Vegetation dynamics in floodplain meadows: influence of mowing and sediment application
Kuupäev
2016-09-12
Autorid
Ajakirja pealkiri
Ajakirja ISSN
Köite pealkiri
Kirjastaja
Abstrakt
Lamminiidud ehk luhad on jõeäärsed, kevadise suurveega üleujutatavad niidud. Oma viljaka mulla ja lopsaka taimekasvu tõttu on nad ajalooliselt olnud väärtuslikud heinamaad. Tänapäeval ohustab Eesti luhtade elurikkust niitmise lakkamine ja sellele järgnev võsastumine. Võsastunud luhad muutuvad sobimatuks nii niidutaimedele kui ka mitmetele luhaga seotud linnuliikidele ning luhal kudevatele kaladele. Oma doktoritöös uurisin, kuidas paarkümmend aastat hooldamata ja osaliselt võsastunud luhtadel taimkate taastub, kui niitmist taas alustada. Niitmine muudab taimkatte madalamaks ning loob paremad valgustingimused madalakasvulistele taimedele, kes ilma inimese abita kõrgekasvulistega konkureerida ei suuda ning niidult kaovad. Leidsin, et kümneaastase niitmise järel soontaimede liigirohkus taastatud luhtadel suurenes, ja seda eelkõige kuivemates taimekooslustes. Liigirikkuse tõusu tagas niitmise ja heina koristamisega kaasnev taimse varise ehk kulu eemaldamine, mille mõju oli olulisem kui heinaga luhast väljakantavate toitainete oma. Ühel multšitaval uurimisalal (hein hekseldati ja jäeti maha) langes väiksekasvuliste rohundite arvukus madalamale kui hooldamata alal – see on üks võimalik tõestus antud hooldamisvõtte sobimatusest. Hooldamisefektiivsuse hindamiseks pakkusin välja ka mitmeid indikaatorliike ehk taimi, kelle esinemine luhaniidul viitab kas hooldatud või hooldamata aladele. Lisaks maapealsele taimestikule uurisin ka luhamullas olevaid taimeseemneid, sest mulla seemnepank võib mõnel puhul niitude taastamisel oluline olla. Leidsin, et ka 25 aastat hooldamata olnud luhtadel moodustub seemnepank kahe kolmandiku ulatuses luhtadele omastest niiduliikidest, mis julgustab luhaniitude taastamisel enam tähelepanu pöörama ka mullas leiduvatele seemnetele. Loodusliku ülejutusrežiimiga luhtadel on väga oluliseks taimeleviste kandjaks ka vooluvesi, mis ühe aastaga tõi uurimisaladele 85 taimeliiki, keda seal enne ei esinenud. Doktoritöö näitas, et luhaniitude taastamiseks on Eesti oludes olemas piisavalt taimeliikide leviseid nii taimkattes kui mullas ning üleujutusvesi on liikidele oluline levikuvektor. Kohane hooldamine koos heina äraveoga tagab luhtadel mitmekesise taimkatte ja aitab säilitada väärtuslikke ökosüsteeme.
Floodplain meadows are riverside grasslands inundated during spring floods. Valued due to their lush vegetation, they were traditionally mown for animal fodder. At present, Estonian floodplain meadows are threatened by management cessation and consecutive shrub encroachment. Meadows covered by shrubs are unsuitable habitats for grassland plants, several floodplain-related birds and for fish that spawn on the floodplain. In my thesis I focused on the vegetation dynamics of floodplain meadows where mowing was re-started after two decades of abandonment. Mowing lowers the vegetation height and provides better light conditions for small statured plant species that would otherwise be out-competed by taller plants in competition for light. I found that the species diversity increased after ten years of management, the changes being more pronounced in relatively drier of the studied plant communities. The effect of management was mediated by litter removal which was more important in explaining changes in species richness than the amount of nutrients carried out of the meadow by hay harvesting. The proportion of small herbs unexpectedly decreased in one of the study sites that was managed by mulching (hay left on ground). This might indicate that mulching is an inappropriate means of management. To assess the management status of a meadow, I proposed several management indicator species. In addition to the vegetation, I also studied soil seed bank which could contribute to grassland restoration. I discovered that in the soil seed bank of meadows abandoned for 25 years, two thirds of the species present were typical to floodplain meadows. This can encourage nature managers to use also the soil seed banks in restoration of floodplain meadows. The naturally meandering rivers with un-altered flooding regime also proved efficient vectors for plant dispersal, carrying in 85 new species to the study sites during one year. The thesis demonstrate that Estonian floodplain grasslands still harbour a viable propagule pool both above- and belowground for floodplain meadow restoration, and that rivers can facilitate plant dispersal. Proper management with hay harvesting can support a diverse vegetation and maintain the complex ecosystem of floodplain meadows.
Floodplain meadows are riverside grasslands inundated during spring floods. Valued due to their lush vegetation, they were traditionally mown for animal fodder. At present, Estonian floodplain meadows are threatened by management cessation and consecutive shrub encroachment. Meadows covered by shrubs are unsuitable habitats for grassland plants, several floodplain-related birds and for fish that spawn on the floodplain. In my thesis I focused on the vegetation dynamics of floodplain meadows where mowing was re-started after two decades of abandonment. Mowing lowers the vegetation height and provides better light conditions for small statured plant species that would otherwise be out-competed by taller plants in competition for light. I found that the species diversity increased after ten years of management, the changes being more pronounced in relatively drier of the studied plant communities. The effect of management was mediated by litter removal which was more important in explaining changes in species richness than the amount of nutrients carried out of the meadow by hay harvesting. The proportion of small herbs unexpectedly decreased in one of the study sites that was managed by mulching (hay left on ground). This might indicate that mulching is an inappropriate means of management. To assess the management status of a meadow, I proposed several management indicator species. In addition to the vegetation, I also studied soil seed bank which could contribute to grassland restoration. I discovered that in the soil seed bank of meadows abandoned for 25 years, two thirds of the species present were typical to floodplain meadows. This can encourage nature managers to use also the soil seed banks in restoration of floodplain meadows. The naturally meandering rivers with un-altered flooding regime also proved efficient vectors for plant dispersal, carrying in 85 new species to the study sites during one year. The thesis demonstrate that Estonian floodplain grasslands still harbour a viable propagule pool both above- and belowground for floodplain meadow restoration, and that rivers can facilitate plant dispersal. Proper management with hay harvesting can support a diverse vegetation and maintain the complex ecosystem of floodplain meadows.
Kirjeldus
Väitekirja elektrooniline versioon ei sisalda publikatsioone.
Märksõnad
luhad, taimekooslused, liigirikkus, taimkattedünaamika, pärandkooslused, maastikuhooldus, ökoloogiline taastamine, niitmine, lammisetted, meadows, plant communities, species diversity, vegetation dynamics, seminatural communities, landscape management, ecological restoration, mowing, floodplain sediments