Age and spatial distribution of the world's oldest trees

Growing old while staying young : The unique mechanisms that defy aging in plants

Although plants age like any other organisms, they have evolved to defy death for millennia and potentially forever.

Ancient trees are essential elements for high-mountain forest conservation: Linking the longevity of trees to their ecological function

Mature forests and their extremely old trees are rare and threatened ancient vestiges in remote European high-mountain regions. Here, we analyze the role that extremely long-living trees have in mature forests biodiversity in relation to their singular traits underlying longevity. Tree size and age determine relative growth rates, bud abortion, and the water status of long-living trees. The oldest trees suffer indefectible age-related constraints but possess singular evolutionary traits defined by fitness adaptation, modular autonomy, and a resilient metabolism that allow them to have irreplaceable roles in the ecosystem as biodiversity anchors of vulnerable lichen species like Letharia vulpina. We suggest that the role of ancient trees as unique biodiversity reservoirs is linked to their singular physiological traits associated with longevity. The set of evolutionarily plastic tools that can only be provided by centuries or millennia of longevity helps the oldest trees of mature forests drive singular ecological relationships that are irreplaceable and necessary for ecosystem dynamics.

Size-focused conservation may fail to protect the world's oldest trees

Old trees are irreplaceable natural resources that provide multifaceted benefits to humans. Current conservation strategies focus primarily on large-sized trees that were often considered old. However, some studies have demonstrated that small trees can be more than thousands of years old, suggesting that conventional size-focused perceptions may hamper the efficiency of current conservation strategies for old trees. Here, we compiled paired age and diameter data using tree-ring records sampled from 121,918 trees from 269 species around the world to detect whether tree size is a strong predictor of age for old trees and whether the spatial distribution of small old trees differs from that of large old trees. We found that tree size was a weak predictor of age for old trees, and diameter explained only 10% of the total age variance of old trees. Unlike large-sized trees that are mainly in warm, wet environments and protected, small old trees are predominantly in cold, dry environments and mostly unprotected, indicating that size-focused conservation failed to protect some of the oldest trees. To conserve old trees, comprehensive old-tree recognition systems are needed that consider not only tree size but also age and external characteristics. Protected areas designed for small old trees are urgently needed.

Large mammals and trees in eastern monsoonal China: anthropogenic losses since the Late Pleistocene and restoration prospects in the Anthropocene

Massive human-induced declines of large-sized animals and trees (megabiota) from the Late Pleistocene to the Anthropocene have resulted in downsized ecosystems across the globe, in which components and functions have been greatly simplified. In response, active restoration projects of extant large-sized species or functional substitutes are needed at large scales to promote ecological processes that are important for ecosystem self-regulation and biodiversity maintenance. Despite the desired global scope of such projects, they have received little attention in East Asia. Here, we synthesise the biogeographical and ecological knowledge of megabiota in ancient and modern China, with relevant data mostly located in eastern monsoonal China (EMC), aiming to assess its potential for restoring functionally intact ecosystems modulated by megabiota. We found that during the Late Pleistocene, 12 mammalian megafaunal (carnivores ≥15 kg and herbivores ≥500 kg) species disappeared from EMC: one carnivore Crocuta ultima (East Asian spotted hyena) and 11 herbivores including six megaherbivores (≥1000 kg). The relative importance of climate change and humans in driving these losses remains debated, despite accumulating evidence in favour of the latter. Later massive depletion of megafauna and large-sized (45-500 kg) herbivores has been closely associated with agricultural expansion and societal development, especially during the late Holocene. While forests rich in large timber trees (33 taxa in written records) were common in the region 2000-3000 years ago, millennial-long logging has resulted in considerable range contractions and at least 39 threatened species. The wide distribution of C. ultima, which likely favoured open or semi-open habitats (like extant spotted hyenas), suggests the existence of mosaic open and closed vegetation in the Late Pleistocene across EMC, in line with a few pollen-based vegetation reconstructions and potentially, or at least partially, reflecting herbivory by herbivorous megafauna. The widespread loss of megaherbivores may have strongly compromised seed dispersal for both megafruit (fleshy fruits with widths ≥40 mm) and non-megafruit plant species in EMC, especially in terms of extra-long-distance (>10 km) dispersal, which is critical for plant species that rely on effective biotic agents to track rapid climate change. The former occurrence of large mammals and trees have translated into rich material and non-material heritages passed down across generations. Several reintroduction projects have been implemented or are under consideration, with the case of Elaphurus davidianus a notable success in recovering wild populations in the middle reaches of the Yangtze River, although trophic interactions with native carnivorous megafauna have not yet been restored. Lessons of dealing with human-wildlife conflicts are key to public support for maintaining landscapes shared with megafauna and large herbivores in the human-dominated Anthropocene. Meanwhile, potential human-wildlife conflicts, e.g. public health risks, need to be scientifically informed and effectively reduced. The Chinese government's strong commitment to improved policies of ecological protection and restoration (e.g. ecological redlines and national parks) provides a solid foundation for a scaling-up contribution to the global scope needed for solving the crisis of biotic downsizing and ecosystem degradation.

Successful In Vitro Shoot Multiplication of Quercus robur L. Trees Aged up to 800 Years

The conservation of the genetic resources of old trees is crucial to their ecological role but is extremely difficult, especially for oak species (Quercus spp.) displaying recalcitrance in seed and vegetative propagation methods. Our study aimed to assess the regenerative potential of Quercus robur trees of different ages (up to 800 years) during micropropagation. We also aimed to determine how in vitro conditions can influence in vitro regeneration responses. Lignified branches collected from 67 selected trees were cultivated ex vitro in culture pots at 25 °C to obtain epicormic shoots (explant sources). The explants were cultivated on an agar medium supplemented with 0.8 mg L^-1 6-benzylaminopurine (BAP) for at least 21 months. In a second experiment, two different shoot multiplication conditions (temporary immersion-RITA^® bioreactor and agar medium) and two culture medium formulations (Woody Plant Medium and modified Quoirin and Lepoivre medium) were tested. The results showed that the mean length of the epicormic shoots obtained in a pot culture was a function of donor age and was similar among the group of younger trees (ca. 20-200 years), and varied between older trees (ca. 300-800 years). The efficiency of in vitro shoot multiplication strictly depended on the genotype. A sustainable in vitro culture (defined as survival after 6 months) was only possible for half of the tested old donor trees, even when they survived the first month of in vitro growth. A continuous monthly increase in the number of in vitro cultured shoots was reported in younger oaks and in some old oaks. We found a significant effect of the culture system and the macro- and micronutrient composition on in vitro shoot growth. This is the first report demonstrating that the in vitro culture can be successfully applied to the propagation of even 800-year-old pedunculate oak trees.

Human activities and species biological traits drive the long-term persistence of old trees in human-dominated landscapes

Old trees have many ecological and socio-cultural values. However, knowledge of the factors influencing their long-term persistence in human-dominated landscapes is limited. Here, using an extensive database (nearly 1.8 million individual old trees belonging to 1,580 species) from China, we identified which species were most likely to persist as old trees in human-dominated landscapes and where they were most likely to occur. We found that species with greater potential height, smaller leaf size and diverse human utilization attributes had the highest probability of long-term persistence. The persistence probabilities of human-associated species (taxa with diverse human utilization attributes) were relatively high in intensively cultivated areas. Conversely, the persistence probabilities of spontaneous species (taxa with no human utilization attributes and which are not cultivated) were relatively high in mountainous areas or regions inhabited by ethnic minorities. The distinctly different geographic patterns of persistence probabilities of the two groups of species were related to their dissimilar responses to heterogeneous human activities and site conditions. A small number of human-associated species dominated the current cohort of old trees, while most spontaneous species were rare and endemic. Our study revealed the potential impacts of human activities on the long-term persistence of trees and the associated shifts in species composition in human-dominated landscapes.

Importance of conserving large and old trees to continuity of tree-related microhabitats

Protecting structural features, such as tree-related microhabitats (TreMs), is a cost-effective tool crucial for biodiversity conservation applicable to large forested landscapes. Although the development of TreMs is influenced by tree diameter, species, and vitality, the relationships between tree age and TreM profile remain poorly understood. Using a tree-ring-based approach and a large data set of 8038 trees, we modeled the effects of tree age, diameter, and site characteristics on TreM richness and occurrence across some of the most intact primary temperate forests in Europe, including mixed beech and spruce forests. We observed an overall increase in TreM richness on old and large trees in both forest types. The occurrence of specific TreM groups was variably related to tree age and diameter, but some TreM groups (e.g., epiphytes) had a stronger positive relationship with tree species and elevation. Although many TreM groups were positively associated with tree age and diameter, only two TreM groups in spruce stands reacted exclusively to tree age (insect galleries and exposed sapwood) without responding to diameter. Thus, the retention of trees for conservation purposes based on tree diameter appears to be a generally feasible approach with a rather low risk of underrepresentation of TreMs. Because greater tree age and diameter positively affected TreM development, placing a greater emphasis on conserving large trees and allowing them to reach older ages, for example, through the establishment of conservation reserves, would better maintain the continuity of TreM resource and associated biodiversity. However, this approach may be difficult due to the widespread intensification of forest management and global climate change.

The methylation landscape of giga-genome and the epigenetic timer of age in Chinese pine

Epigenetics has been revealed to play a crucial role in the long-term memory in plants. However, little is known about whether the epigenetic modifications occur with age progressively in conifers. Here, we present the single-base resolution DNA methylation landscapes of the 25-gigabase Chinese pine (Pinus tabuliformis) genome at different ages. The result shows that DNA methylation is closely coupled with the regulation of gene transcription. The age-dependent methylation profile with a linearly increasing trend is the most significant pattern of DMRs between ages. Two segments at the five-prime end of the first ultra-long intron in DAL1, a conservative age biomarker in conifers, shows a gradual decline of CHG methylation as the age increased, which is highly correlated with its expression profile. Similar high correlation is also observed in nine other age marker genes. Our results suggest that DNA methylation serves as an important epigenetic signature of developmental age in conifers.

Maximum tree lifespans derived from public-domain dendrochronological data

The public-domain International Tree-Ring Data Bank (ITRDB) is an under-utilized dataset to improve existing estimates of global tree longevity. We used the longest continuous ring-width series of existing ITRDB collections as an index of maximum tree age for that species and site. Using a total of 3,689 collections, we obtained longevity estimates for 237 unique tree species, 157 conifers and 80 angiosperms, distributed all over the world. More than half of the species (167) were represented by no more than 10 collections, and a similar number of species (144) reached longevity greater than 300 years. Maximum tree ages exceeded 1,000 years for several species (22), all of them conifers, whereas angiosperm longevity peaked around 500 years. Given the current emphasis on identifying human-induced impacts on global systems, detailed analyses of ITRDB holdings provide one of the most reliable sources of information for tree longevity as an ecological trait.

Physiological mechanisms underlying extreme longevity in mountain pine trees

Ancient trees are life history longevity winners that mostly persist in remote and environmentally harsh mountainous areas. Here, we performed a multifeature analysis in a protected mature mountain pine (Pinus uncinata) forest to identify the morphological and physiological traits that make these trees unique. We compared the physiology of meristematic and somatic tissues (apical buds and needles, respectively) from juvenile, mature young, mature old, and mature ancient trees under cold stress and nonstress conditions. We successfully identified key morphological features of extreme longevity at the organism level, as well as various growth, vigor, stress, and dormancy markers underlying extreme longevity in old and ancient trees. Results indicated that evolution has exerted selective pressure on specific physiological traits that make trees become longevity winners (<0.1% of the tree population were ancient trees, with an average trunk diameter >100 cm and an estimated age of 700 years). Traits entailing longevity not only included apical dominance loss, epicormic growth, and modular senescence, but also an extreme plasticity in both meristematic and somatic tissues (buds and needles, respectively), as shown by various physiological markers. In conclusion, ancient trees are oddities that not only possess a unique ecological value but also show divergent physiological behaviors selected during their evolution to allow them to cope with adversities and attain long life.

Ancient trees: irreplaceable conservation resource for ecosystem restoration

Ancient trees contribute multifaceted ecosystem benefits to old-growth forests, rewilding, and human cultural landscapes. As such, we call for international efforts to preserve these hubs of diversity and resilience. A global coalition utilizing advanced technologies and community scientists to discover, protect, and propagate ancient trees is needed before they disappear.

Appeal: the protection of ancient tree species around the world, taking qilian juniper (Juniperus przewalskii) as an example

Juniperus przewalskii (the Qilian juniper) is a dominant species in the northeast region of the Qinghai-Tibet Plateau. As such, it is of great significance for maintaining the balance and long-term stability of the ecosystem in this biodiversity hotspot. In this paper, we review the literature related to J. przewalskii published in the China National Knowledge Infrastructure and Web of Science. Here, we summarize the main research achievements with regard to this species from ten aspects: tree morphology and phenology, population structure and life history, radial growth and climate response, tree-ring chronology-based history reconstruction, soil physical and chemical properties, chemical composition and activity, physiological ecology, biogeography, breeding and propagation techniques, and occurrence and control of diseases and pests. Considering the ecological importance and research value of J. przewalskii, as well as the shrinking population size, we discuss future research prospects and directions for the conservation of J. przewalskii from four aspects: global climate change, human disturbance, tree regeneration, and pest control. This work provides an important reference for conservation studies of alpine tree species in other biodiversity hotspots around the world.