Trees最新文献

Trees in private yards are subject to a complex assortment of interacting ecological, social, cultural and economic factors, including individual preferences, social networks, multiple stakeholders and social constraints. This study explored residents’ attitudes towards yard trees in China and determined the social factors shaping yard trees and yard tree planting. Nearly 300 questionnaires were collected in-person and online in urban and rural villages and communities in Zhoukou city, Henan. Most trees planted in yards were intentionally planted. Yard size was the main constraint on the number of trees in a yard with respondents repeatedly citing the lack of space as a deterrent to planting trees or planting more trees. The most popular attributes for trees planted in yards were symbolism and edibility. Residents’ attitudes were based upon tree functions. The willingness and attitudes of residents towards yard trees suggested that an increase in yard trees would be supported by residents, who appeared to be yearning for a green living environment. However, a lack of preference found for native species suggests a challenging future for native trees in yards in regard to their role in biodiversity and habitat formation. Men played the dominant role in activities associated with yard trees. Residents were keen to aid wider ambitions for greening through their own tree planting in yards, but need guidance via policies and incentives. Such moves at high levels of government will assist the achievement of sustainable development goals in the future China, such as increased city canopy and carbon targets.

Key message

Red cedar chlorophyll fluorescence remains high during the nongrowing season, while transpiration is reduced.

Abstract

Evergreen trees retain their leaves during the winter and thus can photosynthesize when conditions permit. Eastern red cedar (Juniperus virginiana) is widely distributed in the eastern USA and is known to transpire and photosynthesize outside of the growing season. However, most recent work has been done in the Great Plains, which red cedar has recently invaded, while little work has been done in its original range. I hypothesized that red cedar would behave like other conifers from summer drought-free areas and show reduced chlorophyll fluorescence and transpiration during the winter. Four red cedar trees at a site near the Ohio River in Kentucky were equipped with Granier sap flow probes, while solar irradiance, temperature, relative humidity, and soil volumetric water content (VWC) were measured at the site. Dark chlorophyll fluorescence (F_v/F_m) was measured on northern and southern aspects on an approximately weekly basis from early 2019 through mid 2021. High values of F_v/F_m were measured in both growing (April-September) and nongrowing (October-March) seasons; median values in the nongrowing season were 94% of those in the growing season, which did not support my hypothesis. F_v/F_m data were fit to a Michaelis–Menten curve that used minimum temperature of the previous two nights, aspect, and maximum irradiance on the day of measurement taken before fluorescence was measured. Sap flow was explained by maximum daily temperature, vapor pressure deficit (VPD), mean daily irradiance, and VWC. Sap flow in the nongrowing season was 74% of that seen in the growing season, due to lower values of temperature, VPD, and irradiance, supporting my hypothesis. Thus, red cedar remains physiologically active during the nongrowing season. However, it does not appear to behave like other conifers from summer drought-free areas.

Southern Europe is home to two naturally occurring pear species: the European wild pear (Pyrus pyraster (L.) Burgsd.) and the almond-leaved pear (P. spinosa Forssk.). In addition to these two species, the cultivated pear (P. communis L.) is also grown throughout Europe. Since the cultivated pear is one of the most widespread fruits in Europe, gene flow between the cultivated species and their wild relatives is to be expected. The aim of this study was to determine the genetic diversity of natural populations and whether gene flow from the cultivated pear can alter the genetic composition of wild pear populations. We collected samples from 21 populations of P. pyraster and 22 populations of P. spinosa as well as 24 cultivars of P. communis. DNA fingerprinting based on nine microsatellite markers (SSR) was used to analyze the genetic diversity and structure of the wild pear populations and to assess the relationship between wild and cultivated pears. In general, we found a higher genetic diversity of P. pyraster compared to P. spinosa. In three Mediterranean P. pyraster populations, significant cultivated-to-wild gene flow was observed, whereas in P. spinosa it was rare and only observed in a few individuals. Furthermore, in regions where the ecological niches of the two wild pear species overlap, hybrids between them were also found. This study provides valuable insights into the genetic variability of these species and can significantly advance their use in sustainable forest management, conservation, and breeding programs.

Key message

We have identified poplar clones suitable for dryland forestry, which stand out for their resistance to cavitation, level of anisohydrism, adjustment of cellular water relations and high water use efficiency.

In drylands, such as the arid western region of Argentina, poplar afforestation depends on intermittent furrow irrigation, subjecting the plantations to variable water availability both in time and space. Our objective was to study stem biomass production and drought resistance responses of eight poplar clones, to explore whether there are more suitable varieties for forestry in drylands than those currently cultivated, i.e. the hybrid Populus × canadensis clones ‘Conti’ 12 and ‘Guardi’. We conducted a pot experiment with three levels of water availability (control, moderate stress and severe stress), studying four clones of P. × canadensis, ‘Conti 12’, ‘Guardi’, ‘I-214’ and ‘I45/51’, as well as four clones of the Populus deltoides species, ‘Stoneville 67’, ‘Catfish 2’, ‘Dvina’ and ‘Australiano 129/60’. We found that the clones that were more productive under water stress, ‘I-214’ and ‘I45/51’, were also the most resistant to cavitation. However, these clones were not very productive under high water availability. The ‘Guardi’ and ‘Australiano 129/60’ clones performed best in this situation, showing moderately high productivity under water stress. These clones exhibited the highest degree of anisohydrism, high water use efficiency and ‘Australiano 129/60’ stood out for its low water potential at the point of wilting due to osmotic adjustment. The currently most cultivated variety in Cuyo region, ‘Conti 12’, was less productive, did not make cellular adjustments and had low water use efficiency. These results suggest that other available clones may be more suitable for poplar forestry in drylands and should be evaluated in field trials.

Key message

Red oak provenances responded with high plasticity and intra-annual variability in vessel traits to studied climatic conditions, indicating weak signals of local adaptation and providing opportunities for forest management.

The climate change-induced increase in frequency and severity of extreme events has revealed a high vulnerability of various major tree species in Europe, stressing the need for selecting climate-resilient species for forest management. In this context, adaptive strategies of northern red oak (Quercus rubra L.) were examined, using wood anatomical data derived from a provenance trial. We investigated the interannual variation in vessel traits of red oak provenances planted at three sites along a precipitation gradient in Germany. We compared the climate sensitivity of German provenances with those from North America to analyze plasticity and to identify signals of local adaptation in vessel traits. The results revealed variations in vessel traits between all sites, pointing to site-specific responses to prevailing environmental conditions. Differences between provenances were prevalent for vessel size-related traits, with site-specific higher values for German provenances at wet sites. Climate signals, which varied between traits, were strongest for vessel density and the relative conductive area. Vessel traits were found to depend both on previous-year conditions as and on spring climate conditions during the onset of vessel formation. The site-specific response in extreme years deviate significantly between drought and frost events. A trade-off between resistance to extremes and vessel diameter could not be demonstrated, and provenances with larger vessel diameters showed higher frost resistance. The observed high plasticity in vessel traits and the site-specific variation to climate influences point to an adjustment in vessel formation to the prevailing environmental conditions.

Fire damage can significantly impact fruit productivity in orchards. However, the effects of nonlethal fire injuries on the reproductive development of apple trees remain poorly understood. To investigate these effects, we implemented three treatments: trunk girdling to simulate fire injury to xylem, defoliation of a third of the canopy (simulated crown fire injury), and a combined treatment (simulated surface fire injury), alongside a control. The experiment was conducted during the 2021–22 growing season using a randomised block design with four biological replicate plots. Girdling was less effective than crown and surface fire treatments in influencing fruit composition during the current growing season, and flowering and fruiting in the following season. The crown and surface fire treatments induced localised detrimental effects on fruit sugar and titratable acidity while stimulating peel blush. Additionally, these treatments led to reduced starch reserves by harvest, which likely disrupted subsequent flowering and crop load near the previously defoliated sections of the canopy. When surface fires damage leaves near the base of the canopy in addition to the trunk, fruit production in the lower part of the canopy is more likely to be compromised in the following season. Crown fires, which cause leaf loss near the apex of the canopy, appear to be particularly detrimental to tree productivity, as the top defoliation treatment impaired carbohydrate reserves in shoot terminals and roots. In conclusion, fire-induced loss of leaf area during fruit growth alters fruit composition in the current growing season and may lead to lower yields in the subsequent season.

Key message

Tree bark and wood density are highly variable and weakly positively correlated, with species having more or less dense bark than wood to adapt to different environmental stressors.

Tree bark is a complex, multifunctional structure and bark density varies widely across species. While wood density is recognized as a fundamental indicator of the functional ecology of trees, bark density has received much less attention as a key functional trait. Theoretically, bark and wood density should co-vary to some degree, but comprehensive examinations of this covariation are scarce. How do key functional traits of individual trees and species relate to bark and wood density variation/covariation? How does a tree’s life history and evolved tolerance to environmental stress shape variation/covariation in bark and wood density? This study draws from published literature and a large database of individual tree measurements of trees of diverse species and growing conditions, from forest ecosystems across the United States and Canada, to understand covariation between bark and wood density and its relationship to life-history traits and evolved tolerances to environmental stressors. The results of this study show a high tree-to-tree variation in both bark density and wood density, with inherited differences in tissue formation constraining the range of bark and wood densities. All analyses show that bark density was weakly, positively correlated with wood density. Mixed effects modeling showed a strong phylogenetic signal in variation in bark and wood density that was partially explained by the need for species to produce more or less -dense bark and wood to adapt to different environmental stressors (tolerance of drought, shade, frost, waterlogging and fire were all examined), with clearly different relationships for angiosperms versus gymnosperms.

Key Message

In a provenance trial conducted in Serbia, the provenance of the beech trees exhibited a stronger influence on leaf morphology than on survival rate.

Abstract

Provenance trials are crucial for understanding the genetic diversity within beech provenances and advising forestry management practices. In this study, by integrating leaf morphometric analyses and survival data from a 16-year-old provenance trial in Serbia, we aimed to uncover patterns and mechanisms that govern plant–environment interactions in beech (Fagus sylvatica L.) ecosystems. The provenance trial used in this study was established in 2007, as part of the broader European network, from seedlings of 22 provenances originating across Europe. In the fall of 2007 and 2010, and in the summer 2023, plant vitality was recorded within each provenance. For geometric morphometrics, leaves were collected in 2023. The analyses tested the effects of provenance, provenance geographical origin, and provenance survival trend on leaf size and shape. The results showed significant variation in leaf size and shape and revealed that while there was no clear pattern of correlation between survival percentage and leaf morphology, provenance origin did show significant influence on leaf size and shape. Additionally, source stands environmental factors exerted a stronger influence on leaf shape than on leaf size variation. The observed variability in beech leaf morphology on one side, and survival rates on the other side, serve as indicators of the species' resilience and ability to adjust to changing environmental conditions.

Key Message

Although evergreens and deciduous are considered different functional groups due to their dissimilar strategy in canopy maintenance, they exhibit similar leaf heat tolerance to elevated temperatures in Cerrado savannas of Brazil.

Abstract

The escalating temperatures resultant from recent climate shifts have begun to influence the structure and function of tropical ecosystems, according to the Intergovernmental Panel on Climate Change (IPCC). The rise in average temperatures within the tropics implies significant challenges for plant persistence, pushing them beyond the optimal threshold for critical physiological functions, notably photosynthetic process, which temperatures effects can be inferred by measuring leaves chlorophyll fluorescence. Consequently, species lacking leaf traits associated with thermotolerance to high temperatures face heightened risks of permanent damage. The Cerrado is an extremely diverse tropical savanna ecosystem, with an abundance of species exhibiting different foliar habits that are being threatened by such temperature rises. The present study aimed to understand leaf heat tolerance in tree species of different leaf phenologies (evergreens vs. deciduous) exposed to high temperatures (35–65 °C) and to discern any effects and correlations between morphological traits (such as specific leaf area (SLA) and leaf thickness) and heat tolerance capacity measured by the T₅₀. It was hypothesized that evergreen species, with their persistent foliage, might exhibit greater heat tolerance to high temperatures than deciduous species, and that SLA will be correlated with leaf heat tolerance independent of leaf habit. Contrary to the initial hypothesis, the results indicate similar levels of leaf heat tolerance, with deciduous leaves showing a T₅₀ value around 49 °C and evergreens leaves around 50 °C. We did not find differences in the studied morphological traits between the groups, with SLA and leaf thickness not differing between groups, and neither relationships with heat leaf tolerance measured by the T₅₀ values were found. The importance of additional research considering water scarcity is highlighted, as water potential can influence leaf traits and canopy phenology, thus affecting thermotolerance. In summary, our study suggests that, within the context of global warming, leaf phenology alone might not wield substantial influence over the thermotolerance capabilities of these species, at least for the group of Cerrado species studied here.