Suunisliigid märgalakoosluste taastamisel

Väitekirja elektrooniline versioon ei sisalda publikatsiooneMärgalakooslused 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.https://www.ester.ee/record=b535656

Patterns of Assemblage Structure Indicate a Broader Conservation Potential of Focal Amphibians for Pond Management

<div><p>Small freshwater ponds host diverse and vulnerable biotic assemblages but relatively few conspicuous, specially protected taxa. In Europe, the amphibians <i>Triturus cristatus</i> and <i>Pelobates fuscus</i> are among a few species whose populations have been successfully restored using pond restoration and management activities at the landscape scale. In this study, we explored whether the ponds constructed for those two target species have wider conservation significance, particularly for other species of conservation concern. We recorded the occurrence of amphibians and selected aquatic macro-invertebrates (dragonflies; damselflies; diving beetles; water scavenger beetles) in 66 ponds specially constructed for amphibians (up to 8 years post construction) and, for comparison, in 100 man-made ponds (created by local people for cattle or garden watering, peat excavation, etc.) and 65 natural ponds in Estonia. We analysed nestedness of the species assemblages and its dependence on the environment, and described the co-occurrence patterns between the target amphibians and other aquatic species. The assemblages in all ponds were significantly nested, but the environmental determinants of nestedness and co-occurrence of particular species differed among pond types. Constructed ponds were most species-rich irrespective of the presence of the target species; however, <i>T</i>. <i>cristatus</i> was frequent in those ponds and rare elsewhere, and it showed nested patterns in every type of pond. We thus conclude that pond construction for the protected amphibians can serve broader habitat conservation aims in the short term. However, the heterogeneity and inconsistent presence of species of conservation concern observed in other types of ponds implies that long-term perspectives on pond management require more explicit consideration of different habitat and biodiversity values. We also highlight nestedness analysis as a tool that can be used for the practical task of selecting focal species for habitat conservation.</p></div

The number of studied species in ponds with and without focal species.

<p>Filled bars are ponds of focal species presence (<i>T</i>. <i>cristatus</i> or <i>P</i>. <i>fuscus</i>) and empty bars are ponds of focal species absence; whiskers are 95% confidence intervals; number above the bars represent the N–value of each type of pond with and without focal species.</p

The effects of pond type (3 types) and the presence of target species (<i>T</i>. <i>cristatus</i> or <i>P</i>. <i>fuscus</i>) to the number of other considered amphibian and insect species.

<p>The effects refer to likelihood-ratio tests for Generalized Linear Models based on Poisson error distribution and log link function.</p

Nestedness of the aquatic assemblages by pond type, according to the NODF statistic.

<p>NODF metric (Nestedness based on Overlap and Decreasing Fill) ranges between 0% (maximal scatter) and 100% (perfectly nested).</p

Pond type-specific frequencies of occurrence of amphibians and aquatic insects, and the NODF-based significance of fit with a nested assemblage pattern in protected species (listed in the Annexes II and IV of the EU Habitats Directive).

<p>Pond type-specific frequencies of occurrence of amphibians and aquatic insects, and the NODF-based significance of fit with a nested assemblage pattern in protected species (listed in the Annexes II and IV of the EU Habitats Directive).</p