Browsing by Subject "pirstoutuminen"

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  • Torppa, Kaisa (Helsingfors universitet, 2014)
    The purpose of this thesis was to examine the diversity and species composition of dung beetle (Scarabaeinae) communities in degraded rainforest landscapes in southeastern Madagascar. Several studies elsewhere in the world have revealed that forest-dwelling dung beetle communities and especially large species suffer from forest degradation and fragmentation by decreased species diversity. The most important factors affecting community structure of forest-dwelling dung beetles are habitat area, connectivity and vegetation quality i.e. microclimate. The hypothesis of this study was that the situation is the same in Madagascar. As dung beetles provide several important ecosystem services, like nutrient cycling and bioturbation, loss of dung beetle diversity imposes a secondary threat to the extraordinary nature of Madagascar by decreasing the regeneration ability of vegetation. Material for the study was collected in forest fragments of different size and quality between two areas of primary tropical rainforest – Ranomafana National Park and Vatovavy mountain – in November and December 2011 and January 2012. The sampling was conducted by transects of 30–60 fish- or carrion-baited pitfall traps which were set up in 55 localities in the study area. In each locality, several variables were measured to describe the vegetation and microclimatic conditions. The variables included temperature, humidity, estimate of vegetation quality by 6 observation-based classes, vegetation density, hights of three clearly visible vegetation layers, altitude and slope steepness. In addition, connectivities were measured for the localities using GIS and a satellite image –based vegetation classification. In order to demonstrate the differences between certain localities the study sites were divided into seven zones in terms of their distance from the Ranomafana National Park, average connectivity of the transects and elevation. Altogether 4,199 individuals belonging to 24 species were collected. Six of the species are currently under identification process in the Paris Museum of Natural History. According to the preliminary results they include two species new to science. Largest numbers of species were collected from good quality fragments between Ranomafana and Vatovavy. Also, a clear transition zone in species composition was detected a few kilometers west from Vatovavy, where altitude changes sharply. The study reveals that the species assemblages in the forest fragments and degraded forest areas are surprisingly species rich. This may, however, be partly because of extinction debt, and many of the still surviving species may soon die out due to restricted dispersal possibilities. Connectivity and vegetation quality were shown to have an effect on Canthonini species richness, with less species in less connected areas and lower vegetation quality. Vegetation quality was also shown to have an impact on the proportions of species with different body length: more small and medium-sized (< 8 mm) species were found in fragments where vegetation was more degraded. In addition to revealing how rainforest fragmentation and degradation affect local communities, the study gives interesting information about the distribution of certain species of Epilissus (Scarabaeinae: Canthonini). It has been known before that four species of Epilissus show elevational differentiation in their occurrence in Ranomafana. In this study, two more species of the same genus, E. prasinus and E. emmae obscurpennis, were shown to continue this pattern in lower elevations near Vatovavy mountain, about 50 kilometers east of Ranomafana.
  • Ripatti, Pekka (The Society of Forestry in Finland - The Finnish Forest Research Institute, 1996)
    Questions of the small size of non-industrial private forest (NIPF) holdings in Finland are considered and factors affecting their partitioning are analyzed. This work arises out of Finnish forest policy statements in which the small average size of holdings has been seen to have a negative influence on the economics of forestry. A survey of the literature indicates that the size of holdings is an important factor determining the costs of logging and silvicultural operations, while its influence on the timber supply is slight. The empirical data are based on a sample of 314 holdings collected by interviewing forest owners in the years 1980-86. In 1990-91 the same holdings were resurveyed by means of a postal inquiry and partly by interviewing forest owners. The principal objective in compiling the data is to assist in quantifying ownership factors that influence partitioning among different kinds of NIPF holdings. Thus the mechanism of partitioning were described and a maximum likelihood logistic regression model was constructed using seven independent holding and ownership variables. One out of four holdings had undergone partitioning in conjunction with a change in ownership, one fifth among family owned holdings and nearly a half among jointly owned holdings. The results of the logistic regression model indicate, for instance, that the odds on partitioning is about three times greater for jointly owned holdings than for family owned ones. Also, the probabilities of partitioning were estimated and the impact of independent dichotomous variables on the probability of partitioning ranged between 0.02 and 0.10. The low value of the Hosmer-Lemeshow test statistic indicates a good fit of the model and the rate of correct classification was estimated to be 88 per cent with a cutoff point of 0.5. The average size of holdings undergoing ownership changes decreased from 29.9 ha to 28.7 ha over the approximate interval 1983-90. In addition, the transition probability matrix showed that the trends towards smaller size categories mostly involved in the small size categories, less than 20 ha. The results of the study can be used in considering the effects of the small size of holdings for forestry and if the purpose is to influence partitioning through forest or rural policy.
  • Fourcade, Yoan; WallisDeVries, Michiel F.; Kuussaari, Mikko; Swaay, Chris A. M.; Heliölä, Janne; Öckinger, Erik (John Wiley & Sons Ltd, 2021)
    Ecology Letters 24: 5, 950-957
    Habitat fragmentation may present a major impediment to species range shifts caused by climate change, but how it affects local community dynamics in a changing climate has so far not been adequately investigated empirically. Using long-term monitoring data of butterfly assemblages, we tested the effects of the amount and distribution of semi-natural habitat (SNH), moderated by species traits, on climate-driven species turnover. We found that spatially dispersed SNH favoured the colonisation of warm-adapted and mobile species. In contrast, extinction risk of cold-adapted species increased in dispersed (as opposed to aggregated) habitats and when the amount of SNH was low. Strengthening habitat networks by maintaining or creating stepping-stone patches could thus allow warm-adapted species to expand their range, while increasing the area of natural habitat and its spatial cohesion may be important to aid the local persistence of species threatened by a warming climate.
  • Halonen, Taneli (University of Helsinki, 1999)
  • Juselius, Teemu (Helsingfors universitet, 2017)
    Nowadays a greater number of people live in cities than in earlier times. In Finland, the portion of urban dwellers has nearly doubled in last 50 years. The urbanization has had undisputable benefits for mankind but it has also had widespread negative effects on nature. As cities grow natural habitats are replaced by spreading infrastructure. Remaining mires, forests and other natural habitats are smaller and more isolated than their rural counterparts. These urban habitats are affected by increased pollution and nutrient loads, trampling and other detrimental effects caused by human activity. Alien invasive species may also spread into indigenous vegetation and more of these areas are affected by edge-effects. Ombrotrophic bogs are one of the most nutrient-poor habitats in the North and receive nutrients only by dry and wet deposition. They have been reported to suffer from increased nutrient deposition. Hydrology also has a vital part in function and form of ombrotrophic bogs. Spread of urban infrastructure may alter the way bogs receive water due to increased sealed surface in the catchment areas of these bogs. The effects of urbanization on ombrotrophic bogs in Finland has not been studied previously and the aim of this Master’s thesis is to examine the differences between vegetation in urban and rural bogs and the effects of the size of bog area, nearby population and total N content of surface peat on bog vegetation in different bog types: dwarf shrub pine bogs, low sedge bogs, Sphagnum fuscum pine bog and Sphagnum fuscum bog. Last two were studied together due to their similarities. According to this study the differences between urban and rural bogs in Southern Finland are small. The greatest differences were observed among dwarf shrubs typical for bogs but the effects varied between bog types. In dwarf shrub pine bogs, the amount of dwarf shrubs decreased while in low sedge bogs, the cover of Vaccinium oxyccocos, and in Sphagnum bogs, the occurrence of Empetrum nigrum increased. The bogs studied in urban sites were generally smaller and more isolated than rural bogs. Around urban bogs, there were also significantly higher number of residents than in rural areas, and one of the most distinct effects of urbanization on bog vegetation discovered was reduction of cover and appearance of species vulnerable to trampling. The increased nutrient loads usually reported in urban habitats was not visible in nitrogen content of surface peat. On the contrary, low sedge bogs seemed to have higher nitrogen content on rural bogs, which may be caused by intense agriculture in rural areas. The reason for not detecting increased urban nitrogen deposition based on peat samples may be caused by increased nitrogen uptake of Sphagnum mosses. Sphagnum mosses have been reported to benefit from increased nitrogen deposition until they reach nitrogen saturation point. After this the excess nitrogen enters peat soil. Low nitrogen deposits in Southern Finland can probably be used fully by Spaghnum mosses and thus no increase in nitrogen content was observed. The results of this study indicate that ombrotrophic peat bogs are at least partly resistant to the effects of urbanization. The level of urbanization in Finland is lower than in Central Europe, which may lead to lowered levels of detrimental effects caused by urbanization. Alien species are probably also unable to invade the acidic and nutrient poor urban bogs. The mire types studied here are also usually situated in the centre of ombrotrophic bogs and may have avoided most of the edge effects. However, if studied, the edges of the urban bogs might have shown large number of harmful effects caused by urbanization.
  • Kellomäki, Seppo; Wuorenrinne, Heikki (Suomen metsätieteellinen seura, 1979)
  • Schrader, Marko (Helsingfors universitet, 2011)
    Liito-orava (Pteromys volans) on havumetsävyöhykkeen varttuneissa sekametsissä esiintyvä pieni yöaktiivinen nisäkäs. Suomen liito-oravakannan on arvioitu taantuneen viimeisten vuosikymmenien aikana ja laji on luokiteltu Suomessa vaarantuneeksi. EU:n luontodirektiivissä liito-orava on mainittu erityistä suojelua vaativana lajina, jonka lisääntymis- tai levähdyspaikkoja ei saa hävittää. Liito-oravan suosimat varttuneet kuusivaltaiset sekametsät ovat yleisiä useiden suomalaisten kaupunkien taajama-asutusten tuntumissa. Näihin metsiin kohdistuu suuri kaavoituspaine. Tutkimuksen tarkoituksena on selvittää metsämaiseman rakenteen muutoksen vaikutusta liito-oravaan ja arvioida eroavatko kaupunki- ja metsätalousalueet liito-oravan elinympäristönä. Selvitin Tampereen kaupungin ja Kangasalan kunnan alueella sijaitsevan tutkimusalueen metsärakenteen muutokset vuosina 1966–2004 ja liito-oravaesiintymät vuonna 2004. Tarkoituksena on selvittää miten metsärakenteen muutos on vaikuttanut alueen liito-oravakantaan ja liito-oravien esiintymiseen. Ilmakuvatulkinnalla rajasin 52 km2 kokoisen tutkimusalueen metsät niiden rakenteen perusteella metsäkuvioihin. Keväällä 2004 kartoitettiin tutkimusalueen liito-oravaesiintymiä ja kirjasin metsäkuvioiden tärkeimmät puustotiedot. Luokittelin kaikki metsäkuviot neljään, liito-oravalle soveltuvuuteen perustuvaan luokkaan. Paikkatieto-ohjelmassa annoin kullekin kuvioluokalle eri värin ja lopputuloksena oli monivärinen kartta josta pystyy helposti havaitsemaan liito-oravalle soveltuvat, sopimattomat sekä liikkumiseen soveltuvat alueet. Ilmakuvatulkinnalla tein vastaavia karttoja myös vuosille 1966, 1979, 1987 ja 1995. Metsäkuviotietojen perusteella laskin eri vuosille pirstoutumista kuvaavan läheisyysindeksin. Aiemmin Etelä-Suomesta saatuja liito-orava radiopantatutkimustuloksia ja monivuotisia kartoitustuloksia vertailuaineistona käyttäen tein arvion liito-oravaesiintymien määrän kehityksestä vuosina 1966–2004. Tutkimusalueen liito-oravakartoituksessa löysin 318 papanahavaintopaikkaa. Papanahavainnoista 78 % olivat enintään 500 m päässä lähimmästä ihmisasutuksesta. Tampereen kaupungin alueen havainnoista 73 % sijaitsevat Tampereen kaupungin omistamilla alueilla. Liito-oravalle sopivien metsien pinta-ala on vuosina 1966–2004 laskenut 48,8 %. ja liito-oravalle sopimattomien alueiden pinta-ala on kasvanut 22 %. Liikkumiselle soveltuva metsäpinta-ala on kasvanut 46,3 %. Liito-oravalle sopivien laikkujen keskikoko on laskenut 13,1 hehtaarista 4,7 hehtaariin ja alue on voimakkaasti pirstoutunut. Arvion mukaan Tampereen tutkimusalueen asuttujen liito-orava elinpiirien määrä on laskenut vuosina 1966–2004 yli 59 %. Tutkimusalueen metsiköiden kehitys on ollut vastaava kuin muilla metsätalousalueilla eteläisessä Suomessa. Kaupungin läheisyys ei ole merkittävästi vaikuttanut kehitykseen. Metsänhakkuiden ja asutuksen pirstomassa maisemassa viherkäytävien merkitys korostuu. Kuitenkin suuri osa liito-oravaesiintymistä sijaitsee kaupungin mailla ja jäljellä oleva soveltuvan metsän määrä on niin pieni ja pirstoutunut, että tulevaisuuden kaavoitustoimilla ja metsänkäsittelyllä tulee olemaan suuri vaikutus paikalliseen liito-oravakantaan.
  • Komonen, Atte; Puumala, Ilkka; Várkonyi, Gergely; Penttilä, Reijo (Suomen Metsätieteellinen Seura, 2021)
    Silva Fennica 55: 1
    According to ecology theory, isolated habitat fragments cannot maintain populations of specialized species. Yet, empirical evidence based on monitoring of the same fragments over time is still limited. We studied the colonization–extinction dynamics of eight wood-decaying fungal species in 16 old-growth forest fragments (<14 ha) over a 20-year period (1997–2017). We observed 19 extinctions and 5 colonizations; yet, the distribution of extinctions and colonizations did not differ from the one expected by chance for any of the species. Twenty-six percent of the extinctions took place in two natural fragments amid large forest–peatland complexes. Phellinus nigrolimitatus (Romell) Bourdot and Galzin decreased and Phellinus ferrugineofuscus (P. Karst.) Bourdot increased in abundance (number of logs occupied). The volume of living spruce trees in the forest fragments correlated positively with the number of logs inhabited in five of the study species. Because fragment characteristics did not affect species turnover, it seems that stochastic processes governed colonizations and extinctions. Although the least abundant species in 1997 had declined, and the most abundant species had become more abundant, it appears that specialized wood-decaying fungi can persist for decades in isolated old-growth forest fragments, if suitable dead wood is continuously available.