Justin Wigdahl
A City’s urban forest is a major part of the health of an urban ecosystem. However, cities are harsh environments for trees, limiting what species can be used. Narrowed tree diversity leads to overplanting a few species that can exacerbate disease and pest issues such as Dutch Elm Disease or Emerald Ash Borer. Diversifying a city’s tree canopy can minimize the potential for pest and disease-related loss and provide a wider range of ecosystem services by selected trees, such as supporting soil health, habitat, pollinator resources, and more. Different disciplines in the design and engineering community can propose trees for urban sites, but each discipline receives different levels of training on plant material selection, analyzing site conditions for planting, and evaluating the likelihood of long-term plant success.
This study analyzed the tree species specified in landscape site plans submitted to the City of Des Moines, Iowa over more than 4 years to determine if the disciplinary training of different design and engineering firms contracted to prepare the plans affected the diversity of trees for each project.
After collecting data from 82 site plans, data analysis showed that, although landscape architects had a more diverse plant palette overall, there was no significant difference between the average number of species per site between disciplines. It also showed no significant difference between the Shannon index score (which measures evenness and richness) for each discipline. We found the factor that determined plant diversity was site size. Our data also gives us a glimpse of a large part of Des Moines’s future tree canopy which tells us how the city is meeting up to common urban forestry tree diversity guidelines.
Going forward, more data collection and analysis is needed from other cities to see if the discovered trend persists. In terms of tree canopy, existing tree canopy data should be gathered to determine if planting ratios are within appropriate bounds for each species.
Duration: 04/30/2019
Principal Investigator(s): Dr. Grant Thompson