AHA in northern Sweden – a case study : conservation values of deciduous trees based on saproxylic insects

Abstract: AHA is a Swedish abbreviation of "reveal threatened park and avenue trees" and is a method to assess the conservation value of individual trees, mainly in the park environments but also in natural stands. This method has previously only been practiced in southern Sweden (Sörensson 2008). To see if this method could provide satisfactory results in northern Sweden, I have studied it in areas around the Umeå River. This was done by studying the relationship between trees with different classifications of conservation value (as classed by the AHA method) and their content of species (species richness and abundance). Insects were collected using trunk window traps in a period of 13 weeks during the summer of 2014. The tree species included in my analysis was aspen, birch, grey alder and goat willow and I looked primarily at the wood-dwelling species for the analysis. There was a total of 3015 saproxylic beetles (Coleoptera), 166 true flies (Diptera) and 234 wasps (Hymenoptera) determined to species level. These 3415 individuals were included in the ANOVA analysis and box plots. The result from the data analysis showed a higher species richness and abundance between the highest class of conservation value and the four lower classes for all tree species (p = 0.000) except for the abundance of insects on goat willow (p = 0.086). There was also a high number of special species found, some were new to Västerbotten and two were even new to Sweden. My result shows that deciduous trees in northern Sweden harbour a significantly higher abundance and species richness of saproxylic species in the AHA-class with higher conservation value. Through this study, I show that the AHA methodology also works well in deciduous habitats in northern Sweden. The high species richness found also demonstrates how important it is to preserve these substrates treated in the AHA-method in order to conserve biodiversity.