Location

Jereld R. Nicholson Library

Subject Area

Environmental Studies (science focus)

Description

In 1993, Dr. Nancy Broshot randomly located 25 permanent study sites in Forest Park in Portland, Oregon to examine the effects of urbanization on forest health. Plant community structure was examined. In 2003, Dr. Broshot reexamined the plant communities at each site and found significantly higher tree mortality and reduced recruitment (young trees) in all areas of the park. Many seedlings that had been present in 1993 were absent in 2003. In 2013, a 20-year follow up study of the tree community was conducted. Although the rate of tree mortality had dropped, recruitment of seedlings and saplings was still low. A series of lichen studies completed at each site in 2013 indicated high levels of nitrogenous air pollution at all sites in the park. In 2014, three control sites along a gradient of air quality in the Mount Hood National Forest above Estacada, Oregon were added to the study. Plant community variables were measured in the same manner as in Forest Park. We found significantly more live trees, saplings and seedlings at the control sites than at sites in Forest Park. We also found significantly fewer dead trees at control sites. Indeed, we had more seedlings at the three control sites than at all 25 of the Forest Park sites. We believe the low level of recruitment may be due to nitrogenous deposition from air pollution in Forest Park; we are waiting for results from collected soil samples to evaluate this hypothesis.

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May 15th, 12:15 PM May 15th, 1:30 PM

Tree Composition and Seedling Recruitment in Urban and Rural Forests

Jereld R. Nicholson Library

In 1993, Dr. Nancy Broshot randomly located 25 permanent study sites in Forest Park in Portland, Oregon to examine the effects of urbanization on forest health. Plant community structure was examined. In 2003, Dr. Broshot reexamined the plant communities at each site and found significantly higher tree mortality and reduced recruitment (young trees) in all areas of the park. Many seedlings that had been present in 1993 were absent in 2003. In 2013, a 20-year follow up study of the tree community was conducted. Although the rate of tree mortality had dropped, recruitment of seedlings and saplings was still low. A series of lichen studies completed at each site in 2013 indicated high levels of nitrogenous air pollution at all sites in the park. In 2014, three control sites along a gradient of air quality in the Mount Hood National Forest above Estacada, Oregon were added to the study. Plant community variables were measured in the same manner as in Forest Park. We found significantly more live trees, saplings and seedlings at the control sites than at sites in Forest Park. We also found significantly fewer dead trees at control sites. Indeed, we had more seedlings at the three control sites than at all 25 of the Forest Park sites. We believe the low level of recruitment may be due to nitrogenous deposition from air pollution in Forest Park; we are waiting for results from collected soil samples to evaluate this hypothesis.

 

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