Dendrochronologia最新文献

Small islands that depend on limited freshwater resources are at significant risk from seasonal drought, which poses a major threat to both their ecosystems and communities. Christmas Island, located in the eastern Indian Ocean, presents an example for which severe drought conditions during the wet season not only affects its freshwater resources but also biodiversity on the island, including the migration pattern of the iconic red crab species. However, short-term instrumental climate records on this island make it hard to quantify drought variability and assess its associated risks. Tree growth is affected by drought via reduced soil moisture, and hydroclimate reconstruction from tree-ring chronologies can therefore provide longer-term information on historical variability of dry and wet periods. Here, we reconstructed the wet season (December-May) self-calibrating Palmer Drought Severity Index (scPDSI) for Christmas Island using 64 remote tree-ring chronologies from Asia, Australia, and New Zealand. scPDSI was reconstructed using the Point-to-Point Regression (PPR) method and compared with regional marine coral proxies for independent verification. The remote tree-ring chronologies explained more than 66 percent of scPDSI variance (R-squared) over the calibration period. The trees identified as significant predictors in the regression model were primarily located in areas affected by the Indo-Pacific climate drivers including the Indian Ocean Dipole (IOD). The reconstructions span 1540 CE to 2000. During the first four centuries of this period, the frequency of extreme (5th percentile) droughts and pluvial events rarely exceeded one event per 13 years. In contrast, the frequency of both extremes experienced an unprecedented increase during the 20th century, and with a notable shift towards dry conditions. These findings highlight a significant shift towards more frequent and severe dry conditions during the wet season on Christmas Island, posing a challenge to water resource management and potentially threatening the island's ecosystem and services to the community.

The loss of tropical forest resilience has been linked to increased climate variability and associated droughts, but the response of tropical trees to climate extremes remains poorly understood. This limits our ability to design effective forest adaptation strategies in the tropics. Here we analyse the potential of using young trees to analyse climate variability and extremes, which opens new avenues given the increasing area of secondary forests and tree plantations. We used annual tree diameter measurements and stem discs from 139 16-year-old trees belonging to five native species planted in the Sardinilla tree diversity experiment in Panama and compared three methods to determine annual radial growth. Employing inventory measurements, visual stem disc analysis, and wood density measurements, series of radial growth were calculated to compare relative growth during wet and dry extreme events, and to compute continuous climate-growth correlations. Our results show that annual radial growth data derived from wood density profiles are best suited for climate-growth relationships, as they could capture a common growth signal within the high intraspecific variability of young trees to seasonal climatic variables. Annual radial growth data derived visually and from inventories are still useful for quantifying growth responses during extreme drought. The highest similarity among methods to determine annual radial growth, combined with the strongest climate-growth relationships, were found for Cedrela odorata, a species that shows a pronounced decrease in water use and cambial dormancy during the dry season. Stem discs from young trees planted in tropical forest plantations may thus offer a suitable source for dendroecological analyses.

Riparian forests from semi-arid regions with saline soils are dominated by facultative phreatophytes such as tamarisks (Tamarix spp.). Tamarisks tolerate drought and salt stress by using shallow and deep soil water sources depending on precipitation and flow variability in ephemeral or permanent streams. Therefore, their radial growth and wood anatomy would differently respond to precipitation and drought severity depending on stream ephemerality. To assess these responses, tree-ring-width, earlywood anatomy and sapwood nutrient concentrations were measured in five riparian tamarisk stands located in semi-arid north-eastern Spain. These sites experienced different aridity degrees and were located near ephemeral (e.g., Lanaja-dry site) or permanent streams in intensively irrigated agricultural areas (e.g., Valcuerna). Tree rings were widest in Peñaflor (2.94 mm) and narrowest in the driest Lanaja-dry site (1.11 mm), where tree-to-tree growth coherence was higher than in the other sites. Wet conditions during the water year enhanced growth, particularly in the most responsive Lanaja-dry site and in Lopín, whereas elevated flow increased the earlywood hydraulic diameter in Valcuerna. In the Lanaja-dry site, Ca, Cu, K and Mn wood concentrations were higher than in Valcuerna, but C and N concentrations were lower. Elevated Ca wood concentrations correspond to higher drought stress in the Lanaja-dry site, whereas higher N concentrations reflect eutrophication due to extensive use of agricultural fertilizers in Valcuerna. In sites near permanent streams such as Valcuerna, depth to groundwater may be a more robust proxy of growth than in drier sites located near more ephemeral streams such as Lanaja-dry site where tamarisk growth is constrained by 12-month long spring droughts.

X-ray based microdensitometry is conventionally used to produce climate-related tree-ring records. Micro X-ray fluorescence (µXRF) applications represent another growing area of interest and opportunities in dendrochronology. This paper demonstrates a method to correctly juxtapose and precisely synchronise the densitometry and µXRF profiles. Among µXRF variables, full fluorescence spectrum (FFS) corresponds distinctly well with the microdensitometry-based wood density variations. Accordingly, the FFS provides the most applicable variable to integrate the µXRF and density profiles. The method proposed here can be used to demonstrate the strength and sign of µXRF variables and wood density relations. Moreover, the µXRF based records can be readily compared to density variables, such as the latewood maximum density, which is demonstrated in this paper.

Legacy effects following drought are widely detected across worldwide forests, significantly affecting the growth recovery and susceptibility of trees after droughts. Thinning is a common forest management practice used to alter tree growth and climate-growth relationships. Although the effects of thinning on tree response during drought have been investigated, how thinning modulates post-drought legacy effects remains largely unknown. In this study, based on tree-ring data of 140 trees, we examined the effects of thinning on post-drought legacy effects using the quantile mixed effect model for Chinese fir (Cunninghamia lanceolata) in Southeastern China. The tree-ring data were stratified sampling from a thinning experiment applied 10 years ago in 8-year-old plantations, and included four thinning intensities (20 %, 25 %, 33 %, and 50 % reduction of tree number) and an unthinned control treatment. Drought legacy effects of tree growth positively depended on tree social status with the magnitudes and variations larger in higher status classes. Dominant large trees without thinning management had the greatest drought legacy effects. Although the effects of thinning varied slightly at different quantiles, they all indicated that thinning mitigated the growth legacies after drought and the reduction effect was more pronounced with increasing thinning intensity. Thinning could also reduce post-drought climate sensitivities, but only after moderate thinning (20 % and 25 % thinning intensity). Heavier thinning (33 % and 50 % thinning intensity) instead enhanced tree growth responses to climate changes following drought. Thinning intensity needs to be carefully considered to really reap the post-drought benefits of forest thinning management. Our findings suggested that mild thinning offered an alleviation of climate dependency following drought in addition to reducing drought legacy effects on growth, benefiting tree recovery from drought. The results of this study are useful to inform management adaptive strategies for drought-vulnerable plantations under increasingly frequent droughts.

Dendrochronology traditionally involves invasive techniques that might harm cultural heritage artifacts. Non-invasive approaches using X-ray technology and computed tomography (CT) have emerged, but dedicated CT systems are limited in availability. This study explored the viability of using a recently developed photon counting medical CT scanner for growth ring analysis. Six wood samples from pine, oak and beech with varying growth rates were studied. Comparisons were made between traditional methods and CT scanning with measurements performed on the untreated surface, a prepared surface and on CT images. For samples with annual rings wider than 0.3–0.4 mm, CT scanning performed well, while samples with thinner rings or indistinct ring boundaries presented challenges. The combination of traditional tree-ring measurements and analyses of CT scanned images might be a superior study approach generating extra data and information.

In Europe, people have managed forests and woodlands for centuries. Old pollarded oaks reflect historical legacies, and their conservation is threatened by the abandonment of this traditional forest use. However, site conditions (topography, soil features, land cover, and historical use) and warming-triggered drought stress also contribute to their growth decline, particularly in seasonally dry regions. We investigated two stands of pollarded Mediterranean oaks (Quercus subpyrenaica), where pollarding was abandoned in the 1950s, showing contrasting land cover and tree sizes in north-eastern Spain. Changes in land cover, soil characteristics (texture, pH, and nutrient concentrations), climate conditions, and tree-ring data (basal area increment −BAI−, and ring-width indices) were analysed. The Artosilla site, showing the smallest trees, presented the lowest long-term growth rates (period 1730−2022, mean BAI = 19.7 cm² yr⁻¹) as compared with the Aineto site with bigger oaks (mean BAI = 32.9 cm² yr⁻¹). Old trees were found in both sites with ages ranging 293−311 years. The less fertile soils in Artosilla, where pine plantations diminish canopy thermal amplitude, may contribute to the long-term growth decline observed there. Moreover, more major growth suppressions were found in this site, particularly in the 1940s, which suggest a more intensive historical use. Aineto showed a stronger BAI decline since the 1950s, which could be a response to increasingly warmer and drier summer conditions. In contrast, growth in Artosilla is decoupling from soil and atmospheric drought suggesting chronic growth stagnation. Poor site conditions (steeper slope, less fertile soils, intensive historical use) contributed to the decline of pollarded oaks. Active management is required to preserve these unique old, monumental trees.

With global warming, the frequency, intensity, and duration of extreme climate events are likely to escalate across a broad range of regions in the 21st century. However, the impacts of such extreme climate phenomena on forest ecosystems vary significantly across different geographical areas. Trees in arid zones tend to exhibit heightened sensitivity to climatic anomalies. This study uses dendrochronological methods to examine the relationship between climate extreme and two unique natural forests found on the southern slopes of the Tianshan Mountains—Diversifolious Poplar (Populus euphratica Oliv.) and Schrenk spruce (Picea schrenkiana Fisch. et Mey.). The findings reveal a high degree of climate sensitivity in P. schrenkiana, in contrast to the relative stability of P. euphratica. The warming trend has notably altered the growth responses of both species to extreme climate events, with P. euphratica, due to its lower elevation habitat, experiencing more pronounced effects from extreme precipitation events compared to P. schrenkiana. These outcomes underscore the substantial perturbations that extreme climate changes can inflict upon radial tree growth. In light of these findings, tailored management and conservation strategies should be implemented for distinct climate extremes and tree species.

Platanus orientalis is a key riparian species in central Iran with the potential to serve as a climate and streamflow proxy within this region. However, there are limited studies concerning its dendrochronological potential and climate-growth relationships. Therefore, this study investigates the dendroclimatic potential of P. orientalis along the riparian ecosystem of the Zayandeh-Rud River in central Iran. A total of 50 trees were sampled and analyzed at two distinct basin sites, representing varying elevations, climate characteristics, and water availability. Our findings reveal that the tree-ring width index (TRWI) at the lower basin site, which is characterized by higher temperatures, and lower precipitation, is positively affected by streamflow in May and July. This relationship is highly dependent on the amount of precipitation in the upper and lower basin sites. Moreover, analyses reveal a significant negative relationship between TRWI and temperature during the growing season at the lower basin site. In contrast, trees at the upper basin site, characterized by higher precipitation, show weaker climate-growth relationships. These findings imply that P. orientalis tree-rings could provide insight into long-term climatic patterns within riparian ecosystems in central Iran.

Leaf and stem phenology are critical drivers of tree growth patterns in seasonal climates, but the implications for species differences in radial stem growth dynamics are still poorly studied. In our study, we compared the leaf phenology and stem phenology with the underlying cell development as well as annual stem growth between five diffuse-porous (DP) and five ring-porous (RP) coexisting angiosperm species in cold and humid temperate forests. Our results show that RP species unfolded leaves later but initiated wood growth earlier compared to DP species. Yet, xylem vessel maturation in the stem started in June and was remarkably synchronized between DP and RP, which implies that species from both functional groups can effectively avoid vessel cavitation potentially triggered by late spring frost. DP species exhibited one peak in stem growth across the growing season reflecting a uniform vessel formation pattern. Instead, RP species exhibited two peaks in stem growth, with the first peak reflecting expansion of early-wood vessels and the second peak related to subsequent fiber and vessel proliferation in the late-wood. In general, species with a greater number of growth days from the start of cambium activity until full lignification of cells exhibited higher annual stem growth, regardless of species group. The observed differences in leaf and stem phenology between DP and RP species are discussed with respect to the adaptation potential of the two functional groups to changing climate conditions in cold and humid temperate forests.