Browsing by Author "Sandholm, Laura"

Peatlands are globally important ecosystems as they have been estimated contain about 40 % of the global soil carbon pool. Therefore, in light of the projected increase in temperatures and possible increase in fire frequencies, it is of great importance to understand how peatlands are expected to develop under changing climate conditions. Currently it is estimated that of western continental Canadas 365 000 km2 peatlands, around 28 % are underlain by permafrost which however store about 38 % of the soil carbon in the area. Climate change is expected to affect these peatlands very quickly, because they are situated at the dry limit of peatland distribution. Peatlands develop in areas where production of new organic material exceeds the decomposition rate, whereby dead plant material will start to accumulate as peat, and thus, atmospheric carbon that has been seized in the plant material will become stored. Peat is stored in the peatland in the order that it accumulates, with the oldest material at the bottom end newest at the top, thereby making it possible to infer the succession of the stored vegetation. Permafrost may aggregate in peatlands due to cold climates and the insulating effect of peat moss. Fires usually cause severe combustion of peat plateaus, because they exhibit a dry and aerated surface and high tree vegetation cover. As fires remove peat through combustion, permafrost may collapse. As the permafrost within the peat plateau collapses it causes the peatland surface to subside, producing collapse areas which exhibit different hydrological conditions from the surrounding plateau. Due to a lack in knowledge about how peat plateaus have developed and reacted under different fire regimes, throughout their developmental history, it is difficult to say how they will react to future changes. Also very little is known about the actual mechanism behind initial peat plateau development or about what factors are important in determining whether permafrost will re-aggregate after collapse. With my thesis I will add to the knowledge about the initiation and developmental history of permafrost containing peatlands within the zone of discontinuous permafrost in continental northwestern Canada. I investigate the initiation patterns and effects of fires on peatland development by examining peat cores from three different peatlands in British Columbia, Canada. Each core is analysed for changes in peat main components and plant species composition throughout the peatland developmental history. As different species have different ecological range for example in regards to moisture and nutrient conditions, one can infer these based on the plant species community. In order to see when the peatlands initiated the bottom of the organic material was dated through radiocarbon dating. All peatlands initiated through onto ground formerly occupied by upland forest vegetation, which however also caused the dated samples from the bottom of the cores not to be very informative in regards to the actual peatland initiation time. The northernmost site, with the thickest peat, shows clear signs of being a permafrost affected peatland, starting from the initial peat accumulation to present day. The two other sites are more diverse in their development as they show signs of both permafrost peatlands and of sites that have undergone permafrost collapse. The peat on the permafrost affected peatlands has accumulated very slowly. Current peat accumulation rates, counted based on tree ring data and correlated to charred layers in the peat, show that the peatland areas that have collapsed, actually accumulate peat more quickly than the peat plateau with permafrost. This may indicate that as long as peatlands are still able to endure under warmer climates, it may be that they will actually accumulate more carbon due to higher production under non-permafrost conditions.