By Cypress Lawn Arboretum Director Josh Gevertz
Cypress Lawn Arboretum has grown through the generations from a vision seeded by our founder, Hamden Holmes Noble, who brought the idea of the rural “garden cemetery” to the California coast in the final decade of the 19th century.
Although Mr. Noble did not think of himself as an arborist, nor did he ever use the term “arboretum,” his avid collection and planting of tree species from around the world have impacted a legacy of horticultural diversity thriving to this day on our grounds, nearly 130 years later.
One of these original trees of Cypress Lawn is particularly special, given its phenomenal size, unusual traits, and iconic setting on “Wine Hill” of our historic East Campus. In recent weeks, the proactive care for this singular specimen of cork oak (Quercus suber) has ushered in a new era of tree management at Cypress Lawn, providing a template for action that will be strategically implemented in the months and years to come for countless other trees in our living collection.
At Cypress Lawn, a collaborative team of tree professionals, fondly referred to as “Arboretum Allies” by Arboretum Director Josh Gevertz, has been assembled to provide comprehensive care and attend to the needs of the finest specimens growing throughout our historic Memorial Park. Some of these needs are universal, and this one prodigious cork oak has taken the front seat to show us how to build an action plan for our most cherished trees, all the way from a humble acorn to a sprawling, centurial giant.
Foremost among our valued collective of “Arboretum Allies” are the consulting arborists of the San Francisco-based firm, Tree Management Experts. Roy Leggitt, as well as his colleague Aaron Wang, have been formative in reimagining the potential future of our Arboretum, and in seeing our remarkable collection of trees for what they are — a wonder to be treasured, preserved, and shared with the broader tree-loving community of the Bay Area. Truth be told, without Mr. Leggitt’s foresight to carry forward the original vision of Mr. Noble, Cypress Lawn would not be formally recognized as an Arboretum at all! Thanks to Roy and Aaron’s dedication over several years serving as consultants to manage the trees of Cypress Lawn, our living collection is now internationally designated as a Level I Arboretum by the global accrediting organization ArbNet.
Beyond this indispensable contribution, the team of Tree Management Experts has aided in the development of our Arboretum’s publicly accessible GIS database, which you may explore for yourself in the interactive maps of our virtual Tree Tour. In addition, both Roy and Aaron have played a key role in providing guidance and recommendations for the care and curation of trees throughout our four major campuses – the East Campus, the West Campus, the Hillside Gardens, and our newest addition to the growing collection of Cypress Lawn properties, Olivet Gardens.
A foremost example of this tree care action planning has been for our aforementioned cork oak, whose colossal branches arch towards the main, circuitous avenue through the heart of our original East Campus. When you visit Cypress Lawn, this behemoth is hard to miss if you give your attention — take a walk for yourself, and you will surely find it, ever waiting, the wise and stalwart sentinel of Section K. Looking up at this cork oak allows a visitor to marvel at the rippling bark on undulating, swollen branches. Some of these gargantuan lateral limbs are so very long that they make the tree wider than it is tall. When you do visit it, just imagine the equally massive subterranean root system, coursing through the earth and forever hidden from view.
A critical step in the recent care of our mighty Quercus specimen actually sought to expose some of this immeasurable underground web, through an important tree “surgery” known to the arboriculture industry as a root collar excavation.
To help with this key process, another “Arboretum Ally” has been brought into the tree care collective here at Cypress Lawn — our new and much-valued arborist partners, Christopher Campbell Tree Design. Christopher has been a practicing tree-climbing arborist in the Bay Area for over 25 years and now manages a multi-team crew of highly skilled professional tree climbers and pruners with decades of combined experience.
With CC Tree Design as an ongoing ally, the coming years of tree service and management at Cypress Lawn will truly be an active curation endeavor, in which our specimen trees are thoughtfully cared for as living artifacts, in the outdoor museum and learning laboratory that our Arboretum will grow on in becoming. This is the future manifestation of Noble’s original vision that we and our allies will strive on towards in the seasons to come.
So, what exactly is a root collar excavation, you might ask? Unfortunately, a chronic problem for many old trees at Cypress Lawn, and in countless park and urban tree plantings throughout the world, is that of the buried root collar. Essentially, there is a very precise position in the anatomy of a growing tree, where the aboveground trunk should transition to the belowground roots — it is here where we find the root collar. At this transition, a mature and healthy tree is defined by a very noticeable root flare, where the main vertical stem of the tree splays horizontally to the structural lateral roots.
Simply put, when the root flare and collar is covered with excess soil, the aboveground trunk is suffocated, and the tree will be constantly battling this inhospitable environment to continue growing. As years pass with a buried root collar, the damaged trunk may progressively decline in health, and the tree will become increasingly vulnerable to attack from fungi and other harmful pathogens, causing root decay that may even be fatal. Girdling roots growing in this excess soil layer also have the potential to encircle and eventually choke out the main trunk, further complicating matters.
Thankfully, there are proactive management efforts, such as this excavation procedure, that can slow and even completely stop these damaging effects. Of course, in the Memorial Park setting of our Arboretum, the lawn of Cypress Lawn defines our grounds perhaps more than even the trees themselves, and will always be a signature element of the aesthetic of our landscape here. Unfortunately, the health and growth of this lawn is often at odds with the well-being of our many trees. Therefore, a careful balance in long-term maintenance is needed.
To this end, with our cork oak as a trial case-study in proactive management, we have begun to implement strategic root collar excavation and mulch ring installation around the trunks of our finest specimen trees, so they might breathe — and thrive — for the generations yet to come.
In the case of our cork oak, over one foot in depth of excess soil, plus the top layer of turf, was removed from the base of the tree trunk! Over several decades, burials nearby our giant arboreal ally have likely caused an accumulation of earth, progressively burying the sensitive root collar. This tree is truly a survivor, withstanding over a century of slow, partial suffocation and ever-growing onwards. “Post-surgery” now, with a healthy, encircling layer of wood chip mulch that mimics the growing conditions found in a natural oak woodland setting, our mighty oak can breathe easier. Hopefully, it may now live as a cherished asset to our Arboretum for many decades more.
In addition to leading our efforts in this ground-level tree management action, CC Tree Design has also worked extensively to proactively prune the canopy of our Quercus suber specimen. As is inherent to the growth of many oak species, especially evergreen ones like the cork oak, individual branches may be shaded out over time as new foliage and growth above soak up available sunlight. Over decades, this natural, healthy process can result in an accumulation of deadwood, material that stays hanging in the canopy but is no longer living tissue. Without management, this dead biomass can become a noticeable eyesore. Even beyond this important aesthetic consideration, strategically removing deadwood is generally considered to improve the long-term health outlook of trees. By speeding up the process of wound closure, we can help the tree to keep harmful insects and decay out of its branches.
Selective thinning of living branches also proactively assists the growing cork oak in managing its own gargantuan weight. Branch crowding on the far reaches of the tree’s longest lateral limbs contributes to an accumulation of what arborists call end-weight. Wind forces on long, over-extended branches, such as those found in our specimen oak, can be extreme, potentially even causing the branches to fracture or fail.
In the case of our mighty cork oak, the combination of wind and excess end-weight has caused dozens of interior cracks throughout the branching structure. This one tree, a remarkable survivor, has refused to allow any major limbs to fully break off. Instead, over the years, the tree has compartmentalized these internal fractures and grown additional wood — known as reaction wood — to support and reinforce its over-extended branch system. This mechanical acclimation by the cork oak can be readily seen in girthy limbs throughout the canopy.
With an understanding of these natural tree growth processes and physical forces, CC Tree Design has given our friend a long-overdue trim, strategically shedding hundreds of pounds of deadwood and crowded end-weight branches from the canopy. In the aftermath of this pruning process, our cork oak will now have a fresh opportunity to strive on for available sunlight, encouraging a healthy growth response for the next several years. Our team of “Arboretum Allies” will monitor the health of this tree in the coming months, and a routine pruning and maintenance cycle will proceed as our cork oak continues to thrive.
One additional step in the care and curation of our specimen Quercus suber will allow for future visitors of Cypress Lawn to easily find and appreciate this marvelous living wonder. With the placement of a bronze botanical plaque and stone monument under the canopy of our cork oak in Section K, this special tree, which has shown us the way forward for management action and care throughout Cypress Lawn Arboretum, may now be named and known to all who visit our grounds.
The story of our cork oak is but a single anecdote of a far grander narrative, one that connects the origins and historic roots of Mr. Noble’s living legacy all the way forward to the outstretching branches of tomorrow. Each of the actions and tree care practices we have implemented for this one specimen will define our intentions in managing the entire living collection for many years moving forward.
Just as the mighty cork oak, our team of “Arboretum Allies” will evolve and branch out with each growing season. As we strive to provide the best care possible for the trees of Cypress Lawn, we hope you will join us in learning about, growing alongside, and celebrating the rich diversity of life here at our cherished Arboretum.