Nature vs. nurture is an old debate in human psychology: are we the way we are because of our genetics or our environment? Plant people know that both environment and genetics play a role in plant development. Perhaps one of the most dramatic examples can be found in the Coast Live Oak (Quercus agrifolia) in the Central Coast region of California.
Coast live oak is an evergreen tree native to the Coast Ranges and inland foothills of California, and regularly planted in California urban landscapes. Average height is 50 to 70 feet tall, with a canopy spread often exceeding the height. Recently I had a unique opportunity to visit a “Champion” size Coast Live Oak at Halter Ranch Vineyard, a sustainable winery in Paso Robles.
The National Big Tree Program, spearheaded by American Forests, is a movement to locate and document the largest examples (champions) of each tree species in the United States. Champion status is calculated using a point system based on trunk circumference, height and average crown spread. The California Big Tree Registry lists the Halter Ranch oak (known as the Ancestor tree) as a co-champion with another slightly larger one in Julian, California. Confusingly, neither of these specimens are listed on the national registry.
But this is nitpicking. The Ancestor Tree is mighty impressive. As of 2006 it measured 55 feet tall and 324 inches around, with a crown spread of 104 feet. Branches touch the ground, and it’s about 10 degrees cooler in its shade. Age has been estimated from 350 to 800 years. A core sample might help with determining age, but the owner of the vineyard chose not to have this invasive procedure done. In fact, he’s gone out of his way to preserve all large oak trees on the property when developing the vineyard. Rows of vines stop a good way outside the dripline of each tree and the soil is undisturbed by vehicles or equipment.
The Ancestor Tree shows what Coast Live Oak is capable of under its ideal conditions: inland foothills, undisturbed limestone soil, full sun, no competition, seasonal rainfall and some protection from coastal winds. But what happens in less than ideal conditions? For that we travel less than 50 miles southwest to the El Moro Elfin Forest alongside Morro Bay Estuary.
This amazing 90-acre park owes its existence to the local community, which “adopted” the area in 1994 from the 3 different governmental agencies that own the land. Volunteers perform all of the restoration and maintenance. Visitors can explore the park on a raised boardwalk and carefully delineated trails, punctuated by benches and interpretive signs. There are six different plant communities here including pygmy oak woodland.
These pygmy Coast Live Oaks, estimated at 100 to 200 years old, average 7 to 20 feet high in nutrient-poor, over-drained sand. Coastal winds, erosion and soil salinity are also limiting factors. Historically, horses and off-road vehicles had their way with the land for decades before its restoration. It’s amazing the trees are here at all. Trees grow in groves and from outside, one grove looks like a large shrub. It’s only from underneath the canopies that we get a “forested” feeling.
In such close proximity we find the largest and smallest examples of a single species, clearly dictated by environment. By observing these extremes, we can better understand how the species will behave in our local urban conditions. And have a good time while we’re at it!
The El Moro Elfin Forest Natural Area is open to the public 7 days a week, with docent-led tours on the 3rd Saturday of the month.
Ellyn Shea is a consultant and garden educator in San Francisco.