Jack Putz: Fuel restoration with biomass
Published: Sunday, April 7, 2013 at 6:01 a.m.
Last Modified: Friday, April 5, 2013 at 6:22 p.m.
Correction of a widespread ecological misunderstanding about Florida could bring biodiversity benefits and provide low-cost biofuels for Gainesville's biomass-powered electricity generation facility.
Historically, our region was mostly covered by extensive expanses of grasses and showy flowers beneath widely spaced pine trees. There were some rich hammocks, but it was savannas, not closed-canopy forests, that dominated the landscape.
From slash pine woodlands in the wetlands to longleaf pine savannas on the sandhills, trees were sparse. The biological diversity in these ecosystem — the highest in North America — was in the understory where flowers, gopher tortoises and fox squirrels abounded.
As natural as they seem, the dense stands of laurel oaks, water oaks, sweetgums and grapevines that now blanket much of our landscape are new. Historically, closed canopy forest was restricted to patches of nutrient-rich soils and on the margins of lakes, river, and swamps. Similarly, the thick-as-the-hair-on-a-dog's-back pine plantations that abound today are of human construction.
Our savannas were kept open by frequent, low-intensity fires coupled with the constraints of growing on coarse-grained, severely drained, nutrient-poor, sandy soils. Over the past half century we have managed to suppress the fires and enrich the soils, all to the detriment of our once bountiful biodiversity.
With fires successfully suppressed, broad-leaved trees crept up out of the swamps. Plowing, over-grazing by cattle, and hog-rooting didn't help, but extinguishing fires is the main reason that fox squirrels, gopher tortoises, indigo snakes, and hundreds of other species are currently in jeopardy. Meanwhile, forest industries opted for high density pine plantations that they fertilize and clearcut at short intervals.
Sandy, nutrient-poor soils and frequent fires favor deep-rooted grasses, resprouting wildflowers and thick-barked pines. These same conditions disfavor dense stands of thin-barked and shallowly rooted hardwoods and pines.
Grey squirrels thrive in laurel oak forests but the now seldom seen fox squirrels are savanna beasts. There are birds in dense forests, but not the red cockaded woodpeckers, bobwhite quail, Bachman's sparrows or brown-headed nuthatches that live in savannas.
Until recently, low intensity fires swept across our area every 1-3 years. This astounding fire frequency was sustained by lightning storms — we live in the lightning capital of the USA — supplemented over the past 12,000 years by Amerindian ignitions. Cattle-keeping colonists maintained the burning tradition to freshen forage for their stock, to facilitate pine resin tapping, and to clear brush from their agricultural fields.
Most of our native plant species are adapted to low soil nutrients and are outcompeted when nutrient supplies are augmented. Residual fertilizers from former agriculture coupled with the doubling of atmospheric nitrogen additions due to fossil fuel combustion are making it tough on our wildflowers.
With nearly 98 percent of the pine savannas of the Southeastern coastal plain already gone and more going, ecosystem restoration is desperately needed. The first big step toward pine savanna restoration typically involves biomass removal — getting rid of the invasive trees. Longleaf and slash pines are light-demanding — they don't survive the shade of laurel oaks. Ditto for the hundreds of species of savanna grasses, wildflowers and wildlife that die out when fires are suppressed and hardwoods invade.
Biomass removal is also often among the biggest costs in savanna restoration. But if there is a market for biomass, there are hopes for fox squirrels and blazing stars. And if entire trees and all their nutrients are removed, the chances for natives improve further.
Enter the much debated but soon-to-be-operational biomass plant. The estimates of biomass availability that consultants provided the city did not include the substantial stocks available from ecosystem restoration on private and public lands. Using the biomass of invasive hardwoods and restoring pine savannas would yield even more fuel than thinning pine plantations and would do so at a competitive cost.
Of course, with the way markets work, scrutiny will be required to assure that ecosystems aren't abused in the name of “restoration.” Also, biomass removal is just the first of many challenging steps towards restoration. Along the way, would-be restorationists will need a lot of help as they try to make the world savanna-safe.
Pine savanna restoration and ecologically sound pine plantation management are not just wildlife and wildflower friendly, they make sense for Florida's economy. Hydrologists estimate that conversion of unnaturally dense forests and plantations into savanna-like stands would increase soil water recharge by about 25 percent — what a great collateral benefit from fueling our biomass plant.
Even if the deeply rooted differences of opinion about the biomass plant do not disappear after plant comes on-line, fueling it with restoration carbon will mean that our steps towards carbon neutrality are also towards biodiversity conservation and aquifer recharge. What great collateral benefits!
Francis E. “Jack” Putz is a professor of botany at the University of Florida.