Heinrich Spiecker

Growth Trends in European Forests

Annual ring data collected from strict nature reserves and long-term permanent plots of the Finnish Forest Research Institute (ME1LA) did not reveal any longterm trend in the radial increment of Scots pine (Pinus sylvestris) in the southern part of Finland during the last 100 years. This result was supported by the analysis of stand wise increment data from permanent thinning experiments. The height development of dominant sample trees had been faster than that of previous site index curves. This was supposed to be mainly due to differences in the data of this study and of the index curves. According to our investigations, there were some indications of increasing productivity on some sample plots in the southernmost part of the country during the last 40 years. Possible reasons for non-existing growth trends are as follows: 1. The wide climatic variation of tree growth in northern latitudes could conceal the possible trend. The years 1961-1990 were slightly cooler than the years 1931-1960 in Finland. 2. The S0 2 and N-depositions in Finland during the past few decades have been too low to be able to cause growth trends of such magnitude that could be separated from natural growth variation. 3. The study material consists of untreated stands or stands with known management history. Thus, trends caused by changing silviculture are outside the scope of this study. On the basis of the non-existing trends in this study and results from eight successive national forest inventories beginning as early as in the 1920s, it can be concluded that the main factors leading to a 44% increase in the total growth of Finnish forests during the last four decades are changes in stand structures (age, density) and silvicultural practices (regeneration, thinnings, drainage, fertilization). European Forest Institute Research Report No. 5 Growth Trends in European Forests Edited by H. Spiecl<er, K. Mielikiiinen, M. Kohl and J. P. Skovsgaard ©Springer-Verlag Berlin Heidelberg 1996 42 Growth Trends of Scots Pine in Unmanaged and Regularly Managed Stands

Silvicultural management in maintaining biodiversity and resistance of forests in Europe—temperate zone

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 todays 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.

Radial growth variation of Norway spruce (Picea abies (L.) Karst.) across latitudinal and altitudinal gradients in central and northern Europe

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.

Overview of Recent Growth Trends in European Forests

Natural environmental changes and human activities have altered forest growth for centuries. Recent long-term growth investigations indicate an increasing growth trend in European forests. The investigations are based on forest inventory, permanent plot and tree analysis data. The observed trends are species specific, locally varying and modified by remarkably large periodic growth variations. On a European scale, species and site specific quantitative information about the extent and spatial as well as temporal variation in growth acceleration is lacking. Future growth development may differ from past observations. A better understanding of changes in site conditions, their causes and consequences is needed to guide sustainable management of European forests.

Large-scale climatic variability and radial increment variation of Picea abies (L.) Karst. in central and northern Europe

Abstract. High-frequency variation of Norway spruce radial increment [Picea abies (L.) Karst.] and its dependence on various climatic variables was compared in stands across latitudinal and altitudinal transects in southwestern and eastern Germany, Norway, and Finland. The tested variables included local temperature and precipitation, northern hemisphere temperature anomalies, and the climatic teleconnection patterns (North Atlantic Oscillation, East Atlantic, East Atlantic Jet, East Atlantic/West Russia, and Scandinavian patterns). Climatic impact on radial increment increased towards minimum and maximum values of the long-term temperature and precipitation regimes, i.e. trees growing under average conditions respond less strongly to climatic variation. Increment variation was clearly correlated with temperature. Warm Mays promoted radial increments in all regions. If the long-term average temperature sum at a stand was below 1,200–1,300 degree days, above average summer temperature increased radial increment. In regions with more temperate climate, water availability was also a growth-limiting factor. However, in those cases where absolute precipitation sum was clearly related to radial increment variation, its effect was dependent on temperature-induced water stress. The estimated dates of initiation and cessation of growing season and growing season length were not clearly related to annual radial increment. Significant correlations were found between radial increment and climatic teleconnection indices, especially with the winter, May and August North Atlantic Oscillation indices, but it is not easy to find a physiological interpretation for these findings.

The effect of artificially induced drought on radial increment and wood properties of Norway spruce

We studied experimentally the effects of water availability on height and radial increment as well as wood density and tracheid properties of Norway spruce (Picea abies (L.) Karst.). The study was carried out in two long-term N-fertilization experiments in Southern Finland (Heinola and Sahalahti). At each site, one fertilized and one control plot was covered with an under-canopy roof preventing rainwater from reaching the soil. Two uncovered plots were monitored at each site. The drought treatment was initiated in the beginning of growing season and lasted for 60-75 days each year. The treatment was repeated for four to five consecutive years depending on the site. Altogether, 40 sample trees were harvested and discs sampled at breast height. From the discs, ring width and wood density were measured by X-ray densitometry. Tracheid properties were analysed by reflected-light microscopy and image analysis. Reduced soil water potential during the growing season decreased annual radial and height increment and had a small influence on tracheid properties and wood density. No statistically significant differences were found in the average tracheid diameter between the drought-treated and control trees. The average cell wall thickness was somewhat higher (7-10%) for the drought treatment than for the control, but the difference was statistically significant only in Sahalahti. An increased cell wall thickness was found in both early- and latewood tracheids, but the increase was much greater in latewood. In drought-treated trees, cell wall proportion within an annual ring increased, consequently increasing wood density. No interaction between the N fertilization and drought treatment was found in wood density. After the termination of the drought treatment, trees rapidly recovered from the drought stress. According to our results, severe drought due to the predicted climate change may reduce Norway spruce growth but is unlikely to result in large changes in wood properties.

HIGH-FREQUENCY DENSITOMETRY - A NEW METHOD FOR THE RAPID EVALUATION OF WOOD DENSITY VARIATIONS

A new method called HF-densitometry is introduced, which measures relative density variations along wood surfaces utilizing the dielectric properties ofwood. The method is based on the propagation of continuous electromagnetic waves in a high-frequency (HF) transmitter-receiver link of an extremely small electrode system, which is in direct contact with the wood surface investigated. The electromagnetic field emitted by the transmitting electrode propagates through a small volume of the wood sampie to the receiving electrode, located very close to the transmitting electrode. The received signal strength is directly influenced by the dielectric properties of the material along the propagation path. The variation of the relative dielectric constant in different wood structures is correlated with the density variations in a way the received signal strength increases with increasing wood density. The dielectric measuring device, developed on the basis of the new method, allows non-destructive, extremely fast measurements of wood density variations . The new HF-densitometry method was compared to X-ray densitometry by performing measurements on an identical spruce sampie.

Air pollution and environmental chemistry – what role for tree-ring studies?

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.

Douglas‐fir plantations in Europe: a retrospective test of assisted migration to address climate change

We evaluate genetic test plantations of North American Douglas-fir provenances in Europe to quantify how tree populations respond when subjected to climate regime shifts, and we examined whether bioclimate envelope models developed for North America to guide assisted migration under climate change can retrospectively predict the success of these provenance transfers to Europe. The meta-analysis is based on long-term growth data of 2800 provenances transferred to 120 European test sites. The model was generally well suited to predict the best performing provenances along north-south gradients in Western Europe, but failed to predict superior performance of coastal North American populations under continental climate conditions in Eastern Europe. However, model projections appear appropriate when considering additional information regarding adaptation of Douglas-fir provenances to withstand frost and drought, even though the model partially fails in a validation against growth traits alone. We conclude by applying the partially validated model to climate change scenarios for Europe, demonstrating that climate trends observed over the last three decades warrant changes to current use of Douglas-fir provenances in plantation forestry throughout Western and Central Europe.

Tree rings and forest management in Europe

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.