DIEBACK IN THE ARBORETUM Key symptoms include top dieback , browning of the foliage from the top down , and thinning crowns . ( These are distinct from the western red cedar ’ s seasonal foliage “ flagging ”— a normal browning of older , interior foliage during the fall .) In many cases , entire trees have died .
It ’ s even happening at Washington Park Arboretum :
“ By far our largest concentration of declining and dead cedars is on the west perimeter of the Arboretum , immediately north of Boyer Avenue , where there are about a dozen trees currently affected ,” says UW Botanic Gardens Horticulture Manager David Zuckerman . “ Another area is along the Broadmoor fence up by the composting restroom in the future Australia snow gum forest .”
“ It ’ s been going on here for a few years now and accelerating ,” continues David . “ My theory is that the areas we ’ re seeing decline are wetland sites that have been drying up — perhaps due to climate change and our longer , drier periods in summer . The cedar root zones were already compromised from lack of oxygen due to standing water , and now with areas drying up , it ’ s pushing them over the edge .”
FOREST HEALTH WATCH PROGRAM Changing climate patterns and repeated periods of summer drought do appear to be major drivers in the dieback , however much more data needs to be gathered . A new community-science program called Forest Health Watch ( www . foresthealth . org ) has just launched at Washington State University ( WSU ), with funding from the US Department of Agriculture , and its pilot project is designed to aid and promote research about the western red cedar dieback .
Similar to the Arbutus ARME ( which I wrote about in the winter 2021 “ Bulletin ” and also is run out of WSU ), Forest Health Watch is collecting data about western red cedar from volunteer citizen scientists using a mobile app — in this case iNaturalist .
“ The goal is to map unhealthy trees , identify patterns in the site characteristics of these trees , and figure out what environmental parameters — temperature , moisture , or soil conditions , for example — best explain where the cedars are being affected ,” says Program Director Joey Hulbert , a postdoctoral research associate at WSU . “ This will enable us to predict areas that are vulnerable to dieback and generate solutions specific to these spots .”
For about a year now , I have been using the free iNaturalist app ( see www . inaturalist . org ) to help identify plants and animals in the Arboretum and beyond . It ’ s a fantastic tool — and community resource — for any nature lover . Once you download the app to your smart phone , it ’ s easy to find “ Western Redcedar Dieback Map ” in the “ projects ” section and sign up as a volunteer observer .
I recently used the app to record an observation of the Boyer Avenue dieback in the Arboretum . In addition to taking a photo of the trees , I also answered some basic questions about the tree symptoms and site conditions ( e . g . Is the setting urban or rural ? Are there signs of insect damage ?). Because I had my phone ’ s GPS enabled , the app recorded the precise location of the trees , and this was uploaded to the Dieback Map .
ANALYZING THE DATA Reports in the media have indicated that cedars in sunny sites with thin soils are currently being most affected , and preliminary data from the project appear to support this overall trend .
“ So far , most observations of unhealthy trees have been shared from flat or upland areas with fast-draining soil ,” says Joey . “ However , we sometimes see the problem in wetlands , too , where a tree is used to having lots of water but perhaps a summer drought lowers the water table , and the tree doesn ’ t get the water it ’ s used to . I should stress , however , that at this stage , our data is very preliminary , and we need a lot more observations from our citizen scientists in order to say anything about them with confidence .”
In order to gain a full picture of what ’ s happening , Forest Health Watch is asking participants to report healthy trees as well as sickly ones . “ If you see a site where all the trees are healthy , that ’ s also very useful information ,”
8 v Washington Park Arboretum Bulletin