Hydrological disturbances and naturalness of aapa mires in Finland

Abstract

Peatlands comprise one of the key elements in the boreal landscape. In Finland, almost one third of the land area is covered by different types of peatlands. Half of the Finnish peatland area has been drained, however, and in Southern half of the country, 75 % is drained (1). While drainage has increased forest growth, it has also caused manifold ecological consequences. For example, the state of the remaining undrained peatlands is affected by drainage of surrounding areas and fragmentation.

The undrained peatland area in Finland consists of various sizes of peatland patches that often, at least in the southern areas, are not intact peatland ecosystems but only remnant patches of formerly much larger peatland complexes. How is the surrounding land use affecting the undrained patches? Especially aapa mires and related minerogenic peatlands, which are common in the boreal zone, are dependent on water inflow from upper catchment areas and, thus, sensitive to changes in catchment hydrology. If water inflow from surrounding areas diminishes, an aapa mire may start to develop into ombrotrophic (rain fed) bog (2). This kind of shift means a profound change in the structure and functions of a peatland ecosystem. It can be conceptualized as an ecosystem collapse, in which one ecosystem ceases to exist, and a new type of ecosystem springs up (3).

We conducted a GIS analysis based on Finnish national land survey’s digital map data, air photos, and LIDAR based terrain model. The objective was to yield information on the hydrological naturalness of the remaining undrained peatlands in Finland and to assess the disturbances the surrounding land use exerts on aapa mires. We investigated the amount and size classes of undrained peatland patches and the drainage state of their margins. Then we chose a sample of large (more than 50 hectares) peatland patches (n = 120) containing aapa type vegetation patterns, delineated catchment areas of the aapa mires, and quantified the hydrologic disturbances on them.

Results show the amount of undrained peatlands, how disturbed are their margins, and the average state of hydrological naturalness of large aapa mires in different climatic zones of Finland. Ultimate target of the study is not only to improve the knowledge on the current state of Finnish peatlands, but the results are also prerequisite for assessing the future changes of peatlands in the project SHIFTMIRE: Ecosystem shift potential of northern mires in response to hydrological change, funded by the Academy of Finland.

(1) LUKE 2017. Forest resources. Natural Resources Institute Finland, Helsinki. Web publication: http://stat.luke.fi/en/tilasto/6221.

(2) Tahvanainen, T. 2011. Abrupt ombrotrophication of a boreal aapa mire triggered by hydrological disturbance in the catchment. Journal of Ecology 99, 404–415.

(3) Keith D.A. et al. 2015. The IUCN Red List of Ecosystems: motivations, challenges and applications. Conservation Letters 8, 214–226.