Academic journal article Estonian Journal of Ecology

Factors Affecting the Re-Vegetation of Abandoned Extracted Peatlands in Estonia: A Synthesis from Field and Greenhouse Studies

Academic journal article Estonian Journal of Ecology

Factors Affecting the Re-Vegetation of Abandoned Extracted Peatlands in Estonia: A Synthesis from Field and Greenhouse Studies

Article excerpt

INTRODUCTION

Peatlands have been used for peat extraction for centuries. This practice has left behind spoiled landscapes without vegetation. According to the Estonian legislation, all mining areas, including extracted peatlands, should be recultivated after the end of mining (Raudsep, 2011). Although 20-30 years ago areas where peat harvesting had ceased were sometimes used for agricultural purposes and forestry, most of them were just abandoned during and after the end of the Soviet period up to the early 1990s by the state-owned companies. Only very few extracted peatland areas have currently been recultivated. For successful restoration a better understanding of factors affecting this process and its regional peculiarities is necessary (Campbell et al., 2003; Lavoie et al., 2003; Triisberg et al., 2011).

Abandoned extracted peatlands with deep drainage have a negative impact on the hydrology and microclimate of their surroundings; they cause changes in the local outflow of water rich in dissolved organic carbon and the fragmentation of natural areas. These areas have a high fire risk and they reduce habitat diversity. Currently peat is extracted from 20 000 ha in Estonia and the total area of abandoned extracted peatlands is 9371 ha, but in the coming decades their area will be doubled because of the depletion of peat deposits on mining areas (Ramst & Orru, 2009). Extracted and drained peatlands have a dense drainage system and they are an increasing source for man-induced C[O.sub.2] emission caused by accelerated peat decomposition in such areas (Paavilainen & Paivanen, 1995; Salm et al., 2009). In Estonia drained and extracted peatlands emit annually about 10 million tonnes of C[O.sub.2], being the second most important C[O.sub.2] source in this country after industry and exceeding the emissions from traffic (Ilomets, 2001).

The exposed residual peat layer after peat harvesting is often several thousands of years old where seeds/spores are decomposed or not capable of germination (Salonen, 1987, 1994). Therefore, all the propagules for re-vegetation have to be carried here from elsewhere, mostly by the wind. Due to the unfavourable and highly variable growth conditions on the surface of the extracted peatlands, discussed thoroughly by several authors (e.g. Price et al., 1998; Campbell et al., 2002; Campbell & Rochefort, 2003), the propagules have to go through several ecological filters such as human-imposed barriers, intensive agriculture etc. before arriving the extracted peatlands (Belyea, 2004). Moreover, only a few propagules can germinate and form plant assemblages able to survive there for a longer period (Egawa et al., 2009). Hence, the spontaneous re-vegetation of abandoned extracted peatlands is very slow and uneven. Still, this process offers a useful opportunity to study and understand the propagules arrival, their germination, plant survival, and the formation of early plant assemblages, i.e. the peculiarities of the respective succession. There are several studies about the role of some early arriving species, such as Eriophorum vaginatum and E. angustifolium, which create more suitable conditions for other mire plant species (Tuittila et al., 2000; Groeneveld & Rochefort, 2002; Koyama & Tsuyuzaki, 2010), but these results are to some extent discordant. As we pointed out earlier (Triisberg et al., 2011), considering that the dispersal distance of propagules is limited, there can be differences in plant species number and species content between the marginal parts of larger extracted peatlands close to vegetated neighbouring areas and in the central parts located further from the potential propagules source. Salonen & Setala (1992) showed that besides the seed rain from the adjacent plant communities, the quality of substrate and its microbial activity affect the composition of vegetation in extracted peatlands. However, it is not fully clear how far into the extracted peatlands the propagules could be carried, how much the re-vegetation is influenced by the type of the adjacent vegetated areas, and how much the germination of the arriving propagules and the survival of plants depend on the growth conditions or on autecological differences between plant species. …

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