FIELD ECOLOGY, BIO 303

INSTRUCTOR: DR. JIM TAULMAN

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SOIL CHARACTERISTICS

If you have the equipment available, it is also useful to go below the soil surface and get an idea about the composition and characteristics of the soil at your sample site.

The top layer is called the "O" horizon. This layer consists of fresh or decaying organic materials, such as leaves, dead plants and animal remains and droppings. Forest soils usually contain a thick "O" horizon as these forest areas produce large amounts of organic waste each year. Other areas, such as deserts, produce very little organic waste and therefore have very thin, or even no "O" layers.

The layer directly below the "O" horizon is called the topsoil or "A" horizon. This layer is usually a dark mixture of organic materials and rock particles. The dead organic materials are broken down slowly by soil animals and eaten by decomposers. It is in this layer that most animals live. Plant roots are plentiful in the "A" horizon although many roots grow much deeper into the soil in search of moisture.

The third layer is called the "B" horizon, or subsoil. This layer contains many of the nutrients which have been washed down by the rain from the "A" horizon. This layer also contains the remains of the humus. It is typically a different color from the dark brown of the A layer, containing iron oxides and other minerals from the surface.

The fourth layer, or "C" horizon, has no organic material. This layer consists of weathered stone from the parent material. This parent material is the rock from which the minerals in the soil are removed as well as the source of most of the rock particles found in the soil.

You can sample the soil near the surface with an inexpensive soil probe, such as is shown above. The samples below were taken from a pine/hardwood forest consisting of an overstory dominated by Ponderosa Pine and having a midstory and understory component of Burr Oak.

Decaying organic matter, A horizon

Litter, O, layer

The sample above shows a deep A horizon with lots of dark, decaying organic matter. The thin surface forest floor litter layer, the O layer, is at the left

Mineralized, B, horizon

Decaying organic matter, A horizon

The core above shows a well-developed B horizon with the change in color produced by the decrease in organic matter and by the presence of iron oxides and other lighter colored mineral constituents. The thinner core below also shows horizons O, A, and B.

Mineralized, B, horizon

Decaying organic matter, A horizon

Litter, O, layer

It is also useful to learn something about the acidity of your soil sample, to determine both its suitability for invertebrate organisms and to learn something about the quality of water filtering down to the ground through the vegetation canopy at this site. A pH meter, as shown below, will provide a measure of the acidity or alkalinity of near-surface soil in the A horizon, as well as an indication of soil moisture there.

VERTEBRATE SAMPLING

Techniques for vertebrate sampling and surveys are only touched on in this course, but are covered more fully in the course Wildlife Investigation Techniques, Biology 313. Here a student sets a Sherman small mammal live capture trap along a log in order to increase the chance of catching a mouse or vole as they scurry down such a protected pathway.

In our travels on field excursions, we often come across good examples of ecological principles first hand. In the photo below, taken in Wind Cave National Park, natural fires are not allowed to burn the grassland landscape. As a result, pine seedlings that would otherwise be killed by frequent lightening fires spring up and grow in profusion in open grassy areas near parent forests. In this way the Black Hills is becoming more forested, as grasslands are populated with new forest.

NAVIGATION

After training students to use their compass and hip chain to navigate in the field, and to transfer field distances and angles to an accurate scale map, I took them out for a navigation challenge at night in the forest. I first thoroughly reconnoitered a national forest area during the day time in order to select an area that was safe and convenient to walk through. Then I created a series of azimuths and distances, such as the list shown here. This exercise simulates tracking an animal through the woods, in a radiotelemetry study, for example. In making a list such as shown here, you would record on paper the distance walked in a given direction. When you had to change direction, you would record that angle and start measuring the new distance leg from there. Finally, you would want to quit and return to your vehicle, but you probably would have no idea just where it was, particularly if you were working at night. The scale map you create will allow you to find your way back with confidence.

100 meters at 75°

160 meters at 12°

90 meters at 270°

75 meters at 340°

115 meters at 310°

75 meters at 220°

95 meters at 200°

200 meters at 108°

You can easily chart these vectors on a sheet of notebook paper using a compass and a scale of 50 meters on the ground = 1 cm on the paper. When you are using your compass to make a paper vecgtor map, such as that below, you use the edge ruler to measure distance and set the compass dial to the azimuth that you want, after arbitrarily deciding which direction on your page will be North. In the photo here North has been selected to align with the lines on the paper.

Notice that in this process, you are not using the magnetic needle of the compass at all. That comes when you want to proceed across the ground in a direction that you have determined from your map. In this photo, when you mark your scale line along the edge of the compass you will be drawing a line along an azimuth of 310°.

The map made from the list of distances and angles above would look something like the one below and would be a scale map. Notice that the vectors provided did not bring the students back to the truck where they started. The final exercise was to compute the correct compass azimuth and distance to return to the vehicle. The students calculated a distance of about 125 meters and about 200° to take them from the last point on the list above back to the truck where they started. After they had set their compass dial to 200°, then they used that to guide them back to the truck by aligning the magnetic pointer with the north arrow on the dial and sighting over the mirror so that they could line up with a distant object and at the same time keep the compass needle lined up perfectly with the base dial. They used the hip chain to let them know when they should be coming to the truck, in case they couldn’t see it.

My students had a good time in this navigating adventure and made a very good map as they went, finally arriving back at the truck only about 10 meters off on distance and a couple of degrees off the correct heading. Such a small error over the course distance of 910 meters at night was excellent. This navigational skill will always allow them to travel in unfamiliar terrain without getting lost.

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Reflectors are extremely useful tools for marking trails and monumenting trees that you need to find quickly and easily in night work. It’s always nice to see a friendly face in the woods when you are not sure where you are, so I gave the students these welcoming beacons which they saw as they neared the truck on their final leg.

My Ph.D. research on the ecology of southern flying squirrels in fragmented forests required extensive night radiotelemetry, tracking squirrels during their nightly activity periods. Reflective materials are costly and I needed an inexpensive way to mark trees and trails at night. I ended up using roofing caps and rolls of reflective tape with I cut into squares and stuck on the caps. These are easily tacked to trees and then removed after use and stored until needed again.