Roger Pettersson

Epiphytic Lichen Biomass in Managed and Old-Growth Boreal Forests: Effect of Branch Quality

To maintain biodiversity in managed forests we must understand the patterns and processes that regulate the occurrence and dynamics of species in undisturbed eco- systems. 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 (se- lectively 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, pro- viding 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.

Invertebrate communities in boreal forest canopies as influenced by forestry and lichens with implications for passerine birds

Abstract To investigate the effects of commercial forestry on canopy-living invertebrates in the boreal forest, we sampled branches in northern Sweden for invertebrates and lichens from paired natural spruce Picea abies forests and adjacent managed forests that were selectively logged. The study was conducted during late winter, when invertebrate abundance is lowest, and when small differences may be critical to foraging birds. Natural forests had significantly greater invertebrate diversity than managed forests and nearly five times as many invertebrates per branch. The number of large invertebrates (> 2·5 mm, the minimum prey size for foraging passerine birds) was consistently higher in natural forests, with spiders (Araneae), Lepidoptera and Diptera larvae dominating. The number and biomass of invertebrates were related to the abundance of lichens even after controlling for sampling location and branch size. Other studies have implicated forestry in the decline of non-migratory passerine birds in northern Europe through the destruction and fragmentation of forests, but our study indicates that it may also reduce foraging habitat quality through a reduction in lichen abundance.

Effects of nitrogen supply on the acclimation of photosynthesis to elevated CO2.

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.

Sampling saproxylic beetle assemblages in dead wood logs: comparing window and eclector traps to traditional bark sieving and a refinement

The use of saproxylic beetle community as a metric to evaluate nature conservation measures in forests requires efficient methods. We first compare traditional bark sieving to a potential improvement (extracting beetles from whole bark with Tullgren funnels) to determine the most efficient. Secondly we compare this most efficient bark sampling to eclector and window traps. At the species, family, and functional group levels, we consider species richness, abundance and practical aspects. Traditional bark sieving missed >50% of the individual beetles compared to whole bark sampling so we recommend the latter. Window traps caught large numbers of mobile saproxylic beetles, but a high proportion of non-saproxylics results in high sorting cost; bark sampling and eclector traps had a high proportion of saproxylics and obligate saproxylics. Compared to bark sampling, eclector traps are non-destructive, and monitor the whole saproxylic assemblage (i.e. also beetles inside the wood). Overall, window traps are useful because they capture saproxylic beetles attracted to dead wood and sample the local species pool, whereas eclector traps capture the saproxylics that actually emerge from a particular piece of dead wood, and thus are suited to detailed studies. Overall, we suggest that a combination of these two best methods is highly complementary.

Micro and Macro-Habitat Associations in Saproxylic Beetles: Implications for Biodiversity Management

Restoration of habitats is critically important in preventing full realization of the extinction debt owed as a result of anthropogenic habitat destruction. Although much emphasis has been placed on macrohabitats, suitable microhabitats are also vital for the survival of most species. The aim of this large-scale field experiment was to evaluate the relative importance of manipulated microhabitats, i.e., dead wood substrates of spruce (snags, and logs that were burned, inoculated with wood fungi or shaded) and macrohabitats, i.e., stand types (clear-cuts, mature managed forests, and forest reserves) for species richness, abundance and assemblage composition of all saproxylic and red-listed saproxylic beetles. Beetles were collected in emergence traps in 30 forest stands in 2001, 2003, 2004 and 2006. More individuals emerged from snags and untreated logs than from burned and shaded logs, but species richness did not differ among substrates. Assemblage composition differed among substrates for both all saproxylics and red-listed saproxylic species, mainly attributed to different assemblage composition on snags. This suggests that the practise of leaving snags for conservation purposes should be complemented with log supplementation. Clear-cuts supported fewer species and different assemblages from mature managed forests and reserves. Neither abundance, nor species richness or assemblage composition differed between reserves and mature managed forests. This suggests that managed stands subjected to selective cutting, not clear-felling, maintain sufficient old growth characteristics and continuity to maintain more or less intact assemblages of saproxylic beetles. Thus, alternative management methods, e.g., continuity forestry should be considered for some of these stands to maintain continuity and conservation values. Furthermore, the significantly higher estimated abundance per ha of red-listed beetles in reserves underlines the importance of reserves for maintaining viable populations of rare red-listed species and as source areas for saproxylic species in boreal forest landscapes.

Winter wheat biomass and nitrogen dynamics under different fertilization and water regimes: application of a crop growth model

Abstract Growth, nitrogen uptake and nitrogen allocation between roots, stems, leaves and grains were measured and simulated in winter wheat on a clay soil in three treatments including daily irrigation and fertilization. Special emphasis was placed on biomass and nitrogen allocation within the crop and on the availability of soil nitrogen for crop growth. The model used for the simulations of growth (SOILN-CROP), which was driven by a hydrological model, is based on the light interception concept and empirical allometric functions. Growth is the driving force for nitrogen uptake, which is limited by the availability of mineral N in the soil. The model was calibrated for one treatment. Thereafter, the same parameter set was used to simulate the other two treatments. Frequent irrigation in combination with single-dose fertilization increased crop growth and N leaching compared with the non-irrigated but single-dose fertilized control, whereas irrigation together with daily fertilization increased crop growth and N uptake but not N leaching. Simulated soil mineral N levels agreed well with measurements on a 1-year time scale. Assimilate allocation to roots decreased logarithmically with total crop biomass in all treatments. Allocation to leaves decreased linearly with total above-ground crop mass. The crop availability of mineral N differed considerably between treatments. The model parameter defining the proportion of soil mineral N available for plant uptake had a strong influence on model behaviour. This proportion is indicated to depend on soil water content and the mechanisms of this relation need to be considered in future work to improve our predictions of N uptake.

Root dynamics in a semi-natural grassland in relation to atmospheric carbon dioxide enrichment, soil water and shoot biomass

Plant responses to increasing atmospheric CO2 concentrations have been studied intensively. However, the effects of elevated CO2 on root dynamics, which is important for global carbon budgets as well as for nutrient cycling in ecosystems, has received much less attention. We used minirhizotrons inside open-top chambers to study the effects of elevated atmospheric carbon dioxide concentration on root dynamics in a nutrient-poor semi-natural grassland in central Sweden. We conducted our investigation over three consecutive growing seasons during which three treatments were applied at the site: Elevated (≈ 700 μmol mol-1) and ambient (≈ 360 μmol mol-1) chamber levels of CO2 and a control, without a chamber. During 1997, a summer with two dry periods, the elevated treatment compared with ambient had 25% greater mean root counts, 65% greater above-ground biomass and 15% greater soil moisture. The chambers seemed responsible for changes in root dynamics, whereas the elevated CO2 treatment in general increased the absolute sum of root counts compared with the ambient chamber. In 1998, a wet growing season, there were no significant differences in shoot biomass or root dynamics and both chamber treatments had lower soil moisture than the control. We found that as seasonal dryness increased, the ratio of elevated – ambient shoot biomass production increased while the root to shoot ratio decreased. We conclude that this grasslands response to elevated CO2 is dependent on seasonal weather conditions and that CO2 enrichment will most significantly increase production in such a grassland when under water stress.

Above-ground plant production under elevated carbon dioxide in a Swedish semi-natural grassland

Abstract Plants have shown responses to elevated CO 2 in many experiments under controlled conditions. Yet, predicting responses under field conditions is still difficult and the number of long-term field studies on elevated CO 2 is limited. Here the results from 4 years’ physiology and production studies in the field are presented. In a species-rich semi-natural grassland in central Sweden open-top chambers were used to study the effects of elevated carbon dioxide concentration (twice the ambient level) on plant production, physiology and species composition. The first three growing seasons showed a 30–60% increase in above-ground biomass at harvest under elevated CO 2 . During the fourth year there was no difference in above-ground biomass between the treatments. For all years, leaf-level photosynthesis for measured species was 30–60% higher and stomatal conductance 20–40% lower at elevated CO 2 than at ambient. Nitrogen concentration in stems and leaves was 5–20% lower at elevated CO 2 . Specific leaf area (SLA) did not show any response to elevated CO 2 . The variation in the effect of CO 2 on above-ground production was attributed to variation in water stress, with low water stress (high precipitation) giving the least effect. It is concluded that even in this relatively low-production system CO 2 effects can persist for at least several years and even increase.

Saproxylic parasitoid (Hymenoptera, Ichneumonoidea) communities in managed boreal forest landscapes

Abstract.  1. Species of higher trophic levels are predicted to be more vulnerable to disturbances (e.g. by forestry) than their prey because of low population densities, extreme specialisation and reliance on intact trophic chains.

Root biomass dynamics in a semi-natural grassland exposed to elevated atmospheric CO2 for five years

The effects of elevated atmospheric CO2 on root dynamics were studied in a semi-natural grassland in central Sweden during five consecutive summer seasons. Open-top chambers were used for ambient and elevated (+350 μmol mol−1) concentrations of CO2, and chamberless rings were used for control. Root dynamics were observed in situ with minirhizotrons during the five summers and root biomass production was measured with root in growth cores during the last two years, from which total root biomass was estimated for each of the five years. The elevated CO2 treatment showed both a greater increase in root numbers during the early summer and a greater decline in root numbers during autumn and winter than the ambient CO2 treatment. Mean root production under elevated CO2 was 50% greater than ambient CO2 during the five years, and the difference increased from +25% in the first year to +80% in the last two years. Conversely, during the same period, the elevated to ambient CO2 difference in shoot biomass decreased from +50% to +5%. This resulted in a dramatic change in root to shoot ratios in elevated CO2 compared with the ambient treatment, which increased from −15% in 1996 to +70% in 2000. Similar differences were seen between elevated CO2 and the chamberless grown control plants, where root to shoot ratios increased steadily from −47% in 1996 to +27% in 2000. Less dynamically, the root to shoot ratios of ambient CO2 grown plants compared with the chamberless control plants were consistently −29%±6% during the experimental period. In conclusion, during the 5 years this grassland was studied, there was a clear shift in plant biomass partitioning from above to below ground for plants exposed to elevated CO2.