Publications by Holger Gärtner
Die Bilder grossflächig brauner Laubbäume in weiten Teilen der Schweiz sowie Zentraleuropas im Fr... more Die Bilder grossflächig brauner Laubbäume in weiten Teilen der Schweiz sowie Zentraleuropas im Frühsommer 2018 sind uns noch sehr präsent. Diese um rund drei Monate verfrühte Herbstverfärbung der Wälder war das Resultat der extre-men Hitze und langanhaltenden Dürre. Auch wenn das Ausmass und die Sichtbar-keit der Schäden in Wald und Landwirtschaft 2018 ausserordentlich waren, so stel-len wir eine Häufung von solchen extremen Hitze-und Trockenjahren (2003, 2011 und 2015) fest. Laut dem neuesten Klimabericht für die Schweiz muss davon aus-gegangen werden, dass Hitze-und Dürreperioden in Zukunft noch häufiger auf-treten dürften. Was heisst dies nun für unsere Wälder? Wie viel Trockenheit kön-nen sie ertragen? Wir diskutieren diese Fragen anhand von Daten aus verschiede-nen Monitoringansätzen und zeigen auf, dass die verschiedenen Waldökosysteme sehr unterschiedlich reagieren und die zukünftige Dynamik unserer Wälder von der Kombination und dem zeitlichen Auftreten von Trockenheit und anderen Wetterextremen abhängen wird.
The efficiency of water use and transport are among the main factors affecting competitiveness, g... more The efficiency of water use and transport are among the main factors affecting competitiveness, growth, and distribution of trees under warming climate. The phenotypical and genetic plasticity of tree populations is considered as an indicator of their adaptive capacity under changing environment. Climatic changes are expected to affect growth of Scots pine (Pinus sylvestris L.), and selection of reproductive material among the populations suitable for future climates has been advised for sustaining productivity of stands. In this regard, provenance trials can serve as source of comprehensive information about growth plasticity and climate-growth interactions of diverse populations. Quantitative wood anatomy can provide detailed information about xylo-genesis and factors affecting it, which are crucial for long-term predictions. Wood anatomy of two top-(Gustrow and Rytel), two low-performing (Eibenstock and Dippoldiswalde), and one local (Kalsnava) provenances of Scots pine from the eastern Baltic region growing in three provenance trials in Latvia was studied using mixed models, accounting for the experimental design, as well as using the time-series approach. Provenance had a significant effect on the studied wood anatomical proxies, indicating genetic adaptation of xylogenesis. The top-performing provenances, which originated from warmer and drier conditions, had tracheids with larger lumens and thinner walls, thus indicating adaptation to water deficit. The top-performing Rytel provenance showed the highest phenotypical plasticity of lumen cross-section area and cell wall thickness of stemwood tracheids. The studied low-performing provenances, which originated from the Orr Mountains, had tracheids with thicker wall and smaller lumens, likely to ensure mechanical durability. The local provenance showed intermediate values of the studied wood anatomical proxies. The effect of provenance on wood anatomical proxies showed some variations among the trials, which differed by continentality, likely due to ecological transfer distance. The studied anatomical proxies were affected by weather conditions prior and during formation of a tree ring, yet these relationships differed by trial and provenance. In general, wood anatomy of earlywood was affected by temperature in the dormant period and beginning of summer, as well as precipitation in the end of the previous vegetation period. Proxies of latewood showed correlation with temperature (negative) and precipitation (po-sitive) in summer, suggesting response to the availability of water. Considering the observed relationships, the top-performing provenances, particularly Rytel, have a high potential to sustain productivity of stands within the region in the future.
Plants essentially contribute to the strength of soil and, in particular, steep slopes susceptibl... more Plants essentially contribute to the strength of soil and, in particular, steep slopes susceptible to erosion and shallow landslides. The corresponding functions of vegetation significantly control processes above and below ground such as interception , evapo-transpiration, soil aggregation and root reinforcement. Either way, they are all correlated with plant growth. Consequently, in order to unfold their soil stabilising potential, the plants must grow and sustainably survive. However, what sounds so obvious is anything but given under the often hostile conditions dominating on bare and steep slopes. This is exactly the point where mycorrhizal fungi come into play, known to improve the plants' ability to overcome periods governed by strongly (growth) limiting factors. Within this scope, numerous investigations have been conducted in order to understand and quantify mycorrhizal effects on different plant and soil functions related to eco-engineering and, particularly, to soil and slope stability. Results on plant growth and survival as well as on soil aggregation and slope stabilisation are presented and discussed from a mycorrhizal perspective.
The annual growth and wood characteristics of tree species at southern Mediterranean countries, a... more The annual growth and wood characteristics of tree species at southern Mediterranean countries, and its relationship with climate variables are recently two important topics for the researchers in this region. Although Moringa peregrina (Forssk.) Fiori is a key species in Africa due to its medicinal and economic values (e.g. as fuel, food and water purifier), little is known about its annual growth or its response to climate variables. In this study, we analyze its dendrochronological potential, macroscopic and microscopic wood structure, and correlation with climate. Wood discs were collected from two desert sites in Egypt: Saint Catherine (SC) and Hurghada (HG). Wood discs and micro-slides were prepared, and the distinctness and pattern of rings, vessels, and ray structure were examined microscopically. The ring boundaries of M. peregrina were distinct and marked by thick-walled and flattened fibers. For the HG site, the resulting ring-width chronology spans 16 years, from 2001 to 2016. A significant positive relationship was found between tree growth at HG and precipitation prior to the vegetation period (January-March). April temperature of the year prior to growth had a significant positive relationship with M. peregrina growth. In contrast, April and May-August temperatures of the current growing season had a significant negative relationship with tree growth. We could not develop a chronology for M. peregrina at SC site due to the presence of growth anomalies in the collected wood discs from the site. Consequently, we did not get a clear picture on the climate-annual growth relationship for M. peregrina trees at this site. At SC, M. peregrina trees respond to stressful environmental conditions by adjusting their anatomical structure to produce a high number of small vessels. Moreover, there was spatial variability in the architecture of ray parenchyma that reflected the degree of stress in both sites. The results of this study improve our understanding of the growth-climate relationship in subtropical trees and the potential role of ray parenchyma in stressed environments.
A R T I C L E I N F O Keywords: Ailanthus altissima (tree of heaven) Tree-ring Climate growth rel... more A R T I C L E I N F O Keywords: Ailanthus altissima (tree of heaven) Tree-ring Climate growth relationship Vessel lumen area Wood anatomy Invasive tree A B S T R A C T Knowledge on the ecology of tree species in both their native and introduced range can increase the understanding of their successful establishment and spread outside the native range. Here, we analysed radial growth patterns of Ailanthus altissima (Mill.) Swingle in two sites in its native range in eastern China and in two sites in the introduced range in southern Switzerland, where it started to disperse into forests in the 1950s. Growth rates were similar despite lower amounts of growing season precipitation in China. Furthermore, we found negative correlations between annual radial growth and average temperatures in the growing season at the warmest of the four sites, which suggest that radial growth of A. altissima starts to be limited by average growing season temperatures above 21 °C. Regarding wood anatomy, we did not find clear correlations between vessel lumen area and monthly temperature or precipitation at the time of tissue formation in spring. Overall, our results demonstrate that A. altissima has the potential to grow in drier conditions than currently found in Switzerland, which is in line with previous studies.
A spatiotemporal reconstruction of slope movements on the edge of Lake Lucerne near the municipal... more A spatiotemporal reconstruction of slope movements on the edge of Lake Lucerne near the municipality of Horw, canton of Lucerne, is presented. The reconstruction was realized by analyzing growth reactions of beech (Fagus sylvatica L.) and fir (Abies alba Mill.) trees growing on this slope. Before dendrochronological sampling, a detailed geomorphological mapping of the landslide was conducted with the aim to determine the spatial extent of the sliding area. For tree-ring analyses, 124 increment cores from 62 trees were analyzed following standard techniques of dendrogeomorphology. In addition, long micro-sections were prepared from the entire cores to extend the common eccentricity analyses by microscopic determination of the onset of reaction wood in fir and beech. Results clearly show that the area is moving at least since 1948. A significant concentration of events was observed between the years 1990 and 2000 as well as after 2006. The definition of a threshold to define events using an eccentricity index alone is problematic and needs to be adapted to specific site conditions. For this reason, we recommend always combining the application of an eccentricity index with a detailed visual (anatomical) inspection to check for the occurrence of reaction wood.
Wood anatomical features may be visible on the microscopic as well as on the macroscopic scale. W... more Wood anatomical features may be visible on the microscopic as well as on the macroscopic scale. While the former can often be quantified by detailed wood anatomical analyses, the latter are often treated as qualitative features or as binary variables (present/absent). Macroscopic tree-ring features can be quantified in terms of frequency, intensity, or classified according to their position within a tree ring, like intra-annual density variations (IADFs) in conifers or frost rings in earlywood or latewood. Although some of these tree-ring features, like e.g. missing rings or IADFs are often seen as anomalies, hampering dendrochronologists to perform proper crossdating of tree-ring series, many of these properties are formed under extreme environmental stress or heavy impact, and could mark these extreme events by the manifestation in the wood anatomical structures throughout the lifespan of trees. The described tree-ring features form discrete time-series of extreme events. For example, flood rings may be marked by lunar-shaped earlywood vessels or enlarged latewood vessels in ring-porous oaks. White earlywood rings and light rings indicate reduced cell wall thickness and lignification occurring in very cold years. Frost rings result from cambial cell death during abrupt cooling events in the growing season. Missing rings and IADFs are mainly caused by drought events. Characteristic variations in earlywood vessel size, shape, or number in ring-porous oak species are markers for flood events, defoliation, heat stress, or drought. Traumatic resin ducts may be triggered by a range of biotic or environmental stressors, including wounding, fires or mechanical factors. Reaction wood is indicative of mechanical stress, often related to geomorphic events. In many cases anatomical responses are unspecific and may be caused by different stressors or extreme events. Additionally, the sensitivity of trees to form such features may vary between species, or between life stages within one species. We critically evaluate the indicative value of different wood anatomical tree-ring features for environmental reconstructions.
The type of samples most commonly used in dendro sciences are increment cores of conifers. These ... more The type of samples most commonly used in dendro sciences are increment cores of conifers. These cores
allow for an easy determination and measurement of ring-width variations over long time periods. For
wood anatomical analyses, the cores have to be split into pieces to enable the preparation of high quality
micro sections for detailed measurements of cell properties. A major drawback of this procedure is the
fact that it is labor intensive and time consuming. We present a new technique enabling the preparation of
micro sections of entire increment cores up to a length of 40 cm. For that purpose we combined standard
wood-anatomical techniques with the application of Mowiol glue and common Tesa tape. We tested the
introduced method on increment cores of Larix decidua Mill. sampled years ago for ring-width analyses to
reanalyze them on a microscopic level. The ability to cut these long sections will tremendously reduce the
time needed to prepare micro sections. This is of special interest for wood anatomical image analyses of
cores used before to create long ring-width chronologies for any kind of environmental reconstructions.
Dendroecological research uses information stored in tree rings to understand how single trees an... more Dendroecological research uses information stored in tree rings to understand how single trees and even entire forest ecosystems responded to
environmental changes and to finally reconstruct such changes. This is done by analyzing growth variations back in time and correlating various
plant-specific parameters to (for example) temperature records. Integrating wood anatomical parameters in these analyses would strengthen
reconstructions, even down to intra-annual resolution. We therefore present a protocol on how to sample, prepare, and analyze wooden
specimen for common macroscopic analyses, but also for subsequent microscopic analyses. Furthermore we introduce a potential solution for
analyzing digital images generated from common small and large specimens to support time-series analyses. The protocol presents the basic
steps as they currently can be used. Beyond this, there is an ongoing need for the improvement of existing techniques, and development of new
techniques, to record and quantify past and ongoing environmental processes. Traditional wood anatomical research needs to be expanded to
include ecological information to this field of research. This would support dendro-scientists who intend to analyze new parameters and develop
new methodologies to understand the short and long term effects of specific environmental factors on the anatomy of woody plants.
Based on the Reichert Om E microtome a more sophisticated, nevertheless solely
mechanically opera... more Based on the Reichert Om E microtome a more sophisticated, nevertheless solely
mechanically operated microtome was developed enabling to section specimens
of various forms and sizes. The materials used and the special construction of the
microtome resulted in a higher stability of the moving parts whilst simultaneously
reducing weight. As a result of the high stability of the sledge guidance, bigger
sections can be cut enabling more detailed analyses of anatomical structures
within plant stems, roots or branches as well as their variation back in time.
Consequently, wood anatomical parameters can be integrated more easily in
time-series analyses supporting the aims of a quantitative wood ecology.
Dendrochronologia, 2014
The variability of wood anatomical features in the rings of trees and shrubs is known to be depen... more The variability of wood anatomical features in the rings of trees and shrubs is known to be dependent on multifaceted environmental parameters. The ability to determine anatomical variations over longer time periods as decades or centuries is a step forward in dendroecological and dendroclimatological research. In this regard micro sectioning is still one of the basic requirements but sectioning devices (microtomes) designed for wood anatomical purposes are rarely available. We present an affordable heavy duty, but light-weight microtome operated with removable blades. This portable device enables the production of large sections for dendroclimatological reconstructions as well as various types of common sections for wood anatomical studies.
Dendrochronologia, 2010
A microtome designed for the surface preparation of entire increment cores allows cutting plane s... more A microtome designed for the surface preparation of entire increment cores allows cutting plane surfaces on cores up to a length of 40 cm. Compared to the common sanding procedure, the wood cells of the annual rings remain open, not filled with swarf, and the cell walls are smooth and hence clearly visible. This article aims at describing the functionality of the microtome and the procedures needed for an accurate surface preparation to achieve a good contrast for subsequent image analysis. Possible applications for a more detailed analysis of variations in the tracheid structure of conifers and vessel sizes of oak are presented, which can be included in time series analyses.
Dendrochronologia, 2013
The breakage or distortion of cellular structures is one of the biggest problems in creating micr... more The breakage or distortion of cellular structures is one of the biggest problems in creating micro-sections for wood anatomical analyses in tree-ring as well as other branches of anatomical research. These broken or distorted structures cause artifacts in photomicrographs that require time consuming image manipulation or corrections prior to further analyses. The simple application of a cornstarch, water, and glycerol (CWG) solution (10:8:7 ratio), a so called non-Newtonian fluid to the surface of wooden specimen before sectioning improves the overall quality of the resulting micro-sections. In particular the problem of secondary cell walls splitting off the primary wall while sectioning is drastically reduced. The quality of the sections using this solution is comparable to that obtained from the more laborious and expensive paraffin embedding.
Geomorphology, 2007
Exposed roots have been used in Dendrogeomorphology since the 1960s to determine erosion rates. T... more Exposed roots have been used in Dendrogeomorphology since the 1960s to determine erosion rates. This was done by using the root axis as the relative position of the former soil layer and then relating this measure to the age of the root in order to quantify the amount of soil erosion over time. Recently, wood anatomical research revealed the possibility of determining the first year of exposure of roots due to specific anatomical changes within the respective annual ring. As a consequence, using exposed roots that are still in contact to the soil surface, it is possible to reconstruct the size and position of the root at the time of exposure. Consequently, a new equation is presented to calculate the thickness of the eroded soil layer allowing a detailed reconstruction of erosion rates. The technique also helps to determine if the root was exposed by erosional processes or just by its ongoing secondary growth without any erosion involved.
Dendrogeomorphological applications
Die Wurzel als Anker: Dreidimensionale Erfassung der Wurzelausbreitung unter Berücksichtigung der Holzanatomie
Untersuchungen zu Geschwindigkeit und Volumen von Murgängen im Mattertal, Wallis, Schweiz, in den Jahren 1993 und 1994: ein Beitrag zur Klimafolgen-und Naturgefahrenforschung
Dendrogeomorphological analysis of the enlargement of cracks at the Wellenkalkscarp in the southern Thuringia Basin
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Publications by Holger Gärtner
allow for an easy determination and measurement of ring-width variations over long time periods. For
wood anatomical analyses, the cores have to be split into pieces to enable the preparation of high quality
micro sections for detailed measurements of cell properties. A major drawback of this procedure is the
fact that it is labor intensive and time consuming. We present a new technique enabling the preparation of
micro sections of entire increment cores up to a length of 40 cm. For that purpose we combined standard
wood-anatomical techniques with the application of Mowiol glue and common Tesa tape. We tested the
introduced method on increment cores of Larix decidua Mill. sampled years ago for ring-width analyses to
reanalyze them on a microscopic level. The ability to cut these long sections will tremendously reduce the
time needed to prepare micro sections. This is of special interest for wood anatomical image analyses of
cores used before to create long ring-width chronologies for any kind of environmental reconstructions.
environmental changes and to finally reconstruct such changes. This is done by analyzing growth variations back in time and correlating various
plant-specific parameters to (for example) temperature records. Integrating wood anatomical parameters in these analyses would strengthen
reconstructions, even down to intra-annual resolution. We therefore present a protocol on how to sample, prepare, and analyze wooden
specimen for common macroscopic analyses, but also for subsequent microscopic analyses. Furthermore we introduce a potential solution for
analyzing digital images generated from common small and large specimens to support time-series analyses. The protocol presents the basic
steps as they currently can be used. Beyond this, there is an ongoing need for the improvement of existing techniques, and development of new
techniques, to record and quantify past and ongoing environmental processes. Traditional wood anatomical research needs to be expanded to
include ecological information to this field of research. This would support dendro-scientists who intend to analyze new parameters and develop
new methodologies to understand the short and long term effects of specific environmental factors on the anatomy of woody plants.
mechanically operated microtome was developed enabling to section specimens
of various forms and sizes. The materials used and the special construction of the
microtome resulted in a higher stability of the moving parts whilst simultaneously
reducing weight. As a result of the high stability of the sledge guidance, bigger
sections can be cut enabling more detailed analyses of anatomical structures
within plant stems, roots or branches as well as their variation back in time.
Consequently, wood anatomical parameters can be integrated more easily in
time-series analyses supporting the aims of a quantitative wood ecology.