Oļģerts Nikodemus

Seventy-year changes in tree species composition and tree ages in state-owned forests in Latvia

Abstract During the last 100 years, forest management in Latvia has gradually become more and more focused on industrial logging, which can be expected to have affected the tree species composition and age distribution across the landscape. These changes need to be considered in forest management and conservation of biological diversity. The aim of the study was to use forest records to reconstruct the tree species composition and age distribution in the North Vidzeme Biosphere Reserve in northern Latvia for the period, 1929–1941. These data were compared to a data-set from 2008, to determine the changes that transpired during a period of intensification of forest management. The silvicultural methods in the 1920–1941 period were based mostly on natural regeneration of logged stands. This led to succession to birch on harvested spruce stands and can explain the relatively large cover of mature birch stands today. After 1960, forest management was directed on conifer monocultures, and thus spruce stands today predominantly have age <50 years. An age class >150 years is almost absent for all species, and conservation should be directed to adding a portion of old forests to the protection network, and in maintaining the spatial continuity of overmature deciduous stands.

Soil–vegetation interactions in abandoned farmland within the temperate region of Europe

Forests are becoming increasingly dominant in the landscape of north-eastern Europe as a result of a decline in agriculture, land abandonment and the related trend of afforestation. This is also the case in Latvia, where former agricultural land is either artificially afforested or taken over by the natural process of secondary succession. A large spatial and temporal variety of succession and compositional diversity of tree species colonizing fields is observed in the central part of Latvia. Understanding of the possible scenarios in the development of plant communities after land abandonment is important for deciding on viable management solutions, e.g. restoration of semi-natural grasslands or forest regeneration. The aim of the research was to determine the factors affecting the course of secondary succession at its initial stage and the composition of tree species that are colonizing abandoned fields. Ten abandoned fields were surveyed, recording species composition and vegetation structure, determining soil properties and analysing correlations between these factors. The research results help to explain the mechanisms of how soil properties affect the course of succession. On fertile soils a dense herbaceous layer developed, which in abandoned fields resulted in accumulation of a thick cover of litter. Such conditions hinder establishment of typical pioneer species, e.g. grey alder Alnus incana, aspen Populus tremula and birch Betula pendula, whereas Norway spruce Picea abies is able to compete with grass species and thus can more easily establish in abandoned fields, creating favourable conditions for invasion by other tree species.

Current content of selected pollutants in moss, humus, soil and bark and long-term radial growth of pine trees in the Mezaparks forest in Riga

The aim of this study was to evaluate the use of various indicators in the assessment of environmental pollution and to determine the response of pine to changes of pollution levels. Mezaparks is a part of Riga that has been subject to various long-term effects of atmospheric pollution and, in particular, historically from a large superphosphate factory. To determine the spatial distribution of pollution, moss, pine bark and soil O and B horizons were used as sorbents in this study, as well as the additional annual increment of pine trees. The current spatial distribution of pollution is best shown by heavy metal accumulation in mosses and the long-term accumulation of P2O5 pollution by the soil O horizon. The methodological problems of using these sorbents were explored in the study. Environmental pollution and its changes could be associated with the tree growth ring annual additional increment of Mezaparks pine forest stands. The additional increment increased after the closing of the Riga superphosphate factory.

Impact of climate variability, drainage and land-cover changes on hemiboreal streamflow

ABSTRACT The aim of the study was to determine the effects of climate variability, agricultural land drainage and afforestation of agricultural land on river discharge. The study was conducted in the Vienziemīte stream basin (6 km2), where discharge was monitored on a daily basis during the time period of 1946–2010. In the stream basin, natural afforestation of agricultural land began in the 1950s, and in the mid-1970s artificial drainage systems were installed in all agricultural land (70% of the total basin area). Climate variability and artificial drainage were the main factors observed to be affecting stream discharge. The changes were most evident in annual and seasonal mean, minimum and maximum streamflow. There was no effect of afforestation of agriculture land on stream discharge.