Sometimes scientists test something in particular. Scientists use experiments that include experimental treatments. Experimental treatments are conditions that are created and organized by scientists. Scientists want to understand the results related to these conditions. Scientists may set up one or more experimental treatments. To better understand the results of experimental treatments, results are compared to other experimental treatments. The results are also compared to conditions with no experimental treatments, called a control.

In this research, for example, the scientists were interested in how much downed wood termites and other insects were consuming on the forest floor. Downed wood is the fallen wood, such as tree trunks and branches, on a forest floor.

The scientists had to do a comparison to determine how much downed wood termites consume. They compared wood that was available to termites and other insects with wood that was not available to, or protected from, termites and other insects. The wood that was available to the insects was the experimental treatment, and the wood that was not available was the control. The scientists used this control to compare the results of the experimental treatment in which wood was available to the termites and other insects.

Decomposition is the act or process of breaking up, usually by decaying or rotting. During decomposition, the resulting simpler form of matter becomes available for other organisms to use. The simpler form of matter is usually in the form of nutrients. Organisms need nutrients, which are substances that keep them alive.

Shortly after a living organism dies, it begins to decompose. Decomposition is an important part of every ecosystem. Decomposition is aided by other living organisms. Many of these organisms are not visible to the naked eye, such as bacteria. Some of these organisms, however, are visible without a microscope.

The scientists in this study were interested in learning about the role of termites in a forest ecosystem. When tree trunks and branches fall to the ground, they decompose and provide nutrients for other organisms (figure 1). Termites, beetles, and microbes break down the dead wood into simpler forms.

Scientists know a lot about how termites cause wood in homes and buildings to decompose and weaken. Scientists know little, however, about the role termites play in Southeastern United States forests. The scientists in this study wanted to learn more about the role termites play as forest decomposers.

Wood-eating insects, which function as decomposers, are found wherever trees grow. In Earth’s warm temperate and tropical regions, termites are the most plentiful wood-eating insect (figure 2). Beetles also contribute to wood decomposition. Microbes, including bacteria and fungi, play a role in wood decomposition, too. This process is an important part of the carbon cycle (figure 3).

In the Southeastern United States, subterranean termites are known to damage homes and other buildings (figures 4 and 5). Although this type of decomposition is unwanted by humans in their homes, wood decomposition is essential to the health of a forest ecosystem. Scientists know little about the role termites and other insects play in keeping forests healthy. The scientists in this study, therefore, wanted to learn how much termites contribute to forest decomposition, compared with beetles and other insects.

Subterranean termites, in existence for 55 million years, are social insects that live underground. Social insects live in family groups that are called colonies. In a colony, labor is divided by caste (figure 6). Termite castes are defined by the job done by each termite.

Workers are responsible for all of the labor in the colony. Workers care for young termites, build and repair the nest, locate food, and feed and groom the other termites. Workers are found in infested wood, as well as in the nest.

Soldiers defend the colony against ants and termites form other colonies. These termites have large jaws that they use to kill the colony’s enemies.

The primary reproductives include the colony’s king and queen. A queen can produce over 500 eggs every year. A king and queen have the longest life spans of any termites in the colony. They can live for 10 years or longer.

In the spring, winged termites emerge in large numbers from termite nests. These termites are secondary reproductives and are called swarmers. The swarmers leave the colony in search of a place to begin a new colony. The swarmers pair up and find a place in soft soil. Their wings break off, and they dig a small chamber in the soil. The swarmers crawl inside, seal up the chamber, and mate. These two termites become the new colony’s king and queen. From this point on, they will live underground. As the colony grows, different castes will be produced. Scientists estimate that mature colonies contain more than 60,000 workers.

Look again at figure 2. Which termite castes do you see in this photo?

The scientists studied trees and termites in the Sam D. Hamilton Noxubee National Wildlife Refuge in Mississippi (figure 7).

The scientists selected 34 loblolly pine trees. The trees were cut down, and the tree trunks were cut into sections and disks (figure 8). Each tree section was 1-meter long (figure 9). All trees were chosen from the same 1-hectare area (figure 10).

A total of 187 1-meter tree sections were cut. The tree sections were taken to another forest site in the Sam D. Hamilton Noxubee National Wildlife Refuge. The forest site was divided into equal-sized areas. The center of each area was separated from the center of the next area in all directions by 10 meters (figure 11).

Forty-seven of these areas were identified as places where the tree sections would be fully protected from termites and other insects, such as beetles. In these 47 areas, an area of soil 1 by 2 meters was treated with a pesticide that would kill or repel termites (figure 12).

A pesticide is a chemical that is used to kill animals or insects that damage plants or crops. Each of these 47 tree sections was also covered with mesh that kept out other insects (figure 13).

The combination of applying pesticide and covering the logs with mesh was expected to keep all insects from reaching the protected wood sections. The scientists compared the protected wood sections with the experimental treatments. See “Thinking About Science” for more information about why scientists do these comparisons.

The remaining 140 tree sections were placed directly on the forest floor in one of the remaining identified sections. These tree sections were not covered with mesh, and the soil was not treated with pesticide. Therefore, these wood sections were exposed to termites and other insects such as beetles.

After 1 month, 79 percent of the 140 unprotected tree sections had been infested with termites. The remaining 21 percent had experienced no termite infestation. The scientists decided to move these non-infested tree sections to areas where the soil was treated with pesticide. The pesticide kept any termites from entering the wood. The scientists did not cover these tree sections with mesh. Without a mesh covering, beetles and other insects could enter the wood from all directions except from the ground.

Moving these non-infested tree sections to uncovered pesticide-treated areas enabled the scientists to start another comparison. The scientists were now able to compare the amount of termite wood consumption with the amount of consumption by other insect decomposers.

The scientists did not study 41 of the original 187 wood sections because of unexpected problems. For example, small beetles were able to move through the mesh that covered these sections. So, the scientists removed these 41 sections from the study. The scientists collected data from select wood sections every 4 months until the study was completed. You will see that the scientists completely used up each wood section as they collected data from it. The scientists randomly selected each wood section for data collection.

To collect data, the scientists cut each 1-meter wood section into disks by using a band sawmill (see figure 8). Then they weighed the disks. This weight was called the wet weight, since the disks contained water. All living trees contain water, and the water evaporates slowly from a dead tree over time. To completely dry out the disks, the scientists placed them in an oven for 2 days at 102 ºC. After drying out the disks, the scientists weighed them again. This weight was called the dry weight.

After the disks were dried, the scientists took digital images of each disks’s top and bottom. The areas that had insect damage were colored white (figure 14) using Photoshop® 7.0 (Adobe® Systems, San Jose, CA). Another software program was used to measure the amount of wood left and calculate the amount of damaged wood. The scientists also took digital images of damage caused by beetles in the partially protected wood sections (figure 15).

Termites carry soil into the galleries they create when they consume wood. The scientists did not want to include the soil weight with the dry weight of the disks. Therefore, the scientists cleaned the soil out of the disks with small dental tools (figure 16) and an air compressor. After 32 months, the soil became harder to remove because so much of the wood was decomposing.

To address the challenge of measuring decomposing wood, the scientists completely burned each remaining disk using a propane gas burner (figure 17). After burning each disk, the scientists divided the soil from the wood ash and weighed the soil. Then, they subtracted the soil weight from the total dry weight of the disk. This process gave the scientists the dry weight of the disks that had been filled with soil from termite activity. The dry weight did not include the soil.

After taking these measurements, the scientists knew the wet weight, the dry weight, and the percent of termite and insect damage in each of the disks cut from the wood sections. Only the measurements taken within the first 44 months were used.  After 44 months, the unprotected wood was too decomposed to be accurately measured.

A greater amount of wood was consumed in the unprotected wood sections than in the partially protected wood sections. After 2 years, beetles and other insects had consumed about 1.9 percent of the partially protected wood. The unprotected sections, which termites were able to reach, lost an average of 11.4 percent of their wood (figure 18).

Look at figure 18. Over time, termites consumed more wood than beetles or other insects. The amount of mass lost in the wood sections over time, however, was about equal for all three conditions (figure 19).

Although termites consumed more wood than beetles or other insects, the amount of mass lost was about equal for all three conditions. The scientists thought of a possible explanation for this finding. Termites tend to consume wood with less mass that is soft, light, and easy to consume. Termite consumption is easier to see than beetle or other insect consumption. However, termites may not be consuming more wood mass than these other organisms.

Scientists know that some pesticides contain carbon and nitrogen. Carbon and nitrogen can provide food for microbes, such as fungi and bacteria. Microbes are also a source of decomposition in downed wood. The pesticide application in the fully protected and partially protected conditions, therefore, may have increased microbial activity. If microbial activity was increased by the pesticide, the scientists’ efforts to determine how insects affect wood mass loss may have been less accurate.

Although much is known about the damage termites cause in homes and other wooden buildings, scientists know little about termites living in forests. This study was one of the first experiments measuring the contribution of termites to downed wood decomposition in the Southeastern United States.