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Climate change has had a widespread and profound impact on global temperature and precipitation patterns, especially in semi-arid areas. Plant δ13C and iWUE indicate the trade-off between carbon uptake and water loss, which is pivotal for understanding plant responses to climate change. Information about the long-term responses of the physiological and ecological processes of different tree species to climate change is also required. To investigate the impact of different forest stand structures and site conditions on long-term growth and physiological processes of coniferous and broad-leaved trees in the mountainous area of Beijing, we analyzed the tree-ring δ13C variation of four tree species (Platycladus orientalis, Pinus tabuliformis, Quercus variabilis, Robinia pseudoacacia) sampled from 64 plots with varying site and stand conditions. We found that the tree-ring δ13C of the four tree species varied from each other and was mainly affected by density and slope aspect, followed by slope and age. Both tree-ring δ13C and iWUE of the four tree species showed increasing trends over time, mechanistically linked to long-term changes in global CO2 concentration. This indicates the four native tree species have adapted well to climate change, and the risk of decline is relatively low. The increased iWUE translated into different growth patterns which varied with tree species, site, and stand condition. Different tree species have varying sensitivities to environmental factors. The iWUE of coniferous tree species is more sensitive to climate change than that of broad-leaved tree species, especially to temperature (T), the Standardized Precipitation Evapotranspiration Index (SPEI), and vapor pressure deficit (VPD). [ABSTRACT FROM AUTHOR]

Phytophthora cinnamomi is a devastating soil-borne plant pathogen. The primary source of P. cinnamomi infection is the soil, where the pathogen can persist for long periods. Effective prevention and management of this pathogen in tree crops requires an early and reliable detection method. In this study, we developed a simple, fast, reliable, and sensitive method based on real-time quantitative PCR (qPCR) for P. cinnamomi detection and quantification directly in plant or soil samples. Primers were developed targeting the nuclear single-copy ras-related protein gene Ypt1, suitable for Phytophthora-specific PCR. The specificity of the assay was confirmed by testing it against genomic DNA from 50 isolates across eight different Phytophthora clades, including the very similar P. parvispora. The efficiency and reliability of the qPCR protocol were evaluated in challenging environmental samples, such as plant tissue of different host trees (walnut, chestnut, oak) and naturally infected soils in walnut orchards. The main outcome was the development of a qPCR method for the specific identification and quantification of P. cinnamomi in natural soil samples. Additionally, this study established a systematic and repeatable soil sampling method and developed an efficient soil DNA extraction technique to apply the developed qPCR in naturally infested soils of walnut orchards. [ABSTRACT FROM AUTHOR]

Remote sensing-assisted monitoring of forest health entails methods that can provide up-to-date and accurate information on decline and mortality of individual trees, while maintaining time and cost efficiency. However, the trade-off of applying consumer-grade UAV-RGB data as the most affordable and accessible data source at the catchment level is constrained by its poor spectral information content. We developed a method based on the fusion of UAV-RGB data with space-borne Sentinel-2 Multispectral Instrument (MSI) at the level of tree crowns, with the specific target of supporting studies on semi-arid tree decline. We applied linear spectral unmixing (Spectral Unmixing-Based data Fusion method, LSUBF) by considering a limited number of endmembers and calculating the abundances (fractional covers) from the UAV data, and evaluated the results by high-resolution MSI space-borne data including SPOT-6 (1.5 m spatial resolution) and PlanetScope (3 m spatial resolution). This method suggested an increase in the coefficient of determination of the applied generalized additive model for decline severity estimation at tree crown level from 0.61 to 0.69, while it was improved from 0.70 to 0.91 when fitting a non-parametric random forest model. The results of sensitivity analysis demonstrated that the additional spectral information obtained from the proposed method results in higher accuracy in estimating decline severity. We suggest this method as a cost-effective alternative to monitor periodical tree decline, in particular across semi-arid ecosystems. [ABSTRACT FROM AUTHOR]

Phytophthora cinnamomi is a devastating soil-borne plant pathogen. The primary source of P. cinnamomi infection is the soil, where the pathogen can persist for long periods. Effective prevention and management of this pathogen in tree crops requires an early and reliable detection method. In this study, we developed a simple, fast, reliable, and sensitive method based on real-time quantitative PCR (qPCR) for P. cinnamomi detection and quantification directly in plant or soil samples. Primers were developed targeting the nuclear single-copy ras-related protein gene Ypt1, suitable for Phytophthora-specific PCR. The specificity of the assay was confirmed by testing it against genomic DNA from 50 isolates across eight different Phytophthora clades, including the very similar P. parvispora. The efficiency and reliability of the qPCR protocol were evaluated in challenging environmental samples, such as plant tissue of different host trees (walnut, chestnut, oak) and naturally infected soils in walnut orchards. The main outcome was the development of a qPCR method for the specific identification and quantification of P. cinnamomi in natural soil samples. Additionally, this study established a systematic and repeatable soil sampling method and developed an efficient soil DNA extraction technique to apply the developed qPCR in naturally infested soils of walnut orchards.

The cypress bark beetle, Phloeosinus aubei (Coleoptera, Curculionidae, Scolytinae) prefers to build breeding galleries in decaying host trees. However, volatile cues specific to decaying or actively infested trees have not yet been reported. Any such information would be useful for the management of this invasive, wood-boring species that has become established across Europe in the temperate zone and is now a key pest of ornamental Cupressaceae in nurseries and urban landscapes. Our objective was to reveal key components in host volatiles specific to stressed trees, which could be potential signals for the pest of its suitability for colonisation. Volatile profiles of arborvitae, Thuja occidentalis 'Smaragd' suffering from either dehydration or fresh infestation of P. aubei was collected and compared to that samples from healthy control trees. Analyses of volatiles by gas chromatography coupled to an electroantennographic detector revealed substantial differences between healthy, dehydrated and infested trees. Structural elucidation of the major antennally active components revealed that both α-pinene and α-thujene were prevalent in the volatiles of infested trees, whilst α-thujone was the major component in volatiles of healthy trees. In volatiles collected from trunks housing fresh P. aubei female nuptial chambers, sharp increases of β-pinene, myrcene, limonene, and p-cymene were noticed, alongside trace amounts of camphene and fenchene. Volatiles collected from fresh frass showed a similar profile, but with a somewhat smaller amount of limonene. Fenchone was present in each type of volatiles, however, only in low amounts. Further studies should be directed to reveal the behavioural role of these components, which could be helpful in developing kairomone-based techniques for monitoring the flight of the pest in stands of scale-leafed trees. [ABSTRACT FROM AUTHOR]

The deterioration of farmland shelterbelts in the Ulan Buh desert oases could weaken their protective functions. Therefore, an accurate method is essential to assess tree decline degree in order to guide the rejuvenation and transformation of these shelterbelts. This study selected three typical farmland shelterbelts in the Ulan Buh desert oases as the objects. Terrestrial laser scanning (TLS) and airborne hyperspectral imagery (AHI) were used to acquire point cloud data and detailed spectral information of trees. Point cloud and spectral characteristics of trees with varying decline levels were analyzed. Six models were constructed to identify decline degree of shelterbelts, and model accuracy was evaluated. The coefficient of determination between the structural parameters of trees extracted by TLS and field measurements ranged from 0.76 to 0.94. Healthy trees outperformed declining trees in structural parameters, particularly in tridimensional green biomass and crown projection area. Spectral reflectance changes in the 740–950 nm band were evident among the three tree types with different decline levels, decreasing significantly with increased decline level. Among the TLS-derived feature parameters, the canopy relief ratio of tree points and point cloud density strongly correlated with the degree of tree decline. The plant senescence reflectance index and normalized difference vegetation index exhibited the closest correlation with tree decline in AHI data. The average accuracy of the models constructed based on the feature parameters of LiDAR, AHI, and the combination of both of them were 0.77, 0.61, and 0.81, respectively. The light gradient-boosting machine model utilizing TLS–AHI comprehensive feature parameters accurately determined tree decline. This study highlights the efficacy of employing feature parameters derived from TLS alone to accurately identify tree decline. Combining feature parameters from the TLS and AHI enhances the precision of tree decline identification. This approach offers guidance for decisions regarding the renewal and transformation of declining farmland shelterbelts. [ABSTRACT FROM AUTHOR]

Context: Extreme drought can result in the widespread die-off of forests and dramatically altered ecosystem structure. Such changes are likly to influence fauna using resouces within these forests. Aims: Following a record hot and dry year/summer in 2010/11, large-scale canopy collapse occurred within a Mediterranean-type mixed jarrah (Eucalyptus marginata)–marri (Corymbia calophylla) forest in south-west Western Australia. We investigated the effects of this collapse on bird assemblages in 2016, 5 years after the initial collapse. Methods: We carried out bird surveys using a standardised search method for five paired drought-affected and adjacent healthy forest plots. Key results: A total of 3042 records of 51 bird species were observed across all surveys. Overall, the pooled (mean ± s.d.) reporting rates for drought-affected plots (13.84 ± 0.60 individuals/survey) were significantly less than the reporting rates for healthy plots (34.44 ± 1.03 individuals/survey) (PERMANOVA: F 1 = 54.94, R 2 = 0.31, P = 0.001). Species diversity was also higher in healthy plots (t 26 = 11.21, P < 0.001). Foliage-searching birds were the most abundant guild across all plots and were reported less often in drought-affected plots (t 6 = 2.70, P < 0.04). Conclusions: Drought-affected jarrah forest plots exhibited significant differences in bird assemblages compared to healthy plots. Overall, the drought-affected forest provides a less favourable habitat for birds compared to healthy forest. Implications: With marked variability and extreme climate events predicted for the future, understanding the impacts of such changes will contribute to how we manage forest ecosystems. We investigated the effects of a large-scale drought-induced canopy collapse on bird community assemblages. Overall, the pooled (±s.d.) reporting rates for drought-affected plots (13.84 ± 0.60 individuals/survey) were significantly less than the reporting rates for healthy plots (34.44 ± 1.03 individuals/survey). Foliage-searching birds were the most abundant guild across all plots and were reported less often in drought-affected plots. Overall, the drought-affected forest provides less favourable habitat for bird assemblages compared to healthy forest. [ABSTRACT FROM AUTHOR]

Eucalypt, mostly Eucalyptus globulus, is the exotic tree species occupying the largest area of Portuguese planted forest. Eucalypts were introduced in the country more than one hundred years ago, but it was only in the second half of the twentieth century that the area of plantations grew with the onset of their use in the paper and pulp industry. As an exotic species, it was free from pests and diseases but gradually the number of insects and pathogens affecting these plants increased. In recent year, a new disease causing root rot and dieback has been detected with increasing frequency. In this work, two Phytophthora species, P. cinnamomi and P. alticola, were identified associated with these symptoms. Koch's postulates were fulfilled, proving that these two species are pathogenic to E. globulus. This is the first report of P. alticola outside South Africa. Although presently unknown, the possible factors associated with the increased occurrence of this disease are discussed. [ABSTRACT FROM AUTHOR]

Drought has serious effects on forests, especially semi-arid and arid forests, around the world. Zagros Forest in Iran has been severely affected by drought, which has led to the decline of the most common tree species, Persian oak (Quercus brantii). The objective of this study was to determine the effects of drought on the anatomical structure of Persian oak. Three healthy and three declined trees were sampled from each of two forest sites in Ilam Forest. Discs were cut at breast height, and three sapwood blocks were taken near the bark of each tree for sectioning. The anatomical characteristics measured included fiber length (FL), fiber wall thickness (FWT), number of axial parenchymal cells (NPC), ray number (RN), ray width (RW), and number of calcium oxalate crystals. Differences between healthy and declined trees were observed in the abundance of NPC and in RN, FL, and FWT, while no differences occurred in the number of oxalate crystals. The decline had uncertain effects on the FL of trees from sites A and B, which showed values of 700.5 and 837.3 μm compared with 592.7 and 919.6 μm in healthy trees. However, the decline resulted in an increase in the FWT of trees from sites A and B (9.33 and 11.53 μm) compared with healthy trees (5.23 and 9.56 μm). NPC, RN, and RW also increased in declined individuals from sites A and B (28.40 and 28.40 mm−1; 41.06 and 48.60 mm−1; 18.60 and 23.20 μm, respectively) compared with healthy trees (20.50 and 19.63 mm−2; 31.60 and 28.30 mm−2; 17.93 and 15.30 μm, respectively). Thus, drought caused measurable changes in the anatomical characteristics of declined trees compared with healthy trees. [ABSTRACT FROM AUTHOR]

The deterioration of farmland shelterbelts in the Ulan Buh desert oases could weaken their protective functions. Therefore, an accurate method is essential to assess tree decline degree in order to guide the rejuvenation and transformation of these shelterbelts. This study selected three typical farmland shelterbelts in the Ulan Buh desert oases as the objects. Terrestrial laser scanning (TLS) and airborne hyperspectral imagery (AHI) were used to acquire point cloud data and detailed spectral information of trees. Point cloud and spectral characteristics of trees with varying decline levels were analyzed. Six models were constructed to identify decline degree of shelterbelts, and model accuracy was evaluated. The coefficient of determination between the structural parameters of trees extracted by TLS and field measurements ranged from 0.76 to 0.94. Healthy trees outperformed declining trees in structural parameters, particularly in tridimensional green biomass and crown projection area. Spectral reflectance changes in the 740–950 nm band were evident among the three tree types with different decline levels, decreasing significantly with increased decline level. Among the TLS-derived feature parameters, the canopy relief ratio of tree points and point cloud density strongly correlated with the degree of tree decline. The plant senescence reflectance index and normalized difference vegetation index exhibited the closest correlation with tree decline in AHI data. The average accuracy of the models constructed based on the feature parameters of LiDAR, AHI, and the combination of both of them were 0.77, 0.61, and 0.81, respectively. The light gradient-boosting machine model utilizing TLS–AHI comprehensive feature parameters accurately determined tree decline. This study highlights the efficacy of employing feature parameters derived from TLS alone to accurately identify tree decline. Combining feature parameters from the TLS and AHI enhances the precision of tree decline identification. This approach offers guidance for decisions regarding the renewal and transformation of declining farmland shelterbelts.

Moderate-resolution satellite imagery is essential to detect conifer tree decline on a regional scale and address the threat caused by pinewood nematode (PWN), (Bursaphelenchus xylophilus. This is a quarantine organism responsible for pine wilt disease (PWD), which has caused substantial ecological and economic losses in the maritime pine (Pinus pinaster) forests of Portugal. This study describes the first instance of a pre-operational algorithm applied to Sentinel-2 imagery to detect PWD-compatible decline in maritime pine. The Random Forest model relied on a pre-wilting and an in-season image, calibrated with data from a 24-month long field campaign enhanced with Worldview-3 data and the analysis of biological samples (hyperspectral reflectance, pigment quantification in needles, and PWN identification). Independent validation results attested to the good performance of the model with an overall accuracy of 95%, particularly when decline affects more than 30% of the 100 m2 pixel of Sentinel-2. Spectral angle mapper applied to hyperspectral measurements suggested that PWN infection cannot be separated from other drivers of decline in the visible-near infrared domain. Our algorithm can be employed to detect regional decline trends and inform subsequent aerial and field surveys, to further investigate decline hotspots. [ABSTRACT FROM AUTHOR]

Prosopis cineraria (L.) druce and Ziziphus spina-christi (L.) Desf. are important species of Sahara-Sindhi vegetation. While being native, they have good adaptability, growth and regeneration. This study was conducted to estimate the amount of groundwater required for the sustainability of Z. spina-christi and P. cineraria natural forests in the watershed of Faryab county in Kerman province, Iran. First, using Google Earth images, networking establishment of ninety plots of 100 m2 in one-hectare networks, the average number of Z. spina-christi and P. cineraria trees were counted. Then, using the minimum water requirement of trees, estimated based on lysimetric studies, water consumption of Z. spina-christi and P. cineraria trees in the area was calculated. Using the MODFLOW model, the groundwater balance situation in Faryab plain aquifer for 2017-2018 was calculated. Having the volume of water consumption of Z. spina-christi and P. cineraria in the region, water balance and aquifer storage coefficient, the impact of the forests on groundwater of Faryab plain was calculated. The results showed that the average number of P. cineraria trees is 250 individuals and Z. spina-christi tree stands are 30 individuals per hectare. The results of the study of water balance and groundwater aquifer show a volume deficit of 25 million cubic meters of the reservoir and a 26-meter drop in groundwater level over the past two decades. According to the water balance calculated, the uncontrolled extraction of water by agricultural wells, which is about 160 million cubic meters per year, has caused such a decline in the region. Considering the importance of Z. spina-christi and P. cineraria trees for this ecosystem as the main species, the water right of this forest was estimated to be 2.6 million cubic meters per year in the planning of water resources in the Faryab plain. [ABSTRACT FROM AUTHOR]

The features of the spread of pine stands decline in the Eastern Polissya of Ukraine under biotic and abiotic factors impact are generalized and highlighted. The works were carried out according to the generally accepted methods of forest pathological and forestry-taxation research on the forest pathological routes in pine stands with signs of tree decline and in foci of tree mortality, at the permanent and temporary plots in the dieback foci. To determine the species composition, population indices, and population density of stem insects in the dieback foci, periodic decadal assessments were carried out in the exposed pheromone traps and in different parts of the stem of model trees according to entomological research methods. It is determined that the drying of pine trees in previous years was mainly due to damage of trees by the pathogen of the root rot Heterobasidion annosum (Fries) Bref. At the beginning of the growing season in 2015 the reconnaissance surveys revealed the spread of pathological drying of pine stands. After periodic prolonged droughts during the vegetation periods of 2015–2017, in the following years, the intensity of the group formation , curtain dieback foci increased with a tendency to continuous drying of pine stands. Mainly pines of middle-aged and older age, artificial origin, pure composition, simple form, less stand density in all types of forests dried. Dieback foci initially appeared near the forest edge, narrow strips and low-density pine stands, moving to other pines from the south-western to the north-eastern part of Eastern Polissya. Area of pine stands with dieback foci in the study region annually amounted to 12.5–17.1 thousand ha (6–8% of their total area). Based on detailed forest pathological inspection, it was found that tree weakening and the dieback of stands occurred due to the mass propagation of stem insects – Ips acuminatus Gyll. and Ips sexdentatus Boern. It was determined that the population density of the young generation of Ips acuminatus during 2017–2018 exceeded the average population indices by 10 or more times with production up to 100 juvenile beetles per dm2 of populated stem area. The possibility of three generations of Ips acuminatus development per year under favorable conditions has been revealed. Due to unfavorable weather conditions for wintering of stem insects and exceeding the long-term precipitation with a decrease in temperature at the beginning of the growing season in 2019 the density of bark beetle populations decreased significantly (2–3 times) with the formation of only single and group dieback foci. The number of insects decreased due to the restoration of water supply to pine trees, which made it possible to maintain sufficient resin release and flooding of mother and larval galleries with adult beetles. With sufficient moisture, pine trees of the 1st-2nd categories of health condition are able to maintain a stable level of resin productivity for a long time compared to weakened trees. Therefore, it is important to reproduce more resistant pine stands of mixed composition, natural origin, complex shape structure. For the first time, it has been found that very weakened and drying up pine trees are able to rapidly but briefly release more resin than more viable trees. To reduce and overcome the effects of pine forests dieback, a set of forestry and protective measures should be applied: sanitary felling, attraction of birds and other entomophagous animals, application of mineral fertilizers, and stem injections of the most valuable trees.

Evidence has shown that drought-induced crown dieback has significant interaction with soil-plant water and nutrients relationships, but there isn't sufficient knowledge of the water and nutrients connections in declining Persian oak (Quercus brantii) trees. To investigate the relationships between crown dieback and leaf nutrients concentrations, leaf water content, soil nutrients concentrations and soil moisture, one of the dieback affected stands was selected. This stand was located in Shalam forested area in northern Ilam province, west of Iran. Persian oak trees were evaluated using a crown dieback classification and divided into four classes with four replicates based on the severity of crown dieback. Sampling from leaves of trees and soil was implemented randomly in four sides of tree crown in August. Trees with moderate to severe declining showed reduced leaf water content (WC) and reduced relative leaf water content (RWC). Leaf N and P concentration of declining trees was significantly (p-value <0.05) more than that of healthy trees. The leaf K concentration of declining trees was significantly (p-value <0.10) more than that of the healthy. The leaf N:P amounts of oak trees was statistically different among crown dieback classes. But no significant differences was observed between the healthy and declining trees in terms of soil N, P, K, Ca and Mg concentrations and soil moisture. It was concluded that drought has effects on the nutrients status in the leaves of Persian oak trees and their changing in the declining trees is for resistance to drought condition, improving water use efficiency and possibly performance of vital activities. [ABSTRACT FROM AUTHOR]

This study was done to investigate the effect of slope aspect and crown dieback intensity on the nutrient status of leaves of Persian oak trees influenced by dieback and site soil in the forests of Ilam province. For this purpose, the Forest area of Melah-Siah was considered and two one-hectare areas on the northern and southern aspects with almost the same altitude levels were selected. In each selected area, 10 trees were sampled in two intensities of healthy and dieback affected. Leaf samples were collected from the four main sides of tree crown and the middle part of the crown and from their terminal branches. Furthermore, from the south side of the selected trees, soil samples were prepared from two depths. Collected samples were transferred to the laboratory for analysis of organic carbon (OC), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg). The results showed that the slope-aspect and crown dieback intensities have significant effects on the amount of P, Ca and Mg in Persian oak tree leaves. So that, the amount of leaf P in the northern site was higher than the southern site. Leaf Ca and Mg concentrations were higher in the north site than the south site and in dieback-affected trees than the healthy trees. Also, the amount of soil OC was significantly affected by slope aspect. The OC content in depth of 0-20 cm, in the northern site was less than the southern site. The amount of pH, CaCO3 and soil moisture in the depth of 0-20 cm and soil moisture in the depth of 20-50 cm were also changed under the slope aspect. It was concluded that leaf nutrients had more changes than soil elements under the influence of considered factors and the amount of these changes was more attributed to the slope-aspect. The studied Persian oak trees with different crown dieback degrees had a similar situation in terms of soil macro elements, but had different conditions in terms of leaf macro elements. Considering the differences between their habitats in terms of soil moisture and pH, it can be said that the dieback severity of tree crowns is related to physiological mechanisms in trees for absorbing water and nutrients. [ABSTRACT FROM AUTHOR]

Malus sieversii (wild apple trees) is a tertiary relict tree species and a key ancestor of the cultivated apple trees today. In recent years, serious growth decline and individual death have occurred for M. sieversii. Whether growth decline would lead to the change in twig (composed of leaves and one-year stem) functional traits and their associations of wild apple trees remains unclear. Two long-term monitoring plots (1 hm2) for severely declined and relatively healthy wild apple trees, respectively, were set up in Yili Valley, China. Based on two-year investigations, the differences in tree functional traits and interrelations between the two plots and the influencing factors were analyzed. The crown projective cover, dead branch percentage, and fruit yield were markedly different between two sites and two years. Leaf nitrogen and phosphorous concentrations of declined trees were generally less than healthy trees, although the soil of the former was more fertile. The nitrogen was more susceptible to the stressing, especially for declined trees. Concentrations of stem nitrogen, phosphorous, and potassium and leaf potassium were relatively stable in both plots. The plant trait network analysis indicated that leaf nitrogen (per unit area) that promoted plant growth was the hub trait (meaning that it is correlated with most traits) for healthy trees, while leaf potassium (per unit mass) that related to resistance enhancement became the hub trait for declined trees. Meanwhile, the covariant characteristics of twig traits between the two plots differed obviously, and the soil-trait and growth-trait correlations became more negative for declined trees than healthy trees, indicating that intra-trait and environment-trait associations had changed greatly when trees declined. The ordination analysis revealed that total and available soil nitrogen, phosphorous, and total potassium, pH and plant growth parameters significantly influenced twig traits. Our results demonstrated that twig functional traits and their interrelations of wild apple trees can indicate tree decline trend. We strongly recommend that managers should take measures to prevent the decline of healthy wild apple trees as soon as possible to realize the sustainable existence of this precious germplasm resource. The results provide a theoretical support for scientific management of wild apple populations in the Tianshan Mountains in Central Asia.

Drought has serious effects on forests, especially semi-arid and arid forests, around the world. Zagros Forest in Iran has been severely affected by drought, which has led to the decline of the most common tree species, Persian oak (Quercus brantii). The objective of this study was to determine the effects of drought on the anatomical structure of Persian oak. Three healthy and three declined trees were sampled from each of two forest sites in Ilam Forest. Discs were cut at breast height, and three sapwood blocks were taken near the bark of each tree for sectioning. The anatomical characteristics measured included fiber length (FL), fiber wall thickness (FWT), number of axial parenchymal cells (NPC), ray number (RN), ray width (RW), and number of calcium oxalate crystals. Differences between healthy and declined trees were observed in the abundance of NPC and in RN, FL, and FWT, while no differences occurred in the number of oxalate crystals. The decline had uncertain effects on the FL of trees from sites A and B, which showed values of 700.5 and 837.3 μm compared with 592.7 and 919.6 μm in healthy trees. However, the decline resulted in an increase in the FWT of trees from sites A and B (9.33 and 11.53 μm) compared with healthy trees (5.23 and 9.56 μm). NPC, RN, and RW also increased in declined individuals from sites A and B (28.40 and 28.40 mm−1; 41.06 and 48.60 mm−1; 18.60 and 23.20 μm, respectively) compared with healthy trees (20.50 and 19.63 mm−2; 31.60 and 28.30 mm−2; 17.93 and 15.30 μm, respectively). Thus, drought caused measurable changes in the anatomical characteristics of declined trees compared with healthy trees.

Significant portions of the world's forests have been impacted by severe and large‐scale tree declines characterised by gradual but widespread loss of vigour and subsequent death of either single or several tree species. Tree deaths represent a threat for fauna that are dependent on forest habitats for their survival. Although tree declines have received considerable scientific attention, surprisingly, little is known about their impacts on fauna. In total, we calculated 631 effect sizes across 59 studies that quantified the impact of tree declines on animal abundance. Data representing 186 bird species indicated an overall increase in bird abundance in response to tree declines (meta‐analysis mean ± estimation g = 0.172 ± 0.053 [CI 0.069 to 0.275], P = 0.001); however, there was substantial variability in responses (significant heterogeneity P < 0.001) with a strong influence of diet as well as nesting guild on bird responses. Granivores (especially ground‐foraging species, e.g. Passerellidae species), bark‐foraging insectivores (e.g. woodpeckers), as well as ground‐ and cavity‐nesting species apparently benefitted from tree declines, while nectarivorous birds [and, although not significant, aerially foraging insectivores (e.g. flycatchers) and leaf‐gleaning insectivores (canopy‐feeding)] were less common in the presence of tree declines. Data representing 33 mammal species indicate a tendency for detrimental effects of tree declines on mammals that use trees as refuges, while aerial foragers (i.e. bats) may benefit from opening up the canopy. Overall the average effect for mammals was neutral (meta‐analysis mean estimation g = −0.150 ± 0.145 [−0.433 to 0.134], P = 0.302). Data representing 20 reptile species showed an insufficient range of responses to determine any diet or foraging effect on their responses. Data for 28 arthropod taxa should be considered with caution, as we could not adequately separate taxa according to their specialisations and reliance on key habitat. The data broadly suggest a detrimental effect of tree declines (meta‐analysis mean estimation g = −0.171 ± 0.072 [−0.311 to −0.031], P = 0.017) with ground‐foraging arthropods (e.g. detritivores and predators such as spiders and centipedes) more likely to be detrimentally impacted by tree declines. The range of responses to tree declines signifies substantially altered animal communities. In many instances, altered ecosystem function due to loss of key animal services will represent a significant threat to forest health. [ABSTRACT FROM AUTHOR]

The article discusses a 2021 report on the infection of Arizona ash trees by Candidatus Phytoplasma fraxini-related strain associated with witches-broom symptoms in Arizona ash. It states that the infection causes yellowing leaf symptoms, and shoot proliferation as a result of abnormal forcing of lateral buds. Also noted is the need to manage the strain due its potential threat to other ash species or crops like grapevine.

Field surveys conducted in two urban green spaces in Athens (Greece) revealed the presence of Phytophthora -related diseases on Platanus orientalis and P. x acerifolia trees. Declining trees showed a range of disease symptoms including root rot, stem bleeding cankers and extensive canopy dieback. Since there is little information about the etiology of these diseases, a study was conducted from 2016 to 2021 to define the main pathogens involved. A total of 71 Phytophthora isolates were obtained from bark tissues and rhizosphere samples collected from symptomatic plane trees. Based on morphological traits and DNA sequence data, Phytophthora isolates were identified as Ph. mediterranea (11 isolates) and Ph. nicotianae (60). Over a five-year period 41% of P. orientalis trees associated with Phytophthora infections died and were removed from the park. Pathogenicity tests confirmed that all Phytophthora species including Ph. cinnamomi used for comparison, are pathogenic on both P. orientalis and P. x acerifolia trees. Phytophthora cinnamomi was shown to be the most aggressive species on both P. orientalis and P. x acerifolia. Phytophthora nicotianae was the dominant species, whereas Ph. mediterranea was associated with a few trees. Our finding has contributed to expanding knowledge on the host and geographic range of Ph. mediterranea , an invasive pathogen with a high potential for diffusion in Mediterranean regions and highlights the importance of enhancing biosecurity measures to prevent and limit the spread of invasive pathogens in urban and natural ecosystems. • Phytophthora-related diseases on Platanus orientalis and P. x acerifolia trees. • Phytophthora nicotianae and Ph. mediterranea are involved in the decline of Platanus spp. in Greece. • Platanus orientalis and P. x acerifolia are widespread urban trees. • Ph. nicotianae was more commonly isolated than Ph. mediterranea in urban spaces. • Ph. mediterranea was isolated only from P. orientalis trees. [ABSTRACT FROM AUTHOR]

Widespread tree growth decline and absence of acorn production are observed in formerly coppiced Quercus pyrenaica stands. Attempts to convert oak coppices into high forests by thinning have failed to date, possibly due to the massive root system developed by trees after centuries of coppicing. We tested root trenching and stem girdling as silvicultural treatments to mitigate this hypothetical root-to-shoot imbalance and enhance the physiological performance of multi-stemmed clonal trees. We expected that severing the roots within a clone by trenching would reduce root respiratory carbon losses. Alternatively, stem girdling would increase carbon availability above the girdled zone, whilst the communal root system is maintained by non-girdled stems. After clonal structure delineation in a one-hectare experimental plot, root trenching and stem girdling were applied to stems belonging to different clones. Twig hydraulic traits, leaf water potential, non-structural carbohydrates (NSC) concentration in twigs, stems and roots, stem xylem [CO 2 ] as an indicator of root respiration, stem growth, and acorn production were discretely monitored up to 12 years after treatment application for comparison with control stems. Stem girdling led to short-term enhancements in NSC pools above the girdled zone. However, hydraulic dysfunction symptoms and canopy dieback were observed four years after girdling, eventually causing mortality. Root trenching initially increased root respiration and reduced stem growth without an apparent decline in the hydraulic function and NSC pools above-ground. Ten years after trenching, stem [NSC] increased while stem growth limitations diminished. Although not statistically significant, slight enhancements in acorn production were observed 6 and 12 years after trenching. We discourage stem girdling as a silvicultural practice to mitigate a root-to-shoot imbalance in abandoned oak coppices, as long-term detrimental effects outweighed potential benefits. Root trenching enhanced tree NSC above ground. However, such improvement may not offset the potential costs of root trenching. • Trenching and girdling may help to mitigate the root-to-shoot imbalance in coppices. • Stem girdling is discouraged due to long-term detrimental effects. • Root trenching enhanced the availability of carbohydrates aboveground. [ABSTRACT FROM AUTHOR]

Plant–pathogen interactions are often considered in a pairwise manner with minimal consideration of the impacts of the broader endophytic community on disease progression and/or outcomes for disease agents and hosts. Community interactions may be especially relevant in the context of disease complexes (i.e., interacting or functionally redundant causal agents) and decline diseases (where saprobes and weak pathogens synergize the effects of primary infections and hasten host mortality). Here we describe the bark endophyte communities associated with a widespread decline disease of American beech, beech bark disease (BBD), caused by an invasive scale insect (Cryptococcus fagisuga) and two fungal pathogens, Neonectria faginata and N. ditissima. We show that the two primary fungal disease agents co-occur more broadly than previously understood (35.5% of infected trees), including within the same 1-cm diameter phloem samples. The two species appear to have contrasting associations with climate and stages of tree decline, wherein N. faginata was associated with warmer and N. ditissima with cooler temperatures. Neonectria ditissima showed a positive association with tree crown dieback – no such association was observed for N. faginata. Further, we identify fungal endophytes that may modulate disease progression as entomopathogens, mycoparasites, saprotrophs, and/or additional pathogens, including Clonostachys rosea and Fusarium babinda. These fungi may alter the trajectory of disease via feedbacks with the primary disease agents or by altering symptom expression or rates of tree decline across the range of BBD.

Moderate-resolution satellite imagery is essential to detect conifer tree decline on a regional scale and address the threat caused by pinewood nematode (PWN), (Bursaphelenchus xylophilus. This is a quarantine organism responsible for pine wilt disease (PWD), which has caused substantial ecological and economic losses in the maritime pine (Pinus pinaster) forests of Portugal. This study describes the first instance of a pre-operational algorithm applied to Sentinel-2 imagery to detect PWD-compatible decline in maritime pine. The Random Forest model relied on a pre-wilting and an in-season image, calibrated with data from a 24-month long field campaign enhanced with Worldview-3 data and the analysis of biological samples (hyperspectral reflectance, pigment quantification in needles, and PWN identification). Independent validation results attested to the good performance of the model with an overall accuracy of 95%, particularly when decline affects more than 30% of the 100 m2 pixel of Sentinel-2. Spectral angle mapper applied to hyperspectral measurements suggested that PWN infection cannot be separated from other drivers of decline in the visible-near infrared domain. Our algorithm can be employed to detect regional decline trends and inform subsequent aerial and field surveys, to further investigate decline hotspots.

Throughout the world, numerous tree species are reported to be in decline, either due to increased mortality of established trees or reduced recruitment. The situation appears especially acute for oaks, which are dominant features of many landscapes in the northern hemisphere. Although numerous factors have been hypothesized to explain reductions in tree performance, vertebrate herbivores and granivores may serve as important drivers of these changes. Here, using data from 8- and 14-yearold exclosure experiments, we evaluated the individual and interactive effects of large and small mammalian herbivores on the performance of three widespread oak species in California--coast live oak (Quercus agrifolia), California black oak (Q. kelloggii), and Oregon white oak (Q. garryana). Although impacts varied somewhat by species and experiment, herbivory by black-tailed deer (Odocoileus hemionus columbianus) reduced the height and survival of juvenile coast live oaks and altered their architecture, as well as reduced the abundance of black oak seedlings, the richness of woody species and the cover of nonoak woody species. Small mammals (Microtus californicus and Peromyscus maniculatus) had even more widespread effects, reducing the abundance of black oak seedlings and the height and cover of all three oak species. We also detected numerous interactions between small mammals and deer, with one herbivore having positive or negative effects on oak abundance and cover when the other herbivore was either present or absent. For example, deer often had negative effects on seedling abundance only when, or even more so when, small mammals were present. In summary, mammalian consumers play crucial roles in limiting oak recruitment by reducing seedling abundance, maintaining trees in stunted states, and preventing them from reaching sapling stages and becoming reproductive. Interactions between large and small mammals can also alter the intensity and direction of their effects on trees. [ABSTRACT FROM AUTHOR]

Pathogen diseases are increasingly threatening forest trees under the current climate change, causing a remarkable decrease in the stability of forest ecosystems. Ash (Fraxinus excelsior L.) dieback due to Hymenoscyphus fraxineus has been noted in Poland since 1992 and has spread over many European countries. The aim of this study was to test the hypothesis that ash trees affected by dieback could exhibit a reduced vessel size and density along the trunk, as well as a lowered width of annual wood rings, leading to the weakening of water transport towards the crown. Dead and dying ash trees were sampled in a forest district severely affected by ash decline in southern Poland. Wood samples were collected at different height along the trunk and several wood anatomical characteristics of annual tree rings over the period 2002-2011 were examined. Dead trees showed a stronger reduction in radial growth than dying trees over the period considered. Moreover, the diameter of vessels increased from the crown to the base in both dead and dying trees, while the density decreased. Significant differences between dead and dying trees were detected in size and density of vessels in the period analyzed, as well as in the width of annual rings. DNA extracted from wood samples was analyzed using SSR markers and the main genetic parameters of dead and dying trees were estimated, finding similar levels of polymorphism and only slight non-significant differences between the two health groups. Our results are consistent with the hypothesis that pathogens could disrupt the hormonal control of wood formation by interfering with the polar auxin transport, progressively leading to the death of ash trees.

Severe dieback symptoms were recently observed on apple ( Malus × domestica ) trees in Northern Italy, representing a growing concern for producers. Surveys were conducted over a 3-year period (2019 to 2021), and five apple orchards, from 5 to 12 years old, were monitored. A total of 33 fungal isolates isolated from symptomatic plants was selected for characterization. The species identification was achieved through multilocus phylogenetic analyses performed on sequences of three genomic loci (ITS, tub2 , and tef1 ). Morphological features were assessed, and the average growth rate at different temperatures was determined. Seven species were identified in association with dieback of apple trees: Botryosphaeria dothidea , Cadophora luteo-olivacea , Diaporthe rudis , Diplodia seriata , Eutypa lata , Kalmusia longispora , and Paraconiothyrium brasiliense . All the species were pathogenic when inoculated on healthy apple plants. B. dothidea resulted in the most aggressive infections. This study provides an insight into the fungal species diversity associated with apple dieback and provides basis for further investigations to assess the phytosanitary status of plant materials to recommend and implement effective management strategies., Competing Interests: The author(s) declare no conflict of interest.

Ironwood (Casuarina equisetifolia subsp. equisetifolia) trees on Guam have been in decline since 2002. This study applied proportional odds logistic multiple regression modeling to a set of biological variables in order to find significant decline predictors as a first step towards identifying pathogenic contributors. Based on the analysis of a set of 77 medium and large trees, the bacterium Ralstonia solanacearum and the fungus Ganoderma australe species complex were found to be significant predictors, with p values of <0.001 and < 0.008, respectively. Their respective values for symptomless trees were 18% and 0%, compared to 80% and 35% for those nearly dead trees of which 30% had both organisms and 15% had neither. More complex models were also fit, that included interactions. The R. solanacearum by G. australe interaction was not a strong effect, indicating additive rather than multiplicative behavior of these effects on decline severity (p value>0.087). When nine covariates were applied univariately to a data subset of 30 tree cross-sections, the significance of R. solanacearum was strongly upheld while that of G. australe was moderately reduced. Also significant were percent cross-sectional area with bacterial wetwood and the formation of ooze within 24 h. Wetwood bacteria of Klebsiella spp. and K. oxytoca were found across all levels of decline and were not significant predictors. Other enteric bacteria identified included Kosakonia, Enterobacter, Pantoea, Erwinia, and Citrobacter. [ABSTRACT FROM AUTHOR]

Ganoderma is a cosmopolitan genus that encompasses species with cultural, economic, and pathogenic importance. Despite the importance of this genus, knowledge pertaining to the species diversity of Ganoderma in South Africa is limited. This study aimed at elucidating the identity and phylogenetic placements of Ganoderma samples obtained during a survey of wood-rotting fungi in the Garden Route National Park (GRNP) of South Africa, supplemented with isolates obtained from other localities across the country. Identification was achieved by means of multilocus phylogenetic inference combined with morphological evaluation. In total, eight distinct species of Ganoderma were recovered from different hosts and localities across the country. Of these, Ganoderma cf. cupreum and Ganoderma cf. resinaceum represent possible new records for South Africa. Two novel species are described, namely, G. eickeri. and G. knysnamense. Ganoderma eickeri, sp. nov., is characterized by a triquetrous and broadly attached basidiome, a sulcate or zonate yellowish brown to brown pilear surface, and ovoid to ellipsoid basidiospores. Ganoderma knysnamense is distinguished by an applanate to ungulate, sometimes convex, dimidiate to broadly attached basidiome, a chocolate-brown pilear surface covered with a hard woody-like crust and ellipsoid, broadly ellipsoid to ovoid basidiospores. The discovery of two new Ganoderma species in this study raises the known Ganoderma species in South Africa to 13. [ABSTRACT FROM AUTHOR]

Tree declines have been recorded across forests and woodlands on most continents, causing tree mortality over thousands of square kilometres, yet the impact of tree declines upon mammals have only rarely been quantified. Once the dominant tree over the western parts of the Swan Coastal Plain in Western Australia, tuart (Eucalyptus gomphocephala) forest has been reduced to less than a third of its former range through clearing for agriculture and urban development. Additionally, over the last 30 years, the remnant population has been heavily impacted by a decline that has an unknown cause, but is likely related to a root pathogen coupled with abiotic factors (reduced rainfall, increased salinity and elevated temperatures). Tuart decline is evident as marked canopy dieback, replacement with epicormic growth and increasing bare branches, while leaf litter is lost from the tree surrounds. We examined the effect of tuart decline and other vegetation measures upon bat activity using auditory monitoring. Vegetation structure was correlated with Vespertilionidae bat activity. Falsistrellus mackenziei were more likely to forage around healthy canopies (activity positively correlated with tuart crown density and negatively correlated with tuart crown dieback). By contrast, the other three taxa were more often encountered in declining rather than healthy tuart sites. Chalinolobus gouldii was positively associated with tuart crown dieback. Activity of Vespadelus regulus and Nyctophilus spp. (species not distinguishable from their calls) were significantly positively correlated with an open tall canopy (positively with cover of plants >10 m tall and negatively with overall canopy cover density). There were no vegetation measurements that were strong predictors of activity of two Molossidae species (Ozimops kitcheneri and Austronomus australis), which intercept insects above the forest canopy. This study clearly reveals different factors influencing the activity of bat taxa, which are likely related to where they feed and their manoeuvrability around tree canopies. [ABSTRACT FROM AUTHOR]

Long-term tree growth is significantly affected by climate change, which have become a global concern. Tree-ring width and isotopic information can show how trees respond to climate change on a long-term scale and reveal some phenomena of tree decline or death. In this study, we used isotopic techniques and investigated annual changes in carbon isotope composition and tree-ring width of Populus simonii Carr. in Zhangbei, as well as trends in tree-ring carbon discrimination (Δ13C) and iWUE in normal, mildly declining and severely declining trees, in order to make a retrospective analysis and further understand the process of tree decline. We found that there were significant differences (p < 0.01 **) in δ13C, Δ13C, ci and iWUE at different decline stages, meaning that the δ13C and iWUE could be new indicators of tree health. The iWUE of all groups increased significantly, while the growth rate of declined P. simonii was much higher than that of normal growth P. simonii. According to the analysis, there may be a threshold of iWUE for healthy trees, which once the threshold value is exceeded, it indicates that trees are resistant to adversity and their growth is under stress. Similarly, the changing trend of BAI supports our conclusion with its changes showed that tree growth became slower and slower as degradation progressed. iWUE inferred from tree-ring stable carbon isotope composition is a strong modulator of adaptation capacity in response to environmental stressors under climate change. Elevated annual temperatures and increased groundwater depth are all contributing to the decline of P. simonii in north China.

This article is a Commentary on Domínguez‐Begines et al. (2020), 227: 588–600. [ABSTRACT FROM AUTHOR]

Forest ecosystems characterised by higher tree species diversity have been linked to a reduced susceptibility to pathogens. Conversely, endemic pathogens contribute to forest ecosystem dynamics and process. In the face of global change, however, negative impacts arising from more frequent and severe forest disturbances are increasingly observed. An increase in the susceptibility of Corymbia calophylla, a keystone tree species of southwest Western Australia, to cankers caused by the endemic fungus Quambalaria coyrecup, has emerged in recent decades. Landscape scale assessment of disease incidence has implicated the predisposing role of anthropogenic disturbance, indicating a need for this to be examined at a finer resolution. We assessed the effects of anthropogenic disturbance on the incidence of canker disease caused by Q. coyrecup across a disturbance gradient at 17 forest sites. In addition, we determined the impact of disturbance on tree community composition and stand level structural traits including stem density and stand basal area, and investigated the role of these factors as drivers of canker presence. Canker incidence and associated mortality of C. calophylla increased with anthropogenic disturbance. Disturbed edges showed significantly different overstorey composition from the forest transects. Total stem density increased with increasing disturbance, and disturbed edges contained greater numbers of C. calophylla stems compared to forest transects. There was a much increased basal area of C. calophylla on disturbed edges. Regardless of transect position, an increased incidence of canker resulted on sites with increased C. calophylla basal area. Lastly, increased tree species diversity (as measured by species richness) was associated with decreased canker incidence. We demonstrate that anthropogenic disturbance has altered stand structure and led to an increased susceptibility of C. calophylla to Q. coyrecup, resulting in high disease incidence and mortality of trees on disturbed road edges. Our results highlight the complexity of addressing tree health issues in the presence of multiple global change factors. [ABSTRACT FROM AUTHOR]

White pine ( Pinus strobus ) is commonly found in naturally regenerated even-aged stands on former agricultural lands throughout its range. These stands can be managed for rapid production of high-quality sawtimber, and are thus a valuable timber resource. Yet, periodic growth decline and mortality events have occurred, such as that observed in the late 1990s in southern Maine, USA. The present study uses increment measurements from white pine tree cores collected in the early 2000s to compare increment chronologies in high- and low-mortality stands in southern Maine. Periods and severity of decline were quantified, revealing a growth decline and mortality event that began in 1996 following a late-summer drought in 1995. Further, the sites on which mortality was most pronounced were observed to have soil restrictions resulting in shallow rooting depth, ranging from 19 cm to 32 cm deep. Restrictions included bedrock, lithological discontinuity (loamy cap overlaying sand), and plow pans. Stand stocking was also a predisposing factor; on average, stands that experienced greater mortality during the decline event had higher stocking than those that experienced less mortality. As a consequence, stand densities in declining stands were reduced through mortality to levels more common in nearby non-decline stands; those densities correspond to recommendations for low-density management of white pine (i.e., 330–540 trees ha −1 and 17–25 m 2  ha −1 of basal area at 20–30 cm DBH). The smaller diameters of the affected trees indicate the need to give priority to retention of large-diameter trees when thinning pole- and small sawtimber-sized (20–30 cm DBH) white pine stands. This and other studies demonstrate the need for low-density management of pole-size white pine stands to not only maximize growth and value but also reduce the risk of drought-incited decline and mortality on sites with rooting restrictions. [ABSTRACT FROM AUTHOR]

Tree decline affects forests and woodlands on most continents. The loss of canopy species from these landscapes has marked impacts on the surrounding environment. Understanding the consequences of tree mortality on vegetation structure and composition will contribute to developing management strategies for these ecosystems. The tuart (Eucalyptus gomphocephala), once the dominant tree species on the coastal plain in southwest Western Australia, has been cleared extensively and today occurs over less than a third of its former range. Compounding the effects of this clearing, dramatic declines in tree health over the past two decades has been recorded. We examined whether E. gomphocephala decline is reflected in changes to overall vegetation structure and composition. Using Landsat Thematic Mapper satellite data, we identified 12 sites with stable or improving vegetation vigour over the previous 15 years (‘healthy’ sites) and 12 sites with declining vegetation vigour over this time (‘declining’ sites). Health of E. gomphocephala trees, as well as litter, vegetation structure and vegetation composition were compared across these sites. Four health measures indicated that E. gomphocephala trees from healthy and declining sites were statistically distinguishable (p < 0.001). Trees at declining sites showed marked epicormic growth (up to 96% of canopy), evidence of crown dieback, reduced crown density and increased foliage transparency. The canopy changes were reflected in marked reduction in leaf litter for declining sites (p = 0.024). Despite the changes in E. gomphocephala canopy and leaf litter, however, there were no significant differences in vegetation community composition, relative vegetation cover for five height strata, vegetation structural and compositional diversity, presence of coarse woody debris, or overall canopy cover. There were also no differences in soil chemistry between the healthy and declining sites. The agent of tuart decline therefore appears to be specific to Eucalyptus gomphocephala at these sites, or alternatively the changes to other plant species have been too subtle to detect at this stage. [ABSTRACT FROM AUTHOR]

Summary: Corymbia calophylla (marri), a keystone tree species in the global biodiversity hot spot of southwestern Australia, is suffering decline and mortality associated with a canker disease caused by the endemic fungus Quambalaria coyrecup. Phytophthora species are frequently isolated from the rhizosphere of C. calophylla, and a hypothesis is that Phytophthora root infection is predisposing C. calophylla to this endemic canker pathogen. Field surveys were conducted in both anthropogenically disturbed and undisturbed C. calophylla stands, from where a total of 100 rhizosphere soil samples, from both healthy and cankered trees, were collected. Phytophthora species were isolated from 26% of the samples collected, with Phytophthora incidence significantly higher on disturbed stands than in natural forests (73% and 27%, respectively). Five Phytophthora species were recovered, including P. cinnamomi, P. elongata, P. multivora, P. pseudocryptogea and P. versiformis. Under‐bark inoculations with the Phytophthora isolates caused significant lesion lengths in excised C. calophylla stems. Corymbia calophylla response to pot infestation trials in the glasshouse varied between Phytophthora species and isolates, with isolates of P. cinnamomi and P. multivora causing a significant reduction in seedling root volume and often leading to seedling death. This study demonstrates that root disease caused by Phytophthora species, especially P. cinnamomi and P. multivora, has the ability to adversely affect C. calophylla health. This study leads the way to do a dual inoculation trial with the canker pathogen Q. coyrecup, and different Phytophthora species to investigate if Phytophthora root infection predisposes C. calophylla to this canker disease. [ABSTRACT FROM AUTHOR]

We used molecular profiling with 454 pyrosequencing to identify ectomycorrhizal, arbuscular mycorrhizal fungi, and other fungal communities associated with containerized Eucalyptus gomphocephala seedling roots. We found a higher proportion of ectomycorrizal fungi associated with seedling roots grown in soil collected from sites with healthy trees, and of arbuscular mycorrhizal fungi from seedling roots grown in soil collected from sites with declining trees. We also found a relatively high proportion of pathogenic fungi present in roots from declining sites compared to healthy sites. This research should be extended to the field to further investigate mycorrhizal and pathogenic fungal populations associated with tree declines. [ABSTRACT FROM AUTHOR]

Drought frequency is increasing in many parts of the world and may enhance tree decline and mortality. The underlying physiological mechanisms are poorly understood, however, particularly regarding chronic effects of long-term drought and the response to increasing temperature and vapor pressure deficit (VPD). We combined analyses of radial growth and stable carbon isotope ratios (δ13C) in tree rings in a mature Scots pine (Pinus sylvestris L.) forest over the 20th century to elucidate causes of tree mortality in one of the driest parts of the European Alps (Pfynwald, Switzerland). We further compared trees that have recently died with living trees in a 10-year irrigation experiment, where annual precipitation was doubled. We found a sustained growth increase and immediate depletion of δ13C values for irrigated trees, indicating higher stomatal conductance and thus indeed demonstrating that water is a key limiting factor for growth. Growth of the now-dead trees started declining in the mid-1980s, when both mean temperature and VPD increased strongly. But growth of these trees was reduced to some extent already several decades earlier, while intrinsic water-use efficiency derived from δ13C values was higher. This indicates a more conservative water-use strategy compared with surviving trees, possibly at the cost of low carbon uptake and long-term reduction of the needle mass. We observed reduced climatic sensitivity of raw tree-ring δ13C for the now-dead in contrast to surviving trees, indicating impaired stomatal regulation, although this difference between the tree groups was smaller after detrending the data. Higher autocorrelation and a lower inter-annual δ13C variability of the now-dead trees further indicates a strong dependence on (low) carbon reserves. We conclude that the recent increase in atmospheric moisture demand in combination with insufficient soil water supply was the main trigger for mortality of those trees that were weakened by long-term reduced carbon uptake. [ABSTRACT FROM AUTHOR]

Phytophthora species have caused the decline and dieback of multiple tree species in Australia and around the world. Dieback in invasive trees in Australia has been observed for decades, motivating research into the potential causes of dieback to be used for biological control of these invasive species. Despite wide-ranging and ongoing research into invasive plant dieback, Phytophthora species have been largely ignored as potential causal agents of dieback, with the focus more on latent fungal pathogens living as endophytes. We conducted the first survey of Phytophthora and other oomycetes to determine their association with dieback of the invasive tree, Parkinsonia aculeata L. (Fabaceae). Using zoospore baiting, we recovered 37 oomycete isolates from roots and soil of healthy and dieback-affected P. aculeata in Kununurra, Western Australia and Charters Towers, Queensland. Using molecular taxonomy, we identified ten unique oomycete taxa, predominantly composed of Phytophthora palmivora, Ph. nicotianae and Phytopythium vexans. Parkinsonia dieback occurs across multiple climatic zones including those experiencing severe drought. We recovered fewer oomycete isolates from soil and roots in drought-affected Charters Towers than Kununurra, which had experienced recent rainfall. This may be because oomycetes require soil moisture for the dispersal of zoospores. None of the genotypes identified were consistently isolated from dieback-affected trees suggesting that any association with parkinsonia dieback may be localised. More extensive surveys and pathogenicity screenings of isolated oomycetes are required to evaluate their role in the parkinsonia dieback phenomenon. [ABSTRACT FROM AUTHOR]

During routine surveys of Corymbia calophylla, a widespread tree currently experiencing decline over a large area of its native range of south west Western Australia, a slow growing Phytophthora species was often recovered from roots and rhizosphere soil. This species grew more slowly, produced a wide array of morphological features and was visibly different to all other Phytophthora species present in Western Australia. Phylogenetic analyses of the ITS, cox1, HSP90, β-tubulin and NADH gene regions confirmed this to be a new species closely related to P. quercina and the provisional species P. 'ohioensis'. The new species is described here as Phytophthora versiformis sp. nov. It produces persistent, papillate sporangia of variable shape, oogonia with thick-walled oospores, and paragynous antheridia. To date this species has only been recovered from C. calophylla. Pathogenicity trials indicate that while P. versiformis can infect the roots of C. calophylla it does not lead to seedling death. [ABSTRACT FROM AUTHOR]

Blackline disease, caused by Cherry leaf roll virus (CLRV), is considered a serious threat limiting English walnut (Juglans regia) production in Italy and the EU if walnut species other than J. regia e.g. 'Paradox' hybrid (J. regia × J. hindsii), French hybrid (J. regia × J. major or J. regia × J. nigra) or northern California black walnut (J. hindsii) are used as the rootstock. The virus transmissibility by pollen as well as latent infections can result in the spread of CLRVcontaminated propagative material, which is a major means of the virus dispersal by human activities. In 2014 and 2015 to ascertain the presence and the distribution of blackline symptoms in commercial orchards and to provide a description of the symptomatology, visual inspections and double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) analyses were carried out on 1,684 walnut trees in four different intensively managed grafted English walnut orchards in northeast Italy (Veneto Region). Trees with clear blackline symptoms at the scion-rootstock junction, often associated with general decline of the plant, were found only in one commercial orchard in northeast Italy on trees older than ten years of cvs. 'Tulare' and 'Chandler', grafted onto 'Paradox' rootstock. To our knowledge this is the first report of CLRV (blackline) decline and death in a commercial walnut orchard in Italy. [ABSTRACT FROM AUTHOR]

Tree mortality and forest decline have been attributed to the several factors including mistletoe infection in Oak Zagros forest, western Iran. As a result of climate change and fragmentation Loranthus europaeus has the potential to be more abundant and distributed in these forests. However, little attention has been given to the need for an ecosystem approach to their management. To manage it, scientific understanding of its ecology including recognition of mistletoe spatial pattern and its shaping mechanisms are essential. Using spatial analysis, we examined the spatial distribution pattern of mistletoes in terms of life stages and vertical and horizontal host crown classification in relation to its controlling mechanisms, including host and habitat features. The results showed that twenty-three percent of the trees were infected, infected trees having an average of 4.08 mistletoes. Mistletoes were higher in the middle, lower and inner portion of the infected trees crown, corroborating that mistletoes were aggregated in these parts of the crown. The small scale pattern (451 m) of adult mistletoe distribution was observed, whereas juvenile and medium-aged mistletoes were spread at larger distances of 5110 and 4537 m. Mistletoe prevalence spatially autocorrelated up to about 2 km while plot intensity distributed at small range of 316 m. The results suggest that mistletoes first establish in the middle crown part then develop downward into lower crown. The spatial patterns of plot intensity, adult and lower crown mistletoes with smaller ranges were spatially correlated to host size (crown diameter and area). Whereas habitat features were the predictors of the large ranges of prevalence and juvenile mistletoe. To manage mistletoes, considering their roles as keystone species, a focus on reducing the intensity of infection would be of management value at large distances considering spatial relationship between mistletoe and host and habitat features. [ABSTRACT FROM AUTHOR]

• Urban tree inventories were used to assess growth and failure rates. • The highest growth rates were estimated in trees planted in gardens and for the exotics Celtis australis and Ulmus parvifolia. • During early establishment, vandalism and health decline were the main causes of tree failure. • Long-term monitoring recording tree size, health and management actions are necessary to assess growth and failure rates. The delivery of services and benefits provided by urban forests is threatened by tree limited growth, decline and mortality. Determining drivers of tree decline and mortality is challenging but essential in urban forestry planning to reduce environmental and socio-economic losses associated with tree failures. Urban tree inventories (UTI) are essential for managing and monitoring urban forests, which can help to identify successes (i.e., good tree growth/health) and failures (i.e., removals/dead trees). However, UTI are rarely implemented to assess urban tree growth and failure rates. Here, we used UTI from two Australian cities to demonstrate how these inventories can aid in (1) assessing species' relative growth rates and (2) identifying species failures and their determinant. We found UTI are useful to assess tree growth and failures. However, they require recording trees at the time of planting, long-term monitoring (e.g., recording tree size, health), and incorporating management actions (e.g., irrigation, pruning, removals) to inform species performance and improve urban planning and management. [ABSTRACT FROM AUTHOR]

The numerical simulation of wind and ozone (O3) transport in mountainous regions was performed with a computational fluid dynamics technique. A dry deposition model for O3 was designed to estimate O3 deposition in complex terrain, and the qualitative validity of the predicted O3 concentration field was confirmed by comparison with observed data collected with passive samplers. The simulation revealed that wind velocity increases around ridge lines and peaks of mountains. The areas with strong wind corresponded well with the sites of tree decline at high altitudes, suggesting that it is an important factor in the localization of tree/forest decline. On the other hand, there is no direct relationship between forest decline and O3 concentration. The O3 concentration, however, tends to increase as wind velocity becomes higher, thus the O3 concentration itself may be a potential secondary factor in the localized decline phenomena. While the diffusion flux of O3 is not related to localized tree decline, the pattern of advection flux is related to those of high wind velocity and localized tree decline. These results suggest that strong wind with large advection flux of O3 may play a key role in the promotion of tree/forest decline at high mountain ridges and peaks.