To understand the role of dry stone walls in biodiversity, it’s important to specify the type of wall we’re discussing. Here, we’re mainly referring to dry stone walls, constructed without any cement. Once this is understood, we better grasp that the stones, well-placed on top of each other, leave numerous small spaces, or interstices, often filled with fine soil. These gaps provide niches for many animals and plants.

Plants find some soil, shelter, and moisture there, as the walls tend to retain moisture between the stones. Thus, various plants can settle in, such as small ferns, navelworts, or figworts, plants that are difficult to find elsewhere.

Animals also benefit from these habitats. The walls offer coolness in summer and warmth in winter, which is ideal for reptiles, like snakes that slither between the stones. Lizards use these walls to protect themselves and bask in the sun, even in winter. Many insects and spiders also find refuge in these gaps, spinning webs and catching their prey.

These small spaces provide protection zones for fragile animals. For example, one can find the Etruscan shrew, one of the smallest mammals in the world, weighing only 2 grams as an adult. It hides and searches for food, mainly small insects, in these walls.

Since the Grenelle environmental conferences in the 2010s, the idea of green and blue corridors has been launched. Green corridors ensure the continuity of terrestrial natural spaces, while blue corridors concern the continuity of aquatic environments. Other corridors have been added, such as the black corridor, which aims to preserve nocturnal darkness, and the gray corridor, which concerns built structures.

The gray corridor, formed by dry stone walls, is ecologically significant. These walls provide habitats and micro-habitats similar to those of cliffs, allowing cliff fauna and flora to survive even in urban environments.

Dry stone walls are valuable for both cultural and natural heritage. They represent ancient construction techniques and provide essential habitats for biodiversity. It’s crucial to preserve them. To do this, we must avoid damaging them. This means not climbing on the walls, not running on them, and respecting their integrity. When stones begin to fall, it’s important to repair them immediately to prevent total degradation of the wall.