It happened rather quickly from a biological perspective, a 100’ tall Western Red Cedar (Thuja Plicata) started to turn brown/red in the summer of 2018. Within a year, the tree was clearly dead from the crown to the mid-way-point of the trunk. The cedar next to it, of a similar age, remains healthy. Another young cedar, 25’ feet away is also dead from the mid-trunk upwards.
As many plant lovers, ecologists, foresters, scientists, arborists and landscape architects have observed, the significant die-off of cedars is dramatic in many areas of the Pacific Northwest. The cedars seem to be dying mid-way up the trunk in groups with only a few healthy cedars standing strong among the die-off. After exploring a significant portion of the N. Cascade Region this summer and witnessing the partial death of thousands of cedars first-hand, I set off on a quest to better understand what is going on and what can be done.
Research points to a simple answer to explain the die-off; drought. There have simply been too many hot, dry summers in succession for this shallow rooted, moist-soil-loving tree to survive. Other publications indicate that the drought-weakened trees are vulnerable to insect infestation and may be exasperating the die-off. [1]
However, there is some hope. A Department of Natural Resources publication suggests cedar die-off may not be new or necessarily a sign of mass species extinction.[2] Research indicates that cedars that are thousands of years old may have experienced die-off during historic droughts in the past (Figure 102).
According to this data, while the mighty giants may appear to be dying, the half-trunk die off may be part of a cycle cedars have historically survived. If we subscribe to theses patterns of cedar survival, we can be hopeful that this summer's (2019) interment rains and mild temperatures will provide some re-birth of ailing plant species after several years of hot and dry summers.
As most have discovered by now, there are few clear-cut answers in the environment of rapid climate change. So what do we do in the field of sustainability, resilience, and ecology to save the Western Red Cedar and other native species that are stressed due climate related issues?
Some speculate that we need to stop planting so many cedars in new projects. An article by the Seattle Green Partnership suggests that the stressed trees are more vulnerable to infestation and that we should plant less of them in the future.[1]
I favor a more resilient approach based on the adaptive nature of ecological processes.
1. Plant Sourcing:
Work with your local native plant nursery to specify Western Red Cedars from various bio-regions. For example, if designing a large project in Seattle, specify Western Red Cedars to be sourced from bioregions farther south in addition to local areas. I recently spoke with the Fourth Corner Nursery[3] in Bellingham, WA. They remain optimistic that young trees can adapt to the new climate norms and have witnessed clients specifying a mix of regional origins to create resilient planting mixes.
2. Plant more native plants in general:
I like to think of PNW native plants as a local orchestra. Plants work together to support each other in the unpredictable world of climate change. They need each other to create the "music" of healthy ecosystems. Plants native to the PNW region also preserve important cultural traditions for the Coast Salish peoples and provide biophilic connectivity for everyone. As our built environment continues to become regionally indistinct, plants are often the single reminder as to where we are in the world. Encourage clients to embrace a biodiverse planting palette of native plants in their landscapes. Additionally, in contrast to popular minimalist plant palette practices, it may be time to explore over-seeding and over-planting.[4] We should expect some plant die-off in the short-term, but healthier and more biodiverse landscapes in the long-run.
3. Promote good planting practices:
Work with your clients to create a rigorous plant establishment plan including planting plants in the Autumn season and laying a thick ring of arborist wood chips around the plants (tapered at the trunks/stems) at the time of planting. Regular watering for two to three years is imperative. Removal of invasive species to reduce competition for scarce soil nutrients, sunlight and water supplies is also critical.
3. Discuss Climate Change
Without throwing out the entire rule-book of design and ecological modelling, we need to admit that almost everything we are doing right now is a bit of an experiment. More plants may fail to thrive after planting. Plants that previously were not invasive, may become a serious threat. Plant spacing may need to be adjusted to account for fire-wise landscapes. Perhaps the seemingly dead cedar should remain in place to see if it rebounds vs. immediate removal. We must incorporate discussions around climate change into our design practices to set expectations and to encourage additional experimentation and monitoring which will inform resilient landscapes. This isn't always an easy thing to do on limited budgets and tight deadlines, but it is vital to promote healthy ecological landscapes.
4. A Helping Hand
Although babying plants well known for being "tough and drought tolerant" will only work on a tiny number of native species that happen to exist near hose spigots, encourage clients to deeply water these plants once every two weeks if they notice long stretches without rain. Suggesting interventionist methods for plants that should survive without watering is controversial, but as our previously drought tolerant native species become stressed, we may need to consider helping them along as we hope for cooler temperatures and wetter summers.
If you have additional thoughts, questions or ideas regarding this topic, we would love to hear from you! Please add your comments to this post or email us directly at kpark@ekologidesign.com.
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