Andreas Roloff

Defining ecologically relevant vessel parameters in Quercus robur L. for use in dendroecology: a pointer year and recovery time case study in Central Germany

Key messageThe most promising and representative earlywood vessel parameters were identified for dendroecological applications in oak.AbstractRecent improvements of methods used in tree-ring and quantitative wood anatomical studies have helped to widen the selection of parameters which contain environmental information. In the present study, we identified the most promising parameters with respect to signal strength, representativeness, and applicability in oak (Quercus robur L.) from two sites in Germany with different moisture regimes. We analyzed three tree-ring and 15 vessel parameters. Principal component analysis was used to detect clusters of relatively similar parameters. Correlation analysis and classical dendrochronological methods were used to select the most robust parameters. From the 15 initial anatomical parameters, six proved to be suitable for tree-ring anatomical studies based on our screening criteria. These were mean area of the vessels of the first row, mean of the five largest vessels, total vessel area, total area of the vessels excluding the first row, vessel density, and total vessel area as a percentage of tree-ring area. These parameters were applied to samples to search for lagged responses to positive and negative pointer years using superposed epoch analysis. Negative, i.e., dry, pointer years provoked no lagged changes in analyzed parameters at either site; whereas positive, i.e., moist, pointer years showed a lagged negative response of all parameters, which was more pronounced at the drier site.

Impact of climatic variation on growth of Fagus sylvatica and Picea abies in Southern Sweden

Abstract Growth and its relationship with recent competitive performance of Norway spruce and European beech were investigated in semi-natural mixed forests in southern Sweden. Dendroclimatological methods revealed the main influencing climate variables. The radial growth of beech is mainly determined by the late summer conditions from the previous year. The July temperature has become increasingly more important since the 1950s and even more significant since the 1990s. Before the 1950s, the main factor for spruce growth was the summer precipitation. This influence has nearly vanished, and the spruce trees react more distinctly to temperature of the previous summer. This shift in the climate signal indicates a sensitive response of spruce growth to changed conditions and points to a distinctly increased sensitiveness of spruce under future conditions. The competition interactions between mainly dominating spruce and mostly subordinate beech are already changing. European beech growth potential could benefit from warm summers and prolonged vegetation periods and increase its mean diameter in relation to spruce. In contrast, Norway spruce is more threatened by increased abiotic and biotic disturbances. The higher competitive vigour and changed vitality of beech and the lower vitality of spruce may alter the distribution boundaries of both species in Sweden.

Ökophysiologische Bedeutung von Zweigabsprüngen (Kladoptosis) unter besonderer Berücksichtigung der Symptomatologie von Quercus robur L.

ZusammenfassungIn der vorliegenden Arbeit wurde der als Kladoptosis bekannte Prozeß der Zweigabgliederung anQuercus robur L. untersucht. Danach ist die Anlage zur Ausbildung einer Trennungszone während des Knospenstadiums an allen Seitenknospen vorhanden. Dagegen können Triebe, die aus der Terminalknospe entstanden sind, nicht abgegliedert werden. Bei jungen Stiel-Eichen geht unmittelbar nach dem Austrieb der Seitenknospen ihre Abgliederungsfähigkeit verloren. Mit zunehmendem Baumalter verzögert sich die Formation regulären Xylems im Abzweigungsbereich der Seitentriebe.Die Aufrechterhaltung der Trennungszone bewirkt aufgrund ihres histologischen Aufbaus eine Reduzierung der hydraulischen Leitfähigkeit. Die mit einer Trennungzone ausgestatteten Zweige befinden sich in einer indifferenten Phase, in der sie von dem regulären Hydrosystem des Baumes separiert sind. Sie können nachfolgend durch Abgliederung vollständig von ihm getrennt oder durch Eingliederung permanent an das Hydrosystem angeschlossen werden. Bei zusätzlichen negativen Umweltbedingungen steigt der Anteil der nur provisorisch an das Hydrosystem des Baumes angeschlossenen Zweige. In dieser Situation setzt die Eingliederung — Bildung regulären Xylems — nur noch im Abzweigungsbereich der vitalsten Seitenachsen ein.Aufgrund der Reduzierung der hydraulischen Leitfähigkeit wird es dem Baum möglich, das ihm verfügbare Wasser selektiv in der Krone zu verteilen. Eine reduzierte Eingliederungsdynamik der Trennungszone erhöht den hydraulischen Widerstand des daran anschließenden Sprosses. Die in dieser Situation steigende Anzahl der Trennungszonen führt zur Förderung der eingegliederten Leitäste und schützt diese vor unkontrollierter Xylem-Kavitation.SummaryThe process known as cladoptosis has been investigated inQuercus robur L.. The results show an ontogenetic alteration of the hydraulic architecture which is additionally modified by the vigour of the tree.The preformation of the abscission zone is still present in all lateral buds during bud dormancy. Terminal shoots, however, do not form an abscission zone at their base at any time, which causes their inability to abscise. During juvenile ontogenesis the absciseability of the lateral buds is lost immediately after sprouting. In the further course of ontogenesis the formation of regular xylem (integration) within the stem junctions of the lateral shoots is retarded. The constricted conduits within the abscission zone limit hydraulic conductivity, equivalent to an increase in the hydraulic resistance. However, the absciseable twigs and branches are in an indifferent stage in which they are separated from the regular hydraulic system of the tree. In this stage hydraulically separated shoots are either connected by integration or disconnected by abscission. Negative environmental conditions increase the number of indifferent shoots. In this situation integration only occurs in the junctions of the most vigorous twigs.This special reaction optimizes the hydraulic conductivity by distributing a given water flow selectively within the branching. The hydraulic resistance of the shoot is increased by reduced integration dynamics. The increased number of abscission zones induced by unfavourable environmental conditions enables the tree to avoid runaway embolism during excessive droughts.The active control given by cladoptosis allows the tree to evaluate and control the xylem flow within its branching pattern. The integration and abscission of twigs varies according to environmental conditions. Years with water deficiencies reduce the photosynthesis of the indifferent (less vigorous) twigs and let them cavitate earlier, whereas photosynthesis of the youngest as well as the integrated twigs obviously remains unaffected.

Contrasting strategies for tree species to cope with heat and dry conditions at urban sites

Street trees planted at tree pits with impermeable pavements are exposed to a high level of both, atmospheric and edaphic stress. For many species tree physiology, optimal growth, and consequently long-term vitality may be hampered under these harsh conditions. Therefore, maintaining the vitality and promoting the ecosystem services provided by urban trees, for example aesthetic values and microclimatic benefits, it is important to establish trees with a high tolerance to stressful urban environments. Measurements of leaf gas exchange, leaf water potential, leaf surface temperature and chlorophyll-fluorescence were used for identification of specific response of Corylus corluna L., Ginkgo biloba L., Liriodendron tulipifera L., and Tilia cordata Mill. ‘Greenspire’. The summer months in 2013 with a period of heat and drought over eight weeks only interrupted by two rainy days were appropriate to access tree’s strategies to cope with low water availability. During the measurement period, the influence of high temperatures, high values of vapor pressure deficit (VPD) and low soil water availability on stomatal conductance, water-use efficiency (WUE) and leaf water potential (Ψmin, Ψmax ) was highest for Liriodendron followed by Ginkgo. These species showed high reductions in WUE in case of higher air temperatures and high values of VPD. Results indicate an avoidance strategy under increasing heat and VPD. In contrast, Corylus and Tilia followed a tolerance strategy indicated by decreasing values of Ψmin and lower reductions of WUE. In conclusion, wide species-specific variation in response to high temperatures and high VPD indicates that substantial potential exists in the selection for dry and hot urban places.

Lignicole Pilze an Schwarz-Erle )Alnus glutinosa [L.] Gaertn.) — welche Arten sind bedeutsame Fäuleerreger?

ZusammenfassungIn 5 unterschiedlich alten Schwarz-Erlen-Beständen des Nationalparks Vorpommersche Boddenlandschaft fanden in den Jahren 1997 bis 2000 mykologische Erhebungen und weiterführende phytopathologische Untersuchungen statt. Dabei sollten genauere Kenntnisse über das an Schwarz-Erle vorkommende Artenspektrum lignicoler Pilze gewonnen werden. Es wurde der Fragestellung nachgegangen, welche Spezies bedeutsame Holzparasiten und Fäuleereger sind. Im Ergebnis der mykologischen Erhebungen sind 40 verschiedene Pilzarten (34 Basidio-, 6 Ascomyceten) und bei den phytopathologischen Untersuchungen 4 weitere Basidiomyceten bestimmt worden. Außerdem wurden Hyphomyceten 9 verschiedener Gattungen zum Teil zahl- und formenreich festgestellt. Während die Mehrzahl der identifizierten Basidio- und Ascomyceten Weißfäuleerreger darstellt, geht von den diagnostizierten Deuteromyceten (Fungi imperfecti) überwiegend eine Moderfäuleaktivität aus. Die Untersuchungen ergaben, dass insbesondere folgende Pilzarten an Schwarz-Erle als bedeutende Verursacher der häufigen Stamm- bzw. Wurzel- und Stockfäulen gelten können: Erlen-Schillerporling(Inonotus radiatus), Hochthronender Schüppling(Pholiota aurivella), Hallimasch(Armillaria mellea s. l.) und Schiefer Schillerporling(Inonotus obliquus).SummaryFrom 1997 to 2000 mycological assessments and phytopathological investigations were conducted in five common alder stands of different ages in the national park “Vorpommersche Boddenlandschaft” (Western Pomerania, north-east Germany). The aim of the project was to extend the knowledge of the species spectrum of lignicolous fungi occurring on common alder, and to clarify which of the species are important wood parasites and wood rotting fungi. Mycological surveys resulted in the identification of 40 different fungal species (34 basidio and 6 ascomycetes); another 4 basidiomycetes had been verified in the phytopathological studies. Furthermore, hyphomycetes of 9 different genera — partly occurring in great numbers and great variety — were ascertained. While the majority of the determined asco- and basidiomycetes are white-rot fungi, the deuteromycetes (fungi imperfecti) mainly cause soft rot. As a main result of the mycological and phytopathological investigations the following species can be regarded as important agents of the frequently occurring stem, root and stump rots of common alder, respectively:Inonotus radiatus, Pholiota aurivella, Armillaria mellea s. l. andInonotus obliquus.

Competition in mixed stands of beech and spruce: effects of climate and ozone

The “Growth-DiVerentiation Balance Theory” assumes a trade-oV between parasite defense and increases in growth and competitiveness (Herms and Mattson 1992). Accordingly, increasing resource availability would induce a decrease in secondary metabolites, and hence defense capacity, relative to primary production. Since 1998, about 20 research teams have examined this theory in the interdisciplinary research center “Sonderforschungsbereich 607” (SFB 607), being conducted in Munich and FreisingWeihenstephan (Germany; Matyssek et al. 2005). In this issue, they present results from studies focusing on the eVects of ozone and drought stress on beech and spruce competing in mixed stands. The mature stand as one research object of the reported studies is “Kranzberger Forst”, a 55-year-old Norway spruce stand near Freising/Germany with groups of 62year-old beech. From the year 2000 on, a group of beech and spruce trees has been exposed to experimentally enhanced free-air ozone fumigation (Karnosky et al. 2001). Ozone was applied, through a novel methodological approach, via more than 100 PTFE tubes into the stand canopy in such a way that Wve spruce and Wve beech trees were exposed to a twice-ambient ozone regime, with ozone levels being restricted to below 150 nl li1 (Nunn et al. 2002; Werner and Fabian 2002; Karnosky et al. 2007). The Wrst paper introduces a novel approach to study the hydraulic architecture of coarse roots. Nikolova et al. (2008b, this issue) combined computer tomography, light microscopy, and sap Xow measurements in order to anatomically and functionally compare the conductive sapwood area of coarse roots between beech and spruce. Cumulative sapwood lumen area was 12% of the total coarse root cross-sectional area in both species. Normalized by that parameter, sap Xow rate increased with root diameter. Haberle et al. (2008, this issue) tested a conceptual approach to assess the amount of carbon available for trade-oVs between defense and growth. They monitored the variation in levels of nine defense-related metabolite groups within and between four consecutive growing seasons in mature beech and spruce trees. The diVerence between minimum and maximum metabolite levels was assumed to be dispensable between growth and defenserelated metabolism, ranging between 2 and 5% of gross primary production. A set of papers describes the eVects of ozone and drought, especially during the extreme summer of 2003. Betz et al. (2008, this issue) investigating the shikimate pathway in the greenhouse and in the Weld, caution against uncritical comparisons between greenhouse-grown saplings and mature forest trees. Rodenkirchen et al. (2008, this issue) studied the eVects of ozone and CO2 on the competitiveness of beech and spruce saplings under standardized phytotron conditions. Ozone stress reduced nutrient eYciencies in beech, suggesting a higher demand for N and P in defense at the expense of competitiveness. Elevated CO2 counteracted the eVects of ozone. In mature ozonefumigated trees, the extreme summer of 2003 had no eVect on the concentrations of P and K in the leaves, whereas the control trees had signiWcantly lower levels of these nutrients in 2004 (Gottlein et al. 2008, this issue). Although ozone fumigation reduced absolute tree diameter increment at breast height in spruce, there was no such eVect in beech S. Rust · A. RoloV (&) Institut fur Forstbotanik und Forstzoologie, TU Dresden, Postfach 1117, 01735 Tharandt, Germany e-mail: roloV@forst.tu-dresden.de