Browsing by Subject "density"

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  • Winberg-Wang, Helen; Neretnieks, Ivars; Voutilainen, Mikko (2019)
    Uranine is a dye commonly used in tracer experiments; it is chosen for its high visibility even at low concentrations. Uranine solutions are slightly denser than water at the same temperature. However, in laboratory experiments uranine solutions have been known to occasionally show unpredictable flow behaviors. This paper investigates the possible effect of light-induced density change to explain some of these behaviors. Uranine has a wide light absorption spectrum for visible light, which can heat the dye solution and lower its density to below that of the surrounding water, which induces buoyancy-driven flow. Simulations are made in both one dimension and two dimensions to determine the extent of the effect. The results are then compared to different experiments with unanticipated flow patterns.
  • Kärkkäinen, Matti (Suomen metsätieteellinen seura, 1984)
  • Nirhamo, Aleksi; Pykälä, Juha; Halme, Panu; Komonen, Atte (Wiley, 2021)
    Applied Vegetation Science 24: 2
    Questions: Aspen (Populus tremula) is declining in the old-growth forests of boreal Fennoscandia. This threatens the numerous taxa that are dependent on old aspens, including many epiphytic lichens. Potential methods to aid epiphytic lichens on aspen are centered around treatments which affect the density of Norway spruce (Picea abies). In this study, we investigated how epiphytic lichen communities on aspen are affected by the variation of spruce density in the immediate vicinity of the focal aspen. Location: Southern boreal forests in Finland. Methods: We recorded the occurrence of lichens from 120 aspens in 12 semi-natural forest sites. We used spruce basal area as the measure for spruce density. The selected aspens represented a gradient in spruce basal area in the vicinity of the aspen from 0 to 36 m2/ha. We also measured other tree- and stand-level variables that are known to influence lichen occurrence. Results: Lichen communities on aspen were affected by spruce density, stand age and bark pH. Both lichen species richness and the richness of red-listed species were highest at an intermediate spruce density, and both increased with stand age. Lichen species richness was higher when bark pH was lower. Additionally, community composition was influenced the most by spruce density, followed by bark pH. Conclusions: Our study highlights the detrimental effects of high spruce density on lichen diversity on aspens. This is caused by high spruce density resulting in low light availability. Lichen diversity on aspens was highest when spruce density was intermediate. Spruce thinning in aspen-rich old-growth forests can be helpful in ensuring the long-term persistence of old-growth lichens on aspen in protected forests.
  • Kellomäki, Seppo (Suomen metsätieteellinen seura, 1979)
  • Bhat, K. M.; Ferm, Ari; Kärkkäinen, Matti (Suomen metsätieteellinen seura, 1981)
  • Päivänen, Juhani (Suomen metsätieteellinen seura, 1982)
  • Pöysä, Hannu; Elmberg, Johan; Gunnarsson, Gunnar; Holopainen, Sari Taija; Nummi, Petri Johannes; Sjöberg, Kjell (2018)
    The Whooper Swan (Cygnus cygnus) is a good example of successful conservation, with rapidly growing numbers in Fennoscandia in recent decades. To the contrary, Eurasian Wigeon (Mareca penelope) shows a strong negative trend in breeding numbers, which raises conservation concerns. Previous research suggests a causal link between recent population trajectories of the two species. Both preferentially breed on wetlands with abundant horsetail (Equisetum spp.), a plant providing food for Whooper Swan and crucial feeding microhabitat for Eurasian Wigeon broods. We here test predictions based on the hypothesis that grazing on Equisetum by Whooper Swan reduces breeding habitat or breeding habitat quality for Eurasian Wigeon. We use data from 60 lakes in which waterfowl were counted in 1990-1991 and 2016, and Equisetum was mapped in 1990-1991 and 2013-2014. Lakes colonized by Whooper Swan typically had more abundant Equisetum vegetation in the past than lakes not colonized. Lake-specific decrease of Equisetum was not associated with colonization by Whooper Swan. The number of lakes occupied by Eurasian Wigeon decreased, but the decrease was not stronger on lakes colonized by Whooper Swan than on those that were not. Contrary to our prediction, current Eurasian Wigeon abundance was positively associated with Whooper Swan abundance. Moreover, Eurasian Wigeon did not decrease more on lakes from which Equisetum disappeared than on lakes in which there was still Equisetum left. This study does not support the idea that Whooper Swan affects Eurasian Wigeon negatively by grazing on Equisetum.
  • Schalin, Ilmari (Suomen metsätieteellinen seura, 1964)
  • Kellomäki, Seppo (Suomen metsätieteellinen seura, 1979)
  • Rosa, Elena; van Nouhuys, Saskya; Saastamoinen, Marjo (2017)
    Aggregation can confer advantages in animal foraging, defense, and thermoregulation. There is a tight connection between the evolution of insect sociality and a highly effective immune system, presumably to inhibit rapid disease spread in a crowded environment. This connection is less evident for animals that spend only part of their life cycle in a social environment, such as noneusocial gregarious insects. Our aim was to elucidate the effects of group living by the gregarious larvae of the Glanville fritillary butterfly with respect to individual performance, immunity, and susceptibility to a parasitoid. We were also interested in the role of family relative to common postdiapause environment in shaping life-history traits. Larvae were reared at high or low density and then exposed to the pupal parasitoid wasp Pteromalus apum, either in presence or absence of a previous immune challenge that was used to measure the encapsulation immune response. Surviving adult butterflies were further tested for immunity. The wasp offspring from successfully parasitized butterfly pupae were counted and their brood sex ratios assessed. Larvae reared at high density grew larger and faster than those at low density. Despite high mortality due to parasitism, survival was greater among individuals with high pupal immunity in both density treatments. Moreover, butterfly pupae reared at high density were able to kill a larger fraction of individuals in the parasitoid broods, although this did not increase survival of the host. Finally, a larger proportion of variation observed in most of the traits was explained by butterfly family than by common postdiapause rearing environment, except for adult survival and immunity, for which this pattern was reversed. This gregarious butterfly clearly benefits from high conspecific density in terms of developmental performance and its ability to fight a parasitoid. These positive effects may be driven by cooperative interactions during feeding.
  • Tiitu, Maija; Naess, Petter; Ristimäki, Mika (Taylor & Francis, 2021)
    European Planning Studies, 29:6, 1092-1112
    Situated in northern Europe, the capital regions of Helsinki, and Oslo have many similar premises concerning urban development. However, the structure of the two regions differs by many measures. We explore the differences in urban density and its development in the both regions and the policy instruments that have affected them. Differences are identified by comparing the population densities of urban settlements and the mean distances from residents and workplaces to the city centres of Oslo and Helsinki using GIS methodology and existing literature. In the Oslo region, the population density shifted from a decreasing trend to an increasing one in the late 1980s. In contrast, the Helsinki region only started to densify in the 2010s. Also, the mean distance of residents and workplaces from the city centre is farther in Helsinki. The long period of low-density housing development and the creation of jobs outside centres in Helsinki is related to weaker political steering towards a compact urban form. In Oslo, regulations such as a greenbelt policy but also physical factors, led to densification relatively early. Lagging in densification policies, Helsinki could learn from the experiences of steering land use and mobility in Oslo, which would need additional research.
  • Bhat, K. M. (Suomen metsätieteellinen seura, 1980)
  • Bhat, K. M.; Kärkkäinen, Matti (Suomen metsätieteellinen seura, 1981)