Extreme Winter Cold Research Articles

Kucha and Termez—Caves for Mindful Pacing and Seated Meditation

In this paper, by comparing the archaeological remains of meditation caves in Kucha and Termez and by referring to Buddhist literature, we aim at gaining a better understanding of how meditation was practiced in both regions. In Kucha and Termez the arid climate shifted between extreme summer heat and extreme winter cold, making the caves ideal choices for meditation. In Kucha, various types of meditation caves have been recorded. These include small cells for seated meditation, single corridors, and corridors that intersect to form a cross or an inverted U plan. The latter type is associated with a residence and a courtyard, which show many similarities with the complexes located in the mounds south and west of the monastery of Kara Tepe. Two possible uses of the corridor-shaped caves have been proposed based on various factors, such as the distance of the caves from the surface monastery, the similarity of the type, the presence of a courtyard in front of the caves, and the existence of a cell where a person could repose. Buddhist accounts remark on the importance of mindful pacing (Skt. caṅkrama; Chi. jingxing 經行) along with sitting meditation in the daily practice of bhikṣus. According to descriptions in the vinaya, we can infer the possibility of having several types of pathways for mindful pacing, besides the most common straight path. Note also that various ancient records of Buddhist monks mention monuments associated with mindful pacing. Drawing on both architectural remains of the investigated areas and textual evidence, we suggest that the carved corridors, both single and intersecting, might have been specifically designed for mindful pacing. In the better-preserved complexes, the length of the courtyard’s sides corresponds with that of the corridors. While the courtyard could have been utilized for various activities, the similarity in size between corridors and the courtyard hints at its potential use for mindful pacing in mild weather. Furthermore, because the Kara Tepe monastery could accommodate less than fifteen monks, the presence of several meditation complexes, each consisting of four intersecting corridors and a small cell, implies that these units were intended for a monk to live in seclusion for a period.

Amplified warming of North American cold extremes linked to human-induced changes in temperature variability

How global warming is impacting winter cold extremes is uncertain. Previous work has found decreasing winter temperature variability over North America which suggests a reduction in frequency and intensity of cold extremes relative to mean changes. However, others argue that cold air outbreaks are becoming more likely because of Arctic-induced changes in atmospheric circulation. Here we show that cold extremes over North America have warmed substantially faster than the winter mean temperature since 1980. This amplified warming is linked to both decreasing variance and changes in higher moments of the temperature distributions. Climate model simulations with historical forcings robustly capture the observed trends in extremes and variability. A pattern-based detection and attribution analysis shows that the changes in variability are detectable in observations and can be attributed to human influence. Our results highlight that human emissions are warming North American extreme cold temperatures beyond only shifting the winter mean temperature.

Strengthened impact of late autumn Arctic sea ice on Asian winter cold extremes after 1999/2000

Winter cold extremes (WCEs) frequently plague densely populated areas of Asia, leading to substantial economic losses and even fatalities. It has been found that the late autumn sea ice concentration (SIC) anomalies in the northern (SICN) and southern Arctic (SICS) are significantly positively and negatively correlated with the occurrence frequency of WCE in Asia, respectively (Wang and Su 2024). Our study demonstrates that the impacts of SICN and SICS have strengthened after 1999/2000. Specifically, before 1999/2000, the influences of SICN and SICS on the Asian WCE (AWCE) were relatively weak, possibly related to the weak intensity of SICS and the limited correlation between SICN and SICS. After 1999/2000, the interannual variability of SICS became larger and anti-correlated with that of SICN, resulting in a stronger teleconnection between the Arctic SIC and AWCE. It is revealed that after 1999/2000, the greater loss of SICS modified atmospheric stability through changes in surface heat fluxes and surface upward longwave radiation fluxes. This alteration weakened the magnitudes of westerly winds and increased the frequency of blocking events over the northern Eurasian continent, leading directly to a higher occurrence of cold extremes in Asia. These interdecadal differences in the influence of Arctic SIC on AWCE may be associated with long-term climate change.

The Added Value of Statistical Seasonal Forecasts

Seasonal climate predictions can assist with timely preparations for extreme episodes, such as dry or wet periods that have associated additional risks of droughts, fires and challenges for water management. Timely warnings for extreme warm summers or cold winters can aid in preparing for increased energy demand. We analyse seasonal forecasts produced by three different methods: (1) a multi-linear statistical forecasting system based on observations only; (2) a non-linear random forest model based on observations only; and (3) process-based dynamical forecast models. The statistical model is an empirical system based on multiple linear regression that is extended to include the trend over the previous 3 months in the predictors, and overfitting is further reduced by using an intermediate multiple linear regression model. This results in a significantly improved El Niño forecast skill, specifically in spring. Also, the Indian Ocean dipole (IOD) index forecast skill shows improvements, specifically in the summer and autumn months. A hybrid multi-model ensemble is constructed by combining the three forecasting methods. The different methods are used to produce seasonal forecasts (three-month means) for near-surface air temperature and monthly accumulated precipitation seasonal forecast with a lead time of one month. We find numerous regions with added value compared with multi-model ensembles based on dynamical models only. For instance, for June, July and August temperatures, added value is observed in extensive parts of both Northern and Southern America, as well as Europe.

Climatically robust multiscale species distribution models to support pronghorn recovery in California.

We combined two climate-based distribution models with three finer-scale suitability models to identify habitat for pronghorn recovery in California now and into the future. We used a consensus approach to identify areas of suitable climate now and future for pronghorn in California. We compared the results of climate models from two separate hypotheses about their historical ecology in the state. Under the migration hypothesis, pronghorn were expected to be limited climatically by extreme cold in winter and extreme heat in summer; under the niche reduction hypothesis, historical pronghorn of distribution would have better represented the climatic limitations of the species. We combined occurrences from GPS collars distributed across three populations of pronghorn in the state to create three distinct habitat suitability models: (1) an ensemble model using random forests, Maxent, classification and regression Trees, and a generalized linear model; (2) a step selection function; and (3) an expert-driven model. We evaluated consensus among both the climate models and the suitability models to prioritize areas for, and evaluate the prospects of, pronghorn recovery. Climate suitability for pronghorn in the future depends heavily on model assumptions. Under the migration hypothesis, our model predicted that there will be no suitable climate in California in the future. Under the niche reduction hypothesis, by contrast, suitable climate will expand. Habitat suitability also depended on the methods used, but areas of consensus among all three models exist in large patches throughout the state. Identifying habitat for a species which has undergone extreme range collapse, and which has very fine scale habitat needs, presents novel challenges for spatial ecologists. Our multimethod, multihypothesis approach can allow habitat modelers to identify areas of consensus and, perhaps more importantly, fill critical knowledge gaps that could resolve disagreements among the models. For pronghorn, a better understanding of their upper thermal tolerances and whether historical populations migrated will be crucial to their potential recovery in California and throughout the arid Southwest.

The response of atmospheric blocking and East Asian cold extremes to future Arctic Sea ice loss

The effect of Arctic warming on cold extremes over middle latitude remains a controversial and unresolved issue, particularly considering potential enhanced Arctic amplification in future scenarios. Here we examine the possible responses of winter cold extremes to the projected sea ice loss under 2 °C global warming scenario in four models, based on the atmosphere-only experiments of the Polar Amplification Model Inter-comparison Project (PAMIP). We find agreement with the increased responses of extreme cold days over East Asia (EA), characterized by longer duration or stronger intensity of temperature drop during cold events. Accordingly, most models exhibit a weak response of the Ural blocking in the corresponding composite circulation fields, whereas the westward movement of an anomalous anticyclonic system from eastern Siberia before the maturing of the Ural blocking is notable in four models. We suggest that this westward shifting pattern may prolong the duration of Ural blocking or modulate the strength of the Northeast Asian cold vortex, resulting in longer or stronger cold anomalies in EA. Accordingly, increased blocking frequency with a more pronounced westward response of shipment signals is also found over eastern Siberia, where a reduced meridional potential vorticity gradient (PVy) exists. The background of weak PVy can enhance the atmospheric nonlinearity, resulting in the anticyclonic anomalies less prone to dispersion and presenting a westward characteristic. Our results highlight the impact of the nonlinear response of circulation to Arctic sea ice loss. In contrast to more concerned Ural blocking influence, it is suggested that the downstream impact of eastern Siberia blocking on cold extremes in EA may be more pronounced in an enhanced Arctic amplification climate.

Mitigation of extreme winter stress in European seabass, Dicentrarchus labrax through dietary supplementation

Climate change is driving the dangerous confluence of extreme weather events. Among others, aquatic ecosystems are the most affected one. This study sheds light on how dietary supplements affect the physiological responses of European seabass during extreme winter exposure. Fish were provided with three dietary supplements: vitamins C and E (diet-1), propolis (diet-2), and phycocyanin (diet-3) for 45 days. They were then exposed to a simulated extreme winter cold (7 °C) for 20 days. The results showed that dietary supplements do not have a significant impact on weight, growth rate, and protein efficiency ratio before cold exposure. Levels of Na + and Cl − in the fish remained stable across all diets during both control (20 °C) and 7 °C exposure. However, on the 20th day of cold exposure, fish fed diet-3 exhibited notably higher levels of K+ compared to the other two diets, whereas blood glucose was significantly lower in fish fed diet-1. On day 20, significantly higher GPT activities were observed in fish fed diet-1. No significant effects of dietary supplementation were observed in fish serum cholesterol and protein levels. Before cold stress, fish fed the control diet exhibited significantly lower triglyceride levels (p < 0.05). However, during cold exposure, triglyceride levels increased in fish fed diet-1 and the control diet. On day 20, fish fed diet-3 exhibited a comparatively higher lactate content. Conversely, cortisol levels were significantly lower (p < 0.05) in fish fed diets 2 and 3 on the same day. No dietary effects were observed on fish muscle HSP70 gene expression. On days 10 and 20, SREBP1 was significantly upregulated in fish fed all diets. On day 20 of cold exposure, FADS2 and GLUT2 genes were downregulated in the fish fed control diet compared to those fed diets 2 and 3. Before cold stress, fish on the control diet showed higher TNF-1α expression in the spleen. SREBP1 showed a significant upregulation on day 10 in fish fed diet-2. FADS2 gene expression remained unchanged during cold stress. GLUT2 expression showed no noticeable effects throughout the study. Overall, during extreme cold exposure, we observed decreased levels of blood cortisol, transaminase, dehydrogenase, and metabolites, along with a comparatively higher upregulation of growth, metabolic, and immune genes in fish fed diets supplemented with propolis, phycocyanin, and vitamins C&E. These results suggest that dietary supplements can help European seabass cope better with extreme cold, at least for short periods of up to 20 days.

The linkage between autumn Barents-Kara sea ice and European cold winter extremes

While the Arctic's accelerated warming and sea ice decline have been associated with Eurasian cooling, debates persist between those attributing this to sea ice retreat and those to internal variability. Our study examines the association between autumn sea ice variability over the Barents-Kara Seas and extreme cold winters in Europe. Using the observational data and composite analysis, we explore the interannual variability and the potential linkage between sea ice and atmospheric circulation patterns. It reveals a correlation with shifts toward a negative phase of North Atlantic Oscillation and more frequent episodes of the atmospheric blocking over Greenland and the North Atlantic. Furthermore, the negative phase of the North Atlantic Oscillation and enhanced blocking are closely related and mutually reinforcing, shaping the spatial distribution of cold anomalies over much of the European continent. Our results suggest a link between the unusual decrease in Barents-Kara Sea ice during autumn and the occurrence of intense European weather extremes in subsequent winter months, emphasizing the need for delving deeper into this relationship on monthly time scales to enhance our predictive capabilities for midlatitude extreme events.

Migration patterns and breeding areas of Green Sandpipers Tringa ochropus wintering in southern Britain

ABSTRACT Capsule: Green Sandpipers Tringa ochropus wintering in southern Britain breed in western Scandinavia, from southern Norway to Finland. They leave Britain in late April and return by the end of June/early July. Aims: To determine the breeding areas of Green Sandpipers that spend their winter in southern Britain and to investigate their migration ecology. Methods: Green Sandpipers were fitted with archival tags (light level and GPS) whilst in their wintering area. Location data were collected during their northward migration to the breeding area, the breeding period and their return to southern England. Results: Birds departed from the wintering area in late April (median April 20) and moved rapidly to the breeding areas (median duration two days), a mean distance of 1463 km. Females stayed in the breeding areas for only 42 days and males 60 days. The return migration back to the wintering area took a median of 11.5 days with the first birds back by June 19 and the last by July 6. Conclusions: By spending the winter so far north and close to the breeding areas the birds are balancing the risks of poor survival in extreme cold winters with the benefits of rapid and relatively easy movement to and from their breeding areas.

Karadeniz'de 2000-2022 Yılları Arasında Yüzey Sıcaklığının Mekansal ve Zamansal Değişimi

This study presents a comprehensive assessment of the spatio-temporal variability of Sea Surface Temperature (SST) in the Black Sea at monthly to interannual scales, with a focus on understanding its connection to major large-scale atmospheric forcing during the period 2000-2022. Monthly variations of SST in the Black Sea reveal distinct seasonal patterns. The study evaluates the potential impacts of large-scale atmospheric patterns on interannual SST variations using climate indices such as the North Atlantic Oscillation (NAO), East Atlantic/West Russia (EA-WR) and El Niño-Southern Oscillation (ENSO) during the winter months. The results indicated that these large-scale atmospheric oscillations played a substantial role in influencing SST anomalies, with the NAO and EA-WR indices particularly affecting the Black Sea's SST anomalies. The NAO index exhibited negative values during warm winters and positive values during cold winters, with extreme cold and warm winters corresponding to specific years, as observed in 2003, 2006, 2012, 2017 (cold) and 2018, 2020, 2021 (warm). Notably, the relationship between NAO and SST anomalies was not as dominant during 2000-2022. This difference might be explained by the combined influence of NAO and ENSO, which is beyond the scope of this study. The EA-WR pattern was identified as another significant large-scale atmospheric dynamic affecting the Black Sea's SST. Although it explains the cold SST anomalies in certain years, it cannot account for extreme warm SST years. While the influence of ENSO remains somewhat inconclusive for the extreme warm period, the SST pattern between 2016-2022 aligns closely with El Niño events, particularly in 2018 and 2021 when positive SOI index values coincide with warm SST years in the Black Sea.

Interannual variation of the Warm Arctic–Cold Eurasia pattern modulated by Ural blocking and the North Atlantic Oscillation under changing sea ice conditions

Together with rapid Arctic warming and sea ice decline, especially over the Barents–Kara seas (BKS), extreme cold winters have occurred frequently in mid-latitudes, particularly in Central Eurasia. A pattern with two distinct winter temperature anomalies centered over the BKS and Central Eurasia is known as the Warm Arctic–Cold Eurasia (WACE) pattern. The impacts of sea ice loss over the BKS and internal atmospheric variability on past WACE formation remain under discussion mainly due to the large internal atmospheric variability in the mid-latitudes. This study analyzed a large-ensemble historical experiment prescribing observed sea ice condition to investigate the role of internal atmospheric variability in the observed interannual variation of the WACE pattern. Comparison of ensemble members suggests that internal atmospheric variability is important for regulating the magnitude of the WACE pattern. Besides the strong effect of local sea ice loss, winter temperature over the BKS increases due to warm advection driven by the Ural blocking and positive phase of the North Atlantic Oscillation. A decrease in winter temperature over Central Eurasia is mainly attributable to the cold advection enhanced by Ural blocking rather than the remote effect of sea ice decline over the BKS. Our study reveals the importance of internal atmospheric variability in elucidating the observed interannual variation of the WACE pattern.

Sodium chloride alleviates oxidative stress and physiological responses induced by extreme winter cold in genetically improved farmed tilapia (GIFT; Oreochromis niloticus)

A 6-week trial was designed to investigate the effects of dietary sodium chloride supplementation on physiological, metabolic, and molecular stress response parameters. The findings showed that (1) there were no significant differences between sodium chloride supplementation groups (0.05S, 0.1S, and 0.15S) and the control group (P > 0.05), except for the 0.2S diet, which showed better final body weight, weight gain rate, specific growth rate, and feed conversion ratio than the control group (P < 0.05). (2) The hypothermic stress experiment results showed that the survival rates in the 0.1S and 0.15S diets were significantly higher than the control group (P < 0.05). (3) Transcription results showed that these enriched pathways in the gill were mainly energy metabolism and apoptosis pathways, while the major enrichment pathways in the liver were mainly amino acid metabolism and carbohydrate metabolism. (4) The plasma parameter results showed, compared to the control group, the 0.15S diet significantly increased the plasma GLU, TG contents, and Na+ and K+ concentrations and decreased the plasma ALT activity (P < 0.05). In addition, the 0.1S diet increased the plasma ALB content and Cl− concentration (P < 0.05). The gill Na+/K+-ATPase activity decreased markedly when the fish were fed the 0.1S and 0.15S diets (P < 0.05). The antioxidant enzyme activity results showed that the 0.1S and 0.15S diets significantly increased the T-SOD activities (P < 0.05). Gene expression results showed that compared to the control group, the 0.1S and 0.15S diets up-regulated the expression of gys, hsp70, mlcp, mlc, myosin, tnt mRNA, and down-regulated the akt, gk, and erk mRNA expression. Based on the regression analysis, the optimum dietary sodium chloride levels range from 0.10 % to 0.13 % of the diet, which could facilitate energy regulation, improve the immune response, and ultimately strengthen the cold resistance of GIFT.

Assessing the impact of very large volcanic eruptions on the risk of extreme climate events

Very large volcanic eruptions have substantial impacts on the climate, causing global cooling and major changes to the hydrological cycle. While most studies have focused on changes to mean climate, here we use a large ensemble to assess the impact on extreme climate for three years following tropical and extratropical eruptions of different sulfur emission strength. We focus on the impact of an extremely large eruption, injecting 40 Tg sulfur into the stratosphere, which could be expected to occur approximately twice a millennium. Our findings show that the eruption would have a profound effect on large areas of the globe, resulting in extremely rare drought events that under normal circumstances would occur once every century becoming very likely. Several regions such as West Africa, South and East Asia and the Maritime continent are particularly affected with the expected climate shifting well outside the usual range, by up to five standard deviations. These results have important consequences as they indicate that a severe drought in multiple breadbasket regions should be expected following a large eruption. The risk of heavy rainfall tends to decrease over the same regions but by a reduced amount, heatwaves become extremely rare, however the chance of extreme Winter cold surges do not increase by a corresponding amount, since widespread parts of the Northern Hemisphere display a winter warming. Our results show that the location of the eruption is crucial for the change in extremes, with overall changes larger for a Northern Hemisphere eruption than a tropical and Southern Hemisphere eruption, although there is a regional dependency. Simulations of different eruptions with similar forcing distributions but with different sizes are consistent with a linear relationship, however for smaller eruptions the internal variability tends to become dominant and the effect on extreme climate less detectable.

Impact of tropospheric polar vortex on winter cold extremes over Northeast China

Using CN05.1 dataset and NCEP reanalysis, this study investigated the potential linkage between the tropospheric polar vortex and extreme winter cold events over Northeast China. Results show that Asian part of polar vortex (APV) is expanded and weakened before the cold events, this pattern manifests itself as a significant correlation a week before anomalous cold events. Moreover, these cold events could be classified into two types according to the polar vortex position, i.e., eastward-shifted and westward-shifted polar vortex events (EPVE and WPVE). There are significant differences in tropospheric circulation between these two types of events from 14 to 7 days before the cold event outbreak. More specifically, blockings over western Europe and the Bering strait during early-middle stage of EPVE are favourable for the shift of polar vortex towards the northern Eurasia. The southward-shifted polar vortex enhances Rossby wave activity, favourable for the development of Ural blocking, cold vortex in East Asia and cold air transport. APV is greatly weakened after the onset of cold outbreak, leading to cold air intrusion from the western side of cold vortex into Northeast China. During WPVE, the polar vortex is located over the Baffin Island. APV and cold vortex are weaker before the cold event outbreak. The cold air is mainly induced by the blocking high ridge over East Siberian Sea, with a longer transport path and weaker intensity compared with that during the eastward events. In conclusion, the cooling over Northeast China is more drastic due to stronger cold air transport when the polar vortex centre is shifted towards Eurasia.

Thermoregulation of Tuvan pastoralists and Western Europeans during cold exposure.

This study compared the metabolic and vascular responses, to whole-body and finger cold exposure, of a traditional population lifelong exposed to extreme cold winters with Western Europeans. Thirteen cold acclimatized Tuvan pastoralist adults (45 ± 9 years; 24.1 ± 3.2 kg/m2 ) and 13 matched Western European controls (43 ± 15 years; 22.6 ± 1.4 kg/m2 ) completed a whole-body cold (10°C) air exposure test and a cold-induced vasodilation (CIVD) test, which involved the immersion of the middle finger into ice-water for 30 min. During the whole-body cold exposure, the durations until the onset of shivering for three monitored skeletal muscles were similar for both groups. Cold exposure increased the Tuvans' energy expenditure by (mean ± SD) 0.9 ± 0.7 kJ min-1 and the Europeans' by 1.3 ± 1.54 kJ min-1 ; these changes were not significantly different. The forearm-fingertip skin temperature gradient of the Tuvans was lower, indicating less vasoconstriction, than the Europeans during the cold exposure (0 ± 4.5°C vs. 8.8 ± 2.7°C). A CIVD response occurred in 92% of the Tuvans and 36% of the Europeans. In line, finger temperature during the CIVD test was higher in the Tuvans than the Europeans (13.4 ± 3.4°C vs. 3.9 ± 2.3°C). Cold-induced thermogenesis and the onset of shivering were similar in both populations. However, vasoconstriction at the extremities was reduced in the Tuvans compared to the Europeans. The enhanced blood flow to the extremities could be beneficial for living in an extreme cold environment by improving dexterity, comfort, and reducing the risk of cold-injuries.

Extreme stratospheric wave activity as harbingers of cold events over North America

Extreme cold events over North America such as the February 2021 cold wave have been suggested to be linked to stratospheric polar vortex stretching. However, it is not resolved how robustly and on which timescales the stratosphere contributes to the surface anomalies. Here we introduce a simple measure of stratospheric wave activity for reanalyses and model outputs. In contrast to the well-known surface influences of sudden stratospheric warmings (SSWs) that increase the intraseasonal persistence of weather regimes, we show that extreme stratospheric wave events are accompanied by intraseasonal fluctuations between warm and cold spells over North America in observations and climate models. Particularly, strong stratospheric wave events are followed by an increased risk of cold extremes over North America 5–25 days later. Idealized simulations in an atmospheric model with a well-resolved stratosphere corroborate that strong stratospheric wave activity precedes North American cold spells through vertical wave coupling. These findings potentially benefit the predictability of high-impact winter cold extremes over North America.

Winter cold extremes over the eastern North America: Pacific origins of interannual-to-decadal variability

Winter cold extreme events have been observed to frequently take place over North America mainly over its east side, which show significant interannual and decadal variability and cause huge economic losses in the United States. However, it is unclear what leads to the interannual-decadal variability of winter cold extremes over the eastern North America. In this study, we indicate that the decadal variability of winter cold extremes over the eastern North America, whose period is shortened in the recent decades, is mainly tied to Pacific decadal oscillation (PDO), whereas their interannual variability is mainly regulated by Victoria mode (VM). A positive PDO promotes cold extremes in the lower latitudes of the eastern North America mainly owing to the presence of positive Pacific North American (PNA+) patterns, whereas a positive VM is favorable for intense cold extremes in the higher latitudes of the eastern North America mainly due to the occurrence of negative North Pacific oscillation (NPO−) patterns. Thus, the positive VM and PDO combine to significantly contribute to the interannual-to-decadal variability of winter cold extremes over the eastern North America through changes in the winter NPO− and PNA+ patterns due to the variations of meridional background potential vorticity gradient and basic zonal winds. These new findings can help us understand what are the origins of the interannual-decadal variability of winter cold extremes over the eastern North America.

Arctic-associated increased fluctuations of midlatitude winter temperature in the 1.5° and 2.0° warmer world

In recent decades, the interior regions of Eurasia and North America have experienced several unprecedentedly cold winters despite the global surface air temperature increases. One possible explanation of these increasing extreme cold winters comes from the so-called Warm Arctic Cold Continent (WACC) pattern, reflecting the effects of the amplified Arctic warming in driving the circulation change over surrounding continents. This study analyzed reanalysis data and model experiments forced by different levels of anthropogenic forcing. It is found that WACC exists on synoptic scales in observations, model’s historical and even future runs. In the future, the analysis suggests a continued presence of WACC but with a slightly weakened cold extreme due to the overall warming. Warm Arctic events under the warmer climate will be associated with not only a colder continent in East Asia but also a warmer continent, depending on the teleconnection process that is also complicated by the warmer Arctic. Such an increasingly association suggests a reduction in potential predictability of the midlatitude winter anomalies.

Insights from the first winter weather observations near Mount Everest's summit

Insights from the first winter weather observations near Mount Everest's summit

Restoring a keystone tree species for the future: American chestnut assisted migration plantings in an adaptive silviculture experiment

Species ranges are forecast to change in response to warming temperatures and altered precipitation patterns, yet tree migration rates fail to track the pace of climate change. In anticipation of these changes, various forest adaptation management strategies have been broadly proposed, including intentionally modifying species composition via assisted migration of future climate adapted species. Despite the potential utility of these adaptation measures, practical evaluations are limited, particularly those applied to meet other ecological objectives such as supporting vulnerable, underrepresented, or degraded populations of foundational species. In this study, we examined the 4-year seedling survival and morpho-physiological response of American chestnut (Castanea dentata (Marsh.) Borkh.; n = 959 seeds sown), a functionally extirpated species. American chestnuts were grown within sixteen replicated 0.1 and 0.4 ha harvest gaps as part of a 160 ha co-developed (manager-scientist designed), operational-scale silvicultural trial (conditions of sufficient scope to be representative of commercial forest operations) in a northern-hardwood forest in the northeastern US. Chestnut restoration and migration potential (e.g., survival, absolute and relative growth rates, photosynthetic capacity) was assessed against the biophysical controls exerted on seedlings (e.g., understory competition, injury associated with browse and extreme cold winter temperatures) and in comparison to seedlings planted from eight other tree species (n = 480 planted per species) identified for assisted migration. Our results show the performance of American chestnut seedlings is controlled by the strength of local competition (odds of survival increased 2.6 times between four understory competition classes, p < 0.001) and cumulative winter shoot injury (relative growth in aboveground biomass adjusted for injury R2 = -0.85, p < 0.001) associated with cold intolerance likely linked to northward movement of chestnut seedlings transferred outside of their parental range. Still, the combined survival-growth response for American chestnuts ranked among the highest (2nd out of 6 possible rankings) relative to the other species tested, and even outperformed other comparable assisted migration species introduced from outside of their parental range. The implications of these findings highlight the potential for American chestnut plantings to be incorporated within both restoration and broader climate adaptation frameworks. Despite these promising outcomes, important biophysical (e.g., vegetative competition, harvest treatment, and variability in insulative snowpack) and climatic barriers for the reestablishment of this species remain. Given the paucity of reproductively viable American chestnuts or disease resistant breeding programs along northern range limits, this may generate a reliance on plant material obtained from outside of historically recognized safe transfer distances; however, increasingly shifting climate and species ranges may lead to better climate matches in the long term. Nevertheless, the broader applicability of this work illustrates the potential for cultural and ecological keystone species restoration efforts to be incorporated within climate adaptation frameworks to assist in the establishment of compositionally diverse and future climate-adapted forests.