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When most of us think of National Parks, we think of open spaces and healthy, abundant vegetation. We think of forests and woodlands and meadows and wildflowers—all preserved from development. We think of scenic vistas that inspire poets and artists and millions of everyday citizens. These lands are set aside, as Theodore Roosevelt put it, to preserve "the value of natural beauty as a national asset," and to promote "outdoor life and recreation in the production of good citizenship."
But no matter what laws you pass or fences you build, you cannot shelter entire landscapes from the stresses of changing weather and a warming climate. The National Park Service (NPS) manages more than 400 parks, monuments, and historic sites from north of the Arctic Circle down to the Caribbean and the South Pacific. The NPS challenge is to preserve natural and cultural resources while making them accessible to the public. But land managers and park rangers can only do so much when the environment changes but the park borders do not.
Ecologists know that the trees that add color, beauty, and shade to America’s national parklands are at risk. Unlike animals, trees cannot pull up their roots and quickly migrate to another area. But figuring out which trees are the most vulnerable is complicated. The types of trees and forests vary from park to park, and even within some parks. Projected shifts in rainfall and temperature patterns in the future are just as variable and uneven. Some species will thrive as climate changes, but many are expected to suffer. And the question is: what can park managers do about it?
“There’s been a huge shift in the way the science community approaches climate change," said John Gross, an ecologist with the National Park Service's Climate Change Response Program. "We used to ask: is climate change happening? Then we asked: by how many degrees will the temperature rise? Now we ask: what does that mean for managing things?”
In Yellowstone National Park, for example, spruce and fir forests have adapted to and thrived in a climate where summertime temperatures rarely surpass 90 degrees Fahrenheit (32° Celsius). But 30 years from now, if climate models are right, the park will see an average of two weeks every summer with temperatures surpassing 90°F. Will the spruce and fir trees suffer? Will they adapt and thrive? Will they migrate, seedling by seedling, up to higher altitudes and cooler temperatures? If trees that are already adapted to warmer temperatures take hold, will spruce and fir be able to compete?
In order to figure out what changes the parks can expect, scientists from Montana State University, the Woods Hole Research Center (WHRC), the National Park Service, and NASA established the Landscape Climate Change Vulnerability Project. They want to use scientific observations and computer models to help the parks adapt to climate change.
With mountains of data being collected by satellite- and ground-based instruments, scientists can now paint high-resolution pictures of changes within individual parks—down to the effects on various stands of trees. “Computationally that’s a big deal,” Gross said. “Even on a supercomputer, to produce that data is a big deal.”
The data and models could give park managers context and insight on when and where to let nature manage the park and when human intervention could help. For instance, which species and forest stands should managers focus on? Where would it make sense to plant new stands of trees, and which species would benefit?
“If temperatures keep increasing, things will shift in ways that parks haven’t seen before,” said Patrick Jantz, an ecologist at the Woods Hole Research Center. “So there’s been a shift in the parks from managing for historical conditions—to bring things back to a pristine ecological state—to a whole new way of thinking: managing for species turnover.”
The forests of North America have seen plenty of change in a pretty short period of time, at least geologically speaking. Up until about 18,000 years ago, the Laurentide Ice Sheet covered Canada and much of the eastern United States. When temperatures climbed and the ice sheet retreated, forests gradually reemerged. But how? Did pockets of trees find refuge in sheltered areas during the Ice Age? Or were all tree species pushed to the southern tier of the United States, only to spread north again after the ice disappeared?
Scientists still debate the topic, but one thing is clear: today’s forests in the eastern United States bear little resemblance to post-glacial forests. Starting with European colonial settlers and marching through four centuries of development, drought, and fire, the tree cover of North America became fragmented.
“There are hardly any forests in the eastern U.S. that have never been cleared—maybe only a few percent,” said Jantz. “And younger, re-growing forests tend to have less structural complexity and different species assemblages.”
In many cases, National Parks were created to protect the remaining forests and their ecosystems from further destruction and fragmentation. But changes in temperature, rainfall (or snow), and atmospheric concentrations of carbon dioxide could eventually do as much to remake the forests as humans did with saws and fires and bulldozers.
Today, eastern U.S. forests are composed of a wide array of species. Some are common, like the red maple and American beech. Others are important food or habitat resources, such as black cherry and eastern hemlock. But what happens to these trees if atmospheric carbon dioxide continues to rise?
Jantz and colleague Brendan Rogers of the Woods Hole Research Center have been examining the state of current forest cover in the Appalachian region of the United States, while also modeling what the future will look like. They have been working in the Delaware Water Gap National Recreation Area (Pennsylvania and New Jersey), Shenandoah National Park (Virginia), and Great Smoky Mountains National Park (North Carolina and Tennessee).
Jantz and Rogers used the output from a large number of climate models to simulate future climate conditions, assuming that carbon dioxide emissions would continue to follow the current trend—rising from 400 parts per million to 1370 parts per million by 2100. The climate models showed that warming would accelerate in all three parks. The average increase is about 0.7 to 0.8 °F (about 0.4 °C) per decade until 2040, after which warming will speed up to about 1.2 °F (0.7 °C) per decade.
Along with rising temperatures, the parks of Appalachia should see fewer days of frost, which affects the length of the growing season. Precipitation is expected to increase somewhat, but also become more variable. The combination of small precipitation increases, higher maximum temperatures in the summertime, and a lengthened growing season means the frequency of drought could increase.
Rogers notes that climate models disagree about future precipitation much more than temperature. “It is entirely possible that precipitation will decrease, which would exacerbate droughts and fire weather,” he said. “If, however, precipitation increases substantially, it could enhance growth for many trees in a warmer climate.”
By combining these climate projections with information about topography and soil moisture and composition, Jantz and Rogers are exploring how the suitability of habitats may change for 40 eastern tree species. Their modeled projections are based in part on extensive field observations collected by the U.S. Forest Service. Rogers and Jantz are combining all of this information into a comprehensive vulnerability assessment, aimed at land managers, that is designed to facilitate planning and decision making.
It turns out that sugar maple and eastern hemlock, which Jantz calls “iconic species of eastern U.S. forests,” are expected to lose habitat. Lower elevations and southern latitudes will no longer provide the cool, wet habitats preferred by these species. Other species, however, would do quite well. Blackjack oak and black hickory are expected to gain habitat in areas that become warmer and drier. High-elevation species, like red spruce and balsam fir, may effectively be pushed off the mountains.
The suitability of a landscape is just one factor in the success of a species. “If you look at the overall suitability of land, a lot of species do well,” Rogers said. “But there are other reasons that trees won’t set seed or reach maturity; for instance, the climate might change too quickly, or seeds won’t be able to disperse and establish in fragmented land. It’s humbling and disconcerting to see areas where conditions for growth could improve but the trees have little chance of getting there unless there is active management.”
The craggy silhouettes of iconic whitebark pines rise from the mountain ridges of Yellowstone National Park. Those trees fill a niche in the environment that was left vacant by other species. Grizzly bears share in that success, ambling through stands of the pines to gather their nutritious pine nuts.
But stands of whitebark have been suffering since about 2004. The trees have been extensively damaged by mountain pine beetles and white pine blister rust. The U.S. Forest Service has tried to combat the problem by developing and planting whitebark varieties that are more resistant to the fungus. Now, the species is further threatened by a loss of habitat as climate changes.
Andy Hansen of Montana State University is leading a research team looking at western forests the way Jantz and Rogers are surveying the east. The Great Northern Landscape Climate Cooperative encompasses almost 300 million acres in the ecosystems of the Northern Rockies, including Grand Teton, Glacier, and Yellowstone National Parks.
The parks out west are different. For instance, the greater Yellowstone area is a large, mostly intact ecosystem that was set aside for the U.S. government before much of it could be developed or cleared. This means it is theoretically easier for species to migrate as weather and climate change. But the landscape is also more extreme, with high mountain elevations and a history of drought.
Temperatures in Yellowstone have warmed substantially since 1980, and some tree species have already responded. Hansen and colleagues have started examining those ecological changes by building on the ecological forecasting capability of NASA's Terrestrial Observation and Prediction System (TOPS). Based on inputs of data on historic and projected climate, land use, and vegetation, this computer system simulates past and future ecosystem characteristics such as snow pack, soil moisture, and forest growth rates. The models cover the period from 1950 to 2100.
“TOPS outputs are a unique and important product for federal land managers,” Hansen said. “Relatively few groups have done these types of projections to begin with, and certainly not using the latest climate and statistical information for the projections.”
Climate projections typically have coarse resolution, telling you what is expected over a relatively large area. But Hansen and NASA Ames scientist Forrest Melton have applied a series of additional modeling steps in order to make the projections relevant at scales that work for individual parks. “We delivered sophisticated forecast data in a way that a park manager can readily grasp for his or her place,” Hansen said.
In Yellowstone, species like lodgepole pine, Douglas fir, and sub-alpine fir are all expected to lose suitable habitat. But the biggest loser will be whitebark pine. If greenhouse gases continue to accumulate, and temperatures continue to increase as much as some models suggest, the habitat for whitebark pine will rise to higher and higher elevations until the trees are just about pushed off the mountaintops. Juniper trees, by contrast, are expected to thrive and gain more suitable habitat in Yellowstone National Park.
The Landscape Climate Change Vulnerability Project can help keep the researchers and land managers focused on key questions: Where do you thin existing stands of trees? Where do you protect stands from wildfire? Where should seedlings be planted such that habitat is most suitable 50 to 100 years from now?
The effort is slow and complicated, but worthwhile. Parks are increasingly coordinating to plan for climate change, using the new tools and products derived from climate models, large-scale inventory networks from the U.S. Forest Service, and NASA satellite data.
“You’ll never find a decision of importance in the National Park System where you can simply say ‘someone did this and it led to that,’” Gross said. “The problems we’re working on are big, complicated, and involve a lot of people. We’re not at the helm of the battleship. We’re just one of a number of groups nudging it in the right direction.”