To maintain biodiversity in managed forests we must understand the patterns and processes that regulate the occurrence and dynamics of species in undisturbed ecosystems. We compared biomass and species composition of canopy lichens on 180 lower branches of Norway spruce (Picea abies) in three pairs of old‐growth and managed (selectively logged) stands in northern Sweden (30 branches per stand). The purpose was to evaluate the effect of substrate quality (branch characteristics) on patterns of lichen biomass for two different growth forms (foliose and fruticose). Old‐growth stands had six times higher lichen mass per spruce branch, and two times higher expressed as percentage of branch mass, compared to mature stands of managed forest. Lichen mass was strongly related to mass, diameter, and age of branches. Fruticose, pendulous species (Alectoria sarmentosa and Bryoria spp.) were highly sensitive to forest practices. In contrast, type of forest had no significant effect on foliose species. Species number per stand was the same (15 species) in both types of forest, but there were marked differences in the relative abundance of different lichen groups. Results suggest that limited amount of substrate (i.e., small branches) available to lichens, and young branches, providing only a short time for lichen colonization and growth, are important factors limiting epiphytic lichen abundance in managed forests. Conversion of old‐growth forest into young, managed stands will lead to a significant reduction in epiphytic lichen mass. This in turn may probably affect nutrient cycling in forests and has negative consequences for animals that utilize canopy lichens as food, shelter, or nesting material.

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Small birch plants were grown for up to 80 d in a climate chamber at varied relative addition rates of nitrogen in culture solution, and at ambient (350 μmol mol‐1) or elevated (700 μmol mol‐1) concentrations of CO2. The relative addition rate of nitrogen controlled relative growth rate accurately and independently of CO2 concentration at sub‐optimum levels. During free access to nutrients, relative growth rate was higher at elevated CO2. Higher values of relative growth rate and net assimilation rate were associated with higher values of plant N‐concentration. At all N‐supply rates, elevated CO2 resulted in higher values of net assimilation rate, whereas leaf weight ratio was independent of CO2. Specific leaf area (and leaf area ratio) was less at higher CO2 and at lower rates of N‐supply. Lower values of specific leaf area were partly because of starch accumulation. Nitrogen productivity (growth rate per unit plant nitrogen) was higher at elevated CO2. At sub‐optimal N‐supply, the higher net assimilation rate at elevated CO2 was offset by a lower leaf area ratio. Carbon dioxide did not affect root/shoot ratio, but a higher fraction of plant dry weight was found in roots at lower N‐supply. In the treatment with lowest N‐supply, five times as much root length was produced per amount of plant nitrogen in comparison with optimum plants. The specific fine root length at all N‐supplies was greater at elevated CO2. These responses of the root system to lower N‐supply and elevated CO2 may have a considerable bearing on the acquisition of nutrients in depleted soils at elevated CO2. The advantage of maintaining steady‐state nutrition in small plants while investigating the effects of elevated CO2 on growth is emphasized.

K. 2006. Effects of landscape composition and substrate availability on saproxylic beetles in boreal forests: a study using experimental logs for monitoring assemblages. Á/ Ecography 29: 191 Á/204.Intensive forestry practises in the Swedish landscape have led to the loss and fragmentation of stable old-growth habitats. We investigated relationships between landscape composition at multiple scales and the composition of saproxylic beetle assemblages in nine clear-cut, mature managed and old-growth spruce-dominated forest stands in the central boreal zone of Sweden. We set out fresh spruce and birch logs and created spruce snags in 2001 Á/2002 to experimentally test the effects of coarse woody debris (CWD) type and forest management on the composition of early and late successional, and red-listed saproxylic beetle assemblages. We examined effects of CWD availability at 100 m, and landscape composition at 1 and 10 km on saproxylic beetle abundances. Additionally, we tested whether assemblage similarity decreased with increasing distance between sites. We collected beetles from the experimental logs using eclector and window traps in four periods during 2003. CWD was measured and landscape composition data was obtained from maps of remotely sensed data. The composition of saproxylic beetles differed among different CWD substrates and between clear-cuts and the older stand types, however differences between mature managed and old-growth forests were significant only for red-listed species. Assemblage similarities for red-listed species on clear-cuts were more different at greater distances apart, indicating that they have more localised distributions. CWD availability within 100 m of the study sites was rarely important in determining the abundance of species, suggesting that early successional saproxylic beetles can disperse further than this distance. At a larger scale, a large area of suitable stand types within both 1 and 10 km resulted in greater abundances in the study sites for several common and habitatspecific species. The availability of suitable habitat at scales of 1 Á/10 km is thus likely to be important in the survival of many saproxylic species in forestry-fragmented areas.

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A common observation in plants grown in elevated CO2 concentration is that the rate of photosynthesis is lower than expected from the dependence of photosynthesis upon CO2 concentration in single leaves of plants grown at present CO2 concentration. Furthermore, it has been suggested that this apparent down regulation of photosynthesis may be larger in leaves of plants at low nitrogen supply than at higher nitrogen supply. However, the available data are rather limited and contradictory. In this paper, particular attention is drawn to the way in which whole plant growth response to N supply constitutes a variable sink strength for carbohydrate usage and how this may affect photosynthesis. The need for further studies of the acclimation of photosynthesis at elevated CO2 in leaves of plants whose N supply has resulted in well-defined growth rate and sink activity is emphasised, and brief consideration is made of how this might be achieved.

Small birch plants {Betuta penduta Roth.) were grown from seed for periods of up to 70d in a climate chamber at optimal nutrition and at present (350 |xmol mol"^) or elevated (700|jimol mol"^) concentrations of atmospheric CO2. Nutrients were sprayed over the roots in Ingestad-type units. Relative growth rate and net assimilation rate were slightly higher at elevated CO2, whereas leaf area ratio was slightly lower. Smaller leaf area ratio was associated with lower values of specific leaf area. Leaves grown at elevated CO2 had higher starch concentrations (dry weight basis) than leaves grown at present levels of CO2. Biomass allocation showed no change with CO2, and no large effects on stem height, number of side shoots and number of leaves were found. However, the specific root length of fine roots was higher at elevated CO2. No large difference in the response of carbon assimilation to intercellular CO2 concentration (A/Ci curves) were found between CO2 treatments. When measured at the growth environments, the rates of photosynthesis were higher in plants grown at elevated CO2 than in plants grown at present CO2. Water use efficiency of single leaves was higher in the elevated treatment. This was mainly attributable to higher carbon assimilation rate at elevated CO2. The difference in water use efficiency diminished with leaf age. The small treatment difference in relative growth rate was maintained throughout the experiment, which meant that the difference in plant size became progressively greater. Thus, where plant nutrition is sufficient to maintain maximum grovtrth, small birch plants may potentially increase in size more rapidly at elevated CO2.