Tuesday, 30 October 2012

The urban environment as a habitat for deadwood hoverflies

A recent record of a Callicera from the middle of South Woodham Ferrers reminded me of a long-lingering hobbyhorse. We pay remarkably little attention to trees in our streets and parks, and yet they must be ideal for many deadwood hoverflies. After all, many are regularly pollarded and this must create the conditions needed for rot holes. Other forms of damage will induce sap runs (Horse Chestnuts are especially prone to bacterial cankers and sap runs) and perhaps also decaying roots.

The presence of Callicera in various places, including suburban Wolverhampton, shows how rot holes can be important. There are records of Mallota cimbiciformis from central London parks and plenty of records of that ubiquitous urban species Myathropa florea.

It seems to me that there is therefore a strong case for research into the frequency of rot holes in urban trees and for an investigation into what uses these holes. Perhaps it is time for the conservation agencies to commission such studies? Maybe it could be done as a big ‘citizen science’ project? Whichever means is used, it seems to me that there is a need to develop thinking about the saproxylic biodiversity value of urban trees and to raise awareness amongst tree officers in Local Authorities.

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