Observations on the wall flora of Kyustendil (Bulgaria)

The wall fora of two buildings, the Historical Museum and the Dervish Bath (16t h century), in the central part of the town of Kyustendil was investigated. Previous data for the same area of study has shown that the wall flora includes more than 120 species of vascular plants. This study presents data from five years of observations (2005-2010). During the last three years the town administration has conducted an urban maintenance program, including old town walls. These activities changed the condition of the walls to specific vertical habitats. Restored and cleaned walls present a unique opportunity for spontaneous colonization by the diversified surrounding landscape flora. The present study shows the dynamics of species diversity and analyzes the conformities and trends about the origin of this process. Most of them are associated with wall characteristics such as ferns (Asplenium trichomanes and Asplenium rutamuraria) and typically xerophytes (Arenaria serpyllifolia). New species such as Acer negundo and Catalpa speciosa, were located on the roof of the buildings. Trees negatively affect a walls' structure and present a basic problem for the preservation of walls. Some are accepted as an additional ornamental element and contribute to the complete perception of architectural and historical sites especially mosses, ferns and flowering plants (e.g. Cymbalaria muralis, Sedum hispanicum, Chelidonium majus, Oxalis spp., Trifolium spp.). The total representation of alien species on the studied walls is 17% and the most common families among the alien species are Asteraceae, Brassicaceae, Poaceae, Fabaceae, and Oxalidaceae, a few of them are also highly invasive (e.g. Ailanthus altissima, Acer negundo, Oxalis spp.). On the basis of the previous and present study the present state of the wall was estimated and recommendations were made about maintaining the old walls and their neighboring area.