Factors influencing the re-vegetation of abandoned extracted peatlands in Estonia
Date
2014-04-30
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Eesti on olnud üheks maailma sooderikkamaks riigiks, kuid soid on siin ka ulatuslikult kuivendatud kasutamiseks metsa- või põllumaana ning turba kaevandamiseks. Kui varasemalt kaevandati peamiselt tükkturvast ja mõju loodusele ei olnud suur, siis 1950ndatest võeti kasutusele freestehnoloogia, mistõttu on nii kaevandamisalade kui ka kaevandamise järgselt tekkinud jääksoode pindala kiiresti suurenenud. Praegu on see Eestis 9371 ha jääksoid, kuid nende pindala suureneb lähikümnendil veelgi. Jääksood mõjutavad ümbruskonna hüdroloogilist režiimi ja mikrokliimat, vähendavad looduslikku mitmekesisust, suurendavad kasvuhoonegaaside emissiooni ja on väga tuleohtlikud ning seetõttu tuleks jääksood korrastada. Eestis on see ka seadustega nõutav, kuid jääksoid on seni veel väga vähe korrastatud. Jääksoode spontaanne taastaimestumine toimub väga aeglaselt, kuna elujõuline seemnepank on hävitatud ning ainult mõned tuulega saabunud levised on võimelised seal idanema ning kasvama hakanud taimed püsima. Peamiselt takistavad taastaimestumist ebasoodsad keskkonnafaktorid: ebastabiilsed ning ebasoodsad niiskustingimused, tuuleerosioon ning külmakerge.
Käesoleva doktoritöö peamisteks eesmärkideks oli selgitada välja keskkonnafaktorid, mis mõjutavad jääksoode taastaimestumist; selgitada erinevusi kesk- ja ääreosade taimestumises nii jääksoodel kui ka kasvuhooneeksperimendi põhjal; testida, kuidas mõjutab jääksoo liigirikkust väetamine ja paremate niiskustingimuste loomine ning selgitada, kas üldistatud keskkonnafaktorid – jääkturba omadused ja paksus – on rakendatavad kui indikaatorid jääksoode korrastamise planeerimisel.
Väliuuringute ja jääksoode revisjoniandmete analüüsil tehti kindlaks, et jääksoode taastaimestumine sõltub kõige enam kaevandamise viisist, mikrovormist, ning jääkturba omadustest. Liigirikkus jääksoodel vähenes looduslikult taimestunud kooslustega piirnevatelt äärealadelt keskosa suunas. Kasvuhoonekatse tulemused näitasid aga, et servaefektist olulisemaks on paremad niiskustingimused, mis võimaldasid paljudel liikidel kasvama hakata. Ühekordne väetamine ei avaldanud mõju taimeliikide koguarvule jääksoodest võetud proovides, kuid suurendas keskmist taimeliikide arvu ja katvust, samuti ei mõjutanud väetamine kasvuhoones hoitud proovide üldist liigirikkust, mis osutab sellele, et jääksoode aeglane taastaimestumine on tingitud pigem ebasoodsatest niiskustingimustest. Taastaimestumist mõjutab veel ka jääkturba paksuses ja omadused. Korrastamiseks sobiva suuna valimisel osutus oluliseks piiriks turba paksus 2,3 m: alad, mille turbakihi paksus on alla 2,3 m sobivad korrastamiseks madal- või siirdesookoosluste ning üle 2,3 m alad rabakoosluste suunas. Aladel, kus on võimalik taastada rabakooslust, on soovitatav luua mikrovormi erinevusi kujundades jääkväljadele kuivenduskraavidega risti piklikke lohke. Taastaimestumise protsessi saab kiirendada ja edukust suurendada taimematerjali introdutseerimise teel.
Estonia is one of the most peatland rich countries in the world. The peatlands are here widely drained for forestry, agriculture and peat production. In former times, peat was extracted as block-cut peat, and that had a rather limited impact on surroundings; in the middle of the 20th century a peat milling technique was taken into use that raised rapidly the volume of peat extraction and increased the area of abandoned extracted peatlands. The total area of extracted peatlands is currently 9371 ha, but in the coming decades it will be doubled. Extracted peatlands influence the hydrological regime and microclimate of the neighbourhood, reduce bio-diversity, increase greenhouse gas emission and are risk of fires. The spontaneous re-vegetation of extracted peatlands is a very slow process, because of the totally depleted or spoiled seed bank; therefore only some propagules that arrive by wind can germinate, survive and form a plat cover on those areas. The recovery of vegetation is inhibited by unfavourable environmental factors: unstable and unfavourable moisture conditions, wind erosion and frost heaving. According to the legislative acts all those areas should be recultivated/rehabilitated. However, in Estonia only few extracted peatland areas have been restored so far. The main aim of this PhD-theses was (i) to determine the environmental factors affecting the re-vegetation of the abandoned extracted peatlands, (ii) to clarify the differences of the re-vegetation processes in the central and marginal parts of extracted peatlands, (iii) using a greenhouse experiment to ascertain how the fertilization and favourable moisture conditions influences the germination and species richness and, (iv) to determine if some general environmental factors, such as the properties and the depth of residual peat can be used as indicators for restoration planning. The results from the field studies and inventory of extracted peatlands showed that the main factors influencing the re-vegetation are former treatment, surface microform, and peat properties. Species richness on extracted peatlands decreased from the edges bordering with naturally vegetated areas towards central parts. However, results from the greenhouse experimental study showed that instead of the adjacent vegetated area better moisture conditions enabled the growth of many plant species. A single application of fertilizer did not have an effect on the total number of plant species on extracted peatland, but increased the plant cover and the mean number of species. Neither did the fertilizer have an overall influence on the number of species in the greenhouse experiment. It indicates that the re-vegetation of extracted peatlands is more affected by the moisture conditions than by the lack of nutrients. The re-vegetation of extracted peatlands is also influenced by the depth of the residual peat and its properties. The threshold for choosing the appropriate target community for restoration appeared to be 2.3 m: areas with residual peat depth thinner than 2.3 m should be restored towards fen or transitional mire and areas with residual peat depth over that value towards raised bog communities. If restoration towards bog communities is possible, the microhabitat variability could be additionally supported by creating mounds and furrows positioned perpendicular with ditches. The re-vegetation process can also be accelerated by introducing plant material and creating suitable moisture conditions.
Estonia is one of the most peatland rich countries in the world. The peatlands are here widely drained for forestry, agriculture and peat production. In former times, peat was extracted as block-cut peat, and that had a rather limited impact on surroundings; in the middle of the 20th century a peat milling technique was taken into use that raised rapidly the volume of peat extraction and increased the area of abandoned extracted peatlands. The total area of extracted peatlands is currently 9371 ha, but in the coming decades it will be doubled. Extracted peatlands influence the hydrological regime and microclimate of the neighbourhood, reduce bio-diversity, increase greenhouse gas emission and are risk of fires. The spontaneous re-vegetation of extracted peatlands is a very slow process, because of the totally depleted or spoiled seed bank; therefore only some propagules that arrive by wind can germinate, survive and form a plat cover on those areas. The recovery of vegetation is inhibited by unfavourable environmental factors: unstable and unfavourable moisture conditions, wind erosion and frost heaving. According to the legislative acts all those areas should be recultivated/rehabilitated. However, in Estonia only few extracted peatland areas have been restored so far. The main aim of this PhD-theses was (i) to determine the environmental factors affecting the re-vegetation of the abandoned extracted peatlands, (ii) to clarify the differences of the re-vegetation processes in the central and marginal parts of extracted peatlands, (iii) using a greenhouse experiment to ascertain how the fertilization and favourable moisture conditions influences the germination and species richness and, (iv) to determine if some general environmental factors, such as the properties and the depth of residual peat can be used as indicators for restoration planning. The results from the field studies and inventory of extracted peatlands showed that the main factors influencing the re-vegetation are former treatment, surface microform, and peat properties. Species richness on extracted peatlands decreased from the edges bordering with naturally vegetated areas towards central parts. However, results from the greenhouse experimental study showed that instead of the adjacent vegetated area better moisture conditions enabled the growth of many plant species. A single application of fertilizer did not have an effect on the total number of plant species on extracted peatland, but increased the plant cover and the mean number of species. Neither did the fertilizer have an overall influence on the number of species in the greenhouse experiment. It indicates that the re-vegetation of extracted peatlands is more affected by the moisture conditions than by the lack of nutrients. The re-vegetation of extracted peatlands is also influenced by the depth of the residual peat and its properties. The threshold for choosing the appropriate target community for restoration appeared to be 2.3 m: areas with residual peat depth thinner than 2.3 m should be restored towards fen or transitional mire and areas with residual peat depth over that value towards raised bog communities. If restoration towards bog communities is possible, the microhabitat variability could be additionally supported by creating mounds and furrows positioned perpendicular with ditches. The re-vegetation process can also be accelerated by introducing plant material and creating suitable moisture conditions.
Description
Väitekirja elektrooniline versioon ei sisalda publikatsioone.
Keywords
jääksood, metsauuendus, keskkonnategurid, Eesti, cut-over peatlands, reforestation, environmental factors, Estonia