Focal species in wetland restoration
Kuupäev
2020-07-13
Autorid
Ajakirja pealkiri
Ajakirja ISSN
Köite pealkiri
Kirjastaja
Abstrakt
Märgalakooslused on tuntud oma liigirikkuse ja eripäraste ökosüsteemide poolest. Inimtegevuse tagajärjel on looduslike märgalade pindala maailmas vähenenud 20. sajandist alates enam kui 50%. See on omakorda viinud paljude märgalasid asustavate liikide arvukuse languseni, s.h. niidukahlajad ja kahepaiksed, keda käsitletakse ka antud doktoritöös.
Käesolevas töös uuritakse erinevate märgalaelupaikade (tiigid, märjad hooldatud rannaniidud ja metsanduse eesmärgil kuivendatud siirdesoometsad) taastamist Eestis, lähtudes elupaigatundlikest suunisliikidest. Erinevat tüüpi (looduslikud, inimtekkelised, spetsiaalselt kahepaiksetele rajatud) väikeveekogude liigilise koosseisu ja struktuuri uuringust selgus, et kõige liigirikkamad on peamiselt harivesilikule rajatud veekogud. See tähendab, et harivesiliku tarbeks väikeveekogude taastamine ja rajamine loob sobivaid elupaiku ka teistele (pool)veelistele liikidele. Rannaniitude uuringus leiti, et ohustatud kahlajaliikidele (eriti niidurüdile) on sobivaimaks pesitsuspaigaks suurepindalalised ja laiad karjatatavad rannaniidud, kus puuduvad puud ning leidub ajutisi madalaveelisi lompe. Samuti oli neil niitudel arvukamalt kahepaikseid ja mitmekesisem soontaimestik. Tugevalt kuivendatud siirdesoometsade looduslikkuse taastamine osalise metsaraiega näitas, et kraavide varjulisuse vähenemise järgselt kasvas raba- ja rohukonna sigimisaktiivsus drastiliselt. Kraavide sulgemisest tingitud veerežiimi muutuse tagajärjel tekkisid osaliselt üleujutatud alad ja lombid, mis järgnevatel aastatel muutusid pruunide konnade eelistatud sigimispaikadeks.
Doktoritöös selgub, et erinevates märgalasüsteemides on suunisliikide esinemise peamised tegurid sarnased: päikesele avatud veekogud või märgade laikudega suured killustamata niidualad. Mõnda neist tingimustest saab kiiresti taastada, näiteks võsa eemaldamise või kraavide sulgemisega. Siiski on tõenäoline, et eriti poollooduslikus keskkonnas (näiteks rannaniitudel või rajatud tiikide ümbruses), on vaja edasist võsastumist vältida pideva karjatamise või niitmisega.
Suunisliikide kasutamise kohta märgalakoosluste taastamisel võib seega kokkuvõtvalt öelda, et ohustatud liikidele elupaikade taastamine tagab ka paljude teiste märgaladest ja vee-elupaikadest sõltuvate liikide suurema liigirikkuse.
Freshwater ecosystems are long acknowledged by their rich and unique biodiversity. The natural wetland area has declined by more than 50% during the 20th century. Human-caused habitat degradation and loss has resulted in the reduction of wetlands’ biodiversity. Well known is the decline of amphibians and wetland birds, that are also in the focus of the current doctoral thesis. This thesis explores habitat management and restoration of various wetlands (ponds, managed wet grasslands, and peatlands drained for forestry) in Estonia guided by the most habitat-sensitive focal species among amphibians and waders. A study of the species assemblage and structure of different types of small water bodies (natural, man-made, specially created for amphibians) revealed that pond (re)construction specifically for threatened amphibians (particularly for great crested newt) will also provide suitable habitats for other (semi)aquatic species since these ponds supported relatively species-rich assemblages. Extensively grazed large wide and wet coastal grasslands without woody vegetation provide breeding conditions for threatened waders (in particular Baltic dunlin, Black-tailed godwit and Common redshank), larger brown frogs’ populations (common frog and moor frog), and more diverse vascular plant communities. Restoring the heavily engineered ecosystem of ditched forested wetlands toward more natural states by partial forest cutting and ditch blocking may mitigate the overall afforestation-related negative drainage impact to brown frogs. In my study, such restoration rapidly increased the populations of brown frogs typical of natural wetlands. I found that key factors for the presence of focal species in different wetland systems are similar: the area of open habitat (either sun exposed water table or non-fragmented meadow area), with large wet patches. Some of these conditions can be easily restored, for instance by removing brushwood or by ditch blocking. However, it is likely that maintaining these features, especially in semi-natural settings (such as coastal meadows or around constructed ponds) may need sustained grazing or mowing to prevent future overgrowth. My main conclusion is that amphibians and waders can be used as focal species for the restoration of degraded wetlands and brown frogs could supplement the western capercaillie as a focal species to guide sustainable forest management.
Freshwater ecosystems are long acknowledged by their rich and unique biodiversity. The natural wetland area has declined by more than 50% during the 20th century. Human-caused habitat degradation and loss has resulted in the reduction of wetlands’ biodiversity. Well known is the decline of amphibians and wetland birds, that are also in the focus of the current doctoral thesis. This thesis explores habitat management and restoration of various wetlands (ponds, managed wet grasslands, and peatlands drained for forestry) in Estonia guided by the most habitat-sensitive focal species among amphibians and waders. A study of the species assemblage and structure of different types of small water bodies (natural, man-made, specially created for amphibians) revealed that pond (re)construction specifically for threatened amphibians (particularly for great crested newt) will also provide suitable habitats for other (semi)aquatic species since these ponds supported relatively species-rich assemblages. Extensively grazed large wide and wet coastal grasslands without woody vegetation provide breeding conditions for threatened waders (in particular Baltic dunlin, Black-tailed godwit and Common redshank), larger brown frogs’ populations (common frog and moor frog), and more diverse vascular plant communities. Restoring the heavily engineered ecosystem of ditched forested wetlands toward more natural states by partial forest cutting and ditch blocking may mitigate the overall afforestation-related negative drainage impact to brown frogs. In my study, such restoration rapidly increased the populations of brown frogs typical of natural wetlands. I found that key factors for the presence of focal species in different wetland systems are similar: the area of open habitat (either sun exposed water table or non-fragmented meadow area), with large wet patches. Some of these conditions can be easily restored, for instance by removing brushwood or by ditch blocking. However, it is likely that maintaining these features, especially in semi-natural settings (such as coastal meadows or around constructed ponds) may need sustained grazing or mowing to prevent future overgrowth. My main conclusion is that amphibians and waders can be used as focal species for the restoration of degraded wetlands and brown frogs could supplement the western capercaillie as a focal species to guide sustainable forest management.
Kirjeldus
Väitekirja elektrooniline versioon ei sisalda publikatsioone
Märksõnad
wetlands, biological communities, species