While bird populations are declining, the factors associated with this decline are unclear. Based on laboratory experiments, air pollution has long been recognized as a factor causing oxidative stress and adversely affecting bird health. Recently, studies employing an epidemiological approach have reported significant declines in avian populations in Central Europe and the United States due to air pollution, and ozone in particular. We advocate that urgent actions are needed to mitigate these effects, which threaten biodiversity and environmental health, and propose a series of measures which can enlighten the path toward mitigating air pollution effects on avian populations.
Inventory data were available from 96 plots of even-aged, monoculture, tall-open forests of Eucalyptus pilularis Smith, aged 2–63 years, growing in sub-tropical regions along the east coast of Australia. A model was developed relating the maximum possible stem basal area growth rate of individual trees to their stem basal area. For any tree size, this maximum increased as site productivity increased. However, the size at which this maximum occurred decreased as productivity increased. Much research has shown that, at any stand age, trees of a particular stem basal area are taller on more productive sites than on less productive ones. Taller trees incur greater respiratory costs to ensure maintenance of the photosynthetic capacity of their canopies; this reduces their growth rates. It was concluded that trees with larger basal areas will have the maximum possible growth rate on a less productive site, whilst trees with smaller basal areas will have the maximum possible on a more productive site. The model developed may constitute the first stage of a complete individual tree growth model system to predict wood yields from these forests.
Climate change significantly impacts forest ecosystems in arid and semi-arid regions. However, spatiotemporal patterns of climate-sensitive changes in individual tree growth under increased climate warming and precipitation in north–west China is unclear. The dendrochronological method was used to study climate response sensitivity of radial growth of Picea schrenkiana from 158 trees at six sites during 1990–2020. The results show that climate warming and increased precipitation significantly promoted the growth of trees. The response to temperature first increased, then decreased. However, the response to increased precipitation and the self-calibrating Palmer Drought Severity Index (scPDSI) increased significantly. In most areas of the Tianshan Mountains, the proportion of trees under increased precipitation and scPDSI positive response was relatively high. Over time, small-diameter trees were strongly affected by drought stress. It is predicted that under continuous warming and increased precipitation, trees in most areas of the Tianshan Mountains, especially those with small diameters, will be more affected by precipitation.
α-diversity describes species diversity at local scales. The Simpson’s and Shannon–Wiener indices are widely used to characterize α-diversity based on species abundances within a fixed study site (e.g., a quadrat or plot). Although such indices provide overall diversity estimates that can be analyzed, their values are not spatially continuous nor applicable in theory to any point within the study region, and thus they cannot be treated as spatial covariates for analyses of other variables. Herein, we extended the Simpson’s and Shannon–Wiener indices to create point estimates of α-diversity for any location based on spatially explicit species occurrences within different bandwidths (i.e., radii, with the location of interest as the center). For an arbitrary point in the study region, species occurrences within the circle plotting the bandwidth were weighted according to their distance from the center using a tri-cube kernel function, with occurrences closer to the center having greater weight than more distant ones. These novel kernel-based α-diversity indices were tested using a tree dataset from a 400 m × 400 m study region comprising a 200 m × 200 m core region surrounded by a 100-m width buffer zone. Our newly extended α-diversity indices did not disagree qualitatively with the traditional indices, and the former were slightly lower than the latter by < 2% at medium and large bandwidths. The present work demonstrates the feasibility of using kernel-based α-diversity indices to estimate diversity at any location in the study region and allows them to be used as quantifiable spatial covariates or predictors for other dependent variables of interest in future ecological studies. Spatially continuous α-diversity indices are useful to compare and monitor species trends in space and time, which is valuable for conservation practitioners.
Black locust (Robinia pseudoacacia L.) plantations have contributed significantly to soil and water conservation and ecological reconstruction on China’s Loess Plateau. Understanding the impact of stand and environment on species composition of understory woody plants will improve the stability of existing black locust plantations. Ten stands were selected in second-generation black locust plantations in tableland and gully areas of the Loess Plateau. The number of understory tree species in the tablelands was significantly lower than in the gully stands. Regenerated black locust (19.76%) and Rubus corchorifolius L.f. (64.85%) were the most abundant understory tree and shrub species, respectively, in the tableland stands; Broussonetia papyrifera (L.) L'Hér. ex Vent. (6.77%) and Acanthopanax senticosus (Rupr. Maxim.) Harms. (37.22%) were most abundant in the gully stands. Species richness (S), Shannon diversity (H), and evenness index (J) of the understory plants were significantly lower in the tableland stands than in the gully stands. More diverse understory species and community structures occurred in the gully stands. Differences in species diversity among landform positions may be attributed to differences in soil moisture. In addition, 77.57% of the variation in understory species composition was explained, among which shrub and herb coverage, stand age, leaf area index, slope and total soil phosphorus in the 10–20 cm layer were the main factors. Soil organic carbon and total potassium significantly impacted S, H and J. Considering the environmental conditions and the biological characteristics of the plants investigated, R. corchorifolius should be given priority in the development of tableland stands, while B. papyrifera and Celtis sinensis Pers. should form mixed forests with black locust in gully stands. This management could promote biodiversity and stability of the existing black locust plantations but also optimize regional landscape patterns.
Tsutsusi is one of the eight subgenera of the Rhododendron genus. Four Tsutsusi species, R. indicum, R. simisii, R. oldhamii, and R. schlippenbachii, have high ornamental and medicinal values, resulting in an increasing market demand. These species thrive in cool and humid environments and are widely distributed in Europe and Asia. Whether global climate warming will affect the distribution of these valuable resources remains unclear. Thus, this study analyzed the climatic suitability of these species for the first time on the basis of 1552 geographical distribution points and 19 bioclimatic factors using the maximum entropy model. The results show that a suitable distribution area for all four species would decrease under climate warming. The main bioclimatic factors affecting their distribution are the mean temperature of the coldest quarter for R. indicum, the mean diurnal range for R. simisii, and precipitation of the warmest quarter for R. oldhamii and R. schlippenbachii. In addition, the contribution of the temperature-related bioclimatic factors to the distribution of R. indicum and R. simisii is higher than that of the associated precipitation-related climatic factors; in contrast, the contribution of precipitation-related bioclimatic factors to the distribution of R. oldhamii and R. schlippenbachii is higher than that of the temperature-related climatic factors. These results provide references for the introduction, conservation, sustainable development, and utilization of these four species in the future, and may also provide information with regards to other Rhododendron species.
An oasis is a unique natural landscape in arid and semi-arid areas, significant for regulating regional microclimates and hydrological processes in deserts. However, little is known regarding the response of natural oasis plants communities to various environmental factors. Nineteen sample plots (50 m × 50 m) were selected in the Daliyabuyi Oasis in the Taklimakan Desert hinterland based on the location of groundwater monitoring wells and 76 vegetation quadrats (25 m × 25 m) were established. A two-way indicator species analysis, Mantel test, detrended correspondence analysis, canonical correspondence analysis (CCA), and hierarchical partitioning were used to provide an in-depth analysis of community classification, species composition, and environmental interpretation of the oasis. A generalized linear model was used to verify the results which showed that the current oasis community could be divided into four types according to the dominant species, which is controlled by soil moisture. Measurement of species composition and distribution of communities showed significant differences between species diversity of individual community types. Variations in groundwater depth affects patterns of species diversity which is sensitive to richness, while the degree of surface water disturbance affects the pattern of species evenness. Moreover, the CCA ordination map showed that community distribution and diversity characteristics have their own preferences in habitat gradients. The study concluded that the species dominance of the community and the composition and distribution are not dominated by a single factor. There are differences in the scale and effect of different water resource types in maintaining community characteristics.
Although numerous hypotheses have been proposed to explain the patterns of species diversity of forests at local and landscape levels, it is still difficult to predict the alpha diversity of species, especially in tropical and subtropical natural forests where trees of different sizes and shapes are highly mixed. Size might characterize species diversity, and the possible correlation between these variables may contribute to the development of easy-to-use growth indicators to predict diversity and to understand the status of trees within a stand. In this study, diameter classes were divided using the equal diameter class (EDC) and minimum measured diameter (MMD) methods, and five species diversity indices were calculated for each diameter class of 14 permanent plots in five national nature reserves surrounding the Tropic of Cancer (23.5°), southwest China. The results show that species richness, abundance, and spatial diversity indices decreased in a typical inverted J-shape pattern with increasing diameter class and MMD, and could be easily modeled by a negative exponential function. The Shannon–Wiener index showed a linear decrease while Pielou’s evenness index displayed a linear increase, with a small degree of instability. The results suggest that species diversity in subtropical forests is closely related to tree size, and the relationship is possibly independent of habitat. Measuring DBH of some trees in a stand could be informative regarding species diversity and contribute to the investigation and assessment of biodiversity.
Fire severity classifications determine fire damage and regeneration potential in post-fire areas for effective implementation of restoration applications. Since fire damage varies according to vegetation and fire characteristics, regional assessment of fire severity is crucial. The objectives of this study were: (1) to test the performance of different satellite imagery and spectral indices, and two field—measured severity indices, CBI (Composite Burn Index) and GeoCBI (Geometrically structured Composite Burn Index) to assess fire severity; (2) to calculate classification thresholds for spectral indices that performed best in the study areas; and (3) to generate fire severity maps that could be used to determine the ecological impact of forest fires. Five large fires in Pinus brutia (Turkish pine) and Pinus nigra subsp. pallasiana var. pallasiana (Anatolian black pine)—dominated forests during 2020 and 2021 were selected as study sites. The results show that GeoCBI provided more reliable estimates of field—measured fire severity than CBI. While Sentinel-2 and Landsat-8/OLI images performed similarly well, MODIS performed poorly. Fire severity classification thresholds were determined for Sentinel-2 based RdNBR, dNBR, dSAVI, dNDVI, and dNDMI and Landsat-8/OLI based dNBR, dNDVI, and dSAVI. Among several spectral indices, the highest accuracy for fire severity classification was found for Sentinel-2 based RdNBR (72.1%) and Landsat-8/OLI based dNBR (69.2%). The results can be used to assess and map fire severity in forest ecosystems similar to those in this study.
This study investigated the relationship between climate and biophysical variables in burned areas in Iran. The fire burned area (FBA) product (Fire CCI 5.1.1), land surface temperature (MOD11C3C), vegetation index (MOD13A1), and climate variables such as temperature, wind speed, relative humidity, and volumetric soil moisture from the ERA5 reanalysis dataset were used. Pearson correlation coefficient was used to determine the relationship between biophysical and climate variables and fire occurrence. The results show that FBA increased by 1.7 hectares/decade from 2001 to 2020. The high FBA in 2010 (the black summer of Iran) was due to high temperatures and significant heatwaves that led to extensive wildfires. Although anthropogenic activities are considered a significant cause of wildfires, several variables, including increased temperatures, less precipitation, relative humidity, and wind speed and direction, contribute to the extent and occurrence of wildfires. The country’s FBA hotspot is in the Arasbaran region during the summer season. Temperature and relative humidity are the most significant variables influencing the occurrence of wildfires. The results show the vulnerability of Iran’s forests and their high potential for fires. Considering the frequency of fire occurrences in Iran and the limited equipment, fire prevention plans should be carried out by applying proper management in high-risk regions.
Few studies have compared the variability of soil properties using different types of mulches in semi-arid forests. This study evaluated the changes in physico-chemical soil properties in a semi-arid forest of Central Eastern Spain, where straw and pine wood chips were distributed as mulch three months after a wildfire. Soils were sampled under burned and unmulched and burned and mulched plots three and nine months after the treatments. The data was processed using Principal Component Analysis (PCA) and Analytical Hierarchical Cluster Analysis (AHCA). Mulching with straw or wood chips did not have any significant effects on the texture and chemical properties of burned sites few months after the treatment. In contrast, significant changes are expected over time in organic matter, nutrients and many ions. There were no significant differences in soil properties between the two mulches. These low changes were confirmed by PCA coupled with AHCA, which did not show a clear distinction among the three soil conditions. However, a noticeable and significant variability of many of these properties over time was evident. This study shows that mulching does not degrade of soil properties in the short-term after a wildfire and after post-fire treatments, and thus helps protect semi-arid forest ecosystems against the negative impacts of high-severity fires.
Cleaning up residual fires is an important part of forest fire management to avoid the loss of forest resources caused by the recurrence of a residual fire. Existing residual fire detection equipment is mainly infrared temperature detection and smoke identification. Due to the isolation of ground, temperature and smoke characteristics of medium and large smoldering charcoal in some forest soils are not obvious, making it difficult to identify by detection equipment. CO gas is an important detection index for indoor smoldering fire detection, and an important identification feature of hidden smoldering ground fires. However, there is no research on locating smoldering fires through CO detection. We studied the diffusion law of CO gas directly above covered smoldering charcoal as a criterion to design a detection device equipped with multiple CO sensors. According to the motion decomposition search algorithm, the detection device realizes the function of automatically searching for smoldering charcoal. Experimental data shows that the average CO concentration over the covered smoldering charcoal decreases exponentially with increasing height. The size of the search step is related to the reliability of the search algorithm. The detection success corresponding to the small step length is high but the search time is lengthy which can lead to search failure. The introduction of step and rotation factors in search algorithm improves the search efficiency. This study reveals that the average ground CO concentration directly above smoldering charcoal in forests changes with height. Based on this law, a CO gas sensor detection device for hidden smoldering fires has been designed, which enriches the technique of residual fire detection.
Diameter distribution models play an important role in forest inventories, growth prediction, and management. The Weibull probability density function is widely used in forestry. Although a number of methods have been proposed to predict or recover the Weibull distribution, their applicability and predictive performance for the major tree species of China remain to be determined. Trees in sample plots of three even-aged coniferous species (Larix olgensis, Pinus sylvestris and Pinus koraiensis) were measured both in un-thinned and thinned stands to develop parameter prediction models for the Weibull probability density function. Ordinary least squares (OLS) and maximum likelihood regression (MLER), as well as cumulative distribution function regression (CDFR) were used, and their performance compared. The results show that MLER and CDFR were better than OLS in predicting diameter distributions of tree plantations. CDFR produced the best results in terms of fitting statistics. Based on the error statistics calculated for different age groups, CDFR was considered the most suitable method for developing prediction models for Weibull parameters in coniferous plantations.
Although the distributions of foliage and light play major roles in various forest functions, accurate, nondestructive measurement of these distributions is difficult due to the complexity of the canopy structure. To evaluate the foliage and light distributions directly and nondestructively in a mature oak stand, we used the cube method by dividing the forest canopy into small cubes (50 cm per side) and directly measured leaf area density (LAD, the total one-sided leaf area per unit volume, i.e., cube) and relative irradiance (RI) within each cube. The distribution of LAD and of RI was highly heterogeneous, even at the same canopy height. This heterogeneity reflected the presence of foliage clusters associated with multiple forking branches. The relationship between cumulative LAD at the canopy surface and average RI followed the Beer–Lambert law. The mean light extinction coefficient (K) was 0.32. However, K was overestimated by more than double (0.80) when calculated based on the classical method using RI at the forest floor. This overestimation was caused by the lower RI due to light absorption by nonleaf plant parts below the canopy. Our findings on the complex foliage and light distributions in canopy layers should help improve the accuracy of RI and K measurements and thus more accurate predictions of environmental responses and forest functions.
The diameter distribution of trees in a stand provides the basis for determining the stand’s ecological and economic value, its structure and stability and appropriate management practices. Scots pine (Pinus sylvestris L.) is one of the most common and important conifers in Turkey, so a well-planned management schedule is critical. Diameter distribution models to accurately describe the stand structure help improve management strategies, but developing reliable models requires a deep understanding of the growth, output and constraints of the forests. The most important information derived by diameter distribution models is primary data on horizontal stand structure for each diameter class of trees: basal area and volume per unit area. These predictions are required to estimate the range of products and predicted volume and yield from a forest stand. Here, to construct an accurate, reliable diameter distribution model for natural Scots pine stands in the Türkmen Mountain region, we used Johnson’s S B distribution to represent the empirical diameter distributions of the stands using ground-based measurements from 55 sample plots that included 1219 trees in natural distribution zones of the forests. As an alternative, nonparametric approach, which does not require any predefined function, an artificial intelligence model was constructed based on support vector machine methodology. An error index was calculated to evaluate the results. Overall, both Johnson’s S B probability density function with a three-parameter recovery approach and the support vector regression methodology provided reliable estimates of the diameter distribution of these stands.
A collection representing the native range of pecan was planted at the USDA − ARS Southeastern Fruit and Tree Nut Research Station, Byron, GA. The collection (867 trees) is a valuable genetic resource for characterizing important horticultural traits. Canopy density during leaf fall is important as the seasonal canopy dynamics provides insights to environmental cues and breeding potential of germplasm. The ability of visual raters to estimate canopy density on a subset of the provenance collection (76 trees) as an indicator of leaf shed during autumn along with image analysis values was explored. Mean canopy density using the image analysis software was less compared to visual estimates (11.9% vs 18.4%, respectively). At higher canopy densities, the raters overestimated foliage density, but overall agreement between raters and measured values was good (ρ c = 0.849 to 0.915), and inter-rater reliability was high (R 2 = 0.910 to 0.953). The provenance from Missouri (MO-L), the northernmost provenance, had the lowest canopy density in November, and results show that the higher the latitude of the provenance, the lower the canopy density. Based on regression, the source provenance latitude explained 0.609 of the variation using image analysis, and 0.551 to 0.640 when based on the rater estimates of canopy density. Visual assessment of pecan canopy density due to late season leaf fall for comparing pecan genotypes provides accurate and reliable estimates and could be used in future studies of the whole provenance collection.
The use of unmanned aerial vehicles (UAV) for forest monitoring has grown significantly in recent years, providing information with high spatial resolution and temporal versatility. UAV with multispectral sensors allow the use of indexes such as the normalized difference vegetation index (NDVI), which determines the vigor, physiological stress and photosynthetic activity of vegetation. This study aimed to analyze the spectral responses and variations of NDVI in tree crowns, as well as their correlation with climatic factors over the course of one year. The study area encompassed a 1.6-ha site in Durango, Mexico, where Pinus cembroides, Pinus engelmannii, and Quercus grisea coexist. Multispectral images were acquired with UAV and information on meteorological variables was obtained from NASA/POWER database. An ANOVA explored possible differences in NDVI among the three species. Pearson correlation was performed to identify the linear relationship between NDVI and meteorological variables. Significant differences in NDVI values were found at the genus level (Pinus and Quercus), possibly related to the physiological features of the species and their phenology. Quercus grisea had the lowest NDVI values throughout the year which may be attributed to its sensitivity to relative humidity and temperatures. Although the use of UAV with a multispectral sensor for NDVI monitoring allowed genera differentiation, in more complex forest analyses hyperspectral and LiDAR sensors should be integrated, as well other vegetation indexes be considered.
Precise quantification of climate-growth relationships can make a major contribution to scientific forest management. However, whether differences in the response of growth to climate at different altitudes remains unclear. To answer this, 264 trees of Larix kaempferi from 88 plots, representing different altitudinal ranges (1000–2100 m) and tree classes were sampled and used to develop tree-ring chronologies. Tree-ring growth (TRG) was either positively (dominant) or negatively (intermediate and suppressed) correlated with climate in different tree classes at different altitudes. TRG was strongly correlated with growing season at low altitudes, but was less sensitive to climate at middle altitudes. It was mainly limited by precipitation and was highly sensitive to climate at low altitudes. Climate-growth relationships at high altitudes were opposite compared to those at low altitudes. TRG of dominant trees was more sensitive to climate change compared to intermediate and suppressed trees. Climate factors (annual temperatures; moisture, the number of frost-free days) had different effects on tree-ring growth of different tree classes along altitudinal gradients. It was concluded that the increase in summer temperatures decreased water availability, resulting in a significant decline in growth rates after 2005 at lower altitudes. L. kaempferi is suitable for planting in middle altitudes and dominant trees were the best sampling choice for accurately assessing climate-growth relationships.
In order to ensure the effective analysis and reconstruction of forests, it is key to ensure the quantitative description of their spatial structure. In this paper, a distance model for the optimal stand spatial structure based on weighted Voronoi diagrams is proposed. In particular, we provide a novel methodological model for the comprehensive evaluation of the spatial structure of forest stands in natural mixed conifer-broadleaved forests and the formulation of management decision plans. The applicability of the rank evaluation and the optimal solution distance model are compared and assessed for different standard sample plots of natural mixed conifer-broadleaved forests. The effect of crown width on the spatial structure unit of the trees is observed to be higher than that of the diameter at breast height. Moreover, the influence of crown length is greater than that of tree height. There are nine possible spatial structure units determined by the weighted Voronoi diagram for the number of neighboring trees in the central tree, with an average intersection of neighboring crowns reaching 80%. The rank rating of natural forest sample plots is correlated with the optimal solution distance model, and their results are generally consistent for natural forests. However, the rank rating is not able to provide a quantitative assessment. The optimal solution distance model is observed to be more comprehensive than traditional methods for the evaluation of the spatial structure of forest stands. It can effectively reflect the trends in realistic stand spatial structure factors close to or far from the ideal structure point, and accurately assesses the forest spatial structure. The proposed optimal solution distance model improves the integrated evaluation of the spatial structure of forest stands and provides solid theoretical and technical support for sustainable forest management.
Unlike height-diameter equations for standing trees commonly used in forest resources modelling, tree height models for cut-to-length (CTL) stems tend to produce prediction errors whose distributions are not conditionally normal but are rather leptokurtic and heavy-tailed. This feature was merely noticed in previous studies but never thoroughly investigated. This study characterized the prediction error distribution of a newly developed such tree height model for Pinus radiata (D. Don) through the three-parameter Burr Type XII (BXII) distribution. The model’s prediction errors (
Phloem is the woody tissue for the storage and long-distance transport of organic matter in vascular bundles. To reveal the process of secondary phloem development and differentiation in Pinus massoniana, the structure of the secondary phloem and the distribution of cell inclusions were observed by histochemical staining, spontaneous fluorescence of phenolic substances and cell segregation. Based on tissue development and differentiation characteristics of P. massoniana secondary phloem, the secondary phloem development was divided into seven stages: the functional phloem stage; the sieve cell lignification stage; the phloem ray bending stage; the parenchyma cell dedifferentiation and division stage; the dedifferentiated parenchyma cell population formation stage; the periderm alteration stage, and the rhytidome stage. An analysis of cell morphology and inclusion distribution characteristics showed that the sieve cells were deformed during lignification, the quantities of parenchyma and resin ducts increased with development and the crystal content in cells, as well as the levels of sugars and lipids in phloem parenchyma cells, increased with development. The results indicate that the P. massoniana phloem first lost longitudinal transport function and then increased its secretory, storage and mechanical functions. Ultimately, the parenchyma differentiated into the cortex and periderm, and the tissue outside the new periderm lignified to form the rhytidome, which fully developed into the protective tissue of the stem.
Nighttime sap flow (Q n) is an important physiological activity under which trees manage drought stress. An in-depth understanding of the characteristics of Q n and its response to environmental and canopy conditions are of significance for arid area forest and water management. This study measured daily sap flow (Q s) of a Larix principis-rupprechtii plantation in the Liupan Mountains, northwest China during the 2017–2019 growing seasons, and separated Q s into daytime sap flow (Q d) and Q n. Meteorological conditions (reference evapotranspiration, ETref), canopy structure (leaf area index, LAI), and soil moisture (relative soil water content, RSWC) were considered as the main biophysical factors affecting Q n. The structural equation model and upper boundary line method determined the effects of compound and single factors on Q n. The daily mean Q n values during the growing seasons in 2017, 2018, and 2019 were 0.024, 0.026, and 0.030 mm d−1, accounting for 6.2, 11.2, and 10.1% of Q s, respectively. Q n at different canopy development phases (leaf expanding, LG; leaf expanded, LD; and defoliation, DF) over three years was LD > LG > DF. Q n increased with increasing ETref, whereas the ratio of Q n to Q s decreased. Q n did not show regular variation in the three-year growing seasons under different soil moisture conditions. ETref and LAI mainly controlled Q n by affecting Q d, whereas RSWC had no significant effect on Q n. Q n had a positive and linear relationship with LAI and a quadratic relationship with ETref. Both explained 40% of variation in Q n. Meteorological and canopy conditions are important factors affecting Q n on the semi-humid study site. The application of the Q n model coupled with the impact of ETref and LAI furthers understanding of the impacts of climate and forest structure change on Q n.
Doubled haploid (DH) plants have been widely used for breeding and biological research in crops. Populus spp. have been used as model woody plant species for biological research. However, the induction of DH poplar plants is onerous, and limited biological or breeding work has been carried out on DH individuals or populations. In this study, we provide an effective protocol for poplar haploid induction based on an anther culture method. A total of 96 whole DH plant lines were obtained using an F1 hybrid of Populus simonii × P. nigra as a donor tree. The phenotypes of the DH population showed exceptionally high variance when compared to those of half-sib progeny of the donor tree. Each DH line displayed distinct features compared to those of the other DH lines or the donor tree. Additionally, some excellent homozygous lines have the potential to be model plants in genetic and breeding studies.
A solid understanding of the efficiency of early selection for fiber dimensions is a prerequisite for breeding slash pine (Pinus elliottii Engelm.) with improved properties for pulp and paper products. Genetic correlations between size of fibers, wood quality and growth properties are also important. To accomplish effective early selection for size of fibers and evaluate the impact for wood quality traits and ring widths, core samples were collected from 360 trees of 20 open-pollinated Pinus elliottii families from three genetic trials. Cores were measured by SilviScan, and the age trends for phenotypic values, heritability, early-late genetic correlations, and early selection efficiency for fiber dimensions, such as tangential and radial fiber widths, fiber wall thickness and fiber coarseness, and their correlations with microfibril angle (MFA), modulus of elasticity (MOE), wood density and ring width were investigated. Different phenotypic trends were found for tangential and radial fiber widths while fiber coarseness and wall thickness curves were similar. Age trends of heritability based on area-weighted fiber dimensions were different. Low to moderate heritability from pith to bark (~ 0.5) was found for all fiber dimension across the three sites except for tangential fiber width and wall thickness at the Ganzhou site. Early-late genetic correlations were 0.9 after age of 9 years, and early selection for fiber dimensions could be effective due to strong genetic correlations. Our results showed moderate to strong positive genetic correlations for modulus of elasticity and density with fiber dimensions. The effects on fiber dimensions were weak or moderate when ring width or wood quality traits were selected alone. Estimates of efficiency for early selection indicated that the optimal age for radial fiber width and fiber coarseness was 6–7 years, while for tangential fiber width and wall thickness was 9–10 years.
The genus Thuja is ideal for investigating the genetic basis of the East Asia–North America disjunction. The biogeographical background of the genus is debatable and an adaptive strategy is lacking. Through the analysis and mining of comparative transcriptomes, species differentiation and positively selected genes (PSGs) were identified to provide information for understanding the environmental adaptation strategies of the genus Thuja. De novo assembly yielded 44,397–74,252 unigenes of the five Thuja species with contig N50 length ranging from 1,559 to 1,724 bp. Annotations revealed a similar distribution of functional categories among them. Based on the phylogenetic trees constructed using the transcriptome data, T. sutchuenensis was divided first, followed by T. plicata and T. occidentalis. The final differentiation of T. koraiensis and T. standishii formed a clade. Enrichment analysis indicated that the PSGs of the North American Thuja species were involved in plant hormone signal transduction and carbon fixation of photosynthetic organisms pathways. The PSGs of East Asian Thuja were related to phenolic, alkaloid, and terpenoid synthesis, important stress-resistant genes and could increase plant resistance to external environmental stresses. This study discovered numerous aroma synthetic-related PSGs including terpene synthase (TPS) genes and lipid phosphate phosphatase 2 (LPP2), associated with the synthetic aroma of T. sutchuenensis. Physiological indicators, such as the contents of soluble sugars, total chlorophyll, total phenolics, and total flavonoids were determined, which are consistent with the PSGs enrichment pathways associated with adaptive strategies in the five Thuja species. The results of this study provide an important basis for future studies on conservation genetics.
Climate change is forecast to increase the frequency of extreme hot temperatures and dryer days and is anticipated to have profound impacts on the global carbon budget. Droughts are expected to alter soil respiration (Rs) rates, but the scarcity of data preclude a reliable estimate of this response and its future trajectory. A field experiment using an automated soil respiration machinery (LI-8100A) was conducted in a natural forest and a plantation during a dry period in the Philippines, with the goal of quantifying Rs rates and their relationship with soil temperature and moisture, and air temperature. The natural forest (5.81 µmol m−2 s−1) exhibited significantly higher Rs rates (p < 0.0001) compared with the plantation (1.82 µmol m−2 s−1) and control (3.23 µmol m−2 s−1). Rs rates showed significant negative relationships with air (− 0.71) and soil temperatures (− 0.62), indicating that as temperatures increase, the Rs rates decrease. In contrast, the Rs rates exhibited a significant positive relationship with soil moisture (0.65). Although the low Rs rates in the plantation and high Rs rates in the natural forest are indicators of sensitivities of these two types of tropical forests to warm, dry soil, this observation is only conclusive during the dry period, but not necessarily during wet periods. Further studies are needed to determine the trend of Rs rates during wet periods, considering different site conditions and types of vegetation.
Nitrogen (N) present in drinking water as dissolved nitrates can directly affect people’s health, making it important to control N pollution in water source areas. N pollution caused by agricultural fertilizers can be controlled by reducing the amount of fertilizer applied, but pollution caused by soil and water erosion in hilly areas can only be controlled by conservation forests. The catchment area around Fushi Reservoir was selected as a test site and mechanisms of N loss from a vertical spatial perspective through field observations were determined. The main N losses occurred from June to September, accounting for 85.9–95.9% of the annual loss, with the losses in June and July accounting for 46.0% of the total, and in August and September for 41.9%. The N leakage from the water source area was effectively reduced by 38.2% through the optimization of the stand structure of the conservation forests. Establishing well-structured forests for water conservation is crucial to ensure the security of drinking water. This preliminary research lays the foundation for revealing then loss mechanisms in water source areas and improving the control of non-point source pollution in these areas.
Little is known about C –N – P stoichiometries and content in teak (Tectona grandis) plantations in South China, which are mostly sited on hilly areas with lateritic soil, and the effect of slope position on the accumulation of these elements in trees and rhizosphere soils. Here we analyzed the C, N, P content and stoichiometry in leaves, fine roots and rhizosphere soils of trees on the upper and lower slopes of a 12-year-old teak plantation. The Kraft classification system of tree status was used to sample dominant, subdominant and mean trees at each slope position. The results showed that the C, N and P contents in leaves were higher than in fine roots and rhizosphere soils. The lowest C/N, C/P and N/P ratios were found in rhizosphere soils, and the C/N and C/P ratios in fine roots were higher than in leaves. Nutrient accumulation in leaves, fine roots and rhizosphere soils were significantly influenced by slope position and tree class with their interaction mainly showing a greater effect on rhizosphere soils. Leaf C content and C/N ratio, fine root C and P contents, and C/N and C/P ratios all increased distinctly with declining slope position. The contents of organic matter (SOM), ammonium (NH4 +–N), nitrate-nitrogen (NO3 −–N) and available potassium (AK) in rhizosphere soils were mainly enriched on upper slopes, but exchange calcium (ECa), available phosphorus (AP), and pH were relatively lower. Variations in the C, N and P stoichiometries in trees were mainly attributed to the differences in rhizosphere soil properties. N and P contents showed significant positive linear relationships between leaf and rhizosphere soil, and C content negative linear correlation among leaves, fine roots and rhizosphere soils. Chemical properties of rhizosphere soils, particularly C/N and NH4 +–N, had significant effects on the leaf nutrients in trees on the upper slope. Correspondingly, rhizosphere soil properties mainly influenced fine root nutrients on the lower slope, and soil AK was the major influencing factor. Overall, these results offer new insights for the sustainability and management of teak plantations in hilly areas.
The application of sewage sludge (SS) to forested lands may lead to the downward migration of potentially toxic elements (PTEs) through rainfall and thus pose risk to the subsoil and groundwater. Batch column experiments were conducted using leaching water equivalent to the rainfall amount in the study area over 3 years to investigate changes in concentrations of PTEs, including copper (Cu), zinc (Zn), lead (Pb), cadmium (Cd), and nickel (Ni) in the leachate from the acidic forest soil. Water quality index of leachate, potential ecological risk and human health risk in soil at different leaching stages were compared. Sewage sludge was applied at SS/soil mass ratios of 0:100 (controls), 15:85 (T1), 30:70 (T2), 45:55 (T3), 60:40 (T4), and 75:25 (T5). All treatments resulted in increased PTEs concentration in the upper 20 cm soil, T3–T5 increased potential ecological risk from “low” (control) to “moderate” or “considerable”. During first year leaching, PTEs concentration increased with increasing SS/soil ratios, but the water quality index of T1–T3 was “excellent” or “good”. Pb, Cu, Cd, and Ni in the 20–40 cm soil depth, and Zn in the 60–80 cm soil depth were also enriched, but potential ecological risk was “low”. In subsequent leaching, PTEs concentration of leachate gradually returned to the background value and water quality index was “excellent”. There were no significant changes in PTEs and ecological risk observed. During the monitoring process, the health risk caused by the migration of PTEs to the human body was always within the acceptable range. Overall, this study provides a reference for the management of risks from the application of SS on forestlands, i.e., SS/soil ratios ˂ 45:55 is recommended on forestlands, and special attention should be given to early leaching risk. In addition, it also provides an important assessment method for the risk of PTEs leaching and migration in forested land application.
A non-invasive method to estimate the number of Trypodendron lineatum holes on dead standing pines (Pinus sylvestris L.) was developed using linear and nonlinear estimations. A classical linear regression model was first used to analyze the relationship between the number of holes caused by T. lineatum on selected stem units and the total number of holes on an entire dead stem of P. sylvestris. Then, to obtain a better fit of the regression function to the data for the stem unit selected in the first step, piecewise linear regression (PLR) was used. Last, in an area used to evaluate wood decomposition (method validation), the total and mean numbers of T. lineatum holes were estimated for single dead trees and for a sample (n = 8 dead trees). Data were collected in 2009 (data set D1), in 2010–2014 (data set D2) and in 2020 (data set D3) in forests containing P. sylvestris located within Suchedniów–Oblęgorek Landscape Park, Poland. A model was constructed with three linear equations. An evaluation of model accuracy showed that it was highly effective regardless of the density of T. lineatum holes and sample size. The method enables the evaluation of the biological role of this species in the decomposition of dead standing wood of P. sylvestris in strictly protected areas.
The large larch beetle, Ips cembrae, is a significant pest causing the death of larch. In 2020, the attack density of I. cembrae on larch trap trees and standing trees was evaluated using sample sections placed along the trunk. As a defensive measure against I. cembrae, trap trees were highly effective in both spring and summer. The attack density increased with increasing trap tree surface area/volume. Galleries were established evenly throughout the entire trunk including the thin upper portion. When the number of trap trees was low and their capacity full, a continual aggregation of adults occurred due to pheromone communication, leading to attacks on healthy standing trees in the immediate vicinity. It was found that I. cembrae attacked standing trees from the trunk base, with a continual colonization of the stem up to 70% of the tree height in a time-differentiated progression of development stages. The attack density of I. cembrae on standing trees was up to 40% lower than on the trap trees.
Periodical cicadas (Magicicada spp.) are endemic to deciduous forests in the eastern United States. In successional forests, they must partition resources such as host trees to coexist. We measured tree size, emergence holes, oviposition scar bundles, and chorusing center abundances of Magicicada species on 12 common tree species in a deciduous forest to understand host-tree use. We predicted that the abundance of periodical cicadas and use of specific host-tree species would change depending on the Magicicada species and tree life stage. We considered the size of the tree (diameter at breast height) as a covariate to control for tree size and collected eggs for a greenhouse experiment to assess whether nymphs prefer to feed on Quercus rubra or Acer saccharum. More emergence holes were found below Quercus species than any other tree species. The abundance of periodical cicadas on host trees used for chorusing centers varied depending on the Magicicada species, but were most abundant on Quercus species. Oviposition scar bundles were also more frequent on Quercus. More nymphs were found on Quercus than Acer in the nymph preference study. Though periodical cicadas used Quercus hosts more than other tree species, their abundances on different host tree sizes and species differed significantly. Periodical cicada species may use specific host species and life stages as a way to partition resources and minimize competition among the Magicicada species during emergence years.
Taman Saujana Hijau (TSH), Putrajaya is a 41-ha urban park planted with various coniferous species from around the world. Insect pests and disease incidences of this park are unknown and there is a need for an evaluation of the health status of this urban park. This study assessed the level of pest and disease incidents of coniferous species in 12 plots of 7 species (Araucaria bidwilii, Araucaria haterophylla, Araucaria cunninghamii, Pinus caribaea, Pinus merkusii, Podocarpus polystachyus, and Podocarpus costalis). Termites, canker disease, and foliar disease are three major problems. The highest pest and disease incidence (PnDI) was foliar disease with a 0.49 coefficient correlation between the total number of trees and the PnDI, followed by canker disease with 0.40, and termites with 0.36. Of the seven conifers, A. haterophylla was the most infected followed by A. bidwilii and A.cunninghamii. It was concluded that the incidence of pests and diseases in TSH was moderate. To our knowledge, this may be the first baseline inventory of pests and diseases of coniferous species in Malaysia.
In petroleum-producing territories of West Siberia (Russia), oilwell gas flares have a thermal effect on nearby plant communities. Such communities can be used as models for studying plant acclimation to global warming. In the present study on the effect of the hydrothermal regime at the flare sites on mesophyll and stomatal functional traits of Betula pubescens, leaves were collected from trees at 250 m (control site [CS]), 200, 150 and 100 m (maximum impact site [MIS]) from a flare. From the CS to MIS site, the average annual air temperature increased by 0.5 °C and bog water level decreased by 17 cm. On plants from the MIS, stomata were 16% smaller and density was 20% lower compared to those at the CS, resulting in lower maximum stomatal conductance in plants from the MIS (mean ± SE: MIS 0.84 ± 0.05 mol·m−2 s−1, CS 1.24 ± 0.06 mol·m−2 s−1; F = 12.6, P < 0.01). Mesophyll cell volume was 1.9 times lower at MIS than at CS. Chloroplast numbers per cell also declined with distance from the flares, from 21 (MIS) to 18 (CS; F = 15.6, P < 0.001), and chloroplast volume was 24% higher at the CS, whereas the number of mesophyll cells and chloroplasts numbers per unit leaf area were 1.9 and 1.8 times higher at the MIS than at the CS, respectively. As a result, leaves from the MIS had a large total mesophyll cell (A mes/A) and chloroplast (A chl/A) surface area per unit leaf area, resulting in a 46% increase in mesophyll conductance in plants from the MIS. Thus, structural changes in leaf epidermis consisted of a decrease in stomatal size and number, could lower transpiration losses with higher temperatures and less water. To compensate for the reduction in leaf conductance due to a decrease in stomatal conductance under these conditions, an increase in the number of mesophyll cells and chloroplasts per unit area provides a greater gas-exchange area and mesophyll conductance.
