Plant species occupy different habitats on the fortress walls in Elbasan, Albania

Vegetated walls are an important habitat for urban biodiversity. We conducted an analysis of the plant species that grow on the Elbasan, Albania fortress walls. Walls vary in age from 4th to 21st century, and in composition. On 71 walls we assessed 2,787 plants of 35 species and recorded plant size, presence of flowers or fruits, height from the ground, crevice depth, wall aspect, wall age and composition, and distance to nearest opposing wall. Eleven species, two of which were ferns, composed 93.8% of the plants. The vast majority of plants flowered and fruited on the walls. Plant density ranged from 0.1-70 plants/m2. Species distributions varied significantly based on height on the wall, crevice depth, aspect and distance to the opposing wall. These differences may be influenced by dispersal mechanisms, moisture, substrate composition, and other important environmental factors. For example, Antirrhinum majus was generally found high on south facing walls in deep cracks whereas Umbilicus rupestris was found lower on north facing walls in shallower cracks. It is important that older walls colonized by plants be maintained such that a native flora can persist where natural rocky features are lacking