Biodiversity In a Clearcut?…

About ten years after logging, this site near Sproat Lake on Vancouver Island has a high biodiversity of trees, shrubs, and herbs. It supports a large number of insects, birds and mammals that benefit from the forage, nectar, and new habitat

Biodiversity, or biological diversity, has become the single biggest buzz-word in environmental discussion. If one is “preserving biodiversity” one is doing the work of the Lord. Anyone who “destroys biodiversity”, particularly if they make a profit at it, is Darth Vadar material.

Fortunately, things are not that black and white. In the great cycles of life and death there is no absolute preservation or destruction. True, when a species becomes extinct it is gone forever. But it is equally true that when a species becomes extinct it provides an opportunity for a new species to take its place, one that had never existed before. This, too, is a simplistic picture of the workings of evolution. But it is a fact that every time a single creature dies there is a “loss” and every time a new one is born there is a “gain”. Some people seem fixated on the “loss” side of the equation, predicting total collapse of the ecosystem if “the destruction continues”. I like to keep one eye on the emergence of new life which is happening all around us. As Thoreau said “I have great faith in a seed. Convince me that there is a seed there, and I am prepared to expect wonders”.(Henry D. Thoreau, Faith in a Seed, Island Press, 1993. ISBN 1-55963-181-3)

In my book, http://www.greenspirit.com/trees.cfm“>Greenspirit, I put this idea in these words:

“What a miracle is the west coast rainforest that it can recover in full and total splendour from devastating ruin. Surely we must celebrate this new life at least as much as we mourn life lost elsewhere. The spirit has returned to Pacific Spirit Park as it has to most of the other areas clearcut in British Columbia and the Pacific Northwest.”

Before making up one’s mind about the right or wrong of a particular activity or development, it is helpful to consider the meaning of the term “biodiversity” in more detail. In this excerpt from Pacific Spirit I explore the complexity of the term:

“Variety is the spice of life.” (Anonymous)

The concept of biological diversity is both old and new. Throughout the ages students of nature have understood that some environments have more species and are more varied than others. Rainforests are richer in life than deserts. Coral reefs have many more species of fish than the abyss of the deep sea. While these differences were generally recognized it was not until recently that scientists began to measure and describe the diversity of ecosystems in a systematic fashion.

One of the difficulties in understanding the concept of biological diversity is the fact that there are, so to speak, a diversity of diversities. In trying to keep it simple I have chosen only the three most important measures of diversity within living systems. These are genetic diversity, species diversity and landscape diversity.

Genetic diversity is an indicator of the degree of variation in the genetic make-up of individuals within a species. The basis of genetic differences is contained in the DNA in the chromosomes of an organism. The chromosomes are responsible for passing on the traits of the parents to the offspring during reproduction. Often, but not always, genetic differences can be seen in the features of the individual animal or plant. One of the best examples is the domestic dog. The great variety of breeds are all part of the same species, all derived from the wild wolf. Thousands of years of breeding by selecting particular traits has resulted in this amazing display of genetic diversity. In humans, we recognize the expression of genetic diversity as differences such as those among races, facial features, and the colour of eyes and hair. Underlying many of these differences are specific differences in the genetic material in the DNA of each person. Genetic diversity is higher in multi-racial communities than in communities of a single race.

Genetic diversity in humans, as in all species, is either reduced, maintained, or increased depending on patterns of breeding over time. Inbreeding among members of the same family tree causes a reduction in genetic diversity. Outbreeding with new families and races causes an increase in genetic diversity.

Genetic diversity is not something you can measure by walking into a forest with a ruler and clipboard in hand. While the concept is based on theoretically measurable differences in DNA, in practice it is impossible to determine the full range of these differences for every species in a particular ecosystem. It is usually necessary to deal in generalities and comparative measures rather than actual measures of specific genetic differences. The factors affecting genetic diversity within a given species are themselves very diverse, ranging from the manner in which plant seeds are fertilized and dispersed to the social behaviour of birds and mammals.

Species diversity is the type of biological diversity that most people would associate with the term. It is simply a count of the number of distinct species in a given ecosystem. This is fairly easy for the larger species of plants and animals but becomes a more difficult and expensive task if we want to count all the smaller and microscopic forms of insects, fungi, and bacteria that live in the trees and the soil. While the species count can give us a lot of useful information it doesn’t tell us about the relative abundance of each species. That requires a count of the population of each species, an even more difficult task than cataloguing the number of species. Even if we knew all the species and their populations, meaningful comparisons within and among different ecosystems are not always easy to make.

Landscape diversity, also known as ecosystem diversity, refers to the variety of distinct ecosystems within a given landscape or geographic area. Some landscapes are very uniform such as the vast stretches of lodgepole pine forest growing back after wildfire. Other landscapes are more varied with a mosaic of different plant associations in close proximity. A more diverse landscape usually supports a higher species diversity across that landscape. Landscape diversity is generally measured in comparative terms rather than numerically. There is no logical way to give an exact measure of the number of distinct ecosystems in a given landscape, or for that matter even to define “landscape” or “ecosystem” with precision.