"Forests in Peril"
a book review by Connie Barlow
published in the Winter 2004 issue of Wild Earth
Forests In Peril:
Tracking Deciduous Trees from Ice-Age Refuges
into the Greenhouse World
by Hazel. R. Delcourt
McDonald & Woodward Publishing Co., 2002
234 pages; $22.95
For those who, through book learning or on-the-ground experience, can appreciate the distinctions among diverse forest assemblages of eastern North America, it comes as a shock to witness American beech an hour's drive from the Gulf of Mexico and hanging out with evergreen magnolias and American holly to boot. For beech, this truly is an alien world. Yet northern relicts and odd botanical combinations are the norm in the rare and dispersed "pocket refuges" of the Gulf Coastal Plain, from the Florida panhandle to the bluffs along the lower Mississippi River.
As Hazel Delcourt vividly demonstrates, pocket refuges are not just curiosities. Here, more than anywhere else, one can time-travel 18,000 years back into the Pleistocene, when the entire continent was cooler and lobes of glacial ice advanced as far south as southern Ohio. At that time, many of our most familiar and beloved plants of the Midwest and central-to-southern Appalachians took refuge on rich soils near the Gulf coast. The amazing fact is that residual populations of many of these plants can still be found in former Ice Age refuges, thanks to special habitats created by wind-deposited glacial loess, which erodes into deep ravines that are cool, moist, and fire-resistant.
Those who cherish the richness of forest life in the Smoky Mountains of North Carolina, or the Cumberland Plateau of Tennessee, or the limestone country of southern Indiana, might do well to make a pilgrimage to one of these sanctuaries: perhaps the Tunica Hills of Louisiana or the bluffs along the east side of the Apalachicola River in northern Florida. Were it not for these special places, our continent might have lost many species to climate change, including its dogwoods and its tulip trees.
In her accessible and worldview-shifting book, Delcourt illuminates the dramatic changes in how scientists have understood the origin and dynamics of eastern North America's deciduous forest types-perspectives changed in part because of three decades of her own paleoecological sleuthing. As the title suggests, plant species on the move in response to climate warming or cooling (alternations of which have happened perhaps 20 times during the past two million years) may depend utterly on corridors or archipelagoes of suitable habitats for their survival.
Forests in Peril thus brings a crucial deep-time perspective to one of the central concepts in conservation biology today: corridors. Throughout the Pleistocene, rich soils and moist microclimates traversing sandy, dry landscapes would have hosted mesophytic forest species in transit. These species, moreover, migrated not as integrated communities but opportunistically, species by species, hopscotching from one safe site to the next. The corridor that Hazel Delcourt has mapped out between the Tunica Hills of Louisiana and the Cumberland Plateau of Tennessee is rather narrow: dependent on a thinning wedge of glacial loess blown from the Mississippi shoals onto its eastward bluffs and hills. Sadly, many of the ravines that facilitated plant movement in the last 15,000 years have been turned into reservoirs or recreational lakes, no longer able to function as safe sites for plant migrations.
The conservation implications of this deep-time awareness are profound, given the probability of impending climate warming. We may be rather sure of what is native, but precisely where becomes problematic. For example, a small population of cool-temperate American beech still thrives in the rich soils along the Apalachicola River west of Tallahassee. As climate continues to warm, those southernmost remnant beech trees may be endangered. Their brethren, however, may still be vibrant far to the north, provided that their gene pool remains robust and climate change does not exceed their tolerances. What, however, of other species that are "stranded" in the south in isolated pockets with no stepping stones to accommodate their northward-moving phalanx? How do we, as conservationists, relate to these truly imperiled plants? For example, should we attempt to save one of the world's most endangered conifers, Torreya taxifolia, by helping it "get back" to places like the Smokies, where we suspect it thrived during previous interglacials and for millions of years of prior Cenozoic warmth?
Delcourt suggests that anthropogenic fires set by prehistoric Native Americans for purposes of game management may have disrupted the continuity of habitats that otherwise would have been corridors for northward movement of plants during the current interglacial. If so, human interference with plant migration has not been confined to the modern agrarian and industrial age. Even a pre-Columbian standard for management may thus be a prescription for extinction, especially if our fossil-fuels addiction nudges the current interglacial into a "super-interglacial."
The closing chapter of Forests in Peril is a stunning synthesis. Delcourt lays out patterns and predictions, while posing questions of great consequence for those committed to biological conservation. I was at once exhilarated as Delcourt's breadth of understanding became my own-and horrified by the conservation challenges that suddenly lurched into view. "My personal and professional odyssey as a historian of deciduous trees," she writes, "has brought me to the realization that the future of the eastern deciduous forest is now at risk. (p. 97) We can provide corridors to allow for species to migrate successfully in the face of climate change. We may also need to be prepared to transplant endangered species to new locations where climate will be favorable." (p. 207)
Self-enabled migrations facilitated by effective seed dispersers and served by generous corridors are, unquestionably, the ideal. But when the ideal fails for one species or another, we may need to step in to their rescue, not only with good science, but with a strong dose of intuition, humility, and heart.
CONNIE BARLOW, a proponent of "deep time" awareness in conservation, is a frequent contributor to Wild Earth.