Abstract
Hollow trees are an important habitat for a large number of saproxylic invertebrates, many of which are rare or threatened. Large old trees occur frequently in cities, but the saproxylic fauna inhabiting these trees has been poorly studied. Sampling in urban areas includes the risk of trap failure due to human interference, which needs to be considered when designing sampling. The aim of our study was to find an efficient trap type for sampling saproxylic beetles in hollow urban trees. We compared the species richness and species composition of saproxylic beetle assemblages between trunk window, aluminium foil tray and pitfall traps placed inside hollow trees in the Helsinki metropolitan area, Finland. A total of 30 traps of each trap type were set in 15 trees. The traps caught a total of 4004 saproxylic beetle individuals belonging to 131 species. Trunk window and aluminium foil traps had similar assemblage and trapping efficiency, and were significantly more efficient than pitfall traps. However, pitfall traps caught certain species more efficiently than the other two trap types. Time spent separating insects from samples was the most laborious work stage. The time increased with increasing sample weight, i.e. the amount of wood mould in the trap. Trunk windows were the most efficient trap type also in terms of saproxylic species and individuals per handling time. We conclude that saproxylic beetle fauna living in hollow urban trees can be efficiently sampled with small trunk window traps or containers placed on the inner walls of hollows.
Highlights
Hollow trees are an important habitat for a large number of saproxylic invertebrates
We addressed the following questions: (1) Which trap type is most efficient at catching saproxylic species and individuals? (2) Does species composition differ between trap types? Are certain species caught more efficiently or exclusively with a certain trap type? (3) Does the ranking of the trap types change if the time required for processing the samples in a laboratory is taken into account?
Our findings support the importance of urban old hollow trees to saproxylic beetle communities
Summary
Hollow trees are an important habitat for a large number of saproxylic invertebrates. In most regions of Europe, old hollow trees occur mainly in various semi-natural habitats created and maintained by human activity, including pasture woodlands, hedgerows, avenues and parks (Oleksa et al 2006; Dubois et al 2009; Siitonen 2012b; Hartel et al 2013). Most major cities maintain large tree populations (in the order of tens to hundreds of thousands of trees per city) by actively planting and tending trees in parks and along streets (Nowak et al 2001; Sjöman et al 2012). Some of these trees are sufficiently old to contain hollows
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