The Ecology of Lichens in Kew 

Lichen ecology examines where lichens live, which conditions allow them to establish, and how they interact with their surroundings. At Kew, the useful starting point is the habitat: a tree trunk, a stone face, a patch of soil or an old wooden surface.

This page brings together ecological principles and observation activities for Kew’s landscapes. Habitat descriptions are based on Kew’s published information; explanations of lichen responses draw on scientific literature. Suggested comparisons are questions for investigation, rather than claims that every habitat has already been surveyed (Ellis, 2012; Seaward, 2008).

A substrate is the surface supporting a lichen. Useful recording categories at Kew include living bark, exposed wood, rock, brick and mortar, soil, and moss-covered surfaces. A substrate category describes the point of attachment; it does not by itself explain why a species occurs there.

Mineral chemistry, surface texture, age, water retention and exposure can influence colonisation. Stone and mortar should be recorded separately where possible, because runoff can alter neighbouring surfaces. Bark properties also vary among tree species and individual trees (British Lichen Society, n.d.-a).

Observe at Kew: Compare two adjacent surfaces and record substrate, shade and moisture before interpreting their lichen communities.

Lichens growing on trees are epiphytes. They generally use bark as a supporting surface rather than feeding on the tree’s living tissues. Lichen cover alone is therefore not evidence of disease (Royal Horticultural Society, n.d.).

At Kew, compare trunks and branches, shaded and exposed sides, and trees in open settings with those under a canopy. Record tree identity where known, bark texture, approximate sampling height and canopy cover. These observations help distinguish tree-related habitat differences from wider environmental influences (Ellis, 2012).

A garden contains many small climates. Light, humidity, temperature, airflow and the duration of wetting can differ across a single tree or rock. These conditions affect when a lichen is hydrated and able to photosynthesise.

Most lichens tolerate drying, but species differ in their physiological responses. More shade or more moisture does not automatically mean a better habitat for every species (Kranner et al., 2008).

Observe at Kew: In the Rock Garden, compare an exposed stone face with a sheltered crevice. In wooded areas, compare canopy shade with a nearby opening. Note weather and recent rainfall.

Lichens as Pioneer Species

Lichens are among the most effective pioneer species in terrestrial ecosystems, capable of colonising bare substrates such as rock, bark, soil crusts, and newly exposed surfaces after disturbance. Their unique symbiosis enables them to tolerate extreme environmental stress while initiating key biological processes. By secreting organic acids, lichens contribute to the gradual weathering of rock, facilitating the formation of early soils. Their thalli trap dust, retain moisture, and create microhabitats that support bacteria, fungi, algae, and small invertebrates. Through these functions, lichens pave the way for subsequent plant establishment, playing a foundational role in ecological succession and landscape development.

Lichens and Climate Adaptation

Lichens demonstrate remarkable climate adaptation, thriving in habitats ranging from arid deserts to polar tundra. Their symbiotic structure enables flexible metabolic responses: they can enter prolonged dormancy during drought, rapidly reactivating when moisture becomes available. Many species adjust their photosynthetic partners or pigment production to cope with shifting temperatures and solar radiation. Lichens also serve as sensitive indicators of climate change, with shifts in their distribution, growth rates, and community composition reflecting altered environmental conditions. By adapting physiologically and structurally, lichens persist where few organisms can, offering valuable insights into ecosystem resilience under changing climates.

Lichens and Climate Change Research

At the Royal Botanic Gardens, Kew, lichens play an important role in climate change research as sensitive indicators of environmental change. Their growth, distribution, and species composition respond quickly to shifts in temperature, rainfall patterns, air quality, and nitrogen deposition. Long-term lichen records at Kew allow scientists to track ecological change over decades, revealing both past pollution impacts and recent recoveries linked to improved air quality. Today, lichen studies at Kew help interpret how climate change interacts with urban environments, historic landscapes, and biodiversity, contributing valuable evidence for conservation planning within this UNESCO World Heritage Site.

Lichen Colonisation on Historic Structures

Historic buildings, walls, and stone features within the Royal Botanic Gardens, Kew provide important substrates for lichen colonisation. Crustose and foliose lichens gradually establish on brick, stone, and mortar, responding to surface chemistry, texture, moisture retention, and light exposure. At Kew, these communities reflect both the age of structures and the improvement of London’s air quality since the mid-twentieth century. While lichens add ecological and educational value, their presence also raises conservation questions, requiring careful monitoring to balance biodiversity with heritage preservation. As a UNESCO World Heritage Site, Kew offers a unique setting where lichen growth records environmental change while informing sustainable management of historic fabric.

Lichens as Cultural Heritage Indicators

Lichens are increasingly recognised as valuable indicators of cultural heritage condition. Their presence, absence, species composition, and growth forms on stone, brick, and historic surfaces reflect environmental quality, material properties, microclimate, and management history. Some lichens signal long-term stability and low disturbance, while others indicate pollution, moisture imbalance, or surface decay.

In heritage sites such as the Royal Botanic Gardens, Kew, lichen studies help conservators distinguish between natural patina and active biodeterioration. By integrating lichen ecology with conservation science, these organisms provide a non-invasive, cost-effective tool for monitoring and safeguarding historic structures within living landscapes.

Many lichens respond to atmospheric pollution and nutrient deposition. Responses differ among species, so changes in community composition can be more informative than total lichen cover. The presence of one species does not establish that the air is clean.

Research on London’s epiphytic lichens found evidence of communities remaining at early successional stages, with historical pollution and present habitat conditions relevant to their recovery (Llewellyn et al., 2020). This provides regional context for Kew; it is not a measurement of pollution at a particular tree or garden location.

Monitoring at Kew: Compare repeat observations from defined locations using similar tree species, sampling heights and exposure. Record habitat differences alongside lichen identifications, and interpret patterns with environmental measurements where available.

A lichen patch forms part of a wider community. Lichens can provide resources and shelter for invertebrates and microorganisms, while grazing and other interactions can influence the community around them (Seaward, 2008).

Some lichen secondary compounds discourage certain herbivores; this response varies among compounds, lichens and grazing animals (Solhaug & Gauslaa, 2012).

Observe at Kew: Photograph lichens together with neighbouring mosses or visible animals. Close contact alone does not demonstrate competition or causation.

Lichens participate in carbon and mineral cycling and can contribute to weathering of mineral surfaces. Certain partnerships containing cyanobacteria fix atmospheric nitrogen; this function is not shared by all lichens (Nash, 2008; Seaward, 2008).

At Kew, distinguish these general ecological processes from demonstrated changes to a particular stone or soil patch. Lichen cover is not, by itself, proof of stone damage. Historic surfaces require assessment that considers material condition, biological growth and conservation priorities.

Trees and Woodland

Kew’s Natural Area and Woodland Garden provide settings for comparing canopy shade, tree surfaces and woodland edges. These habitat descriptions do not establish the presence of particular lichen species.

The Rock Garden

The Rock Garden includes sandstone features, changes in level and waterfalls. It offers an observation setting for contrasting exposure and wetting. Identify the material of each sampled surface rather than assuming that every rock has the same chemistry.

Ground Surfaces and Open Areas

Where access permits, examine soil, moss-covered ground and small exposed patches near paths or planting. Record vegetation cover, shading and signs of disturbance. A lawn or bare patch is not automatically suitable for terricolous lichens.

Built Surfaces and Worked Wood

Brick, mortar, stonework and wooden structures add further recording categories. Surface age, maintenance and local exposure can affect colonisation. Compare these surfaces using the same careful recording approach used for natural substrates (British Lichen Society, n.d.-a).

A lichen may look different after rain without its community having changed. Seasonal differences in hydration and light can alter appearance and activity. Longer-term changes in habitat, pollution and management may influence which species persist or establish (Kranner et al., 2008; Llewellyn et al., 2020).

Monitoring at Kew: Revisit fixed photograph points. Record date, weather, wet or dry condition, sampling height and any visible changes to the surrounding habitat. Use comparable framing and scale before assessing a trend.

Lichen conservation begins with understanding the habitats and species involved. For Kew, useful priorities for assessment include continuity of tree surfaces, variation in light and moisture, and the effects of maintenance on colonised stone or wood.

Cleaning, repair, tree work and changes in shading should be considered alongside safety, horticulture and heritage requirements. These are suggested assessment principles, rather than a statement of current Kew policy. Experience from British built habitats shows the importance of considering lichens before changing established surfaces (British Lichen Society, n.d.-b).

For visitors: Photograph lichens in place and follow garden access rules. Avoid scraping, collecting or applying substances to a surface.

Photographs and careful habitat notes can support learning and future ecological comparisons. A useful record includes location, date, substrate, habitat, an overview photograph and a close view of diagnostic features. Keep an uncertain identification provisional (British Lichen Society, n.d.-c).Potential research questions at Kew include how communities differ among tree surfaces, between exposed and sheltered stone, and across maintained and less disturbed areas. Reliable answers require a defined sampling method, checked identifications and repeat observations. These are research opportunities, not claims that such studies have already been completed.

Kew’s lichens can be studied through the surfaces they occupy and the conditions surrounding them. The habitat categories above provide a framework for comparing tree surfaces, rock, ground and built features. Reliable conclusions about diversity, pollution or change require checked species records and a consistent survey method (Ellis, 2012; Llewellyn et al., 2020).

The photographs below illustrate substrate categories already recorded on this site. They are examples of surfaces, rather than proof that every material supports the same lichen community. Record the actual material, surface condition and exposure at each observation point. Mineral type and runoff can influence which species establish (British Lichen Society, n.d.-a).

Limestone — substrate example at Kew. Record surface condition, exposure and moisture when observing lichens.

Sandstone — substrate example at Kew. Record surface condition, exposure and moisture when observing lichens.

Granite — substrate example at Kew. Record surface condition, exposure and moisture when observing lichens.

Cast Iron — substrate example at Kew. Record surface condition, exposure and moisture when observing lichens.

Wood — substrate example at Kew. Record surface condition, exposure and moisture when observing lichens.

Historic brick — substrate example at Kew. Record surface condition, exposure and moisture when observing lichens.

Granite — substrate example at Kew. Record surface condition, exposure and moisture when observing lichens.

Travertine — substrate example at Kew. Record surface condition, exposure and moisture when observing lichens.

British Lichen Society (n.d.-a). Lichen Ecology. Online resource.

British Lichen Society (n.d.-b). Churchyard Lichens. Habitat and management guidance.

British Lichen Society (n.d.-c). Studying Lichens. Online resource.

Ellis, C.J. (2012). Lichen epiphyte diversity: A species, community and trait-based review. Perspectives in Plant Ecology, Evolution and Systematics, 14(2), 131–152. DOI.

Kranner, I., Beckett, R., Hochman, A. & Nash, T.H. III (2008). Desiccation-tolerance in lichens: A review. The Bryologist, 111(4), 576–593. DOI.

Llewellyn, T., Gaya, E. & Murrell, D.J. (2020). Are urban communities in successional stasis? A case study on epiphytic lichen communities. Diversity, 12(9), 330. DOI.

Nash, T.H. III (ed.) (2008). Lichen Biology. 2nd edition. Cambridge University Press. DOI.

Royal Botanic Gardens, Kew (n.d.-a). Natural Area. Habitat information.

Royal Botanic Gardens, Kew (n.d.-b). Rock Garden. Habitat information.

Royal Botanic Gardens, Kew (n.d.-c). Woodland Garden and Temple of Aeolus. Habitat information.

Royal Horticultural Society (n.d.). Algae, Lichens and Moss on Trees and Shrubs. Online guidance.

Seaward, M.R.D. (2008). Environmental role of lichens. In: Nash, T.H. III (ed.), Lichen Biology. 2nd edition. Cambridge University Press, pp. 274–298. DOI.

Solhaug, K.A. & Gauslaa, Y. (2012). Secondary lichen compounds as protection against excess solar radiation and herbivores. In: Lüttge, U., Beyschlag, W., Büdel, B. & Francis, D. (eds), Progress in Botany 73. Springer, pp. 283–304. DOI.