Chris Maser

To really understand how Nature protects soil, we must consider it from the "eye" of a bacterium to the infinity of space. The dimension of scale is important, because it adds greatly to our perception of diversity in the landscape that supports our agricultural fields and tree farms, as well as our perception of the way one part of the landscape relates to another. And both perceptions are necessary for us to make the wisest possible decisions concerning the best use of such things as our backyard gardens, agricultural fields, and national forests.

Scale is a progressive classification in size, amount, importance, rank, or even a relative level or degree. When dealing with diversity, however, we often overlook space or distance as a dimension of diversity.

Space and distance as a scale of diversity is right in our own backyard—and always has been. If, for example, you study a pinch of soil through a high-powered microscope, you will see things that you never imagined to be living in your backyard, but you cannot see the roses or even your house as long as you focus your attention into the microscope. Oribatid mite

Oribatid mite

If you use a ten-power hand lens to look at the same pinch of soil, you cannot see what you saw through the microscope, but you can see more of the way the particles of soil and some of the larger soil organisms, such as oribatid mites, relate one to another. Yet, as long as you are looking through the hand lens, you still cannot see the roses or your house.

On the other hand, if you put the pinch of soil back where you got it, stand up straight, and look down, you have still a different scale of diversity. Now you see a wider patch of soil, but without the detail. If you climb onto the roof of your house and look down on the patch of soil, you now see even less detail of the soil, but you see the roses growing out of it, and you see your house. Imagine, therefore, what you would see if you hovered in a helicopter 100 feet (30 meters), 1,000 feet (304 meters), or 10,000 feet (3,048 meters) above the patch of soil in your backyard. What would you see from a satellite in outer space?


Termite tunnels made of fine grains of soil going up trees in the jungle of Malaysia.

Let's look for a moment at the scale of distance and space in still another way. What would you see in your backyard if you were a microorganism peeking out of the soil from under a grain of sand? What would you see in your backyard if you were an ant, a mouse, a cat, or a dog? Then again, what would you see if you were a sparrow, first feeding on the ground, then flying into a tree, and then flying to the other end of the neighborhood?

Scale, as we perceive it, is an aspect of diversity in size, shape, distance, and space. Diversity includes every conceivable scale, such as time, viewed from every conceivable place in distance and space simultaneously, from the viewpoint of a soil bacterium, to the viewpoint of an ant, to the viewpoint of a sparrow, and beyond.

From a human perspective, for example, it's relatively common knowledge that trees, shrubs, herbaceous plants, and grasses hold soil in place; thereby slowing or even preventing gravitational soil erosion. After all, that is the major purpose of a lawn in suburbia. Less well know, however, are the biological soil crusts commonly found in semiarid and arid environments throughout the world, such as deserts. In fact, crust communities occur on all continents and in most habitats.

Biological soil crusts are composed mainly of cyanobacteria (formerly called blue-green algae), green and brown algae, mosses, and lichens, although liverworts, fungi, and bacteria are also important components in some soil crusts. These organisms form the crusts when their organic by-products, such as sticky polysaccharides, cement the particles of soil together, thereby aiding soil aggregation. (A polysaccharide is a complex carbohydrate, such as a starch, that is compose of linked molecules of sugar.) Which organisms dominate a particular soil crust is partly determined by microclimate, but may also represent different successional stages in crust development. Because these crusts occupy the soil surface, they aid soil stability (help prevent erosion by wind and water), take part in atmospheric nitrogen fixation, as well as soil-water-plant relations that include: (1) increasing the infiltration of water, (2) providing stable sites wherein seeds can germinate, (3) contributing nitrogen, phosphorus, potassium, iron, calcium, magnesium, and manganese to plants, thereby enhancing plant growth.

Although well adapted to severe growing conditions, these living crusts are ill adapted to grazing by domestic livestock, recreational activities (hiking, biking, and off-road driving), and military activities—all of which simultaneously fragment and compact the crust. Once biological soil crusts are broken, they are vulnerable to deterioration by wind erosion, the subsequent demise of species, and thus the simplification of the community.1


  1. The discussion of biological soil crusts is based on: (1) J. Belnap and D. A. Gillette. Disturbance of Biological Soil Crusts: Impacts on Potential Wind Erodibility of Sandy Desert Soils in Southeastern Utah. Land Degradation & Development, 8 (1997):355-362; (2) Jayne Belnap and Dale A. Gillette. Vulnerability of Desert Biological Soil Crusts to Wind Erosion: The Influences Of Crust Development, Soil Texture, and Disturbance. Journal of Arid Environments, 39 (1998):133-142; (3) B. Wilske, J. Burgheimer, A. Karnieli, and others. The CO2 Exchange of Biological Soil Crusts in a Semiarid Grass-Shrubland At the Northern Transition Zone of the Negev Desert, Israel. Biogeosciences, 5 (2008):1411-1423; and (4) An Introduction to Biological Soil Crusts. USGS Canyonlands Research Station_Southwest Biological Science Center. (accessed on April 8, 2009).

Volcanic ash soils in the Painted Hills National Monument near the town of Mitchell in northcentral Oregon.

Illustration by Paula Reid, USDA Forest Service.

©Chris Maser 2009. All rights reserved.

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