Soil Chemistry and Ground Cover in Urban Forests
Ecology and Evolutionary Biology | Environmental Indicators and Impact Assessment | Environmental Monitoring | Environmental Sciences | Forest Management | Soil Science
In 1993, I began doing research at 25 permanent study plots in Forest Park in Portland, Oregon. In 2003 and 2013, I found high mortality of trees in Forest Park including seedlings and saplings (recruitment). To determine if the lack of recruitment was an urban phenomenon, I added three control sites in the Mount Hood National Forest in 2013. Significantly lower numbers of young trees were found in the urban forest than at rural sites. In 2015, I found deeper O horizons, higher C/N ratios, and higher levels of soil respiration at more rural sites. Last summer we collected soil samples at all sites to test for a wider range of elements. We are still processing the soil samples so they can be analyzed and will send them to the Central Analytical Laboratory at OSU later this semester to test for calcium, magnesium, and aluminum, in addition to carbon and nitrogen. To better quantify impacts of urbanization on the forest, we also measured ground cover by herbaceous plants and shrubs, downed woody debris, and canopy cover at all sites.
We found significantly deeper O horizons, higher rates of soil respiration, and lower levels of electroconductivity (EC) at rural sites than at urban sites. We believe changes to the soil may be related to the lack of recruitment in urban forests and are looking forward to getting the chemical data back from OSU later this spring to see if there are any differences among locations relative to urbanization. We also will be analyzing the other data we collected. The herbaceous data will be especially interesting. A major die-off of sword ferns has been noticed in the Pacific Northwest, and comparing the data we collected last summer to that previously collected will help determine if the die-off has spread to the Portland area.
Broshot, Nancy E., "Soil Chemistry and Ground Cover in Urban Forests" (2020). Post-Grant Reports. Report. Submission 193.
This research was conducted as part of a Linfield College Student-Faculty Collaborative Research Grant in 2019, funded by the Office of Academic Affairs.
Student collaborators were William McCuen and Jordan Leis.