Part Two of Sustainability: Easily Described, Tough to Measure - The measure of biodiversity should not be about a count, but rather about what counts.
Measurement and value are two overarching themes in all sustainability discussions. In my last blog, I posed some questions about how to measure sustainability in the context of food and energy crops and challenged the notion that the preservation of crop land over forest land was a proper measure of sustainability. In this post, I want to explore some of the issues that arise when biodiversity is used as a proxy for sustainability.
When I think about the measures of biological diversity, I’m reminded of a story the comedian Ron White tells about being thrown out a bar in New York City, by bouncers who picked him up and threw him “like a Frisbee to the curb.” It was an impressive feat, he says, because “depending on which convenience store I’m leaving, I’m between 6’ 1”and 6’ 6.”
That joke provides the perfect analogy for the problems associated with using biodiversity as an indicator of sustainability—your results will depend on which measures of biodiversity you are using.
The term biodiversity was coined in 1985 as a contraction of biological diversity and is defined as “the degree of variation of life forms with a given ecosystem, biome, or planet.”
Unfortunately, the definition neither accounts for natural changes in an ecosystem over time nor does it define the exact boundaries of an “ecosystem” or “biome.” There is no help in the definition of ecosystem either, as it is defined as “all of the organisms and the nonliving features of an area.” Gratefully, “planet” is pretty straightforward (as long as we can agree Pluto isn’t one). Until our means of measuring biodiversity can account for these things, using them as a yardstick to determine sustainability will be inadequate at best.
Today, ecologists measure biological diversity as an index that accounts for:
- Richness: the number of species present, and
- Evenness: the number of individuals of each species present and how close in number each species in the measurement area are
For example, an area containing two species with 5 individuals of both species is considered more biologically diverse than an area containing two species where there are 9 individuals of one species and 1 individual of the other.
A high biodiversity index as a measure of sustainability seems to work when the individuals are dandelions and wild strawberries. It is inadequate, however, when applied to more complex animal species. For predator and prey communities to maintain sustainability, for instance, larger numbers of prey-species individuals than predators are needed. Bobcats are few in number in the United States when compared to the population density of the species they prey on--rabbits and wild sheep to name just two.
A high biodiversity index is also inadequate as a measure of sustainability for some of the longest lived ecosystems on the planet. The Sahara Desert, for instance, is as dry today as it was at the end of the last ice age. It sustains remarkably few species (around 500) in an area that is approximately 60 percent that of the continental United States: 1.8 million of 3.1 million square miles.
Another issue that needs to be more rigorously vetted before biodiversity can adequately be measured is that of boundaries. Most animals, except very young individuals, are mobile. Except for very fast moving cataclysmic events like volcanic eruptions, individual animals move out of the way of natural or man-made ecosystem changing events: birds fly out of forests on fire and deer move off of land being logged. Nature abhors a vacuum, however, and those animals or their offspring return. The biodiversity measured in an area immediately after an event will be significantly lower than a measure taken of a larger area, one that includes the displaced (but not destroyed) species.
If loss of biodiversity is the measure of the difference between the diversity present prior to an event and that present immediately after the event, then every natural disaster—wildfire, volcanic eruption, blow-down, snowstorm, and flood—decreases biodiversity. (All of these natural disasters affect contiguous areas that are hundreds if not thousands of times larger than the contiguous area affected by a timber harvest, by the way.)
For a striking visual look at this set of NASA color enhanced, before-after-now (2010) photos of the Mount St. Helens eruption. Here you will see the two important things. The return to near normal vegetation after a relatively short amount time (geologically speaking) is striking. These photos also illustrate the immensity of the area affected by the volcano and the relatively small areas that have been logged.
The notion that the effect of natural disasters is a decrease in biodiversity is (forgive my bluntness) nonsense. Without volcanoes there would be no Hawaii – perhaps one of the most biologically diverse ecosystems in the world. River bottom land is some of the richest, most fecund land on the planet (currently, the third rock from the sun is still classified as a planet). Without snowstorms, there would be no snowshoe hare, no ermine, and no snow leopard. Without wildfires there would be no ponderosa pine. Very strong evidence exists to suggest that the habitat preferences of some very rare species like the Florida panther, the gopher tortoise and the red-cockaded woodpecker are enhanced by fire and selective log harvests.
As these examples demonstrate, using measures of biodiversity as a proxy for sustainability presents three challenges:
- The measure itself seemingly ignores the sustainability of some ecosystems with low biodiversity.
- A high biodiversity would seem to favor ecosystems that are out of balance; one where predator and prey species are present in equal numbers
- To be meaningful, the boundaries of the area measured before and after should be large enough to include displaced individuals or must be taken after a sufficient amount of time to allow those displaced individuals to return.
I am going to close this post with one more thought about biodiversity, sustainability and renewable energy. Before we throw the use of wood as a replacement for fossil fuels “like a Frisbee to the curb” let’s make sure the measures used to determine the real environmental effect are realistic. If you believe climate change is real and will be (or has the potential to be) globally catastrophic. If you believe the major contributor to climate change is the release of ancient sequestered carbon from the burning of fossil fuel, what do you suppose the effect on biodiversity will be if the release of greenhouse gas isn’t mitigated?
I invite you to join me in my efforts to think through these very complex issues by leaving your comments below.
Forest2Market: July 14, 2023
