Duration and extension of anatomical changes in wood structure after cambial injury

Cambial injury has been reported to alter wood structure in broad-leaved trees. However, the duration and extension of associated anatomical changes have rarely been analysed thoroughly. A total of 18 young European ash (Fraxinus excelsior L.) trees injured on the stem by a spring flood were sampled with the aim of comparing earlywood vessels and rays formed prior to and after the scarring event. Anatomical and hydraulic parameters were measured in five successive rings over one-quarter of the stem circumference. The results demonstrate that mechanical damage induces a decrease in vessel lumen size (up to 77%) and an increase in vessel number (up to 475%) and ray number (up to 115%). The presence of more earlywood vessels and rays was observed over at least three years after stem scarring. By contrast, abnormally narrow earlywood vessels mainly developed in the first ring formed after the event, increasing the thickness-to-span ratio of vessels by 94% and reducing both xylem relative conductivity and the index for xylem vulnerability to cavitation by 54% and 32%, respectively. These vessels accumulated in radial groups in a 30° sector immediately adjacent to the wound, raising the vessel grouping index by 28%. The wound-induced anatomical changes in wood structure express the functional need of trees to improve xylem hydraulic safety and mechanical strength at the expense of water transport. Xylem hydraulic efficiency was restored in one year, while xylem mechanical reinforcement and resistance to cavitation and decay lasted over several year

Defining an Adequate Sample of Earlywood Vessels for Retrospective Injury Detection in Diffuse-Porous Species

Vessels of broad-leaved trees have been analyzed to study how trees deal with various environmental factors. Cambial injury, in particular, has been reported to induce the formation of narrower conduits. Yet, little or no effort has been devoted to the elaboration of vessel sampling strategies for retrospective injury detection based on vessel lumen size reduction. To fill this methodological gap, four wounded individuals each of grey alder (Alnus incana (L.) Moench) and downy birch (Betula pubescens Ehrh.) were harvested in an avalanche path. Earlywood vessel lumina were measured and compared for each tree between the injury ring built during the growing season following wounding and the control ring laid down the previous year. Measurements were performed along a 10 mm wide radial strip, located directly next to the injury. Specifically, this study aimed at (i) investigating the intra-annual duration and local extension of vessel narrowing close to the wound margin and (ii) identifying an adequate sample of earlywood vessels (number and intra-ring location of cells) attesting to cambial injury. Based on the results of this study, we recommend analyzing at least 30 vessels in each ring. Within the 10 mm wide segment of the injury ring, wound-induced reduction in vessel lumen size did not fade with increasing radial and tangential distances, but we nevertheless advise favoring early earlywood vessels located closest to the injury. These findings, derived from two species widespread across subarctic, mountainous, and temperate regions, will assist retrospective injury detection in Alnus, Betula, and other diffuse-porous species as well as future related research on hydraulic implications after wounding

The potential of broad-leaved trees for dendrogeomorphic research: wood anatomical analysis of injuries

The objective of this thesis is to determine and exploit the potential of broad-leaved trees for dendrogeomorphic research. Wounded trees from several broad-leaved species were sampled along torrents in the Swiss Alps as well as in snow avalanche paths in Norway and Iceland. Injuries were studied at the macroscopic level to date events and at the microscopic level to analyze wound-induced changes in wood anatomy so as to improve the detection of injuries in tree-ring series. Xylem cells were examined radially (before and after the injury) and tangentially (around the tree circumference) in order to identify variations in wood anatomical features. The formation of more and narrower earlywood vessels as well as the initiation of more and larger rays were obvious in a very short time after the disturbance, emphasizing that altered wood anatomical features can serve as proxy records of past events with seasonal to annual resolution

Dating of snow avalanches by means of wound-induced vessel anomalies in sub-arctic Betula pubescens

Dendrogeomorphic research has long relied on scarred trees to reconstruct the frequency of mass-movement processes. Injuries have mostly been dated macroscopically by counting the tree rings formed after wounding. Tree-ring anatomical anomalies induced by cambial injury, in contrast, have only recently been recognized as proxy records of past events. We investigated 12 sub-arctic downy birch (Betula pubescens Ehrh.) trees scarred by snow avalanches in Norway and Iceland. Earlywood vessel lumina were measured for each tree in the xylem tissue bordering the scars. Seven successive rings were examined, namely two control rings laid down prior to wounding and five rings in the wound xylem. We provide evidence that snow-avalanche-induced wounding resulted in atypically narrow earlywood vessels over at least two years. Our data demonstrate that wound-associated vessel anomalies represent tangible markers of mass-movement processes, and as such make a viable tool for reconstructing past events. Similar dendrogeomorphic studies based on tree-ring anatomy can be readily conducted with other mass-movement processes, as well as with other broad-leaved tree species. Ultimately, this new approach will foster increment coring over more invasive sampling techniques

Reconstitution dendrogéomorphologique d'événements de lave torrentielle à l'aide de feuillus blessés

Tree-ring records from conifers have been regularly used over the last few decades to date debris-flow events. The reconstruction of past debris-flow activity was, in contrast, only very rarely based on growth anomalies in broad-leaved trees. Consequently, this study aimed at dating the occurrence of former debris flows from growth series of broad-leaved trees and at determining their suitability for dendrogeomorphic research. Results were obtained from gray alder (Alnus incana (L.) Moench), silver birch and pubescent birch (Betula pendula Roth and Betula pubescens Ehrh.), aspen (Populus tremula L.), white poplar, black poplar and gray poplar (Populus alba L., Populus nigra L. and Populus x canescens (Ait.) Sm.), goat willow fSalix caprea L.) and black elder (Sambucus nigra L.) injured by debris-flow activity at Illgraben (Valais, Swiss Alps). Tree-ring analysis of 315 samples from 154 injured broad-leaved trees allowed the reconstruction of 14 debris-flow events between AD 1965 and 2007. These events were compared to archival records on debris-flow activity at Illgraben. It appears that debris flows are very common at Illgraben, but only very rarely left the channel over the period AD 1965-2007. Furthermore, analysis of the spatial distribution of disturbed trees contributed to the identification of six patterns of debris -flow routing and led to the determination of preferential breakout locations of events. The results of this study demonstrate the high potential of broad-leaved trees for dendrogeomorphic research.Les cernes de croissance des conifères ont régulièrement été utilisés durant ces dernières décennies pour dater les événements de lave torrentielle. La reconstitution de l'activité des laves torrentielles n'a en revanche que très rarement été basée sur les anomalies de croissance des feuillus. Par conséquent, cette étude vise à dater les événements de lave torrentielle à partir des cernes de croissance des feuillus et à déterminer la valeur des feuillus pour les recherches en dendrogéomorphologie. Les résultats proviennent de l'aulne blanc (Alnus incana (L.) Moench), du bouleau blanc et bouleau pubescent (Betula pendula Roth et Betula pubescens Ehrh.), du tremble (Topulus tremula L.), du peuplier blanc, peuplier noir et peuplier grisard (Populus alba L., Populus nigra L. et Populus x canescens (Ait.) Sm.), du saule Marsault (Salix caprea L.) et du sureau noir (Sambucus nigra L.) blessés par l'activité des laves torrentielles à l'illgraben (Valais, Alpes suisses). L'analyse des cernes de croissance de 315 échantillons extraits de 154 feuillus blessés a permis la reconstitution de 14 événements de lave torrentielle entre 1965 et 2007. Les données d'archives ont révélé que les laves torrentielles sont très fréquentes à l'illgraben. Elles n'ont toutefois que très rarement quitté le chenal durant la période 1965-2007. En outre, l'analyse de la distribution spatiale des arbres perturbés a permis d'identifier six chemins de propagation des laves torrentielles et de déterminer ainsi les lieux de débordement préférentiels des événements. Les résultats de cette étude démontrent le potentiel élevé des feuillus pour les recherches en dendrogéomorphologie.Arbellay Estelle, Stoffel Markus, Bollschweiler Michelle. Reconstitution dendrogéomorphologique d'événements de lave torrentielle à l'aide de feuillus blessés. In: Collection EDYTEM. Cahiers de géographie, numéro 11, 2010. Panorama de la dendrochronologie en France. pp. 99-108

Dendrogeomorphic reconstruction of past debris-flow activity using injured broad-leaved trees

Tree-ring records from conifers have been regularly used over the last few decades to date debris-flow events. The reconstruction of past debris-flow activity was, in contrast, only very rarely based on growth anomalies in broad-leaved trees. Consequently, this study aimed at dating the occurrence of former debris flows from growth series of broad-leaved trees and at determining their suitability for dendrogeomorphic research. Results were obtained from gray alder (Alnus incana (L.) Moench), silver birch and pubescent birch (Betula pendula Roth and Betula pubescens Ehrh.), aspen (Populus tremula L.), white poplar, black poplar and gray poplar (Populus alba L., Populus nigra L. and Populus x canescens (Ait.) Sm.), goat willow (Salix caprea L.) and black elder (Sambucus nigra L.) injured by debris-flow activity at Illgraben (Valais, Swiss Alps). Tree-ring analysis of 104 increment cores, 118 wedges and 93 cross-sections from 154 injured broad-leaved trees allowed the reconstruction of 14 debris-flow events between AD 1965 and 2007. These events were compared with archival records on debris-flow activity at Illgraben. It appears that debris flows are very common at Illgraben, but only very rarely left the channel over the period AD 1965–2007. Furthermore, analysis of the spatial distribution of disturbed trees contributed to the identification of six patterns of debris-flow routing and led to the determination of preferential breakout locations of events. The results of this study demonstrate the high potential of broad-leaved trees for dendrogeomorphic research and for the assessment of the travel distance and lateral spread of debris-flow surges

Wood anatomical analysis of Alnus incana and Betula pendula injured by a debris-flow event

Vessel chronologies in ring-porous species have been successfully employed in the past to extract the climate signal from tree rings. Environmental signals recorded in vessels of ring-porous species have also been used in previous studies to reconstruct discrete events of drought, flooding and insect defoliation. However, very little is known about the ability of diffuse-porous species to record environmental signals in their xylem cells. Moreover, time series of wood anatomical features have only rarely been used to reconstruct former geomorphic events. This study was therefore undertaken to characterize the wood anatomical response of diffuse-porous Alnus incana (L.) Moench and Betula pendula Roth to debris-flow-induced wounding. Tree microscopic response to wounding was assessed through the analysis of wood anatomical differences between injured rings formed in the debris-flow event year and uninjured rings formed in the previous year. The two ring types were examined close and opposite to the injury in order to determine whether wound effects on xylem cells decrease with increasing tangential distance from the injury. Image analysis was used to measure vessel parameters as well as fiber and parenchyma cell (FPC) parameters. The results of this study indicate that injured rings are characterized by smaller vessels as compared with uninjured rings. By contrast, FPC parameters were not found to significantly differ between injured and uninjured rings. Vessel and FPC parameters mainly remained constant with increasing tangential distance from the injury, except for a higher proportion of vessel lumen area opposite to the injury within A. incana. This study highlights the existence of anatomical tree-ring signatures — in the form of smaller vessels — related to past debris-flow activity and addresses a new methodological approach to date injuries inflicted on trees by geomorphic processes

Dating of snow avalanches by means of wound-induced vessel anomalies in subarctic Betula pubescens

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Macroanatomy and compartmentalization of recent fire scars in three North American conifers.

Fire scars are initiated by cambial necrosis caused by localized lethal heating of the tree stem. Scars develop as part of the linked survival processes of compartmentalization and wound closure. The position of scars within dated tree ring series is the basis for dendrochronological reconstruction of fire history. Macroanatomical features were described for western larch, ponderosa pine, and Douglas-fir injured by fire in 2003 and harvested in 2011 at the Lolo National Forest near Missoula, Montana, USA. Bark scorch did not necessarily indicate the formation of a scar. Wound-initiated discoloration inward from the scar face was bounded tangentially by reaction zones. In western larch, the transition between earlywood and latewood was much less abrupt in woundwood rings than in rings formed the same year but not associated with a scar. Wood formed the year after injury contained tangential rows of resin ducts in the earlywood. Compartmentalization plays a key role in resisting the spread of infection and the loss of healthy sapwood and heartwood. Wound closure restores some degree of circumferential continuity of the vascular cambium and reinforces stem structure. The terminology presented here should facilitate communication among tree pathologists, wound anatomists, and dendrochronologists.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author