Ascribing plant diversity values to historical changes in landscape: a methodological approach

This paper analyses the way in which the present levels of plant diversity in different patches of an area are affected by changes to landscape heterogeneity. The change to heterogeneity is analysed through the variations in the number and nature of boundaries between the patches, native leafy forests and pine plantations, and the other patches adjacent to them between 1946 and 1990. The changes are due to the replacement of traditional farming methods by more modern, intensive uses. The result has been a growing predominance of pine trees in the landscape, the shrinking size of patches, and increased fragmentation and boundaries between a given patch and different uses. Three histories of change in the type of boundaries between land uses can be recognised: (i) the persistence of contacts between traditional uses; (ii) contacts between traditional uses and new pine plantations; (iii) contacts between pine plantations since 1946. All three are related significantly to the current values of plant diversity, measured by the Shannon-Wiener index. These values decline as the antiquity of contact with the pines increases. The patches that have preserved contacts with traditional uses thus have a greater plant diversity than those which have had many contacts with pine plantations since the 1940s.