Western Redcedar Health and Urban Heat in Portland, Oregon

Community science links Western Redcedar dieback with urban heat

Western Redcedar

Importance of Western Redcedar

  • Many of the remaining large redcedar trees may be important cultural trees, still capable of providing resources for ceremony, shelter, transportation, textiles, and more.
  • Western Redcedar is also an important tree to the industrial heritage of the Northwest. Many Redcedar trees are grown and harvested for specialty wood products because of its natural durability.
  • Western Redcedar trees provide many services to our communities and environments by sequestering carbon, shading spaces such as bus stops, intercepting and absorbing stormwater, and sheltering wildlife.
  • Understanding the factors affecting the health of Western Redcedar is critical because of its broad distribution and footprint in Northwest forests.



The Problem


Hypothesis

Given the link between dieback and recent consecutive longer and hotter droughts, we hypothesized Western Redcedar trees would be less healthy in hotter areas of Portland.


Methods


Ten examples of the random trees visited by community scientists

The below map displays 10 trees shared on iNaturalist by volunteers from  Hoyt Arboretum .


Linking observed Redcedar trees with urban heat data

Air temperature data were extracted for location of a Redcedar observation.


Results

Preliminary analyses indicated the probability of a tree having top dieback increased with afternoon air temperatures. Evidence for a relationship between afternoon temperatures and tree health was found with a general linear model using a binomial distribution.

Please note the results presented below are preliminary and have not been formally peer-reviewed. This analysis is part of a larger study involving trees from multiple Northwest cities. Contact hulbe@wsu.edu to get involved or learn more about the broader analyses.


Western Redcedar trees with dead tops

Discussion

Portland's western redcedar are feeling the heat.

This preliminary analysis indicates Portland's Western Redcedar trees are vulnerable to urban heat.

More severe summer droughts are likely to increase Western Redcedar canopy dieback and mortality.

As  Andrus et al. (2024)  indicated, Western Redcedar may indeed be a canary in our forests, especially our urban forests. Climate may be changing more quickly than our trees and communities can cope with.

Which communities have the most Redcedar?

Western Redcedar Street Tree Density Map

This heatmap indicates where Redcedar is planted the most abundantly on the streets of Portland. These neighborhoods and communities may therefore be vulnerable to Western Redcedar dieback.

Please note - although this map is a 'heatmap', it does not include heat data, it only shows where Redcedar trees are the most densely planted along Portland's streets. Data from  Portland's Street Tree dataset .

Keeping redcedar trees healthy together

The Need for More Research

It is unclear if Western Redcedar are good candidates for planting in hot, urban areas into the future. It is possible we are only seeing the dieback of trees that established during a previously wet period (i.e. the trees did not have to root as deeply as they could).

However, trees already established in hot, urban environments likely need extra care to survive the longer and hotter droughts in the future.

More research is needed to understand how to mitigate the impacts of longer and hotter droughts on Western Redcedar.

Engage with us to continue the story. Together we can determine the best practices for keeping Western Redcedar trees healthy in a changing climate.

Join us to determine best practices for keeping Redcedar healthy

Sign up for the Redcedar Intensive Care Collaborative at  https://treehealth.wsu.edu/redcedar/  to join a network of researchers, city staff, and tree care professionals to identify best practices for keeping Redcedar trees healthy.


A stand of western redcedar with dieback

Get Involved

iNaturalist Project

Do you want to be involved with documenting Western Redcedar dieback? Join the iNaturalist project called ' Western Redcedar Dieback Map ' and add observations.

Field Manual

Check out the field manual at  https://foresthealth.org/map  to learn more.

Become a Community Scientist

Anyone is welcome to get involved and become a community scientist! Learn more and sign up at  https://foresthealth.org/scientists/  

Learn More

Visit the Forest Health Watch website to learn more about Western Redcedar dieback and their importance to our forest ecosystems.

Support Portland's Urban Forest

Check out the below links to learn more about programming and opportunities to support the livelihood of Portland's urban forest


Stand of western redcedar with dying tops

Many Thanks

Thank You Community Scientists

This study was only possible because of the generous dedication of many incredible community scientists. We are grateful from their support and engagement to advance the understanding of this issue. This story is very much a celebration of the accomplishments and possibilities from working together with many community scientists. Thank you!

Incredible Hoyt Arboretum staff standing beneath a healthy redcedar at Hoyt Arboretum

Hoyt Arboretum Friends

Many staff and volunteers from  Hoyt Arboretum Friends   shared their time to investigate the hypothesis presented here. The breadth and distribution of observations, covering most of Portland, could not have been achieved with out them. Thank you!

Forest Health Watch Partners

Many partners helped shape the Forest Health Watch program. Redcedar dieback was selected as the pilot project because of partner concerns for the species. The  Western Redcedar Dieback Map  project on iNaturalist was co-created with partners from the Forest Service, Oregon Department of Forestry, and Washington Department of Natural Resources. Thank you to Betsy Goodrich, Melissa Fischer, and Christine Buhl for their collaboration in developing the project.

This project is part of the  Forest Health Watch  program.

Program Funding

The Forest Health Watch is currently supported by the US Forest Service through funding made available in the Bipartisan Infrastructure Law.

Support for this project was also made possible through generous support of the Albert Victor Ravenholt Fund. Learn more about their support of this work at the  WSU Ravenholt Urban Forest Health Lab. 

Feedback

Have feedback or want to get in touch with us about this story map? Visit the page linked below to share. We would love to know how this analysis could be better or how it has impacted you.

Support more research like this

Gifts to the Forest Health Watch program can be made through the  WSU Foundation . Please feel free to  contact us if  you have any questions.

J Hulbert 1 , N Avila 2 , C Bridges 2 , B Schreiber 2 , M Agne 3 , F Dewitz 1   1 Washington State University  2 Hoyt Arboretum Friends  3 USDA Forest Service PNW Research Station

Thank you to the many community scientists and volunteers involved in the making of this story.

Forest Health Watch

https://foresthealth.org/

Ravenholt Urban Forest Health Lab

https://treehealth.wsu.edu/

Joey Hulbert

hulbe@wsu.edu

Keeping redcedar trees healthy together

A stand of western redcedar with dieback

Stand of western redcedar with dying tops

Incredible Hoyt Arboretum staff standing beneath a healthy redcedar at Hoyt Arboretum

This project is part of the  Forest Health Watch  program.