On the deterioration and restoration of mire invertebrate communities

Field: Environmental Science (Physical Sciences)

Negative anthropogenic disturbances (e.g., drainage and urbanization) are causing biotic homogenization through the replacement of specialist species with generalists. The identification and conservation of biodiversity hotspots within degraded (e.g., highly urbanized) landscapes, and ecological restoration (i.e., positive anthropogenic disturbance) have the potential to be important tools to counteract these negative effects. Mires are suitable targets for the investigation of these homogenization-reducing activities since they host many mire specialist species of, e.g. invertebrates. \n\nThe main aim of this PhD thesis was to investigate the effects of negative anthropogenic disturbances [urbanization (Chapter I) and drainage for forestry (Chapters II-IV)] on the invertebrate communities of boreal mires and how effective efforts are to reverse these negative effects through ecological restoration [i.e. positive anthropogenic disturbance (Chapters II-IV)]. In addition, the purpose was to determine which environmental variables are key in supporting mire specialist invertebrate species and communities. Therefore, this thesis started by reviewing current knowledge on the responses of mire invertebrate species and communities to anthropogenic disturbances. The effects of urbanization were studied on spiders and carabid beetles (Chapter I), while the effects of drainage for forestry and subsequent restoration were investigated on five solitary invertebrate groups (Chapter II) and social insects, i.e. ants (Chapter III). Finally, a powerful Before-After Control-Impact (BACI) design was used to reveal the effects of drainage and restoration on butterflies (Chapter IV). \n\nGenerally, both high levels of urbanization (Chapter I) and mire drainage for forestry (Chapters II-IV) had negative effects on mire specialist species (lower abundances) and invertebrate communities (homogenized and very different in structure from pristine mire communities). However, these detrimental effects can be reduced or even reversed through appropriate urban mire conservation and ecological restoration. \n\nLocal habitat conditions were shown to be particularly important for the survival of specialist invertebrate species in urban mires (Chapter I) and for the successful recovery of restored mire invertebrates (Chapters II-IV). Individual mire specialist species responded negatively to environmental variables associated with deteriorated (i.e. drained or highly urbanized) mire conditions [number of high (> 3m) trees for carabid beetles, crane flies, micromoths (Chapter II), ants (Chapter III) and butterflies (Chapter IV)] and positively to pristine mire-associated variables [Sphagnum cover for carabid beetles and spiders (Chapters I-II), crane flies (Chapter II) and suggestively for ants (Chapter III); larval food plant cover and number of lower (1.5 - 3m) trees for butterflies (Chapter IV)]. The more specialized the mire species were, the more negatively they were affected by deteriorated-mire-associated variables and the more positively they responded to pristine-mire-associated variables. \n\nI conclude that the restoration actions taken (removing tall trees but leaving smaller trees, and raising the water table level) are appropriate in creating suitable habitat conditions for mire invertebrates, as both individual specialist species and communities showed positive responses already 1-3 years since restoration (Chapters II-IV). Finally, the appropriate restoration actions in well-prioritized locations as well as urban mire conservation should reverse the trend of biotic homogenization.