Dendrochronologia最新文献

Xylem structure optimizes water conductivity while preventing hydraulic failure via embolism resistance, but how this process is modulated by climate variability and how it affects secondary growth in mature trees is still not fully understood, particularly in water-limited environments. Using quantitative wood anatomy techniques, we estimated xylem anatomical proxies for hydraulic efficiency (xylem specific conductivity, Ks) and safety (cell wall reinforcement, wrein) in two western US conifers, Pinus flexilis and Pinus longaeva, at a montane and subalpine location respectively. We built two large datasets (570 rings for P. flexilis, 635 rings for P. longaeva) to investigate 1) the variability of anatomical parameters (i.e lumen diameter, cell wall thickness) and hydraulic proxies along the stem in the five outermost rings (2009–2013); 2) the response of hydraulic proxies to daily climate over a period of 24 years (1990–2013); and 3) the relationship between xylem hydraulic architecture and basal area increment (BAI). Lumen diameter scaled along the stem following a power function, but the scaling patterns of cell wall thickness and hydraulic proxies differed significantly between species. From 1990–2013, Ks decreased in both species, whereas wrein increased only in P. longaeva, while no trends were observed in BAI. Climate sensitivity of Ks peaked over a longer period (84–102 days) compared to wrein (20–55 days), responding to increasing minimum temperature. In both species, Ks was a better predictor of BAI than wrein, indicating that, even under severely water-limited conditions, radial growth is linked to hydraulic efficiency rather than safety. Based on the variability of cell density along the stem, the trade-off between hydraulic efficiency and safety in P. longaeva appeared to be controlled by a strategy of space occupation. Characterizing the mechanistic relationship between xylem anatomy, plant hydraulic functioning, and stem growth is necessary to better understand climate-growth relationships in the western US and species’ growth plasticity under future climate change scenarios.

This Special Issue presents recent advancements in tropical dendrochronology in the tropical and subtropical Americas, focusing on the identification of new species for dendrochronological studies, the assessment of climate information contained in tree-ring records, and systematic reviews of past research. The studies included in this issue significantly contribute to our understanding of tree species suitable for dendrochronology and the improvement of dating techniques. Moreover, they delve into the relationships between climate variables and tree growth, offering insights into the response of tropical forests to environmental change and providing tools for reconstructing past climate conditions. These studies also shed light on the challenges associated with accurately distinguishing annual ring boundaries in tropical species with complex anatomical structures and emphasize the importance of integrating complementary dating methods and visualization techniques to enhance the reliability of dendrochronological studies in the tropics. By synthesizing diverse research findings, this Special Issue offers a comprehensive overview of tropical dendrochronology in the American (sub) tropics, revealing gaps in knowledge, and suggesting potential avenues for future research. Ultimately, these advancements promote a deeper understanding of tropical forests, their role in the global climate system, and the need for their sustainable management and conservation.

Although climate variables have been shown to strongly affect plantation growth processes, little is known about the roles of tree size and nutrient element in radial growth processes during stand development on the Loess Plateau (LP), China. Total 98 tree-ring cores of Robinia pseudoacacia L. were collected from four stand age-class on LP. We redefined the growth period of R. pseudoacacia based on all combined tree rings and analyzed the influencing factors of each growth period based on the detrending tree ring width chronologies. The effects of climate, tree size, element concentrations, and their interaction effects on tree growth were investigated using linear model and variation partitioning analysis. The results showed that radial growth of R. pseudoacacia was redefined as two growth periods: Decreased Growth Period (1–20 years) and Stable Growth Period (21–40 years). Climate factors mainly controlled tree radial growth in the Stable Growth Period rather than the Decreased Growth Period. The radial growth in the Stable Growth Period was primarily promoted by summer drought, which has 34.1 % of the variables effect percentage. Tree radial growth of R. pseudoacacia in the Decreased Growth Period was mainly promoted by phosphorus (P) concentration, which explained 41.1 % of the variables effect percentage. Contrary to expectations, tree size and the interaction effect of all variables hardly impact on tree radial growth in the two growth periods. Our research illustrated that appropriate nutrient supplementation, such as P elements, occurred during the Decreased Growth Period, followed by thinning practice and tree composition to alleviate climate effects. Overall, our results provide valuable information for formulating appropriate management strategies for R. pseudoacacia plantations on the LP in changing climate.

The expected intensification of the dry season, and concentration of rainfall during the wet season, can disrupt tree growth and regional biodiversity in the Cerrado-Pantanal transition zone. Thus, this study aims to assess the climatic responses of Hymenaea stigonocarpa tree growth, a common tree species in this region. Incremental cores were collected at breast height (ca. 1.3 m) from 67 trees to construct a dendrochronological series to correlate annual growth with local meteorological variables and large-scale atmospheric circulation indices from the Pacific and Atlantic Oceans. Significant positive correlations were observed between tree growth and the Pacific Ocean indices. Maximum and average air temperatures of the previous dry season negatively influenced growth, while precipitation at the beginning of the growth season (November) positively influenced growth. Tree growth was not correlated with temperature or rainfall during the wet season. However, at the end of the wet season (February), tree growth was negatively correlated with air temperature and positively correlated with rainfall, but the relationship shifted in the next month (March) suggesting that soil water saturation reduced growth. Our results indicate that dendrochronological studies of H. stignocarpa are useful for assessing the environmental change on the Cerrado-Pantanal ecotone. Furthermore, variations in water availability and temperature associated with changes in large-scale oceanic circulation and local meteorological conditions will impact the growth dynamics of this important Cerrado tree species.

Quantitative wood anatomy (QWA) has proven to be a powerful method for extracting relevant environmental information from tree-rings. Although classical image-analysis tools such as ROXAS have greatly improved and facilitated measurements of anatomical features, producing QWA datasets remains challenging and time-consuming. In recent years, deep learning techniques have drastically improved the performance of most computer vision tasks. We, therefore, investigate three different deep learning models (U-Net, Mask-RCNN, Panoptic Deeplab) to improve the main bottleneck, cell detection. Therefore, we create a Conifer Lumen Segmentation (CoLuS) dataset for training and evaluation. It consists of manual outlines of each cell lumen from anatomical images of several conifer species that cover a wide range of sample qualities. We furthermore apply our deep learning model to a previously published high-quality QWA chronology from Northern Finland to compare the warm-season (AMJJAS) temperature reconstruction skill of our deep learning method with that of the current ROXAS implementation, which is based on classical image analysis. Based on our evaluation dataset we show improvements of 7.6% and 8.1% for our best performing deep learning model (U-Net) for the computer vision metrics mean Intersection over Union (mIoU) and Panoptic Quality (PQ) compared to automatic ROXAS segmentation, in addition to being much faster. Furthermore, U-Net reduces the percentage error compared to automatic ROXAS analysis - which tends to systematically underestimate lumen area - by 57.8% for lumen area, 63.2% for average cell wall thickness, and 54.1% for cell count. In addition, we show higher performance for the U-Net compared to the Mask-RCNN previously used for tree cell segmentation. These improvements are independent of sample quality. For the Northern Finland QWA chronology, our U-Net model matches or outperforms ROXAS with and without manual post-processing, showing a common signal (Rbar) of 0.72 and a AMJJAS temperature correlation of 0.81 for maximum radial cell wall thickness. A clear improvement is especially visible for the anatomical latewood density, likely due to the better detection of small cell lumina. Our results demonstrate the potential of deep learning for higher-quality segmentation with lower manual post-processing time, saving weeks to months of tedious work without compromising data quality. We thus plan to implement deep learning in a future version of ROXAS.

Lannea microcarpa is a deciduous tree with high socio-economic value in West African agroforestry systems. While climate-growth relationships remain unknown, this species is exposed to climate extremes. Knowledge of its response to climate variations is needed for its sustainable management. Therefore, the present study aimed to examine the growth of Lannea microcarpa in two climatic zones in West Africa (Sudanian zone of Mali and Sudano-Sahelian zone of Burkina Faso) using standard dendrochronological methods. In both sites, Lannea microcarpa forms distinct growth ring-boundaries characterized by a wider band with more parenchyma cell rows and is also marked by its solitary vessels. The two standard chronologies developed were significantly correlated with the precipitation records in both Burkina Faso (r² = 0.41, n = 30 years, p < 0.01) and Mali (r² =0.60, n = 53 years, p < 0.001). Furthermore, a strong relationship between major seasonal precipitation (between June and September) and residual chronology was observed in Burkina Faso (r² = 0.51, n = 28 years, p < 0.01) and Mali (r² = 0.65, n = 52 years, p < 0.001). The formation of annual growth rings is clearly influenced by climate variability, but not all variance is accounted for. The insignificant correlation between the chronologies of the two regions may be due to various factors, including differences in climate factors and soil conditions influencing buffered water availability. Similar studies on other tree species in West Africa will be useful.

Tree-ring studies are still lacking in tropical African forests. This is the case in the seasonally dry miombo forests located in Southern Africa. In the Angolan miombo, subject to intense charcoal exploitation, tree-ring data is urgently needed to estimate the age at which the minimum permitted cutting diameter is reached. Further, climate-growth relationships must be also investigated to understand how major miombo tree species respond to climate constraints and teleconnections such as the El Niño Southern Oscillation (ENSO). To achieve both aims, we studied radial growth data of two miombo tree legume species (Brachystegia spiciformis, Julbernardia paniculata) in wet (Bailundo) and dry (Caála) Angolan sites using dendrochronological methods. Both species have diffuse porous wood and conspicuous ring boundaries delimited by terminal parenchyma in latewood. Sampled individuals had ages (at 1.3 m) between 28 and 34 years with ring widths ranging 3.8–4.3 and 5.5–6.0 mm in dry and wet sites, respectively. In the wet (dry) site, Brachystegia and Julbernardia reached maximum diameter increment rates of 1.05–1.32 (0.74–0.91) cm yr⁻¹ at an age of 12 (14−20) years. Both species took 12–15 years to reach a minimum cutting diameter of 15 cm. The growth variability among conspecific individuals was lower in the dry (mean standard error, 1.4 cm) than in the wet site (mean standard error, 2.7 cm). We also found that wet conditions from November to February, often linked to El Niño events, enhanced growth for both species, with greater growth consistency among individuals and higher sensitivity to climate found in the dry site. This information may help to estimate the optimal age for minimum cutting diameter that guarantees the sustainable use of charcoal and fuelwood.

This paper discusses the findings of frost rings in three supra-long Northern Hemisphere tree-ring chronologies. Comparison between recently published data representing bristlecone pine from western North America, Scots pine from northern Fennoscandia and Siberian larch and Siberian spruce from the Yamal Peninsula shows the rare occurrence of frost rings dated to exactly same calendar years in more than one of these chronologies. The frost ring dates evident in all three datasets are dated to 1627 BC and AD 536. Previously, tree-ring features indicative of adverse growing conditions around 1627 BC have been discussed in the literature. Here, it is emphasised that the frost rings 1627 BC and AD 536 are dated to exactly same calendar year in all available tree-ring records, which demonstrates the value of such an event as a definitive time marker. Other major events of frost rings from multiple sites were dated to 421 BC, 251 BC, AD 627, AD 884, AD 985, AD 1109, AD 1259, AD 1453, AD 1601 and AD 1884. Similar to 1627 BC and AD 536, some of these events have been attributed to volcanic forcing and climate anomalies that led to human consequences and disasters. The case of the 1650 s BC appears different, with possibility of more than one major eruptions, as suggested by frost ring events dated to 1656 BC and 1653 BC in Yamal and western USA, respectively.