In an old-growth longleaf pine savanna, the absurdly long pine needles sing in the wind. Once considered forests, these landscapes in the southeastern U.S. coastal plain are open-canopied and sunny, more grassland than forest, with underbrush kept clear by frequent fires.
Longleaf pines – their needles can be up to 18 inches long – are among the longest-lived trees in eastern North America, surpassing 500 years if they are lucky enough to escape lightning strikes from the region’s frequent thunderstorms. Almost more fascinating is the ground cover, with up to 50 species per square meter, including some plants that are thousands of years old, with the vast majority of their biomass below ground. Picture an underground forest.
In the American West, there are other types of old-growth forest. Dry ponderosa pine woodlands are similarly open in structure and contain trees up to nearly 1,000 years old. But perhaps the most familiar old-growth forests are the complex, wet old-growth forests of the Pacific Northwest, which stretch from northwestern California to southeastern Alaska.
These forests, which contain Douglas fir, coast redwood, western hemlock, western red cedar, Sitka spruce and many other tree species, have been compared to cathedrals, providing an otherworldly experience of gigantic, ancient trees festooned with mosses and lichens and with fallen trees strewn like buses across the forest floor.
I’m fortunate to have lived among and studied both southeastern pine savannas and Pacific Northwest conifer forests. The contrast between them could not be greater. And there are many other old-growth forests across the continent – including northeastern spruce fir and northern hardwoods forests, Great Lakes red pine and jack pine woodlands, southern Appalachian mixed mesophytic forests, and Great Basin bristlecone pines reaching nearly 5,000 years old. Each of these forests has a unique ecology, but all are under threat from human activity and climate change.
I recently co-authored a research paper with two colleagues and my collaborator, Carlos Carroll, who is a conservation biologist at the Klamath Center for Conservation Research. In it, we explain that there are some key reasons it’s so difficult to conserve the nation’s varied old-growth landscapes.
In general, the challenge is that it’s possible to conceive of all these areas as a single group – old growth landscapes – where large, old trees dominate the canopy but where small-scale disturbances such as treefall gaps create a mosaic of age classes. Foresters often call this an “uneven-age forest.”
But they really constitute a wide range of landscapes with different, often unique needs for protection, restoration and management. For example, in some old-growth forests, the trees live thousands of years, whereas in others the maximum lifespan of the dominant tree species is much less, sometimes only around 200 years. And some old-growth forests have abundant deadwood, both standing and on the ground, whereas others are kept largely clear of deadwood by frequent fires.
Large, old trees can be removed quickly but require hundreds of years to be replaced. When seeking to balance conservation goals with other priorities, including local economic needs, some foresters use a method called “thinning,” in which wooded areas aren’t clear-cut completely. Instead, only some trees are cut down. This can involve cutting smaller, younger trees while protecting older trees from logging – but at times it has included logging older trees as well. Even if it spares old trees, though, thinning can still harm biodiversity and old-growth ecosystems.
But it isn’t always clear how old a tree must be to protect it from logging. Some conservationists argue that the rules should protect some or all forests that are considered mature – say, 80 or so years old – but not yet old growth. As those stands of trees age, they will become old growth, taking the place of trees logged in the past.
However, a rule as simple as sparing trees above a certain age is not necessarily best for every old-growth region. In longleaf pine savannas, for instance, the standard practice of rapidly extinguishing wildfires has meant hardwood trees typically associated with denser, moister forests have grown up amid the pines. Some threatened species, such as the red-cockaded woodpecker, has adapted to survive only in areas that are extensive open-canopy, old-growth pine savannas with few hardwoods.
Restoration of those forests may require cutting down the invading hardwoods, even if they are decades old, as well as using fire to manage the resulting pine-dominated landscape. In some other types of old-growth forests, careful use of fire may be enough to restore the ecosystem without cutting any trees.
A key challenge for protecting old-growth areas is the importance of balancing immediate risks with long-term needs, considering how ecosystems change as trees age and die, and across larger areas such as watersheds.
Old-growth forests are rare – less than 7% of the area of U.S. forests today – and are still often logged. To recover forest ecosystems across the U.S., it will not be enough to protect just old-growth areas.
Especially valuable for biodiversity are areas of regenerating forests that grow after fires or other disturbances such as windstorms, in places where live and dead trees in the disturbed forests have not been cut. These disturbed forests provide habitats for species associated with more open conditions. Many woodpeckers, epitomized by the black-backed woodpecker in western North America, depend on conditions created by severe fires.
Beyond trees, there are many species of plants and animals that depend on old-growth landscapes. Perhaps most famous among them are the red-cockaded woodpecker of the southeastern U.S. and the northern spotted owl of the Pacific Northwest.
Those plants’ and animals’ needs can give conservationists and ecologists insights into what territory is most useful to preserve, not just for the trees but for the larger ecosystem. That includes finding ways to connect conservation areas across the landscape so life can grow and spread.
Efforts to preserve old-growth landscapes protect more than just the trees. These forests also store carbon, keeping it out of the atmosphere where it drives climate change. They help provide clean water for people and aquatic ecosystems, along with space for recreation, reflection and other cultural activities.
Ecological science cannot resolve the debates about how to prioritize and preserve old-growth forest. But it can help inform the public about the rising costs of doing nothing, and of the wide benefits of maintaining, recovering and restoring functioning old-growth ecosystems.
Carlos Carroll, a conservation biologist at the Klamath Center for Conservation Research, also contributed to this article.
This article is republished from The Conversation, a nonprofit, independent news organization bringing you facts and trustworthy analysis to help you make sense of our complex world. It was written by: Reed Frederick Noss, University of Florida
Read more: Keeping trees in the ground where they are already growing is an effective low-tech way to slow climate change How forests lost 8,000 years of stored carbon in a few generations – animated maps reveal climate lessons for tree-planting projects today Old forests are critically important for slowing climate change and merit immediate protection from logging
Reed Frederick Noss receives funding from the University of Florida and the Southeastern Grasslands Institute. 
