Bioreceptivity

Bioreceptivity refers to the inherent or evolving potential of a material to be colonized by living organisms, including bacteria, fungi, algae, mosses and lichens. First formally defined by Olivier Guillitte in 1995, the concept has become a central theoretical and practical framework for understanding biological colonisation and its role in biological weathering of building materials. In the context of natural outcrops and built cultural heritage, bioreceptivity helps explain why some stone surfaces rapidly host microbial or lichen communities while others remain largely uncolonised.

Guillitte’s original formulation sought to address a fundamental ecological question: What controls the colonisation and growth of organisms on buildings and stone structures? He emphasised that three sets of factors regulate biological colonisation: the characteristics of the organisms themselves (e.g., dispersal mechanisms, growth rates, ecological requirements), the environmental context (climate, microclimate, solar exposure, humidity, shading), and, crucially, the material properties of the substrate. Bioreceptivity conceptualises this third category by framing colonisation potential as an intrinsic property of the material. Guillitte’s definition separates bioreceptivity from accessibility, a term derived from plant ecology and introduced by Heimans in 1954, referring to the capacity of the environment to permit diaspores to reach and settle on a surface. While accessibility concerns the biological potential of the environment, bioreceptivity expresses the colonisation potential rooted in the physical, chemical and structural characteristics of the material.

Guillitte proposed several types of bioreceptivity: primary, referring to the inherent condition of a fresh, unweathered material; secondary, which emerges when a material’s properties have been modified by environmental exposure; and tertiary, where colonising organisms themselves alter the substrate in ways that facilitate further growth. He also described intrinsic, extrinsic, and semi-extrinsic subdivisions, although these categories were later considered problematic by subsequent researchers.

Primary bioreceptivity is associated with materials before they undergo environmental alteration. Smooth, hard, low-porosity stones such as fresh granite typically show low primary bioreceptivity, while more porous, rough or chemically reactive stones—such as limestones, sandstones and travertines—exhibit higher primary receptivity. In contrast, secondary bioreceptivity is dynamic and usually far more relevant in real-world contexts. Environmental weathering, air pollution, salt crystallisation, surface roughening, deposition of dust or organic matter, and moisture fluctuations alter the material’s surface and subsurface properties. As a result, materials that were originally minimally receptive may become progressively more susceptible to microbial colonisation. This is particularly important in built heritage, where stone surfaces have been exposed for decades or centuries, making secondary bioreceptivity the dominant state.

Tertiary bioreceptivity is observed when established biological communities modify the substrate, increasing its receptivity to subsequent colonisers. Lichens, for example, may produce organic acids that etch or chemically weather minerals, while microbial biofilms can trap particles, retain moisture and create microhabitats. These processes can accelerate biological weathering and create feedback loops that increase both colonisation intensity and diversity.

Although Guillitte noted in 1995 that many aspects of bioreceptivity required further study, the concept was not substantially revised for 25 years. In 2021, Sanmartín, Miller, Prieto and Viles revisited the concept, providing the first major update since its introduction. Through a bibliometric analysis, they showed that bioreceptivity had become widely adopted within built heritage science, yet often applied narrowly or inconsistently. Their reanalysis highlighted that Guillitte’s model needed refinement to remain useful for contemporary research.

Sanmartín et al. proposed that the intrinsic, extrinsic and semi-extrinsic categories of bioreceptivity should be abandoned due to conceptual ambiguity and limited practical application. Instead, they suggested adding a new category—quaternary bioreceptivity—to capture processes not fully encompassed by the original framework. They also recommended expanding the concept to include submerged and subsoil environments, where colonisation dynamics and material responses differ markedly from above-ground settings.

A major critique raised by the 2021 study is that very few investigations of bioreceptivity have been conducted in situ on actual built heritage. As a result, bioreceptivity has largely remained an experimental and laboratory-based concept, often tested on small samples under controlled conditions. While laboratory studies are valuable, they frequently exclude organisms that cannot be easily cultivated, such as many lichen species, and they often ignore the temporal dynamism of bioreceptivity. Real materials in real environments undergo continuous alteration, making static “snapshot” evaluations insufficient.

Understanding bioreceptivity is essential for predicting and managing biological colonisation, whether the goal is to prevent biological weathering on heritage surfaces or to harness bioreceptive materials in sustainable architecture. In modern building design, bioreceptivity is increasingly viewed as an opportunity rather than a threat—especially in the development of bioreceptive concretes that promote moss or lichen growth as part of ecological design strategies. Conversely, in the conservation of historic stone, knowledge of bioreceptivity helps identify surfaces at risk of accelerated colonisation and informs policies for cleaning, maintenance and environmental management.

After 25 years, bioreceptivity remains a vital concept, providing insight into the drivers, patterns and consequences of biological colonisation of stone materials. Its continued evolution and refinement—particularly through integrated field-based studies—are essential for advancing both scientific understanding and practical applications in the management of stone structures, natural landscapes and heritage environments.