Climate change forecast to alter the Pine Barrens

Due to climate change, the iconic New Jersey forest known as the Pine Barrens may start to lose its namesake trees over the next century, a recent study concludes.

As temperatures rise, the Pine Barrens may become the Oak Barrens.

"The regeneration potential of pitch pine - the likelihood that they would be able to establish in a place - really plummets in the middle of the century, and that's purely a climate change signal," said Alec Kretchun, a forest ecology researcher at Portland (Ore.) State University.

Kretchun led a recent study published in the journal PLOS One that used computer modeling to project what will happen to the Pine Barrens over the next 100 years. They found that obvious and quick-moving disturbances including gypsy moths and wildfires will not matter as much as the inexorable violence of rising temperatures.

The forest, now dominated by pitch pines, short-leaf pines, and a few other pine species, will shift toward an oak-dominated landscape instead.

Climate change is just the latest in a long series of indignities humans have foisted on the Pine Barrens, the largest contiguous forest on the eastern seaboard. It occupies almost a quarter (22 percent) of New Jersey, stretching from near the northern end of Cape May almost all the way up to Route 195, 70 miles away.

Logging, charcoal, and "bog iron" production, even glass making from the "barren" sandy soils, have shaped the forest for good or ill for hundreds of years.

Oaks - the white, black, and chestnut varieties - have already been creeping into the Pine Barrens, thanks largely to fire suppression over the last century. Pines need areas of bare ground to take hold, and without fire, the forest floor is covered with litter. Pines are also very fire-resistant - some even need fire to release their seeds - while oaks are not.

In the future, the modeling done in Kretchun's study suggests that all those inputs will push further toward a more oak-dominated forest, leaving the whole system far more sensitive to disturbances such as gypsy moths and fires.

Such a disturbance could open the door for pines again, but climate change says no: Kretchun said that by midcentury the pitch pine, one of the Barrens' dominant species, will have a much lower chance of reestablishing itself after a disturbance.

The species simply survives better in lower temperatures than will soon be common, and without fires, some of those pitch pine cones and seeds would never open. Kretchun's group's modeling showed a "probability" of establishing pitch pines dropping close to zero by 2050 or so.

Gordon Bonan, of the National Center for Atmospheric Research in Boulder, e-mailed that this result relies solely on a single model that he called "rather dated." Ideally, studies like this would compare results from multiple models; others may have differing temperature increases or precipitation changes, all of which play into the forest's future composition.

The best regulatory response to this is far from clear. Nancy Wittenberg, executive director of the New Jersey Pinelands Commission, which oversees the forest, agrees that climate change is "something we need to address," but "we have not in any formalized way done anything to date."

Wittenberg said that the commission's science office is aware of the Kretchun team's paper. "It's pretty early on for us," she said. "We are accumulating those kinds of research documents now and . . . just trying to wrap our arms around how climate change is an issue for the Pinelands, and what we as a regulatory agency should or shouldn't be doing."

For now, simply keeping an eye on things is a start. Kenneth Clark, another of the study's authors, works for the U.S. Forest Service at the Silas Little Experimental Forest in the Pine Barrens. He explained how the Forest Service uses flux towers to measure how much carbon dioxide is actually entering and leaving the forest all the time. One such tower is surrounded by a stand of trees heavily dominated by oaks already, and the skeletal victims of a massive 2007 gypsy moth outbreak yields gaps in the canopy above.

"As the temperature rises, carbon sequestration drops," Clark said, referring to the forest's ability to store carbon dioxide, which makes them a key tool in the fight to hold back global warming. So we could be creating dangerous feedback loops, he said: warming temperatures, less carbon sequestered, more warming temperatures, and so on.

But warming may also lead to longer growing seasons, which means more time for leaves to store carbon. A "PhenoCam" on top of the flux tower, used to track vegetation, will help tease out that interaction in the future.

A few hundred yards from the first sits a somewhat more solid-looking monitoring tower. Up the 56 feet of spiraling steps through the tower's innards, all that is visible are pines. Pitch pine and short-leaf pine dominate, though a slightly taller stand of nonnative loblolly pine stands a short ways off.

These are the trees that - excluding the loblolly - are in some sense "meant" to be here. Oaks, as well as enormous Atlantic white cedar (Kretchun compared them to sequoia trees, big enough "to drive a car through") that have all but disappeared here, likely used to have some hold before Europeans arrived, but pines have ruled for centuries at this point.

It requires a series of value judgments to pick one species of tree over another, but keeping pines is likely best for stability, said Amy Karpati, director of conservation science for the Pinelands Alliance.

But the way forward is unclear. "Climate change is a more difficult threat to tackle, because this stressor is not exclusively locally generated or locally solvable," Karpati said. All one can do in the Pine Barrens is try and restore fire regimes, keep out invasive species, and so on, she said. But if the modeling study is right, such actions won't really matter as temperatures rise.