Introduction
What is it about dry-stone walls? They are all around me, a defining feature of where I live, the English Lake District. They stand there, both in the valleys and high on the fells and say nothing. They are motionless, sometimes crumble, although are more often proudly and tidily erect, and are always watching, Dry-stone walls have seen more of life than I ever will and form part of the world’s silent history. They not only contribute to the region’s cultural heritage but also serve as practical boundary markers for agricultural land.
The history of dry-stone walls goes back 3500 years at least, likely much longer. Some dry-stone walls in north-west Europe have been dated back to the Neolithic Age (10000BCE-2200BCE). In Ireland’s County Mayo, an entire field system was made from dry-stone walls, subsequently covered in peat, and has been carbon-dated to 3800 BCE[i].These walls are near contemporary with the dry-stone neolithic village of Skara Brae on the Orkney Islands[ii], or the Corrimony Chambered Cairn in Scotland’s Glen Urquhart, near Inverness[iii].
Adding to these, the cyclopean walls of the acropolis of Mycenae in Greece have been dated to 1350BCE and those of Tiryns slightly earlier[iv]. This name – cyclopean - applied to a primitive method of prehistoric masonry construction, found throughout Greece, Italy, and the Middle East. The term was derived from Cyclopes, the mythological beings who were supposed to have built walls in this way. The Cyclopean technique involved the use of huge, irregular boulders, carefully fitted together without the use of mortar, thereby creating a massive wall with an uneven face.
The dry-stone walls of Lakeland, constructed without mortar, rely on careful interlocking of stones for structural integrity. Over time, natural processes such as erosion, vegetation growth, and animal activity contribute to the formation of defects in these walls. While repairs are often undertaken to maintain their functionality, such interventions may have unintended ecological consequences, particularly for wildlife that use the walls as corridors or passageways.
Rumour says that if a wall collapses from the bottom, tree roots are the cause. Should it collapse from the top, then the damage is likely to be animal-induced. This includes unruly visitors, of which the Lake District has many, who decide to climb walls rather than searching for the nearest gate. The truth? I have no clue, although sense the myriads of visitors to England’s Lake District could be far more careful than they are. However, the dry-stone walls of the Lake District have a clear ecological role and a more nuanced approach to wall restoration, incorporating wildlife monitoring and ecological issues, should perhaps be considered. This is a further way of balancing the preservation of cultural heritage with the promotion of biodiversity.
The Ecological Role of Dry-Stone Walls
Dry-stone walls provide a variety of ecological benefits. Their porous structure offers shelter and nesting sites for small mammals, birds, reptiles, and invertebrates. When finished, dry stone walls contain between 15% and 25% of air, creating an ecosystem with its own microclimate and a natural niche for biodiversity[v]. In agricultural landscapes, these walls also act as corridors that facilitate wildlife movement, connecting fragmented habitats. Studies have highlighted the importance of such linear features in maintaining biodiversity, particularly in landscapes dominated by human activity[vi]. A very large number of animals can use defects in dry-stone walls as passageways. I have seen sheep, deer, badger, fox, squirrel, and so much more besides, pass through defects in dry-stone walls.
In addition to offering passageways, dry-stone walls serve as microhabitats with varying thermal conditions, moisture retention, and wind protection. This makes them particularly valuable for ectothermic species such as reptiles and amphibians. Studies have shown that slow worms (Anguis fragilis), and common frogs (Rana temporaria) frequently use dry-stone walls for refuge and thermoregulation[vii].
For small mammals, the base of dry-stone walls can provide crucial cover from predators while simplifying movement across fragmented landscapes. Meanwhile field voles (Microtus agrestis), wood mice (Apodemus sylvaticus), and bank voles (Myodes glareolus) use dry-stone walls as dispersal routes[viii].
Moreover, birds such as wrens (Troglodytes troglodytes), robins (Erithacus rubecula), and house sparrows (Passer domesticus) frequently nest in dry-stone walls, capitalising on the protective environment they offer[ix]. Invertebrates, including bumblebees (Bombus spp.), solitary bees, beetles, and spiders, also benefit from the structural complexity of dry-stone walls, which mimic natural rocky habitats[x]. These invertebrates can sometimes be found to nest in the crevices of sunlit wall sections[xi],[xii].
It is not just animal life. The walls also host a variety of bryophytes and lichens, contributing to local biodiversity and playing a clear role in carbon sequestration[xiii]. Mosses are major carbon sinks. Moss-covered ground, annually and globally, absorbs 6.43 billion tonnes of carbon from the atmosphere. For reference, the USA emits 4.4 billion tonnes of carbon dioxide (CO2) each year, and China emits 9.9. billion tonnes[xiv]. As with all vegetable matter, mosses capture CO2 through photosynthesis, reducing atmospheric levels of the gas, the main contributor to the greenhouse effect, which causes global warming[xv]. Watch that space when it comes to the climate-improving effects of moss[xvi].
Drivers of Wall Defects
Defects in dry-stone walls can be caused by a combination of natural and anthropogenic factors. These are:
1. Erosion and Weathering: Exposure to wind, rain, and frost contributes to the gradual degradation of dry-stone walls. Freeze-thaw cycles, particularly in winter, cause water to seep into cracks between stones. When temperatures drop, this water expands as ice, exerting pressure that dislodges stones and weakens the wall structure. This process, known as frost heave, is a primary driver of wall instability in upland environments[xvii].
2. Vegetation Growth: Plants and tree roots play a significant role in wall deterioration. Mosses and lichens colonising the stones can accelerate weathering by trapping moisture, which exacerbates the freeze-thaw process. Larger plants such as brambles and ivy take root in wall crevices, gradually prying apart stones as their root systems expand. In some cases, the weight of overhanging branches can cause sections of a wall to collapse[xviii].
3. Animal Activity: This is a significant problem. Dry-stone walls often act as conduits for wildlife movement, but this interaction also contributes to structural damage[xix]. In the Lake District, I have frequently seen animal tracks on both sides of collapsed wall sections, suggesting that certain defects serve as wildlife corridors[xx]. These findings align with broader research on the role of linear features in facilitating animal movement across fragmented landscapes[xxi]. Large mammals such as deer, sheep, and badgers frequently push through weak sections of a wall, creating passageways that eventually lead to collapse. Smaller mammals such as rabbits and voles burrow beneath walls, undermining their foundation and causing gradual displacement of stones. It has been estimated that burrowing mammals are responsible for over 60% of recorded dry-stone wall failures in agricultural settings[xxii].
4. Human-Induced Damage: Agricultural and recreational activities also impact dry-stone wall integrity. The use of heavy machinery near walls can result in direct collisions or ground vibrations that weaken the structure over time. Additionally, walkers and climbers inadvertently contribute to wall degradation by removing stones for makeshift seating or handholds[xxiii], or climbing over dry-stone walls when they should not.
5. Structural Age and Material Weakness: Many dry-stone walls in the Lake District date back several centuries, and their original construction materials may have deteriorated because of prolonged exposure to environmental stressors. The use of suboptimal stone types or poor initial construction techniques can also make certain walls more susceptible to collapse[xxiv]. Anyone who has attempted to construct a dry-stone wall with limestone will know what this means. So often the stone shatters, just when you least wish to see it. There is a right way and a wrong way to build a dry-stone wall.
Impacts of Wall Repairs on Wildlife
Traditional wall repairs aim to restore structural integrity without considering the ecological implications. By sealing gaps and stabilising stones, repairs can inadvertently obstruct wildlife movement and disrupt habitat connectivity. For example, a wall repaired without consideration for animal activity might block a well-used passageway, forcing animals to alter their movement patterns or abandon the area entirely. This can have cascading effects on local ecosystems, particularly for species reliant on interconnected habitats.
Amphibians and reptiles are especially vulnerable to such disruptions. For instance, frogs and newts migrating to breeding ponds may find their routes blocked by newly repaired walls, increasing their exposure to predators and road traffic[xxv]. Similarly, small mammals that rely on wall crevices for shelter may be displaced by overly rigid repair practices[xxvi].
Bird species that nest or roost in dry-stone walls may also be negatively impacted. The sudden closure of these spaces during repair work may lead to habitat loss and decreased reproductive success[xxvii]. Moreover, bats, which sometimes use dry-stone walls as roosting sites, can be inadvertently excluded if wall repairs are carried out without earlier assessment[xxviii]. Invertebrates that rely on dry-stone walls, and there are plenty, can also be disturbed as the removal or rearrangement of stones during repair work can eliminate microhabitats, thereby reducing the local abundance of beneficial insect species and subsequently affect pollination dynamics in nearby vegetation.
To mitigate these impacts, it is essential that repair efforts integrate ecological considerations, including pre-repair wildlife surveys and adaptive restoration strategies. Installing small purpose-built gaps in dry-stone walls can help maintain connectivity for smaller wildlife while ensuring structural stability. Holes in drystone walls have a plethora of names that sometimes explain their purpose. Lunky is common in some parts of the country, hogg hole in others, a hogget being a yearling sheep. But the gaps are too narrow for all but the youngest lambs to squeeze through. Wallers might also construct a smuse or smoot hole for rabbits, to trap them as they pass through, or stop them burrowing underneath and weakening the structure. Smoots likely exist for rabbits, and maybe badgers, too. Certainly, 100 years ago, rabbit farms were countryside features and were known to supply London furriers[xxix].
Additionally, staggering repairs over time rather than conducting large-scale restorations at once can allow wildlife populations to adapt to habitat modifications more gradually.
Proposed Monitoring and Mitigation Strategies
It seems clear that dry-stone walls play a more major part in our ecosystem than we might realise. Their problem is that they are inert, static, motionless, and silent, yet meanwhile are busy doing plenty. Perhaps, to minimise the ecological impacts of wall repairs, a systematic approach to monitoring and mitigation is wise. Maybe the following:
1. Pre-repair Monitoring: Trail cameras should be installed at wall defects for at least one week before any repair. These will provide insights into the type and frequency of animal activity associated with a defect. Longer monitoring periods may be warranted in areas with high biodiversity.
2. Adaptive Repair Practices: Based on monitoring results, repair strategies should be adapted to accommodate wildlife. For example:
· Leaving defects unrepaired: In cases where a defect is heavily used by wildlife, allowing the gap to persist may be the best option for biodiversity.
· Creating managed passageways: Larger gaps can be formalised into open passageways that facilitate animal movement while maintaining the wall’s structural integrity.
· Incorporating smoots: These small, purpose-built gaps allow smaller animals to pass through while preventing larger species from causing further damage. Personally, it seems unfair to allow small animals through a smoot while denying access to larger mammals such as deer and sheep.
3. Community Engagement and Training: Landowners, wallers, and conservationists should be educated on the ecological role of dry-stone walls and trained in wildlife-friendly repair techniques. Workshops and community initiatives can foster collaboration and promote sustainable practices. Several studies illustrate the benefits of integrating ecological considerations into wall repairs. One project in the United Kingdom involved the installation of smoots in repaired walls, which successfully maintained habitat connectivity for small mammals and amphibians[xxx]. Similarly, adaptive repair practices in Scotland’s Cairngorms National Park demonstrated the feasibility of balancing heritage preservation with biodiversity conservation[xxxi].
Policy and Research Implications
The ecological implications of dry-stone wall repairs highlight the need for updated policies and research priorities. National and local conservation strategies should incorporate guidelines for wildlife-friendly wall restoration. Funding for research on the ecological role of dry-stone walls, including long-term monitoring of repaired sites, is also essential.
For the future, I clearly have more work to do. Certainly, as I look at my seemingly inert, but actually hyperactive dry-stone walls, I have fashioned multiple queries, most of which are presently unanswered. For example:
· How do different repair techniques impact specific wildlife species?
· What are the long-term ecological outcomes of leaving defects unrepaired?
· How can traditional walling practices be adapted to support biodiversity without compromising cultural heritage?
I have a busy future.
Conclusion
Dry-stone walls are more than just cultural artefacts. They are vital components of the Lake District’s ecological landscape. Repairing these walls without considering their ecological role risks disrupting wildlife movements and diminishing habitat connectivity. By incorporating wildlife monitoring and adaptive repair practices, these iconic structures can continue to serve both cultural and ecological functions.
This integrated approach requires collaboration among landowners, wallers, conservationists, and policymakers. Together, they can strike a balance between preserving the region’s heritage and promoting its biodiversity, thereby ensuring that dry-stone walls remain a symbol of coexistence between human activity and the natural world.
***
Here are some videos, taken with my trailcam, of one wall defect. How can I possibly repair the defect now that I have seen these?
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#DryStoneWalls #WildlifeCorridors #EcologicalConservation #BiodiversityMatters #HabitatConnectivity #LakeDistrictUK #EnvironmentalSustainability #CulturalHeritage #NaturePreservation #RewildingUK
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