Plant communities of field margins : the effects of management and environmental factors on species composition and diversity

Agri-environmental schemes have so far resulted in only minor positive implications for the biodiversity of agricultural environments, in contrast to what has been expected. Land-use intensification has decreased landscape heterogeneity and the amount of semi-natural habitats. Field margins are uncultivated areas of permanent vegetation located adjacent to fields. Since the number of these habitats is high, investing in their quality may result in more diverse agricultural landscapes. Field margins can be considered as multifunctional habitats providing agronomic, environmental and wildlife services. This thesis aimed at examining the plant communities of different types of field margin habitats and the factors affecting their species diversity and composition. The importance of edaphic, spatial and management factors was studied on regional, landscape and habitat scales. Vegetation surveys were conducted on regional and landscape scales and a field experiment on cutting management was conducted on a habitat scale. In field margin plant communities, species appeared to be indicators of high or intermediate soil fertility and moist soil conditions. The plant species diversity found was rather low, compared with most species-rich agricultural habitats in Finland, such as dry meadows. Among regions, land-use history, main production line, natural species and human induced distribution, climate and edaphic factors were elements inducing differences in species composition. The lowest regional species diversity of field margins was related to intensive and long-term cereal production. Management by cutting and removal or grazing had a positive effect on plant species diversity. The positive effect of cutting and removal on species richness was also dependent on the adjacent source of colonizing species. Therefore, in species-poor habitats and landscapes, establishment of margins with diverse seed mixtures can be recommended for enhancing the development of species richness. However, seed mixtures should include only native species preferably local origin. Management by cutting once a year for 5 years did not result in a decline in dominance of a harmful weed species, Elymus repens, showing that E. repens probably needs cutting more frequently than once per year. Agri-environmental schemes should include long-term contracts with farmers for the establishment, and management by cutting and removal or grazing, of field margins that are several metres wide. In such schemes, the timing and frequency of management should be planned so as not to harm other taxa, such as the insects and birds that are dependent on these habitats. All accidental herbicide drifts to field margins should be avoided when spraying the cultivated area to minimize the negative effects of sprayings on vegetation. The harmful effects of herbicides can be avoided by organic farming methods.

Population genetics of the invasive plant species Impatiens glandulifera in Southern Finland

Biological invasions affect biodiversity worldwide, and, consequently, the invaded ecosystems may suffer from significant losses in economic and cultural values. Impatiens glandulifera Royle (Balsaminaceae) is an invasive annual herb, native to the western Himalayas and introduced into Europe in the 19th century as a garden ornamental plant. The massive invasion of I. glandulifera is due to its high reproductive output, rapid growth and its ability to outcompete native species. In Finland, the first observations regarding the presence of I. glandulifera date from the year 1947, and today it is considered a serious problem in riparian habitats. The aim of this master’s thesis research is to reveal the population genetic structure of I. glandulifera in Finland and to find out whether there have been one or multiple invasions in Finland. The study focuses on investigating the origin of I. glandulifera in Southern Finland, by comparing plant samples from the Helsinki region with those from its native region and other regions of invasion. Samples from four populations in Helsinki and from the United Kingdom, Canada, India and Pakistan were collected and genotyped using 11 microsatellite markers. The genetic analyses were evaluated using the programs Arlequin and Structure. The results of the genetic analyses suggested that I. glandulifera has been introduced to Finland more than once. Multiple introductions are supported by the higher level of genetic diversity detected within and among Finnish populations than would be expected for a single introduction. Results of the Bayesian Structure analysis divided the four Finnish populations into four clusters. This geographical structure was further supported by pairwise Fst values among populations. The causes and potential consequences of such multiple introductions of I. glandulifera in Finland and further perspectives are discussed.

Litter quality and its response to water level drawdown in boreal peatlands at plant species and community level

Changes in the structure of plant communities may have much more impact on ecosystem carbon (C) cycling than any phenotypic responses to environmental changes. We studied these impacts via the response of plant litter quality, at the level of species and community, to persistent water-level (WL) drawdown in peatlands. We studied three sites with different nutrient regimes, and water-level manipulations at two time scales. The parameters used to characterize litter quality included extractable substances, cellulose, holocellulose, composition of hemicellulose (neutral sugars, uronic acids), Klason lignin, CuO oxidation phenolic products, and concentrations of C and several nutrients. The litters formed four chemically distinct groups: non-graminoid foliar litters, graminoids, mosses and woody litters. Direct effects of WL drawdown on litter quality at the species level were overruled by indirect effects via changes in litter type composition. The pristine conditions were characterized by Sphagnum moss and graminoid litters. Short-term (years) responses of the litter inputs to WL drawdown were small. In longterm (decades), total litter inputs increased, due to increased tree litter inputs. Simultaneously, the litter type composition and its chemical quality at the community level greatly changed. The changes that we documented will strongly affect soil properties and C cycle of peatlands.