SEMBRAR AIRE

Ecotones

Long walks help me rest my body in a city. To give me a step-sized knowledge of where I am invited to built a temporary home. This time, I was landing in Paris. While looping through touristic sites, well-trimmed gardens and finding my way to supermarkets and affordable restaurants, I wondered how plants made their way through the city. How have they been able to land? Which maps do they follow?

Seine’s riverbank

Paris is famous for its tree-lined boulevards, laid out in the 19th century under Napoleon III and overseen by Georges-Eugène Haussmann. They facilitated troop movement and helped break up irregular neighborhoods that had allowed rebels to build barricades.

But which trees to plant?
Definitely male ones! Accordingly to urban planners, female trees create a nuisance in public spaces. To avoid the messiness of fruits and seeds, which can attract life to feed on them for free, male trees are cultivated preferably. For instance, the seeds of female ginkgo trees emit a strong odor of butyric acid, a scent similar to vomit or rancid milk.

Visit fallingfruit.org to see where fruit trees are growing near you

But this botanical sexism has an unintended consequence: massive pollen production, which intensifies seasonal allergies and asthma rates in the city-damaged lungs. Paradoxically, exactly ginkgo seeds are used in traditional Chinese medicine to treat respiratory diseases such as asthma. Moreover, ginkgos withstand any gender categories. They can switch their gender during their life and are therefore unpredictable when it comes to the selection of urban trees.

Today trees are graded higher in the governmental rank: they are ambassadors for “green governance”. They decorate our streets, absorb our emissions, and serve as proof of sustainability.

Plane trees, horse chestnuts, and lindens flanking the boulevards at regular intervals. They are not allowed to step outside their role. Even if underpaid, squeezed into too tiny uniforms or disabled, they need to perform. Companies are therefore building prostheses for trees, making sure that their fragile bodies can withstand the weight of winds, vehicles and steps. For what the government does not have any solutions, is the high absence due to illness: pollution and diseases are spreading too fast in the homogeneous environment.
Yet beyond these ordered lines, other plants seem to grow effortlessly.

Tree with a metal protheses, Notre Dame

A variety of lichens

Notre Dame drown 2019 in yellow smoke containing lead. The metal particles sank into the river, the soil and into our lungs. Yet, the reconstruction continues with exactly the same material. Miraculously, amid layers of historical ash, plants sprout around Notre Dame. Between cobblestones, along river embankments, in cracks of asphalt—life erupts. They adapted to these conditions and became pioneers. For instance, the dandelion, with its bright yellow flowers, adapts to street pits by producing seeds that do not disperse. This means multiple generations co-exist in close-knit communities, thereby becoming trampling-tolerant.
I guess this is not what Georges-Eugène Haussmann had in mind when proclaiming “aerate, unify and embelish” Paris.
Yet life always creates conditions conducive to life — even in the narrowest fissures.

Neither wild nor domesticated, these plants make tensions their home, existing at the intersection of contrasting environments within one ecosystem. Laying out world-beginnings and world-endings side-by-side. In ecology these plants called “ruderals”. These communities emerge spontaneously in disturbed environments usually considered hostile to life: the cracks of sidewalks, the spaces alongside train tracks and roads, vacant sites, waste disposal areas etc. But essentially these are not hostile environments. It seems that the ruderals want to be here, they made themselves a home.
Where does the family of lichens get their energy from when growing on stony walls? How come that the Stinging Nettle is surviving next to public unirals?

The crack is leading us into Earth’s memory of when the sea once covered Paris. As the sea slowly withdrew 45 million years ago, coral reefs dried to dust and, over endless aeons, compressed into stony bones. We reached into Earth’s belly, laid open its stony bones, and stitched them together over ground, forming Paris iconic houses, churches, bridges.

Shell impressions on the Seine riverbank

By exposing these marine fossils to air, the stones started to breathe.

We are breathing with a variety of microorganisms that populate the city. But they do not compete for attention, just their variety of colors and shapes indicate that there is a universe in each of them.
Lichens – a holobiont of fungi, algae and cyanobacteria – form symbiotic relationships to adapt to the atmospheric conditions. The first step is up to the fungal partner, which first needs to find a suitable free-living alga. Apparently, a match only happens when both the fungus and the algae are in a “starved” “longing” state, urgently in need of nutrients. The alga provides nutrients through photosynthesis, turning carbon dioxide into sugar. In return, the fungal partner provides protection, water and a stable anchor.

Notre Dame with a brilliant green biopatina: probably algea, lichens and mosses

Lichens are pioneers.
They push through ruins and tombs that we eliminate from our progressive life. Lichens prepare surfaces, opening spaces for mosses and seeds. They know the city, the belly, the sea and everything that happened in between these 600 million years. In their 1000 years of life, sometimes dormant and thriving again, they are the first ones settling on surfaces that are very low in nutrients, burnt or frozen, dark or bright, you will find them surviving.

Mosses and lichens on a tomb

Viarity of lichens on a historical monument

Lichens are alchemists.
Their colors indicate what they have been metabolised in their lifetime. Lichens with dark pigmentation are rich in melanin. They can survive high solar exposure or pollution. Therefore, the darkening urban patina that we find close to streets are fungi forming long-lasting protective crusts, feeding on pollutants. In contrast, the golden lichen prefers areas with high levels of nitrogen. We breathe in nitrogen gas all the time – it makes up a large part of Earth’s atmosphere. But when nitrogen is heated and combined with oxygen, it can be a powerful toxin: from road traffic, fertilisers, and livestock excrements. However, lichens with brilliant pigmentation and other nitrogen-loving plants, like the Stinging Nettle, thrive in these environments. For them the city is not entirely foreign. They already pre-adapted. Long before urbanization, nitrogen-rich patches existed in river floodplains, around bird colonies, in places of decay and animal congregation. With little more than air, light, and rain, lichens fasten themselves to stone and begin the slow work of habitation. They are neither guests nor intruders. They return to a mineral landscape that long preceded architecture.

Golden lichen on a bridge

The bones that we dig up from the underbelly are fragile. Too thin-skinned. Without the protective epidermis of microorganisms that grow across surfaces, our houses will erode back into marine dust. They hold everything in place.
And still, we remove these alchemists until only a skeleton remains to please our visual consistency. The culture of cleanliness does not lead to the perpetuation but rather to the degradation of our uninterrupted care for monuments. With every piece of lichen that is removed, a layer of the facade is removed, a layer of the history we are so eager to preserve.¹

Different from trees, ruderals as lichens are not (yet) part of the green initatives. They cannot be cultivated and monitored like charismatic flora and fauna. And therefore, are less protected and valuable in capitalistic systems. They can be removed, weeded, or poisoned without consideration. Yet, each of them fulfills a duty; not to serve human aims, but to live. Lichens learned how to rest their bodies in the city, inhabiting the liminal spaces: the Ecotones.

Ecotone comes from the Greek oikos (home) and tonos (tension). It refers to transition areas where two or more ecosystems meet. These zones are rich in biodiversity, exhibiting unique characteristics that are absent in the adjacent ecosystems. Think of a shoreline, where aquatic life meets terrestrial life, or salty water meets fresh water. The intertwining of habitats provides critical space for courtship, nesting, and foraging. These places maximise connections rather than progressive developments.

Where lichens meet our cities, they also meet us humans. We both depend on infrastructures. We both must have faith that the elements and life-givers (winds, carriers, rain, oxygen, communities, shelter etc.) will cross our paths. That they will still exist when we land and begin again.

If lichens already inhabit the thresholds of the city, perhaps the question shifts: What if cities were designed as Ecotones? A city like this would not only support what humans value or cultivate. It would create space for organisms with various senses of time and transformation. In such a city, life would not merely survive within human infrastructure. It would move through it, reshape it, and perhaps even exceed and predate human life.

¹See previous article and https://www.e-flux.com/architecture/sick-architecture/360099/chronic-whiteness

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