Forests are increasingly impacted by climate change, affecting tree growth and carbon sequestration. Tree-ring width, closely related to tree growth, is a key climate proxy, yet models describing ring width or growth often lack comprehensive environmental data. This study assesses ERA5-Land data for tree-ring width prediction compared to automatic weather station observations, emphasizing the value of extended and global climate data. We analyzed 723 site-averaged and detrended tree-ring chronologies from two broadleaved and two gymnosperm species across Europe, integrating them with ERA5-Land climate data, CO2 concentration, and a drought index (SPEI12). A subset was compared with weather station data. For modelling interannual variations of tree-ring width we used linear models to assess parameter importance. ERA5-Land and weather-station-based models performed similarly, maintaining stable correlations and consistent errors. Models based on meteorological data from weather stations highlighted SPEI12, sunshine duration, and temperature extremes, while ERA5-Land models emphasized SPEI12, dew-point temperature (humidity), and total precipitation. CO2 positively influenced the growth of gymnosperm species. ERA5-Land facilitated broader spatial analysis and incorporated additional factors like evaporation, snow cover, and soil moisture. Monthly assessments revealed the importance of parameters for each species. Our findings confirm that ERA5-Land is a reliable alternative for modeling tree growth, offering new insights into climate-vegetation interactions. The ready availability of underutilized parameters, such as air humidity, soil moisture and temperature, and runoff, enables their inclusion in future growth models. Using ERA5-Land can therefore deepen our understanding of forest responses to diverse environmental drivers on a global scale.

Soil creep is a slow type of mass movement that, despite its low velocity, can significantly influence slope stability and landscape evolution over time. Understanding its mechanisms and spatial variability is essential for assessing slope stability. However, obtaining high-quality long-term data on creep activity remains a challenge. Dendrogeomorphic methods offer a promising approach to reconstruct past creep movements, but their application to shallow creep processes still requires further refinement. Therefore, this research undertakes a dendrogeomorphic analysis of shallow creep movements on flysch rock slopes, utilizing tree-ring eccentricity as an indicator of this geomorphic process. A total of 136 increment cores from 68 Norway spruce (Picea abies (L.) H. Karst.) trees were analysed, revealing the spatio-temporal dynamics of shallow creep and its relationship with slope morphometry and weathering mantle thickness. The eccentricity values were spatially interpolated to visualize the evolution of creep activity over decades, which showed its significant spatial variability. Statistical analyses, including Pearson's and Spearman's correlation coefficients, were employed to examine the relationships between tree-ring eccentricity and various environmental factors. Results indicated that tree age influences the sensitivity to creep signals, with older trees showing increased eccentricity, suggesting a heightened response to creep movements. The study also explored the impact of precipitation on creep activity, identifying a weak, non-significant positive relationship. This comprehensive analysis enhances the understanding of shallow creep mechanisms and contributes to the broader field of dendrogeomorphology.

AimsCentral and northern Europe experienced extremely dry conditions in 2018, which caused dieback events in many ecosystems, including coastal heathlands. Our aim was to determine the causes of the varying drought responses observed in Calluna vulgaris on the Baltic island of Hiddensee after this extreme drought.LocationIsland of Hiddensee, Baltic Sea, NE Germany.MethodsWe assessed heathland community damage in autumn 2018 and 2019 with drone-based remote sensing. In addition, we measured water table depths and excavated root samples of C. vulgaris. In 2019, we sampled neighboring C. vulgaris individuals showing contrasting vitality statuses (dead, weakened or healthy), measured their height and canopy width, and prepared cross-sections of the main stem at the root collar or soil surface level to count and measure their xylem rings. We also assessed climate-growth correlations in these individuals.ResultsAn 8.0% of all heathland plants showed damage in 2018, while this value decreased to 6.6% in 2019. Only 18% of the plants showing damage in 2018 recovered in 2019. Plant damage was positively related to elevation. Groundwater measurements showed that water table depth dropped below C. vulgaris rooting depth during 2018 and 2019. Healthy plants were taller and had a larger crown area than neighboring weakened and dead individuals, but they did not differ in age nor in previous years' growth. C. vulgaris growth was positively correlated with June and July precipitation.ConclusionsOur study evidences the negative impacts of extreme droughts on C. vulgaris in coastal heathlands, especially in individuals growing in elevated areas and/or relatively small-sized a, and emphasizes the need for adapting heathland management planning accordingly.

Climate change is projected to increase the frequency and severity of droughts, possibly causing sudden and elevated tree mortality. Better understanding and predictions of boreal forest responses to climate change are needed to efficiently adapt forest management. We used tree-ring width chronologies from the Swedish National Forest Inventory, sampled between 2010 and 2018, and a random forest machine-learning algorithm to identify the tree, stand, and site variables that determine drought damage risk, and to predict their future spatial-temporal evolution. The dataset consisted of 16,455 cores of Norway spruce, Scots pine, and birch trees from all over Sweden. The risk of drought damage was calculated as the probability of growth anomaly occurrence caused by past drought events during 1960-2010. We used the block cross-validation method to compute model predictions for drought damage risk under current climate and climate predicted for 2040-2070 under the RCP.2.6, RCP.4.5, and RCP.8.5 emission scenarios. We found local climatic variables to be the most important predictors, although stand competition also affects drought damage risk. Norway spruce is currently the most susceptible species to drought in southern Sweden. This species currently faces high vulnerability in 28% of the country and future increases in spring temperatures would greatly increase this area to almost half of the total area of Sweden. Warmer annual temperatures will also increase the current forested area where birch suffers from drought, especially in northern and central Sweden. In contrast, for Scots pine, drought damage coincided with cold winter and early-spring temperatures. Consequently, the current area with high drought damage risk would decrease in a future warmer climate for Scots pine. We suggest active selection of tree species, promoting the right species mixtures and thinning to reduce tree competition as promising strategies for adapting boreal forests to future droughts.

Tree-ring width chronologies are a critically important material to reconstruct past precipitation variability on the northeastern Tibetan Plateau (NTP). However, temperature signals are often encoded in these chronologies, which complicate the precipitation reconstructions and should be carefully assessed. Here, a dataset of 487 Qilian juniper (Juniperus przewalskii Kom.) tree-ring width series from 16 sites on the NTP were collected to investigate the influence of different temperature signals on the precipitation reconstructions. Correlation analysis showed that all tree-ring series recorded similar precipitation information, but had positive (p 0.05, Group1), weak (p 0.05, Group2), and negative (p < 0.05, Group3) correlations with temperature, respectively. In view of this, all tree-ring series were divided into three groups to develop chronologies to reconstruct local precipitation. During the calibration period of 1957?2011 CE, the Group1 reconstruction had the fastest uptrend, which almost overlapped the observed precipitation; the Group2 reconstruction showed a slower uptrend, whereas the Group3 reconstruction lacked an uptrend. As a result, we get different results when the reconstructions were used to assess the current precipitation status over the past millennium. The Group1 (Group2) reconstructions showed that the recent 20 (10) years were the highest precipitation period over the past millennium, whereas the Group3 reconstruction did not capture this phenomenon. Therefore, we caution that the temperature effects should be evaluated carefully before tree-ring width chronologies being employed to study past precipitation variability.

In mountainous regions, global warming will likely affect the frequency and magnitude of geomorphic processes. This is also the case for rockfall, one of the most common mass movements on steep slopes. Rainfall, snowmelt, or freeze-thaw cycles are the main drivers of rockfall activity, rockfall hazards are thus generally thought to become more relevant in a context of climate change. At high elevations, unequivocal relationships have been found between increased rockfall activity, permafrost thawing and global warming. By contrast, below the permafrost limit, studies are scarcer. They mostly rely on short or incomplete rockfall records, and have so far failed to identify climatically induced trends in rockfall records. Here, using a dendrogeomorphic approach, we develop two continuous 60-year long chronologies of rockfall activity in the Vercors and Diois massifs (French Alps); both sites are located clearly below the permafrost limit. Uncertainties related to the decreasing number of trees available back in time were quantified based on a detailed mapping of trees covering the slope across time. Significant multiple regression models with reconstructed rockfalls as predictors and local changes in climatic conditions since 1959 extracted from the SAFRAN reanalysis dataset as predictants were fitted to investigate the potential impacts of global warming on rockfall activity at both sites. In the Vercors massif, the strong increase in reconstructed rockfall can be ascribed to the recolonization of the forest stand and the over-representation of young trees; changes that are observed should not therefore be ascribed to climatic fluctuations. In the Diois massif, we identify annual precipitation totals and mean temperatures as statistically significant drivers of rockfall activity but no significant increasing trend was identified in the reconstruction. All in all, despite the stringency of our approach, we cannot therefore confirm that rockfall hazard will increase as a result of global warming at our sites.

Intra-annual variability of tree-ring oxygen stable isotopes (delta O-18) can record seasonal climate variability and a tree's ecophysiological response to it. Variability of sub-annual tree-ring delta O-18 maxima and minima, which usually occur in different parts of the growing season, may exhibit different climatic signals and can help in understanding past seasonal moisture conditions, especially in Asian monsoon areas. We developed minimum and maximum tree-ring delta O-18 series based on sub-annual tree-ring delta O-18 measurements ofPinus massonianaat a humid site in southeastern China. We found that interannual variability in minimum tree-ring delta O-18 is primarily controlled by the July-September soil water supply and source water delta O-18, whereas the maximum latewood tree-ring delta O-18 is primarily controlled by the relative humidity (RH) in October. The maximum of variability of earlywood tree-ring delta O-18 records the RH of October of the previous year. We used minimum and maximum tree-ring delta O-18 to develop two reconstructions (1900-2014) of seasonal moisture availability. The summer soil water supply (July-September self-calibrated Palmer drought severity index) and the RH in fall show contrasting trends, which may be related to late-growing seasonal warming leading to a high vapor capacity and high atmospheric moisture. Our findings are valuable for research that aims to explore seasonal moisture changes under anthropogenic climate change and the ecological implications of such contrasting trends.

Recently, forests in the Tianshan Mountains have shown a marked decline in growth and an increased mortality rate because of the more frequent and severe effects of extreme drought, which threatens the ecosystem services they provide. To achieve forest conservation and sustainable development benefits, it is crucial to understand the post-drought recovery trajectory of tree growth and its driving factors. In this study, we quantified the growth recovery performance of dominant tree species in the Tianshan Mountains after extreme drought events and determined the influences of climate factors on forest growth resilience using tree-ring proxy data. The results showed that post-drought moisture conditions may determine the post-drought growth recovery of trees. The post-drought growth for 1997 was higher than that for 1974, which may be attributed to the subsequent period of 1997 experiencing very high precipitation, whereas the year following the 1974 drought was dry (Stan-dardized Precipitation Evapotranspiration Index < 0). Because of the more favorable climate conditions in the post-drought period, the observed relationship between resistance and recovery in 1997 showed a closer fit to the hypothetical line of full resilience which sets resilience to a constant value of 1, allowing trees to recover fully at any given value of resistance. Trees showed lower mean values of the tree growth recovery index (RC) and average recovery rate (ARR) and higher mean values of total growth reduction (TGR) and recovery period (RE) for the drought event in 1974 than that in 1997. We distinguished the relative influence of temperature and precipitation on different drought phases using Boosted Regression Tree (BRT) model. The results showed that the climate conditions during the drought year and subsequent precipitation variation were most influential variables for tree growth recovery. Specifically, post-drought precipitation explained up to 20 % of the variance in RC, TGR, RE, and ARR. These findings deepen our understanding of the impacts of prolonged drought on tree growth, which could aid in developing forest management and conservation strategies to respond to extreme drought.

A dramatic increase in winter (December-February) temperature by 7.2 K (1.1K per decade) since 1950 has occurred in the Ulan Bator basin, Mongolia. This increase in temperature strongly exceeds the global average of late twentieth century warming and even exceeds warming in most of the polar regions with pronounced increases in temperature. The exceptional warming is restricted to Ulan Bator within the Mongolian forest-steppe region and to wintertime. This suggests that the observed warming could result from radiative forcing by black carbon aerosols. In winter, Ulan Bator's air is heavily polluted by particulate matter, including black carbon, originating from the combustion of low-quality fuel at low temperature. Winter smog has strongly increased in recent decades, concomitant to the increase in winter temperature, as the result of a strong increase in the city's population. Exponential growth of Ulan Bator's population started in the mid-twentieth century, but since 1990, altered socioeconomic frame conditions and a warming climate have driven more than 700,000 pastoralists from rural Mongolia to Ulan Bator where people live in provisional dwellings and cause Ulan Bator's heavy air pollution. Tree-ring analysis from larch trees growing at the edge of the Ulan Bator basin shows negative correlation of stem increment with December temperature. This result suggests that milder winters promote herbivores and, thus, reduce the tree's productivity. The negative impact of winter warming on the larch forests adds to adverse effects of summer drought and the impact of high sulfur dioxide emissions. Winter warming putatively associated with high atmospheric concentrations of black carbon aerosols in the Ulan Bator basin is an interesting example of a case where greenhouse gas-mediated climate warming in an area where people themselves hardly contribute to global greenhouse gas emissions affects both humans and ecosystems and causes additional local climate warming.

The boreal forest accounts for approximately 22% of the Northern Hemisphere landmass with nearly 40% of this huge biome growing on continuously frozen soils. Projected climate change leading to degradation of permafrost and increasing drought situation at high latitudes in Eurasia will seriously affect productivity of forests on permafrost. Here we present the results of an on-going research of tree radial growth in the midst of the permafrost zone in Siberia, Russia (Tura region, 64 degrees N, 100 degrees E, 140-610 m a.s.1.). Tree-ring width and density chronologies of Gmelin larch and Siberian spruce from a great variety of sites characterized by different thermo-hydrological regime of soils are analyzed. The obtained results reveal that current tree radial growth and tree-ring structure in permafrost region in Siberia are largely dependent on local site conditions and may be constrained by low air and soil temperatures as well as soil water availability. Varying climatic responses and seasonal radial growth of trees at different habitats indicate a range of possible scenarios of further development of northern larch stands. Forest fire is another important factor strongly affecting tree stand dynamics and forest ecosystem functioning in the continuous permafrost zone. Analysis of tree-ring parameters indicate that post-fire dynamics of tree-ring structure is in accordance with the changes in habitat conditions caused by removal by fire and then gradual recovery of ground vegetation resulting in an alteration in soil active layer depth. In general, the results of this multi-proxy analysis for trees growing under various conditions in the continuous permafrost zone in Siberia allow assumptions about changes in tree productivity, stand dynamics and therefore carbon uptake under projected climate change and permafrost degradation.