Effects of disturbance on biological diversity of beetles (Coleoptera) in the field layer: a comparison between power-line corridors and closed-canopy forests.
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- Master's theses (INA) 
Since the start of industrial forestry in the 1700 century Norwegian boreal forests have gone true a dramatic change. Modern forestry practices have made the forests more homogenous, due to clear cutting of old forest, which reduces the number of old and dead trees. Because of a frequent maintenance cutting of trees, power-line corridors may constitute a reservoir of dead wood, litter biomass, enhanced shrub cover and especially in the edge zones also increased grass cover. Question raised in this thesis are as follows: 1) Does the frequent cutting of tree vegetation under the power-line, increase beetle (Coleoptera) species richness, biodiversity and species abundance? 2) Is there a difference in species richness, composition, functional feeding groups and biodiversity between the edge and the interior habitat, and if this difference is the same in early i.e. power-line corridor and later successional stages of forest? To capture beetles sweep nets were used on 20 sites in 2009 and 31 other sites in 2010. Within each of the 51 x 20 plots, sweep netting was carried out in a systematic manner so that the whole area was covered once, in five different habitat types A) power-line corridor, B) edge of power–line corridor, C) forest edge, D) forest, distance into forest equal to one half of the corridor width, and E) 100 m into the forest from the corridor/forest edge. In addition, data on field layer vegetation, trees and habitat characteristics were sampled in 2009 and 2010. In 2011, additional data on forest characteristics and habitat characteristics were sampled at the same 51 sites. A total of 3048 individuals belonging to 210 species of 32 beetle families were collected. Main findings where that beetle species composition varied significantly between different habitats. Detritivores where more associated with forest habitats, while herbivores were more associated with early succession habitats. Species richness was higher in the centre of the early succession habitat the power-line corridor than along the edge of the early succession, whereas the forest edge had higher species richness than the forest interior. Early succession stages appeared to be positively affected by the frequent clearing of vegetation, because of increases in the cover of grass, deciduous shrubs and dwarf shrubs. Beetle species diversity was higher in the power-line corridor than in the forest interior. Whereas biodiversity in the forest edge zone was intermediate. The relative proportion of individuals and species within different ecological groups differed among the five different habitats. Interestingly, the herbivore/predator ratio shifted from strong herbivore-bias in the center of the power-line corridor (early successional stage forest) to a strong predator-bias 100 m into the later successional stage forest, with gradual change in the ratio in the plots in between these different habitats. In conclusion, I found that regular maintenance cutting of trees in power-line corridors, with associated changes in field layer vegetation, influenced biological diversity of beetles and may increase biological diversity on a local scale.
Master's thesis in Natural resource management