Landscapes Forest and Global Change - ESA - Escola Superior ...

J. Gaspar et al. 2010. Visibility analysis and visual diversity assessment in rural landscapes
487
2. Methodology
The methodology uses data on elevation, land use and the height of features, focusing on forest
areas, to derive and analyse the visibility of each land use. The method is based on the
measurment of the extent of land from which different land cover types may be visibile (Bolós,
1992), on a cell-by-cell basis. The visibility calculations use a Digital Terrain Model (DTM), to
which the height of the different forest species derived from growth models or inventory data
were added, in order to obtain visibility results for each land cover class across the municipality.
Data were compiled for three dates: 1954, 1974 and 1995. The 1954 and 1974 data were
digitised from paper maps of the land use as mapped by the agriculture surveying services. The
1995 data were produced by aerial photo-interpretation of false color imagery.
The calculation of visibility is applied to the coverage of each type of land cover, for each date,
thus enabling an analysis of the combinations of visual influences of different types of land
cover at any point in the landscape (Miller, 2001; Gaspar and Fidalgo, 2002). Due to the extent
of the study site, this study does not consider the effects of distance decay (Bolós, 1992) on the
visibility of features (Gaspar et al., 2004).
The individual visibility maps are combined to derive the land cover types visible from each
point in the municipality, as represented by a regular grid across the area. Three different levels
of landscape content were used to characterise the diversity of the views.
3. Results
To enable comparisons between land use maps from different sources and with different
classification schemes, a general classification scheme was developed with 9 classes (Gaspar,
2005).
Table 1. Extent of land cover classes for 1954, 1974 and 1995.
Land cover class
1954 1974 1995
Dry cropland 13,7% 10,1% 8,5%
Irrigated crops 7,5% 7,9% 2,7%
Maritime pine 49,5% 64,4% 22,9%
Eucalyptus 0,0% 1,7% 11,4%
Broadleaved species 1,6% 1,4% 3,9%
Other needle leaved species 0,1% 0,1% 0,2%
Water 0,4% 0,4% 1,3%
Other land uses 26,7% 13,1% 47,5%
Social areas 0,5% 0,9% 1,8%
Total 100% 100% 100%
The 1954 to 1974 period was marked by the progressive abandonment of agriculture areas and
large plantations of Maritime pine (Pinus pinaster) (Table 1). Although tourism is now
considered as one path towards a prosperous future, one of the main sources of income for the
population is forest production, mainly associated to the paper industry, with the lower valleys
Forest Landscapes and Global Change-New Frontiers in Management, Conservation and Restoration. Proceedings of the IUFRO Landscape Ecology
Working Group International Conference, September 21-27, 2010, Bragança, Portugal. J.C. Azevedo, M. Feliciano, J. Castro & M.A. Pinto (eds.)
2010, Instituto Politécnico de Bragança, Bragança, Portugal.