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Hitherto, there are only few studies that have analysed the variation of P contents in individual tree rings to reconstruct fluctuations in soil P availability. Therefore, this pilot study aimed to assess the relationship between changes in P content in tree rings and known changes in soil P availability resulting from fertilization of Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) in fertilization trials at two different sites. We compared P contents in single tree rings from fertilized and unfertilized plots formed before and after P fertilization and assessed (1) whether fertilization leads to an immediate increase in P uptake and higher P contents in tree rings formed after fertilization, and (2) whether P is translocated to older tree rings that were formed before fertilization. After application of 70 kg P ha−1, a prompt and extended increase in relative wood P contents could be observed in both Norway spruce and Scots pine. However, only at the Norway Spruce site, this increase could be properly assigned to a P fertilization signal in heartwood rings formed after fertilization. In sapwood rings, however, P fertilization signals were masked by the inherent increase in P content from older towards younger sapwood rings, which was at least one order of magnitude higher than the increase from fertilization. We could not observe a P translocation into older tree rings, which existed as sapwood rings at the time of fertilization. This pilot study underlines the potential of dendrochemistry for reconstructing changes in soil P availability and improves the conceptual basis for further dendrochemical research, not only in fertilized but also in unfertilized forest ecosystems.

In the Mediterranean climate regions, drought events are expected to affect the growth of forests ecosystems by changing trees growth rates and eventually inducing shifts in their growth patterns. Cork oak ( Quercus suber L.) is a strictly western Mediterranean tree species periodically harvested for its bark, the cork. So far, cork oak has received limited attention for dendroclimatological studies due to its typical faint and erratic tree wood rings. Moreover, its distinct cork rings chronologies have been completely neglected. In this study we introduce an approach using cork ring chronologies dated back 9–10 years for climate response. Despite enhancing interannual variability and increasing statistical response to short-term climatic variability, still poorly understood, this study will possibly allow infer long-term climate response. We analyzed the cork ring chronologies of 55 cork samples collected in mature (under exploitation) trees in three distinct locations in southwestern Portugal. Cork growth recorded a high climate signal, with highly significant and coherent responses to the yearly climate-related sources of variation. We successfully assessed trends of cork growth via correlation analysis including selected climate variables among mean monthly temperature, monthly precipitation and, on an annual basis, eight precipitation indices. The high mean sensitivities and inter-series correlations found for cork ring chronologies combined with the significant variance explained by climate variables suggest that climate is likely one dominant signal that affects cork growth, but local environmental stresses can decisively affect this (climate) signal. Assuming cork growth as a proxy for cork oak growth, it seems conceivable that despite the trees being highly resistant to drought stress, cork oak woodlands in southwestern Portugal would have to face lesser growth in a global warming scenario.

Studying intra-annual wood formation dynamics provides valuable information on how tree growth and forests are affected by environmental changes and climatic extreme events. This study has the aim to evaluate and to quantify synergetic potentials emerging from a combination of current state of the art techniques used to monitor intra-annual wood formation processes. Norway spruce trees were studied in detail during the growing season 2009 with weekly sampling of microcores, high resolution point-dendrometers and wood anatomical analysis. The combination of the applied techniques allowed us to convert the spatial scales of radial tracheid diameter profiles to seasonal time scales and to synchronize fluctuations in intra-annual cell diameter profiles. This spatiotemporal information was used to validate the recently introduced software MICA ( Multiple interval-based curve alignment ) . In comparison to the conventional approach of averaging profiles of tree ring variables, the MICA aligned profiles exhibit a significantly higher synchronicity of the averaged data points. We also demonstrate two new features in the MICA application that enable to extrapolate spatiotemporal information between intra-annual profiles for the construction of robust mean (consensus) profiles that are representative for the population dynamics. By using a set of complementary techniques in an integrated approach, this study highlights a new methodological framework that can contribute to a better understanding of the environmental control of wood formation during the growing season.

The crossdating of tree-ring series is typically based on tree-ring width sequences, which is a crude abstraction of the growth signal stored in tree rings. In contrast, intra-annual wood density data allows a much more detailed comparison of wood growth processes and new measurement techniques scale well to measure large amounts of samples. Thus, chronologies of intra-annual densitometric curves can be built. Here, we investigate to what extent intra-annual wood density information can improve crossdating. We evaluate different approaches on a data set of Norway spruce trees (Picea abies) and compare the results to standard methods that are based on ring width or maximum density. Our results show that intra-annual densitometric data indeed increases crossdating success rate notably for short tree ring series that cover less than 25 years.

Preparation of micro sections to measure cell wall thickness and lumen diameter is a widely used method in the fields of dendroecology, dendroclimatology and tree physiology. Efficient sample preparation and image analysis are critical for studies with long time series and large sample sizes. Recently, there have been substantial improvements in micro section preparation techniques, including a corn starch-based non-Newtonian fluid treatment. This method reduces cell wall damage during cutting with a microtome, which in turn decreases artifacts during image analysis. Although this procedure does in fact improve sample quality, we found starch grains sometimes to be difficult to remove and to cause artifacts during image analysis. This technical note outlines a simple, fast and effective steam treatment that causes starch gelatinization and a reduction in the number of starch grain artifacts.

High frequency (HF) densitometry has been suggested as an alternative to X-ray densitometry for high resolution measurements of wood density. The propagation of this innovative technology so far has been limited somehow due to several unanswered questions, e.g. concerning requirements of sample preparation or integration widths of differently sized dielectric probes used. This study shows that the measurement precision of HF densitometry is high, its accuracy, however, is dependent on perfect probe-sample contact and thus requires high quality sample surface preparation as well as stable mechanics of the densitometer mounting. Preparation with an ultra-precise diamond flycutter is a reliable standard technique with precisely done sanding of samples being a possible alternative. Different geometrical setup and dimensions of individual probes’ electrodes result in different integration widths. The integration width is determined by the distance between electrodes and the thickness of the electrodes in the probe tip.

Knowledge gaps still exist concerning the resilience of Norway spruce growth to changing climate conditions especially outside their natural range. We used a dendroecological approach to assess growth resilience of Norway spruce to changing moisture availability on different sites in southwest Germany near the xerothermic range limits of this species. We described the temporal and spatial variation of Norway spruce tree-ring width, comparatively assessed the response of tree-ring width to changes in moisture availability between different study sites and assessed the capacity of Norway spruce growth to absorb disturbance by drought. To assess the capacity, we applied the concept of resilience and the concept of early-warning signals to tree-ring width data. The results indicated no adequate short-term adaptive capacity to changing climate conditions for the respective Norway spruce trees within the study period. Furthermore the results showed an enhancement of growth synchronicity among the trees at each study site which is highly correlated with changes in moisture availability. Critical slow down, loss of buffering ability and simultaneous increase in spatial correlation are indicative of a loss in growth resilience of Norway spruce. We assume that the capacity of Norway spruce trees to absorb disturbance in terms of their growth response to moisture deficits decreased presumably as a consequence of a series of drought events in the more recent past.

Wood density is a trait of paramount importance for the assessment of wood quality, in dendroclimatology and in attempts to enhance biomass and carbon estimations. X-ray densitometry is the established but costly and time consuming method for high resolution measurements of wood density. An inexpensive and rapid alternative is high frequency (HF) densitometry, which until now has only been yielding relative density variation profiles that were not calibrated to true volumetric mass density. This study examines the potential of calibration functions for density values obtained from HF scanning and compares the results to volumetrically determined true wood density and density derived from optical image analysis. We found that mean HF values of 112 stem discs of different tree species were highly correlated (R2 of 0.9) to the samples’ true densities. Species specific calibration functions performed significantly better than a pooled model, whereas grouping according to basic wood anatomical types did not improve the model significantly. Prediction errors for species specific calibration functions were reasonably low (S(Yˆi)

Projected changes in climate highlight the need for a better understanding of the effects of forest meteorological factors on the growth of Central European forests. In this study, we used automatic point dendrometers to investigate day-to-day stem radius variations of 24 European beech trees ( Fagus sylvatica L.) in relation to daily forest meteorological conditions. Study trees were located at opposing north-east (NE) and south-west (SW) exposed slopes of a valley in southwestern Germany, and monitored over a six-year period (2001–2006). Seasonal courses of day-to-day stem radius variation (SRV) were analyzed in hierarchical mixed models based on first-order derivatives of cumulative Weibull functions. Responses of SRV to weather conditions were found to be remarkably synchronic within and between the NE and SW aspect. This latter finding suggests that trees at both slopes may have adapted to prevailing environmental conditions. Further, responses were found to be mostly linear within the range of forest meteorological conditions encountered in this study. Highly distinct effects of forest meteorological fluctuations were observed when daily lags were considered. The daily parameters mean air temperature at lag1 (=one day lag), maximum air temperature and soil water content at lag1 were found to explain 59% of the variance in day-to-day stem radius variations. We discuss the complex responses of SRV to lagged and current-day weather variables in relation to stem hydraulics and growth, varying time scales of tree physiological processes, and pre-conditioning of tree water status.

The High-Frequency (HF) densitometry measures relative density variations on wood samples utilizing the dielectric properties in wood. This method is based on the propagation of an electric stray field through the surface-near region of a wood sample. We studied experimentally the penetration depth and the differentiation abilities of the HF-densitometry method on wood samples. Two experimental approaches showed that penetration depth is related to the geometrical dimensions of the micro-electrode measuring system. Characteristic patterns of the HF-output signal were used to determine the resolution abilities of each HF-probe. Due to a very small integration area geometric structures of earlywood cells of Norway spruce were indicated by stepwise profiles in the HF-output signal pattern. With the High-Frequency densitometry it was possible to distinguish different cell structures due to their variations in wood density up to a resolution of 1 μm. In addition it was possible to determine wood density variations at various resolution levels. Based on the respective resolution abilities and penetration depths of five different purpose-built HF-probes we show the optimal operating conditions for measurements on wood of this indirect densitometry method.

Mediterranean environments are of special interest for the study of the relationships between climate, growth and anatomic features. Dendrochronological techniques were applied at eight sampling sites that were selected throughout the natural distribution area of Pinus halepensis in the Iberian Peninsula. The objectives of this paper were: (i) to identify relationships between radial growth and climate for different crown classes of Aleppo pine ( P. halepensis Mill.); (ii) to quantify the presence of intra-annual density fluctuations (IADFs) according to crown class and cambial age; (iii) to establish the relationships between IADFs and climate. In the more mesic sites, dominant trees showed higher climatic sensitivity than suppressed trees, while in the more xeric sites suppressed trees showed higher sensitivity than dominant trees. Tree-ring growth of both crown classes correlated positively with precipitation during and prior to the growing season. IADFs were more frequent in young than in old stands without differences between crown classes. Precipitation in April and December was positively correlated to the occurrence of IADFs, while precipitation in July correlated negatively. A higher frequency in IADFs occurred in the last 50 years, which coincides with the increase in drought events in the Iberian Peninsula.

In densely populated regions, forests can help protect communities and infrastructures from natural hazards such as avalanches and rockfall. To promote the protective function, substantial efforts are made to actively manage forest stands. In 2009 alone the Swiss government invested more than 60 million sfr for the maintenance of protection forests. However, to date there has been no comprehensive evaluation of how the structural development of actively managed stands differs from that of passively managed stands in the Alps. Over the past century the structure of Norway-spruce dominated subalpine forests of the Swiss Alps has been changing and it is not clear how these changes affect the potential protective function of these forests, as well as other forest functions such as wildlife habitat. Furthermore, it is not clear how stand dynamics and structural changes differ between stands that are actively managed and those that are passively managed, and thus to what degree active efforts of forest management are contributing to stands that actually have a greater protective function than passively managed forests. In this study, we analyzed the dynamics of subalpine forests using time series of forest inventory data and examined the influence of active vs. passive management, exposition, distance to treeline, elevation and slope steepness on stand structure and dynamics. We analyzed data from 395 plots in dense, subalpine, spruce-dominated forests in the Swiss Alps. Data were collected during three distinct periods (1983–1985, 1993–1995 and 2004–2006) as part of the Swiss National Forest Inventory (NFI). Using regression trees and multivariate statistics, we investigated which factors have the most important influence on tree growth and stand development. Overall, forest density increased significantly over the last 20 years and the predominance of dense forests increased at higher elevations. However, forest density has not increased in actively managed forests over the past 10 years. In passively managed stands, density was higher on south-facing slopes than on north-facing slopes. The volume and density of dead wood has increased over the last 20 years in both actively managed and passively managed forests. Active management over the last 20 years has maintained forest conditions that adequately maintain stands’ protection functions in the Swiss Alps. However, stand development, especially increasing density, in the passively managed stands of the Swiss Alps suggests that the majority of passively managed stands also provide adequate protective functions against rock and avalanche hazards without the high costs of active management.

Producing high value veneer wood requires that the tree bole be branch-free. This can be accomplished by natural or artificial pruning. Since wild cherry does not self prune well, pruning artificially is the only practical option. The study analysed the effect of conventional whorl-wise pruning and selective pruning, on height growth, diameter growth and secondary shoot development of wild cherry. Four pruning treatments were applied on cherry trees in summer 2007, one group of cherries was left unpruned to serve as a control: treatment C1 (upper 5 whorls left), C2 (upper 3 whorls left), S1 (removal of branches larger than 3 cm or with an angle to the stem

The formations of compression wood and eccentric radial increment are two phenomena that are so closely associated that they cannot be readily discussed separately. However, various studies suggest that their formation is stimulated by different mechanisms and that there is no functional relationship. While the formation of compression wood is a reaction of coniferous trees to negative gravitroptic scenarios which enables the trees to recover from displacement, one-sided radial growth promotion is stimulated by unilateral mechanical strain on the cambium for lowering stress peaks. This study offers an approach to quantify the relation of both phenomena in stem cross-sections and single growth rings. Samples of 56 Norway spruces ( Picea abies [L.] Karst.) from sites differing in slope and exposure to the prevailing wind direction were examined for their cross-sectional compression wood distribution and eccentricity in radial increment. The assessment of both phenomena on stem cross-sections was based on their spectral properties in reflected light. Hyperspectral image analysis allowed detection of compression wood distribution as well as measurement of annual radial increment along eight radii, oriented by compass direction. Since the distributions of both phenomena comprise both a directional component as well as amplitude in annual reference, these data were handled as vectors. Circular statistics were applied to describe and quantify their relationship and to test both phenomena for the inducing environmental factor that stressed the tree. The direction of compression wood formation and eccentric growth is significantly positively correlated. In the majority of observations a unimodal distribution of both phenomena is given. Mostly strong one-sided compression wood formation is associated with a coincident direction of eccentric radial increment. However, stem cross-sections with a distinct direction of compression wood were observed without a dominating direction of eccentric growth, and vice versa. Bivariate statistics that consider vector direction as well as vector length have proved to be very helpful in retrospectively identifying possible initiating environmental factors for both phenomena at a given site. The location of standard and confidence ellipses in relation to the assumed direction of action is a strong indication for or against an assumed environmental factor.

Two-photon microscopy is indispensable for deep tissue and intravital imaging. However, current technology based on single-beam point scanning has reached sensitivity and speed limits because higher performance requires higher laser power leading to sample degradation. We utilize a multifocal scanhead splitting a laser beam into a line of 64 foci, allowing sample illumination in real time at full laser power. This technology requires charge-coupled device field detection in contrast to conventional detection by photomultipliers. A comparison of the optical performance of both setups shows functional equivalence in every measurable parameter down to penetration depths of 200 μm, where most actual experiments are executed. The advantage of photomultiplier detection materializes at imaging depths >300 μm because of their better signal/noise ratio, whereas only charge-coupled devices allow real-time detection of rapid processes (here blood flow). We also find that the point-spread function of both devices strongly depends on tissue constitution and penetration depth. However, employment of a depth-corrected point-spread function allows three-dimensional deconvolution of deep-tissue data up to an image quality resembling surface detection. © 2007 by the Biophysical Society.

Variations in tree-ring structure from pith to bark of mature Norway spruce (Picea abies Karst. (L)) grown under contrasting climate conditions (warm-dry vs. cool-humid) in south-western Germany were investigated. Sample trees were from even-aged stands where no intensive silvicultural treatments had taken place. The cell number (CN), diameter (CD), lumen diameter (CL) and wall thickness (CW) were measured from stem cross-sections taken at breast height. A raw data chronology of each cell parameter was established for the whole annual ring (AR), earlywood (EW), latewood (LW), and transition wood (TW). The long-term trends of the cell parameters were generally non-linear, parameter-specific in AR and EW and similar over sites. Those in LW were site-specific and similar over cell parameters. The variation of the same parameter, expressed by the coefficient of variance (CV), tended to increase from EW towards LW and was clearly higher for CN than for other cell parameters of all tree-ring zones. Trees from the warm-dry site had more LW cells and substantially thicker CW, whereas those from the cool-humid site had larger EW cells. These observed differences are likely due to the hydraulic adaptation mechanisms of trees to different site conditions.

At the macroscopic level, the detection of tree rings of diffuse porous wood is still a major issue. As an alternative method to conventional preparation techniques, wood decay fungi were employed as analytic tools for tree ring analysis in diffuse porous wood. Wood blocks of sycamore (Acer pseudoplatanus L.), silver birch (Betula pendula Roth.) and aspen (Populus tremula L.) were incubated for 4, 8 and 12 weeks with two brown rot fungi, Fomitopsis pinicola and Laetiporus sulphureus, respectively. In addition, exposure of tree rings in wood degraded under controlled conditions was compared with several sanding and staining techniques and/or combinations of the latter. The ability to discern tree rings in the treated wood varied depending on the wood spp., method applied and duration of degradation. Exposure of annual ring borders in degraded sycamore and birch wood samples was apparently superior to conventional methods. In contrast, annual ring detection in aspen wood was greatly enhanced when both methods were applied. Further studies are required to improve the potential use of wood decay fungi as analytical tools in tree ring analysis.

In Europe temperate forests play a prominent role in timber production, nature protection, water conservation, erosion control and recreation. For centuries temperate forests in Europe have been affected by forest devastation and soil degradation. Applying great efforts to eliminate the severe wood shortage of those days, countermeasures were taken during the last 150 years by regenerating and tending highly productive forests. High growth rates and an increasing growing stock of these forests indicate that formerly stated goals have been successfully achieved. Coniferous species were often favoured because they were easy to establish and manage, and gave reason for high volume growth expectations. Today coniferous forests expand far beyond the limits of their natural ranges. These changes have been accompanied by a loss of biodiversity, a shift to nonsite adapted tree species and reduce the resistance against storms, snow, ice, droughts, insects and fungi. Some of these hazards were further intensified by the increasing average stand age, as well as in some areas by severe air pollution. Climatic fluctuations, especially changes in the frequency and intensity of extreme warm and dry climatic conditions and of heavy storms, had considerable impact on forest ecosystems. The changing demands of today require a widened scope of forest management. Society is asking for sustainable forestry emphasizing biodiversity and naturalistic forest management. It is of great economic and ecological relevance to know on which sites today's forests are most susceptible to climatic and other environmental changes and hazards. In those areas adjustments of management through a conversion the prevailing forests towards more site adapted mixed forests needs to be considered with priority. The high diversity in site conditions, ownership, economic and socio-cultural conditions require strategies adapted to the local and regional needs. Higher resistance of forests will increase economic and social benefits of forests and reduce the risks by maintaining sustainable forestry.

Regional and temporal growth variation of Norway spruce (Picea abies (L.) Karst.) and its dependence on air temperature and precipitation were compared in stands across latitudinal and altitudinal transects in southwestern and eastern Germany, Norway, and Finland. The temporal variation of radial growth was divided into two components: medium- and high-frequency variation, i.e. decadal and year-to-year variation, respectively. The medium-frequency component was rather different between regions, especially the southern and northern ones. However, within each region the medium-frequency growth variation was relatively similar, irrespective of altitudinal and latitudinal differences of the sample sites. A part of the high-frequency variation was common to all four regions, which suggests that some factors synchronising tree growth are common for the entire study area. The high-frequency component of growth was more strongly related to monthly air temperature and precipitation than was the medium-frequency variation. The limiting effect of low temperatures was more significant at northern as well as high-altitude sites, while the importance of precipitation increased in the south and at low altitudes.

Summary Information about forest growth is essential for sustainable forest management. Not only site conditions, species composition and age structure have been modified by human activities but also economic, political and social conditions and aims have changed. Updated site – and species related growth information is needed for efficient management. Information on forest growth does not only describe the volume production potential of forests and the dimension and quality of the produced wood but also is a valuable base for understanding interactions between trees and their environment. Tree rings provide precise information on past growth reaction to environmental changes. They allow a better understanding of sensitivity of species on a given site to environmental changes and provide information for risk assessment. Tree rings support the choice of tree species composition and the analysis of age effects on forest growth. Effects of spacing are indicated by ring width. Tree rings analyses improve wood quality control and contribute to cost efficient forest management.

Summary Tree-rings are a unique source of long-term data and have often been used in studies aimed at understanding and quantifying the impact of air pollution on forests. A variety of approaches have been used, ranging from traditional dendrochronology to studies focussing on the chemical and physical properties of tree-rings. However, there are some issues to be considered when attempting to use tree-rings as a response indicator in air pollution studies and when inferences over large geographical scales are being made. These issues include the inherent ambiguity of tree-ring width as indicator of air pollution effects, the absence of reference data, the problems associated with integrating traditional dendrochronology with more complex ecosystem studies and the relatively poor attention paid to sound statistical design in some air pollution impact studies. Together with progress in specific disciplines like climatology, biochemistry, genetics, tree physiology, tree nutrition and soil science, the interdisciplinary and international collaboration in the analysis of environmental effects on tree growth will increase the research potential of tree-rings.