Trees最新文献

Key message

Picea crassifolia shows varying growth patterns, climate-growth relationships, and ecological resilience across climatic habitats.

Abstract

Significant unknowns persist concerning how forest ecosystems globally react to climate change. Dryland trees exhibit increased sensitivity to rising temperatures, threatening the survival of regional forest ecosystems. Therefore, understanding growth patterns of trees and assessing their ecological resilience to extreme drought events are of critical environmental importance. Dendrochronological samples of Picea crassifolia were obtained across elevational gradients in both humid and arid regions of the Qilian Mountains, positioned within northwestern China’s arid and semiarid belt. We evaluated tree growth patterns, their climatic sensitivity, and key indicators of ecological resilience to drought using tree-ring data. Our findings were as follows: (1) Trees at three elevations in the arid region demonstrated uniform growth trajectories: initial augmentation, intermediate suppression, and terminal resurgence. Tree growth at high elevation in the humid region exhibited a continuous upward trend, whereas trees at mid and low elevations initially increased before declining. (2) Drought imposed limitations on arboreal development across tripartite elevational tiers in the arid region. High temperatures had suppressive effects on arboreal development within middle and low elevational belts in the humid region, while low temperatures limited tree growth at high elevation. (3) Trees in the humid region exhibited greater drought resistance, while those in the arid region demonstrated higher recovery. Drought resistance increased with increasing elevation, whereas recovery decreased. Consequently, developing and implementing adaptive silvicultural strategies is imperative for proactive climate response.

Key message

The Montgomery equation accurately estimates leaf area in two Quercus species using either midrib-based or conventional leaf length measurements, even under bilateral asymmetry.

Abstract

Estimation of leaf area is crucial for assessing photosynthetic potential and light interception in plants. The Montgomery equation (ME), which assumes a proportional relationship between leaf area (A) and the product of leaf length (L) and width (W), i.e., A ∝ LW, is widely used, but its validity under leaf bilateral asymmetry requires further testing, particularly when using a midrib-based length definition. Using over 300 leaves each from Quercus acutissima and Q. chenii, we compared a midrib-based approach (curvilinear midrib length as L, and maximum width perpendicular to the midrib tangent as W) with the conventional approach (straight-line distance from leaf apex to base as L). Leaf asymmetry was quantified using two indices. Quercus chenii exhibited significantly greater bilateral asymmetry than Q. acutissima (p < 0.05). Both methods predicted leaf area accurately, with mean absolute percent errors (MAPE) below 5%. The midrib-based approach showed slightly better statistical performance, but the conventional approach remained highly accurate. The ME is valid for estimating leaf area in asymmetric leaves. The conventional approach is recommended for its practicality and sufficient accuracy in field applications.

Quantifying conducting sapwood width and area in trees facilitates studies of water and nutrient transport. Yet, distinguishing conducting from nonconducting xylem is not always straightforward due to the species-specific presence or absence of visible color differences. To improve field-based measurements, we present a novel method that uses a thermal infrared sensor to pinpoint the common temperature change at the transition between conducting and nonconducting xylem on increment cores. Sapwood width estimated this way matched the values obtained from the traditional “touch test” in Pinus ponderosa (PIPO; R² = 0.99) and Pinus strobiformis (PISF; R² = 0.98). A more rigorous evaluation against the visible color difference in Pseudotsuga menziesii (PSME) also resulted in an R² = 0.96. In a case study at the Mt. Bigelow flux-tower site (US-MtB, Arizona), we integrated these thermal sapwood measurements with observations of tree size, radial growth, and its climate sensitivity. PIPO had a larger sapwood (mean width = 7.6 cm) and exhibited less growth decrease under extreme drought compared to PSME (mean width = 4.7 cm). Conversely, PSME was the most productive species, hinting at its competitive strategy but also drought susceptibility under continued aridification. Based on this successful study, we encourage broad application of this user-friendly and species-independent method of quantifying sapwood width towards research on water, growth, and carbon dynamics.

Key message

Manipulating nitrogen and micronutrient concentrations in MS medium significantly enhances Ilex paraguariensis shoot regeneration and reduces oxidative stress, offering a more efficient approach for large-scale plant production

Abstract

Ilex paraguariensis, commonly known as yerba mate, is an economically important plant cultivated in South America. Its propagation is hindered by low rates of rooting by stem cuttings in traditional vegetative methods and high contamination levels in tissue culture. This study aimed to optimize in vitro shoot production from nodal explants. of yerba mate by adjusting the concentrations of NH₄NO₃, KNO₃, and micronutrients in the Murashige and Skoog (MS) culture medium using a Box-Behnken experimental design. The results identified the best-performing combination for shoot regeneration: NH₄NO₃ at 0.5× MS or 0.2× MS, KNO₃ at 0× MS or 0.10× MS, and micronutrients at 1.5× MS, achieving shoot regeneration rates of up to 30%. Lower KNO₃ concentrations favored regeneration, while interactions between NH₄NO₃, KNO_3, and micronutrients significantly influenced shoot formation. However, oxidation remained high (90%) and was not directly affected by nutrient composition, and 26.93% of explants were lost due to contamination. Among the surviving explants, a higher NH₄NO₃ / KNO_3, ratio was correlated with a lower accumulation of phenolic compounds, but no direct impact on oxidation was observed. These findings reinforce the importance of precise nutrient optimization in improving shoot formation from axillary buds efficiency, bringing the possibility to future large-scale production of genetically uniform plants for food and medicinal applications.

Tree stem surfaces are widely recognized as sites of carbon dioxide (CO₂) efflux and oxygen (O₂) influx, reflecting the dynamics of aerobic respiration of photosynthate substrates, such as sugars, delivered via the phloem. Stems are also largely considered passive conduits for methane (CH₄) produced in anoxic soils via microbial methanogenesis, where CH₄ is thought to be transported upward through the transpiration stream and/or diffusion and emitted through stem surfaces and the canopy. However, recent observations from dynamic stem chambers suggest that stems may also act as active sinks for atmospheric CH₄. Despite these findings, the extent and drivers of stem CH₄ consumption remain poorly characterized across biomes, species, and environmental gradients, and its quantitative relationship to stem respiration has not been established. Moreover, previous studies captured only snapshot fluxes, leaving diurnal patterns of CH₄ exchange uncharacterized. Here, we address these limitations by combining real-time measurements of stem CH₄ and O₂ uptake under ambient conditions in a California cherry tree, using a dynamic stem gas exchange system with three chambers receiving a continuous flow of ambient air and automated chamber and reference air sampling every 10 min. Our results confirm that stems of upland trees can actively consume both atmospheric CH₄ and O₂, but with decreasing temperature sensitivity as daily temperatures increase. Early mornings were marked by rapid influxes of both gases, followed by declining uptake as temperatures rose further. Methane uptake was tightly coupled with O₂ influx and represented a minor (0.012% ± 0.002%) fraction of stem respiratory activity, as determined by concurrent O₂ uptake. These findings suggest that while atmospheric CH₄ oxidation is a minor respiratory process in stems, it is strongly linked with stem physiological activity. This challenges the current assumption that terrestrial CH₄ uptake is driven solely by microbial methanotrophy and raises the possibility that living stem tissues may contribute to CH₄ oxidation through an as-yet-unidentified plant-based mechanism.

Key message

The study investigates how wind exposure influences wood density and microfibril angle in two Pinus taxa, revealing greater sensitivity in Pinus elliottii × caribaea and highlighting MFA as a better wind-response indicator.

Abstract

Wind is one of the most persistent natural forces affecting plants, driving them to adapt their properties for survival. With the projected increase in wind intensity and coverage, commercial forests face growing vulnerability. This study investigated how environmental factors, particularly wind, influence wood density and microfibril angle (MFA) in 14.5-year-old South African-grown Pinus taxa. A 2 × 2 factorial experiment was conducted with two taxa—P. elliottii × caribaea and P. radiata—under high and low wind exposure. Over nine months, solar-powered anemometers recorded wind speed in the plots. Sixteen randomly selected trees were sampled and bark-to-bark wood cores extracted from the north–south and east–west directions at 1.3 m height. Density and MFA were analyzed using SilviScan, and mixed-effects models were developed using weather variables as predictors. Pinus radiata demonstrated better growth in diameter, height, and crown length but showed no significant wind-related effects on wood properties. In contrast, P. elliottii × caribaea was more responsive to wind, with MFA significantly lower in trees from less windy plots. Pinus elliottii × caribaea exhibited distinct annual rings with wide earlywood and narrow latewood, whereas P. radiata had less defined rings with more latewood. Growth rings near the pith were indistinct in both taxa. Cardinal direction significantly influenced MFA, with the highest values in the northern direction. Weather variables notably impacted density and MFA on the northern side across treatments. This study contributes valuable insights into the effects of environmental factors on wood properties. However, growth and development during the juvenile stage remain a complex process, requiring further research to clarify the factors driving property variation in commercial forestry species.

Key message

During drought conditions, Austrocedrus chilensis closes its stomata in order to use water more efficiently and survive, even though this results in reduced growth.

Abstract

Climate change and its associated events, such as droughts, are exerting increasing pressure on ecosystems. Forests provide essential ecological, economic, and social functions, making their resilience a key concern. In South America, the temperate Andean forests are home to Austrocedrus chilensis, one of the longest-lived conifers in the region, which is highly sensitive to variations in climate conditions. Although it is among the most drought-resistant species in Patagonia, several studies have reported forest decline associated with drought events in recent decades. With projections indicating increasingly frequent and severe droughts in this region, understanding the adaptive strategies of this species is essential for developing effective management and conservation strategies to maintain ecosystem functioning. To investigate these strategies, we developed the first stable carbon isotope (δ¹³C) chronologies from A. chilensis cellulose. Using samples from two sites located at the drier margin of its distribution in Argentina, we developed annual resolution records spanning the period from 1818 to 2018. From δ¹³C, we derived estimates of carbon isotopic discrimination (Δ¹³C), intrinsic water-use efficiency (iWUE), and internal CO₂ concentration (C_i). Basal area increment (BAI) chronologies were also developed from tree-ring width data. The resulting chronologies reflect both environmental conditions and site-specific disturbance histories. Our results indicate increasing iWUE and C_i, accompanied by reduced growth, especially from the second half of the twentieth century onward. These trends suggest that Austrocedrus chilensis copes with drought primarily through stomatal regulation, enhancing iWUE at the expense of carbon assimilation and growth.

The age of trees in forests, open land, or urban areas is important for biodiversity monitoring, sustainable management, or hazard assessment; but it is often unknown. The height of trees, on the other hand, is often known from remote sensing or can be measured easily and non-destructively. However, there is a sigmoidal relationship between tree age and height, whose inverse function can be used to estimate age from height. Here, we compiled measurements of tree height and age from pre-dominant and dominant trees on long-term experimental plots for the parameterization of a density- and site index-dependent height-age function, tree height = ({text{f}}_{1})(tree age, site index, stand density). The study focused on Norway spruce (Picea abies (L.) Karst.), Scots pine (Pinus sylvestris L.), European beech (Fagus sylvatica L.), and sessile and common oak (Quercus robur L. and Quercus petraea (Matt.) Liebl.) in Central Europe. The extended Chapman-Richard function was used and its inverse function tree age = ({text{f}}_{2})(tree height, site index, SDI) enables age estimation from tree height. To quantify prediction uncertainty, a non-parametric bootstrap was applied to the inverted model, providing height-dependent 95% confidence intervals that account for both parameter variability and the non-linearity of the inversion. The accuracy of the age estimation was higher for low and medium height trees ((11-21%)) and decreased with tree height ((14-22%)), a pattern confirmed by the bootstrap-derived confidence intervals. We discussed the application possibilities and limitations of the functions for estimating tree age in the context of monitoring, inventory, evaluation or management of forests or urban trees.

The aim of this study was to investigate the variation of reserves in dormant and bud break branches of local and introduced plum genotypes in Morocco. An ex situ collection of twenty-eight Japanese and European plum cultivars, installed at the INRA experimental field in Taoujdate, Morocco, was examined during the period of 2019–2020 and 2021 to assess their total soluble solids (TSS), soluble sugar (SSC), and amino acid (AAC) content in branches during the two phases of dormancy and bud break. The results showed significant differences between cultivars and years for each characteristic analyzed. During the transition from the two phenological phases monitored, TSS and SSC in the shoots decreased significantly, while AAC increased. The correlation coefficients showed significant differences for each of the traits studied. The correlations highlighted the particular involvement of sugars in the lifting of dormancy and amino acids in bud break and flowering, emphasizing that the correlation between SSC and AAC is negative. This research is of great importance for the expansion of the plum growing area, taking climatic conditions into account, and for contributing to our understanding of the biochemical mechanisms involved in dormancy breaking and flowering.

Key message

Our study reveals spatial patterns and meteorological drivers of urban tree falls, enabling enhanced urban tree risk management.

Abstract

Urban forestry plays a crucial role in maintaining the safety and resilience of urban environments yet understanding the spatial dynamics and underlying factors of tree fall incidents remains a complex challenge. In this study, we conducted a comprehensive analysis of tree fall incidents in Maringá, Paraná, Brazil, from 2015 to 2021, using kernel density estimation, inhomogeneous L function analysis, and regression tree modeling. Our findings reveal intriguing spatial patterns, with higher concentrations of incidents in the northern and northeastern regions of the city. Moreover, we identified dynamic changes in spatial distributions over time, emphasizing the need for proactive urban planning and risk management strategies. Regression tree analysis highlighted meteorological factors as significant contributors to tree falls, providing actionable insights for risk mitigation efforts. Overall, our study contributes to a better understanding of the spatial dynamics of tree fall incidents and advocates for standardized data collection methods and the development of tools to enhance urban forestry management and promote safer urban environments.