Dynamics of grassland plant diversity in changing landscapes
Date
2018-05-08
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Elurikkuse vähenemine on 21. sajandil ühiskonna üheks suurimaks väljakutseks. Looduslikele kooslustele asulate või põllumaade rajamine, traditsioonilistest majandusvõtetest loobumine ja väetamine on vaid mõned näited elurikkust viimase saja aasta jooksul oluliselt mõjutanud teguritest. Kunagiste pool-looduslike niitude pindala on mitmel pool Euroopas vähenenud kuni 97% võrreldes nende liigirikaste koosluste ajaloolise levikuga. Elurikkuse pideva vähenemise ja kliimamuutuste kontekstis vajame põhjalikke teadmisi, milliseid liike ohustab elupaikade pindala kadu või kvaliteedi halvenemine enim. Doktoritöös uurisin, millised protsessid mõjutavad koosluste koosseisu ja kujunemist erineva maakasutuse ajalooga niitudel. Leidsin, et kuigi regulaarselt hooldatud, st. karjatatud või niidetud, liigirikkad niidukooslused on teeveertel kujunevate noorte kooslustega pealtnäha sarnased, kasvavad ajaloolistel niitudel kõrvuti pigem erinevate tunnustega liigid, mis viitab pikaajalise majandamise tähtsusele elurikkuse kujunemisel. Noortes kooslustes ja metsastuvatel endistel niitudel olid koos kasvamas sarnaste tunnustega liigid, tõenäoliselt seoses levimispiirangutega ja konkurentsiga ressursside pärast. Unikaalsed ajaloolised liigiandmed võimaldasid võrrelda liigilist koosseisu tugevalt kahjustunud ja killustunud niidukooslustes samade alade taimkatte analüüsidega ajast, mil nende koosluste olukord oli veel hea. Liigiandmete võrdlemisel selgus, et 30% ajalooliselt esinenud liikidest on nüüdseks koosluste kahjustumise ja pindala vähenemise tõttu lokaalselt kadunud. Tundlikumad olid eeskätt liigid, mis on hea levimis-, kuid nõrga konkurentsivõimega ning piiratud taluvusega kasvukohtade keskkonnatingimuste muutustele. Killustunud maastikes on seega olulisemad tunnused, mis soosivad liikide püsimist olemasolevates kasvukohtades. Tuvastasin, et väljasurnud liigid olid oma tunnustelt võrreldes stabiilsete liikidega eripärasemad, mis viitab, et Euroopa niidud on kaotamas unikaalset osa oma funktsioonidest. Liikide tunnustega arvestades saame teha tulevikus targemaid looduskaitselisi otsuseid elurikkuse püsimiseks, suunates tähelepanu veel laialt levinud või alles hiljuti laialt levinud liikidele, mis on muutuste tõttu enim ohustatud.
Over the last century, human-induced changes have influenced considerably biodiversity in grasslands, causing both declines and increases in plant species occurrence and abundance. Ongoing biodiversity decline and anticipated changes in climatic conditions require thorough knowledge of the factors that determine species colonization and extinction dynamics following changes in area and habitat quality. I studied the processes that drive community assembly in grassland ecosystems at different spatial scales. By comparing the species trait composition of habitats at different successional stages in the same landscape, I was able to detect the vegetation dynamics and the mechanisms behind the changes. My study revealed that at small scales, species with dissimilar traits occurred together in stable grasslands with long grazing regime, whereas species with more similar traits grew together in abandoned grasslands without management and in young developing grasslands, where management activity was started recently. The results suggest the important role of long and stable land-use in the development of grasslands with high biodiversity. I studied which species suffer and benefit most under changing conditions in grasslands by comparing unique vegetation data up to 300 years old to current species lists from the same locations. Analysing re-survey data in Estonian dry calcareous grasslands and grasslands across different parts of Europe, I discovered that ~30% of grassland species had gone locally extinct or showed decreasing occurrence following habitat change. Species more vulnerable to local extinctions had different functional traits and habitat preferences than the more successful species. The losers had good dispersal ability, but poorer ability for local persistence and competition, showing that nutrient enrichment, fragmentation, lack of grazing and mowing and climate change are the main drivers of change in European grasslands. The results of this thesis led to a better understanding of grassland plant diversity dynamics in changing landscapes. When species’ functional traits are considered, better decisions can be made to mitigate further decline of biodiversity. Research shows that conservation measures also have to focus on species that are still common or have recently been common, as they too are threatened
Over the last century, human-induced changes have influenced considerably biodiversity in grasslands, causing both declines and increases in plant species occurrence and abundance. Ongoing biodiversity decline and anticipated changes in climatic conditions require thorough knowledge of the factors that determine species colonization and extinction dynamics following changes in area and habitat quality. I studied the processes that drive community assembly in grassland ecosystems at different spatial scales. By comparing the species trait composition of habitats at different successional stages in the same landscape, I was able to detect the vegetation dynamics and the mechanisms behind the changes. My study revealed that at small scales, species with dissimilar traits occurred together in stable grasslands with long grazing regime, whereas species with more similar traits grew together in abandoned grasslands without management and in young developing grasslands, where management activity was started recently. The results suggest the important role of long and stable land-use in the development of grasslands with high biodiversity. I studied which species suffer and benefit most under changing conditions in grasslands by comparing unique vegetation data up to 300 years old to current species lists from the same locations. Analysing re-survey data in Estonian dry calcareous grasslands and grasslands across different parts of Europe, I discovered that ~30% of grassland species had gone locally extinct or showed decreasing occurrence following habitat change. Species more vulnerable to local extinctions had different functional traits and habitat preferences than the more successful species. The losers had good dispersal ability, but poorer ability for local persistence and competition, showing that nutrient enrichment, fragmentation, lack of grazing and mowing and climate change are the main drivers of change in European grasslands. The results of this thesis led to a better understanding of grassland plant diversity dynamics in changing landscapes. When species’ functional traits are considered, better decisions can be made to mitigate further decline of biodiversity. Research shows that conservation measures also have to focus on species that are still common or have recently been common, as they too are threatened
Description
Väitekirja elektrooniline versioon ei sisalda publikatsioone
Keywords
meadow plants, species richness, species composition, population dynamics, extinction, environmental factors, land use, Estonia