"Citizen science urban forest inventory and monitoring projects should use data validation and quality assurance procedures to enhance and document data quality," the researchers, from several US and Swedish institutions, conclude.
Having compared street tree data collected by both volunteers and experts in three US and one Swedish city, they found that volunteers:
- occasionally missed trees (1.2%) or counted extra trees (1.0%);
- were around 90% consistent with experts for site type, land use, dieback, and genus identification;
- recorded species consistent with experts for 85% of trees;
- scored 99.8% on "mortality status", though they note there were few dead trees to record;
- slightly overstated diameter at breast height (DBH), by 0.33cm on average.
They also found that crown transparency and wood condition "had the poorest performance and participants expressed concerns with these variables", and concluded "these variables should be dropped from future citizen science projects".
However, "volunteer data collection may be a viable option for some urban forest management and research needs, particularly if genus-level identification and DBH at coarse precision are acceptable", they stated.
The findings are published in Urban Forestry & Urban Greening.