Land Cover and Land Use

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Introduction

The beauty of the tropics draws tourists, and tourists demand food, shelter, and services. In order to provide these necessities, land must be developed for food production, resorts and vacation homes, and housing for workers. Such development often leads to environmental degradation through increased air and water pollution, solid waste, and disturbance and destruction of both flora and fauna (Andereck 1995). Consequently, nature-based tourism has the potential to become trapped in a self-destructive cycle: increased tourism negatively impacts the environment which in turn undermines the ability of the area’s natural beauty to attract tourists. On the Honduran island of Roatán, a rapidly growing tourism industry has instigated the widespread conversion of land from forests, mangroves, and grazing land to resorts, vacation houses, and housing for people hoping to take advantage of the thriving economy. For Roatán, the interplay between tourism development and environmental damage has important consequences for the sustainability of nature-based tourism on the island.

This section presents the methodology developed to study land cover and land use on Roatán. Although similar, land cover provides information on the physical features of an area such as vegetation and urban development while land use focuses on how humans are utilizing a given piece of land. The research presented herein utilizes remote sensing techniques in conjunction with data collected on the ground in order to quantitatively measure and map land cover and land use on Roatán.

Methods

In order to study land conversion on Roatán, three types of data are being utilized: satellite images, aerial photographs, and field measurements and observations made during an 11-week research trip from June to August 1996. Satellite imagery allows for rapid assessment of the land cover of large portions of the island. The use of aerial photographs helps to overcome the limitations associated with the relatively coarse resolution of satellite imagery as well as provide a mechanism for determining the accuracy of the interpretation of the satellite images. Field work establishes ground control points required to reference the aerial photos to a known map projection as well as enables the researcher to associate land cover with land use.

During the first stage of this research in November and December 1995, a multispectral satellite image of Roatán taken on 21 December 1993 by the French satellite system, Système Probatoire pour Observation de la Terre (SPOT) was utilized to produce a land cover classification map. The SPOT image has a 20 m spatial resolution and consists of three bands of data covering the visible green, visible red, and near infrared portions of the electromagnetic spectrum (Lillesand and Kiefer 1994). Using the imagery analysis program ERMapper, a land cover classification of five watersheds on the south side of the island was generated based on the spectral differences between the bands.

However, interpreting the results of this classification proved difficult because neither aerial photographs nor other detailed information were available upon which to base an interpretation (Rehmus and Tighe 1995). Therefore, a 1:24,000 scale topographic map was used to assign each class to one of two categories: disturbed lands or undisturbed lands. Although this process quantified the relative amount of development between the study watersheds, our findings had limited utility because of the uncertainty surrounding their accuracy and precision.

In order to improve upon this work, two types of data were collected during the research trip: aerial photographs and field measurements taken to reference the remote sensing data. An airplane was rented from which photographs and videos of the island from an elevation of approximately 700 feet were taken. Four watersheds in our study area were completely photographed. Subsequently, objects identifiable on the film such as trees, docks, and roads were located on the ground. Using a Magellan global positioning system (GPS), the position of these objects was determined within 2 to 5 m. This process created "ground control points" which associated objects in the photographs with known coordinates.

As the research project progresses, these ground control points (GCPs) will be used in conjunction with the aerial photographs to improve upon the previous land cover classification map. The aerial photographs will be digitized and the GCPs in each photo will be identified. Using ERMapper, the appropriate latitude and longitude will be linked to each GCP. Through a process known as geometric correction, the digitized photographs of each watershed will be reshaped to conform to a standard map projection (Lillesand and Kiefer 1994). When viewed simultaneously, the corrected photographs will create a montage of images for each watershed. These photographic montages will be used in conjunction with field notes to delineate areas of contiguous land cover such as palm trees, grazed cattle land, and development. Once delineated, the boundaries of these contiguous areas will be overlaid on top of the satellite image. ERMapper will utilize these boundaries as "training regions" whereby it will classify all other pixels of the satellite image based on similarities between the spectral signature of each pixel and that of the training regions. This analysis will produce a more detailed and accurate land classification map of Roatán.

Discussion

An accurate classification map of land cover on Roatán offers several benefits to the research goals of this long-term study. First, this land cover map can be interpreted using information collected in the field in order to develop a land use map of the watersheds. Even though land cover can offer a great deal of insight into how the land is being used, it is important to use information collected in the field to confirm assumptions about land use based on land cover classification maps (Adeniyi 1986). The first stage of this research included an analysis of a previous study of Roatán which produced land cover and land use map utilizing only remote sensing data (Vega et al. 1993). When compared to the SPOT image and to observation made in the field, these maps poorly represented the actual land use patterns on the island (Rehmus and Tighe 1995).

Second, these maps will provide a baseline record of the status of development on the island to which future land cover/land use analysis can be compared. With the acquisition of additional remote sensing data over time, the amount and rate of change on the island can be measured. As this paper goes to press, we have contracted for a second image of Roatán to be acquired by the sensors aboard SPOT, and have purchased from the Honduran government black and white aerial photographs of the island taken in 1989. These remote sensing data will greatly enhance our research efforts by both extending in time the information available for analysis and providing a set of aerial photographs which will be only slightly distorted during the geometric correction process because they were taken from an angle nearly horizontal to the ground.

Third, analysis of these maps will quantify the actual area of specific land cover and land use types in each watershed. Once this information is incorporated into the project database, researchers will be able to determine statistical correlation between land use patterns and various coral reef health measurements and water quality parameters. With the addition of information over time, the long term effects of different types of development and land use can be monitored and quantified. By quantifying these relationships, our research will help identify land use patterns which negatively impact the reefs and near shore waters as well as provide a means to measure the relative amount of damage and rate of environmental degradation associated with these land use patterns. Such an understanding of the relationship between changes on land and the health of coral reefs is vital to creating a plan for controlling the development on the island. Only a development plan which incorporates this relationship between the land and the water will insure the sustainability of a tourism industry based on the natural beauty of Roatán.