What is Flora Grottensis all about?
In 2005, I undertook a botanical survey within 1km square (monad) at the heart of the city of Geneva. The monade surveyed was 118000 499000 with the Swiss grid system. It is centred on the area called Les Grottes, hence the name of this project: Flora of Les Grottes, but in made-up Latin.
The aim of this survey was to record all species present, to estimate their abundance and to identify locations and habitats where floristic biodiversity was highest within the urban matrix.
What species did I encounter and how many?
There is an exceptional diversity within this monad! And the area does not seem to be particularly richer than any other I have visited in the City of Geneva.
I recorded 313 species, 100 of which were only present at one location, 55 at two locations, 32 at three locations and 126 at four locations of more. Eleven native species were either Vulnerable or Endanged at the (Swiss) national level according to the IUCN criteria (Swiss Red List 2002) (Fumaria capreolata, Heliotropium europaeum, Kickxia elatine, Kickxia spuria, Minuartia hybrida, Picris echioides, Polycarpon tetraphyllum, Ruta graveolens, Stachys annua, Thlaspi alliaceum, Verbascum blattaria).
Nine neophytes had the same IUCN status (Coronopus didymus, Datura stramonium, Euphorbia prostrata, Herniaria hirsuta, Lepidium graminifolium, Mentha spicata, Quercus ilex, Silybum marianum, Torilis nodosa) and there were many other unusual floristic findings, such as Bromus tectorum (see list below).
Seven species recorded were also stated as Vulnerable or Endangered in the 2006 Geneva red list by Lambelet-Haueter and colleagues: Acinos arvensis, Bromus tectorum, Buglossoides arvensis, Medicago minima, Herniaria hirsuta, Hernaria glabra and Lepidium graminifolium.
What areas had high plant biodiversity?
Brownfields (waste grounds) and parks were the ‘hottest’ biodiversity hotspots within the monade, in particular: gravely areas and car parks near the station and Park Beaulieu, Park Geisendorf and Park des Cropettes. Also, courtyards between blocks (e.g. square Spon, Schtroumpfs) and public spaces around large institutional buildings (e.g. Cathedral Notre Dame, Engineering School) had a high score in unusual species. These hotspots were calculated by only including scarce species within the monade (three or less populations observed).
Looking at species only found at one location within the monade, the area near the station was by far the richest of all, with 21 species including: Acinos arvensis, Bromus tectorum, Buglossoides arvensis, Cerastium semidecandrum, Medicago minima, Silybum marianum, to mention a few.
All hotspots appear to be places where there is more surface area that can be colonised by vegetation. This makes sense in that we are more likely to find more species in larger area. However, I was fascinated to experience how very artificial habitats (e.g. car park) can be as species-rich, or even richer than more natural habitats (grassland and woodland in parks).
The recording was a combination of opportunistic observation in the monade (where I was living at the time) and full days of systematic recording. Systematic recording days covered every place with public access within the monade. The location of every plant species population was recorded for up to three distinct locations. Frequency of species that could be found at more than three locations was estimated as either ‘abundant’ or ‘very abundant’ at the end of the field season.
One difficulty encountered was to exclude deliberately planted herbs and trees, while including all self-sown and spontaneous individual. Spontaneous seedlings of ornamental trees were included despite not knowing whether they had the potential of reaching maturity. Well established population of spring bulbs such as Crocus and Eranthis were included as well although they are likely to have been planted in the first place. Otherwise, the populations included are all spontaneous and self-sustaining as far as it could be told.
Identifications followed Aeschimann and Burdet’s Flore de la Suisse (second edition, 1994) and nomenclature Lauber and Wagner’s Flora Helvetica (second edition, in French)