Think Like the Scientist: Ariel Lugo
Meet the Scientist | About the Study

Below is a Natural Inquirer article that details one of Dr. Lugo's studies of change over time in Guanica Forest in Puerto Rico. Use the links to see an example of developing a testable question (introduction), planning to test your question (method), analyzing your data (results), and explaining it all (discussion).

View the full version of Some Things Will Always Change.

Introduction | Method | Results | Discussion

Some Things Will Always Change

Guanica Forest on a map

Figure 1: Location of Guanica Forest in Puerto Rico.


Guanica (gwa ne kä) Forest is a tropical dry forest in the southwest corner of Puerto Rico (Figure 1). In 1981, the United Nations recognized it for being one of the best examples of a dry tropical forest.

Before 1919, Guanica Forest was used for agriculture and other human activities. In 1919, Guanica Forest became legally protected from most human development. Since 1919, more acres have been added to Guanica Forest. Land that had been used in the past for human activities is now inside the forest boundaries.
It is mostly protected from development inside the boundaries.

The land in and around Guanica Forest has been changing. The scientists in this study wanted to know how Guanica Forest and the land around it has changed over the years.

For example, they wanted to know whether the trees have been growing back where crops used to be. They were interested in the land use history of Guanica Forest and the surrounding land. You have probably learned about the history of your country, state, or commonwealth. Land use history is like your country’s, state’s, or commonwealth’s history, except that it is a history of how people used the land.


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Based on aerial photographs taken in 1936, 1950, 1963, 1983, and 1989, the scientists determined how the land was being used over the years. They looked at the photographs of land within the Guanica Forest and outside of the forest boundaries. They saw that land had been used for buildings, roads, and agriculture. They also saw the natural areas of the forest, including trees, wetlands, and barren land. The scientists calculated the percentage of the forest that was in each category. The categories included:

  • Urban land (with buildings, parking lots, roads, and other structures)
  • Agricultural land
  • Water
  • Forests
  • Wetlands
  • Barren land

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Relative change in land use in Guanica Forest

Figure 2: Relative amount of change in land use over time within and outside of Guanica Forest.

Actual change in land use in Guanica Forest
Figure 3: Actual change in number of hectares by land use type within and outside of Guanica Forest. A hectare is a metric measure equal to 2.47 acres.

arial photos of land use over time

Figure 4: Aerial photographs showing land use changes over time in an area outside of Guanica Forest.

Proposed protected area around Guanica Forest
Figure 5: Example of the proposed protected area around Guanica forest.


The scientists found that land use had changed over the years. Although the portion of urban land within the forest increased much more than outside of the forest, there were many more hectares of urban land outside of the forest (See Figures 2 and 3). The amount of agricultural land within the forest decreased much more than outside of the forest.

Overall, urban land increased and agricultural land decreased, while the amount of forested land stayed about the same. Figure 4 shows some of the actual photographs used by the scientists.

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The scientists found that land use outside of Guanica Forest was changing quickly. Urban uses, such as buildings and roads, were replacing the native forest. When native forests are removed, animals that do not naturally live in the forest can move into the area.

These non-native animals might gradually move close to or over the boundary of Guanica Forest. Once they do that, they will compete with the native animals for food and habitat. An example in North America is the European starling, a bird that competes with native American songbirds.

The scientists suggest that some of the land surrounding the forest should remain mostly forested with limited buildings or other construction (Figure 5). That way, non-native animals will not be as likely to move into Guanica Forest, and the forest’s native animals will be protected.

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