Here at the Washington Park Arboretum we are lucky to care for many extraordinary trees. One of these amazing trees is our single specimen of Montezuma pine, Pinus montezumae var. lindleyi (Accession number 506-65-A) planted at the northeast corner of Crabapple Meadow in 1969. I first became acquainted with this tree in the spring of 2017 when I was the Teaching Assistant for a Landscape Plant Recognition class at the University of Washington. While we did not teach the Montezuma pine specifically, it always seemed to steal the show away from the more common neighboring trees that students were supposed to be learning. The needles of the tree can reach up to ten inches long and gracefully cascade downwards in tufts at the end of branches, giving the tree a unique pendulous appearance that draws you in for a closer look.

Montezuma pines are native to the mountains of Mexico and Guatemala where they are known as Ocote and grow at elevations from 4,000 to 12,000 feet. The tree’s Latin name honors the ninth emperor of the Aztec empire, Motechzoma Xocoyotzin who ruled from 1502 until 1520. Our specimen came to us as seed collected by Fred Lape of the George Landis Arboretum in 1965. Fred collected the seed in the central Mexican state of Hidalgo somewhere along the winding mountainous road between the small city of Zimapan (6,000 feet in elevation) and the town of Jacala (4,500 feet in elevation) in the Sierra Gorda and Sierra de Pachuca mountains, part of the Sierra Madre Oriental range. Two seedlings, then identified as Jelecote Pine (Pinus patula) were planted in the area in 1969, although the second tree did not survive. In 1985 local tree expert Arthur Lee Jacobson corrected the identification of our species to Montezuma Pine (Pinus montezumae var. lindleyi).  However, synonymy is rampant in this species’ taxonomy and some sources have lumped into P. montezumae. Our surviving tree currently tops out at over 100 feet high and has been the state champion for many years.

In 2019 during routine monitoring of our pine collection, our Plant Health Specialist, Ryan Garrison, noticed that the tree had signs of a bark beetle infestation. Bark beetles are native to our region and historically have had minimal impact on healthy trees. However, in recent decades our winters have become warmer, allowing more of the beetles to survive through the winter, and our summers have become warmer and drier increasing the stress levels of all trees including otherwise heathy established trees such as our Montezuma pine. Adult beetles bore into the tree and lay their eggs. When the larvae hatch, they feed on the inner bark and when present in large numbers the beetles can girdle a tree. The beetles also commonly introduce fungal pathogens such as blue stain fungi. In 2019 the tree was treated for the bark beetle infestation and subsequently showed some signs of improvement including putting on new growth.

In 2022 Arthur Lee Jacobson reached out to our arborist team concerned about the health of the tree.  A few small wounds were found at the base of the trunk, and we brought in an outside consulting arborist company, Tree Solutions, to conduct more advanced testing including sonic tomography. Sonic tomography is a relatively new technology that uses sound waves to create a three-dimensional model of the interior of a tree. This testing revealed a column of decay from the base of the tree extending upwards to nine feet high. The consultants deemed the pine still structurally sound and low risk, but recommended continued close monitoring of the tree, including looking for fungal signs such as mushrooms, conks, or mycelium.

By the summer of 2023 the decay at the base of the tree was more pronounced Tree Solutions came back to perform a pull test on the tree to determine its likelihood of failure in a windstorm. During a pull test a cable is attached to the trunk, a known amount of force is put on the tree, and inclinometers are used to measure the tree’s response to the force. The pull test determined that the tree would likely fail at wind speeds of 80 mph and could fail at lower wind speeds. A windstorm of this intensity would likely cause many tree failures not just in the Arboretum, but throughout the region. In recent years in Seattle the highest wind gusts tend to be around 50 mph, and we have not had a wind gust of 80 mph in the past twenty years. Regardless of these averages, the results of the pull test were concerning, and we began cordoning off the area around the tree before wind events.

In the fall of 2023, a conk grew at the base of the tree and was positively identified as Phaeolus schweinitzii, the fungal pathogen causing Schweinitzii root and butt rot. This pathogen attacks many conifers in our region, most commonly Douglas-firs and Sitka spruces. The fungus weakens the base of the affected tree usually without causing obvious symptoms to the canopy.

The results of the pull test combined with the presence of this fungal pathogen have led us to make the difficult choice to remove the tree this spring. This tree is beloved by our staff and the community, and it is a heartbreaking decision for all of us.

Because of the presence of both the bark beetles and the fungal pathogen the wood will have to be treated carefully and cannot be moved to other locations. We are still in discussion about whether some of the wood can remain on-site. We generally follow the best practices recommending that beetle infested wood be removed to protect nearby trees from infestation. We are working on procuring a replacement tree, both by taking cuttings from the existing tree to propagate and by sourcing seed of known wild origin. The species is rare in cultivation in the Pacific Northwest because it is sensitive to cold winter weather, especially when young.

Besides being a beautiful and unique tree, our Montezuma pine has provided an incredible number of other benefits during its 58-year lifespan. According to i-Tree calculations, this tree has removed a hundred pounds of air pollutants such as ozone and particulate matter. It has sequestered an estimated 14,505 pounds of carbon, the same amount of carbon it would take to fly ten people from Seattle to New York, and has intercepted an incredible 198,722 gallons of rainfall. The tree has provided habitat for birds and other wildlife like our native Douglas squirrels who have been seen in the area and has provided shade for generations of Arboretum visitors. It will be sorely missed.

Sources:

https://npgsweb.ars-grin.gov/gringlobal/taxon/taxonomydetail?id=28489

https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/fsbdev2_043575.pdf

https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5347109.pdf