Holger Gärtner

400 Years of Debris-Flow Activity and Triggering Weather Conditions: Ritigraben, Valais, Switzerland

Abstract Three major rainfall events have caused considerable damage in the Valais region (Swiss Alps) since 1987. Substantial debris flows originating from periglacial environments were recorded during the August 1987 and September 1993 rainfall events, whereas no debris flows occurred in October 2000. This paper aims at putting these large-area events and the apparent increase in debris-flow frequency into a wider context by reconstructing the past debris-flow activity in the Ritigraben torrent (Mattertal, Valais) with dendrogeomorphological methods. Tree-ring analysis allowed the reconstruction of 53 events, going back to the year 1605. Previously, only 10 debris flows had been known for the torrent, and these were limited to the period between 1922 and 2002. Results further show that the apparently above-average concentration of events since 1987 was mainly caused by insufficient and short archival data. In fact, debris flows occurred even more frequently in the nineteenth century than they do today. The spatial distribution of injured trees in particular years further indicates that significant events, like the one in 1993, always occurred in the torrent. Finally, reconstructed event years were compared with archival data on flooding in neighboring catchments. The comparisons prove that large-area events like those in 1987, 1993, or 2000 have at least been as common in the past as they are today.

Microscopic Preparation Techniques for Plant Stem Analysis

Microscopic Preparation Techniques for Plant Stem Analysis by Holger Gartner and Fritz H. Schweingruber was published in 2013 by Kessel Publishing House (ISBN 978-3-941300-76-7) and is available directly from the publisher. The authors have team-taught a workshop on wood anatomy for almost a decade, and this book clearly benefits from their extensive experience in teaching the basic techniques of microscopic plant stem preparation to researchers from a broad spectrum of disciplines. The book’s structure leads readers through the sequential steps involved in plant stem analysis. It begins with short sections on fieldbased sampling strategies and methods. Then the book transitions to its dominant focus: laboratory methods for masceration and thin-sectioning of plant material. It provides details on how to stain, bleach, fix, and preserve plant materials for viewing with a microscope. The excellent photographs in these sections let readers ‘‘see’’ the steps involved in microscope slide preparation. The book ends with very brief sections on common errors during sample preparation and microscopy tips for improved viewing of prepared samples. This book takes the extensive experience in microscopic preparation possessed by Dr. Gartner and Prof. Schweingruber and presents it to readers in a highly accessible format. The authors intentionally created an image-rich book to make it easier for readers lacking strong English skills to understand the content; however, this format also serves as a source of inspiration for future research projects. There were many pages where we saw a new technique being demonstrated and realized we had the perfect application for that method in one of our current studies. Although the book is aimed at an international audience, at times it falls short in that goal. Sometimes these shortcomings are entertaining, as in the paragraph on how to hold the razor blade during sectioning by hand, where readers are told to ‘‘cut the object like you would cut a salami, not like you would cut butter’’ (p. 21). This recommendation left us laughing, but having no idea how to hold the razor blade. Occasionally, the stilted language becomes annoying for native English speakers to read, but the meaning is always clear even if the noun and verb agreement is incorrect. One area where we wish the authors had spent more time was on the economics of these laboratory techniques. For example, they advocate the use of Canada balsam for embedding microsections and say, ‘‘for all other embedding resins we have no long-term experience’’ (p. 63). From our perspective, we look at having to pay US

Olive Tree-Ring Problematic Dating: A Comparative Analysis on Santorini (Greece)

210 for 100mL of Canada balsam vs. having to pay US

Variations in Tension Wood of Two Broad‐Leaved Tree Species in Response to Different Mechanical Treatments: Implications for Dendrochronology and Mass Movement Studies

15 for 100mL of permanent mounting medium and are left wondering whether the extra US

Tension wood formed in Fagus sylvatica and Alnus glutinosa after simulated mass movement events

195 is really worth it. Unfortunately, the authors offer no suggestions for alternative techniques for researchers with more limited funds. Overall, this is a useful reference book for any dendrochronology, wood anatomy, or plant sciences laboratory. In our own work, we have already used this book twice in the past week to find the appropriate solvent for a Safranin stain solution and to find suggestions for eliminating air bubbles during permanent slide preparation. In both cases, the Table of

The formation of traumatic rows of resin ducts in Larix decidua and Picea abies (Pinaceae) as a result of wounding experiments in the dormant season

Olive trees are a classic component of Mediterranean environments and some of them are known historically to be very old. In order to evaluate the possibility to use olive tree-rings for dendrochronology, we examined by various methods the reliability of olive tree-rings identification. Dendrochronological analyses of olive trees growing on the Aegean island Santorini (Greece) show that the determination of the number of tree-rings is impossible because of intra-annual wood density fluctuations, variability in tree-ring boundary structure, and restriction of its cambial activity to shifting sectors of the circumference, causing the tree-ring sequences along radii of the same cross section to differ.

New Tree-Ring Evidence from the Pyrenees Reveals Western Mediterranean Climate Variability since Medieval Times

Reaction wood formation, in particular compression wood in conifers, has often been used to date geomorphic events such as debris flows or snow avalanches. However, very little is known yet about the variations of tension wood formation and particularly cross‐sectional vessel characteristics in response to different mechanical impacts. To test whether different intensities and characteristic forms of tension wood formation induce the formation of vessels with changing sizes, growth experiments with different treatments were conducted with alder and beech followed by wood anatomical analysis of the vessels. The experiments comprised bending treatments of varying severities in combination with cambium wounding and other alterations. The treatments were successful in inducing different intensities in tension wood expressed by variations of vessel lumen area (VLA). An increasing bending stress resulted in the formation of lower VLA values. When the apex or the root system was damaged or the apex remained vertical, VLA values decreased less and the tension wood formation was regarded as less intense. Our research shows that VLA is affected by mechanical impacts and that the application of wood anatomical techniques can potentially provide supplementary information about type and intensities of past mechanical impacts in angiosperm tree growth.

A Technical Perspective in Modern Tree-ring Research - How to Overcome Dendroecological and Wood Anatomical Challenges

Due to the likelihood of global climate change, the frequency and magnitude of natural hazards such as mass movements may likewise change, thus favouring the refinement of methods to detect and quantify geomorphic events when precise records are not available. Geomorphic events typically have a significant effect on tree growth, e.g., reaction wood marked by changes in ring widths and wood density. To date, several dendroecological techniques have been developed to document the occurrence of these events but it rarely has been possible to retrieve additional information from reaction wood concerning the precise kind and intensity of geomorphic events. Additional qualitative information inferred from reaction wood of trees holds the potential to not only document but also estimate important characteristics of natural hazard events. To refine the methods already used in dendrogeomorpology, experiments simulating various geomorphic events were used to monitor subsequent wood anatomical responses of Fagus sylvatica and Alnus glutinosa. The preliminary results indicate that these two common broadleaf tree species show variations in their reactions to different experimental treatments.

A new sledge microtome to combine wood anatomy and tree-ring ecology

Wounding experiments, imitating the impact of geomorphic processes such as rock fall, were performed on Larix decidua Mill. and Picea abies (L.) Karst., before the beginning and at the end of the growing season. This was done to evaluate the timing and spread of traumatic rows of resin ducts (TDs) as a result of wounding during dormancy, when most mass movements occur. All treatments were successful in inducing TDs. However, a high inter- and intra-species variability concerning the timing and position of the TDs was noted. In larch, TDs were formed as first cells after wounding (immediate reaction) only in the vicinity of the wound. In contrast, none of the spruce trees exhibited immediate reactions. Neither larch nor spruce formed continuous TDs around the stem. TDs in larch were more extensive if, in addition, stems were bent before the growing season. In contrast, spruce showed this reaction when bent at the end of the growing season. The results indicate that the varying lengths of the growing seasons at different geographical locations need to be taken into account before an immediate wound reaction can be clearly defined, if an increase of the reliability and accuracy of process reconstructions is aimed for.

The olive-branch dating of the Santorini eruption

AbstractPaleoclimatic evidence is necessary to place the current warming and drying of the western Mediterranean basin in a long-term perspective of natural climate variability. Annually resolved and absolutely dated temperature proxies south of the European Alps that extend back into medieval times are, however, mainly limited to measurements of maximum latewood density (MXD) from high-elevation conifers. Here, the authors present the world’s best replicated MXD site chronology of 414 living and relict Pinus uncinata trees found >2200 m above mean sea level (MSL) in the Spanish central Pyrenees. This composite record correlates significantly (p ≤ 0.01) with May–June and August–September mean temperatures over most of the Iberian Peninsula and northern Africa (r = 0.72; 1950–2014). Spanning the period 1186–2014 of the Common Era (CE), the new reconstruction reveals overall warmer conditions around 1200 and 1400, and again after around 1850. The coldest reconstructed summer in 1258 (−4.4°C compared to 1961...