Of Rocks and Flowers
Nurse logs are a well known forest feature. Lesser known are nurse buildings, where the structure provides a good home for plants to grow. Consider Rome’s Colosseum as perhaps the finest example. In 1855, an erudite English chap named Richard Deakin published The Flora of the Colosseum, in which he described 420 species festooning the walls of the great structure. (He was also a bit of a bloodthristy, writing favorably of the “noble and graceful animals” who tore “each other to pieces” and made meals of “numberless human beings.”)
Filled with wonderful drawings, The Flora is a delight to read. Like the best interpretive writing, Deakin delves into history and science, giving each plant a story and something for the inquisitive botanist to discover. For example, said plant lover could find cures for dysentery, gout, and rheumatism; learn that she could dine on the Colosseum’s strawberries, lettuce, onions, and asparagus: and alleviate the effects of “too great potations” of wine. If you are interested in testing Deakin’s hangover cure, all you have to do is find some Hedera helix, better known as English ivy.
The nursery-like environment of the Colosseum is due to its travertine building blocks. Travertine is a type of limestone that forms in hot springs and tends to be pockmarked with abundant cavities, which provide splendid habitat for seeds to accumulate and germinate. Quarried about 50 miles east of Rome in Tivoli (formerly Tiburtino, hence the name), the travertine is about 80,000 to 120,000 years old.
Alas, archaeologists in the 1870s recognized how damaging plants were to the structure and stripped the green mantle. Diversity also decreased with the loss of grazing animals and their contributions to soil fertility. But plants are persistent and a 2002 floristic study reported that alien species, particularly those associated with humans, have flourished. The 2002 study described 242 species, and a total of 684 species recorded in the Colosseum, mainly composites, grasses, and legumes.
While writing on my book Stories in Stone, I had the good fortune to encounter another nurse building, in St. Augustine, Florida. Started in 1672 and finished in 1695, the Castillo de San Marcos was built by the Spanish and is the oldest fort in the United States. It is now owned by the National Park Service.
Fire, tide, and decay destroyed the ten previous forts in St. Augustine, leading the Spanish to seek a more resistant building material. Located in a region decidedly devoid of really hard things, the Spanish turned to their local, so-called rock, coquina (ko-KEE-na). For those not familiar with coquina, it’s a sort of rock-in-the-making with the texture of a granola bar, except that shells, broken and whole, have replaced the oats. The Florida coquina (around 110,000 years old) turned out to be an ideal choice because it is so soft and semi-ductile that cannonballs fired at the fort either bounced off or sank into the rock, and no one ever successfully overran the Castillo.
Plants though have successfully had their way with the coquina. A botanical survey conducted in 2003 and 2004 found 56 plant species, ranging from moss to elm, growing on the coquina walls. Cyanobacteria, nematodes, fungi, and diatoms have also established themselves on the cozy coquina miniforest.
My favorite place to see the plants was in the dry moat, where hanging gardens rife with ferns, grasses, and forbs dotted the walls. Found every 30 feet or so, the little gardens occur wherever water drips from scuppers that drain the courtyard roof. Back in the 1930s, the park service used to maintain an interior “fern room” almost completely covered in maidenhair fern. Now, only a few ferns grow in this room.
Like travertine, coquina has a holey texture, and plenty of calcite, where water and seeds accumulate and form a nursery-like environment. Despite the beauty of the flowers, maintenance workers at the Castillo constantly pull out the plants by hand. They don’t want the roots to get established and weaken the fort. Cleaning the walls of plants takes about six months, though workers can’t get it all clean, which pleases plant lovers like me.
In Seattle, I know of a few nurse buildings and structures with a handful of plants, such as stinky bob and blackberry growing in the cracks of one wall or fireweed on a ledge. Another flora-filled building I like is the F5 in downtown with its fabric wall of plants, including azaleas, ferns, and junipers. (Coincidentally, the building incorporates travertine from the same quarries as supplied the Colosseum though they are not cut to highlight the holes, which means no plants have colonized the F5’s building stones.)
I wish more builders would emulate the F5’s designers and create living walls. They certainly add grace to the building and provide some nice and nifty habitat in the overly inhospitable urban cityscape. If builders don’t want to go to that effort to create green space, then benign neglect always works well and the plants will do the rest.
I am also honored and humbled to write that Homewaters is an award winner from Nautilus Book Awards. It is in the Ecology and Environment category. I’d also like to congratulate my pals Lyanda Haupt and Lynda Mapes for also being Nautilus Award winners.
Word of the Week - Festoon - Originally a reference to a garland of flowers hanging in a curve but now also used to mean to decorate or adorn. Festoon comes from the Latin festa, or feast, and the garland received its name from its use in feasts.