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Active Learning and Research
Active Learning and Research
Geographer Bill Turner and economist Jackie Geoghegan teamed up to examine the impact of changing land use in Mexico's Southern Yucatán. Melissa Floyd '01, working with Turner and several graduate students, developed a method to classify protected land based on levels of biodiversity.

Seeing the forest for the trees

Research conducted by Professors Bill Turner and Jackie Geoghegan
What can happen to a tropical rainforest when the logging industry moves in? Or to protected land when a nearby highway is built? Deforestation. Professors Bill Turner (geography) and Jackie Geoghegan (economics), along with several graduate and undergraduate students, have been studying changes in land cover and land use, especially in relation to deforestation.

Turner, Geoghegan and graduate students are focusing on Mexico's Southern Yucatán in a project conducted in cooperation with scientists at Harvard University and El Colegio de la Frontera Sur (ECOSUR), Mexico. Undergraduate Melissa Floyd '01 examined protected land in central Massachusetts.

What is land use and land cover?

Land use and land cover are variables used to create a model of a landscape. Land cover describes what currently exists at a place on the earth's surface. For example, land cover classes in Mexico's Southern Yucatán peninsula can include wetland forest, upland forest, secondary growth, cropland, pasture, bracken fern (an invasive species) and inundated/semi-inundated savannas. Land use refers to the way in which society uses a particular area of land, whether for agriculture, recreation, commercial activity or industry, to name a few examples. Land cover and land use are interrelated and are often studied together. The same type of land cover can have different land uses. An area of forest might be used for logging, for recreation, or for conservation. Researchers are particularly interested in being able to predict how land cover and land use might change over time.

Mexico's Southern Yucatán

The Southern Yucatán peninsula in Mexico was once the heartland of the ancient and mysterious Mayan civilization, and descendents of the Maya still live there. Nowadays, in addition to Mayan ruins, the Southern Yucatán is home to a large expanse of humid tropical forest that has been increasingly vulnerable to logging and agriculture since the construction of a highway in 1967. Concerns about deforestation led to part of the region being converted to a protected area. Global deforestation is currently of great concern to scientists around the world because it is thought to affect the earth's climate.

Research questions

Turner and his colleagues are exploring the following questions in regard to a 10,000 square kilometer region in the Southern Yucatán :
  • How much deforestation has occurred since the 1960s, and how fast has it occurred
  • What types of land use and land cover are taking the place of the forest
  • How plant and animal communities are being affected
  • Who are the people making decisions about where deforestation occurs and how do they make those decisions
  • How an understanding of change in the Southern Yucatán region can be used to predict land use and land cover change in other places

Sources of information

The researchers are using several different sources of information to study these questions. Some sources provide information about the natural environment, while others provide information about the people that change the environment.

One of the most important information sources consists of remotely sensed images taken at different time periods. Remote sensing technology has made the study of land use and land cover much easier because it can provide pictures of large areas of the earth's surface all at once. However, interpreting the remotely sensed imagery is a complex process and an important problem for study in itself. Different methods of interpretation can result in slightly different maps of land use and land cover. Geographers still need to travel to different parts of the study area to confirm that they are interpreting the images correctly-- a process called field checking

The images, along with their geographical locations, can be stored in a computer. Remotely sensed images are divided into pixels (squares) of the same size, each of which represents an area on the earth's surface. Each individual pixel can be linked to a database describing its characteristics such land use, land cover, soil type, and elevation. Turner and his colleagues are fortunate in having two types of Landsat imagery available for study covering the whole time period of interest, from the 1960's to the present.

Geographers need to go "into the field" for another reason. In order to understand fully why a place is characterized by a particular land cover/land use, they must talk directly with the people who manage the land. Decisions about how land is used are often made by an individual, such as a farmer. But decisions affecting land use are also made at many different levels of government—local, regional and national. At each level, geographers must understand how and why these decisions are made. They must also study census records and other archival material to understand the characteristics of the people who live there.

Predicting change

Turner and his colleagues are trying out three different statistical methods in order to predict the probability that land use will change or remain the same in the future. Each of these methods is based on the assumption that a given parcel of land can only support one type of land use at a given time.

Markov chain analysis. This method assumes that a parcel's current land use is the best predictor of how it will be used in the future. For example, assume that there are two possible types of land use, forest or agriculture. Four types of transitions over time would be possible, and, based on an examination of such transitions in the past, each would be assigned a probability score that:

  • an agricultural parcel remains agricultural
  • a forest parcel remains forest
  • an agricultural parcel changes to forest
  • a forest parcel changes to agricultural

Discrete choice probabilistic method. In this technique, each parcel of land is given a "utility" ranking, based on how suitable it would be for each possible kind of land use. Suitability can involve many factors, including distance to the nearest road or market, soil type, elevation, etc. A given parcel of land might be highly suitable for cultivation of chiles, but very unsuitable for logging, thus receiving a high utility rank for chile farming, but a low one for logging. Researchers can then look at an unknown parcel and its utility rankings and make an educated guess about which land use is most likely occuring there.

Hazard or duration model. This technique blends aspects of the Markov chain and discrete choice approaches. Like the Markov model, it assumes that current use is a good predictor of future use. It extends the Markov model by looking a how long the current land use has been active. Also considered in the equation are independent factors that influence a parcel's suitability for a particular use.

Graduate student research in the Southern Yucatan

Rinku Chowdhury: How have different organizations involved in forest conservation affected the way forests have evolved over the past 15 years?

Eric Keys: How are forests likely to be impacted by the widespread adoption of intensive chile production by small farmers?

Steve Manson: How will biodiversity and the release of carbon dioxide into the atmosphere be affected by different trends in deforestation?

Undergraduate research in central Massachusetts

Melissa Floyd: Are protected lands providing an environment favorable to biodiversity and wildlife habitats?


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Black rectangle indicates area of Professor Turner's research
Figure 1: Black rectangle indicates area of Professor Turner's research.

Grad students Laura Schneider and Rinku Chowdhury standing among Mayan ruins
Figure 2: Grad students Laura Schneider and Rinku Chowdhury standing among Mayan ruins.

The Maya still farm in their ancestral area, growing corn (maize), beans and squash
Figure 3: The Maya still farm in their ancestral area, growing corn (maize), beans and squash.

A Mayan house
Figure 4: A Mayan house.

Forest area
Figure 5: Forest area.

Preparing land for Intensive chile production leads to deforestation
Figure 6: Preparing land for Intensive chile production leads to deforestation.

1987 land cover map created from satellite imagery
Figure 7: 1987 land cover map created from satellite imagery. Enlarge.

1997 land cover map created from satellite imagery
Figure 8: 1997 land cover map created from satellite imagery. Enlarge.

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