Changes in peatland vegetation dynamics and their link to climate in a southern boreal bog during the last centuries

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Title: Changes in peatland vegetation dynamics and their link to climate in a southern boreal bog during the last centuries
Author: Huilla, Miika
Contributor: University of Helsinki, Faculty of Science
Publisher: Helsingin yliopisto
Date: 2020
Thesis level: master's thesis
Abstract: Northern peatlands form a globally significant carbon reservoir holding almost one third of global terrestrial organic soil carbon. Peatlands are in constant interaction with the atmosphere and their carbon balance can change from a sink to a source. Climate is the one of the most important factors controlling peatland dynamics and subsequently carbon dynamics. As global warming is predicted to have increasingly strong impacts over the high latitudes, also peatlands will be affected. Peatlands are an environment defined by a certain type of vegetation, which can tolerate excess moisture and of often low pH. Peatland vegetation can be divided based on the preferred habitat conditions. Peatland vegetation compositions are not static, but instead everchanging and they react to changes in climate and environment, observed as shifts from vegetation assemblage to another. I studied the climatic response of peatland vegetation compositions in Lakkasuo bog in Southern Finland. High resolution macrofossil approach was carried out to observe peat vegetation changes trough time, in particular I studied responses to known climate phases. To obtain robust chronologies, both 210Pb and 14C dating was applied. Peat bulk density and C/N ratio was also analysed, carbon accumulation rates calculated, and current vegetation and water table depth (WTD) measured in the field. Three peat sections, 50-60cm from the top, were analysed. Dating revealed that the peat sections reached back c. 300 years. Plant data was statistically analysed using Changepoint to make an objective core-to-core comparison of the changes and the timing of vegetation shifts. Because WTD is largely defining the vegetation compositions in bogs, for Lakkasuo sites three bog microforms, i.e. microhabitats, currently representing different WTD levels were chosen for the palaeoecological analyses. Vegetation was inspected in high plant taxonomical level and as larger compositional groups (plant functional types). For changepoint analyses plant taxa were classified as “dry”, “intermediate” and “wet” based on their preferred moisture conditions today. Macrofossil data indicated clear shifts in vegetation composition in Lakkasuo as a response to the Little Ice Age (LIA) cool period and to current warming. LIA was characterised by presence of wet taxa. Current warming, in turn, is visible as an increase in dry taxa. This leads to the conclusion that climate has been the prevalent controlling factor for the bog vegetation during the last c. 300 years. Current development towards dry conditions in Lakkasuo will affect the peatland carbon dynamics. The peatland is projected to experience decrease in effective moisture hindering carbon uptake capability.
Subject: boreal peatlands
climate change
environmental change
bog vegetation
plant macrofossil
Discipline: Geologia

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