Several issues in stewardship and in conservation involve the values of various ecological entities. Sometimes our actions or our plans change those values. Recently, we frequently trade pieces of environment believing that they are equally valuable. Stocking splake in a lake means changing the value of that fishery and of that lake.
Tree planting promoted in many stewardship programs almost always involves inserting a monoculture plantation of conifers to take the place of a complete forest ecosystem. Progressive forest management does not allow dead and dying trees or fallen rotting trees. This restructures the forest and its biodiversity. In all of these cases, what is being substituted is judged to have equivalent value to that which is being replaced. This raises the question of what is environmental equivalence?
Equivalence by science crept into early discussion of biodiversity. By default, using a count of species as a measure of biodiversity assumed that all species were equal. Equal how? Entries on a list? Certainly not ecologically equivalent. Loss of one species from a high species number in a tropical system clearly is not ecologically equivalent to losing the polar bear, the apex predator, in a simpler arctic system with fewer species. So equivalence as stated or implied by science is not a safe baseline for comparisons.
Recently the political process of “biodiversity offsetting” has become common. In offsetting the bargain allows the destruction of one ecological unit, such as a wetland, provided an equivalent unit is constructed elsewhere. If replacement by an ecological equivalent is too difficult, the unit may be replaced by some different ecological type. A woodlot could be substituted for a wetland. So equivalence may be reduced to simply mean an equal area of relatively untrammeled environment. At this point, the use of the notion of “equivalent” should be abandoned.
Even if the same ecological type is required in the replacement but it is located somewhere else, is it equivalent? Many say no! The environmental context was part of the value of the destroyed environmental unit. Not just the internal composition but also the surrounding environmental mosaic must be included if we are to have equivalent value. Local unique meanings cannot be traded between locations.
Value equivalence is not the same as equivalence by science let alone equivalence by economic-political bargaining. For some, value equivalence goes even further and includes the historical context of the unit. Fully equivalent value may require inclusion of intrinsic values. These can’t be measured or traded.
Several aspects of value equivalence are seldom accounted for in the political-economic trade-offs of biodiversity offsetting. The losses of environmental value in countryside planning where the proffered trade-offs may be non-ecological and solely in economic units usually are even more severe. They definitely can be described as loss of ecological value and the discussion above brings question to the assurance of “no net loss” commonly offered in many planning proposals.