The potential for using Larix decidua ring widths in reconstructions of larch budmoth (Zeiraphera diniana) outbreak history: dendrochronological estimates compared with insect surveys

In the Alps, larch (Larix decidua Mill.) forests show periodic discolouration due to larch budmoth (LBM) outbreaks (Zeiraphera diniana Guénée, Lepidoptera: Tortricidae). Tree defoliation causes severe reductions in radial growth, visible in tree rings. This paper aims at reconstructing LBM outbreak history, and critically examining the potential for using dendrochronological data by comparing tree-ring estimates with insect surveys. The occurrence of LBM outbreaks was investigated using 249 cores from larch growing near the timberline in three regions of the French Alps (Briançonnais, Maurienne, and Tarentaise). Years with an abrupt decrease in radial growth (-40%) were considered as negative pointer years reflecting the potential impact of LBM. The comparison with three non-host conifers (Norway spruce, stone and mountain pines) permitted us to distinguish growth reductions in larch due to climatic effects from those due to defoliation by LBM. The dendrochronological data were matched with information reporting conspicuous discolouration in old forestry reports or recovered from systematic field observations. Twenty-two outbreaks are discernible within the period 1800-1983. A peak reduction in larch growth occurred at intervals of 8.86ǃ.01 years in the following years: 1801, 1811, 1820, 1830, 1838, 1846, 1857, 1867, 1875, 1884, 1892, 1901, 1909, 1918, 1926, 1936, 1945, 1953, 1963, 1972, 1980, and 1987. Our objective method based on ring measurements and comparison with non-host trees was compared with qualitative techniques based on the visual detection of conspicuous latewood anomalies. Larch in the Briançonnais (which experiences a continental climate) are infested first, whereas the Tarentaise region exhibits a much weaker impact of LBM. Complete tree recovery was observable 3 years after outbreak peaks.     

The role of larch budmoth (Zeiraphera diniana Gn.) on forest succession in a larch (Larix decidua Mill.) and Swiss stone pine (Pinus cembra L.) stand in the Susa Valley (Piedmont, Italy)

In the Alps, larch (Larix decidua Mill.) is severely affected by larch budmoth (Zeiraphera diniana Guénée) (LBM) attacks. The impact of these outbreaks on the Swiss stone pine (Pinus cembra L.) and on the dynamic processes acting in subalpine forest stands are still not well known. Dendroecological methods were used in this study to reconstruct past LBM outbreaks in Susa Valley, Piedmont, Italy. The analysis was carried out on 62 cores from larch and 101 cores from stone pine. The length and severity of each outbreak was quantified for both species and for each tree by means of the programme OUTBREAK. The frequency of the outbreaks was determined using singular spectral analysis and superposed epoch analysis was used to test the significance of the associations between outbreaks and tree-ring growth. In order to verify if trees belonging to different age classes are differently affected by LBM, the reconstructed outbreaks are then classified taking into account the cambial age of the tree at the moment of the outbreak. From 1760 to 1999, 19 outbreaks were recorded in the larch chronologies, while only three outbreaks in the stone pine chronologies. The larch growth is strongly influenced by LBM and the identified outbreaks are equally distributed in all the three age classes. On the stone pine the sporadic occurrence of the identified events made difficult any interpretation of the eventual effect of LBM. Our results lead us to argue that LBM has not played an important role both in determining the stone pine growth rate and in influencing the present observed succession from the stage dominated by larch, to a stage dominated by stone pine or by a mixed stone pine-larch forest.     

Dendroecological reconstruction and interpretation of larch budmoth (Zeiraphera diniana) outbreaks in two central alpine valleys of Switzerland from 1470 – 1990

 Outbreaks of the larch budmoth (LBM) (Zeiraphera diniana) recur cyclically approximately every 7 to 10 years in subalpine larch-cembran pine and montane to subalpine larch-Norway spruce forests of the relatively dry valleys of the European Alps. By dendroecologically analyzing increment cores from 570 host (European larch –Larix decidua) and non-host trees (cembran pine –Pinus cembra, Norway spruce –Picea abies) through the use of skeleton plots, at least 57 (59) outbreaks could be reconstructed in the optimum Upper Engadine Valley (suboptimum Goms Valley), Switzerland, during the time period 1503 (1472) to 1990. The average interval between initial years of successive outbreaks was 8.58 (8.95) years, SD 1.66 (2.13) years. Over the centuries spatial shifts of LBM activity between the two study areas occurred, probably due to climatic changes. Clear, site-specific differences in LBM attack could only be found in the suboptimum area where high-lying (>1800 m) and/or south-facing stands were infested most. LBM-afflicted trees proved to be unsuitable for climate reconstructions because the impact of the persistently recurring outbreaks on tree growth is dominant. In order to provide sufficient information for a detailed ecological interpretation of the course of an outbreak, latewood widths and/or densities have to be analyzed in addition to the ring-widths. Received: 11 February 1995 / Accepted: 19 July 1996     

Tracing the influence of larch-bud-moth insect outbreaks and weather conditions on larch tree-ring growth in Engadine (Switzerland).

Tree-ring analysis of insect-defoliated trees has so far been used for detecting past insect outbreaks only. We hypothesize that the impact of the larch-bud-moth (LBM) Zeiraphera dinian outbreaks on the growth of larch Larix decidua in the Engadine (Switzerland) is closely coupled to the spatial development of the outbreak and the ecological characteristics of the respective sites and weather conditions. We tested this hypothesis by reviewing data sets available in the literature and by analysing original data. We monitored LBM population densities and the needle phenology, growth and defoliation of larch over 28 years, i.e. over four outbreak cycles. In addition, information on defoliation patterns covering six earlier outbreaks over 50 years was matched with tree-ring information. Tree-ring chronologies of 18 larch stands were analysed with regard to abrupt growth changes and latewood events. Defoliation induces an immediate reduction in latewood, followed by a reduction in needle length and a significant decrease in radial growth in the subsequent year. We have called this tree-ring pattern the "larch-bud-moth syndrome". A careful analysis of the various parameters of the LBM syndrome for two specific population cycles enabled us to define different interaction patterns between weather conditions and tree growth. These can then be included in climate change models to help disentangle the impact of insect defoliation from that of adverse climatic conditions.     

Dendroentomological and forest management implications in the Interior Douglas-fir zone of British Columbia,Canada

Douglas-fir (Pseudotsuga menziesii var. glauca Mirb. Franco) forests in the Interior of British Columbia, Canada, show periodic defoliation due to western spruce budworm (WSB) (Choristoneura occidentalis Freeman) outbreaks. Tree defoliation causes a reduction in radial growth and is therefore visible in tree rings. In this paper, we identify WSB defoliation history, and critically examine the potential for using dendrochronological analysis by comparing tree-ring estimates with insect surveys. WSB defoliation history was investigated using cores from Douglas-fir growing in the Lac du Bois region of the Kamloops Forest District. Years with an abrupt decrease in radial growth were considered as negative pointer years that potentially reflected WSB outbreaks. The comparison with ponderosa pine (Pinus ponderosa Dougl., ex P. & C. Laws.) (a non-host species) permitted differentiation between growth reductions in Douglas-fir due to climatic effects and those due to defoliation by WSB. The dendrochronological data were matched with information reporting visible damage in Forest Insect Disease Survey (FIDS) and British Columbia Ministry of Forest records. Our objective-based method using ring-width measurements from host and non-host chronologies was compared with qualitative techniques based on the software program OUTBREAK. We were able to distinguish seven distinct outbreak events in 300 years of record.     

Consequences of larch budmoth outbreaks on the climatic significance of ring width and stable isotopes of larch

Tree-ring widths and stable carbon and oxygen isotopes of five European larch trees from Lötschental, Switzerland were investigated for the period 1900–2004. The objective was to test the suitability of each of these parameters for high-frequency climate reconstructions. This is of special interest with regard to the problem of cyclic larch budmoth (LBM) infestations of alpine larch trees. The results clearly demonstrate that tree-ring width chronologies are not suitable for high-frequency reconstructions because infestations lead to variably reduced tree-ring increments, largely suppressing climate signals. On the other hand, the stable isotope chronologies proved less affected by larch budmoth outbreaks, independent of the strength of the infestations. The correlation of the carbon isotopes with summer temperatures was especially high (r = 0.73) and with precipitation lower but nevertheless significant (r = ?0.43). Oxygen isotopes were also correlated with summer temperature (r = 0.46); however, a certain perturbation of normal oxygen isotope signatures due to LBM outbreaks was evident. Contrary to tree-ring widths, none of the LBM outbreaks caused a significant disturbance of the current year’s isotopic climate signal and, most importantly, there were no delayed effects in the following years. Thus, stable carbon isotopes in tree-ring chronologies of the European larch provide an excellent opportunity for high-frequency temperature reconstructions.     

Dendroentomological and forest management implications in the Interior Douglas-fir zone of British Columbia, Canada

Douglas-fir (Pseudotsuga menziesii var. glauca Mirb. Franco) forests in the Interior of British Columbia, Canada, show periodic defoliation due to western spruce budworm (WSB) (Choristoneura occidentalis Freeman) outbreaks. Tree defoliation causes a reduction in radial growth and is therefore visible in tree rings. In this paper, we identify WSB defoliation history, and critically examine the potential for using dendrochronological analysis by comparing tree-ring estimates with insect surveys. WSB defoliation history was investigated using cores from Douglas-fir growing in the Lac du Bois region of the Kamloops Forest District. Years with an abrupt decrease in radial growth were considered as negative pointer years that potentially reflected WSB outbreaks. The comparison with ponderosa pine (Pinus ponderosa Dougl., ex P. & C. Laws.) (a non-host species) permitted differentiation between growth reductions in Douglas-fir due to climatic effects and those due to defoliation by WSB. The dendrochronological data were matched with information reporting visible damage in Forest Insect Disease Survey (FIDS) and British Columbia Ministry of Forest records. Our objective-based method using ring-width measurements from host and non-host chronologies was compared with qualitative techniques based on the software program OUTBREAK. We were able to distinguish seven distinct outbreak events in 300 years of record.     

Effects of host abundance on larch budmoth outbreaks in the European Alps

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Tree-ring analysis of larch sawfly (Pristiphora erichsonii (Hartig)) defoliation events and hydrological growth suppression in a peatland

Insect defoliation events are a major forest disturbance in the boreal forest in Canada. Reconstructing previous events are crucial to understanding natural factors that lead to insect defoliation periods, improving our ability to predict future infestations and increasing the reliability of forest management plans and pest control programs. Researchers have often been limited in their ability to draw accurate conclusions regarding the history of larch sawfly (Pristiphora erichsonii (Hartig)) infestation events in North America. It is well known that floods can affect survival of larch sawfly populations, as well as suppress radial growth of eastern larch (Larix laricina (Du Roi) K. Koch) trees. Eastern larch often inhabits peatlands where high water-table levels can lead to a decrease in tree-ring widths. Water-table level increases result in similar radial-growth patterns to when trees are defoliated by larch sawfly, making accurate diagnoses of larch sawfly events a challenge. This fact becomes more accentuated when non-host species used for standard dendroecological analyses (often black spruce (Picea mariana (Mill.) Britton) present an opposite relationship to water-table variability, enhancing chances of drawing erroneous conclusions when using program OUTBREAK.This paper introduces a novel case study to advance the understanding of the complex landscapes where these larch sawfly events are taking place. It stresses the necessity of using upland sites less influenced by the hydrological regime to accurately reconstruct larch sawfly defoliation events. We found that where investigations are taking place solely in peatlands or lowlands, and where they are heavily influenced by hydrological conditions, the use of other lines of evidence such as pale rings and long-term hydrological records are crucial to understand the dynamics in the system. In our case study, program OUTBREAK identified five defoliation events in a peatland and upland site; however, hydrological data and pale ring evidence indicated that the last event identified in the peatland site by the host/non-host analysis was confounded by hydrological growth suppression.     

Does Soil Organic Layer Thickness Affect Climate–Growth Relationships in the Black Spruce Boreal Ecosystem?

The observed long-term decrease in the regional fire activity of Eastern Canada results in excessive accumulation of organic layer on the forest floor of coniferous forests, which may affect climate–growth relationships in canopy trees. To test this hypothesis, we related tree-ring chronologies of black spruce (Picea mariana (Mill.) B.S.P.) to soil organic layer (SOL) depth at the stand scale in the lowland forests of Quebec’s Clay Belt. Late-winter and early-spring temperatures and temperature at the end of the previous year’s growing season were the major monthly level environmental controls of spruce growth. The effect of SOL on climate–growth relationships was moderate and reversed the association between tree growth and summer aridity from a negative to a positive relationship: trees growing on thin organic layers were thus negatively affected by drought, whereas it was the opposite for sites with deep (>20–30 cm) organic layers. This indicates the development of wetter conditions on sites with thicker SOL. Deep SOL were also associated with an increased frequency of negative growth anomalies (pointer years) in tree-ring chronologies. Our results emphasize the presence of nonlinear growth responses to SOL accumulation, suggesting 20–30 cm as a provisional threshold with respect to the effects of SOL on the climate–growth relationship. Given the current climatic conditions characterized by generally low-fire activity and a trend toward accumulation of SOL, the importance of SOL effects in the black spruce ecosystem is expected to increase in the future.     

Return of the moth: rethinking the effect of climate on insect outbreaks

The sudden interruption of recurring larch budmoth (LBM; Zeiraphera diniana or griseana Gn.) outbreaks across the European Alps after 1982 was surprising, because populations had regularly oscillated every 8–9 years for the past 1200 years or more. Although ecophysiological evidence was limited and underlying processes remained uncertain, climate change has been indicated as a possible driver of this disruption. An unexpected, recent return of LBM population peaks in 2017 and 2018 provides insight into this insect’s climate sensitivity. Here, we combine meteorological and dendrochronological data to explore the influence of temperature variation and atmospheric circulation on cyclic LBM outbreaks since the early 1950s. Anomalous cold European winters, associated with a persistent negative phase of the North Atlantic Oscillation, coincide with four consecutive epidemics between 1953 and 1982, and any of three warming-induced mechanisms could explain the system’s failure thereafter: (1) high egg mortality, (2) asynchrony between egg hatch and foliage growth, and (3) upward shifts of outbreak epicentres. In demonstrating that LBM populations continued to oscillate every 8–9 years at sub-outbreak levels, this study emphasizes the relevance of winter temperatures on trophic interactions between insects and their host trees, as well as the importance of separating natural from anthropogenic climate forcing on population behaviour.     

Temporal instability in tree-growth/climate response in the Lower Bavarian Forest region: implications for dendroclimatic reconstruction

This paper explores the temporal stability of growth/climate relationships in ring-width chronologies of Norway spruce [ Picea abies (L.) Karst] and silver fir ( Abies alba Mill) in the Lower Bavarian Forest region in southern Germany. These chronologies were compiled, using both historic and living tree-ring data, with the main aim of developing a dendroclimatic reconstruction for the region covering the last 500 years. Moving window correlation analysis shows that prior to the twentieth century, both species co-vary in a similar way (1480–1899 mean r =0.66). There is no significant correlation between the species chronologies since ca. 1930, which partly reflects anomalous growth trends in the fir chronology since ca. 1960. Multiple regression analysis was utilised to assess the ability of both species chronologies to model March–August precipitation. The precipitation signal of the spruce data was found to be both stronger than the fir data (1872–1930 calibration: r ²=0.45 vs 0.25) and more time stable. After ca. 1930, the fir chronology loses it ability to model March–August precipitation until there is no climate signal at all in the fir data in recent decades. The spruce data also express a later weakening in their climate signal in the mid 1970s. We present compelling evidence indicating that the anomalous trends observed in the fir data, since the mid 1960s, appear to be predominantly related to local SO₂ emissions from power plants and refineries. It is also likely that this local anthropogenic forcing is the cause of the weakening of the climate signal in the spruce data since the mid 1970s. The conclusions from this study are: (1) The fir tree-ring data cannot be used for traditional dendroclimatic calibration, although prior to the twentieth century the decadal variability in the fir data is very similar to spruce and so these data could be used to extend potential reconstructions in the future; (2) The recent decline and recovery event in the fir data appears to be unique to the twentieth century and is not part of a natural episodic phenomenon; (3) Traditional dendroclimatic calibration of March–August precipitation will be made using solely the spruce ring-width data. However, due to SO₂ forcing in recent decades, the calibration period will be shortened to the 1871–1978 period.     

1200 years of regular outbreaks in alpine insects

The long-term history of Zeiraphera diniana Gn. (the larch budmoth, LBM) outbreaks was reconstructed from tree rings of host subalpine larch in the European Alps. This record was derived from 47513 maximum latewood density measurements, and highlights the impact of contemporary climate change on ecological disturbance regimes. With over 1000 generations represented, this is the longest annually resolved record of herbivore population dynamics, and our analysis demonstrates that remarkably regular LBM fluctuations persisted over the past 1173 years with population peaks averaging every 9.3 years. These regular abundance oscillations recurred until 1981, with the absence of peak events during recent decades. Comparison with an annually resolved, millennium-long temperature reconstruction representative for the European Alps (r=0.72, correlation with instrumental data) demonstrates that regular insect population cycles continued despite major climatic changes related to warming during medieval times and cooling during the Little Ice Age. The late twentieth century absence of LBM outbreaks, however, corresponds to a period of regional warmth that is exceptional with respect to the last 1000+ years, suggesting vulnerability of an otherwise stable ecological system in a warming environment.     

Tree-ring growth of Gmelin larch under contrasting local conditions in the north of Central Siberia

While the forest-tundra zone in Siberia, Russia has been dendroclimatologically well-studied in recent decades, much less emphasis has been given to a wide belt of northern taiga larch forests located to the south. In this study, climate and local site conditions are explored to trace their influence on radial growth of Gmelin larch (Larix gmelinii (Rupr.) Rupr.) trees developed on permafrost soils in the northern taiga. Three dendrochronological sites characterized by great differences in thermo-hydrological regime of soils were established along a short (ca. 100 m long) transect: on a river bank (RB), at riparian zone of a stream (RZ) and on a terrace (TER). Comparative analysis of the rate and year-to-year dynamics of tree radial growth among sites revealed considerable difference in both raw and standardized tree-ring width (TRW) chronologies obtained for the RZ site, characterized by shallow soil active layer depth and saturated soils. Results of dendroclimatic analysis indicated that tree-ring growth at all the sites is mostly defined by climatic conditions of a previous year and precipitation has stronger effect on TRW chronologies in comparison to the air temperatures. Remarkably, a great difference in the climatic response of TRW chronologies has been obtained for trees growing within a very short distance from each other. The positive relation of tree-ring growth with precipitation, and negative to temperature was observed in the dry site RB. In contrary, precipitation negatively and temperature positively influenced tree radial growth of larch at the water saturated RZ. Thus, a complicate response of northern Siberian larch forest productivity to the possible climate changes is expected due to great mosaic of site conditions and variability of environmental factors controlling tree-ring growth at different sites. Our study demonstrates the new possibilities for the future dendroclimatic research in the region, as various climatic parameters can be reconstructed from tree-ring chronologies obtained for different sites.     

Combining tree-ring analyses on stems and coarse roots to study the growth dynamics of forest trees: a case study on Norway spruce (Picea abies [L.] H. Karst)

We show the potential of a new method combining tree-ring analyses on stems and on coarse roots of individual trees in order to advance the understanding of growth dynamics in forest trees. To this end, we studied the root–shoot allometry of trees and its dependence on site conditions. Along a gradient in water supply in Southern Germany from dry to moist sites we selected 43 Norway spruce trees (Picea abies [L.] H. Karst.) aged 65–100 years. Increment cores were taken from stem and main roots revealing aboveground and belowground growth course over the last 34 years. Annual growth rates in roots and stems and their allometric relationships were applied as surrogate variables for tree resource allocation to aboveground and belowground organs. The mean sensitivities of both stem and root chronologies were found to be site-specific, and increased from the moist through the dry sites. No temporal offset between aboveground and belowground growth reactions to climate conditions was found in Norway spruce at any of the sites. These results suggest that the root–shoot allometry depends on the specific site conditions only at the driest site, following the optimal biomass partitioning theory (the more restricted the water supply, the more organic matter allocation into the belowground organs).     

Temperature reconstruction in the Ob River valley based on ring widths of three coniferous tree species

Tree core samples of larch (Larix sibirica Ledeb.), spruce (Picea obovata Ledeb.) and pine (Pinus sibirica Du-Tour.) from the northern taiga of West Siberia were collected to assess their potential for summer temperature reconstructions in the Ob River region. Bootstrapped response functions showed that annual growth was mainly influenced by May to June temperatures in pine and by June to July temperatures in spruce and larch. Spruce and pine chronologies showed high positive correlations with previous October temperature. June–July temperatures were reconstructed based on spruce (1795–1996) and larch (1615–1999) tree ring chronologies. The pine chronology could not be used for a reliable temperature reconstruction, due to low values of explained May–June temperature variance (11–15%) but the species has a high potential to help clarify the May–June and October climatic influence on ring width observed in all three species. We explained the effect of the early vegetation period (May–July) and the differences in the temperature signals between spruce and larch tree ring chronologies with the influence of previous September and October temperature on tree growth with the warming effect of the Ob River and differences of the species’ photosynthetic possibilities and the activity of chloroplasts and bud meristem tissues.     

Variability of climate–growth relationships along an elevation gradient in the Changbai Mountain, northeastern China

In order to explore climate–growth relationships at different elevations, tree-ring width chronologies of larch (Larix olgensis) were developed from three sampling sites on the northern slope of the Changbai Mountain, northeastern China. There were no consistent trends in statistical characteristics of the tree-ring chronologies along the elevation gradient, since trees in the forest interior had a complacent growth pattern. Monthly mean temperature and monthly total precipitation were used for the analysis. Correlation analysis indicated that temperatures in winter had negative correlations with tree growth (previous November, December and current March for the low-, mid- and high-elevation sites, respectively). The correlations between tree growth and June temperature varied from weakly negative at low elevations to significantly positive at high elevations. Precipitation in June of the growth year had negative relationship with the high-elevation chronology. However, high precipitation was associated with low temperature in early growing season, further supporting that temperature is a growth-limiting factor at high elevations. Our results suggest that along the elevation gradient, L. olgensis may respond in different ways to local climate change.     

The climate sensitivity of Norway spruce [Picea abies (L.) Karst.] in the southeastern European Alps

To investigate the potential of Norway spruce (Picea abies L. Karst) as a palaeoclimate archive in the southeastern European Alps, tree ring chronologies were developed from trees growing at two sites in Slovenia which differed in their ecological and climatological characteristics. Ring width, maximum latewood density, annual height increment and latewood cellulose carbon isotope composition were determined at both sites and the resulting time-series compared with and verified against instrumental climate data for their common period (AD 1960–AD 2002). Results indicate that ring width sensitivity to summer temperature is very site-dependent, with opposing responses at alpine and lowland sites. Maximum density responds to September temperatures, indicating lignification after cell division has ceased. Stable carbon isotopes have most potential, responding strongly to summer temperature in both alpine and lowland stands. Height increment appears relatively insensitive to climate, and is likely to be dominated by local stand dynamics.     

Analysis and modelling of tree succession on a recent rockslide deposit

Dendroecological methods were combined with vegetation and soil mapping to study recolonisation of European larch (Larix decidua), silver birch (Betula pendula) and Norway spruce (Picea abies) on a recently formed rockslide cone (deposit of 30 × 10⁶ m³) in the Valais Alps (Switzerland). Tree density and tree height were predicted with regression models that we derived using an information-theoretic model selection approach. Results demonstrate that the deposits of the 1991 rockslide have been colonised relatively rapidly with larch (ecesis time 2 years), birch (5 years) and spruce (2 years). Most of the colonisation occurred 5–11 years following the rockslide. Clast size was the primary factor driving tree colonisation with the highest tree densities found on plots with mainly smaller (<30 cm) clast sizes. Tree height was affected by a combination of different influences, with tree age and tree density showing the most obvious effects. This study demonstrates how dendroecological methods allow reconstruction of spatio-temporal patterns of tree succession on rockslides, which may ultimately facilitate a more accurate dating of similar landforms of unknown age.     

Testing for tree-ring divergence in the European Alps

Evidence for reduced sensitivity of tree growth to temperature has been reported from multiple forests along the high northern latitudes. This alleged circumpolar phenomenon described the apparent inability of temperature-sensitive tree-ring width and density chronologies to parallel increasing instrumental temperature measurements since the mid-20th century. In addition to such low-frequency trend offset, the inability of formerly temperature-sensitive tree growth to reflect high-frequency temperature signals in a warming world is indicated at some boreal sites, mainly in Alaska, the Yukon and Siberia. Here, we refer to both of these findings as the ‘divergence problem’ (DP), with their causes and scale being debated. If DP is widespread and the result of climatic forcing, the overall reliability of tree-ring-based temperature reconstructions should be questioned. Testing for DP benefits from well-replicated tree-ring and instrumental data spanning from the 19th to the 21st century. Here, we present a network of 124 larch and spruce sites across the European Alpine arc. Tree-ring width chronologies from 40 larch and 24 spruce sites were selected based on their correlation with early (1864–1933) instrumental temperatures to assess their ability of tracking recent (1934–2003) temperature variations. After the tree-ring series of both species were detrended in a manner that allows low-frequency variations to be preserved and scaled against summer temperatures, no unusual late 20th century DP is found. Independent tree-ring width and density evidence for unprecedented late 20th century temperatures with respect to the past millennium further reinforces our results.