Impacts of forest drainage on biodiversity and habitat quality: implications for sustainable management and conservation

Date

2015-01-16

Journal Title

Journal ISSN

Volume Title

Publisher

Abstract

Töö koondab senised teadmised metsakuivenduse mõjust elurikkusele, hinnates selle pikaajalist toimet elupaigaomadustele ja liikidele ning juhendab, kuidas kuivendamist elustikku säästvamalt korraldada. Kuivendamist rakendatakse laialdaselt metsa tootlikkuse suurendadmiseks. Selle keskkonnamõjudele on aga, nt raiega võrreldes, vähe tähelepanu pööratud. Pärast kraavide kaevamist, toimuvad ökosüsteemis mitmesugused muutused, mis ökoloogiliste ja sotsiaalmajanduslike tagasisidemehhanismide tõttu on suuresti pöördumatud. Pikaajalise kuivenduse tagajärjel korralduvad sadade liikide asurkonnad ümber, nii leidsime, et vähemalt viiendikule lodumetsa liikidest on kuivendus kahjulik, kuid nende asemele levib umbes sama palju uusi liike. Kuivenduse mõjud on suuresti viibega ja kaudsed, toimides näiteks puistuga seotud mikroelupaikade aeglase muutumise kaudu. Puistu struktuuri muutumise suhtes olid eriti tundlikud samblad ja samblikud . Kuivenduse mõju neile saaks leevendada suurendades puistu mitmekesisust ja lamapuude hulka. Kuivendatud metsad polnud üheselt vaesunud, vaid neis leidus väärtuslikke elupaigakomponente ja tänu sellele ka ohustatud liike. Näiteks ei paistnud kuivendus väikeste veekogude üldhulka vähendavat, küll aga muutis nende omadusi – looduslikud väikeveekogud asendusid osaliselt kraavidega. Metsaaladel laialt levinud inimtekkelised veekogud, nagu kraavid ja rattarööpad, pakuvad mitmekesiseid elupaiku, sobides täiendama looduskaitsevõtteid. Viimased on aga tulemuslikud kui need suunata võimalikult paljudele sarnase nõudlusega liikidele ning kõige tõhusamatesse paikadesse maastikul. Töös kirjeldatakse süsteemset lähenemist metsakuivenduse ühendamiseks looduskaitse eesmärkidega. Selleks tuleb maastikust lähtuvalt valida elustiku sihtrühm, piiritleda suunisliigid ning jaotada ruumis erinevad majandamisvõtted, et tagada nii puidutootmine kui ka elustiku säilimine  
This thesis integrates the present knowledge on the impacts of forest drainage on biodiversity, assess the long-term impact of the drainage on habitat quality and species assemblages, and gives implications, how to harmonize ditching practices with sustainable management. Forest drainage manipulates the key components of the ecosystem – hydrology and dominating organisms (trees, Sphagnum mosses) – and consequently the whole biota and ecosystem functioning. Forest drainage is practised in vast areas to increase timber production. Its environmental impacts, yet, have gained little attention, compared to e.g. effects of harvesting. The harpoon heuristic depicts the post-drainage transformation of the ecosystem. After the initial stick – i.e. the ditching – the harpoon penetrates deeper pressing its barbs ( i.e. irreversible changes) one after another into the ecosystem. The irreversibilities are caused by several ecological and socio-economical feedback mechanisms. During the long-term draining, populations of hundreds of species reorganize. For example, drainage is detrimental for at least one fifth of the species in swamp forests, though about the same number of new species colonizes the area after drainage. A large part of drainage impacts are delayed and indirect, functioning via slowly changing forest structure. Lichens and bryophytes were especially sensitive to the latter. Thus the impact of forest drainage could be mitigated by increasing the diversity of overstory and abundance of logs. Drained forests were not unambiguously impoverished, but contained valuable habitat components and therefore also threatened species. For example drainage did not seem to decrease the overall amount of small water bodies, though it did change their features – natural water bodies were replaced with ditches. Widespread anthropogenic water bodies, such as ditches and wheel rut pools provide varied habitats, thus could complement local restoration and conservation attempts. The latter are effective if targeted to multiple species with similar habitat requirements, and to key sites in the landscape. In the thesis a systematic approach for harmonizing forestry ditching practices with the aims of biodiversity protection is described. According to this, representative ‘focal species’ from sets of sensitive species should be selected, depending on landscape context and the stands allocated into four main groups of management approaches. Hundreds of species should be examined to identify a few representative biodiversity targets for drainage mitigation programmes. Some bryophytes and lichens growing on live and dead trees were provided as representatives of the biota of natural swamp forest. The general implications based on this thesis suggest paying more attention to the impacts of forest drainage on biodiversity and applying appropriate mitigation measures according to landscape context. The further research to support biodiversity conservation practises includes assessing less studied but potentially sensitive species groups, details of the impact mechanisms, searching for and testing of focal-species and habitat management approaches.

Description

Väitekirja elektrooniline versioon ei sisalda publikatsioone.

Keywords

metsakuivendus, keskkonnamõjud, bioloogiline mitmekesisus, elupaigad, looduskaitse, forest drainage, environmental effects, biodiversity, habitats, nature preservation

Citation