Prioritizing long-lived giant trees could maximize the carbon sequestration and biodiversity of city parks and other green spaces.
By Marie E. Antoine and Stephen C. Sillett
Current environmental crises can seem overwhelming in scale. Confronting climate change and conserving biodiversity will require huge changes in how humans manage the landscape and in our use of fossil fuels. But one part of the solution is growing all around us, we call them intentional forests.
Our team studies trees and forests. Coast redwood, giant sequoia, Douglas-fir, Sitka spruce — the four tallest conifers have been our main focus for over two decades. This work has helped us understand how, though trees alone can’t save the world, they can help.
Few organisms are as incredible as giant trees. Contemplate the sheer magnitude of what they do. A tiny seed finds a nook for germination. The seedling roots connect to symbiotic soil fungi. The sapling forages for resources — light, water, nutrients. The treetop grows hopefully ever upward. The trunk and appendages thicken annually as new wood is deposited, until someday a giant stands in the forest. Its lifespan may be long enough for human civilizations to rise and fall.
Primary forests — our term for forests untouched by logging, like much of the Olympic, Sequoia, and Great Smoky Mountains national parks — are biodiversity refuges and massive carbon sinks. These remaining forests should be 100 percent protected. They occupy only a small portion of the planet’s surface, but they store huge amounts of carbon and provide critical arboreal habitat.
While primary forests show us what’s possible, though, we need more than just conservation of these forests. If trees are to help us, then we must help trees. We suggest new kinds of “intentional forests.”
Managing trees and forests for particular purposes clearly isn’t new. Timber and fiber plantations are intentional forests, for example. What we’re talking about is paying more careful attention to trees planted and nurtured in settings such as city parks and recovering timberlands. If we think about the ecological functions that large trees could be performing far beyond the scale of typical forestry, these intentional forests could still be improving the world a thousand years from now.
Perhaps you’ve noticed the phenomenon whereby some trees seem taller and more robust than neighboring trees of the same species. These are the trees most likely to thrive and survive over the long term. Let’s call them potentially elite trees, or PETs.
Trees are incredibly responsive — pamper the PETs and they will grow quickly. Their well-being can even be enhanced by periodic selective logging of other trees.
PETs eventually become Elite Trees (ETs) as their crowns develop ecologically significant structures supporting arboreal plants and animals. ETs are easy to recognize as unusually large and complex individuals of a given species. A few big gnarly trees make an enormous difference in supporting forest biodiversity. They’re also carbon-sequestration champions, although how long the carbon remains sequestered depends on species longevity. Trees generally have competing priorities of growth versus durability — rapid growth comes at the expense of longevity. For example, Sitka spruce reaches near-maximum size after only two centuries but rarely lives beyond 400 years. In redwoods and giant sequoias, the trees’ heavy investment in protection against fire and fungi makes them grow slowly at first but allows them to live 2,000 or even 3,000 years.
Intentional forests could be created and nurtured at various scales. At the small end are innumerable bits of land that could hold a few special trees, ones that could live for hundreds or thousands of years with deliberate curation that would differ from typical urban forestry. Consider all the city parks and yards where PETs could be tucked into current landscaping or areas needing restoration.
Careful long-term land use planning and creative thinking with economic incentives could also make it feasible for larger coordinated efforts in which systems of PETs and ETs gain official recognition and protection and go on to do their important ecosystem-protecting work for centuries or even millennia.
Such efforts could begin with an inventory of existing PETs and ETs that may be hiding in plain sight. Monitoring the growth of these trees and tending to them — and planting the seeds of new ones — would be the next steps in creating intentional forests. If PETs and ETs were considered long-term assets with increasing value over time, then fostering these trees would become an essential service and a deeply rewarding career prospect for generations to come. With intentional forests, we do see the forest for the trees.
Marie Antoine is a lecturer in the Department of Biological Sciences at Humboldt State University in California. Stephen Sillett is the Kenneth L. Fisher Chair in Redwood Forest Ecology at Humboldt State.
This article was reposted with permission from the authors. It was originally posted in the Boston Globe on July 14th, 2021.