Scientists want other scientists and the public to trust the methods, results, and conclusions of their research. They want to show that methods are reliable. Research is considered reliable when the same methods produce the same, or similar, results again and again. How is this process the same as the process you use to show that you are a reliable person?

One way scientists show that their research is reliable is by repeating the methods multiple times and comparing the results. For example, many States test the water quality of rivers. Small amounts of water, called samples, are collected from each river. The water quality samples are then sent to a laboratory to be tested for pollution. The scientists can conclude that the results are reliable if each of the samples from a river has the same, or similar, results. If the results are different, the scientists may question whether the results are reliable and may need to repeat the results.

The research in this article features scientists who repeated the same scientific methods at multiple locations. Repeating the scientific methods at each location helped the scientists show that their results were reliable.

Quaking aspen forests are important across much of North America (figures 1 and 2). In the Western United States, quaking aspen forests are especially important because they are home to many animals and other plants.

Quaking aspen reproduce in two ways, by seed and by “suckering” (figure 3). Suckering is when adult quaking aspen trees send out shoots. The shoots, called “suckers,” become quaking aspen trees.

In the Western United States, quaking aspen reproduce mostly by suckering. To start the process of suckering, quaking aspen need disturbance. Disturbance is a short-term change in the environment that leads to a larger ecosystem change. In particular, quaking aspen often rely on wildland fire disturbance.

As you just read, one way quaking aspen grow and reproduce is by suckering. Without disturbance, like wildland fire, quaking aspen produce fewer suckers. Some scientists believe that a decline in the number of quaking aspen trees in the Western United States is related to less wildland fire disturbance.

Some scientists believe, however, that the decrease in wildland fire disturbance is not the only cause for the loss of quaking aspen. These scientists are also interested in how ungulates (un gyǝ lǝts) affect quaking aspen (figure 4). Ungulates are animals with hooves, which are hard coverings on the animals’ feet.

Many ungulates in the Western United States browse quaking aspen (figure 5). Quaking aspen can survive some browsing. However, the suckers cannot survive repeated browsing by ungulates. Combined, browsing and less wildland fire disturbance may be especially harmful to quaking aspen.

The scientists in this study observed that some quaking aspen forests that experienced wildland fire disturbance were still not successfully growing. They predicted that this was caused by ungulates browsing on suckers. The scientists knew that barriers, such as fences, could keep ungulates from browsing on suckers.

The scientists in this study asked three questions:

1. Which barriers are the most effective in protecting quaking aspen suckers from ungulate browsing?
2. What is the cost to construct each barrier type?
3. Which barrier type would be most affordable and effective to use?

The scientists identified three study sites in Western South Dakota. Of the three study sites, two were in Black Hills National Forest and one was in Custer State Park (figure 6). All locations had similar characteristics, including quaking aspen forests.

Within each of the 3 study sites, the scientists identified 10 smaller locations to be used as plots (figure 7). Plots are small pieces of land that are used for a distinct purpose. In this research, plots were used as either experimental plots or control plots.

Experimental plots were used to test four types of barriers. The four barriers chosen to be tested included: wildlife exclosures (figure 8A), livestock fences (figure 8B), slash treatments (figure 8C), and hinging treatments (figure 8D).

The scientists also used two control plots at each study site. The control plots remained unchanged with no barriers. These plots enabled the scientists to compare the effects of each barrier with the effects when humans did not construct barriers.

The scientists began collecting data in May 2004. Data collection was repeated in August 2004 and May 2005. The scientists collected the same data at each of the 30 plots.

At each plot, the scientists used a transect tape and a plot frame to collect data (figure 9). The transect tape was placed randomly within each plot for data collection. The scientists then walked down the 60-meter transect tape and placed the plot frame on the ground every 3 meters.

The scientists completed a few tasks each time they put the plot frame on the ground along the transect tape. First, the scientists counted the number of quaking aspen suckers within the plot frame (figure 10). These numbers were used to estimate the number of suckers in the entire plot.

Second, they noted evidence of ungulate browsing on suckers (figure 11). Third, the scientists measured the height of browsed and unbrowsed suckers. An average height for both browsed and unbrowsed suckers was calculated within each plot.

The scientists were also interested in determining which barriers were both effective and affordable. To determine the cost of each barrier, the scientists asked the staff at Black Hills National Forest and Custer State Park to provide the cost per acre to build each barrier.

The data showed that the two Black Hills National Forest study sites had an overall decrease in the number of suckers during the study. The Custer State Park study site had an overall increase in the number of suckers during the study.

When data were first collected in May 2004, 78 percent of suckers in all plots showed signs of ungulate browsing. In over one year of data collection, the control plots had an increase in percent of suckers with signs of ungulate browsing. Experimental plots, however, showed no change or a decrease in signs of ungulate browsing (figure 12).

The average difference in height between browsed and unbrowsed suckers also showed that ungulates had less impact on quaking aspen inside the barriers. The difference between browsed and unbrowsed suckers was 20.8 centimeters (cm) in May 2004. By May 2005, the difference between browsed and unbrowsed suckers was 14.4 cm.

The staff at Black Hills National Forest and Custer State Park also provided the scientists with estimates of the costs of the barriers (table 1).

In the Western United States, ungulates can hinder the growth of quaking aspen suckers. This damage is common after disturbance when adult quaking aspen trees send out many suckers. Barriers, such as fencing, can help manage ungulate access to quaking aspen forests. The scientists found that the four barriers tested in this research are better for protecting quaking aspen suckers than using no barrier.

The scientists’ goal was to identify barriers that were both effective and affordable. The scientists believe that this research helps public land managers and private landowners determine how to best protect quaking aspen forests.

Wildlife exclosures were the most effective against ungulates but also the most expensive to build. The scientists noted that wildlife exclosures may be the best solution in areas with very high numbers of ungulates. For most quaking aspen forests, however, the scientists concluded that hinge and slash barriers are good alternatives. Hinge and slash barriers are good alternatives because they are both effective and affordable.