An alien fish threatens an endangered parasitic bivalve: the relationship between brook trout (Salvelinus fontinalis) and freshwater pearl mussel (Margaritifera margaritifera) in northern Europe

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Abundance of ammonia oxidizing microbes and denitrifiers in different soil horizons of an agricultural soil in relation to the cultivated crops

The role of subsoils and their microbial communities for the nutrient supply for plants is to a large extent unknown, especially in comparison to well investigated topsoil layers. Therefore, in this study, the influence of three different plant species with different rooting systems and different N uptake strategies on ammonium and nitrate levels and microbial communities involved in ammonia oxidation and denitrification was investigated in different soil horizons. Overall, our results show a higher genetic potential for both processes in topsoils than in subsoils independent of the present plant. Although we found accumulation of N in top and subsoils in plots with legumes, we could not observe an impact of the higher nitrate content on the genetic potential of denitrification and ammonia oxidation. However, differences in the ratios of ammonia oxidizing archaea to bacteria and also between denitrifying bacteria harboring genes for copper- (nirK) or cytochrome- (nirS) dependent nitrite reductase in top and subsoil samples reveal different ecophysiologies of microbes involved in N turnover in top and subsoil habitats.     

Productivity and optimal management of the uneven-aged hardwood forests of Hyrcania

Hyrcania is a productive region near the southern coast of Caspian Sea. Her forests are mostly uneven-aged beach-dominated hardwood mixtures. There is increasing willingness to treat these forests without clear-felling, following the ideas of continuous cover management. However, lack of growth and yield models have delayed this endeavor, and no instructions for uneven-aged management have been issued so far. This study developed a set of models that enable the simulation of stand development in alternative management schedules. The models were used to optimize stand structure and the way in which various initial stands should be converted to the optimal uneven-aged structure. The model set consists of individual-tree diameter increment model, individual-tree height model, survival model, and a model for ingrowth. The models indicate that the sustainable yield of the forests ranges from 2.2 to 7 m³ ha^?1 a^?1 in uneven-aged management, depending on species composition. Better ingrowth would substantially enhance productivity. The optimal stand structure for maximum sustained yield has a wide descending diameter distribution, the largest trees of the post-cutting stand being 80–100 cm in dbh. If cuttings are conducted at 30- or 40-year intervals, they should remove 20–40 largest trees per hectare. Despite moderate growth rate, uneven-aged management produces high incomes, 850–1,000 UDS ha^?1a^?1, because the timber assortments that are obtained from the removed large trees have very high selling prices. Optimal conversion to uneven-aged structure showed that the steady-state stand structure depends on initial stand condition and discount rate when the length of the conversion period is fixed. Discount rates higher than 1 % lead to reduced wood production, heavy cuttings, and low basal areas of the steady-state forest.     

Growth models for six Eucalyptus species in Angola

This study developed growth models for Eucalyptus saligna Sm., E. camaldulensis Dehnh., E. macarthurii H.Deane & Maiden, E. resinifera Sm., E. siderophloia Benth. and E. grandis Hill ex. Maiden, for the central highlands of Angola, and used these models to simulate the development of stand characteristics. The obtained model set included dominant height, diameter increment, tree height and self-thinning models. The study was based on 10 499 radial increment observations measured on cores taken from about 700 trees growing in 22 plots located in seven sites in the Angolan highlands. The model set makes it possible to simulate stand development on an individual tree basis. Comparison of simulated stand development and measurements indicated good performance of the models. A non-linear fixed-effects diameter increment model performed best for most species, but a non-calibrated linear mixed-effects model used with the Snowdon correction was better for E. saligna and E. macarthurii. This study showed a similar dominant height development of young stands as found in most previous studies done for southern Africa. Some differences emerged at older ages.     

Applied 3D texture features in ALS-based forest inventory

Airborne laser scanning (ALS) data are not usually considered to be very informative with respect to tree species, and this information is often obtained by combining such data with spectral image material. The aim was to test the ability of height, density, intensity and applied 2D and 3D texture variables derived solely from a very high-density ALS point cloud to describe the crown shape and structure characteristics required for tree species discrimination. Linear discriminant analysis was used to find optimal combinations of variables within the predictor groups, and classifications based on variables from different groups were compared. The third power of the tree diameter was used as a stem volume approximate, and rather than examining species alone, the classification was evaluated with respect to the volume approximates assigned to the predicted species. The sensitivity of pulse density to the methodology presented here was determined by simulating thinned data sets by reducing the initial pulse density. The reliability of the estimates was analysed both with functions generated using the original data and with new functions for each thinning level. Alpha shape metrics developed for describing tree crowns constructed from the 3D point clouds proved capable of discriminating between all three species groups evaluated, and several height distribution and textural variables were found to discriminate between the coniferous tree species. The results demonstrate the importance of species interpretation in forest inventories based on allometric modelling, but then indicate that species-specific estimation could be carried out using ALS-derived variables alone.     

PCR-based monitoring of recent isolates of tobacco blue mold from Europe reveals the presence of two genetically distinct phenotypes differing in fungicide sensitivity

Bioassays testing the fungicide sensitivity against metalaxyl of Peronospora tabacina isolates collected in German tobacco fields in 2005 revealed the presence of two phenotypes, resistant and sensitive. DNA fingerprints using SSR and minisatellite primers allowed separation of the samples into two groups. The differences in amplification patterns coincided with the sensitive and resistant reaction of the isolates in metalaxyl bioassays. New primers were developed which allowed PCR-based detection of P. tabacina and differentiation of the metalaxyl-sensitive and the metalaxyl-resistant phenotype, respectively. Screening of recent blue mold isolates from Germany and other European countries for metalaxyl sensitivity with leaf disk bioassays coincided completely with the PCR-based identification of the two phenotypes. In Germany, exclusively resistant isolates were found between 2002 and 2004. These still dominate. Since 2005 the co-occurrence of sensitive isolates has been shown. No similar monitoring has been done in any other European country. However, we found the resistant phenotype reaction in a French isolate of 2004 and in two out of three Italian isolates in 2007. Two isolates from Poland and Bulgaria in 2007 were sensitive to metalaxyl. For all 58 isolates tested since 2002 the metalaxyl bioassay-based resistance type and the PCR-based tests for sensitive and resistant genotype coincided. Using genotype-specific primers for future population studies may help to trace the sources of the pathogen from which yearly propagation starts.     

Landscape Position, Local Environmental Factors, and the Structure of Molluscan Assemblages of Lakes

Biotic communities are structured by both regional processes (e.g., dispersal) and local environmental conditions (e.g., stress). We examined the relative importance of landscape position (position within the hydrologic flow system and distance from other lakes) and local environmental factors in determining the assemblage structure of lake-dwelling snails and fingernail clams in a boreal landscape. Both landscape position and local environmental factors were highly influential in structuring the molluscan assemblages. In canonical correspondence analysis, 53.6% of snail and 48.2% of fingernail clam assemblage composition were accounted for by both sets of variables. The pure effects of landscape position were higher than those of environmental variables, and a considerable amount of variability was shared by the two sets of variables. In regression analysis, 95.5% of snail and 62.2% of fingernail clam species richness was accounted for by the explanatory variable groups, with most of the variability being related to shared effects, followed by landscape position. The effects of landscape position on species composition suggest that passive dispersal increases the similarity of molluscan assemblages in adjacent lakes. This process does not lead to an overall homogenisation of assemblage composition across the landscape, however, because local conditions set a strong environmental filter, excluding species that arrive at an unsuitable lake. These environmental filters may reflect either extinction probability (area, productivity) or species niche differences (calcium levels, abiotic stress). Landscape position may also be important in maintaining the species richness of lake-dwelling molluscan assemblages. By providing potential colonists, nearby source lakes are likely to be important in countering local extinctions. Our test of the relative importance of landscape position and local drivers of assemblage structure was partly confounded by their co-variation. Nevertheless, studying the relationship between landscape position and local variables is useful because it can tell us about the importance of local and regional processes in shaping lake communities.     

Communal pair spawning behaviour of vendace (Coregonus albula) in the dark

Mating in nature is rarely random, and most fish species have refined mating systems. The vendace (Coregonus albula) is a short‐lived, small‐sized, cold‐water‐adapted pelagic schooling species that is known to spawn in groups, but the actual mating system of this species, like many other group‐spawning fishes, has not been described in detail. Vendace typically spawn in the littoral or sublittoral zones of lakes in late autumn, and the hatching of larvae occurs close to icebreak in the following spring. In our large study lake, vendace larvae were caught in 93% of 1,149 random sampling locations lake‐wide. We examined the courtship and mating of vendace under experimental conditions by nonintrusive observation of the natural behaviour, to clarify whether spawning activity is associated with illumination and to assess the postspawning mortality of vendace. Here, we describe and document in detail for the first time the spawning behaviour of vendace: they spawn in the dark, and females release a small portion of their eggs (on average 1% of mean total individual fecundity) when the female and male, side by side, dart from near the bottom up towards the surface, that is perform a spawning rise. Males and females had several spawning rises (on average 1,200). Our results showed high postspawning mortality (56%). The spawning stress seems to be a potential component of mortality regulating the lifespan duration of vendace.     

The influence of storm-induced microsites to tree regeneration patterns in boreal and hemiboreal forest

We reviewed studies dealing with regeneration under variable conditions in boreal and hemiboreal forests as affected by different microsite types by tree species functional groups. Generally, the importance of storm-induced microsites for regeneration dynamics in boreal forests depends on several factors: (1) distribution and type of microsites (generated by storm characteristics and stand conditions); (2) viable seed supply (stand history, species dispersal traits and status of surviving trees) and their species’ life history strategy; (3) climatic and site conditions (pre-storm conditions and storm-induced changes); and (4) delayed storm effects, such as retarded falling of trees, favoured vegetation growth, etc. Studies acknowledging the significance of microsites were mostly related to intermediate or severe events, causing sufficient changes in resource levels and growth conditions, and influencing extrinsic factors such as frost heaving, erosion and browsing. Also, the dispersal traits of available tree species, including sprouting and response of surviving trees, such as canopy expansion, should be considered in evaluating microsite importance in individual cases. In intermediate to severe windstorm events, pioneer species are generally profiting most from the additional offer in microsites, requiring bare mineral soil and elevated locations for their establishment and growth. Under gap dynamics, shade-tolerant species benefit from dead wood and elevated locations as these offer safe sites in stands with abundant understorey vegetation.     

Epiphytic lichen diversity in late-successional Pinus sylvestris forests along local and regional forest utilization gradients in eastern boreal Fennoscandia

Pinus sylvestris-dominated forests have been heavily utilized across all of boreal Fennoscandia and the remaining natural forests are generally highly fragmented. However, there are considerable local and regional differences in the intensity and duration of past forest utilization. We studied the impact of human forest use on the diversity of epiphytic and epixylic lichens in late-successional Pinus sylvestris-dominated forests by assessing species richness and composition along both local and regional gradients in forest utilization. The effects of local logging intensity were analysed by comparing three types of stands: (i) near-natural, (ii) selectively logged (in the early 20th century) and (iii) managed stands. The effects of regional differences in duration and intensity of past forest use were analysed by comparing stands in two contrasting regions (Häme and Kuhmo–Viena). The species richness of selectively logged stands was as high as that of near-natural stands and significantly higher in these two stand categories than in managed stands. Species richness increased with the density of small understorey Picea, which correlated strongly with decreasing intensity of local forest use and increasing structural complexity of selectively logged and near-natural stands. Stands in the Häme region hosted a lower number of species, and were less likely to host many old-growth indicator species than the Kuhmo–Viena region, suggesting that species have been lost from stands in the Häme region due to a longer history of intensive forest use. We conclude that selectively logged stands, along with near-natural stands, are valuable lichen habitats particularly for species confined to old-growth structures such as coarse trees and deadwood. In landscapes where natural forests have become fragmented, the management or restoration of the remaining late-successional Pinus-dominated forests, e.g. through the use of fire, should be carefully planned to avoid adverse effects on lichen species richness.