Scale Viewer

A. Introduction

One of the most useful beginning steps in looking at a problem in Environmental Science is to determine the scale of the objects and processes. This simultaneously gets you to focus on the main processes that are acting on some physical objects and the space and time scale of those problems. From this starting point, there are several levels of inquiry. The most basic is to simply characterize and describe the scales of these objects and processes. The second level is to design studies that have observations that span several scales. The third level is to study and model that proceses across scales. Each of these levels is more sophisticated and requires more effort than the previous level. It may not be required, or even desirable, to study every problem to the most demanding level.

The three levels are described below with examples of how they can be applied to environmental problems. One important aspect of the scale viewer is that this approach sets up the use of other viewers, in particular the systems viewer needs to know the major processes, objects and boundaries of the system being investigated. So, even though the viewers are supposed to provide different information on the problem, that doesn't mean that each viewer is independent of the others.

B. Level 1: Identifying scales of physical objects and processes

1. Describe the objects and projects. This level is numerically descriptive. The goal is to identify the range and a characterisitic value for the time and space scales of each object and process that is involved in the problem. For example, if part of the study deals with the interaction between birds, trees, and insect damage, then the characteristic space scales for birds would be size/weight and foraging range. Similarly the trees size and distance to neighboring trees might be important. In both cases the range of size of birds, trees and insects could also be of interest if it is very broad. The processes of interest would probably be the growth rate (doubling time for all organisms), the insect spreading rate (distance that the infestation moves per day), and other weather processes or disturbances that might affect the health of the trees, birds or insects. These ranges should all be listed in consistent time and space units (such as days and meters). Some made-up values for this example are given in Table scale-1 and these are visualized in the accompanying figure "scale-1.png". Because there is a wide range of values it is best to visualize this on a log-log plot (log of time vs. log of distance).

Table scale 1 process time or space scale insect size - 0.5 to 4 cm bird size - 10 to 30 cm tree size - 5 to 30 m insect doubling time - 10 days bird doubling time - 40 to 80 days tree doubling time - 5 years (1500 days) drought frequency- 1 every 10 years (3650 days)

Figure "scale-1.png". The green is trees, red is the birds, and blue is the insects.

 

refer to Hollings budworm studies.

2. Examine the texture of your surroundings. Another way to interpret the effect of scale is to examine the "texture" of your environment. As you look around, what are the relative sizes of objects and how many are there. An easy example if you are sitting on river bank, looking into a pool that is about 1 x 1 meter. You may see a range of rock sizes from little pebbles to larger cobble. The texture of that system would be determined by the relative distribution of different rock sizes. An example from a slow flowing stream is given in Table "scale-2" with a frequency distribution diagram given in the accompanying figure ("scale-2.png").

If you are doing a study in the middle of a pasture or meadow, there maybe very little texture that is obvious from your vantage point but if you do transects across the meadow you may see patterns of grasses that relates to the underlying soil types and moisture. Several 10 meter transects in different directions may help illuminate this structure. A cartoon of an aerial photograph of a meadow with the transects is shown in Figure "scale-3.png" and the % of different grass types found is given in table "scale -3".

The texture of these environments is very important for the organisms that exist at these scales.

3. Look for homogenizing processes. One of the crucial impacts that humans have on their environment is that we tend to homogenize small scale diversity and sometimes even large scale diversity. Some of the most obvious anthropogenic effects are leveling of the ground, habitat destruction and construction of roads. The worry with "habitat fragmentation" is not that humans are breaking up homogeneous habitats, but rather that fragmentation allows the incursion of other forces into the middle of otherwise highly diverse environments. Habitat simplification and the construction of human cooridors that are actually barriers for natural processes is evident at all scales in the human/nature interface.

4. Identify edge effects, dissipation zones and human energy intensity. These three concepts are related as they help describe the borders between human and natural areas and the coexistance of humans in a partially natural world. If we consider a fairly cleanly delineated human/nature border such as a road along a park. The edge effect is the distance from the road into the natural area for which the effect is felt. This effect depends on the target species or community, it may be only meters for grass because cars don't disturb grass, but it may be tens or hundreds of meters for small mammals or amphibians because any little turtle trying to cross that road may suffer a disasterous fate. If the road is between upland and pond habitats for amphibians, the edge effect might include the entire habitat for that animal.

A dissipation zone is the region for which the stress is greater than the natural growth capacity of the community. The dissipation zone deals with the direct release of energy from the human structure. One example of a dissipation zone is along a roadside. In this case, it is similar to the idea of an edge effect. Other more useful examples are the heat that is produced by a power plant warms the receiving water in a river or bay. The dissipation zone is the region that has stress from the heat.

Figure "scale 4 - dissipation zone"

One of the consequences of human industry is to concentrate processes for efficiency. This concentration leads to high energy intensities at particular locations, high power production or use. These power zones range from cars (kWatts/m^2), to American homes that might have an average power consumption of 200 kWatts and are 200 m^2, which leads to a 1 kW m^-2 power density to nuclear plants for which the reactor generates 20 mega Watts and yet it is only 100 m^2 in size. Nuclear power plants have about the same power density as the inside of a volcano.

typical American home

200 horsepower car

nuclear power plant

These levels should be compared to the range of solar energy