Acorns and Adaptation: On Oaks and the Struggle for Existence

By Teresa Helms

It is remarkably improbable for a mature oak tree to even exist. Of the abundance of acorns produced every few years—an irregular cycle linked to predator satiation—many will be parasitized by acorn weevils and similar insects. The majority of what remains will be foraged by wildlife. Perhaps a few will get lucky and end up in the cache of a less-than-lucky rodent, left to sprout after their keeper has been predated. Of those that manage to germinate, another percent age will succumb to unideal climatic conditions or be browsed by deer and moose before the seedlings are able to grow out of reach. Ultimately, only about one in every 10,000 acorns will develop into a tree. And yet, Quercus contributes more biomass to northern temperate forests than any other genus of woody plants, its species providing critical sources of hard mast sustenance for wildlife populations. Ubiquitous and essential to these ecosystems, every oak in the forest is inherently unlikely, a testament to persistence, grit, and random chance; Darwin’s “struggle for existence” at play before our eyes. In the grand scheme of evolution, oak species display a certain tenacity, with numerous lineages that have diverged and dominated across the Northern Hemisphere. At the individual level, physi ology contributes to this resilience, including long tap roots that prove useful in times of drought.

Globally, the Quercus genus boasts roughly 435 species of oaks. Of this array, 60 percent occur in North America, a subset that can be broken down into two major lineages: white oaks and red oaks. Variation between these groups presents itself both genomically and functionally. Beyond this distinction, however, the lines of biology become blurred. When determining speciation among organisms, the most foundational methodology is Ernst Mayr’s biological species concept, which defines a species as a group of organisms that may successfully interbreed to produce fertile offspring. This theory generally holds that certain reproductive characteristics allow for populations to remain distinct, restricting gene flow within closed systems. Oak species complicate this with their readiness to hybridize. Many white oak species are known to hybridize naturally, and red oak varieties are even more apt to do so—black oak, for instance, is particularly promiscuous, frequently found hybridized with northern red oak, plaguing dendrologists and confounding the scientific community. Subsequently, many scientists posit that these “species” may not be distinct, but rather phenotypic variations of singular species. This appears to defy such a central tenant of biological thought: oaks expand beyond their categories. Or, perhaps, is it more accurate to say that our categories fail to account for their complexity?

Rather than attempting to restrict the natural world to our understanding, we might allow room for the morethan-human world to exist as is. W. John Hayden, in his paper “Hybrid Oaks: Full of Vexation and Wonder,” asks us to embrace this complexity, arguing that “[rather] than vexation, maybe we should adopt an attitude of awe and respect for the complexity of biological processes that, playing out on continental scales, involving untold millions of individual trees, and millennial time frames, challenge our best efforts at comprehension.” As we embrace multiplicity in the forest, we might also embrace complexity in each other, prompting us to en gage in more meaningful relationships and build more holistic remedies to our collective challenges. Allow ing openness to shape our relationships with the forest may in turn change the way we see the world. ingly consequential as the ramifications of global cli mate change continue to appear in unprecedented and multitudinous ways; not exempt from this is the fate of northern forests. The evolutionary history of oak species, as well as their tendency toward drought resilience, is part of what makes them strong candidates for certain experiments aimed at accelerating the adaptation of forest communities to shifting climates. As the climate warms, species are moving. Trees native to warm, southern climates are expanding their ranges northward, and species quintessential to northern re gions will begin to struggle. Forests are adapting, but not at a rate that can match the haste of climate change. In light of this, many scientists are exploring manage ment strategies involving assisted migration: planting historically southern species—including oaks—out side of their typical ranges in hopes of building resil ience in northern forests. As extreme weather events increase in frequency, these drought-adapted trees may prove to be an important resource of durability within their ecological communities.

There is more unknown than not in terms of this po tential approach to forest management under novel con ditions: whether assisted migration is feasible, which species will prove most viable, what regional climates will look like years into the future, the list goes on. As scientists, the looming unknown of the world can be simultaneously captivating and frustrating, making solutions to imminent problems feel infinitely out of reach. Recognizing that which we cannot know in the face of global change requires a certain humility, which, with their inability to be captured by human-constructed categories, the oaks might implore of us as well.

When we become willing to approach the world with humility—with grace toward ourselves and each other—we will be able to step closer to solutions in the face of our biggest challenges. Northern forests are changing with or without us, presenting an immense responsibility to us as we determine how to respond. Adapting to this changing world will require persistence—from us, from oak seedlings. Just as we hope these trees provide fortitude to their communities, may we strive to lend resilience to each other, and learn to live in our landscapes with a renewed sense of grace. H