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A new method for the preparation of wood samples for high-resolution reflected-light microscopy in combination with a species-specific image analysis system is introduced. The method is based on an ultraprecise single-point diamond flycutter equipped with air bearings and functions on the basis of a rotating diamond edge. Extensive and very smooth surfaces can be produced on increment cores as well as entire cross sections. Hence, this technique provides the prerequisites for a continuous microscopic analysis across large tree-ring sequences, or entire cross sections. Patching or sub-sectioning is not required. The high-resolution analysis of cell structures of spruce and oak presented here introduces new approaches for describing and predicting reactions of diameter growth to various environmental events.

In this paper the rst measurement of the hy- perne population of a photofragment is presented. The population of the hyperne levels of the 2 3=2(J =7 =2) state of OH out of photodissociation of cold H2O turns out to be statistical. After photodissociation of water at 157 nm within a Fabry-Perot microwave cavity the nascent OH formed in the v =0 , J =7 =2 state (probed by LIF) is stimulated by microwave radiation. From saturation data the population in each hyperne level in both -doublets is determined.

A mathematical model for the explanation of OH masers in regions of star formation is presented. The model is based on the assumption that grains of different sizes are present at the border of the HII regions where they are exposed to the heat- and VUV-flux of a new born star. The grains evaporate water because of the heat flux from the central star. The subsequent dissociation of water by VUV together with IR relaxation generates a high OH abundance and yields strong inversion in the OH Λ -doublets for all maser transitions observed in star forming regions. The gain of the observed masers is determined as a function of the photodissociation rates for different evaporation rates. In this first approach IR pumping and collisions are neglected although they may change the quantitative predictions. The results show that gain may be high enough to explain all observed masers near new born stars under reasonable assumptions for the astrophysical conditions found at the border of HII regions. Based on the model predictions are made concerning intensities, locations and variability of the different maser transitions.

The photodissociation of tert-butyl nitrite, (CH3)3CONO, at 193 nm, is examined by a new experimental setup for photofragment imaging. Probing nascent NO fragments time delayed (several μs) and spatially displaced (relative to the dissociation event) by planar laser-induced fluorescence (PLIF) yields quantum state specific velocity distributions. In this way the internal and the translational energy distributions are determined simultaneously, permitting a very detailed understanding of the energy partitioning of the available energy among the product degrees of freedom and allowing one to analyze correlated product formation. The results differ very strongly from previous photodissociation studies of aliphatic nitrites performed at smaller photon energies, since a different dissociation channel is taken.

Laser induced fluorescence of microwave stimulated OH molecules from H2O photodissociation is investigated as a first step in a series of laboratory experiments to understand features of astronomical OH masers. The inversion between the Π3/2, J=7/2 Λ‐doublet states of OH generated via photodissociation of cold H2O at 157 nm is shown to be 1.8:1. Within a microwave, Fabry–Perot cavity tuned to the resonance of one of the main hyperfine transitions in this Λ doublet it is possible to stimulate all inverted OH molecules. The linewidth of the two main microwave transitions is measured as a function of the microwave power and interaction time. The results show that Doppler broadening is negligible at short interaction times of the molecules with the microwave field.

This article describes a new, direct way to measure the time evolution of single light pulses in the subnanosecond region using time‐of‐flight analysis. The light pulse is coupled into a set of 40 optical fibers of increasing length arranged in an array. The output of the fiber array is imaged onto a fast gated optical imager (gatewidth 100 ps) coupled to a CCD camera (12 bit). The intensified part of the pulse of each fiber corresponds to the intensity of the light pulse at a different time due to the different transmission time of each fiber. Additional, two‐dimensional (2D) spatial resolution is possible if image guides are used instead of fibers. The temporal resolution is limited by the gatewidth of the detector. The difference in length between the longest and the shortest fiber determines the total period of time displayed by the system (1 ns). The pulse characteristics of a recently developed short‐pulse Raman‐excimer laser are analyzed as an example of an application. Laser parameters like pulse ...

The choice between different forest management practices is a crucial step in short, medium, and long-term decision making in forestry and when setting up measures to support a regional or national forest policy. Some conditions such as biogeographically determined site factors, exposure to major disturbances, and societal demands are predetermined, whereas operational processes such as species selection, site preparation, planting, tending, or thinning can be altered by management. In principle, the concept of a forest management approach provides a framework for decision making, including a range of silvicultural operations that influence the development of a stand or group of trees over time. These operations vary among silvicultural systems and can be formulated as a set of basic principles. Consequently, forest management approaches are essentially defined by coherent sets of forest operation processes at a stand level. Five ideal forest management approaches (FMAs) representing a gradient of management intensity are described using specific sets of basic principles that enable comparison across European forests. Each approach is illustrated by a regional European case study. The observed regional variations resulting from changing species composition, stand density, age structure, stand edges, and site conditions can be interpreted using the FMA framework. Despite being arranged along an intensity gradient, the forest management approaches are not considered to be mutually exclusive, as the range of options allows for greater freedom in selecting potential silvicultural operations. As derived goods and services are clearly affected, the five forest management approaches have implications for sustainability. Thus, management objectives can influence the balance between the economic, ecological, and social dimensions of sustainability. The utility of this framework is further demonstrated through the different contributions to this special issue.

Les forets de chenes sont economiquement et ecologiquement importantes en Europe et dans l'est des Etats-Unis d'Amerique. Dans le premier cas, les chenaies sont revenues grâce a la regeneration artificielle sur de nombreux sites ou elles avaient ete remplacees par d'autres especes. Des methodes pour la regeneration naturelle et artificielle sont recherchees. Les taillis sont remplaces par des futaies dans beaucoup d'endroits en Europe. Les methodes utilisant de larges espacements et des rotations courtes qui produisent des bois de haute qualite adaptes aux stations sont maintenant prises en consideration (.)

The amount, fluctuation and duration of increment response to fertilization (liming) in three regions of southwestern Germany is described. After liming, additional yield increases slowly while after N-fertilization, there is a rapid yield increase. A long-lasting high response was found to a combination of liming, P- and N-fertilization. This response was regionally different and was influenced by climatic conditions during the years after fertilization.

For chemical analysis of submicron particles, mass spectrometric methods have the disadvantage of being destructive. Thus, a nondestructive elemental and chemical mapping with a high spatial resolution prior to mass analysis is extremely valuable to precharacterize the sample. Here, first results are presented of combined XANES (x-ray absorption near-edge structure) and PEEM (photoemission electron microscopy) measurements on a cosmic grain fraction from the Murchison meteorite. This nondestructive full-field imaging method is well suited for a quantitative analysis and for a preselection prior to detailed mass spectrometric investigations with isotopic resolution/selectivity. A spectral unmixing algorithm helped to distinguish between elements in different binding surroundings and therefore to obtain lateral information about the elemental composition and the chemical structure. Individual ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ and $\mathrm{Si}{\mathrm{O}}_{2}$ grains as well as Cr-rich grains could be identified among the majority of SiC grains. This method is suited not only for meteoritic material but can in general be applied to composite grain materials of submicron sizes.

Trotz der Hinwendung vieler Forstbetriebe zum naturnahen Waldbau und der konsequenten Begrundung naturnaher Mischwalder befinden sich in Sudwestdeutschland heute noch auf groser Flache Waldbestande, bei denen sich die Frage des Waldumbaus stellt. Waldumbau zielt unter diesen Bedingungen darauf ab, die Stabilitat der Walder zu erhohen, und die an sie gestellten Anforderungen der Gesellschaft besser als bislang zu erfullen (Kapitel 3 in diesem Buch). Orientiert an dem Leitbild laubbaum- und strukturreicher Walder setzt der Waldumbau bevorzugt in nicht standortsgemasen, gleichaltrigen Fichtenreinbestanden an, die mit Laubbaumen, insbesondere der Buche, im Zuge des Voranbaus angereichert werden. Dem Entwicklungsziel entsprechende Mischbestande zeichnen sich durch eine hohe strukturelle Vielfalt und geringere Risikodisposition gegenuber baumartenspezifischen Schadigungen aus. Die folgenden Ausfuhrungen tragen dazu bei, die Eignung von Bestanden fur Uberfuhrungsvorhaben zukunftig umfassender beurteilen und hieraus betriebliche Entscheidungen und Strategien ableiten zu konnen. Fur die Uberfuhrung von gleichaltrigen Fichten- und Tannen-Bestanden spielt die Stabilitat der Einzelbaume eine entscheidende Rolle fur die Wahrung der Bestandesstabilitat in der Uberfuhrungsphase. Das Zuwachspotenzial der spater als Stabilitatstrager fungierenden vorherrschenden Fichten und Tannen des Uberfuhrungsbestandes nach einer starken Freistellung ist eine wichtige Grundlage fur Uberfuhrungsentscheidungen. So wird der Frage nachgegangen, welche Eigenschaften Fichten und Tannen aufweisen mussen, um einen Altersklassenwald fur Uberfuhrungsvorhaben geeignet erscheinen zu lassen. Ist die Buche in Uberfuhrungsbestanden bereits vorhanden, sind zusatzlich

Time series are time-stamped sequences of values which represent a parameter of the observed processes in subsequent time points. Given a set of time series describing a set of similar processes, the model of the behavior of processes is constructed as a range of classification trees which describe the characteristics of each particular time point in series. An algorithm for matching a sequence of values with the model is used for searching common patterns in the sets of time series, and for predicting the starting time points of undated time series. The algorithm was developed and analyzed in the frame of the study of tree-ring time series. The implementation and the empirical analysis of the algorithm on the tree-ring time series are presented.

After analyzing nutrient contents of the soils and needles in Norway spruce stands in the northern Black Forest in the 1960s, Moll (1965) noted that the magnesium content of the sites with well-growing stands on higher variegated sandstone was 40–300 times as high as that of the poorly growing stands. He described the role of magnesium ‘as an essential activator within the nutrient cycles, especially in the roots’ and drew attention to its stimulating effects on leaf-substance production.

Growth of European forests has changed considerably in recent decades. Although the methods applied in the 22 studies varied according to the data available, most studies showed the same general trend: site productivity has increased on many sites (Table 1). An increasing growth trend has been observed in the southern regions of Northern Europe, in most regions of Central Europe and in some parts of Southern Europe (Fig.1). No clear trend was found in the most northern part of Europe, in rare cases in Central Europe and in some observations in Southern Europe. A decreasing trend was found in exceptional cases where extreme growth conditions such as intense exposure to pollutants or exceptional climatic conditions occurred.

The annual volume increment of Norway spruce and silver fir stands in the Black Forest varies greatly and is correlated with precipitation during the growing season and to some extant with temperature. Mortality is also correlated with climatic variation. Thus, low precipitation ouring the growing season is considered to be a main stress factor even at higher elevations in the Black Forest mountains where the average precipitation level is high. By silvicultural treatment, climatic stresses may be reduced to some extent. Increment on fertilized Norway spruce plots reacted more sensitively to drought when fertilizer effect on increment was high. The high productivity in recent decades may have been caused partly by atmospheric deposition. A higher susceptibility to environmental stresses may be a consequence.

A theoretical ansatz for correction of the chromatic and spherical aberration of round-lens systems in photoemission and low-energy electron microscopy (PEEM/LEEM) is presented. The method is based on fast switching of electrical acceleration or lens fields. It exploits the highly precise time structure of pulsed photon sources like electron storage rings for synchrotron radiation or pulsed lasers as well as pulsed photocathodes of a LEEM. The initial results indicate that the approach is a promising alternative to the implementation of multipole or mirror correctors in the electron optical column of a microscope.

Occurrence of severe dieback, decline, and mortality in oak (Quercus spp.) stands have been reported frequently during the last 20 years in various parts of the world. As a result, numerous research activities have been initiated. 'Recent Problems in Oak Decline' was also the topic of a meeting of the International Union of Forestry Research Organizations (IUFRO) units Sl.06.00, S2.06.00 and S2.07.00 at the IUFRO XX World Congress held in Tampere, Finland during August 1995. A selection of five papers presented during this meeting is published in this issue in which symptoms of oak damage are characterized and potential causal factors as well as factor combinations (insects and fungi, climatic factors, site-related aspects, genetics) are described. DONAUBAUER, Austria, summarizes the macroscopic symptoms of oak decline and reports on the regional role of parasites as predisposing and as contributing factors. S!WECKI and UFNALSKI, Poland, give a review of oak stand decline in Poland with special reference to the role of climatic factors. They found that climatic conditions had a decisive influence on the vigour of Quercus robur. Increased frequency of dry years resulted in the complex phenomenon of oak decline. STEINER, USA, observes oak decline in the context of genetic management. In order to minimi ze susceptibility to oak decline he suggests forest practices which favour the maintenance of high levels of genetic variation and the use of local provenances in artificial regeneration and large seedling populations. Prediction models for estimating mortality of oak due to gypsy moth (Lymantria dispar), based on a new analysis using defoliation intensity classes as a variable along with species, crown position, and crown condition, are presented by GOTTSCHALK et al. USA. STANDOVAR and SOMOGYI, Hungary, stress the importance of site characteristics and tree growth. Oaks seem more susceptible to decline outside of their natural range. Most presentations stressed the necessity for further investigations because the results are still preliminary and there is a wide variation in responses . The various methodological approaches used in these papers are of special interest. We hope that this collection of papers contributes to the progress on the long path to a better understanding of oak ecosystems and of improving the health of the world's oak forests.