On 5 November at 10:15 Maarja Vaikre will defend her doctoral thesis „The impact of forest drainage on macroinvertebrates and amphibians in small waterbodies and opportunities for cost-effective mitigation“ (in Animal Ecology).
Researcher Riinu Rannap, University of Tartu
Researcher Liina Remm, University of Tartu
Professor Kari-Matti Vuori, Finnish Environment Institute (Finland)
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.