Tree Populations Research Articles

Genetic variation and population structure of the rice accessions maintained in the AfricaRice genebank using DArTseq

AbstractUtilizing the full potential of rice collections mainly depends on an in‐depth exploration and understanding of the vast diversity in its germplasm. The AfricaRice genebank holds the largest collection of rice germplasm originating from the African continent. In the present study, we comprehensively characterized a collection of 9013 accessions, including Oryza barthii A. Chev., Oryza glaberrima Steud., Oryza longistaminata A. Chev. & Roehr., Oryza sativa L. ssp. indica, and Oryza sativa L. ssp. japonica, for genetic diversity and population structure using genotyping‐by‐sequencing through DArTseq analysis. We identified 27,718 high‐quality single nucleotide polymorphism markers after the genotypic data were filtered. Based on the analyses, the collection has extensive genetic diversity, and the average genetic distance of the entire set was 0.267 (range 0.001–0.469), with 45.1% of pairs of accessions being highly distant and 40.1% moderately distant from each other. Neighbor‐joining tree, principal component, and Bayesian population structure analyses clustered the 9013 accessions into six groups, based roughly on their taxonomic and biological status. The first, second, and third groups consisted of accessions belonging to O. glaberrima, O. barthii, and O. longistaminata, respectively. The fourth, fifth, and sixth groups were improved‐indica, japonica, and traditional‐indica accessions, respectively. The highest value of genetic variance proportion (PhiPT) was found in the species group followed by groups based on cluster analysis and on Bayesian population structure at K = 6. These results allow us to better understand the genetic diversity present in 9013 rice accessions maintained in the AfricaRice genebank and offer a valuable tool for pre breeding, breeding, and further genetic applications.

A practical framework for applied forestry assisted migration

Recent and projected changes in climate over this century pose an unprecedented threat to the health, diversity, and productivity of forest ecosystems. Forests have migrated and adapted to long-term changes in climate over thousands to millions of years; however, natural migration rates and adaptive responses of tree populations cannot match the rapid pace of current climate change. Consequently, more climate-informed approaches to reforestation are needed as current reforestation strategies using local seed sources may no longer be adequate to meet forest management objectives. Assisted migration is a climate change adaptation technique that can help maintain the ecosystem services and economic value that forests provide. Forestry assisted migration (FAM) focusses on the movement of populations of widespread, commercially, or ecologically important forest tree species within or just beyond their current ranges as a way to maintain forest productivity and health in the face of climate change. Although the forestry community recognizes FAM as a reforestation tool, guidance for planning and implementation of FAM is lacking and a framework that provides this guidance can prove useful to land managers with limited time and resources available who want to undertake FAM. We developed a practical framework (the FAM Framework) to provide a structured approach to ensure the most important considerations and best available science are utilized by land managers wanting to implement FAM on their land base. The FAM Framework incorporates multiple factors for the application of FAM in four sequential phases: assessment and analysis, climate-based plant material selection, seed procurement and deployment, and documentation and monitoring. The FAM Framework was tested by developing an assisted migration plan for the Superior National Forest, Minnesota (MN), and lessons learned from the development of this specific plan were used to revise and improve the FAM Framework for suitability across all lands. While originally designed to meet the needs of National Forest System land managers, it is relevant and applicable across the spectrum of land ownership because it incorporates consideration of critical elements in planning and implementing FAM on any landscape while facilitating adaptive management for active learning and future implementation.

Circadian fruit phenology: An overlooked crucial aspect of plant‐frugivore interactions

Abstract The intrinsic ability of plants to face environmental diel changes is paramount for flowering and interactions with pollinators and herbivores. Surprisingly, despite the commendable research efforts on the ecology and evolution of fruit‐frugivore interactions, very little is known about how fruit ripening and dropping vary throughout 24‐h cycle. Even less is known about the potential consequences of circadian fruit phenology on plant interactions with mutualistic and antagonistic frugivores. We illustrate for the first time how the circadian pattern of fleshy fruit dropping and its matching/mismatching with the diel activity of functionally diverse frugivores (fruit/seed predators, seed dispersers, pulp feeders) can drive the outcome of complex multispecies plant‐frugivore interactions. To that end, we used camera trapping to quantify the circadian fruit dropping of a mammal‐dispersed tree, Pyrus bourgaeana, and the diel activity patterns of its functionally diverse vertebrate frugivores during two fruiting seasons in two tree populations of Mediterranean Spain. Using a large data set (20,878 frugivore visits and 701 fruit‐dropping records), we evaluate the adaptive hypothesis that the circadian pattern of fruit dropping will match the diel activity of seed dispersers rather than that of fruit/seed predators. Fruit dropping during daytime doubled that at night‐time, being considerably consistent across and within seasons, study sites and individual trees. Specifically, overlaps between circadian patterns of fruit dropping across and within seasons (0.83 and 0.84 ± 0.02, respectively), study sites (0.95) and individual trees (0.68 ± 0.01) were always high. Whereas seed dispersers (mammalian carnivores) were mostly nocturnal, the most frequent fruit/seed predators (cervids) were mostly diurnal. Consequently, and contrary to our expectations, circadian fruit dropping was more aligned with the diel activity of overabundant fruit/seed predators than with that of carnivore seed dispersers. Our study illustrates how quantifying the circadian patterns of fruit dropping, the diel activity of functionally diverse frugivores, and the matching/mismatching between both patterns can contribute to a better understanding of multispecies plant‐frugivore interactions. Circadian fruiting phenology is an overlooked key attribute for most tropical and temperate fruiting plants, which patterns, mechanisms and outcomes must be fully investigated. Read the free Plain Language Summary for this article on the Journal blog.

A mammalian herbivore selects local and cooler provenance trees in a restoration common garden experiment: implications for community‐assisted migration efforts

Rapid changes in climate have the potential to alter habitats faster than evolution may respond, leading to maladapted tree populations. Assisted migration may help foundation tree species persist in future climates by identifying populations and genotypes that are robust to expected climate change‐induced alterations. Importantly, community‐assisted migration accounts for impacts of those populations and genotypes on the broader community, including herbivores, often adapted to local plants. These impacts have been examined in arthropod communities, but few studies have assessed mammals, and fewer still have leveraged an experimental design to disentangle genetic contributions to herbivore selection among genotypes and populations. We tested whether North American porcupine (Erethizon dorsatum) browsing on Fremont cottonwood (Populus fremontii) is under genetic control in a common garden to uncouple genetic and environmental contributions on browse selection. Porcupines selected trees from climatically similar and cooler areas, where trees from cooler climates suffered greater than 2× more herbivory than trees from warmer areas. Plant genotype was a significant factor for selection, with the most heavily browsed genotype having greater than 10× more herbivory than the least browsed. Broad‐sense heritability of porcupine tree selection was H2B = 0.27 among genotypes, indicating a genetic component to tree defenses against porcupine herbivory that can be predicted by source population climate. Our results have important implications for future mammalian herbivore populations, should climate change render local tree genotypes maladaptive. We recommend assisted migration efforts plant stock from areas up to 3°C warmer and climatically similar areas to maintain productivity and mammalian herbivore browsing.

Dynamics of standing dead wood and severe fire in north Australian savannas: implications for carbon management

Background Many fires in north Australian savannas are severe enough to cause canopy scorch, tree death and removal of stags. Better fire management may increase carbon sequestration in trees, perhaps including stags. Aims To describe and analyse dynamics of stags in tropical savannas (600–1000 mm annual rainfall) in relation to fire and better understand their role in biomass sequestration. Methods We monitored marked populations of live and dead trees over 12 years. Statistical models describing influences on stag creation and loss are applied in stag dynamics simulations. Key results Immediately following severe fire, stag biomass increases acutely because many more live trees are killed than stags removed. Between severe fires, stag losses exceed tree deaths, so peaks are quite short. Many ‘new’ stags are lost (fallen or consumed) quickly. Conclusions Between fires, stags comprise ~7.5–8.9% of standing above-ground biomass, more under dry conditions and during recovery from severe fire or other drivers of increased tree mortality. Fire management is unlikely to increase proportions of total woody biomass in stags unless it also reduces live biomass. Implications Reducing frequency of severe fires can increase total carbon sequestration in dry tropical savannas. Prediction uncertainties and management risks around sequestration present daunting challenges for policy-makers and fire management practitioners.

Opportunities for the Early Diagnosis and Selection of Scots Pine with Potential Resistance to Root and Butt Rot Disease

Pine stands affected by root and butt rot (Heterobasidion annosum s.l.) contain pines (Pinus sylvestris L.) that can survive for a long time without showing external symptoms of the disease (‘conditionally resistant’ refers to trees that survive without symptoms despite infection). The establishment of stands from the seeds of such trees can significantly increase the effectiveness of artificial afforestation. Since the growth and development of pine trees is determined to a certain extent by the number of cotyledons after seed germination, this article examines this trait in the progeny of trees that are potentially resistant and those that have already been attacked by root pathogens. The number of cotyledons and the resilience of trees is fascinating and not generally known. Presumably, the number of cotyledons can be linked to disease resistance based on increased vigour. Biologically, a larger area for carbon assimilation leads to better photosynthetic efficiency and the production of more assimilates (sugars) necessary to trigger defence processes in the event of infection. From an ecological point of view, this can give tree populations in areas potentially threatened by root system diseases a chance of survival. The aim of this study was to analyze the potential of using the number of cotyledons and other seedling characteristics to predict the resistance of trees to root and butt rot disease. The collected data show that the seedlings from the group of diseased trees exhibited lower growth rates and vigour. However, the seedlings from the group of potentially resistant trees are similar to the control, meaning the trees that show no disease symptoms because they have not come into contact with the pathogen. Our observations suggest that monitoring germinating cotyledons could serve as an early diagnostic tool to identify disease-resistant pines, although further research is needed.

Asymmetric responses of EVI and tree ring growth to extreme climate on the northeastern margin of the Tibetan Plateau.

Extreme climate events have increased in terms of their amplitudes, frequency and severity, greatly affecting ecosystem functions and the balance of the global carbon cycle. However, there are still uncertainties about how extreme climate change will affect tree growth. This study characterized the responses of tree growth to extreme climate on the northeastern Tibetan Plateau from 2000 to 2020. Meanwhile, a back propagation neural network was used to predict tree growth trends under two future emission scenarios from 2020 to 2050. This study revealed that: (1) the tree-ring width index (RWI) showed a decreasing trend (- 0.04/decade) in the eastern region, but the enhanced vegetation index (EVI) showed an increasing trend (0.05/decade) from 2000 to 2020. While both RWI and EVI in the middle and western regions showed increasing trends. (2) The responses of RWI and EVI to extreme climate were regionally asymmetric. In the eastern region, extreme precipitation inhibited tree radial growth, while extreme warm nights promoted tree canopy growth. In two other regions, both extreme precipitation and extreme warm nights promoted tree growth. (3) The model predicts that there was no significant change in RWI and EVI in the western region, but both RWI and EVI showed an increasing trend in the middle and eastern regions under the low emission scenario. Under the high emission scenario, the growth of tree stem and canopy in all three regions shows a general decreasing trend. The results of this study both improved the understanding of the differences in carbon allocation between tree stem (RWI) and canopy (EVI) and identified vulnerability thresholds for tree populations.

A Convolutional Neural Network-based Intelligence System for the Identification of Copra Maturity Levels

The North Sulawesi Province, widely recognized as the Coconut Waving Province owing to its substantial coconut tree population, primarily depends on copra production. This research presents a novel methodology for determining copra maturity levels by utilizing a Convolutional Neural Network (CNN) on digital photographs, classifying them into three distinct stages: raw, half-ripe, and ripe. By employing a rigorous 10-fold cross-validation technique, our models demonstrated remarkable performance. Notably, even the model with the lowest performance achieved a commendable accuracy of 87.78% during the training and validation phases. The model that exhibited the highest level of performance achieved a perfect accuracy rate of 100%. Moreover, when subjected to real-world testing situations using novel data, the model with the lowest performance exhibited a noteworthy accuracy of 83.34%. In contrast, the highest-performing model achieved a flawless accuracy of 100%. Based on the findings above, an online system has been built that leverages the most optimal model, facilitating the assessment of copra maturity in real-time. The prospects encompass the integration of this methodology into copra sorting machinery, thereby yielding advantages for both agricultural producers and industrial sectors. This research enhances copra quality control processes and promotes sustainability in the copra industry. Further research could explore refining the CNN model to accommodate a broader range of copra variations and investigating automation possibilities in copra production processes. These endeavors would advance the efficacy and applicability of copra maturity classification methods, fostering continued innovation in the industry.

UMBU TREE (Spondias tuberosa Arr. Cam. - Anacardiaceae): FROM EXTRACTIVE TO PLANTED CULTURE IN BRAZIL

Umbu tree (Spondias tuberosa Arr. Cam.) is botanical species native to the Caatinga that plays significant cultural and economic role in Northeast Brazil. The aims of this study to evaluate the trend in umbu fruit production over a period of 21 years and to discuss the cultivation of the species, associated with its socioeconomic and environmental advantages in the semiarid region of Northeast Brazil. Data on extractive production and the monetary value of umbu fruit were obtained from the official platform of the Brazilian Institute of Geography and Statistics. Silvicultural aspects cultivation, management, and its market was obtained from specialized literature. Descriptive statistics on the data set and a trend analysis through regression model fitting was carried out using JMP® software. A downward trend in umbu tree fruit was estimated for most states, except for Alagoas, Paraíba, and Rio Grande do Norte. Alagoas was the only one with the best average variation (74.6%) in production and price (US$ 0.83) per kg of production via extractivism. The cultivating through plantations for commercial fruit umbu production is an alternative to overcome the declining trend in extractivism, ensuring continuation of family income and environmental protection of umbu tree populations in their natural habitats.

Tracing 40,000 years of vegetation change in the Baetic-Rifan biodiversity hotspot

This study presents a 40,000-year-old pollen record from Los Tollos Lake in the Baetic-Rifan region of southernmost Spain. The data offer insights into the past ecosystems of a current biodiversity hotspot situated at the ecotone between the Atlantic and the Mediterranean. This new sequence encompasses Mediterranean and Ibero-North African sclerophylls, broad-leaf trees, conifers, and Tertiary relicts. The full-glacial abundance of mesothermophytes, particularly oaks, is among the highest recorded for the European Quaternary. Notably, the presence of ecologically significant pollen taxa, which are poorly dispersed and currently occur outside the study area, suggests that this biodiversity hotspot was more extensive in the Pleistocene. During the period of c. 40.8–36.5 ka, three Artemisia maxima at 40.6, 38.9, and 36.9 ka coincide with decreases in Quercus, indicating the spread of steppes in response to the abrupt coolings of the GS10, GS9 (HS4), and GS8 events. Similarly, increases in Quercus around 41, 40, and 37.2–38.3 ka parallel the GI10, GI9, and GI8 warm events. A forested period from 36.5–32 ka includes oak expansions during the GI7 and GI6 interstadials. From 32 to 19.2 ka, more xerophytic vegetation is observed, including the HS3, GS5-GS3, HS2, and GS2.1b-c cold spells, although the correlation with vegetation changes is not synchronous. As early as approximately 21 ka, Artemisia definitively declines, while the region was reforesting, likely due to the presence of stationary populations of broadleaf trees and conifers in the southern Baetic mountains. From approximately 12 ka onwards, the highest values of angiosperm trees are recorded, with oaks dominating throughout most of the Holocene. The pollen record and the correlation with marine records suggest a more intense hydrological regime during the first half of the Holocene, but there is also archaeobotanical evidence for human activity during the second half, resulting in a more open landscape, making it difficult to discriminate the impact of each factor. Some abrupt aridity events during the Holocene coincide with small variations in tree cover, particularly at 9.2, 8.2, 6.8, 5.5–4.8, 4.2, and 2.8 ka. Since the Neolithic and during the metallurgic stages, forest species, especially broad-leaf trees, experienced range retraction accompanied by population extinctions. The region's plant communities have been subject to fire regimes since the Pleistocene, seemingly dependent on the available tree biomass.

Topping sweet orange trees as Diaphorina citri bait on the farm edge for huanglongbing management: Opportunities and limitations

Flush shoots of citrus have an important role in huanglongbing (HLB) epidemiology, as the insect vector of HLB, the Asian citrus psyllid (ACP), prefers them for feeding and reproduction. Additionally, ACP's acquisition and transmission of HLB bacteria mainly occurs in these flushes. As pruning stimulates sprouting, we hypothesized that periodically topping sweet orange trees on the orchard's edge (from 0 to 100 m) would attract ACPs from external areas to these flush shoots as bait, instead of ACPs dispersing throughout the orchard. Hence, it would direct HLB management on this edge width. For that, topped trees (TT) were compared to non-topped trees (NTT) located on the orchard's edge, with only NTT after edges (from 100 to 200 m). Vegetative growth, flushing frequency, ACP population, spray coverage, HLB incidence, fruit yield, and quality of Hamlin and Valencia Americana sweet orange trees were evaluated in commercial orchards over three growing seasons. Topping was performed frequently (every 30–45 d) on alternate rows to stimulate the year-round presence of shoot flushes within the orchard's edge. Insecticides were sprayed monthly to control ACP. Topping reduced tree height and canopy volume by 24 % and 20 % on average. Topped trees presented, on average, 3-fold more flush shoots than NTT over time. On Hamlin blocks, ACP numbers and cumulative HLB incidence were 70 % and 90 % higher, respectively, in TT compared to NTT. However, no consistent differences were observed for the Valencia Americana orchard. Moreover, ACP abundance and HLB incidence were similar after the edge regardless of topping. In the edge areas, although tree yield was reduced (∼65 % on average) on TT compared to NTT, topping significantly enhanced external fruit quality. This treatment increased fruit size and weight and promoted intense yellow coloration. Topping increased spray coverage at the top of Hamlin trees by 1.5-fold compared to control. Frequent topping as bait for ACP poses significant risks if the ACP population is not rigorously controlled, potentially leading to further reductions in yield from edge trees.

The abundance and distributional (in)equalities of forageable street tree resources in Lagos Metropolis, Nigeria

AbstractForaging for wild resources links urban citizens to nature and biodiversity while providing resources important for local livelihoods and culture. However, the abundance and distributional (in)equity of forageable urban tree resources have rarely been examined. Consequently, this study assessed the abundance of forageable street trees and their distribution in Lagos metropolis, Nigeria. During a survey of 32 randomly selected wards across 16 local government areas (LGAs) in the metropolis, 4017 street trees from 46 species were enumerated. The LGA with the highest number of street trees was Ikeja, with 818 trees, while Lagos Island had the lowest count, with two trees. This disparity in tree numbers could be attributed to variations in human population density within each LGA. Ninety‐four percent of the street trees surveyed had at least one documented use and 76% had two, making them potentially forageable. However, the most common species had relatively low forageability scores. Only 5.6% of the total street tree population was rated as highly forageable, with a usability score of at least 11 out of 15. The most forageable street trees were fruit trees and non‐native species. The forageable street trees in the LGAs showed a significant disparity in their distribution, as evidenced by a Gini coefficient of 0.81. Overall, richer neighborhoods had a higher street tree abundance, richness, and forageability potential. To meet greening and foraging goals and address the current inequitable distribution, we suggest allocating more funds for greening, particularly in low‐income neighborhoods. Further research should evaluate forageable species from other sites to acquire a detailed understanding of the distribution and abundance of forageable resources in Lagos metropolis.

The ant and the grasshopper: Contrasting responses and behaviors to water stress of riparian trees along a hydroclimatic gradient

Riparian trees are particularly vulnerable to drought because they are highly dependent on water availability for their survival. However, the response of riparian tree species to water stress varies depending on regional hydroclimatic conditions, making them unevenly vulnerable to changing drought patterns. Understanding this spatial variability in stress responses requires a comprehensive assessment of water stress across broader spatial and temporal scales. Yet, the precise ecophysiological mechanisms underlying these responses remain poorly linked to remotely sensed indices. To address this gap, the implementation of remote sensing methods coupled with in situ validation is essential to obtain consistent results across diverse spatial and temporal contexts. We conducted a multi-tool analysis combining multispectral and thermal remote sensing indices with in situ ecophysiological measurements at different temporal scales to analyze the responses of white poplar (Populus alba) to seasonal changes in drought along a hydroclimatic gradient.Using this approach, we demonstrate that white poplars along the Rhône River (France) exhibit contrasting responses and behaviors during drought depending on the latitudinal context. White poplars in a Mediterranean climate show rapid stomatal closure to reduce water loss and maintain high minimum water potential levels, although this results in a decrease in remotely sensed greenness. Conversely, white poplars located upstream in a temperate climate show high transpiration and stable greenness but lower minimum water potential and water content. A site in the middle of the gradient has intermediate responses. These results demonstrate that white poplars along a climate gradient can have a range of responses to drought along the iso/anisohydricity continuum.These results are important for future climatic conditions because they show that the same species can have different mechanisms of drought resilience, even in the same river valley. This raises questions regarding how these riparian tree populations will respond to future climatic and hydrological conditions.

Thirty years of stasis in the dynamics of the Knysna Afro‐montane forest, South Africa

AbstractWe analysed nearly 31 years (1991–2022) of tree population dynamics in 108 permanent plots each 0.04 ha of the Lilyvlei Nature Reserve, a section of the Knysna Forest in South Africa which has not historically been disturbed by harvesting. The Knysna Forest is the only large piece of forest in South Africa and is marginal for tall forest, having low mean annual rainfall of only about 1000 mm and occurs on nutrient poor soils. In contrast to many studies of other forests globally, we found almost no change in overall biomass. Even at the scale of our small plots and on 10–30 year time scales, there has been little change. The forest has very low recruitment and mortality rates and thus low growth rates. Climatic changes too were minimal over this 30‐year period. The proportion of stems that died per size class was concentrated in the larger size‐classes per species, even for shorter species. This suggests that senescence rather than external disturbances determines the low mortality and thus the low dynamism and the high biomass (approx. 600 Mg ha−1AGB or 41 m2 ha−1 basal area) of the forest. Mortality of some species exceeded conspecific recruitment, a trend accompanied by non‐significant declines in biomass. However, these trends are not significant. In conclusion, neither composition nor biomass has changed significantly in these forests over a period of 30 years. This suggests that not all Southern Hemisphere forests are in a state of decline.

Street Tree Inventory: A Case Study Comparing Systematic Sampling vs. Stratified Systematic Sampling in Piracicaba City, Brazil

AbstractBackgroundThe inventory of street tree populations has acquired new importance due to interest in the provision of ecosystem services. That said, this paper aims to compare systematic sampling with stratified systematic sampling using different sizes of sampling units to estimate the variables of interest: number of trees per kilometer of sidewalk (DF), basal area per kilometer of sidewalk (Dg), mean total height, volume per kilometer of sidewalk (DV), and number of species per kilometer of sidewalk (DE). An innovative contribution here is testing new alternative density variables.MethodsIn the densely urbanized area of Piracicaba (Sao Paulo State, Brazil), 90 sets of 4 blocks were systematically sampled. They were used to compose sampling units of 1, 2, 3, and 4 blocks. Stratification was based on the percentage of street tree cover obtained with geoprocessing tools. Only public trees with a circumference at breast height greater than or equal to 12 cm and planted on sidewalks or avenue medians were included.ResultsThe effect of sampling unit size and stratification on estimate accuracy, sample size, and sampling intensity were analyzed. The results show that stratified systematic sampling was the more accurate process, especially forDF,Dg, andDV.ConclusionsReductions in sample size were more significant when stratified systematic sampling of 2-block sampling units were used.

Intraspecific variation in leaf (poly)phenolic content of a southern hemisphere beech (Nothofagus antarctica) growing under different environmental conditions

Nothofagus antarctica (G.Forst.) Oerst. (Ñire) leaves are a valuable source of (poly)phenolic compounds and represent a high-value non-timber product from Patagonian forests. However, information on the variability of their chemical profile is limited or non-existent. The aim of this study was to evaluate the (poly)phenolic variability in Ñire leaf infusions. To this end, different tree populations growing under different temperature regimes and soil characteristics were considered. Interestingly, a cup of Ñire leaf infusion could be considered as a rich source of quercetin. Significant differences in the (poly)phenolic content, especially in flavonoid conjugates and cinnamic acids, were found among the populations studied. These results suggest metabolic variability among the forests studied, which could be related to the species response to its growing conditions, and also provide some clues about the performance of N. antarctica under future climate scenarios. The N. antarctica forests growing in environments with lower frequency of cold and heat stress and high soil fertility showed better infusion quality. This study showed how a South American beech interacts with its local environment at the level of secondary metabolism. In addition, the information obtained is useful for defining forest management strategies in the Patagonian region.

Searching for laurel wilt resistance in avocados of Mexican and Mexican-Guatemalan ancestry.

Laurel wilt (LW), a lethal vascular disease caused by the ambrosia fungus Harringtonia lauricola, has severely reduced avocado (Persea americana Mill.) production in Florida and decimated populations of native lauraceous trees across twelve U.S. states. All commercial avocado cultivars evaluated to date succumb to the disease, but the speed at which the tree declines varies. Cultivars with West Indian (WI) genetic background develop severe symptoms faster than those with Mexican (M) and Guatemalan (G) pedigree. Genetic resistance to LW is urgently needed, as management relies on costly cultural practices. We screened non-commercial open-pollinated progenies from 19 Mexican and 6 Mexican x Guatemalan accessions, and 2 Guatemalan x West Indian cultivars recognized as tolerant by growers. From the five disease response parameters evaluated, the final disease intensity index and disease severity on the last evaluation day were used to classify genotypes. A wide variability of responses was observed within and among families. Symptomatic plants were present in all families, while some individuals within 15 families remained asymptomatic. 'Colín V-33' (M×G) family was identified as tolerant, and Libres 3 (M), Bladimiro M-06 (M) 'Colinmex' (M×G), 'Collinson' (G×WI), Libres 5 (M) and Rag-13 (M) families were classified as moderately tolerant. This is the first-time tolerance to laurel wilt in avocado is formally reported, though surviving material needs to be propagated for response validation and field testing. Identifying tolerant accessions can help understand the underlying mechanisms and provide breeders with genetic resources for the future incorporation of resistance genes into commercial cultivars.

Epigenetic responses of trees to environmental stress in the context of climate change.

In long-lived tree populations, when environmental change outpaces rates of evolutionary adaptation, plasticity in traits related to stress tolerance, dormancy, and dispersal may be vital for preventing extinction. While a population's genetic background partly determines its ability to adapt to a changing environment, so too do the many types of epigenetic modifications that occur within and among populations, which vary on timescales orders of magnitude faster than the emergence of new beneficial alleles. Consequently, phenotypic plasticity driven by epigenetic modification may be especially critical for sessile, long-lived organisms such as trees that must rely on this plasticity to keep pace with rapid anthropogenic environmental change. While studies have reported large effects of DNA methylation, histone modification, and non-coding RNAs on the expression of stress-tolerance genes and resulting phenotypic responses, little is known about the role of these effects in non-model plants and particularly in trees. Here, we review new findings in plant epigenetics with particular relevance to the ability of trees to adapt to or escape stressors associated with rapid climate change. Such findings include specific epigenetic influences over drought, heat, and salinity tolerance, as well as dormancy and dispersal traits. We also highlight promising findings concerning transgenerational inheritance of an epigenetic 'stress memory' in plants. As epigenetic information is becoming increasingly easy to obtain, we close by outlining ways in which ecologists can use epigenetic information better to inform population management and forecasting efforts. Understanding the molecular mechanisms behind phenotypic plasticity and stress memory in tree species offers a promising path towards a mechanistic understanding of trees' responses to climate change.

Assisted migration outcomes for oak species and seed sources in southern Ontario, Canada

IntroductionForest assisted migration has been proposed as a means to align tree populations with shifting climate habitats under climate change. Here we report on the growth and survival of oak species and seed sources at five assisted migration trials in southern Ontario – an important transition zone between boreal and temperate ecosystems.MethodsEach trial featured one or more oak species – including red oak (Quercus rubra), white oak (Q. alba), burr oak (Q. macrocarpa), and swamp white oak (Q. bicolor) – and seed sources from Ontario, Pennsylvania, and/or Tennessee. The trials were measured for survival and height at between 7 and 13 years after planting.ResultsFor several trials and species, southern seed sources performed nearly as well as local sources. However, southern seed sources of burr oak performed significantly worse than local sources at 2 trials in eastern Ontario. These outcomes may have been influenced by reduced quality of southern seed source planting stock at these trials.DiscussionOur findings generally support previous work that suggests northward movements of seed sources of several hundred kilometers may be safe for assisted migration efforts involving broadleaf tree species. Notably, the trial sites were located at the northern range limits of two oak species in this study (Q. alba and Q. bicolor), suggesting the potential for modest range expansions in this boreal-temperate transition zone. These findings help forest managers to better understand potential assisted migration outcomes under climate change.

Determinants of tree population temporal stability in a temperate mixed forest over a gradient of nitrogen addition

Nitrogen (N) deposition is a significant threat to the functioning of forests and negatively impacts the delivery of forest goods and services. Contemporary management approaches seek to adapt forests to such N-deposition stressors, but to date how plant populations in natural forests respond to N deposition and what factors determine the contrasting responses among populations are still unclear. Here, we investigated the impact of N-addition (control: 0 kg ha−1 yr−1; low: 25 kg ha−1 yr−1; medium: 50 kg ha−1 yr−1; high: 75 kg ha−1 ha yr−1) on tree population temporal stability and how initial tree size, mycorrhizal type, and leaf N content (LNC; as a surrogate for functional trait composition) mediate tree population responses to N-addition in a Korean pine and mixed broadleaved dominated temperate forest in northern China. We quantified tree species population temporal stability as the ratio of mean to standard deviation of the year-by-year stem increments recorded in individual trees from 2015 to 2022 experimental period. The results showed different temporal stabilities of tree species among four N-addition levels, with the highest population stability observed within the high N-addition plots. Furthermore, initial tree size had significantly (p < 0.001) positive effects on population temporal stability. The effect of LNC and initial tree size were also contingent on the level of N applied. Specifically, increase in tree population LNC reduced population temporal stability in all plots where N was added. Our results imply that retention of large-sized trees and species with resource-conservative strategies (e.g., low LNC) could enhance forest stability under N deposition.