Human impact on biodiversity
Biodiversity in traditional cultural environments, such as meadows and pastures, has been the key issue in most environmental studies carried out at the institute since 1990s. The main results of several single projects were drawn together in the two academic dissertations described below.
For his thesis, Kimmo Saarinen studied butterfly communities in both semi-natural grasslands and field margins in arable landscapes under different management history, methods and intensity in southeastern Finland and adjacent Russian Karelia. Despite the long history of different agricultural practices in Finnish and Russian Karelia, the present butterfly faunae were alike. The higher species richness and diversity observed in more intensively managed farmland in Finland was in contrast to expectations, as the agriculture in Russian Karelia is assumed to resemble Finnish old fashioned practices.
In SE Finland, the butterfly communities were fairly similar in the margins of semi-natural grasslands and arable fields. The species diversity, however, was slightly higher in grasslands because of more diverse field vegetation, which provides food resources for adults and larvae. Although field margins may support a large variety of butterfly species, the communities are usually dominated by Aphantopus hyperantus or Pieris napi. Butterflies on arable farmland are likely to benefit from organic farming methods, i.e. reduced use of chemical fertilisers and pesticides. On the other hand, communities may be adversely affected by loggings in adjacent forests, which provide shelter for species living in margin habitats. Thus, the species richness is higher in field margins bordering forests than it is in margins between adjoining fields.
During the 1990s, a decrease of some meadow-living species and an increase of species inhabiting forest verges and clearings in Finland indicate the effects of a widespread decrease in open habitats and increased afforestation. The trend is likely to continue in the future. In addition, migrations and the expansion of some butterfly species associated with agricultural landscapes may be accelerated due to the predicted global warming.
Juha Jantunen investigated the effects of agricultural practices on the abundance of semi-natural grasslands and their vegetation in southeast Finland and Russian Karelia. Semi-natural grasslands which have been created and maintained by grazing and mowing without the use of fertilisers and ploughing are among the most species rich biotopes of agricultural environments in Finland. Changes in agricultural practices during the 20th century have led to a dramatic reduction in the amount and area of these environments.
In the province of South Karelia, the area of semi-natural grasslands has decreased from 25,000 ha to less than 100 ha due to agricultural intensification and abandonment. The maintenance of the plant communities of semi-natural grasslands can be ensured by grazing or hay cutting, but half of the remaining sites in the province were abandoned. In addition, only a fraction of the sites, still in use, were sustainably managed. The main problems in the managed sites were eutrophication and overgrazing, which through changes in species composition lead towards reduced biodiversity.
Changes in the management may cause adverse, or even irreversible, changes in the species composition. A problem species in grassland plant communities is usually considered to be one that is tall and broadleaved, but a vigorous growth of clover, such as Trifolium medium, can also be deleterious to grassland species. The follow-up of the vegetation after resumed and reorganised management is essential in order to preserve both the floristic and the faunistic values of grasslands.
In Finnish Karelia the loss of semi-natural grasslands combined with decreased quality of the remaining habitats has impoverished the grassland vegetation in comparison to Russian Karelia, where changes in agricultural practices have taken place on a much smaller scale. Agriculture in Russian Karelia is concentrated around animal husbandry and grasslands are still traditionally managed. Semi-natural meadows and pastures have remained in larger quantities, thus providing better circumstances for grassland vegetation in comparison to Finland. The old fashioned hay cultivation in Russia has also maintained a larger variety of grassland flora in field margins and other uncultivated areas than the more intensive cereal/ forage cultivation in Finland.