Global environmental change, including increasing atmospheric CO2 and tropospheric O3 is likely to impact forest growth and wood properties. Increase in CO2 enhances photosynthesis, growth and productivity. On the contrary, O3 is detrimental to forest vitality and yield. At present reports of long-term studies on the effects of combined exposures of CO2 and O3 on stem wood chemistry of deciduous trees are lacking. The aim of this study was to investigate the effects of CO2 and O3, singly or in combination, on stem wood chemistry of four-year old saplings of trembling asspen (Populus tremuloides) clones differing in ozone tolerance, paper birch (Betula papyrifera) and sugar maple (Acer saccharum)

Elevated CO2 was shown to influence the nutritional status of exposed ecosystems. In an earlier experiment in model ecosystems in open-top chambers with young spruce and beech, the nitrate concentration of the soil solution was dramatically reduced after 4 years exposure to elevated CO2. This phenomenon was mainly interpreted as an immobilization of nitrogen in the soil. To test if such effects occur also in mature, undisturbed natural forests, we used facilities of the Swiss Canopy Crane project. Here in a mixed 120 years old forest the crowns of 30-35 m high broadleaved trees are fumigated with CO2 during the growing season since spring 2001. According to the results the soil is probably not yet much influenced by the fumigation of the tree crowns, and it is too early to estimate whether the observed nutrient effects are due to the CO2 treatment or to the natural variability of the soil

The future productivity of forests will be affected by combinations of anthropogenic stresses including elevated atmospheric CO2 and O3. Because the productivity of forests, will be in part, determined by the growth of young trees, we evaluated the responses of Pinus ponderosa seedlings to ambient or elevated CO2 and/or high O3. Shoot growth and whole plant biomass were evaluated for seedlings growing under the CO2 and O3 treatments for 3 years in sun-lit mesocosms with ambient temperature and humidity. This study indicated the potential for CO2 but not O3 effects on Pinus ponderosa seedlings under realistic field conditions as used in this study

The biological effects of both elevated CO2 and N deposition on model ecosystem were investigated in the Birmensdorf open-top chamber facility. Each of the 16 chambers was divided into two compartments with a ground area of 3 msub2 and filled with natural unfertilized forest soils from two sites (one acidic, the other calcareous). Elevated CO2 significantly increased O and Zn concentrations in beech leaves and those of Zn in spruce needles on the calcareous soils. Enhanced N deposition also led to a dilution of nutrients and increased N contents

Stimulation of photosynthesis by elevated CO2 has been consistently found for aspen but not for maple. Similar responses have been shown for growth. In contrast, O3 causes decreased levels of photosynthesis and growth in aspen but does not appear to impact sugar maple significantly. When the pollutants co-occur, CO2 induced enhancements in photosynthesis and growth are moderated so that trees in CO2 and O3 treatments respond similarly to those in control rings. In this presentation, we will provide a physiological interpretation of our results in modelling growth response under future atmospheric conditions

Both CO2 and ozone increased the diseased leaf area of clone V5952 in Exp. 1 in the year 2000. The size of spots increased most under ozone fumigation, and the number of spots under ozone and CO2 + O3 fumigations. In clone K1659 all fumigation treatments decreased or had no effect on the DLA, or the number and size of the leaf spots. Also the number of fallen leaves under fumigation treatments was higher in clone V5952 than in clone K1659. Analysis of the year 2001 monitoring results is currently going on

We studied elevated CO2 and ozone effects in single and in combination on crown structure of two Betula pendula clones. Shoot ramification, shoot length, number of metamers, leaves and buds were measured at four heights in every tree. Chamber effect was substantial on sylleptic branching and on shoot length and ramification. However these responses differed between the clones. Ozone treatment affected shoot length and caused slight decrease in shoot ramification. Elevated CO2 affected appearance of long shoots in complex manner, but in lower crown positions CO2 caused increased number of long shoots in both clones