Post-Grant Reports


The Relationship between Fungi and Tree Recruitment in Urban Forests

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Biology | 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 tree mortality in Forest Park including seedlings and saplings. I added three control sites in the Mount Hood National Forest in 2013, which showed significantly lower numbers of young trees (recruitment) in the urban forest than at rural sites. Soil analysis showed deeper O horizons, higher C/N ratios, and higher soil respiration at more rural sites. My hypothesis is that nitrogenous air pollution at urban sites is affecting mycorrhizal fungi that should be associated with trees. Last summer, two students and I collected and identified macrofungal fruiting bodies (i.e., mushrooms) at my sites, and we noted characteristics associated with them. We also set up an iNaturalist site so citizen scientists could become involved.

We identified 40 genera of mushrooms; citizen scientists using iNaturalist identified 48 (note they collected all year whereas we only collected in the summer). We found more mushrooms per site in the old growth and National Forest areas than in Forest Park; we also found the greatest percent of mycorrhizal mushrooms in the National Forest where there is less nitrogenous air pollution. Neither of these findings were significant, however we had a low sample size and only a few months of data collection. The data from iNaturalist showed similar trends. We intend to continue the study this coming summer to increase our sample size and to compare our mushroom results to soil chemistry data from 2019.


This research was conducted as part of a Linfield University Student-Faculty Collaborative Research Grant in 2020, funded by the Office of Academic Affairs.

Student collaborators were Jordan Leis and Trinity Ronk-Degraffenreid.

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