Rows Of Traumatic Resin Ducts Research Articles

Assessment of the Annual Erosion Rate along Three Hiking Trails in the Făgăraș Mountains, Romanian Carpathians, Using Dendrogeomorphological Approaches of Exposed Roots

Mountain hiking trails are vital components of tourist infrastructure and provide recreational opportunities for a large number of tourists. Exposed roots along the tourist trails in the forested mountains are impacted by tourist trampling and various natural processes, thus becoming even more exposed and eroded. The aim of our study was to estimate the annual erosion rates along three hiking trails in the Făgăraș Mountains using dendrogeomorphological approaches. The three used routes were: Bâlea Hotel—Bâlea Waterfall (BWFHT), Bâlea Hotel—Bâlea Glacial Lake (BLHT), and Bâlea Hotel—Doamnei Glacial Valley (DVHT). The average annual erosion rates in BWFHT, BLHT, and DVHT were 10.6 ± 4.4, 6.8 ± 3.9, and 6.1 ± 3.3 mm·y−1, respectively. Over a 56-year interval (1965–2021), 610 scars were recorded among the annual growth rings of the sampled tree roots; 172, 213, and 225 scars were recorded in BWFHT, BLHT, and DVHT, respectively. Moreover, we identified 1022 rows of traumatic resin ducts (TRDs) associated with scars: 237, 343, and 442 in BWFHT, BLHT, and DVHT, respectively. Additionally, the climate of the Făgăraș Mountains is humid with a multiannual average precipitation of 1366.2 mm; the precipitation in 24 h, between 1979 and 2021 in seven and three cases exceeded 70 mm/24 h and 100 mm/24 h, respectively. Thus, there were synchronous situations of root exposure with 24 h rainfall. However, it is unclear whether precipitation plays a decisive role in root exposure or in triggering erosion processes on tourist trails. We considered that tourist traffic plays a decisive role in root exposure and erosion, however locally and complementarily, 24 h precipitation must also be considered.

Tree ring archives of debris flow contamination in a post-mined area: Combined dendroecological research

The degradation of forest ecosystems represents a severe environmental issue in anthropogenically modified landscapes worldwide. We demonstrated the negative impact of contaminated debris flow deposits on riparian forest in the Romanian Carpathians through the innovative combination of several dendroecological approaches. Reconstruction of debris flow activity using 95 individuals of Picea abies (L.) Karst. was performed to identify 11 events during the period 1952–2018. Recent events (e.g., 2007, 2014, 2016–2017) filled the valley floor after the stream was dammed in the 1980s, which deteriorated tree growth. This state was worsened by site acidity (pH = 3.8), low organic carbon, high sulfur content, and high concentrations of several metals in debris flow deposits. Wood anatomical analyses confirmed that trees producing tangential rows of traumatic resin ducts as a possible response to burial by toxic debris material subsequently produced smaller and flatter earlywood tracheids. In particular, the most obvious changes (average decrease in tracheid lumen area by 62.9% over two years) occurred after the 2016 debris flow event. Using inductively coupled plasma optical emission and/or mass spectrometry, we identified peak or increased concentrations of thallium (max. 0.7 mg kg−1), caesium (max. 0.4 mg kg−1), and aluminium (max. 434 mg kg−1) in tree biomass that could be related to debris flow activity in 1996, 2007, and 2016. Regarding the individual-specific responses of sampled trees, we conclude that the forest decline is caused by complex interaction between the depth of tree burial by debris flow deposits, the mechanical weight and chemistry of deposits, and the rate of nutrient and toxic element uptake.

Traumatic Resin Ducts in Alaska Mountain Hemlock Trees Provide a New Proxy for Winter Storminess

AbstractWinter is a critical season for land‐surface feedbacks and ecosystem processes; however, most high‐latitude paleo‐environmental reconstructions are blind to cold season conditions. Here we introduce a winter‐sensitive, paleo‐proxy record that is based on the relative frequency of tangential rows of traumatic resin ducts (TRDs) in the annual growth rings of mountain hemlocks (Tsuga mertensiana) growing near treeline in Southeast Alaska. Hemlocks produce a row of TRDs in the earlywood portion of their annual rings in response to cambial damage incurred during winter. Multidecadal bouts of TRD production were followed by growth‐leader replacement, reaction wood formation, and divergence in radial growth between storm‐damaged trees and less exposed mountain hemlock forests. These patterns are consistent with TRDs being a response to tree damage caused by ice and snowstorms, a conclusion supported by the krummholz tree architecture at these sites. This relationship is further corroborated by significant correlations between our TRD record and the strength of the wintertime Aleutian Low (AL) pressure system that is linked to tree‐damaging agents like wind, precipitation, and ice storm strength in Southeast Alaska. The combined TRD/krummholz architecture record indicates that abrupt shifts between strong and weak AL phases occurred every several decades since CE 1700 and that the 1800s had relatively long AL phases with heavy snowpacks. In addition to describing the magnitude and tempo of wintertime climate change in Northwestern North America, these results suggest that North Pacific Decadal Variability underlies the long‐term dynamics of treeline ecosystems along the northeast Pacific coast.

Assessment of the recurrence intervals of rockfall through dendrogeomorphology and counting scar approach: A comparative study in a mixed forest stand from the Vercors massif (French Alps)

As direct observations of rockfalls are rare and difficult to obtain over long timescales, stem injuries and their dating with dendrogeomorphic techniques have been applied frequently in the past to reconstruct process activity. However, the analysis of tree-ring samples requires considerable temporal efforts, which can be detrimental in applied research and expert opinions. To compensate for this shortcoming, several studies have lately explored the potential of the counting of visible scars as an alternative method to dendrogeomorphology as it requires much less time and human efforts to reconstruct spatial patterns of rockfall activity. Yet, to date, both approaches have not been compared at the same site. In this paper, based on the extensive analysis of 278 conifer and broadleaved trees (from which 1097 tree-ring cores were extracted) from a mixed forest plot of the Vercors Massif (French Alps), we demonstrate that both methods provide similar spatial patterns of rockfall activity with a strong increase of recurrence intervals down the talus slope and a clear lateral zonation of activity. Despite this apparent convergence between both approaches, our study also evidences that rockfall frequencies strongly differ with tree species and diameter: the visual inspection of conifer stems and the analysis of tree-ring signals in large-diameter broadleaved trees typically lead to an overestimation of recurrence intervals. Based on these findings, we recommend giving priority to the scar-counting approach on small diameter (<15 cm) broadleaved stems and to restrict tree-ring analysis to old conifers that are more susceptible – through the identification of tangential rows of traumatic resin ducts – to provide reliable estimations of long recurrence intervals (as generally observed in the lower portions of the slope). These guidelines should help to improve the reliability of recurrence interval maps of rockfall process activity in forests further, but also to improve cost-benefit ratios of future studies.

Multitrophic interactions in a geothermal setting: Arthropod borings, actinomycetes, fungi and fungal-like microorganisms in a decomposing conifer wood from the Jurassic of Patagonia

A permineralized araucarioid conifer stem, preserved in state of partial decay, is described from the Middle to Late Jurassic Chon-Aike Formation (Bahía Laura Group) at Laguna Flecha Negra, in the Deseado Massif, Santa Cruz Province, Argentina. The tree-stem, which comprises periderm to the secondary xylem, shows evidence of interactions with xylophagous borers, fungi, actinomycetes and other fungal-like microorganisms. In the secondary phloem, it displays rows of traumatic resin ducts, which host abundant mycelium comprising very thin hyphae differentiated into spore-producing structures comparable to actinomycete bacteria and spherical fungal-like resting structures. In the cortical and phloem regions, there are cell groups with structural changes, which appear variably degraded by fungi. The secondary xylem displays decay of cellulose and lignified components, at various spatial scales, comparable with fungal decay patterns in modern wood. Further septate fungal filaments, sometimes bearing clamp connections are associated with decayed regions. The degraded secondary xylem shows circular to oval borings filled with frass containing degraded tracheids, comparable to those bored by different wood boring beetles. Development of traumatic resin ducts in the phloem could have been triggered by penetration of the living stem by these xylophagous arthropods. The association of the different components present suggests pathogenic and saprotrophic interactions promoting decomposition of the stem, and represents a rarely-documented example of multitrophic biological interactions involving several different biological groups in Jurassic terrestrial paleoecosystems.

Disentangling the impacts of exogenous disturbances on forest stands to assess multi-centennial tree-ring reconstructions of avalanche activity in the upper Goms Valley (Canton of Valais, Switzerland)

Abstract The purpose of dendrogeomorphic analyses is to amplify the signal related to the geomorphic process under investigation, and to minimize the noise induced by other signals in the tree-ring series. Yet, to date, no study accounts specifically for interferences induced by climate conditions or exogenous disturbances and which can, potentially, affect the quality of tree-ring based process reconstructions. In this paper, we develop a specific procedure allowing evaluation of the quality of reconstructions in five avalanche paths at Oberwald (Swiss Alps). The study is based on possible interferences between snow avalanches, climatic conditions and ecological signals in the tree-ring series. Analysis of past events was based on tree-ring series from 564 heavily affected, multi-centennial European larch trees ( Larix decidua Mill.) growing near or next to the avalanche paths. A total of 2389 growth disturbances, such as scars, tangential rows of traumatic resin ducts, compression wood as well as abrupt growth suppressions or releases, were identified in the samples, indicating 43 destructive snow avalanches since AD 1780. At the same time, 31 potential events, which were detected with the conventional Shroder index value, were rejected from the final reconstruction due to potentially strong interferences between the different signals. This high rejection rate underlines the necessity to systematically–and carefully–discriminate ecological and climatic noise from avalanche-related disturbances. This discrimination is even more so crucial as a significant proportion of dendrogeomorphic studies in the Alps are based on L. decidua trees which are cyclically affected by larch budmoth outbreaks.

Age-dependent sensitivity of trees disturbed by debris flows – Implications for dendrogeomorphic reconstructions

Abstract Dating of geomorphic events using dendrogeomorphic methods has increased rapidly during the last years to provide a systematic overview on event frequencies, spatial reach and magnitudes. Despite the recent advances in methodology, multiple questions remain when it comes to the age-dependent sensitivity of trees which may further influence the quality of dating. Yet, the impacts of ageing effects on dendrogeomorphic reconstructions have not been assessed in detail so far. This study clearly shows the evolution of numbers, types, and intensities of growth disturbances (GDs) across the lifespan of three different tree species ( Larix decidua Mill., Picea abies (L.) Karst., and Pinus sylvestris L.) affected by debris flows in the European Alps. Based on the re-analyses of datasets from past dendrogeomorphic reconstructions and calculation of statistical tests we investigated decreased ability of all studied tree species to record the debris-flow impact with increasing age. The great abundance of GDs occurred between 31 and 60 year of a tree life. By contrast, below-average number of GDs started around the 10th decade. L. decidua and P. abies show almost twofold number of GD per tree and decade compared to P. sylvestris . Injuries and compression wood are the most frequent GDs at rather young ages of L. decidua and P. abies specimens while tangential rows of traumatic resin ducts and abrupt growth increases are much more scattered. The most balanced distribution of GD is obvious across the lifespan of P.sylvestris . Unequivocal signals (GD of intensity reactions: 5, 4, and 3) of all tree species occur at significantly younger ages than uncertain signals of debris flow impacts (GD of intensity reactions: 2, 1, and 0). Based on the findings of this study and with the aim of improving detection of debris flows we proposed options of sampling strategy and laboratory steps (namely identification of an event) for forest stands with different age structure. Whereas the study sites across the world may not provide the “ideal” age composition of forests due to, for instance, forest management interventions or presence of high-magnitude disasters, the list of recommendations provided here seems to be a good alternative when the conditions are somewhat limited.

The changing ability of Norway spruce (P. abies) to record hydro-geomorphic processes based on the age and diameter of the tree stem – A dendrogeomorphic approach

Dendrogeomorphic reconstructions of debris flows and related hydro-geomorphic processes (i.e. debris floods and flash floods) are widely used in territories with incomplete chronologies and potential future hazards. In recent years, the tree-ring analysis of disturbed trees affected by dangerous geomorphic processes has developed into a discipline with sophisticated methodical approaches and with annual up to monthly accuracy of dating. Field sampling strategies are based on various ranges of sample depth (i.e., different amounts of sampled trees of different age structures). The age and diameter of trees influence the ability of trees to respond to geomorphic processes; therefore, we investigate age-dependent and diameter-dependent tree sensitivity. Our study, for the first time, addresses the sensitivity to hydro-geomorphic processes in detail. We tested 462 individuals of Norway spruce (Picea abies (L.) Karst.) – a very common species used in the dendrogeomorphic reconstructions – in the apical part of the medium-high-mountains where there is widespread occurrence of debris flows and debris floods. The tree sensitivity analysis was performed based on the position of growth disturbances within the increment cores of trees (original age and original diameter of the tree before the tree was affected). P. abies shows very high tree sensitivity in the first two decades of the tree lifespan. With increasing age and diameter, trees are less sensitive recorders of debris flows/floods. Moreover, the intensity of growth disturbances significantly decreases with tree age. Mature trees (51–120years) record the geomorphic events mainly through abrupt growth changes (suppression and release) and tangential rows of traumatic resin ducts. In contrast, scars, the onset of reaction wood and traumatic resin ducts are dominant growth disturbances in young, thin trees (11–30years; diameter 0–15cm). Different occurrences of particular growth disturbances as well as the different age- and diameter-dependent sensitivities emphasize the need for the inclusion of new variable that will take into account the amount of sensitive trees for each year. After that, adequate mixture of sampled tree (i.e. mixture of age classes), which is necessary for the completeness of debris flow/flood chronologies, could be balanced regarding their sensitivity.

Reconstruction of glacial lake outburst floods in northern Tien Shan: Implications for hazard assessment

Glacier lake outburst floods (GLOFs) and related debris flows are among the most significant natural threats in the Tien Shan Mountains of Kyrgyzstan and have even caused the loss of life and damage to infrastructure in its capital Bishkek. An improved understanding of the occurrence of this process is essential so as to be able to design reliable disaster risk reduction strategies, even more so in view of ongoing climate change and scenarios of future evolutions. Here, we apply a dendrogeomorphic approach to reconstruct past debris-flow activity on the Aksay cone (Ala-Archa valley, Kyrgyz range), where outbursting glacier lakes and intense rainfalls have triggered huge debris flows over the past decades.A total of 96 Picea abies (L.) Karst. trees growing on the cone and along the main channel have been selected based on the evidence of past debris-flow damage in their trunks; these trees were then sampled using increment borers. The dating of past events was based on the assessment of growth disturbances (GD) in the tree-ring records and included the detection of injuries, tangential rows of traumatic resin ducts, reaction wood, and abrupt growth changes. In total, 320 GD were identified in the tree-ring samples. In combination with aerial imagery and geomorphic recognition in the field, reactions in trees and their position on the cone have allowed reconstruction of the main spatial patterns of past events on the Aksay cone.Our findings suggest that at least 27 debris flows have occurred on the site between 1877 and 2015 and point to the occurrence of at least 17 events that were not documented prior to this study. We also observe high process activity during the 1950s and 1960s, with major events on the cone in 1950, 1966, and 1968, coinciding with phases of slight glacier advance. The spatial analyses of events also point to two different spatial patterns, suggesting that quite dissimilar magnitudes probably occurred during glacier lake outburst floods and rainfall-induced debris-flow events. The results presented here represent the longest, annually resolved GLOF series in the region, which in turn has key implications on risk assessment, not just in the Ala-Archa valley, but also in the entire Kyrgyz range (northern Tien Shan).

Testing dendrogeomorphic approaches and thresholds to reconstruct snow avalanche activity in the Făgăraş Mountains (Romanian Carpathians)

Snow avalanches are a widespread natural phenomenon in steep mountain environments, where they modulate landscapes and frequently disturb forest stands. Such disturbances in trees have been used since the 1970s to retrospectively date avalanches, study their extent and reach, as well as to document their triggers. Although virtually every dendrogeomorphic paper is still based on the concepts established by Shroder (1978), important methodological improvements have been achieved in the field ever since and more particularly over the last decade. This study therefore reports on recent methodological progress and employs three different approaches (i.e. Shroder index value and Kogelnig-Mayer weighted index value) and different sets of signals in trees (i.e. inclusion of tangential rows of traumatic resin ducts as evidence of past avalanching) to record snow avalanche activity. Using 238 increment cores from 105 Picea abies (L.) Karst trees which colonize a snow avalanche path in the Romanian Carpathians, we illustrate possibilities and limitations of the different approaches for the period covered by the chronologies (1852–2013). In addition, we sampled 30 undisturbed P. abies trees from a forest stand north of the avalanche path, where no geomorphic disturbance was identified, so as to build a reference tree-ring chronology. The three avalanche chronologies constructed with the disturbed trees allow identification of past process activity, but results differ quite considerably in terms of avalanche frequency, number of reconstructed events and their temporal distribution. Depending on the approach used, 15 to 20 snow avalanches can be reconstructed, with the best results being obtained in the dataset including tangential rows of traumatic resin ducts. The addition of this anatomical feature, formed after mechanical impact enlarges the number of growth disturbances by 43.5%, and can thus explain the increase of reconstructed avalanches by one-third as compared to the results of the chronology using the “conventional” Shroder approach.

Effects of open‐cast sulphur mining on sediment transfers and toxification of riparian forests

The spoil heaps of the sulphur mines of the egoiul omânesc volcanic cone are intensely reworked by mass movement processes which not only lead to severe sedimentation in downstream rivers, but also to the toxification of riparian orway spruce (icea abies (.) arst.) forests. Along the lateral borders of the Dumitrelul retention basin, recent sedimentation has covered . abies trees with up to 160 cm of toxic, sulphur‐rich material originating from the spoil heaps deposits. This study documents the deposition of toxic sediments and illustrates the effects that these sulphur‐rich sediments have on tree growth. The results show that trees affected by sedimentation reacted with severe growth suppression and the formation of tangential rows of traumatic resin ducts, and that the intensity and persistence of growth anomalies in trees are positively correlated with local depths and granulometry of sediments.

Resin duct size and density as ecophysiological traits in fire scars of Pseudotsuga menziesii and Larix occidentalis.

Resin ducts (RDs) are features present in most conifer species as defence structures against pests and pathogens; however, little is known about RD expression in trees following fire injury. This study investigates changes in RD size and density in fire scars of Douglas fir (Pseudotsuga menziesii) and western larch (Larix occidentalis) as a means to evaluate the ecophysiological significance of traumatic resinosis for tree defence and survival. Transverse and tangential microsections were prepared for light microscopy and image analysis in order to analyse axial and radial RDs, respectively. Epithelial cells of RDs and fusiform rays associated with radial RDs were also examined. RDs were compared between normal xylem and wound xylem at four different section heights along the fire-injured stem. Following fire injury, P. menziesii axial RDs narrowed by 38-43 % in the first year after injury, and the magnitude of this change increased with stem height. Larix occidentalis axial RDs widened by 46-50 % in the second year after injury. Radial RDs were of equivalent size in P. menziesii, but widened by 162-214 % in L. occidentalis. Fusiform rays were larger following fire injury, by 4-14 % in P. menziesii and by 23-38 % in L. occidentalis. Furthermore, axial RD density increased in both species due to the formation of tangential rows of traumatic RDs, especially in the first and second years after injury. However, radial RD density did not change significantly. These results highlight traumatic resinosis as a species-specific response. Pseudotsuga menziesii produce RDs of equivalent or reduced size, whereas L. occidentalis produce wider RDs in both the axial and radial duct system, thereby increasing resin biosynthesis and accumulation within the whole tree. Larix occidentalis thus appears to allocate more energy to defence than P. menziesii.

Registration of rock blocks movements using dendrogeomorphic methods: new methodical approach in a case of localities in the Moravskoslezské Beskydy Mts.

This study proposes a new systematic procedure for the dendrochronologic dating of the movement (esp. lateral spreading, backward rotation and toppling) of large boulders with precision to seasons. The methodology is based on the dendrogeomorphic analysis of trees which have been deformed by tilting blocks. Based on the research carried out in four localities within the Moravskoslezské Beskydy Mts, we have identified 22 event years revealing deformations caused by blocks. The interaction between tree stems and tilting blocks is represented by various macroscopic changes as well as growth disturbances within tree-ring series. These most frequently involve tangential rows of traumatic resin ducts and abrupt growth suppression/release. An analysis of meteorological characteristics identifies potential triggers of movements featuring especially summer heavy rainfalls.

Seven centuries of avalanche activity at Echalp (Queyras massif, southern French Alps) as inferred from tree rings

The purpose of this study was to reconstruct spatiotemporal patterns of avalanche events in a forested avalanche path of the Queyras massif (Echalp avalanche path, southeast French Alps). Analysis of past events was based on tree-ring series from 163 heavily affected multicentennial larch trees ( Larix decidua Mill.) growing near or next to the avalanche path. A total of 514 growth disturbances, such as tangential rows of traumatic resin ducts, the onset of compression wood as well as abrupt growth suppression or release, were identified in the samples indicating 38 destructive snow avalanches between 1338 and 2010. The mean return period of snow avalanches was 22 years with a 4% probability that an avalanche occurs in a particular year. On a temporal plan, three maxima in snow avalanche frequency were reconstructed at the beginning of the 16th and 19th centuries and around 1850, correlating with below-average winter temperatures and glacier advances. Analysis of the spatial distribution of disturbed trees contributed to the determination of four preferential patterns of avalanche events. The comparison of dendrogeomorphic data with historical records demonstrate that at least 18 events – six of which were undocumented – reached the hamlet of Echalp during the last seven centuries, but no significant temporal trend was detected concerning the frequency of these extreme events.

Frequenz und Fliesshöhen der Plattlaui (Uri), rekonstruiert mithilfe von Jahrringen

Frequency and flow heights in the Plattlaui avalanche couloir (Uri) – a reconstruction based on tree growth rings The Maderaner Valley (Uri) is one of the regions in Switzerland most heavily affected by snow avalanches, and in the past has also regularly been ravaged by devastating events. The present article is intended to contribute to the database of known avalanche events, and to improve understanding of past avalanche activity. In order to do this, the annual rings of spruce trees (Picea abies [L.] Karst.) were investigated for growth disturbances which could indicate the frequency and flow height of past avalanches in two adjacent couloirs of the Plattlaui avalanche track. The dendromorphological analysis was based on growth ring samples taken from a total of 42 spruce trees on a transect at an altitude of 1570 m. The occurrence of past snow avalanches was primarily reconstructed from evidence of injuries and the associated tangential rows of traumatic resin ducts, but also included abrupt growth suppression, sudden increase in increment and the presence of compression wood. Altogether 19 avalanche events extending back to 1940 were reconstructed and the flow height of individual events demonstrated. Based on the spatial distribution of damaged trees, it was possible to distinguish between unusually high (2 events; 1986, 1999), high (7), medium (7) and small (3) flow heights of snow avalanches. The growth ring reconstruction contains considerably more events (19) than the local archive indicates (7), but fails to document two of the known events. The study therefore also demonstrates the limits of the approach in the case of low flow height avalanches, and at the beginning of the reconstruction with fewer trees available for analysis.

Possibilities and Limitations of Dendrogeomorphic Time-Series Reconstructions on Sites Influenced by Debris Flows and Frequent Snow Avalanche Activity

Past debris-flow and snow avalanche activity was assessed for the Reiselehnrinne (Tyrol, Austria) using growth disturbances in growth-ring series of 372 Norway spruce (Picea abies (L.) Karst.) trees. Determination of events was performed by analyzing (a) the number and (b) intensity of growth disturbances within tree-ring series and (c) the spatial distribution of affected trees. Differentiation of debris flow from snow avalanche events was based on the intra-annual position of scars, callus tissues or tangential rows of traumatic resin ducts, and on the spatial distribution of trees with simultaneous reactions in the tree-ring series. We introduce a weighting factor to substantiate the dating of past process activity in a comprehensive way and to compare individual events as to their intensity and total number of tree-ring responses. The accuracy of the dendrogeomorphic assessment was then evaluated by comparing the reconstructed event frequency with chronologies available for the Reiselehnrinne. Comparison of tree-ring with historical data demonstrated clearly that the reconstructed event frequency contains the majority of past debris flow and snow avalanche events in the Reiselehnrinne, but that dating of events is not always possible, especially if they are clustered in time or have a limited spread on the cone.

Spatio-temporal reconstruction of snow avalanche activity using tree rings: Pierres Jean Jeanne avalanche talus, Massif de l'Oisans, France

Snow avalanches are a major threat in many parts of the Alps, where they periodically damage infrastructure, disrupt transportation corridors or even cause loss of life. Nonetheless, the spatial behavior of past avalanche activity and the analysis of areas affected during particular events remain often imprecise. It was therefore the purpose of this study to reconstruct spatio-temporal patterns of past avalanche activity on a forested avalanche talus in the French Alps (Pierres Jean-Jeanne talus, Massif de l'Oisans, France). A total of 232 European larches (Larix decidua Mill.) with clear signs of snow wasting events was analyzed and growth disturbances (GD) related to avalanche activity was assessed, such as tangential rows of traumatic resin ducts, the onset of compression wood or abrupt growth suppression and release. In total, 901 GD were identified in the tree-ring samples, indicating that 20 high-magnitude avalanches occurred between AD 1919 and 1994. The mean return period of snow avalanches was ~4 years with a ~26% probability that an avalanche occurs in any particular year. Interpolated maps allowed for explicit spatial estimates of return periods throughout the talus, showing a rapid increase of return frequency from 2.5 to 50 years with increasing distance from the talus apex. The distribution of avalanche years seems to be quite homogeneous in time with a gap between 1951 and 1959. Snowfall from a nearby meteorological station (Saint-Christophe en Oisans; 10 km from the study site) indicated that the five most recent high-magnitude events on record occurred due to above-average snowfall anomalies in December and January associated with abnormally low air temperatures. Findings suggest that a strong snow metamorphism under high temperature gradients in January could explain the occurrence of high-magnitude snow avalanches. 2010 Elsevier B.V. All rights reserved.

Three-dimensional analysis of the anatomical growth response of European conifers to mechanical disturbance

Studies on tree reaction after wounding were so far based on artificial wounding or chemical treatment. For the first time, type, spread and intensity of anatomical responses were analyzed and quantified in naturally disturbed Larix decidua Mill., Picea abies (L.) Karst. and Abies alba Mill. trees. The consequences of rockfall impacts on increment growth were assessed at the height of the wounds, as well as above and below the injuries. A total of 16 trees were selected on rockfall slopes, and growth responses following 54 wounding events were analyzed on 820 cross-sections. Anatomical analysis focused on the occurrence of tangential rows of traumatic resin ducts (TRD) and on the formation of reaction wood. Following mechanical disturbance, TRD production was observed in 100% of L. decidua and P. abies wounds. The radial extension of TRD was largest at wound height, and they occurred more commonly above, rather than below, the wounds. For all species, an intra-annual radial shift of TRD was observed with increasing axial distance from wounds. Reaction wood was formed in 87.5% of A. alba following wounding, but such cases occurred only in 7.7% of L. decidua. The results demonstrate that anatomical growth responses following natural mechanical disturbance differ significantly from the reactions induced by artificial stimuli or by decapitation. While the types of reactions remain comparable between the species, their intensity, spread and persistence disagree considerably. We also illustrate that the external appearance of wounds does not reflect an internal response intensity. This study reveals that disturbance induced under natural conditions triggers more intense and more widespread anatomical responses than that induced under artificial stimuli, and that experimental laboratory tests considerably underestimate tree response.

Formation and spread of callus tissue and tangential rows of resin ducts in Larix decidua and Picea abies following rockfall impacts

After mechanical wounding, callus tissue and tangential rows of traumatic resin ducts (TRDs) are formed in many conifer species. This reaction can be used to date past events of geomorphic processes such as rockfall, debris flow and snow avalanches. However, only few points are known about the tangential spread or the timing of callus tissue and TRD formation after wounding. We analyzed 19 Larix decidua Mill. (European larch) and eight Picea abies (L.) Karst. (Norway spruce) trees that were severely damaged by rockfall activity, resulting in a total of 111 injuries. Callus tissue appeared sparsely on the cross sections and was detected on only 4.2% of the L. decidua samples and 3.6% of the P. abies samples. In contrast, TRDs were present on all cross sections following wounding and were visible on more than one-third (34% in L. decidua and 36.4% in P. abies) of the circumference where the cambium was not destroyed by the rockfall impact. We observe different reactions in the trees depending on the seasonal timing of wounding. The tangential spread of callus tissue and TRDs was more important if the injury occurred during the growth period than during the dormant season, with the difference between seasons being more pronounced for callus tissue formation than for TRD formation. We observed an intra-annual radial migration of TRDs with increasing tangential distance from the wound in 73.2% of the L. decidua samples and 96.6% of the P. abies samples. The persistence of TRD formation in the years following wounding showed that only L. decidua trees produced TRDs 2 years after wounding (10.5%), whereas P. abies trees produced TRDs 5 years after wounding (> 50%).

Rockfall and snow avalanche impacts leave different anatomical signatures in tree rings of juvenile Larix decidua

Rockfall and snow avalanche events often cause injury to European larch (Larix decidua Mill.) trees, giving rise to the formation of callus tissue and tangential rows of traumatic resin ducts (TRDs). We analyzed and quantified anatomical reactions of juvenile trees injured before the start of the growing season by snow avalanches (15 trees, 324 cross sections) or rockfalls (18 trees, 270 cross sections). Traumatic resin ducts were observed in the growth ring formed following injury in 94.3% of the rockfall samples and 87.3% of the snow avalanche samples. Traumatic resin ducts were formed at the beginning of the new annual ring around wounds caused by rockfalls. In contrast, in trees injured by snow avalanches, TRDs were not formed until after the formation of several rows of early earlywood (EE) tracheids (mean +/- SD = 4.19 +/- 2.56 rows). The dimensions of the EE tracheids observed in the snow avalanche samples were greatly reduced in the tissues bordering the wound, with radial width reaching an average of only 50% and lumen cross-sectional area an average of only 46% of pre-event values. It is therefore possible to differentiate injuries due to past snow avalanches from injuries due to rockfall based on anatomical growth reactions in the tissues bordering scars.