Poems are made by fools like me,
But only God can make a tree.
Joyce Kilmer, 1913
More and more frequently I hear about ecosystem restoration—the attempt to reestablish a natural ecosystem on degraded land. Sometimes I even hear that “designer ecosystems” might provide services or experiences similar to or better than nature.
When we come to realize that straightened and channelized drainage-ways do not provide much flood control and fish production, ecosystem restoration is frequently recommended for streams. And in many areas wetlands were drained before we appreciated their importance in cleansing runoff waters and providing wildlife habitat. They too are often recommended for restoration.
It is worth asking just how well ecosystem restoration works. Where once wetlands removed nitrogen from inflowing waters by converting it to nitrogen gas in the process of denitrification, how similar are the denitrification rates in restored wetlands? If forests slow soil erosion and store carbon, how well do reforested strip-mine spoils provide these services?
We might be tempted to evaluate ecosystem restoration by counting how many of the species in an undisturbed area are found in the restored area. This test is favored by conservation biologists who value biodiversity. Unfortunately, in a survey of 89 restoration projects in different types of ecosystems worldwide, only an average of 44% of the native biodiversity was restored. Restoration can provide valuable habitat for some, but not all, of the species lost to degradation. Many species may not find the restored habitat or they may find that the specialized niche they once occupied is no longer available.
Some might argue that biodiversity doesn’t matter as much as services. Who cares if all the species are there so long as waters are cleansed, erosion is controlled, and fisheries are restored? Duke University’s Dr. Emily Bernhardt found that most stream restoration projects have failed to achieve levels of ecosystem function that were once found in nature. And a study by Greg Bruland of the Duke Wetlands Center suggests that denitrification rates are significantly lower in created and restored wetlands compared to natural wetlands on the coastal plain of North Carolina. Similar results were found for wetlands in New York State.
Carbon accumulation is lower in forests replanted on mountain-top removal sites in West Virginia than in neighboring undisturbed areas of the same age. We should realize that we are not replacing nature. In fact, the same global survey of restoration projects found only 25% of the ecosystem services provided by nature were found in the restored systems.
When development projects include damage or removal of natural ecosystems, in trade for mitigation and restoration elsewhere, we should realize that the trade is not even. Restoration may be better than nothing and sometimes it yields a valuable habitat, but we fall short when we try to replicate nature.
Best to leave nature as it is whenever we can.
This post originally appeared on William H. Schlesinger’s blog Citizen Scientist, published by Duke’s Nicholas School of the Environment.