Typen biologinen sitoutuminen metsäpalon jälkeen boreaalisen metsän eri sukkessiovaiheissa

• Main Author: Ritala, Kaisa
• Other Authors: Helsingin yliopisto, Maatalous-metsätieteellinen tiedekunta, Metsätieteiden laitos, University of Helsinki, Faculty of Agriculture and Forestry, Department of Forest Sciences, Helsingfors universitet, Agrikultur- och forstvetenskapliga fakulteten, Institutionen för skogsvetenskaper
• Format: Master Thesis
• Language: Finnish
• Published: Helsingin yliopisto 2015
• Subjects: typpi; typensidonta; boreaalinen metsä; metsäpalo; sukkessio; Skoglig ekologi och resurshushållning; Forest Ecology and Management; Metsien ekologia ja käyttö; Northern Finland
• Online Access: http://hdl.handle.net/10138/155781

Nitrogen is an important nutrient for forest growth. The sources of nitrogen in boreal forests are underground processes, biological nitrogen fixations and depositions. The availability of nitrogen in boreal forests is limited, which is why biological nitrogen fixation is a crucial thing. In natural forests, nitrogen is fixed in bottom layer vegetation and in the bacteria that live on the ground, especially in cyanobacteria. The fixing activity of bacteria depends on many environmental factors, of which the temperature, moisture and species of the bottom layer are the most important. It’s been predicted that forest fires will increase in the boreal zone, due to climate change. This will increase the number of different successional stages. Forest fires are the most important disturbance in boreal forests, since they can initiate the succession from the beginning and affect the circulation of nutrients. Fires also affect the activity of biological nitrogen fixation by releasing nutrients and, partly or completely, destroying the bottom layer vegetation. The results of fires at different successional stages are poorly known and there’s no research concerning the whole bottom layer. The purpose of the study was to find out the effects to biological nitrogen fixation when a forest fire has started succession at the beginning. The material was collected at Värriö nature reserve in Northern Finland (67?46´ N, 29?35´ E). Four forests were chosen for the research. In these areas, fires had occurred 5, 45, 62 and 156 years ago. The forest type was sub-xeric heath forest, dominated by Scots pine (Pinus sylvestris L.). To measure the nitrogen fixation, a sample plot was built in each forest. Ten samples of the ground vegetation and humus layer were collected four times during the summer from each plot. The biological nitrogen fixation was defined with acetylene reduction assay. The samples were analyzed for both the field moisture and saturation humidity at the different moisture stages. The inventory of the vegetation was ...