A Mast Year: An Excerpt from “What We Sow”

By Jennifer Jewell

Valley oak (Quercus lobata) and owl’s clover (Castilleja exserta); Image: Ger Erickson

The great oaks of this canyon, as the world over, hold, house, and hide, welcome, feed, and nurture these many creatures—natives, residents, migrants, and migrators alike. California is home to a great biodiversity of plant life in general. The California portion of the California Floristic Province, a designation for the plant life in an area covering most of California, up into Oregon and down into Baja California, Mexico, and sharing a similar Mediterranean climate, is home to more than 20 distinct species and more than 20 known hybrids of oaks, and some of the species lines date back more than 20 million years. 

The cover of What We Sow by Jennifer Jewell

Oak woodlands became a dominant feature here after the last ice age, according to current scientific research and thought. For the past 5000 years or so, these oaks have been coevolving with humans. With improved tools for historical analysis of plant and landscape—from dendrology to carbon testing of lake beds and soil cores—it becomes more and more clear that the Indigenous peoples of what is now California have actively managed the landscape with sophisticated thinking and oversight for thousands of years. The Mechoopda of this region have used, and still use, low-intensity, high-frequency fire regimes to maintain the health and structure of the oak woodlands. These accomplish several things—they keep small conifers under control in oak-dominated environments so that oak succession and therefore acorn production are ensured for both wildlife and humans.

This traditional use of fire simultaneously reduces dead dry wood and grass buildup in these same areas so that naturally occurring brush fires (often started by lightning) do not get too big, and so that each year’s acorns have a better chance of reaching fertile soil. Subsequent oak seedlings then also have a greater chance of establishing without overwhelming or overshadowing competition. And all of this shows a remarkable understanding of place and keen observation of the most productive natural cycles by the people who have long called it home. 

A collection of acorns; Image: CNPS

While the cycle of masting is understood generally, a lot of mystery and theorizing remains as to how they know when to do it, or why a whole region will mast at the same time. Could it be due to the previous season’s rainfall, or summer heat, or overall temperatures, or which way the wind blew during spring pollination? No one theory is reliably predictive. What is clear is that when the oaks are masting, acorns fall in remarkable numbers, with a mature oak (between 40 and 120 years old) producing upwards of 10,000 acorns. This abundance can alter migration routes of acorn eaters—from mice to deer and bear, to jays and acorn woodpeckers. The generous food source affects the lifecycles and populations of acorn-eating wildlife as well as the oaks’ own succession success. The more acorns they are healthy enough to produce, the greater chance some will survive to maturity. I’ve been watching the thick bunches of green acorns forming and growing fatter all season. In their development stage, these acorns are bright young-apple green and clearly visible even from some distance against the restrained and contrasting late-season leathery, forest-green valley oak foliage. The acorn clusters, which will age over their six-to-seven-month development to a deep chocolatey brown, speckle the canopies of these largest and most stately of our oaks. 

Valley oaks, along with the blue oaks, are a keystone species here—the entire ecosystem depends on them to exist in its current iteration. They are the charismatic megaflora, so to speak, of this plant and human community. The valley oaks, which can live up to 600 years and reach 100 feet high and almost as wide in ideal circumstances, favor the lowest elevations of the canyon for its deep, rich soils. The blue oaks (Quercus douglasii), stouter and somewhat shorter lived (between 100 and 400 years), prefer a little rise in elevation, and are the dominant species partway up the small canyon’s slopes. The intermingling gray pines (Pinus sabiniana) are often taller than many of the oaks around them—they shoot up to 80 feet quickly. As evergreens, with their very specific glaucous blue-green-grayish needles arranged in airy bundles, they stand out to the eye amid the oaks. Their cones are among the largest in the pine genus and, where the valley and blue oak acorns can swell to three rounded or pointed inches in length, the gray pine’s seed-bearing cones easily reach nearly a foot in length.  

Woodpecker; Image: Matthew Ferretti
Woodpecker with oak acorns; Image: Matthew Ferretti

Similarly, though, both the valley and blue oak acorns and the nuts filling the large and heavy gray pine cones are critically important food sources for all manner of life along the food chain here. Collectively, valley oak riparian—creek or riverside—forests, which are endemic to California, support 67 nesting bird species, more than any other California habitat. . . . The sheer number of plant genera, species, and subspecies native to the Floristic Province, to say nothing of the endemics that occur only here, means that there is a corresponding richness of plant communities and ecosystem types. Wildlife likewise coevolved to be interdependent with and take full advantage of this cornucopia of plant life.  

In the simplest symbiotic terms, wildlife needs the plants for food, and the plants need the wildlife for pollination, seed dispersal, for pruning, and to achieve other kinds of evolutionary selection. And we as humans—no matter where we live or how divorced or “protected” we believe ourselves to be from this environment—are ultimately reliant on the success of them all. If we want to make the places we have chosen to insert ourselves our true homes, we must remember that we have things to learn from these diverse lives, cycles, and epic adaptation stories.

Taken from What We Sow © Copyright 2023 by Jennifer Jewell. Published by Timber Press, Portland, OR. Used by permission of the publisher. All rights reserved.


Jennifer Jewell is a gardener, garden writer, and gardening educator and advocate. Since 2016, she has written and hosted the national award-winning, weekly public radio program and podcast, Cultivating Place, a coproduction of North State Public Radio in Chico, California. Jennifer has been writing about gardening professionally since 1998, and her work has appeared in Gardens Illustrated, House & Garden, Natural Home, Old House Journal, Colorado Homes & Lifestyles, and Pacific Horticulture. 

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