Tree-ring Data Research Articles

Growth data of outlying plantations allows benchmarking the tolerance to climate extremes and drought stress in the European larch.

Plantations located outside the species distribution area represent natural experiments to assess tree tolerance to climate variability. Climate change amplifies warming-related drought stress but also leads to more climate extremes. We studied plantations of the European larch (Larix decidua), a conifer native to central and eastern Europe, in northern Spain. We used climate, drought and tree-ring data from four larch plantations including wet (Valgañón, site V; Santurde, site S), intermediate (Ribavellosa, site R) and dry (Santa Marina, site M) sites. We aimed to benchmark the larch tolerance to climate and drought stress by analysing the relationships between radial growth increment (hereafter growth), climate data (temperature, precipitation, radiation) and a drought index. Basal area increment (BAI) was the lowest in the driest site M (5.2 cm2 yr-1; period 1988-2022), followed by site R (7.5 cm2 yr-1), with the youngest and oldest and trees being planted in M (35 years) and R (150 years) sites. BAI peaked in the wettest sites (V; 10.4 cm2 yr-1; S, 10.8 cm2 yr-1). We detected a sharp BAI reduction (30% of the regional mean) in 2001 when springto-summer conditions were very dry. In the wettest V and S sites, larch growth positively responded to current March and June-July radiation, but negatively to March precipitation. In the R site, high April precipitation enhanced growth. In the driest M site, warm conditions in the late prior winter and current spring improved growth, but warm-sunny conditions in July and dry-sunny conditions in August reduced it. Larch growth positively responded to spring-summer wet conditions considering short (1-6 months) and long (9-24 months) time scales in dry (site M) and wet-intermediate (sites S and R) sites, respectively. Larch growth is vulnerable to drought stress in dry slow-growing plantations, but also to extreme spring wet-cloudy events followed by dry-hot conditions in wet fast-growing plantations.

Demonstration of process-based reconstruction of annual temperatures from tree ring oxygen isotope

Forecasting the global warming of the post-industrial period requires knowledge of natural variations in climatic parameters, especially temperature in preceding times. Due to its stable time resolution and known physiochemical formation process, tree ring cellulose isotope datasets have immense potential to yield climatic variability information. The first standardized site-independent temperature reconstruction model from tree-ring cellulose oxygen isotope data is demonstrated here using data from a montane site in the western Himalayas. This model does not require any statistical calibration and can be directly compared with instrumental or modelled data. The resulting temperature amplitude is dependent on moisture availability and this input is needed to modulate the reconstruction. The present work tests the possibility of input of carbon isotope discrimination as a proxy of relative humidity. This input achieved amplitude control but additional frequency components were introduced to the reconstruction.

Drought-induced growth phenotypes are associated with genetic variation across a white pine hybrid zone

Understanding relationships among warming climate, increased drought severity, and the genetic architecture of hybrid drought resilience is necessary for forest conservation and management. We calculated three drought-related tree-ring-growth indices (dendrophenotypes) using tree-ring data from hybrid Pinus strobiformis–Pinus flexilis study trees at nine sites across Colorado, New Mexico, Arizona, and Texas. Along with hybrid index (percentage of P. strobiformis ancestry inherited by a single tree) and climate variables, we used dendrophenotypes to (Q1) examine relationships among climate and hybrid index, (Q2) examine relationships between dendrophenotypes and hybrid index, and (Q3) conduct a genotype–phenotype analysis. We observed a significant correlation between hybrid index and dendrophenotypes resulting from high-temperature drought in addition to a significant correlation between those dendrophenotypes and our dataset of single-nucleotide polymorphisms. We conclude that P. strobiformis–P. flexilis trees exhibiting higher hybrid indices are more resilient to high-temperature drought events and encourage future research that identifies a genetic linkage between relevant loci and their conferred physiological benefits.

Trends in Atmospheric CO2 Fertilization Effects with Stand Age Based on Tree Rings

The increase in global carbon emissions has intensified the effects of CO2 fertilization on the carbon cycle. CO2 fertilization is shaped by several factors, including the physiological differences among trees of varied forest ages and types, as well as the influence of different climatic conditions. It is essential to investigate the differences in CO2 fertilization effects across diverse climate zones and delve into the association between these effects and forest age and type. Such exploration will deepen our knowledge of forest responses to environmental changes. This study used annual ring width data from the International Tree-Ring Data Bank, employing the generalized additive mixed models and the Random Forest model to discern the pattern of the CO2 fertilization effect concerning forest age in the Northern Hemisphere. This study also explored the variations in the effect of CO2 fertilization across unique climate zones and the disparities among various forest types within the same climatic zone. The results indicated a link between forest age and the CO2 fertilization effect: it tends to increase in sapling forests and middle-aged forests and diminish in mature forests. Warmer, drier environments had a more marked effect of increased CO2 on tree fertilization. Additionally, coniferous forests demonstrated a more substantial CO2 fertilization effect than broadleaf forests, and deciduous needle-leaf forests surpassed evergreen needle-leaf forests in this regard. This research is pivotal in understanding the shifting patterns of CO2 fertilization effects and how forests respond to atmospheric changes.

Ecosystems dynamics and environmental management: An NDVI reconstruction model for El Alto-Ancasti mountain range (Catamarca, Argentina) from 442 AD through 1980 AD

Vegetation dynamics play a crucial role in understanding the complex interactions between climate variability, ecosystem changes and human land use. In this study, we use the Hindcasting Ecosystems Model (HEMO) to reconstruct the paleo Normalized Difference Vegetation Index (paleo-NDVI), which provides valuable insights into the historical vegetation patterns. Our research focuses on the El Alto Ancasti mountain range, a region characterized by its rich environmental diversity, and archaeological evidence of pre-Hispanic agricultural village landscapes, showcasing the knowledge and management of diverse environments and their fluctuations.To reconstruct the paleo-NDVI, we employed a Neuronal Network trained with two datasets. First, we utilized NDVI data extracted from AVHRR/NOAA satellite images spanning from 1982 to 2015, representing 8 km pixels from the Global Inventory Modeling and Mapping Studies. Second, we incorporated growth ring chronologies from Northwest Argentina sourced from the International Tree Ring Data Bank, enabling the calibration of the NDVI-ring relationship. This methodology allowed us to reconstruct the paleo-NDVI back to 442 AD and to calculate anomalies.Our analysis revealed significant negative anomalies around 600 AD, coinciding with previous research conducted in the nearby Ambato valley. These anomalies may be attributed to the eruption of Tres Cruces volcano in Catamarca during that period. Additionally, extensive positive anomalies emerged from 1600 AD onwards, which align with anomalies detected in earlier studies. The eruption of Huaynaputina volcano in southern Peru in 1600 AD is a possible factor contributing to these positive anomalies.Ongoing investigations focusing on the paleoenvironment and human occupations in the El Alto-Ancasti area aim to provide further insights into how these detected changes could have influenced environmental management decisions. By integrating multidisciplinary approaches, we can better comprehend the complex relationship between vegetation dynamics, climatic events and human activities, ultimately enhancing our understanding of past environmental transformations and their implications for sustainable management strategies.

Evaluating the Effect of Vegetation Index Based on Multiple Tree-Ring Parameters in the Central Tianshan Mountains

Combining tree ring data with remote sensing data can help to gain a deeper understanding of the driving factors that influence vegetation change, identify climate events that lead to vegetation change, and improve the parameters of global vegetation index reconstruction models. However, it is currently not well understood how climate change at different elevations in the central Tianshan Mountains affects radial tree growth and the dynamics of forest canopy growth. We selected Schrenk spruce (Picea schrenkiana) tree core samples from different elevations in the central Tianshan Mountains. We analyzed the relationships of various tree-ring parameters, including tree-ring width, maximum latewood density (MXD), and minimum earlywood density (MID) chronologies, with 1982–2012 GIMMS (Global Inventory Modelling and Mapping Studies) NDVI (Normalized Difference Vegetation Index), 2001–2012 MODIS (moderate resolution imaging spectroradiometer) NDVI, and meteorological data. (1) There were strong correlations between tree-ring width chronologies and the lowest temperatures, especially in July. Tree-ring width chronologies at higher altitudes were positively correlated with temperature; the opposite pattern was observed at lower altitudes. MID chronologies were positively correlated with July temperature in high-altitude areas and mean temperature and highest temperature from May to September in low-altitude areas, and negatively correlated with precipitation during this period. MXD chronologies were mainly negatively correlated with precipitation. MXD chronologies were mainly positively correlated with temperature in April and May. (2) The correlations between MXD chronologies at each sampling point and NDVI in each month of the growing season were strong. Both MID and MXD chronologies were negatively correlated with GIMMS NDVI in July. The overall correlations between tree-ring parameters and MODIS NDVI were stronger than the correlations between tree-ring parameters and GIMMS NDVI in high-altitude areas; the opposite pattern was observed in low-altitude areas. Drought stress may be the main factor affecting tree ring parameters and NDVI. In the future, we should combine tree ring parameters with vegetation index to investigate a larger scale of forests.

Transplanted Ginkgo growth rates indicate common Chinese nursery techniques may severely limit urban ecosystem services

China has experienced history's largest rural-to-urban migration. The social, economic, and environmental challenges brought about by urbanization are diverse and complex. Given China's national goal to achieve carbon neutrality by 2060 and commitment to urban sustainability, large cities have focused on urban greening initiatives. Yet, studies seeking to quantify ecosystem services and disservices only assess healthy, mature trees, rather than those with severe damage, declining health, or lack of vitality due to poor management. In this short communication, we conducted a case-study in one of China's major nursery stock-producing cities, Chengdu, on a common street tree, Ginkgo biloba, to assess the long-term impact of one of the most common yet extreme nursery transplant practices on tree growth (traumatic root-cutting of ‘super-large’ nursery stock). We used tree-ring data collected in a typical urban greenspace from 23 Ginkgo trees, including 18 trees transplanted as ‘super-large’ nursery stock and a control group (5 trees) transplanted as small-caliper trees. We found the trees transplanted as ‘super-large’ nursery stock experienced declining tree growth with decades of lost landscape potential likely due to traumatic root-cutting at the time of transplant from nursery to landscape. The control group allowed contrast between the growth patterns of ‘super-large’ transplanted trees with those that remained healthy, being transplanted as smaller-caliper trees. For the ‘super-large’ trees, we found a decrease in carbon sequestration from 7.6 kg C yr−1 on average per tree in 2001 to about 1.5 kg C yr−1 on average per tree in 2021, while no decreasing trends were observed among the control trees. This implies a negative impact on multiple expected ecosystem services including carbon sequestration, shade, canopy coverage, and pollutant mitigation. These results highlight the unrecognized costs of common Chinese nursery and transplant techniques on urban landscape trees, necessitating more research, science-based policies, and better management techniques.

Reduced accuracy in dendroglaciological mass balance reconstruction of Storglaciären since the 1980s

Recent studies have raised concerns regarding the reconstruction of glacier mass balance using tree-ring data. The method relies on a stable relationship between both variables and summer (June–August) or melt season (May–September) temperature. However, with recent anthropogenic climate change the stability of this relationship is challenged by both, a divergence between tree-ring and temperature, as well as mass balance and temperature data. Establishing to what extent this divergence influences the reconstruction of mass balance using tree-ring data is important to assess the future viability and applicability of the method. In this paper we analyze the relationship between the Torneträsk tree-ring and Storglaciären mass balance records, their response to climate change, and investigate changes in the relationship. We provide evidence for a sensitivity loss in the Torneträsk record and quantify its impact on the reconstruction of summer mass balance of Storglaciären. We find that by including years post 1980, the amplitude of reconstructed variability is reduced, but it remains possible to explain the variance of the record significantly. Our results suggest that for glaciers without an extensive mass balance record the applicability of the method is challenged.

Dendrochronological reconstruction of arborvitae leafminer (Argyresthia spp.) outbreaks on northern white-cedar (Thuja occidentalis) in Maine, USA

Although northern white-cedar ( Thuja occidentalis; henceforth cedar) is thought to have few insect pests, arborvitae leafminers (primarily Argyresthia thuiella) have been known to cause leaf necrosis. Yet, historical evidence for leafminer outbreaks is limited. We combined leafminer larval surveys conducted between 1950 and 1992 with tree-ring analyses from eight cedar stands to reconstruct a history of leafminer outbreaks in Maine, USA. Our tree-ring data show distinctive 2- to 3-year growth reductions that we attribute to leafminers. Several such growth reductions correspond to peak leafminer larval abundances, providing evidence that the reductions are reliable indicators of leafminer activity. Outbreak severity within a site was unrelated to cedar abundance. Outbreak periods thus identified (beginning ca. 1919, 1937, 1950, 1962, mid-1970s, but not at all sites) suggest that leafminer damage may have been more prevalent (albeit patchy) than previously thought. This historical information is relevant given current outbreaks in Maine and elsewhere.

Assessment of climate extremes at the regional scale during the last millennium using an annually resolved stalagmite record

In public awareness, extraordinary floods, heat-waves, or drought episodes rank amongst the most tangible indications of a changing climate. Forecasting the magnitude of such extreme events at regional and local scales is a major challenge. Development of reliable small-scale climate models requires testing against past climate records, but these are often incomplete, or cover only partial aspects in a spectrum of environmental parameters, e.g., due to seasonal bias as it is the case for tree-ring records. Here, we study a stalagmite from the “Kleine Teufelshöhle” (KTH) in the Franconian karst (Germany) to obtain independent information on local climate conditions at multi-annual to multi-decadal time scales. Radiocarbon and 230Th/U dating provide constraints for linear growth models, which were then successfully refined by correlating high spatial resolution O isotope data for the KTH stalagmite with a published regional tree-ring width record at annual resolution for the past 1000 years. Besides the availability of the tree-ring record, the KTH site offers the additional advantage that direct comparison between tree-ring and speleothem climate proxies with historical documents is possible due to the proximity of the speleothem and tree-ring sites to the former “Free imperial city” of Nuremberg. Historical documents provide precisely dated records of extreme events, in particular for destructive floods. Higher O isotope values in the stalagmite characterize the “Litte Ice Age" (LIA), an interval coinciding with frequent and devastating floods, sometimes associated with river blockage related to accumulation of ice rafts. Prior to approximately 1500 Common Era (CE), O isotope values were generally lower and only show minor overlap with historical flooding accounts. Conversely, some known drought events for Central Europe as well as the climatic influence of large-volume volcanic eruptions with hemispheric to global impact may be recorded in the speleothem as negative excursions in speleothem O isotopic values. The correlated tree-ring and speleothem data for the first time provide a complementary paleohydrology record that is uniquely suited to resolve extreme short-term climate events at the regional scale.

Contrasting growth responses to drought in three tree species widely distributed in northern China

Tree species-specific responses to drought are urgently needed for assessing the impacts of current climate change on forest ecosystems. Here, we characterized the resistance, recovery, resilience, and growth recovery periods in response to different drought events based on tree-ring width index data (>30 years) for three tree species widely distributed in northern China, among which larch (Larix principis-rupprechtii Mayr) and Mongolian pine (Pinus sylvestris L. var. mongolica Litv.) are two major species used for afforestation, and birch (Betula platyphylla Suk.) is one of the most common natural tree species. Despite no significant effects of mild drought on tree growth, severe drought events significantly reduced the growth of all species, with contrasting species-specific responses. Larch trees had the lowest resistance and resilience among the three species, and Mongolian pine trees were more resistant but had a longer recovery period than birch trees. The drought responses varied with tree size. Large Mongolian pine and birch trees were more resistant but large larch trees were much more vulnerable than small trees during severe droughts. Smaller birch trees had higher resilience to severe droughts. Our study shows species-specific differences in drought responses and suggests that drought responses are tree-size dependent and drought-intensity associated, which further provides a guidance for selecting optimal cultivated tree species and designing forest managements in this region.

Increasing precipitation variability and climate-growth responses of five tree species in North Carolina, USA

We examined the effects of increasing summertime precipitation variability from 1950 to 2022 on the radial-growth responses of five tree species native to central North Carolina, USA. Tree-ring data were collected from chestnut oak, post oak, longleaf pine, shortleaf pine, and Virginia pine and processed following standard dendrochronology procedures. Adjusted latewood chronologies for each species were created and correlated with either monthly or multi-monthly combinations of summertime precipitation for above average (AA, > 1 σ above mean), below average (BA, <−1 σ below mean), and near average (NA, <−1, and 1 > σ) precipitation years. June–September precipitation variability and other summertime monthly combinations significantly increased during the study period, with a 10.2% increase in AA/BA years during the 21st century. Climate-growth correlations ranged from 0.40–0.51 using all years within the study period. However, using AA and BA years exclusively, climate-growth responses ranged from 0.44–0.71, with post oak and longleaf pine experiencing significantly higher correlations. No significant changes in climate-growth responses occurred for chestnut oak, shortleaf pine, and Virginia pine. These findings suggest the effects of increased precipitation variability on climate-growth responses are species-dependent and affected by the precipitation classification (i.e. AA or BA years). These responses help explain temporal variations in the strength of climate-growth responses, particularly for some species, and offer additional considerations for dendroclimatological research.

Global tree growth resilience to cold extremes following the Tambora volcanic eruption

Although the global climate is warming, external forcing driven by explosive volcanic eruptions may still cause abrupt cooling. The 1809 and 1815 Tambora eruptions caused lasting cold extremes worldwide, providing a unique lens that allows us to investigate the magnitude of global forest resilience to and recovery from volcanic cooling. Here, we show that growth resilience inferred from tree-ring data was severely impacted by cooling in high latitudes and elevations: the average tree growth decreased substantially (up to 31.8%), especially in larch forests, and regional-scale probabilities of severe growth reduction (below −2σ) increased up to 1390%. The influence of the eruptions extended longer (beyond the year 1824) in mid- than in high-latitudes, presumably due to the combined impacts of cold and drought stress. As Tambora-size eruptions statistically occur every 200–400 years, assessing their influences on ecosystems can help humankind mitigate adverse impacts on natural resources through improved management, especially in high latitude and elevation regions.

Vegetation Index Research on the Basis of Tree-Ring Data: Current Status and Prospects

The normalized difference vegetation index (NDVI) and tree-ring parameters are commonly used indicators in the research on forest ecology and responses to climate change. This paper compiles and analyzes the literature on vegetation index research on the basis of tree-ring information in the past 20 years and provides an overview of the relationship between tree-ring parameters and NDVI, as well as NDVI reconstruction. The research on the vegetation index based on tree-ring data is mainly concentrated in the middle and high latitudes, and relatively few studies are concentrated in the low latitudes. The tree-ring parameters have a strong correlation with the NDVI in the summer. In terms of tree-ring reconstruction NDVI, Sabina przewalskii is the tree with the longest reconstruction sequence so far, and the tree-ring width is the main proxy index. In addition, combining tree rings with the NDVI is useful for assessing forest decline, quantifying the forest response to drought, and monitoring forest productivity. In the future, it is necessary to consider a variety of environmental factors to find the optimal model construction parameters and carry out research on the climate response of forest tree growth and the reconstruction of the historical sequence of the vegetation index at large spatial scales.

Comparing the impact of live-tree versus historic-timber data on palaeoenvironmental inferences in tree-ring science, eastern North America

Dendroarchaeological data from historic structures and artefacts have the potential to extend tree-ring chronologies spatially and temporally, especially where old-growth forests have been extensively modified or harvested. While these data may contribute to an improved understanding of past climate and ecology, critical differences in the properties of live-tree and historic-timber data might affect results and interpretations of large-scale studies, such as those relying on large datasets from public databases like the International Tree-Ring Data Bank (ITRDB). The objective of this work was to compare summary measures of live-tree versus historic-timber datasets likely to affect outcomes and inferences of typical paleoenvironmental applications. We used 99 live-tree (LT) and 41 historic-timber (HT) datasets collected in the Appalachian region of the eastern United States and compared common analytical measures for understanding past climate and ecology, including temporal coverage, species composition, recruitment patterns, segment length, series coherence/mean interseries correlation (as Rbar), expressed population signal (EPS), subsample signal strength (SSS) and response to drought and extreme climate events. We found that tree-ring data from historic timbers record some ecological events similarly to live trees and are sensitive to some climate conditions, with important caveats related to the influence of site and tree selection on analytical measures. In some cases, these caveats can be overcome through improved collection of metadata and additional analyses. In all cases, potential differences in LT and HT data should be considered by those who perform large-scale analyses using public tree ring databases, especially as more scientists contribute historic-timber datasets.

Quercus ilex L. dieback is genetically determined: Evidence provided by dendrochronology, δ13C and SSR genotyping

Quercus ilex L. dieback has been reported in several Mediterranean forests, revealing different degree of crown damages even in close sites, as observed in two Q. ilex forest stands in southern Tuscany (IT). In this work, we applied a novel approach combining dendrochronological, tree-ring δ13C and genetic analysis to test the hypothesis that different damage levels observed in a declining (D) and non-declining (ND) Q. ilex stands are connected to population features linked to distinct response to drought. Furthermore, we investigated the impact of two major drought events (2012 and 2017), that occurred in the last fifteen years in central Italy, on Q. ilex growth and intrinsic water use efficiency (WUEi). Overall, Q. ilex showed slightly different ring-width patterns between the two stands, suggesting a lower responsiveness to seasonal climatic variations for trees at D stand, while Q. ilex at ND stand showed changes in the relationship between climatic parameters and growth across time. The strong divergence in δ13C signals between the two stands suggested a more conservative use of water for Q. ilex at ND compared to D stand that may be genetically driven. Q. ilex at ND resulted more resilient to drought compared to trees at D, probably thanks to its safer water strategy. Genotyping analysis based on simple-sequence repeat (SSR) markers revealed the presence of different Q. ilex populations at D and ND stands. Our study shows intraspecific variations in drought response among trees grown in close. In addition, it highlights the potential of combining tree-ring δ13C data with SSR genotyping for the selection of seed-bearing genotypes aimed to preserve Mediterranean holm oak ecosystem and improve its forest management.

Long-term dynamics of the iconic old-forest lichen Usnea longissima in a protected landscape

Long-term data on spatial dynamics of epiphytic lichens associated with old-growth forests are fundamental for understanding how environmental factors drive their extinction and colonization in heterogeneous landscapes. This study focuses on Usnea longissima, a flagship species for biodiversity conservation. By using a long-term data set (37 yr.) of U. longissima in old Picea abies forests in Skuleskogen National Park, Sweden, we examined changes in the number of host trees, population size (sum of thallus length), extinction, colonization, dispersal, and distribution in a protected landscape. We surveyed the lichen in 1984–1985 by applying a line transect inventory and a total population inventory and tagged 355 occupied trees with an aluminium plate buried in the ground. We repeated the survey in 2021 using a metal detector and recorded GPS-position of host trees, tree and lichen population characteristics. We also measured the structure and age (tree-ring data) of the forest to understand how disturbance history influenced lichen populations. Usnea longissima occurred on 66 of the tagged trees and we recorded 141 new host trees. The number of host trees decreased with 41.7% and the population size with 41.9%. One third of the decline was caused by deterministic extinction (treefalls) and two thirds by stochastic extinction on standing trees. The probability of stochastic extinction on live trees decreased with population size in logistic regression. The decline in the sites with largest populations (35–87% loss) was more influenced by limited colonization than extinction. Colonization was highest in humid north-facing hillslopes with multi-layered forests driven by gap dynamics. The lichen was strongly dispersal-limited, with a median effective horizontal dispersal of only 3.8 m in 37 yr., explaining its strong dependence of long continuity of forest cover. The populations were clustered and had substantial local turnover, yet with stable distribution at landscape scale. The tree-ring index, growth releases and gap recruitments indicate extensive harvesting ∼ 1860–1900, but without major disturbances during the last 70–80 yr. Instead, the decline of U. longissima was probably driven by air pollution, climate change (autumn/winter mortality and heatwaves) and denser forests. Our findings highlight that the long-term survival of this lichen may be at risk even in forests having a strong level of protection.

Growth and drought reaction of European hornbeam, European white elm, field maple and wild service tree

Key messageConsidering their drought tolerance and growth characteristics, rare native tree species are well-suited admixed species for the development of climate-stable forests in Central Europe.In our study, we assessed the growth and drought reaction of the four rare native tree species European hornbeam (Carpinus betulus L.), European white elm (Ulmus laevis Pall.), field maple (Acer campestre L.), and wild service tree (Sorbus torminalis (L.) Crantz). Based on tree-ring data, we (I) evaluated their species-specific growth characteristics and variability and examined the influencing site and tree characteristics on annual growth. (II) We quantified their reaction to single drought events, also depending on site and tree variables. (III) We compared our results to oak (Quercus robur L., Quercus petraea (Matt.) Liebl.) and European beech (Fagus sylvatica L.). As they are well-known Central European tree species, there is a broad knowledge about their growth and drought response across wide geographical ranges available. Bringing the results of European beech and oak in relation with the rare native species, it allows to categorise their growth and drought reaction and to contextualise their performance. Our results show, that besides European white elm, the rare species showed an overall lower annual growth with a higher variability than European beech and oak. However, especially field maple and wild service tree were better adapted to drought than European beech and partially even recovered better than oak. Combining the aspects of growth stability and drought tolerance, we conclude that rare native tree species are well suited as admixed species in future forest stands. European hornbeam is a suitable match for European beech on wetter sites, while field maple and wild service tree are a sensible complement for the climate stable oak on drier sites.

A multi-proxy framework to detect insect defoliations in tree rings: a case study on pine processionary

Assessing and reconstructing the impacts of defoliation caused by insect herbivores on tree growth, carbon budget and water use, and differentiating these impacts from other stresses and disturbances such as droughts requires multi-proxy approaches. Here we present a methodological framework to pinpoint the impacts of pine processionary moth (Thaumetopoea pityocampa), a major winter-feeding defoliator, on tree cover (remote-sensing indices), radial growth and wood features (anatomy, density, lignin/carbohydrate ratio of cell walls, δ13C and δ18O of wood cellulose) of drought-prone pine (Pinus nigra) forests in north-eastern Spain. We compared host defoliated (D) and coexisting non-defoliated (ND) pines along with non-host oaks (Quercus faginea) following a strong insect outbreak occurring in 2016 at two climatically contrasting sites (cool-wet Huesca and warm-dry Teruel). Changes in tree-ring width and wood density were analyzed and their responses to climate variables (including a drought index) were compared between D and ND trees. The Normalized Difference Infrared Index showed reductions due to the outbreak of –47.3% and –55.6% in Huesca and Teruel, respectively. The D pines showed: a strong drop in growth (–96.3% on average), a reduction in tracheid lumen diameter (–35.0%) and lower lignin/carbohydrate ratios of tracheid cell-walls. Both pines and oaks showed synchronous growth reductions during dry years. In the wet Huesca site, lower wood δ13C values and a stronger coupling between δ13C and δ18O were observed in D as compared with ND pines. In the dry Teruel site, the minimum wood density of ND pines responded more negatively to spring drought than that of D pines. We argue that multi-proxy assessments that combine several variables have the potential to improve our ability to pinpoint and reconstruct insect outbreaks using tree-ring data.

Tree-ring data reveal trees are suffering from severe drought stress in the humid subtropical forest

The young secondary forests in subtropical regions of China play an important role in the global carbon cycle and China’s ecological and economic security. These values are closely related to tree radial growth (RW), primarily affected by climate changes, especially climate warming. Here, we measured the RW of six common tree species in subtropical China (Cunninghamia lanceolata, Pinus massoniana, Metasequoia glyptostroboides, Liquidambar formosana, Choerospondias axillaris, and Lithocarpus glaber) and quantified how each responded to climate warming. Temperature and moisture were the main climate factors limiting the growth of tree species in the study area. The growth of tree species other than L. formosana and P. massoniana was negatively correlated with temperature and positively correlated with relative humidity. Precipitation in the growing season was negatively correlated with the growth of L. formosana and M. glyptostroboides and positively affected the growth of the other tree species. The radial growth trends of trees growing in similar terrain and climate conditions were similar, but their degree of variation was different. Compared to broad-leaved tree species (L. formosana, C. axillaris, and L. glaber), coniferous tree species (C. lanceolata, P. massoniana, and M. glyptostroboides) were more climate-sensitive, particularly C. lanceolata. Climate warming can potentially extend the growing period and promote the radial growth of the study tree species, but more often leads to drought stress that inhibits radial growth. The long-term drought during 2004–2015 significantly reduced the radial growth of most species, especially conifers which are more vulnerable to drought than broad-leaved trees. Our results highlight that most tree species in the humid subtropical forest in South China are suffering from severe drought stress, which significantly affects forest carbon sequestration. It is probably a good warning for current plantation policy and species selection to better achieving the “Carbon Peaking & Carbon Neutrality” goals of the Chinese government.