In 2002 and 2003, two field work campaigns were conducted in the study area. I spent my time in the Dominican Republic (20 February to 27 March 2002 and 4 March to 6 April 2003) mainly in the UCRYN (based in Jarabacoa), apart from a round trip through the country accompanying a geographical field course during the first two weeks and two short geobotanical field trips in the Sierra de Baoruco. The time in the UCRYN was used to establish contacts with people working in the area, to collect ground data and other locally available information, and to gain firsthand experience of the physiogeographical nature of the Cordillera Central and the conditions under which its rural population lives and farms. The main purpose of the field work was the collection of spatially determined land cover information. These field data were acquired primarily as a basis for the establishment of training areas for the intended supervised image classifications and secondarily to enable a subsequent verification of results.
In 2002, 49 field plots, including all the desired classes for the Landsat classification (chapter 7.1), were established. This was done with the help of two geography students from the University of Göttingen and two students of the Instituto Superior de Agricultura (ISA) in Santiago who were interns at PROCARYN. The field plots were required to be located in an area of at least 1 ha of the class under consideration to make sure that at least a couple of pure Landsat pixels representing the particular class could be identified. The position of the plot was described and recorded using a handheld GPS (Global Positioning System). Each plot was assigned to a class and the dominant species of trees, shrubs and herbs (or a more general description where the exact species could not be determined) were recorded together with the estimated tree crown cover, overall vegetation cover and, in mountainous terrain, slope and aspect. Distinctive features of the plots, like observations of soil characteristics or evident land use or additional information about the land use history, were also noted down and photographs of the plots were taken with a digital camera. As one and a half years had passed since the acquisition of the Landsat imagery in September 2000, local farmers were asked for information about land use changes during the last years in some cases where it was possible that such changes had happened. There was for example a hillside covered by fern and small bushes which we were told had been an unprofitable coffee plantation in 2000 and which still looked like the neighbouring coffee plantations with low vegetation cover in the Landsat image. In other cases, there were young pine plantations which had not yet been there in 2000, or recently established chayote fields.
In addition to these standardised field plots for the Landsat classification, several hundred land cover observations were recorded in 2002 and 2003 with different levels of detail. For these potential training and testing areas, at least the position and the vegetation type (land cover class) are known, partly with additional information including distinctive species, estimated crown cover and tree height or age. The land cover was documented with ground photographs (see examples in
appendix 1) and the location was measured with the GPS and/or marked directly onto the paper copies of the IKONOS images carried in the field. These observations, recorded mainly as a basis for a more detailed image analysis involving the IKONOS imagery, include a larger number of different forest types, and the minimum area of 1 ha does not apply here, so that for example narrow riparian forests, small agroforestry plots or small groups of pine trees are also recorded.
The field plots were distributed over the whole UCRYN study area, as far as the access and the time frame permitted, i.e. mainly in the vicinity of roads and of tracks that were negotiable with all-terrain vehicles. For field work further away from the roads, access on foot was gained during several hikes in the Scientific Reserve Ebano Verde and its surroundings and in the mountains of the westernmost UCRYN. In order to gain a third perspective of the study area, intermediary between the satellite imagery and the view from the ground, and also to have a look at some more remote areas with difficult access, a flight in a Cessna 172 was conducted over the study area in March 2003. Oblique aerial photographs were taken from the low flying aircraft (chapter 4.2).
These aerial photographs also served to document the land cover situation in the UCRYN in 2003 and to identify some cases of short-term land cover change in comparison to the IKONOS images, most of which were acquired in 2001 and 2002.
The area of the Scientific Reserve Ebano Verde and its western surroundings in the south-eastern UCRYN is a main focus of this study with a high data density including good quality IKONOS data and black-and-white aerial photography. Accordingly, the field work was also concentrated here resulting in a high density of training areas. This eastern test area is about two thirds forested.
Another focus area with a high overall density of field plots and observations is the region of Manabao in the western UCRYN.
In addition to establishing training areas, ground control points identifiable in the IKONOS images, like road junctions, footpaths, corners of buildings or individual trees, were measured on the ground with a GPS in order to improve the possibility to geometrically correct the imagery of the special interest areas. Measurements were taken with a handheld GPS (Garmin GPS 12) and averaged over a period of time before saving them, aiming at accuracies of ±8 m or better depending on the reception (terrain and vegetation dependent visibility of satellites).
Apart from the field work as such, the stays in the Dominican Republic were used to get into contact with local scientists like Ramón Elias Castillo of the PROGRESSIO foundation, who accompanied me into the Scientific Reserve Ebano Verde, botanist Dr. Thomas May, who is a resident of Jarabacoa, and staff members and freelance technical advisers of the PROCARYN project. Information in the form of maps and literature about the study area was collected in Jarabacoa and Santo Domingo, through visits at the Botanical Garden of Santo Domingo, the
Geographical Institute of the Universidad Autónoma de Santo Domingo, the Instituto Cartográfico Militar (Military Geographic Institute) and the Head Office of National Parks in Santo Domingo.
Figure 11: Field work. Above: Entrance to the core area of the ‘Reserva Scientífica Ebano Verde’, eastern test area.
Below left: Crossing the Río Yaque del Norte on the way into the westernmost UCRYN. Below right: On foot in the
‘Reserva Scientífica Ebano Verde’, measuring the location of a calimetal area in the eastern test area.