The Economist | Conservation: Restoration drama
The science of ecology is helping to bring "ecosystem services" to market
The Economist Auqust 10th 2002
The science of ecology is helping to bring "ecosystem services" to market
RESTORING damaged habitats to something like their pristine condition is a relatively recent idea. For most of humanity's history, the trend has been in the opposite direction, as people have logged forests, drained marshes and cleared land for agriculture. But as folk have grown more knowledgeable, they have realised that some habitats are useful in their original condition. The result is an increasing desire to recover part of what has been lost. That is helping to change ecology from an academic to a practical science, as the subject's insights are applied both to the task of restoration and to hard-headed assessments of the value of that restoration.
To help the flow of theory into practice, Margaret Palmer, a biologist at the University of Maryland, ran a symposium on the subject at a recent meeting of the Ecological Society of America and the Society for Ecological Restoration, in Tucson, Arizona. According to Dr Palmer, every habitat has an "envelope" of natural variation in its possible structure and composition. Knowing what lies within this envelope is crucial to knowing what to restore, and when to stop. Thus, successful habitat restoration requires an understanding of theories about population biology, competition between species, biodiversity and the stability and variation of ecosystems.
Putting theory into practice, Steve Handel, at Rutgers University, in New Jersey,
has shown that derelict urban lands, including such unpromising sites as landfill rubbish dumps, can be restored to resemble old fields with the help of pieces of ecological science known as metapopulation theory and patch-dynamics. These rely on the idea that populations of animals and plants are not permanent, contiguous collections of organisms, as was once believed, but are actually shifting collections of smaller groups that are partly isolated from one another and often exist only temporarily. By manipulating the sizes of patches of plants, Dr Handel has been able to improve insect pollination and seed dispersal, and thus kick-start the restoration process in landfills near New York.
The restoration of surplus agricultural land, too, can benefit from the appliance of science. Sara Baer, at Southern Illinois University, and her colleagues, have shown that previous tillage hampers the restoration of prairie on former farmland in the Great Plains. Ploughing homogenises the soil. That is fine for crops, which are monocultures, but no good for wild plants, which come in a range of species that prefer subtly different conditions. By tweaking the soil's moisture and nutrient content to increase its heterogeneity, Dr Baer has found that she can affect how well a piece of habitat functions once it has been restored. And Dr Palmer has found something similar in aquatic systems.
There, having a variety of different particle sizes in the sediment of a stream will affect the rate at which it recovers from environmental damage, and also its eventual biological productivity.
Similar ideas apply to marine environments. Charles Peterson, of the University of North Carolina at Chapel Hill, has found that mathematical models of the communities of animals and plants in oyster reefs can help to show which animal species may successfully be re-established in a damaged reef.
The most effective attempts at restoration, though, have been those in wetlands. Besides pleasing people who like nature, restoring wetlands brings practical benefits. Not only has ecology shown how to do this, it has also demonstrated that wetland habitats provide valuable "ecosystem services" such as recharging groundwater, attenuating floods and acting as natural filter beds that remove pollutants.
Muck and brass
To give one example, the run-off from an area of land that includes a lot of impervious surfaces such as roads, car parliis and driveways tends to contain pollutants, particularly nitrates, phosphates, petrochemicals and bacteria. According to Michael Mallin, a marine biologist at the University of North Carolina, if more than 20% of a catchment area is paved in this way, any bathing or fishing areas into which its water drains will start to become unacceptably polluted by bacteria.
In situations such as this, it is frequently cheaper to restore previously drained wetlands (or even to build. new ones from scratch) than to construct water filtration plants. The city of Riverside, in California, for exarr~ple, saved itself $18m by constructing wetlands rather than a denitrification plant to meet nitrate effluent standards for its local water supply. Water extraction authorities in both Washington, Dc, and New York have also found it cheaper to pay for natural filter beds to handle water contamination than to build concrete ones. And in Florida, a 3,5oo-acre (1,4oo-hectare) artificial marshland has dealt with agricultural wastewater, bringing phosphate levels down to 17% of what they had previously been.
Applied ecology is also helping, in America, to lubricate "trade" in wetlands. it is not the wetlands themselves that are bought and sold, but rather "wetiand credits". These are issued by so-called mitigation banks to companies or other organisations that protect or restore pieces of wetland. They can then be sold to third parties who wish to destroy some wetland elsewhere. Such transactions are, however, meaningless unless ecologists can confirm that a newly constructed piece of wetland has real environmental benefits. That involves measuring factors such as nutrient uptake, flood alleviation and the presence of suitable plants. Researchers are still learning about what, precisely, makes one piece of wetland equivalent to another. indeed, in less understood habitats such as the Grand Canyon, attempts at restoration are proving to be a powerful test of the accuracy of ecological theory.
The first mitigation banks appeared at the start of the iggos, as a result of regulations drawn up by the country's Environmental Protection Agency for the granting of permits for the removal of wetlands. A state's department of transport that wishes to build a road through a wetland, may, for example, be required by the regulations to create an equivalent piece of wetland elsewhere. Rather than actually sending its navvies in to install a new
marsh, the state can buy an appropriate amount of wetland credit from people who have earned it the hard way.
There are now around 300 mitigation banks in America, and loo more are planned. John Ryan, until recently the president of the Wetland Mitigation Banking association, estimates that 8,oooacres' worth of credits were issued last year. Generally, restored wetland costs between $25,ooo and $'3o,ooo an acre, depending on the amount of engineering required, the type of wetland and the risk that the restoration project in question may not succeed. it also depends, of course, on the local price of other sorts of land. In New Jersey, wetland credits have been sold for as much as $250,Ooo an acre.
Such sums are having an impact on the property business. Companies such as GreenVest, based in Newjersey, call themselves "environmental capitalists" and help landowners to value their property in a way that takes account of "eco-assets" such as potential wetland credits. Indeed Tenneco Energy, a utility firm based in Houston, Texas, which has large land holdings in New Jersey, used such a procedure to wipe out the cost of its liability for cleaning up contaminated soil on its property. Restoring the land to wetland not only removed the contaminants, it also allowed Tenneco to sell wetland credits. Furthermore, since conservation areas are not taxed in this part of New Jersey, it saved the firm $3oo,ooo a year in land taxes.
Not surprisingly, some individual mitigation banks and restoration projects have been environmental failures. But the environmental capitalists hope that progress in reconstructing wild places will eventually provide a robust way of establishing that a wetland really works, and thus has a market value.
Link to Economist article