Succulent carpets sporting pale yellow, rich magenta, or light purple flowers blanket the bluffs and hang over the cliffs along the coast of California. Joining oleander and cotoneaster as historic roadside plants, ice plant has been dropped by public works landscapers for many good reasons. Several species of ice plants are quite invasive in parts of California, spreading 3’ a year, wiping out rich assemblages of native plants and changing wildlife communities.
Native Ice Plant??!
When my mentors taught me the native flora, they wanted me to recognize the difference between the ‘native’ and non-native ice plant species. However, the ‘native’ ice plant turned out not to be native, proven by a clever scientist who sleuthed for a pollen record in pond sediment from an ancient pond in Marina, California on the Monterey Bay. The trick is to find an old pond, drill into the sediment with a hollow tube, and pull out a long plug of mud: deeper muck is older. Scientists can reference ash layers from volcanoes in the sediment and use carbon dating of bits of organic matter to index the history in the sediment core. In that pond sediment, they discovered ice plant pollen beginning in the 1800’s and occurring steadily in the pond sediment ever since. That was the age of lots of Old World species’ arrival…a time when invasive grasses and herbs spread rapidly across the landscape. Some species spread faster than the invading people so that the first Old World botanists didn’t know whether something was native or not. How did ice plant get there?
South Africa: Iceplant Home
South Africa is home to many ice plant relatives. That Mediterranean region is a biodiversity hot spot for many interesting plants, including plants in the ice plant family. Many ice plant relatives have stunningly bright colors and thin, reflective petals. There might still be a patch of ice plant relatives in the South African collection at the UCSC Arboretum. When I worked there, I came across that patch on a sunny spring day and was mesmerized by the color, gazing at first one intensely bright color and then the next. Peeling my eyes away from those flowers, I was shocked to find a world of temporarily muted color (a world of gray!). Something in my eyes had been overloaded and it took a while to get normal colors back. Only a few of the South African ice plant relatives have become weedy in California- not to say that more won’t in the future, should they find their way via the nursery trade.
Scurvy is a horrible disease of malnourishment caused by too little Vitamin C. Part of the ‘success’ of the Imperialist British Navy is due to the recognition of the need to pack limes on board ships, earning those sailors the name ‘limeys.’ Some sailors might have been better called ‘iceys’ but that term doesn’t appear in the history books. The term for ice plant seed pods was “Sea Fig,” and the fruit was packed aboard ships to combat scurvy the same way limes did.
Ice plant fruit is ripe when the pods are wrinkly and shriveled, having narrowed from their once plump shiny tautness just after the flower fades. If you try eating one too early, it is very disappointing. Wait a while and you get to enjoy sweet, tart, and salty fruit loop flavor. Like figs, ice plant seeds are on the inside of the fruit, suspended in a sticky, stretchy slightly slimy gelatinous goo- that’s the tasty stuff to harvest out of the pods. I am pretty picky about where to harvest the fruits because of what I’ve seen dogs do on ice plant carpets. The biggest flowering of ice plant is under way now, so you have to wait a while for the pods to ripen.
Us bipeds aren’t the only ones who like the ice plant fruit- they are favored food for all sorts of small mammals. The moisture in the fruit might be attractive, but the protein-rich seeds are nutritious – so much so that all that food elevates small mammal populations above what might normally occur. Ground squirrel, rat, and rabbit numbers increase, and herds of these animals scurry into areas surrounding the ice plant patches and graze down native vegetation, making way for still more ice plant with seeds dispersed in the critters’ poop. Sit on some of the large cliff-erosion combating rock piles near West Cliff’s ice plant carpets some evening and watch the cracks between the rocks. You will probably get to see part of that ice-plant fed thriving rat population.
Salting the Earth
Feeding the ice plant gardening small animals is one way that the plant is clever, but there’s an even more genius method of invasion: salt. Ice plant is very salt tolerant. As it grows it concentrates salts in the soil under it, creating more saline conditions than much of the native ocean bluff flora can tolerate.
As I mentioned above, there once was a fondness for ice plant for stabilizing soil along roads and railroads. Many older readers probably recall ice plant lined roads; CalTrans maintained at least 6,000 acres of ice plant in the 1970s. Native plant enthusiasts never really liked that ice plant landscaping, long recognizing the species’ invasibility, and so they rejoiced when an iceplant pest made it to the New World and started killing ice plant patches. The scale insect was taking a serious toll on highway and railroad plantings, and native plant conservationists were transporting sick ice plant to new areas to spread the pest. Others regarded the pest with disdain, and they ended up winning. Cal Trans funded and UC Berkeley launched a biological control program to fight the ice plant pest. UC researchers found a few species of wasps that controlled the scale insects and released those wasps in masses. The wasps established and now control the ice plant destroying pest.
Don’t worry: ice plant is controllable! Volunteers for the California Native Plant Society and other groups have embarked on ice plant pulling sprees to protect particularly rich areas of dunes and ocean bluffs. While the plants are quite heavy, they aren’t particularly well rooted, so are easy to yank. Pulled up parts of the plants are piled high and slowly decompose. You have to keep coming back to make sure some of the piled plants don’t re-root, but that follow up work isn’t very hard. And, one typically finds a few plants that were so small they got missed the first time pulling in an area. Ice plant is easy to recognize, so you might get to know it and pull it when it is out of place. Turn a pulled plant upside down, roots in the air, and it will probably die. After a while, the bare patches left from pulling ice plant might grow native plants. Often, old patches of ice plant leave behind a thick carpet of dead leaves and salty soil that takes some time to get back to something that can support native plant species. Hopefully, this essay will help prevent more people from planting ice plant in new places!
-post originally published at Bruce Bratton’s online weekly.