USC Citizens for Land Stewardship
Conservation and stewardship of land and natural resources in Upper St. Clair

Biodiversity: What, How and Where?

Biodiversity is a word that gets bandied about as readily as the phrase “global economy” and perhaps for the same reason: they are both big enough concepts to embrace almost anything you may choose to talk about. The global economy may be the foundation for our way of life, but biodiversity is the foundation for our lives.

A condensation of “biological” and “diversity”, biodiversity is a relatively new word in our collective vocabulary. Often defined as the sum total and diversity of all living things and the processes that maintain them, biodiversity does not lend itself to easy or comprehensive measurement.

First of all, species diversity is generally recognized a basic unit of biodiversity, although there are many levels of diversity: genetic, community, ecosystem, and landscape. Understanding just species diversity is a challenge, especially in the tropics where a large percentage of species (particularly insects) remain unknown or uncharacterized. Often, studies to measure diversity will consider a group of species like birds or flowering plants as representative of a place’s diversity. However, big, numerous groups like insects, fungi, and bacteria are seldom fully considered because of their sheer numbers and complexities.

Remember several important points about characterizing diversity. First, a large number of species does not necessarily make a place more diverse – it makes it more species rich. There are other measurements that consider how closely related species or groups of species are within an area. There are others that look at distribution of species over the landscape. Together, these measurements show different facets of diversity. Even taken together, numerous measurements do not tell the whole story – they only serve as indicators.

Secondly, diversity (and ultimately, biodiversity) is geographically dependent. Some places, like an Amazon rainforest, have many species representing a large number of groups and hence show high values for almost all measures of diversity. Conversely, some deserts score relatively low on most counts because the number of species is low and many are closely related (e.g. many species in the Cactus family but few other families). That does not make a desert less biological important – it makes it less diverse. For example, it may be that several species of lizard living in the desert are found nowhere else in the world. Therefore, this particular desert may have low diversity but high biological importance because of its uniqueness.

So the take home message about diversity measurements is that you must understand the natural limits of diversity of a certain geographic area and chose a measurement that will allow a comparison to other places and over time. The National Audubon Christmas Bird Count circle that CLS has worked to establish in this part of the Chartiers Creek Watershed is one way of tracking a group of organisms (birds) over time and in a way that areas across the country can be compared.

To overcome some of the difficulties inherent in counting individual species, another approach is to look at habitat diversity. Habitat, from the French habitaire – to dwell, is simply the place where a plant or animal is normally found. Water lily, for example, grows on the surface of still water. Ponds or channels are therefore habitat for the water lily. Because many species of plants and animals may share the same habitats or habitat types, counting habitat types within an area can substitute for counting species. The same ideas and measurements apply to habitats, however, because species are not actually counted, the results are less direct and more assumptive. The ecological analysis that WRT (Wallace, Roberts and Todd) applied to Boyce Mayview relied heavily on habitat characterization and mapping. They applied certain size criteria and looked at the balance between interior (deep, contiguous forest) and edge habitat. To actually know if these habitats support the full potential of regional diversity, further inventory will have to be done. Still, the approach is quite valid and a good way of characterizing diversity within a limited time frame.

We can all help to maintain and, in some cases, restore the natural diversity of an area through our individual and collective choices. We can work to minimizing the area that we develop, restore forest cover, provide habitat corridors along our streams, control exotic species, encourage the planting of native species, improve water quality in our streams and rivers, reduce the (casual) use of pesticides and herbicides, and utilize a whole host of other approaches. Biodiversity is a big concept to wrap our arms around but the collective arms of CLS are making a difference right here in this small sliver of the world.