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 response of Betula pubescens Ehr., B. pendula Roth and two provenances of Pinus sylvestris L. to solar ultraviolet radiation were investigated in a UV exclusion field experiment during the 1997-1999 growing seasons in Finnish Lapland. The seed-grown seedlings were grown under UV-B exclusion and UV-B/UV-A exclusion as compared to control treatment and ambient plants. The only significant impacts of UV exclusion were found in P. sylvestris provenance Enontekio. Longer-term field studies are needed to detect the cumulative characteristics of the UV responses

We studied the effects of elevated CO2 and elevated temperature on photosynthesis and composition of Scots pine needles during three years of treatments, started in August 1996. CO2 and temperature were elevated day- and year- round in closed-top chambers, which were constructed around naturally regenerated Scots pine trees growing at a nitrogen poor site. Our aim was to study, whether there is photosynthetic acclimation during three years of growth at elevated CO2 and elevated temperature in Scots pine, and whether acclimation response is connected to the aging of the needles

The attention was focused on the diameter increment of beech timber forest growing on the partial plots with various stand density. The individual parts of the originally homogenous stand, were subjected to regeneration cutting of various intensity resulting in several partial plots. On the different partial plots we found different proportions of trees belonging to the individual diameter classes. We also found that the differences between the individual plots were statistically very significant. Beech is a tree species which is capable to continue creating considerable light increments even long after the stand opening

The main objective of this paper is to analyse regeneration regularities of damaged trees during the period of decreased environmental pollution load. Investigations concentrated on Scots pine tree height and radial increment, branch length increment, amount of branches on the verticil and needle and whole crown mass. Model trees were selected in 3 stands located on 3.5, 10 and 21 km from the plant according to their development classes and condition

Increased ozone sensitivity of larger soil-growing trees with growth in the multi-year exposure was a result of several interactive senescence-related physiological factors: lower net photosynthesis to stomatal conductance ratio at the end of the growing season promoted high ozone uptake and low photosynthetic carbon gain, leading to onset of visible injuries and impaired bud formation. This was expected to affect negatively the early growth of the next year foliage, This clone showed a major change in allocation pattern during the early ontogeny at the expense of foliage growth towards the stem height increase

This paper summarizes the data on growth response and N uptake in open-top chambers planted with ponderosa pine (Pinus ponderosa Laws.) treated with both N (0, 10, and 20 g N msub-2 yrsub-1 as ammonium sulfate ) and CO2. Both N and elevated CO2 caused increased growth. The effects of N on growth response to elevated CO2 were assessed in various ways and various interpretations could be drawn depending on which metric was used, including a negative effect of N on growth response to CO2. These calculations suggest that expressing growth as percentages can be misleading, especially when done on a grams per tree basis

Atmospheric carbon dioxide (CO2) and ozone (O3) are increasing by 1-2% per year and are expected to double by the year 2100 compared to the end of the last millennium. Carbon dioxide at twice the current atmospheric concentrations has the potential to increase the productivity of forest trees while increasing ozone is expected to cause significant reductions in growth. The present study was undertaken to investigate the effects of CO2 and O3, singly or in combination, on growth and allocation of two European silver birch (Betula pendula Roth) clones under field conditions to verify the future predicitons in regard to silver birch. Our data show that growth of clone 80 was benefitted by ambient CO2 singly and in combination with ambient O3. Clone 4 was more responsive to ambient O3 than clone 80 which is opposite to results from previous pot experiments with these clones