by Wendy Herniman, Pepperwood Steward
Have you ever wondered how old the trees at Pepperwood are?
Whenever I come to a magnificent oak stretching its curving limbs in every direction – upwards towards the sky, downwards like buttresses to the earth and intertwining with the branches of its neighbors – I wonder how many years have passed since the acorn put out its first delicate shoots. I pause and think of the creatures which have spent time enjoying its shade, nibbling at the leaves, flowers and fruits of the tree itself and of the plants and fungi growing on its surfaces as well as beneath it. There’s one tree on the preserve which has drawn me to it repeatedly over the years: an ancient coast live oak, known as the Grandmother Oak, which towers over the grassy rock-strewn hillside near the beginning of the Wappo Trail.
I recently decided to do a little research into some of the oaks which I’ve been spending so much time with at Pepperwood and included this beloved tree in my study. As part of that research, I embarked on a dendrochronology, or tree-coring, project. With some help from two strong young men, my son Peter and Pepperwood’s own Ryan Ferrell, I collected a couple of cores from each of the trunks of 19 oak trees on the preserve using an increment core borer. These cores are long, thin cylinders of wood which show narrow bands of varying thickness, which are the growth rings laid down each year by the trees. Each spring, with the arrival of warmer days and enough rain, our trees produce flushes of new leaves which power their growth for the year, so that warm, wet years result in wide growth rings, while drought years or cooler years slow down growth rates and produce narrower rings.
We can use these growth rings visible in the tree cores to get an idea of the ages of the trees as well as to assess their growth rates over time. Additionally, the tree cores give us clues about the history of the trees themselves and the history of the landscape. We may be able to see evidence of pests and diseases and also to see when fires have occurred and left their charred marks on the trunks of these fire-adapted oaks.
This spring of 2020, I was very fortunate to find myself safely at home with time to spare and so was able to concentrate on examining the tree cores and developing some insight into when these trees began their lives at Pepperwood. I had collected cores from a number of blue oaks (Quercus douglasii), black oaks (Quercus kelloggii), Oregon oaks (Quercus garryana) and a number of hybrid oaks, but the tree which I was most excited about was one of the coast live oaks (Quercus agrifolia) – the Grandmother Oak.
I was able to estimate the ages of about half of the trees, namely those whose trunks were narrow enough for the increment core borer to reach the center, and identify the inner early growth rings. For those trees with much wider trunks, like the enormous Grandmother Oak with its circumference of 580 centimeters or 228 inches, I extrapolated from the number of rings seen in the tree core to the total radius of the trunk to get an estimate of the tree’s age.
The most eagerly anticipated results were naturally for the larger coast live oaks, three of which were estimated to have begun growing around the 1760s, while the Grandmother Oak itself was found to be around 540 years old, dating back to approximately 1480.
I found that the oldest black oak which I had sampled dated back to around 1809; the oldest blue oak dated from 1845; the Oregon oaks were much younger, dating back to 1922; and the hybrid oaks had been growing since around 1820. The most eagerly anticipated results were naturally for the larger coast live oaks, three of which were estimated to have begun growing around the 1760s, while the Grandmother Oak itself was found to be around 540 years old, dating back to approximately 1480.
As I stand within its maze of branches, I wonder about the people who have passed by the Grandmother Oak – those in recent decades like young elementary students on field trips and visiting artists pausing to capture its image – who enter through the gates into the preserve and share a little glimpse of the world of interconnected creatures here. But more particularly, I think about the people who lived in this place, most recently the homesteaders who were here for perhaps a few decades and the Wappo, who have been stewarding this land with such care for millennia and continue this work through the Native Advisory Council. Oaks were treasured as the source of the Wappo’s staple food, acorns, so that oak woodlands, especially the favored black oaks, were tended regularly with fire to ensure this supply, and these fires have left indelible marks upon the landscape – on the trees themselves. Indeed, I had noticed that a number of the tree cores showed fire scars in the rings of the mid-1960s, perhaps resulting from the 1964 Hanly Fire which severely impacted Sonoma County.
To have been part of this landscape through so many seasons and centuries, while standing sentinel for more than 500 years simply amazes me.
As much as I had expected the Grandmother Oak to be old, I am astounded by the age of this beautiful tree. To have been part of this landscape through so many seasons and centuries, while standing sentinel for more than 500 years simply amazes me. I cannot begin to express my gratitude for everything which this tree represents and for the bounty which it shares with us, even giving us oxygen and helping to take care of our watershed. These ancient trees tower over us with their roots stretching deeply into the earth, supporting a rich abundance of life, while human history unfolds around us. I cannot help but wonder what they make of us all.