Stop No. 02 Cracks in a wall and interstices in paving stones as a living space of “Hinterm Zwinger”

Explore the little alleyway near the “stork’s well”, which leads from the Kurt-Schumacher-Park past the inner and outer town wall to the old town.

Interstices in natural stone walls and paving stones serve as living space for myriads of plants and animals. Unfortunately, humans become aware of these biotopes only when they are bothered by them and, in consequence, try to get rid of them with the help of pesticides and high-pressure water blasters. However, it is worth looking closely at this microcosm’s diversity within the interstices.

 

You cannot win against concrete

Between the shadows of the interstices there is neither moss nor summer,

The children are left bereft of their voices:

Languishing is silent. (Elke Oertgen)

 

You can find these particular biotopes between natural stone walls or in places and streets paved with cobblestone. Many of the plants which are able to survive in this stark environment are rather small and inconspicuous: small ferns, lichens, mosses, herbs such as the ivy-leaved toadflax or the smooth rupturewort, and weeds such as meadow grass form a downy green between the interstices – if the plants are left in peace. Some plants are even named after their exposed location: the Greater Plantain or the Wall Pepper.

Nonetheless, conditions could not be any harsher. All of the leaves, blossoms, or stalks jutting out from the interstices are in constant danger of being damaged by passing cars or humans. Moreover, interstices provide only a limited space for growth. In case of rain, water seeps through interstices only slowly, thus ‘drowning’ the plants. In the summer, the plants must endure a sweltering heat. In the winter, the interstices are covered by snow, ice, or, in a worst case scenario, thawing salt.

The plants must meet these conditions with particular survival strategies: their survival and reproduction are secured by highly adapted regenerative properties, elastic and resistant tissues, small size, and a long flowering time. Many of the interstices’ inhabitants are annuals: they live for a season only. Their seeds are so resistant that they are able live through hard times and, in case of improvement, can begin to germinate quickly. Other plants such as mosses are even able to survive with an almost neutral metabolic rate and without any loss of energy. Although some mosses dry up in the summer, they are nevertheless ready to soak themselves full in case of rain or other improving conditions.

In most cases, the “wallflowers” have all the nutrients they need. Nutrients may be supplied by rain, inorganic mineral salts in plaster, dust, and dog waste.

Fauna is dominated by invertebrates such as insects, spiders, and small crustaceans. Surely some walls could serve as both feeding place and nesting place for birds, mice, or bats. However, interstices and holes are diligently pointed and thus only inhabitable for small creatures such as woodlice, daddy longlegs spiders, or jumping spiders. From time to time, you might encounter snails, ants, or stone mites.

Plants growing on sidewalks or interstices are regarded as ‘weed’ and are considered untidy and ugly. But is green in the midst of all this grey really that big a deal? Walls with a good static equilibrium are not bothered by moss, lichen, or other vegetation in interstices. They are able to stand the test of hundreds of years without a decrease of stability. Surface gaps in the structure of interstices are not a problem as well.

Schneider, Association of Nature Conservation: Jürgen Holl