The impact of forest drainage on macroinvertebrates and amphibians in small waterbodies and opportunities for cost-e ffective mitigation
Kuupäev
2020-10-02
Autorid
Ajakirja pealkiri
Ajakirja ISSN
Köite pealkiri
Kirjastaja
Abstrakt
Väikesed ja/või ajuti kuivavad veekogud on erilised elupaigad: olles omadustelt väga heterogeensed, tõstavad need kohalikku liigirikkust ning pakuvad elupaika mitmetele unikaalsetele liikidele. Kuna väikeveekogude arv ja levik maastikus on seotud veehulga muutustega, on need inimtegevusest tugevalt mõjutatud. Oluline väikeveekogude elustiku vaesumist põhjustav tegur on metsakuivendus. Vahetult pärast kraavide rajamist alaneb põhjaveetase, väheneb üleujutuste kestus ning suureneb äravool, kuna liigne vesi juhitakse kraavidega alalt välja. Tulemuseks on ulatuslikud kuivenduskraavide võrgustikud, mida perioodiliselt rekonstrueeritakse, st puhastatakse põhjasetetest ja taimestikust. Käesolevas töös uurisin kuivenduse ja kraavide rekonstrueerimise mõju väikeveekogude elustikule majandusmetsades ja kuivendatud kaitsealadel, keskendudes muuhulgas elustikumõju leevendusvõimalustele tiikide ja kraavilaiendite rajamise näol. Kuivenduse mõju väikeveekogude elustikule ilmneb nii elupaikade kao (lompide kuivamine), kui sellega kaasneva koosluste teisenemise ja üheülbastumise kaudu – väheneb veeselgrootute liigirikkus ning arvukus lompides ning teisenevad kraavide kooslused. Kaitsealadel ei ole kraavide looduslikule suktsessioonile jätmine jätkusuutlik, kuna varjulised kraavid kahepaiksetele väärtuslikke sigimispaiku ei paku, välja arvatud juhul kui kraavidel tegutsevad koprad. Ka majandusmetsades on kahepaiksete elujõuliste populatsioonide säilitamiseks vajalik leevendusmeetmete rakendamine, kuna nende eelistatud veekogud – kraavid ja raiesmikulombid – kipuvad rekonstrueerimisjärgselt suurema tõenäosusega kuivama. Veeselgrootutele ei ole leevendusveekogud n-ö “no net loss” meede, kuna kooslused erinevad loodulike lompide omadest, kuid sellegipoolest soodustavad leevendusveekogud kuivendatud maastikes neis harvemini esinevate liikide esinemist. Kokkuvõttes on leevendusveekogude rajamine üsna tõhus meede väikeveekogudega seotud liikide toetamiseks majandatavates metsades
Small and/or temporary waterbodies are unique habitats that contribut to regional diversity and support many unique and endemic species. As temporary waterbodies are sensitive to changes in water volumes, their numbers and distribution are strongly affected by human activities. Wetland drainage, including for forestry, could be one of the main reasons why freshwater biodiversity is in decline. Drainage has significant effects on site hydrology by lowering the water table and leading excess water away via ditches. As a consequence, ditch networks constitute a very significant aquatic habitat in drained areas but are subject to periodic ditch network maintenance (DNM). Here I examined the effect of forest drainage and DNM on small waterbodies and their associated fauna in forest and fen landscapes, focusing on the ways to mitigate the loss of biodiversity. The effect of drainage and DNM on macroinvertebrates manifests through habitat loss (desiccation of pools) and subsequent shift and homogenization of assemblages as ditching and DNM substantially decreased the total number and abundance of taxa in remnant pools and changed ditch communities, though mean diversity was unaffected. Leaving drained protected peatlands for natural succession is not a feasible for supporting amphibian populations, as overgrown ditches do not substitute natural floods as breeding habitats presumably because of dense canopy cover. Ditches with beavers on the other hand provide high quality reproduction sites. Special measures are essential to mitigate the effect of DNM to macroinvertebrates and amphibians in drained forests. Remnant pools and newly cleaned ditches, preferred by brown frogs, have higher desiccation risk; therefore their populations in may not be sustainable in the long run without mitigation measures. For macroinvertebrates, construction of mitigation pools cannot be used as a “no net loss” measure, but rather as a means to supplement the species pool as they add species not common in drained forests. Nevertheless, creating mitigation pools alongside DNM seems to be feasible and cost-effective method to increase the diversity and number of available waterbodies in drained forest and thus support biodiversity.
Small and/or temporary waterbodies are unique habitats that contribut to regional diversity and support many unique and endemic species. As temporary waterbodies are sensitive to changes in water volumes, their numbers and distribution are strongly affected by human activities. Wetland drainage, including for forestry, could be one of the main reasons why freshwater biodiversity is in decline. Drainage has significant effects on site hydrology by lowering the water table and leading excess water away via ditches. As a consequence, ditch networks constitute a very significant aquatic habitat in drained areas but are subject to periodic ditch network maintenance (DNM). Here I examined the effect of forest drainage and DNM on small waterbodies and their associated fauna in forest and fen landscapes, focusing on the ways to mitigate the loss of biodiversity. The effect of drainage and DNM on macroinvertebrates manifests through habitat loss (desiccation of pools) and subsequent shift and homogenization of assemblages as ditching and DNM substantially decreased the total number and abundance of taxa in remnant pools and changed ditch communities, though mean diversity was unaffected. Leaving drained protected peatlands for natural succession is not a feasible for supporting amphibian populations, as overgrown ditches do not substitute natural floods as breeding habitats presumably because of dense canopy cover. Ditches with beavers on the other hand provide high quality reproduction sites. Special measures are essential to mitigate the effect of DNM to macroinvertebrates and amphibians in drained forests. Remnant pools and newly cleaned ditches, preferred by brown frogs, have higher desiccation risk; therefore their populations in may not be sustainable in the long run without mitigation measures. For macroinvertebrates, construction of mitigation pools cannot be used as a “no net loss” measure, but rather as a means to supplement the species pool as they add species not common in drained forests. Nevertheless, creating mitigation pools alongside DNM seems to be feasible and cost-effective method to increase the diversity and number of available waterbodies in drained forest and thus support biodiversity.
Kirjeldus
Väitekirja elektrooniline versioon ei sisalda publikatsioone
Märksõnad
forest drainage, macroinvertebrates, amphibians, water bodies, forest economics