Loss Of Trees Research Articles

Habitat Degradation Facilitates the Invasion of Neophytes: A Resurvey Study Based on Permanent Vegetation Plots in Oak Forests in Slovenia (Europe).

The spread of neophytes (non-native plant species) challenges the conservation status and ecological integrity of forests, especially in lowland areas. Long-term resurvey studies are needed to evaluate the temporal dynamics of neophytes in forests; however, such data are scarce. In 2023, we resampled a set of 45 permanent vegetation plots (established in 1992/93) in two forest vegetation types: oak-hornbeam forests dominated by Quercus robur and colline oak-beech forests dominated by Q. petraea. Over the last 30 years, oak forests have experienced extensive oak tree mortality, with the degree of habitat degradation being greater in Q. robur forests. In the early 1990s, only three neophytes with low abundance were recorded across all plots. In the 2023 resurvey, the total number of neophytes increased to 22 species (15 herbaceous and 7 woody species), comprising 6.9% of the total species pool in the understory layer. The increase in the plot-level number and cover of neophytes was significant in plots dominated by Q. robur but not in those with Q. petraea. The most frequent neophytes were Impatiens parviflora (present in 31% of plots), Solidago gigantea (27%), Erigeron annuus (16%) and Erechtites hieraciifolia (16%). The richness and cover of neophytes were significantly affected by the tree layer cover (negative correlation) and the degree of soil disturbance (positive correlation). All neophytes established in disturbed patches, whereas the occurrence of I. parviflora was exceptional as it was able to colonize less degraded, shaded understory environments. Habitat degradation (the mortality-induced loss of stand-forming oak trees resulting in extensive tree layer cover decrease) emerged as a key driver promoting neophyte proliferation, coupled with the impact of management-induced disturbances affecting overstory and soil conditions. The spread is expected to continue or even intensify in the future because novel light regimes and disturbances make forest habitats less resistant to neophyte proliferation.

Putting down roots: Relationships between urban forests and residents’ place attachment

Many cities seek to improve their urban forests to provide a diverse range of benefits for residents. One of these potential benefits, place attachment, is linked with its own positive outcomes including increased social cohesion, life satisfaction, and environmentally-friendly behaviour. However, it is currently unclear how urban forests relate to place attachment. This case study sought to clarify that relationship. A survey measuring residents’ place attachment, satisfaction/dissatisfaction with urban forest services/disservices respectively, perceived urban forest characteristics, and sociodemographic variables was distributed to residents of the Perth Metropolitan Area in Western Australia. The survey measured these variables at three spatial scales: residents’ homes, streets, and neighbourhoods. The 638 responses were combined with GIS datasets to calculate objective measures of average canopy cover. SEM was used to test relationships between different groups of variables and understand their relationship with place attachment. We found that place attachment was positively associated with residents’ satisfaction with key urban forest services: sense of place, social interactions encouraged by the trees, and fresh air. In turn, place attachment and satisfaction with services were associated with objective canopy cover, both directly and indirectly via perceived characteristics. An analysis of qualitative feedback from residents helped to illustrate nuances around how urban trees relate to sense of place and how the loss of trees can be a source of distress and solastalgia. As such, we recommend that actual and perceived urban forest characteristics, residents’ agency, and tree removal be adequately considered in efforts to maximise urban forest benefits.

Predictors of street tree survival in Philadelphia: Tree traits, biophysical environment, and socioeconomic context

Street trees are highly visible components of the urban forest, providing ecosystem services to city residents, but tree mortality can result in a loss of these essential benefits. Here, we focus on how street tree survival in Philadelphia, Pennsylvania (US) has been influenced by 1) tree traits and attributes, 2) the local biophysical environment, and 3) socioeconomic context. We used a longitudinal monitoring approach with a 6-year time interval and 103 randomly-located, fixed-length permanent plots, containing a range of tree size classes, to assess street tree survival rates, predictors of survival, and the balance of tree losses and gains. Street trees surveyed in this study experienced an annual mortality rate of 3.68% and followed a Type III mortality curve, with the highest annual mortality rates in the smallest size class. On the surveyed plots, there was a net decrease of live trees over the study period (2657 to 2542; 4.33% decline). Multivariate logistic regression revealed significant associations between street tree survival and tree crown vigor, species traits (expected mature stature and drought tolerance), site type, land use type, % impervious surface in a 15 m buffer, parcel-level demolition events, % of residents in poverty, % unoccupied households, and % renter-occupied households. Additionally, the final model included a multiplicative interaction term between crown vigor and tree size with separation in pattern of small (DBH < 7.6 cm) from larger (DBH ≥ 7.6 cm) trees. Our findings suggest that targeted management interventions may enhance overall street tree survival, such as focusing on small trees, as well as trees in sidewalk cut-outs, commercial or industrial areas, or near demolition activity. Longitudinal monitoring studies such as ours provide valuable information about how urban forest systems change over time, with assessments that are valuable for management by municipal foresters and other street tree stewards.

Long-term effects of a tornado: Impacts on woody native vegetation and invasive Amur honeysuckle (Lonicera maackii) in an urban forest.

As tornados become increasingly common with global climate change, recovery of the woody vegetation in temperate forests is imperative to maintain an intact ecosystem. In many urbanized landscapes, invasive species are also increasing and could interfere with natural recovery from environmental disturbance. We quantified the impact and 17-year recovery from a major tornado in a temperate deciduous forest. We used vegetational surveys in southwestern Ohio at the Harris M. Benedict Nature Preserve, where approximately a third of this site was damaged by a tornado in 1999. Plots were established in the tornado-damaged area and the nearby undisturbed forest to examine forest recovery of trees/saplings, shrubs and vines, and tree seedlings during 2003, 2006, 2010, and 2016/2017. The number of tree saplings, shrubs, and vines increased immediately after the tornado, but then declined by 2010, relative to the undisturbed forest. Forest tree recruitment was lower in tornado-damaged sites with fewer tree seedlings, but more saplings. Tree diversity was also affected by Agrilus planipennis (Emerald Ash borer) which targeted native ash trees within this time period. Despite an initial increase in shrubs and vines in the damaged area, the diversity and density of shrubs approached equality in both sites by 2016. Most shrubs in both sites were the invasive Lonicera maackii (Amur honeysuckle). In tornado sites, honeysuckle thinned out over time, leaving larger shrubs with greater mean basal diameter compared to the undisturbed forest. Other woody invasive species were also more prevalent in the damaged area, but increased in number in both locations by 2017. The forest has the capability to begin to recover from the initial tornado, but its future composition may differ from its initial trajectory due to invasive species, loss of ash trees, and anthropogenic impacts within the urban landscape.

Emergent trees in Colophospermum mopane woodland: influence of elephant density on persistence versus attrition.

Colophospermum mopane (mopane) forms mono-dominant woodlands covering extensive areas of southern Africa. Mopane provides a staple foodstuff for elephants, who hedge woodland by reducing trees to small trees or shrubs, leaving emergent trees which are too large to be pollarded. Emergent trees are important for supporting faunal biodiversity, but they can be killed by ringbarking. This study first examined the influence of elephant density on woodland transformation and the height distribution of canopy volume, and, second, whether canopy volume is maintained, and tall emergent trees too large to be broken can persist, under chronic elephant utilisation. Three regimes of 0.23, 0.59 and 2.75 elephants km-2 differed in vegetation structure and the height structure of trees. Areas under the highest elephant density supported the lowest total canopy volume owing to less canopy for plants >3 m in height, shorter trees, loss of most trees 6-10 m in height, but trees >10 m in height (>45 cm stem diameter) persisted. Under eight years of chronic utilisation by elephants, transformed mopane woodland maintained its plant density and canopy volume. Plant density was greatest for the 0-1 m height class, whereas the 3.1-6 m height class provided the bulk of canopy volume, and the 1.1-3 m height layer contained the most canopy volume. Emergent trees (>10 m in height) suffered a loss of 1.4% per annum as a result of debarking. Canopy dieback of emergent trees increased conspicuously when more than 50% of a stem was debarked, and such trees could be toppled by windthrow before being ringbarked. Thus relict emergent trees will slowly be eliminated but will not be replaced whilst smaller trees are being maintained in a pollarded state. Woodland transformation has not markedly reduced canopy volume available to elephants, but the slow attrition of emergent trees may affect supported biota, especially cavity-dependent vertebrate species, making use of these trees.

Tree species and drought: Two mysterious long-standing counterparts.

Around 252 million years ago (Late Permian), Earth experienced one of its most significant drought periods, coinciding with a global climate crisis, resulting in a devastating loss of forest trees with no hope of recovery. In the current epoch (Anthropocene), the worsening of drought stress is expected to significantly affect forest communities. Despite extensive efforts, there is significantly less research at the molecular level on forest trees than on annual crop species. Would it not be wise to allocate equal efforts to woody species, regardless of their importance in providing essential furniture and sustaining most terrestrial ecosystems? For instance, the poplar genome is roughly quadruple the size of the Arabidopsis genome and has 1.6 times the number of genes. Thus, a massive effort in genomic studies focusing on forest trees has become inevitable to understand their adaptation to harsh conditions. Nevertheless, with the emerging role and development of high-throughput DNA sequencing systems, there is a growing body of literature about the responses of trees under drought at the molecular and eco-physiological levels. Therefore, synthesizing these findings through contextualizing drought history and concepts is essential to understanding how woody species adapt to water-limited conditions. Comprehensive genomic research on trees is critical for preserving biodiversity and ecosystem function. Integrating molecular insights with eco-physiological analysis will enhance forest management under climate change.

Assessing Trends in Tree Cover, Wildfire and Population Growth in Zimbabwe since 2000

Zimbabwe’s woodland and forests have experienced substantial change over the last two decades. In this study, our objective was to assess national-scale spatio-temporal changes in tree loss, wildfire, and population growth since 2000 using global data. Our results showed rates of tree loss were highest in the urbanized Harare and Bulawayo provinces between 2000–2004, followed by Masvingo and Manicaland provinces. We found agricultural versus non-agricultural land type classes had higher tree loss, with the highest rates in small resettlement farms (‘A1’ farms, averaging 5 ha in size) between 2000–2008. The findings from our analysis of wildfire showed burning peaked in 2010, impacting 12% of the country. In the peak fire years of 2008–2012, 30% of A2 self-contained resettlement farms (‘A2’ farms, averaging 318 ha in size) burned, along with 19% of A1 resettlement farms. Analysis of global population data showed increases across all provinces, particularly in large-scale commercial farming areas, with gradual increases seen in A1 and A2 farms. Understanding the trends over two decades and the patterns in three key pressures—tree loss, population change, and fire—provides an important contribution to help guide regional assistance efforts in Zimbabwe.

Woody species alongside earth contour bunds enhance the soil water‐infiltration capacity in the Sahel, West Africa

AbstractLand degradation, including the loss of tree, forest and vegetation cover, and its related loss of water availability are the main constraints affecting the rainfed agricultural systems in West African Sahel and dry savanna. Therefore, farmers are implementing various soil and water conservation techniques such as zaï pits, half‐moons, contour stone and earth bunds to improve crop production through reduced erosion and enhanced water retention. This study explores the effect of woody and herbaceous vegetation established along earth contour bunds on soil infiltration capacity in southern Mali. The soil infiltration measurements were carried out from September to December 2019 using single ring infiltrometers up‐slope and down‐slope of the bunds built on contour lines in 2015 and 2016 with four types of vegetation: (1) natural annual herbaceous vegetation; (2) planted Andropogon gayanus (perennial grass); (3) planted Gliricidia sepium (woody species) and (4) planted Acacia colei (woody species). The field‐saturated hydraulic conductivity (Kfs) was estimated from the infiltration data and subjected to statistical analysis to compare the effect of the four types of vegetation on soil infiltration capacity. The results revealed significant differences in infiltration rate and Kfs between the four vegetation types. The highest infiltration rate and Kfs were observed for earth contour bunds reinforced with woody species G. sepium (299.5 ± 0.6; 45.3 ± 1.4 mm h−1), followed by A. colei (232.2 ± 2; 38.2 ± 1.6 mm h−1). These were followed by the grass A. gayanus (189.4 ± 2.5; 33.0 ± 1.7 mm h−1) and natural annual herbaceous vegetation (132 ± 2.3; 20.7 ± 1.9 mm h−1). In addition, soil water‐infiltration rate and Kfs were higher for down‐slope compared to up‐slope areas for the two woody species. In practice, it is appropriate for farmers to reinforce contour bunds with woody species and perennial herbs given the beneficial effect on soil water infiltration and retention capacity and the expected socio‐economic benefit they can get from them.

The importance of forests in the environment

The importance of forests in the environment

Assessment of Environmental and Social Impact of Benin-delta Power Transmission line Expansion Project

This study examined the environmental and social impacts and household vulnerability of the 107 km Benin-Delta (Ughelli) 330 kV power transmission line (TL) expansion project right of way (ROW). Questionnaires were administered to 56 communities and 344 households to obtain information on their livelihood and the perceived environmental and social impacts of the TL expansion. Results revealed the TL on land use, community socio-cultural and health Status, employment and opportunities, community agitation and social economic status, they were found to be high, low, beneficial, medium and low in that order. Loss of land and economic trees were identified as the highest impacts of the project. All communities within the sphere of influence of the project had encroached on the existing ROW. The most vulnerable groups affected by the project are the non-indigenous elderly, widows and female-headed households, children, herdsmen, unemployed and those that have lost their lands and are now without means of livelihood. The valuation of assets and losses suffered suggests the need for resettlement and compensation. Specific mitigation measures which could help ameliorate suffering of the economically vulnerable households should be put in place.

More than just a tree: Ecolinguistics and responses to the felling of ‘Hadrian’s tree’

In the current climate ecolinguistic research has arguably never been more important, as its basic premises regard the survival of life on Earth and key philosophical questions hitherto under-acknowledged by mainstream science. In recent decades, environmental thinking has made great advances in shaping current opinions towards nature and the non-human world. The goal of this paper is to explore certain currents of mediated thinking in modern Britain regarding nature, in order to assess how far expressions of sorrow for the felling of a prominent tree might correspond to a genuine ecological sentiment. The study explores public responses to an apparent case of eco-vandalism, the felling of the Sycamore Gap tree in September 2023 in Northumberland, using data taken from social media and other online sources such as e-newspapers. From the point of view of Ecolinguistic theory and that of Positive Discourse Analysis it applies critical lenses such as Evaluation and Discourse Pragmatics to dig beneath the surface of texts produced on the topic, in order to explore diverse current attitudes to trees in the UK. The paper finds that, though there are instances in which people appear to express grief for the loss of the Sycamore Gap tree, it is possible to account for these in ways that lessen the likelihood that they are motivated by purely ecological sentiment. In practice human attitudes towards trees tend to be superficial and instrumental, and this tendency is also found here. The Sycamore Gap event brings many latent social attitudes into play, and this paper thus contributes to the developing field of Ecolinguistics by focusing on tree-centred narratives, distinguishing between inherent ideologies of pseudo- and authentic environmental sensitivity.

Tree diversity and arbuscular mycorrhizal trees increase soil carbon sequestration and stability in 1-m soils as regulated by microbial CAZymes-coworking in high-latitude Northern Hemisphere forests

Biodiversity loss and tree alternations often occurred in high-latitude Northern Hemisphere forests owing to climatic changes and human disturbance, while their effects on soil carbon sequestration remain unclear. In this paper, tree richness and arbuscular mycorrhizal (AM)-tree dominance experiments were settled in an experimental forest, and soil organic carbon (SOC) and glomalin-related soil protein carbon (Total, TG-C and easily extracted, EEG-C), stability (heterotrophic respiration, Rh, temperature sensitivity, Q10 and humidity sensitivity, Hs), in situ soil CO2, CH4, N2O fluxes, and CAZymes activities from the microbial metagenome technique were measured to identify their impacts and underlying mechanism. Both analysis of variance (ANOVA) and linear regression found tree richness and AM tree loss accompanied by soil carbon sequestration loss of total SOC storage, their mycorrhizal components (TG-C) and Rh. In 0–20 cm soils, high tree richness quadrats had 16–126.6 % higher SOC, TG-C, Rh, and in situ N2O flux, while AM-dominated stands had 34–39 % higher SOC and Rh than the EcM-dominated stands. In the 1 m soil profile, the effect size from tree richness and AM trees were more evident than the 0–20 cm soils. Compared with the richness gradient, much significant differences occurred between AM- and EcM-dominated stands. Structural equation modeling found that tree richness directly improved C stability, while the SOC accrual from the tree richness enrichment and AM-tree dominance were indirectly achieved by their decreasing in multiple CAZymes activities. Of CAZymes, glycoside hydrolases, polysaccharide lyases, carbohydrate esterases, glycosyl transferases, auxiliary activities, and carbohydrate-binding modules cooperated in their regulation of the soil C accrual. Our findings support carbon sequestration via biodiversity conservation and proper forest management related to tree mycorrhizal symbionts.

Applying genomic approaches to identify historic population declines in European forest bats

Abstract Anthropogenically driven environmental changes over recent centuries have led to severe declines of wildlife populations. Better tools are needed to assess the magnitude and consequences of these declines. Anecdotal evidence suggests European bat populations have suffered substantial declines in the past centuries. However, there is little empirical evidence of these declines that can be used to put more recent population trends into historic context. This study is a collaboration between academics and conservation practitioners to develop molecular approaches capable of providing evidence of historic population changes that can inform conservation status assessments and management. We generated a genomic dataset of 46,872 SNPs for the Western barbastelle, Barbastella barbastellus, a regionally Vulnerable bat species, including colonies from across the species' British and Iberian ranges. We used a combination of landscape genetics and model‐based inference of demographic history to identify both evidence of population size changes and possible drivers of these changes. Levels of genetic diversity increased and inbreeding decreased with increasing broadleaf woodland cover around the colony. Genetic connectivity was impeded by artificial lights and facilitated by rivers and broadleaf woodland cover. The demographic history analysis showed that both the northern and southern British barbastelle populations have declined by 99% over the past 330–548 years. These declines may be linked to the loss of large oak trees and native woodlands due to shipbuilding during the early colonial period. Synthesis and applications. Genomic approaches can provide a better understanding of the conservation status of threatened species, within historic and contemporary contexts, and inform their conservation management. Our findings of will directly influence the definition of the Favourable Conservation Status of the barbastelle, in turn influencing considerations of the conservation of the species in development plans. Knowledge gained will also help set species recovery targets. Policymakers are interested in using our approach for other species. This study shows how we can bridge the implementation gap between genomic research and direct conservation applications. There is an urgent need to carry out such collaborative studies for other priority species to enable informed species recovery interventions via policy mechanisms and project delivery.

Root water uptake and water transport to above-ground organs compensate for winter water losses and prevent shoot dehydration in apple trees

Plants need to maintain a minimum moisture content in their tissues to preserve their living functions not only during the growing season but also during periods of dormancy. Whereas water uptake of trees during the growing season has been widely investigated, very little attention has been paid to tree water uptake and losses during winter dormancy. A study was therefore conducted aiming at quantifying root water uptake of apple trees in winter, comparing the water content of two groups of field-grown apple trees for two winter seasons. One group of trees was isolated from its roots by a transversal cut at the base of the trunk and the other was left intact. In an additional experiment, deuterium-enriched water was added to the soil of potted apple trees during winter dormancy, to monitor water uptake and translocation within the plant. The field experiment revealed incrementing moisture losses of annual shoots in late winter, driven by the rising evaporative demand of the atmosphere. Trees with unimpaired water transport systems compensated shoot water losses by root water uptake and internal translocation, whereas trees with severed trunks only partially mitigated losses by internal translocation from trunk and larger branches. Root water uptake during winter dormancy was also confirmed in the potted tree experiment with deuterium-enriched water. This work provides evidence that water flow along the soil-plant-atmosphere continuum in apple trees takes place also in winter, with possible impacts on tree survival during prolonged periods of soil or trunk freezing.

Selected Leaf Diseases of Rubber: Symptoms and Control – A Review

This paper is a review article with the objective of providing valuable, recent and solid information and critical understanding of symptoms and control of selected leaf diseases of rubber tree (Hevea brasiliensis Muell. Arg) using secondary information and data harvested from previously published studies found online. Data gathered showed that H. brasiliensis is subject to a plethora of economically important diseases mainly of fungal origin, classified as leaf, stem and branch, panel and root disease. Some fundamental causal organisms of leaf diseases in H. brasiliensis includes Pseudocercospora ulei, Oidium heveae, Colletotrichum gloeosporioides and Corynespora cassiicola. Corynespora leaf fall caused by Corynespora cassiicola is currently accepted as the leaf disease which causes about 45% of yield loss to rubber in mostly Asian and African continents. The symptoms of South American Leaf Blight (SALB) range from discoloration of lamina to death of tree when untreated. Leaf disease symptoms range from white powdery patches to shriveling and falling off of tender leaves and translucent brownish yellow spots in semi-matured leaves in Oidium leaf disease. Colletotrichum leaf disease symptoms range from necrosis of tender leaves of young plants to defoliation and death of entire plant. Disease control is achieved by the use of chemicals and planting of disease-resistant varieties. Some phylloplane fungi are prospective biological control agents. The best treatment to manage Corynespora leaf fall disease (CLFD) in nurseries is the introduction of overhead shading coupled with application of the fungicide mancozeb. Diseases affecting the leaves of H. brasiliensis can be devastating and can lead to loss of multiple rubber trees and reduction in the latex production of the trees. Therefore, adequate preventive, curative and control measures against the diseases should be taking to ensure maintenance of a healthy rubber tree plantation.

Diversity of Mycorrhizal fungi in Eastern Hemlock stands will significantly change with the effects of Hemlock Woolly Adelgid infestation in southwestern Nova Scotia, Canada

A foundation tree species, eastern hemlock (Tsuga canadensis) is threatened by the invasive hemlock woolly adelgid (Adelges tsugae) (HWA) in southwestern Nova Scotia, Canada. The loss of this key species and its heavily shaded ecosystems may alter the diversity of important mycorrhizal fungi in hemlock forests. Mycorrhizal fungi share a vital mutualistic relationship with their host trees; consequentially, understanding if and how the predicted eastern hemlock decline will affect mycorrhizal diversity is paramount. Using available literature, we discuss three major consequences of HWA on eastern hemlock ecosystems – changing forest composition, loss of old-growth trees, and increased insect stress on host trees – and how they will likely influence mycorrhizal communities as adelgid infestations intensify. Environmental variables are also discussed as another major influence on fungal diversity. We conclude that the mycorrhizal community of eastern hemlock forests will likely change significantly as old-growth hemlock is replaced with mixed forest. We also suggest that mycorrhizal community composition will shift in favour of generalist mycorrhizae which form symbioses with multiple tree species. These conclusions illuminate the future of hemlock forest fungi in southwestern Nova Scotia and underline the importance of conserving old-growth eastern hemlock forests and their unique fungal communities.

The breeding biology of the Western Red-tailed Cockatoo Calyptorhynchus escondidus in the wheatbelt of Western Australia

ABSTRACT A breeding population of Western Red-tailed Cockatoos Calyptorhynchus escondidus was studied between July 1974 and December 1981 at Nereeno Hill, in the northern wheatbelt of Western Australia. Egg-laying occurred during two clearly defined periods each year; with peaks mid-March to mid-April (Autumn breeding) and early-August to mid-October (Spring breeding). Thirty-two percent of the 459 eggs laid during the study were laid in Autumn and 68% in Spring. Growth rates of nestling wings and body mass were similar between seasons and years. Nearly one third of breeding attempts failed during incubation and 40.7% successfully fledged a nestling. Fledgling survival in the first year was low (17.5%), however, annual survival was higher after the first year; 80.0% after four years. Birds were killed by Wedge-tailed Eagles Aquila audax, shot by farmers, and drowned in stock troughs. Based on evidence from one individually-marked pair, Western Red-tailed Cockatoos may form long lasting pair bonds. While females breed every 12 months, some have bred in both Autumn and Spring seasons. Young Red-tailed Cockatoos remain with their parents up to two years after fledging, and adults may have young from two breeding seasons accompanying them. The breeding biology of Red-tailed Cockatoos is compared with that of closely related species from the genera Calyptorhynchus and Zanda. Threats to the species are loss of mature hollow-bearing trees and almost complete dependence on the seeds of Double Gee Emex australis, an introduced agricultural weed, for food.

Protecting the resource: an assessment of mitigation methods used to protect large trees from African elephant impact in a savanna system

African elephants Loxodonta africana can alter the structural components of savanna ecosystems, often through the reduction of the large tree (≥ 5 m height) cover component. Elephant impact can be amplified in small, protected areas, or areas where water is readily available to elephants. One management option is to protect large trees directly using applied mitigation methods to limit elephant impact. In this paper, we assessed and compared the effectiveness and logistical requirements of four mitigation methods that have been applied to protect large trees from elephant impact in South Africa's Greater Kruger National Park – namely African honeybees Apis mellifera scutellata in beehives; creosote oil in glass jars, concrete pyramids arranged in circles around trees, as well as wire‐netting the trees' main stems. For each method, elephant impact levels and tree mortality rates were measured over a 2–5‐year period depending on the method in use. Sample sizes ranged from 43 to 59 trees per mitigation method, with a comparable control, which was a tree of the same species and morphological dimensions but lacking any mitigation application. Beehives were the most effective method at reducing tree loss, significantly reducing tree mortality from 34% (6.8%/year) in control trees to only 10% (2% year‐1) over the five‐year experimental period. However, beehives were the most expensive method to apply to a tree, although this cost can be compensated through honey sales. Concrete pyramids reduced tree loss when the combined pyramid radius was &gt; 1.5 m in length, whilst wire‐netting was effective against bark‐stripping by elephants but was still vulnerable to heavier forms of impact such as uprooting and stem snapping. Creosote jars did not prevent elephants from impacting treated trees. Our results provide managers with a toolkit for protecting large trees against elephant impact, commenting on both the efficacy and the logistical constraints for each method.

Mortality thresholds of juvenile trees to drought and heatwaves: implications for forest regeneration across a landscape gradient

Tree loss is increasing rapidly due to drought- and heat-related mortality and intensifying fire activity. Consequently, the fate of many forests depends on the ability of juvenile trees to withstand heightened climate and disturbance anomalies. Extreme climatic events, such as droughts and heatwaves, are increasing in frequency and severity, and trees in mountainous regions must contend with these landscape-level climate episodes. Recent research focuses on how mortality of individual tree species may be driven by drought and heatwaves, but how juvenile mortality under these conditions would vary among species spanning an elevational gradient—given concurrent variation in climate, ecohydrology, and physiology–remains unclear. We address this knowledge gap by implementing a growth chamber study, imposing extreme drought with and without a compounding heatwave, for juveniles of five species that span a forested life zones in the Southwestern United States. Overall, the length of a progressive drought required to trigger mortality differed by up to 20 weeks among species. Inclusion of a heatwave hastened mean time to mortality for all species by about 1 week. Lower-elevation species that grow in warmer ambient conditions died earlier (Pinus ponderosa in 10 weeks, Pinus edulis in 14 weeks) than did higher-elevation species from cooler ambient conditions (Picea engelmannii and Pseudotsuga menziesii in 19 weeks, and Pinus flexilis in 30 weeks). When exposed to a heatwave in conjunction with drought, mortality advanced significantly only for species from cooler ambient conditions (Pinus flexilis: 2.7 weeks earlier; Pseudotsuga menziesii: 2.0 weeks earlier). Cooler ambient temperatures may have buffered against moisture loss during drought, resulting in longer survival of higher-elevation species despite expected drought tolerance of lower-elevation species due to tree physiology. Our study suggests that droughts will play a leading role in juvenile tree mortality and will most directly impact species at warmer climate thresholds, with heatwaves in tandem with drought potentially exacerbating mortality especially of high elevation species. These responses are relevant for assessing the potential success of both natural and managed reforestation, as differential juvenile survival following episodic extreme events will determine future landscape-scale vegetation trajectories under changing climate.

In vitro and in vivo efficacy of Larrea divaricata extract for the management of Phytophthora palmivora in olive trees

Phytophthora palmivora is a ubiquitous pathogen responsible for “dry branch” disease, causing significant economic losses in olive trees. Synthetic chemical fungicides are currently used for the control of P. palmivora. The general concern about the negative consequences of using synthetic products prioritizes the search for eco-friendly alternatives. In this context, plant extracts have emerged as an interesting and promising alternative for crop protection. This work studies the inhibitory activity of Larrea divaricata extract on P. palmivora mycelial growth, sporangium and zoospore production. The extract showed fungicidal activity against P. palmivora mycelial growth at concentrations over 150 mg mL-1. Specifically, the extract at 50 mg mL-1 completely suppressed the production of P. palmivora sporangia and zoospores. The alkaloid piperine in L. divaricata extract showed antimicrobial activity against P. palmivora mycelial growth. Extract effectiveness was also evaluated on olive trees in a greenhouse, showing 63% of disease reduction. These results support the use of L. divaricata extract as another environmentally friendly tool to be included in an integrated disease management program for dry branch disease caused by P. palmivora. Highlights: L. divaricata extract showed an effective antimicrobial activity against P. palmivora. Piperine was identified in the divaricata extract by HPLC/MWD. The alkaloid piperine in divaricata extract showed antimicrobial activity on the mycelial growth of P. palmivora. L. divaricata extract could be included in an integrated management programme for dry branch disease caused by P. palmivora.