因素对亚热带红壤区针叶纯林坡面水土保持功能的影响

使用"地理探测器（GeoDetector）"对亚热带红壤区水土流失影响因素的定量分析结果可为当地森林生态修复和侵蚀模型完善提供科学依据。基于福建省龙岩市新罗区龙门溪小流域森林调查数据和径流小区监测数据，利用地理探测器探测不同生态修复措施和环境因素对针叶纯林坡面水土保持功能的影响及交互作用，结果表明：（1）对比中幼龄针叶纯林，补植阔叶树使针阔混交比例为7 ： 2可减少46%的径流量和76%的泥沙量，生态修复效果较好。对重侵蚀区"老头树"少量施肥难以产生效果。（2）影响坡面径流的因素由强到弱依次是：降雨因子（0.53），土壤容重、林分密度、灌草层盖度、树高和针阔比（均在0.08左右）；影响泥沙流失的因素依次是：地表径流量（0.84），降雨因子（0.2），林分密度、土壤容重、灌草层盖度、土壤含水率、灌草层生物量（均在0.12左右）。（3）各影响因素交互后主要呈增强作用；林分密度、灌草层盖度和土壤容重还可与其他因子产生强烈非线性增强作用（交互后影响力>0.9），是在森林修复和模型参数优化时需重点关注的对象。;The quantification results of the GeoDetector for the impact factors of the soil and water loss in the subtropical red soil area provide the scientific base for the local forest ecological restoration and the improvement of erosion models. This study explored the direct and interactive influences of different ecological restoration measures and environmental factors on water and soil conservation of the slope in forest by introducing the GeoDetector and using the forest survey data and the observation data of the runoff plots in Longmen Creek Watershed, Xinluo District, Longyan City, Fujian Province. The results showed that:(1) to compared with the middle and young age pure coniferous forest, the mixed conifer-broadleaf forest with the mixed ratio 7:2 could cut down the runoff and sediment load by 46% and 76%, respectively which represented that the ecological restoration effect of this measure was excellent. The small amount of fertilization hardly worked on the old tree in the heavy erosion area. (2) The rank of the strong impact factors of the runoff of the slope was rainfall (q value was 0.5), soil bulk density, stand density, shrub coverage, tree height and forest mixed ratio (q values were around 0.08). The rank of the strong impact factors of the sediment loads was surface runoff (q value was 0.84), rainfall (q value was 0.2), stand density, soil bulk density, shrub coverage, soil moisture content, total biomass of shrub (q values were around 0.12). (3) There were complex interactions among the factors of soil and water conservation function. The enhance effect mode accounted for most of the total pairs of the interactions between two factors. The interaction between the weak factors (such as stand density, shrub coverage, and soil bulk density, etc.) and other factors could result in the nonlinear enhancement, and the influence was greater than 0.9. Therefore, they should be paid more attentions when we performed the forest restoration and model parameter optimization.

Latitudinal and altitudinal variations across temperate to subtropical forests from southern Kyushu to the northern Ryukyu Archipelago, Japan

ABSTRACT We studied the latitudinal and altitudinal variations in composition and species richness of trees in 24 plots across temperate to subtropical regions from southern Kyushu to the northern Ryukyu Archipelago, Japan. Cluster analysis based on presence/absence of species in 0.25-ha segments of the plots identified three forest zones reflecting climate and geohistory: cool-temperate mixed conifer-broadleaf forest (MF) north of the Tokara Gap (Kyushu and Yakushima), warm-temperate evergreen broadleaf forest (EBF) north of the Tokara Gap, and subtropical EBF south of the Tokara Gap (Amami-Oshima, Tokunoshima, and Okinawajima). The MF zone corresponded to Kira’s Warmth Index (WI) < 100°C. The two EBF zones overlapped in the range of WI, and thus their boundary was determined by geohistory rather than by climate. Plot-level species richness per 400 stems increased with increasing WI, with decreased values in Yakushima, suggesting that geohistory (isolations from Kyushu as well as by the Tokara Gap) depressed the species richness of Yakushima. Greater species richness in the subtropical EBF was explained by the presence of species whose distributions were restricted to the south of the Tokara Gap, indicating that the size of tree flora influences the plot-level species richness. By contrast, lower species richness of MF in Yakushima than in Kyushu was due to the absence of species whose distributions were restricted to Kyushu northward, indicating the impoverishment of the cool-temperate flora of Yakushima. In conclusion, climate and geohistory shape the tree-community composition and diversity of old-growth forests in this transitional zone from temperate to subtropical regions.

Tree Species Classification and Health Status Assessment for a Mixed Broadleaf-Conifer Forest with UAS Multispectral Imaging

Automatic discrimination of tree species and identification of physiological stress imposed on forest trees by biotic factors from unmanned aerial systems (UAS) offers substantial advantages in forest management practices. In this study, we aimed to develop a novel workflow for facilitating tree species classification and the detection of healthy, unhealthy, and dead trees caused by bark beetle infestation using ultra-high resolution 5-band UAS bi-temporal aerial imagery in the Czech Republic. The study is divided into two steps. We initially classified the tree type, either as broadleaf or conifer, and we then classified trees according to the tree type and health status, and subgroups were created to further classify trees (detailed classification). Photogrammetric processed datasets achieved by the use of structure-from-motion (SfM) imaging technique, where resulting digital terrain models (DTMs), digital surface models (DSMs), and orthophotos with a resolution of 0.05 m were utilized as input for canopy spectral analysis, as well as texture analysis (TA). For the spectral analysis, nine vegetation indices (VIs) were applied to evaluate the amount of vegetation cover change of canopy surface between the two seasons, spring and summer of 2019. Moreover, 13 TA variables, including Mean, Variance, Entropy, Contrast, Heterogeneity, Homogeneity, Angular Second Moment, Correlation, Gray-level Difference Vector (GLDV) Angular Second Moment, GLDV Entropy, GLDV Mean, GLDV Contrast, and Inverse Difference, were estimated for the extraction of canopy surface texture. Further, we used the support vector machine (SVM) algorithm to conduct a detailed classification of tree species and health status. Our results highlighted the efficiency of the proposed method for tree species classification with an overall accuracy (OA) of 81.18% (Kappa: 0.70) and health status assessment with an OA of 84.71% (Kappa: 0.66). While SVM proved to be a good classifier, the results also showed that a combination of VI and TA layers increased the OA by 4.24%, providing a new dimension of information derived from UAS platforms. These methods could be used to quickly evaluate large areas that have been impacted by biological disturbance agents for mapping and detection, tree inventory, and evaluating habitat conditions at relatively low costs.

Migration characteristics and potential determinants of mercury in long-term decomposing litterfall of two subtropical forests

It is of great importance to elucidate the mechanism of mercury (Hg) migration in the forest litterfall so as to clearly understand global Hg deposition. However, it is still unclear for the migration and transformation of Hg in different forest litters during long-term decomposition. Therefore, the dynamics of total Hg (THg), methylmercury (MeHg), carbon, nitrogen, microbial biomass carbon and nitrogen in the litterfall of the evergreen broadleaf (EB) and mixed broadleaf-conifer (MBC) forests, southwest China were investigated, aiming to understand the migration characteristics of Hg in the two-year decomposing litterfall. Results showed that carbon decreased, while nitrogen accumulated slightly in the process of litterfall decomposition. THg levels in the second year of the EB and MBC forests decreased by 16.9% and 11.3%, while MeHg levels reduced by 141.4% and 210.7% respectively comparing with those in the first year. The total percentage of hydrochloric acid-soluble mercury (Hg-h) and water-soluble mercury (Hg-w) had a significant impact on the migration of THg and MeHg in the two forest stands. The C/N ratio in the EB forest bore a positive correlation with THg and MeHg levels, whereas that in the MBC forest was adverse. Besides, microbial biomass C and N were positively related with THg and MeHg levels in both the EB and MBC forests. It is proposed that THg and MeHg accumulation in the second year drastically decreased probably due to finite nutritional conditions, which implies that Hg accumulation risks alleviate with degradation time.

Seasonal variation of diversity and co-occurrence patterns of arbuscular mycorrhizal fungal communities in mixed broadleaf-conifer forests

Arbuscular mycorrhizal (AM) fungi are an important determinant of plant performance. The temporal distribution patterns of AM fungal communities, important groups in forest soil, are affected by various environmental factors. However, the effect of seasonal variation on AM fungal communities in forest soil is still not fully understood. To improve knowledge regarding the seasonal dynamics of AM fungal communities in forest soil, the Juglans mandshurica rhizosphere soil in a 30-year-old natural J. mandshurica and Larix gmelinii mixed forest in northeastern China was sampled and studied during different seasons. AM fungal community composition and structure in the rhizosphere soil were determined by using the Illumina MiSeq sequencing platform. The results showed that forest type significantly affected soil pH and the microbial biomass carbon (Cmic), microbial biomass nitrogen (Nmic), C, N, P, NH4+-N and NO3−-N contents. Similarly, soil moisture significantly decreased with seasonal progression in all forest types. Glomus and Diversispora were the dominant genera. The Shannon, Sobs and Chao1 indices of the mixed forest were higher in July than in May and September. The NO3−-N and water-soluble phenol (WSPh) contents were the most important factors driving the shift in the soil AM fungal community across the seasonal gradient. Network analysis revealed that AM fungal network structure was significantly different between seasons, and the number of links between species significantly increased with time. We observed a clear tendency for mixed forest management to significantly affect AM fungal community structure and composition but not diversity. Furthermore, the co-occurrence network and keystone taxa among AM fungi can change in response to environmental filtering due to mixed management in different seasons.

Predicting individual tree growth of high-value timber species in mixed conifer-broadleaf forests in northern Japan using long-term forest measurement data

ABSTRACT Quantifying individual tree growth of economically high-value timber species is important for the simulation and development of forest management options. Long-term permanent plot data provides crucial information of forest stand dynamics that can be used to predict individual tree growth. In this study, we developed individual tree basal area growth models of three high-value timber species: monarch birch (Betula maximowicziana), castor aralia (Kalopanax septemlobus), and Japanese oak (Quercus crispula) in a cool temperate mixed forest in northern Japan using long-term measurement data (1968–2016) collected in permanent plots. Data included species, diameter at breast height, and survival status, and stand management history. We applied linear mixed-effects modelling to predict the individual tree basal area growth as a function of individual tree size, competition, and forest management. Model prediction followed by leave-one-out cross validation revealed a correlation between predicted and observed basal area increments with r values of 0.62, 0.73, and 0.70 and root mean square errors values of 10.44, 7.91, and 11.62 cm2/year for monarch birch, castor aralia, and Japanese oak, respectively. The individual tree growth models developed in this study will provide valuable information for species-specific forest management of economically high-value timber species.

Patterns of diversity change for forest vegetation across different climatic regions - A compound habitat gradient analysis approach

Biotic diversity of ecological communities can be driven by a mixture of climatic, soil and biotic factors from local to regional scales. Patterns of diversity change were often examined along latitudinal or elevational gradients, which were mainly driven by climatic factors. However, few studies have assessed biodiversity patterns along both abiotic and biotic gradients simultaneously. Here, we established 309 forest dynamics plots of typical forest vegetation types (tropical rainforest, subtropical evergreen deciduous broad-leaf mixed forest, warm temperate conifer broad-leaf mixed forest, and temperate conifer forest) in seven biogeographic regions across four climatic regions (tropical, subtropical, warm temperate, and temperate regions) in China. A total of 46,280 tree individuals of 801 species in these plots were tagged, investigated and mapped, and six functional traits and seven soil factors were sampled and measured, in addition, data on three climatic factors were extracted from Worldclim. Principal component analysis (PCA) was used to build the compound habitat gradient (CHG) combining the biotic and abiotic factors. Patterns of changes in species and functional diversity along the CHG were analyzed. Results showed that species richness, Shannon-Wiener index and functional richness (FRic) increased but functional divergence (FDiv) decreased along the first axis of the CHG. The models using the first four PCA axes of the CHG and models with the individual variables had more power to explain species diversity than functional diversity. PC1 was the most important predictor in explaining patterns of diversity variation. The null models of FRic and FDiv were significantly negatively correlated with PC1 in the compound habitat gradient, and not with other axes. Our study demonstrates that the compound habitat gradient analysis is an effective approach of exploring patterns of biodiversity change and understanding both the abiotic and biotic factors driving community assembly across different climatic regions.

Changes in leaf stomatal traits of different aged temperate forest stands

Stomata control carbon and water vapor exchange between the leaves and the atmosphere, thus influencing photosynthesis and transpiration. Combinations of forest patches with different stand ages are common in nature, however, information of which stomatal traits vary among these stands and how, remains limited. Here, seven different aged forest stands (6, 14, 25, 36, 45, 55, and 100 years) were selected in typical temperate, mixed broadleaf-conifer forests of northeast China. Stomatal density, size and relative area of 624 species, including the same species in stands of different ages were selected. Stomatal density, size and relative area were distributed log-normally, differing across all species and plant functional groups. Stomatal density ranged from 4.2 to 1276.7 stomata mm–2, stomatal size ranged from 66.6 to 8315.7 μm2, and stomatal relative area 0.1–93.3%. There was a significant negative relationship between density and size at the species and functional group levels, while the relative stomatal area was positively correlated with density and size. Stomatal traits of dominant species were relatively stable across different stand ages but were significantly different for herbs. The results suggest that stomatal traits remain relatively stable for dominant species in natural forests and therefore, spatial variation in stomatal traits across forest patches does not need to be incorporated in future ecological models.

Effects of Different Forest Vegetation Types on Soil Nitrogen-Related Microbial Communities and Functions in Jinyun Mountain

To clarify the response of a nitrogen-related microbial community and function to different vegetation types in subtropical forest, soil samples were collected for analysis from the topsoil of five vegetation types in the Jinyun Mountain National Nature Reserve, i.e., coniferous forest, broadleaf forest, mixed broadleaf-coniferous forest, P. pubescen forest, and grassland. To analyze the microbial abundance, community, and function discrepancy between different vegetation soils, multiple molecular techniques, such as terminal restriction fragment length polymorphism (T-RFLP) and quantitative polymerase chain reaction (qPCR) analysis, and nitrogen-related microbial enzyme activity procedures were used. The results showed:① The denitrifying enzyme activity was much higher than nitrifying potential in Jinyun Mountain National Nature Reserve, and the two enzyme activities were much lower in coniferous forest soil than in the other vegetation soils (P<0.05). In addition, dissolved organic carbon, soil water content, and total nitrogen were the key environmental factors controlling enzyme activity. ② The qPCR data showed that the abundance of nitrogen-related microbes was highest in P. pubescen forest, whereas it was lowest in coniferous forest. The abundances of the three nitrogen-related microbes were all significantly correlated with dissolved organic carbon, total nitrogen, available nitrogen, total potassium, and available potassium (P<0.01). ③ Based on T-RFLP data, the α-diversity of nitrogen-related microbes was highest in broadleaf forest, whereas it was lowest in P. pubescen forest. Principal co-ordinates analysis (PCoA) showed that the community structure of ammonia-oxidizing archaea responded significantly to different vegetations, and the community structure of nitrogen-related microbes showed the most difference in coniferous forest. In addition, distance-based redundancy analysis (db-RDA) showed that the community structure of nitrogen-related microbes was mainly shaped by dissolved organic carbon (P<0.001), available nitrogen (P<0.002), and soil water content (P<0.001). ④ Soil-denitrifying enzyme activity was mainly affected by the abundance of nirS-denitrifiers, ammonia-oxidizing archaea, and the community structure of nitrogen-related microbes, whereas nitrifying potential was only controlled by the abundance of ammonia-oxidizing archaea. Above all, subtropical forest vegetation significantly affects the abundance and community structure of soil nitrogen-related microbes, thereby changing their function of controlling the soil nitrogen cycle. This study can provide basic data for the coupling mechanism between soil microbes and N2O release in subtropical forests in China.

Sustainability of High-Value Timber Species in Mixed Conifer–Broadleaf Forest Managed under Selection System in Northern Japan

Understanding the sustainability of high-value timber species in managed forests provides useful information for the management of these species in the long-run. Using nearly 50 years of census data in long-term permanent plots, we investigated the sustainability of three high-value timber species—monarch birch (Betula maximowicziana Regel), castor aralia (Kalopanax septemlobus (Thunb.) Koidz), and Japanese oak (Quercus crispula Blume)—in cool-temperate mixed forest under a selection system in northern Japan. We used stocking, demographic parameters, and species proportions of these species as measures of sustainability. Results showed that the tree density and basal area of the three high-value timber species increased during the study period. Moreover, the basal area increment of these species showed an increasing trend across census periods. However, while no significant differences in the tree mortality of these species were observed, the numbers of in-growth fluctuated across census periods. Increasing trends in species proportions of monarch birch and Japanese oak were observed. Even though there were some fluctuations across census periods, especially in smaller diameter classes, diameter distribution curves of high-value timber species followed a reversed J-shaped pattern. The results revealed that the sustainability measures of high-value timber species can be achieved in forest stands managed under single-tree selection system. In addition, the results also indicated the changing structure and composition of the forest stand. The stocking and basal area increment of conifers decreased while those of broadleaves increased. The proportion of conifers decreased to 33.01% in 2008–2016 from 48.35% in 1968–1978. The results of this study would be useful for adapting silvicultural practices and harvesting practices as well as for simulating various silvicultural and management options for high-value timber species.