Tree Survival Research Articles

Demographic and genetic impacts of powdery mildew in a young oak (Quercus robur L.) cohort

Key messageBy monitoring a field experiment over nine years, we investigated the impacts of the two main pathogen species Erysiphe quercicola S. Takam. and U. Braun and Erysiphe alphitoides (Griffon and Maubl.) U. Braun and S. Takam causing powdery mildew on a young cohort of pedunculate oak (Quercus robur L.), both from a demographic and genetic point of view using SNP markers. We show that survival rate is affected by mean disease severity. But while the growth-related tolerance to infection of the oak individual seems to be more determinant than resistance against infection, no equalizing effect of the disease could be detected.ContextStudies on the effects of pathogens on the survival and population dynamics of forest trees are scarce. Yet a better understanding of these interactions could prove strategic in the challenging context of climate change.AimsOur general objective was to characterize the demographic and genetic impact of the two main pathogen species Erysiphe quercicola S. Takam. and U. Braun and Erysiphe alphitoides (Griffon and Maubl.) U. Braun and S. Takam causing powdery mildew in the early stages of a Quercus robur L. population.MethodsAn ad hoc field design with two disease exposures, natural and protected, was surveyed over nine years. This enabled a detailed phenotypic monitoring of 1733 emerging individuals from 15 progenies, and the genotyping of 68% of them.ResultsThe pathogen induced high levels of seedling mortality several years after sowing, associated with reduced growth and capacity to overwinter. Fast-growing families showed the highest survival rate under both natural and protected disease exposure. Contrary to a possible trade-off hypothesis between growth and defense, family height potential was not negatively related to disease resistance across the studied oak mother trees. While supporting a deleterious effect of very low individual heterozygosity on the probability of survival, average genomic diversity was not significantly affected by mortality associated with powdery mildew. Our study also points to a few candidate genes for several fitness-related traits.ConclusionOverall, our results suggest that in oak natural populations, infection levels (related to resistance sensu stricto) may be less determinant than growth-related tolerance to infection for the fate of seedlings. However, an equalizing effect of powdery mildew on relative oak genotype performances cannot be excluded at later stages.

A decade of rain exclusion in a Mediterranean forest reveals trade-offs of leaf chemical defenses and drought legacy effects

Increasing aridity in the Mediterranean region will result in longer and recurrent drought. These changes could strongly modify plant defenses, endangering tree survival. We investigate the response of chemical defenses from central and specialized metabolism in Quercus pubescens Willd. to future Mediterranean drought using a long-term drought experiment in natura where trees have been submitted to amplified drought (~ –30% annual precipitation) since April 2012. We focused on leaf metabolites including chlorophylls and carotenoids (central metabolism) and flavonols (specialized metabolism). Measurements were performed in summer from 2016 to 2022. Amplified drought led to higher concentrations of total photosynthetic pigments over the 2016–2022 period. However, it also led to lower AZ/VAZ and flavonol concentrations. Additionally, chemical defenses of Q. pubescens responded to previous precipitation where low precipitation 1 year and/or 2 years preceding sampling was associated to low concentrations of VAZ, flavonol and high neoxanthin concentrations. Our study indicates that the decline of flavonol concentration under long-term drought is counterbalanced by a higher production of several central metabolites. Such results are potentially due to an adjustment in tree metabolism, highlighting the importance of performing long-term experimental studies in natura for assessing drought legacy effects and thus forest adaptation to climate change.

Intensive leaf cooling promotes tree survival during a record heatwave

Increasing heatwaves are threatening forest ecosystems globally. Leaf thermal regulation and tolerance are important for plant survival during heatwaves, though the interaction between these processes and water availability is unclear. Genotypes of the widely distributed foundation tree species Populus fremontii were studied in a controlled common garden during a record summer heatwave-where air temperature exceeded 48 °C. When water was not limiting, all genotypes cooled leaves 2 to 5 °C below air temperatures. Homeothermic cooling was disrupted for weeks following a 72-h reduction in soil water, resulting in leaf temperatures rising 3 °C above air temperature and 1.3 °C above leaf thresholds for physiological damage, despite the water stress having little effect on leaf water potentials. Tradeoffs between leaf thermal safety and hydraulic safety emerged but, regardless of water use strategy, all genotypes experienced significant leaf mortality following water stress. Genotypes from warmer climates showed greater leaf cooling and less leaf mortality after water stress in comparison with genotypes from cooler climates. These results illustrate how brief soil water limitation disrupts leaf thermal regulation and potentially compromises plant survival during extreme heatwaves, thus providing insight into future scenarios in which ecosystems will be challenged with extreme heat and unreliable soil water access.

Evapotranspiration and Rainfall Effects on Post‐Storm Salinization of Coastal Forests: Soil Characteristics as Important Factor for Salt‐Intolerant Tree Survival

AbstractFlooding and salinization triggered by storm surges threaten the survival of coastal forests. After a storm surge event, soil salinity can increase by evapotranspiration or decrease by rainfall dilution. Here we used a 1D hydrological model to study the combined effect of evapotranspiration and rainfall on coastal vegetated areas. Our results shed light on tree root uptake and salinity infiltration feedback as a function of soil characteristics. As evaporation increases from 0 to 2.5 mm/day, soil salinity reaches 80 ppt in both sandy and clay loam soils in the first 5 cm of soil depth. Transpiration instead involves the root zone located in the first 40 cm of depth, affecting salinization in a complex way. In sandy loam soils, storm surge events homogeneously salinize the root zone, while in clay loam soils salinization is stratified, partially affecting tree roots. Soil salinity stratification combined with low permeability maintain root uptakes in clay loam soils 4/5‐time higher with respect to sandy loam ones. When cumulative rainfall is larger than potential evapotranspiration ETp (ETp/Rainfall ratios lower than 1), dilution promotes fast recovery to pre‐storm soil salinity conditions, especially in sandy loam soils. Field data collected after two storm surge events support the results obtained. Electrical conductivity (a proxy for salinity) increases when the ratio ETp/Rainfall is around 1.76, while recovery occurs when the ratio is around 0.92. In future climate change scenarios with higher temperatures and storm‐surge frequency, coastal vegetation will be compromised, because of soil salinity values much higher than tolerable thresholds.

Navigating neighborhoods: Density, size, and species diversity influences on tree survival in subtropical secondary forests

Neighborhood effects significantly impact individual tree survival through mechanisms of resource competition and species interactions within forest ecosystems. However, the specific impacts of these effects, particularly how biodiversity feedback affects survival across diverse life stages and spatial scales in subtropical secondary forests, remains insufficiently documented. To bridge this gap, we conducted an extensive analysis of neighborhood effects at different life stages and spatial scales in the subtropical secondary forests of the Wuyi Mountains in Southeast China, uncovering key insights into the community structure and dynamics. Our investigation over a five-year period encompassed all individuals within our study plot, quantifying effects of neighborhood density, individual size in resource competition, and species diversity in the neighborhood across various life stages. Employing mixed-effects models, we established quantitative relationships to assess the impact of these factors on tree survival at different spatial scales. Our findings confirmed that density dependence adversely affects sapling survival at smaller scales. As trees mature and spatial test scales expand, the detrimental effects of conspecific resource competition on individual mortality decrease, whereas heterospecific resource competition notably impairs survival probabilities in later successional stages, suggesting a shift from intraspecific to interspecific competition as the dominant influence on mortality during secondary succession. Additionally, we detected consistent patterns in conspecific and heterospecific density effects with increasing spatial scale. These effects transitioned from interspecific differences at smaller scales to more uniform positive effects at larger scales, which may be attributed to the strong spatial dependency of neighborhood density effects, potentially due to increased habitat heterogeneity. Furthermore, our study highlights the crucial role of heterospecific neighborhood effects in enhancing survival. We observed significant positive impacts of species diversity and heterospecific interactions on individual tree survival, particularly at smaller spatial scales during the sapling stage. Importantly, our research unveils significant variability in species sensitivity to different neighborhood effects, which change with life stage and spatial scale. This underscores the necessity of accounting for life stage variations among species and the influence of spatial heterogeneity on neighborhood effects such as density. Our findings delineate distinct competition mechanisms between the earlier and later phases of forest succession, emphasizing the distinctive recovery processes of subtropical secondary forests. These insights are essential for informing forest management and conservation strategies, ensuring a nuanced understanding of forest community dynamics.

Identifying indicators of apple bud dormancy status by exposure to artificial forcing conditions.

Dormancy in temperate fruit trees is a mechanism of temporary growth suspension, which is vital for tree survival during winter. Studies on this phenomenon frequently employ scientific methods that aim to detect the timing of dormancy release. Dormancy release occurs when trees have been exposed to sufficient chill, allowing them to resume growth under conducive conditions. This study investigates dormancy dynamics in two apple (Malus × domestica Borkh.) cultivars, 'Nicoter' and 'Topaz', by sampling branches in an orchard over 14weeks (2019 to 2020) and over 31weeks (2021 to 2022) and subjecting them to a 42-day budbreak forcing period in a growth chamber. Temporal changes in budbreak percentages demonstrated dormancy progression in the studied apple cultivars and allowed the three main dormancy phases to be distinguished: paradormancy (summer dormancy), endodormancy (deep dormancy) and ecodormancy (spring dormancy), along with transition periods between them. Using these data, we explored the suitability of several alternative methods to determine endodormancy release. Tabuenca's test, which predicts dormancy release based on the differences in dry weights of buds with and without forcing, showed promise for this purpose. However, our data indicated a need for considerable adjustments and validation of this test. Bud weight and water content of buds in the orchard did not align with budbreak percentages under forcing conditions, rendering them unsuitable for determining endodormancy release in 'Nicoter' and 'Topaz'. Shoot growth cessation did not seem to be connected with either dormancy progression or dormancy depth of the studied cultivars, whereas leaf fall coincided with the beginning of the transition from endo- to ecodormancy. This work addresses methodological limitations in dormancy research and suggests considering the mean time to budbreak and budbreak synchrony as additional criteria to assess tree dormancy status.

Determinants of Deadwood Biomass under the Background of Nitrogen and Water Addition in Warm Temperate Forests

Climate change is exacerbating the vulnerability of temperate forests to severe disturbances, potentially increasing tree mortality rates. Despite the significance of this issue, there has been a lack of comprehensive research on tree survival across extensive forest areas under the background of global climate change. To fill this gap, we conducted a detailed analysis of tree survival within a canopy nitrogen and water addition experimental platform in central China, utilizing data from two censuses and evaluating contributing factors. Our findings revealed 283 dead trees within the plots, predominantly of very small diameters (1–10 cm). The distribution of these dead trees varied among subplots, influenced by both biotic and abiotic factors. Notably, three dominant tree species were responsible for 64.8% of the deadwood biomass. The study determined that both the breast diameter and the quantity of dead trees, affected by surrounding trees and environmental conditions, played a critical role in deadwood biomass accumulation. This research offers an in-depth examination of deadwood biomass patterns in a temperate forest, highlighting the need to consider both experiment treatments and abiotic elements like topography in studies of forest ecosystem carbon. The insights gained from this study enhance our understanding of warm temperate forests’ role in the global carbon cycle and offer valuable guidance for forest conservation and management strategies.

Densely stocked neighborhood reduces the risk of tree mortality in drylands: Evidence from Populus euphratica forests along the Tarim River corridor

To mitigate forest loss under current environmental challenges, it is increasingly urgent to model how tree mortality is mediated by both biotic and abiotic agents. However, the role of neighborhood interactions in mediating tree survival in dryland forests has been poorly understood, as it is often presupposed to be irrelevant in low-density stands coupled with overriding drought stress. Here, we conducted a failure time analysis of Populus euphratica forests (known as Tugay forests) in the Tarim River corridor (NW China) to examine the presupposition. We collected a spatial-explicit population inventory dataset with >7000 trees on ca. 14-ha land area with varying vapor pressure deficit (VPD), groundwater table depth (GWD), and stand density. Hegyi's competition index (CI) and stand density index (SDI, the number of large trees with an equivalent diameter of 25.4 cm) were employed to characterize neighborhood structures of each individual tree. Aridity stresses (higher VPD and GWD) tended to elevate tree mortality risk, and showed weaker effects than neighborhood structures did. Tree mortality risk increased drastically with higher CI, suggesting a strong role of competition for critical water resource. However, tree mortality risk reduced with higher SDI, likely due to ameliorated stresses of excessive light and/or temperature under less open canopies. This study highlights the importance of localized inter-tree interactions in regulating tree populations under prevalent drought stress and reiterates classic cautions against inferences about competition/facilitation in absence of spatial-explicit contexts. We recommend the priority of preserving large trees aggregated as closed stands in dryland forest conservation.

Assessing the phytotoxic effects of class A foam application on northern Europe tree species: a short-term study on implications for wildfire management and ecosystem health

Wildfires are an ever-increasing issue due to the driving forces of climate change. Weather events that lead to higher wildfire potential are likely to increase and thus new fire management methods via more sustainable fire suppressant class A foams rather than retardants are being developed. However, despite their adherence to regulations, foam impact on targeted ecosystems, namely forests and forest trees is poorly studied. We aimed to investigate how three tree species (Pinus sylvestris, Alnus glutinosa and Picea abies) will react to a one-time class A foam application. Two separate trials were conducted. During the first the foam was applied to seeds and during the other – to 1-year-old seedlings. Tree growth and physiological status were evaluated. Stress criteria for cellular damage, non-antioxidant and antioxidant stress response and photosynthesis efficacy were measured. Results showed an obvious species effect, as all three reacted differently. The dose effect was also notable, with the higher application rate leading to a proportionally bigger response. Overall, pines were negatively impacted, spruce were positively affected, and alders didn’t experience a notable change. This leads us to conclude that pending the limitation of this experiment the tested foam while phytotoxic in some cases, is unlikely to affect tree survival rates under field conditions and any physiological responses are likely transient in nature.

Survival and plasticity in Acacia saligna growth across Contrasting management practices and growing niches

Reforestation and afforestation either through natural regeneration, tree planting or both methods have been globally promoted to motivate ecological restoration of degraded lands and to improve livelihoods. However, moisture stress and infertile soils limit the survival and growth of trees planted for restoration in drier areas. Hence, understanding the factors that determine the restoration success of drylands through tree planting is critical. We conducted a factorial experiment in Tigray, Ethiopia to evaluate the survival, growth performance and biomass of planted seedlings of the multipurpose agroforestry tree species Acacia saligna over 24 months. The treatments were application of watering (W), mulching (M) and compost (C) separately and in combinations (WM, WMC). We established experimental plots on farmland and on a nearby hillside-exclosure to examine the role of planting niches on seedling performance. Seedlings treated with watering, mulching, and compost (WMC) revealed significantly greater height, root collar diameter (RCD), and dry biomass compared to the other treatments. Seedlings planted in farmland showed significantly greater height, RCD, and total dry biomass compared to those planted at the hillside-exclosure. Although the survival rate was slightly higher in farmland, we also found sufficient survival rates in the hillside-exclosures. Therefore, post-planting care and activities including mulching, watering and fertilization are crucial to enhance the survival and growth performance of A. saligna or other tree species so that efforts in reversing land degradation and restoration of drylands will be successful.

Bite Me: Bark Stripping Showed Negligible Effect on Volume Growth of Norway Spruce in Latvia.

Over the past few decades, increasing populations of cervid species in the Baltic region have reduced the quality and vitality of cultivated Norway spruce (Picea abies (L.) Karst.) stands. This study evaluated the effect of bark stripping on the volume growth of spruce trees in Latvia. Data collection took place in two forest stands. In each stand, 20 Norway spruce trees were sampled, 10 with visible bark damage scars and 10 control trees. Stem discs were collected from control trees at specified heights (0 m, 0.5 m, 1 m, 1.3 m, and 2 m, and then at one-metre intervals up to the top) and from damaged trees at additional specific points relative to the damage. Each disc was sanded and scanned; tree ring widths were measured in 16 radial directions using WinDendro 2012a software. Annual volume growth reconstruction was performed for each tree. Changes in relative volume growth were analysed in interaction with scar parameters, tree type (damaged/control), and pre-damage volume using linear regression models. The significance of parameter interactions was assessed using analysis of variance (ANOVA). Pairwise comparisons of estimated marginal means (EMMs) were conducted using Tukey's HSD post hoc test. No significant effect of bark stripping on the total stem volume increment was detected. However, the length of bark stripping scars had a significant impact on relative volume growth in the lower parts of the stems. These findings underscore the importance of further research examining a broader spectrum of cervid damage intensity and the effects of repeated damage on tree survival and growth.

Sensitivity of Fire Indicators on Forest Inventory Plots Is Affected by Fire Severity and Time since Burning

Forest inventory data are useful for determining forest stand structure, growth, and change. Among the information collected on forest inventory plots by the USDA Forest Service Forest Inventory and Analysis Program, attributes characterizing various types of disturbance provide researchers a means of selecting plots specifically affected by disturbances, such as fire. We determine the performance of three of these attributes as indicators of recent fires on forest inventory plots of the United States by comparing them to independent records of wildland fire occurrence. The indicators are plot-level observations of fire effects on (1) general site appearance, (2) tree mortality, and (3) damage to live trees. Independent spatial layers of wildland fire perimeters provide an approach to test indicator performance and identify characteristics of fires that may affect detection. The sensitivities of indicators are generally higher in the West relative to the East. Detection rates exceed 90 percent for the Pacific Coast forests but seldom reach 80 percent in the East. Among the individual indicators, site appearance has higher identification rates than tree indicators for fires in the Pacific Coast, Great Plains, North, and South regions. Tree mortality is the most important single indicator for identifying Rocky Mountain fires. Tree damage is more important than tree mortality in the South; otherwise, the tree damage indicator is of relatively lower importance, particularly where high-severity fires are common, and tree survival is low. The rate of detection by the indicators is affected by the severity of the fire or the recency of the fire. The joint effect of severity and recency influence all three indicators for the Pacific Coast and Rocky Mountain fires, as well as the site appearance indicator in the South. Only a small proportion of fires are clearly missed by all three of the indicators.

An Affordable System Solution for Enhancing Tree Survival in Dry Environments

Water scarcity inhibits plant growth, especially in arid regions. Traditional irrigation methods often lack efficiency and sustainability. This study investigates AquaTrap, a biomimetic design, as a potential solution. The study highlights AquaTrap’s advantages by analyzing its design and previous research on bioinspired water harvesting. It highlights its ability to increase water efficiency and support sustainable plant growth in dry areas. Biomimicry inspires AquaTrap’s design, which mimics natural systems to capture and deliver water to plant roots. To collect condensation while repelling water, the stack uses superhydrophobic materials. Plant roots then receive this accumulated water for growth. Compared to traditional methods, AquaTrap offers many advantages. Its stand-alone design eliminates complex infrastructure and minimizes evaporation. Additionally, delivering water directly to the roots reduces waste and increases water efficiency. This technology holds promise for introducing new vegetation, restoring plant life, and promoting sustainable agriculture in arid regions. Further research is needed to explore the potential of AquaTrap in a variety of field conditions, optimize it for different plants and environments, and evaluate its economic feasibility for widespread use. AquaTrap also has significant potential for sustainable forestry, as it can significantly increase the survival and growth of trees in water-scarce environments. System solution opportunities and modular structure provide crucial support during the most critical adaptation period of afforestation. By reducing water consumption and increasing efficiency, it supports the establishment and maintenance of healthy forests, which are vital for ecosystem resilience and biodiversity.

Resin duct production of loblolly pine (Pinus taeda) in southeastern Oklahoma, USA is positively related to water availability, fertilization, and thinning

Bark beetle outbreaks frequently kill large areas of loblolly pine (Pinus taeda). Resin production is the main defense against these insects and resin duct metrics and areas are correlated with both resin flow and tree survival post bark beetle attack. Whether the number, area, or size of resin ducts is increase when trees grow faster or whether there is a tradeoff between tree growth and resin ducts is currently debated. We determined the impacts of water availability (ambient vs 30 % throughfall reduction), nutrient availability (fertilized vs non-fertilized), and thinning on vertical resin duct count (ducts per 5 mm strip of annual ring), density (ducts mm−2), area (duct area per 5 mm strip of annual ring), relative area (% duct area per ring), and average duct size (mm−2) in planted stands of loblolly pine (ages 6–13) in southeastern Oklahoma. Fertilization increased diameter growth (10 %) and metrics that scale to ring width, i.e., duct count (15 %) and duct area (22 %), but also duct relative area (8 %). Throughfall exclusion decreased diameter growth and duct count in some years, increased duct density, and reduced duct average size (8 %). The net effect was that fertilized stands with ambient water availability had the greatest resource availability among treatments in this study and had the greatest duct count, duct area, and duct relative area as well as average duct size greater than the throughfall exclusion treatments. During the post thinning period, i.e., ages 10–13, thinning increased diameter growth from 9.63 to 12.05 mm year−1, duct count from 9.69 to 12.22, duct area from 0.384 to 0.514 mm2, duct relative area from 1.67 % to 1.84 %, and average duct size from 0.0396 to 0.0428 mm2. Earlywood composed approximately 2/3 of the annual ring, but latewood had almost 5 times greater duct density such that there were more ducts and greater duct areas in the latewood. Our assessment of duct metrics provides a link between tree growth rate, resource availability, and duct metrics associated with resistance to bark beetles. Therefore, silvicultural practices used to increase tree growth likely also increase resistance to bark beetles.

The Bursaphelenchus xylophilus Effector BxNMP1 Targets PtTLP-L2 to Mediate PtGLU Promoting Parasitism and Virulence in Pinus thunbergii.

Pinus is an important economic tree species, but pine wilt disease (PWD) seriously threatens the survival of pine trees. PWD caused by Bursaphelenchus xylophilus is a major quarantine disease worldwide that causes significant economic losses. However, more information about its molecular pathogenesis is needed, resulting in a lack of effective prevention and treatment measures. In recent years, effectors have become a hot topic in exploring the molecular pathogenic mechanism of pathogens. Here, we identified a specific effector, BxNMP1, from B. xylophilus. In situ hybridization experiments revealed that BxNMP1 was specifically expressed in dorsal gland cells and intestinal cells, and RT-qPCR experiments revealed that BxNMP1 was upregulated in the early stage of infection. The sequence of BxNMP1 was different in the avirulent strain, and when BxNMP1-silenced B. xylophilus was inoculated into P. thunbergii seedlings, the disease severity significantly decreased. We demonstrated that BxNMP1 interacted with the thaumatin-like protein PtTLP-L2 in P. thunbergii. Additionally, we found that the β-1,3-glucanase PtGLU interacted with PtTLP-L2. Therefore, we hypothesized that BxNMP1 might indirectly interact with PtGLU through PtTLP-L2 as an intermediate mediator. Both targets can respond to infection, and PtTLP-L2 can enhance the resistance of pine trees. Moreover, we detected increased salicylic acid contents in P. thunbergii seedlings inoculated with B. xylophilus when BxNMP1 was silenced or when the PtTLP-L2 recombinant protein was added. In summary, we identified a key virulence effector of PWNs, BxNMP1. It positively regulates the pathogenicity of B. xylophilus and interacts directly with PtTLP-L2 and indirectly with PtGLU. It also inhibits the expression of two targets and the host salicylic acid pathway. This study provides theoretical guidance and a practical basis for controlling PWD and breeding for disease resistance.

Adaptación de leguminosas arbóreas en un sistema silvopastoril para ovinos en clima templado

The objective was to evaluate, over a one-year period, the survival, production, and nutritional value of forage from tree legumes as well as grasses and weeds in a silvopastoral system. A mixed protein bank was established, consisting of two plots: in the first plot, planting orientation was East to West, and in the second, North to South. The planted tree species were leguminous: pata de vaca (Bauhinia forficata), albizia (Albizia lebbeck), leucaena (Leucaena leucocephala), and palo dulce (Eysenhardtia polystachya). Three planting densities were used, with tree spacings of 70x70, 90x90, and 110x110 cm. Survival was assessed visually and manually by identifying the species and recording their condition as either alive (1) or dead (0). A three-way classification model with an unequal number of repetitions was used, employing the Generalized Linear Models procedure of the statistical analysis system under a fixed effects model. The nutritional value of thetree legumes ranged from 11% to 18% protein. Differences (p ≤ 0.05) were observed between treatments and orientation regarding height. There was a significant effect (p ≤ 0.05) of treatment, orientation, period, and species on foliage production. Differences (p ≤ 0.05) were found in species survival, with albizia (Albizia lebbeck) being notable. The period also significantly influenced (p ≤ 0.05) tree survival. It is concluded that the survival rate of forage tree legume species determines their capacity to establish silvopastoral systems in a subhumid temperate climate in mixed protein bank arrangements

Effects of stand structure on ecological benefits and tree growth of Haloxylon ammodendron plantations: A meta‐analysis

AbstractHaloxylon ammodendron is a typical tree species in arid region for windbreak and sand fixation. Understanding how stand structure (i.e., afforestation density, forest type, and stand age) of H. ammodendron impacts ecological benefits and tree growth status has great implications for desertification control in arid area. We obtained a dataset of 446 observations from 79 studies related to H. ammodendron plantations for meta‐analysis. Stand age was the key factor affecting performances of windbreak, tree canopy, and soil properties while afforestation density was more important in determining tree survival rate. Wind speed in H. ammodendron plantations was reduced by 52% in general compared to that at the site without any plantations and decreased as the increasing density. With the increase of stand age, soil carbon, nitrogen, and phosphorus accumulated continuously, but soil moisture in 0–60 cm depth decrease when trees grew up to nearly 20 years. Within 4000 plants ha−1, responses of survival rate, tree height, ground diameter, and canopy decreased with the increase of afforestation density. Compared with mono‐species plantation, mixed afforestation was more beneficial to windbreak and survival, while it damaged tree growth. Combining the ecological functions and tree growth of H. ammodendron plantations, the afforestation density and forest age should be controlled to 450–900 plants ha−1 and 20 years, respectively, as the upper limit. Therefore, besides reasonable afforestation density, management measures for regulations of forest age and existing stand density were important to maintain higher ecological benefits and better tree growth of H. ammodendron plantations.

High-carbon wood ash biochar enhances native tree survival and growth on sand-capped mine tailings.

Use of waste wood biomass for bioenergy produces wood ash as a by-product; this ash is typically landfilled, but can potentially play an important role in soil improvement and forest restoration. In particular, high-carbon wood ash biochar (HCWAB) could supply nutrients, improve substrate water-holding capacity and pH, and emulate the ecosystem benefits of wildfire residues. Thickened tailings sites at metal mines across Canada are subject to stringent restoration regulations that entail planting of native trees to promote rapid reforestation. While HCWAB may prove beneficial in this context, field trials have been very limited to date. We conducted a large-scale, replicated field trial on sand-capped tailings at an operational gold mine in the Canadian boreal forest to assess the impact of HCWAB (at dosages of 0, 6.4, 12.8, and 19.1 t/ha) on survival and growth of four native tree species, as well as substrate chemical properties and element uptake in tree tissues. After 2years, the survival of planted, native trees was highest at low to moderate application rates; HCWAB dosages above 13 t/ha presented reduced tree survival to levels comparable to unamended substrates. Tree growth was higher across all HCWAB doses relative to growth in samples planted on untreated substrates; tree species and initial size also had large impacts on final tree survival and aboveground growth. The survival of Betula papyrifera was significantly higher than other species, while smaller transplanted trees in general survived in greater numbers compared to larger size classes. Volunteer herbaceous vegetation significantly increased at the higher HCWAB application dosages and tree performance was negatively correlated with vegetation cover, consistent with a resource competition effect. HCWAB additions to sand-capped mine tailings did not significantly alter tree tissue concentrations or substrate availability of potentially toxic metals (Cd, Cu, Al). We conclude that low to moderate dosages of HCWAB on sand-capped tailings, particularly between 6.4 and 12.8 t/ha, may offer benefits to early tree survival, growth, and substrate nutrient status without causing significant risks of phytotoxicity and recommend future field trials focus on strategies to reduce tree competition with competing vegetation.

Trees to remember: culturally modified boab trees in the face of climate change

ABSTRACT Culturally modified trees (CMTs) are a unique form of archaeology and cultural heritage. There are several factors affecting the survival of culturally modified trees in Australia, and these will all likely be exacerbated by climate change. Boab trees (Adansonia gregorii), which are endemic to northwest Australia, have been subject to modification by Indigenous people both prior to and following the settlement of the Kimberley region by European and Anglo-Australians. Many of the potential impacts of climate change on boab tree survival are yet to be determined, but a range of new threats are emerging as potential endangerment. Through the insights of Indigenous knowledge, this paper discusses one particularly significant boab tree in Nyikina Country and how its demise may be linked to erroneous human actions in the recent past. This provides a unique perspective on how the complexities of climate change may be conceptualised through living knowledge and experience.

Persistence of the African baobab (Adansonia digitata L.) in a system experiencing chronic utilization by elephants

AbstractChronic utilization of woody vegetation by African savanna elephants may transform woodland vegetation to open savanna and threaten the extirpation of targeted species. This situation has arisen in Gonarezhou National Park (GNP), Zimbabwe, where a large elephant population (>2 km−2) threatens the persistence of the long‐lived baobab (Adansonia digitata) tree, through elevated mortality levels. This study investigated whether complete or partial refugia from elephant utilization existed for baobabs, and whether protection of trees by management, using wire netting or log‐ or rock‐packs around a tree base, had been effective. A total of 563 baobabs were sampled across northern GNP. Elephants had debarked 99% of trees to some degree, and gouged holes in the stem of 22% of trees. The probability, and severity, of debarking and gouging decreased with increasing distance to permanent water, increasing slope, and the amount of boulder cover. Slope gradient had the greatest effect on elephant impact, with trees located on steep slopes being less affected by elephants than those on flat ground. Distance to water had an effect despite the farthest tree, at 9 km from water, being within the 15 km foraging range of bull elephants. Large boulders partly protected trees even on gentle terrain. None of these factors provided a complete refuge from elephant impact within GNP, but, individually and collectively, provided a partial refuge at current elephant densities. Protection measures doubled tree survival over approximately 5 years, with fencing wire wrapped around baobab stems proving to be the most effective method. Assessment of the future security of baobabs in GNP requires knowledge of their distribution and that of the refugia provided by distance from permanent water, slope, and boulder cover.