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MAY-JUNE 11

QUARTERLY NEWSLETTER OF THE LANDSCAPE OBSERVATORY - 29

THE OBSERVER

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Dry-Stone Walls: Living Walls

Martí Boada
Geographer, Naturalist and Ph.D. in Environmental Sciences

Appreciation for dry-stone walls is currently on the rise, and even though there is still much progress to be made, there has recently been a widespread movement to revive this important and popular architectural tradition.

As well as serving a function, dry-stone architecture used in the construction of walls and other structures enhances biotic communities wherever they are built. Scientifically speaking, this is a significant and perhaps even controversial point, since it challenges the myth that ideal landscapes are the ones that are untouched by man; in other words, it is the concept of the much-celebrated wilderness, which for many epitomizes the perfect landscape and is at its best when strictly regulated by natural cycles, without any interference from man. However, in landscapes with similar geographical features in terms of morphology, latitude and altitude, those with dry-stone walls tend to have much greater biodiversity than those without them. These vertical, rocky structures with numerous openings that lead to morphologically and thermally diverse internal nooks represent a unique refuge for many arthropod and vertebrate fauna. Dry-stone walls provide important sanctuaries for breeding and hibernation, which is why dry-stone walls are sometimes referred to as living walls.

In terms of vertebrate fauna, I recently supervised a research project* in a small area of Ribera d'Ebre County, where dry-stone walls were used by many different species for the purpose of breeding, including many herpetofauna species: four species of frog, five species of saurian and five species of snake. Eight non-flying mammals were also found, and in terms of birds, six nesting species were found. This last group was significantly less abundant, since the dry-stone system attracts a high number of predators. In dry-stone walls in humid or high mountainous regions, where there are fewer predatory saurians and snakes, the number of bird species is greater. The difficulty of prospecting explains the lack of information relating to the biodiversity of arthropods and other groups, such as gastropods. However, the direct relationship between the amount of well-preserved dry-stone wall and the number of snails is well known. When it has been possible to observe the interior of a dry-stone structure following the collapse of a wall, an abundance of oothecae have been found belonging to species such as the mantis, as well as wasp nests, the hunting structures of spiders and a wide variety of invertebrates that thrive in dark, humid environments, including myriapods, cockroaches and countless others.

Vegetation also plays an important role in dry-stone walls, and in particular rupicolous vegetation usually found growing mainly on north-facing humid cliffs and crags, although not always, because dry-stone walls provide an ideal habitat for various species of Crassulaceae, including the Sedum genus, and navelwort (Umbilicus rupestris), a beautiful flowering plant that gives dry, shaded walls a distinctive appearance. Numerous different ferns, including the maidenhair fern, are uniquely associated with this ecosystem and the plant biodiversity associated with dry-stone walls is never more evident than in the case of the German iris. The bulbs of this flower were traditionally used to bind the clay on the roofs of dry-stone huts.

Dry-stone walls are living walls that help challenge the myth that anything man made in a landscape detracts from its "naturalness".

Martí Boada Geographer, Naturalist and Ph.D. in Environmental Sciences

*Arnau Sabaté (2009). Marges i biodiversitat a Vandellós i l'Hospitalet de l'Infant. Report of final degree project in Environmental Sciences at the Universitat Autňnoma de Barcelona, supervised by Martí Boada.

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