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M.T.C. Rodrigues & V. Silva 2010. Landscape changes in a watershed in the southwest of Portugal
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Landscape changes in a watershed in the southwest of Portugal
Maria Teresa Calvão Rodrigues * & Vanessa Silva
Faculdade de Ciências e Tecnologia/Universidade Nova de Lisboa, Portugal
Abstract
Over the centuries human intervention has altered the landscape of the south of Portugal, the
most dramatic changes having taken place during the last one hundred and fifty years: the
dominant component of the landscape has changed first from natural/semi-natural shrubby
communities to cereal crops and later to oak tree montados through processes of farmland
abandonment, reforestation, change in the type of crops and trees grown, cutting or burning. All
of these changes affected landscape composition and configuration and thus the functioning of
natural systems.
The objective of this paper is to study landscape dynamics of a watershed in the southwest of
Portugal over a century, using data from different time periods and the consequences of
changes. Within the context of a GIS land-use changes were quantified through the analysis of
land use maps and ortophotomaps.
Keyword: Land cover change, landscape
1.Introduction
Human intervention significantly altered the landscape of southern Portugal, the primitive
forests having disappeared long ago. The landscape of the South of the country suffered major
changes in its structure and composition over the past 150 years. In the late nineteenth century
the landscape matrix essentially consisted of shrublands (Feio 1998). From that date on
significant modifications that contributed decisively to soil degradation occurred. Successive
campaigns to promote the production of cereals in the first half of the twentieth century led to a
sharp increase of the cultivated area at the expense of farming on unsuitable land: steep slopes,
rocky soils, shallow and of low infiltration capacity. As Feio (1998) points out, within a time
period of about 50 years the shrublands almost disappeared from the landscape of southern
Portugal while at the same time the plowed area with grain duplicated.
However, crop cultivation on unsuitable land led to intense erosion which in short time
conditioned new sowings and consequently led to the abandonment of the sites less apt for
agriculture or its replacement by other forms of soil use. Thus, “Carta Agrícola e Florestal” for
the decade 50-60, shows that in areas of steeper slopes, agriculture had been replaced by forests
(montados) or left abandoned, leading to a progressive recovery of the natural vegetation. In the
70s there was a strong expansion of the eucalyptus culture. In most cases, the deployment of
plantations was not well conducted, which once again led to soil degradation. From the 90s on a
tendency for the abandonment of cultivation of eucalyptus began to occur, or at least a lack of
significant new investments due to the low economic profitability.
* Corresponding author. Teresa Calvão Tel.: 212948397 - Fax: 212948554
Email adress: mtr@fct.unl.pt
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.