Tuesday, September 8, 2009
Letting Forests Grow Old: Saving Biodiversity and Absorbing Carbon through Compact Green Forestry
Settlers arriving at the end of the Oregon Trail in the 1840s and 1850s quickly filled up the Willamette Valley, a grassland that had been kept free of trees because of fires set by Indians to attract game to fresh grasses for easy hunting. Much of the rest of western Oregon and Washington were covered with thick forests of huge trees at which settlers and lumberjacks alike marveled, some as much as 10 feet in diameter and 400 feet in height. Settlers wanted agricultural land not trees, but forests were all that was left. They tried the laborious process of clearing away the trees, but were usually rewarded with cropland of little value. Some were able to supplement their income by selling timber where there was a market for it near emerging urban centers, such as Portland and Seattle. The Donation Land Act of 1850 that allowed a settler to claim 320 acres, or 640 acres for husband and wife, failed to create a Jeffersonian paradise of small yeoman farmers in the Pacific Northwest.
The way to make money at this point in the history of the Northwest was to harvest timber, mill it into lumber, and ship it off to the booming gold fields of California, and this is what the early lumber barons did. Rather than the family farm, the basis of the region's economy became the lumber camp with its army of lumberjacks, the mill, and the port for loading and shipping lumber. Later with the arrival of the railroad, and a new class of timber barons such as Frederick Weyerhaeuser, the orientation of the market shifted to feeding the booming urban markets of the East. Within a century, the vast old-growth forests were reduced to a shadow of their former selves.
Foresters of the old school viewed old-growth as something to be cut down. Mature Douglas-fir forests contain a huge amount of biomass, more on a per hectare basis than any other plant species in the world. Mild, wet winters and warm dry summers provide ideal conditions for a conifer—a tree that doesn’t loose its leaves in the winter—to accumulate a huge amount of woody material. The tree can photosynthesize the sun’s energy year around. Douglas fir will live up to 750 years, obtaining a height of up to 100 meters (300 plus feet) and a diameter of 2 meters (6 plus feet) or more. Once a Douglas-fir crashes to the floor from old age, chances are it won’t be replaced by one of its own kind because its seedlings don’t survive in the deep shade of old-growth forests. More than likely a shade tolerant tree, such as the western hemlock, will pop up into the canopy and replace the Douglas-fir. If a forest is struck by a massive blow-down, or better yet a fire, then Douglas-fir seedlings will emerge in the open sun and grow rapidly, creating a thick forest that will eventually prune itself with a few large trees surviving.
The trouble with an old-growth Douglas fir from a forester’s perspective is its failure to add woody biomass once it reaches maturity. Forests, like people, grow in their youth but stop adding biomass in old age. A mature tree gains branch growth in its sunny upper canopy, but sheds branches in its shady lower reaches. After roughly a hundred years of age, the net addition to woody material in a Douglas fir slows dramatically. While an old-growth Douglas-fir forest (200 plus years of age) contains a huge amount of biomass, it doesn’t add any. Conversely a young Douglas-fir forest adds biomass at an exceptionally high rate. The economic logic of forest exploitation in such circumstances is simple—clear-cut remaining old-growth, replant it with seedlings, let it grow 75-100 years, and cut it again. This amounts to converting a natural forest to a plantation. Forestry becomes tree farming.
Today foresters recognize the ecological virtues of old-growth ignored by the older logic of exploitation. The pioneering research of Jerry Franklin, a forestry professor, and his colleagues established the ecological significance of Pacific Northwest old-growth forests. Old-growth forests possess special biological features lacking in their younger counterparts starting with really big trees that perform a host of ecological functions and provide habitat for a multitude of species. By intercepting fogs and mists in their huge canopies, old-growth forests add substantially to local terrestrial water supplies. Lichens love to hang from the upper branches of the canopy, suck up still more moisture, and fix nitrogen that adds to the nutrient base of the forest as a whole. The same canopies take on an irregular shape that causes spotty light flows to the forest floor and a patchiness and diversity to understory vegetation. An absence of much light at all beneath densely packed young stands of Douglas fir excludes understory vegetation in such forests and reduces biodiversity. Age in forests reduces growth but supports much greater species diversity than youth. Large old trees with their big tall trunks and diverse climate niches, beginning with the cool, quiet, damp forest floor and ending at the top with crowns often broken up from exposure to the elements, provide all sorts of potential homes for a variety of species. The irregularities of the crown attracts rare nesting Spotted Owls and perches for Bald Eagles watching nearby waterways for prey. An abundance of insects find their home on and in the bark of big, old trees and serve as a source of food for a variety of birds and mammals, including bats that feed on flying insects above the crown. As many as 1,500 species of invertebrate insects can be found in, on, and around a large, old-growth Douglas fir.
The special role that big trees play in old-growth forests don’t end with tree death. Large, dead snags become feeding grounds for all sorts of bacteria, fungi, and insects. Most important of all, snags become the home of cavity-excavating birds such as the Pileated Woodpecker and other birds that move in after woodpeckers move on. Once the snags come crashing down, they still have work to do as habitat for a variety of organisms. Fallen logs turn out to be an important nursery for tree seedlings that have trouble competing with ground-layer plants, and provide a path into open areas for small mammals that eat fungi and inject spore laden feces near seedlings. The spores grow to become fungi which form a symbiotic relationship with new tree roots and help accelerate reforestation.
Some snags end up falling into streams to the benefit of juvenile salmon who hang out in the resulting pools, waiting for prey to float by. Adult salmon roam the Pacific in search of food until the time for reproducing arrives. They then return to the forest stream of their birth, and find a gravel bed where the females can lay their eggs and the males fertilize them. Adults with their energy spent from the long and perilous trip die and add what remains of their biomass to the local forest ecosystem. The cycle is completed once the juvenile salmon head out to sea.
In the ordinary timber harvesting cycle, the biological riches that old-growth forests support are lost to the economic desire for the vigor of youth. Income from creating woody biomass achieves a maximum by keep forests in a young, high-growth state. Conservationists have responded by advocating for the placement of old growth in a protected status, such as designated wilderness, to keep it out of the hands of the forest products industry. The trouble with this solution is the insufficient amount of forests around the country that contain big, old trees. If we care about preventing species that depend on old growth from heading down the path to extinction, we could use more old-growth forests. This can be accomplished by simply letting some of our young forests grow old. In the age of global warming, a key benefit of doing so is carbon sequestration. As young forests grow old, they add carbon rich biomass to trunk, branches, roots, and soil.
Let’s now consider how to pull off letting forests age more and accumulate carbon while extracting from them a reasonable flow of wood fiber for human use.
The Forest Stewardship Council (FSC) was founded in 1994 by a broad array of environmental groups, forest products industry interests, and others to improve forest management practices globally and bring into reality the notion of environmentally sustainable forestry. The FSC pursues this ambitious goal by certifying forests around the world as being managed in an “ecologically, socially, and economically exemplary” fashion. The products of these forests can then by sold as FSC certified to customers who desire environmentally friendly products and are willing to pay for them. The ultimate benefit for forest landowners is the receipt of a price premium for certified wood. The LEED building certification process we discussed earlier awards points to developers who use FSC approved forest products in their buildings.
A list of core principles drives the certification process and includes compliance with all valid local laws and international agreements; assurance of clear tenure rights; protection of the rights and interests of local community members, workers, and indigenous peoples; efficient delivery of a wide range of economic, social, and environmental benefits from forests; and the protection and enhancement of biological diversity and ecological functioning in forests. The FSC has developed customized standards that fit local forest conditions around the world, including a set that applies to the old-growth forest of the Pacific Northwest. These particular standards call for not only the protection existing old growth, but its long-term expansion by letting some timber stands age and take on old-growth characteristics. To get certification, a Pacific Northwest forest landowner must keep a specified portion of trees under management in old growth or in stands that will become old growth as they age. The essential idea behind certification is to encourage the human use of forests, but to accomplish such use in a manner that is at once ecologically sustainable and protective of all native forest species. This does not mean that big, old trees would all be put away in a natural museum and never harvested. It simply means that the amount of old-growth in the aggregate will be brought up to a level that will conserve total forest-based biological riches over the long haul. Big, old trees with their fine grain woods can be harvested, but only if they get replaced by growing other big, old trees.
FSC certification around the world now includes roughly 100 million hectares—an amazing accomplishment in such a short time, but more needs to be done. One path to increasing certified forests in the U.S. and elsewhere is to combine the whole certification process with marketable carbon emission allowance trading. FSC-certified forest landowners could sell carbon emission allowances created by simply letting their forests age and accumulated carbon-laden biomass. To participate in carbon allowance markets in this fashion, forests would have to be certified by the FSC or other equivalent organizations, and would be monitored not for just forest management practices, but also for carbon accumulation. To get paid for accumulating carbon, you would have to be certified.
Forests suck up carbon by simply growing, but how much? The current average for all our forests is about 3.2 tons per hectare (1.3 tons per acre) and sums up to roughly 1,000 million metric tons a year. Forests clearly possess a substantial ability to absorb carbon. How much added carbon dioxide can be soaked up by forests in a year on top of what’s already being done? This of course depends on the rewards available for doing so. A recent study suggests that the ability sell carbon allowances at $100 per ton for sequestration would yield roughly an added 500 million metric tons of CO2 reduction annually from forest landowners, or about 8 percent of our current fossil fuel related emissions. This would be accomplished by landowners through added planting of forests, increasing the amount of time between harvests, and the use of forest management practices that reduce carbon emissions from plant matter breakdown.
Harvesting of commercial Douglas-fir forests in the Pacific Northwest occurs roughly on a 60-year cycle. At harvest, a forest is clearcut and either replanted or allowed to grow back through natural reseeding. Carbon storage in the vegetation, the woody debris on the ground, and the soils just before harvest equals nearly a million metric tons CO2 per hectare for a typical 60-year old forest. A representative old-growth Douglas-fir forest (250 years plus) stores nearly 2.3 million metric tons CO2 per hectare, more than twice as much as its younger counterpart. A clearcut harvest removes carbon from the forest in the cut trees and accelerates the breakdown of carbon-rich debris on the forest floor. In the milling process, a significant portion of the harvested wood ends up as waste or being burned for fuel, causing the embodied carbon to find its way back into the atmosphere fairly quickly. Roughly 45 percent of the woody-carbon ends up being stored in building materials and other products.
The future of newly cut Douglas-fir forest can take two paths. One is to treat it like a tree farm and replant and cut trees every 60 years. The other is to let the forest grow old. After 250 years, the old-growth forest will have stored about 2.3 million metric tons CO2 per hectare, but the comparable tree farm will only have stored about 70 percent of that assuming generously a permanent 45 percent wood products storage rate for harvested carbon. In short, allowing forests to age will significantly accelerate carbon sequestration. While the additions of harvestable wood may slow fairly quickly in the aging process, because big, old trees are always shedding branches that decompose slowly and add to soil carbon, carbon stores continues to accumulate well into very old age for a Douglas-fir forest.
Whether a forest certification program combined with marketable carbon allowances would increase or decrease total wood fiber production cannot be easily predicted. If a forest landowner received credit for the CO2 permanently embodied both in harvested wood (40-45 percent) and the forest itself, harvests could go up if a landowner plants more land to trees because of the added income from carbon allowances. On the other hand, if landowners are required to devote more land to old growth for certification and adopt longer periods between timber harvests to accumulate more carbon, then harvests could actually drop, even if the total amount of land devoted to forests expands. This drop could be mitigated somewhat by selectively harvesting old-growth trees through low-impact methods using horses to drag trees out of the woods or lifting them out with helicopters. Since trees would grow back in gaps and harvested carbon would be partially embodies in wood products, the net impact on total carbon accumulation could actually be positive. Moderate selective harvesting could be undertaken without substantially altering the old-growth structure of a forest and its functionality as habitat. Still such moderate harvesting would not likely produce the volume of wood that could be produced from a comparable land base of 60-year rotation tree farms.
Forest productivity statistics suggest the presence of a fair amount of wiggle room for expanding harvests from younger forests to compensate for old-growth protection. Publicly owned timberland unreserved for habitat protection or any other purposes constitutes about 29 percent of all land in the U.S. potentially usable for timber harvesting. On this land, only about 20 percent of the total annual growth is harvested annually at present. After World War II, the public forests came under intense harvesting pressure to provide raw material for the housing boom. In recent years, these same forests have been in a recovery mode. Clearly there is plenty of room for harvest expansion on public lands in the future even if more old growth is protected. Non-industrial forests, those owned by individuals who don’t process wood for living, compose about 58 percent of the timberland in the U.S. and currently remove about 75 percent of their annual growth. Even with additional old growth protection, there is some room for sustainable expansion in harvests on these lands. Industrial forests, mostly tree plantations with young, planted, fast growing trees, currently harvest about 105 percent of annual growth. Plantation forests indirectly play a role in the protection of their natural counterparts by reducing harvesting pressure on the latter. Certification allows for plantation forestry so long as it is done in an environmentally sound manner and a portion of the certified land is sustained in natural forests including old growth. Plantations look a bit like row crop agriculture, but they do have a role to play in protecting forest ecosystems and if managed right they can accumulate carbon.
Irrespective of whether wood-fiber supply expands or contracts because of forest certification, demand for housing related wood products will shrink if we adopt a true compact living strategy of the kind described earlier. Why? If we increase the share of multi-family housing in the total mix, the amount of building material required per house will decline. Remember in a four unit townhouse, each housing unit shares two of its walls with others. The amount of building material for walls can be cut roughly in half. Similarly in apartment buildings, walls are shared. The point is simple—urban high-density housing uses less material per unit of floor space than the low-density, detached, suburban kind. Also, high density living will favor older cities where many solid older buildings can be recycle for housing, saving on virgin materials. The stimulation of LEED-certified construction with tax credits and LEED-points for recycled building materials should also reduce the demand for virgin lumber. Forest certification and carbon sequestration could put a dent in the supply of virgin wood fiber, but compact living will dampen demand as well, keeping lumber prices from shooting up too far.
Pushing the domestic supply of wood fiber in an environmentally friendly direction will tend to push up the demand for less costly, uncertified imports. This would amount to transferring bad forestry practices in this country to the rest of the world, something we want to avoid given the degree to which ecologically rich forests overseas stand threatened by exploitation. Requiring the certification of imported wood products in one fell swoop avoids this problem and gives good forest management a global boost.
Along with compact living, compact energy, and compact cuisine, we can have compact forestry in the sense that we leave more of the forest to nature itself and make use of the rest in a manner friendly to biological diversity. At the same time, we can absorb some extra carbon and diminish the extent of global warming. Compact living will make compact forestry more economically feasible than otherwise by reducing our demand for wood fiber.