Park & Recreation work crew at Sunset Cliffs last month
The California gold rush didn't only bring myriad fortune-seeking people to the Golden State. It also brought trees. Specifically, an Australian species very familiar to anyone who lives in San Diego: the eucalyptus.
However, nearly as common a sight as the tall trees of peeling light gray bark are the stumps of eucalyptus trees left behind by attempts to get rid of them. A few new stumps were added to the landscape at Sunset Cliffs Natural Park last month, where a Park & Recreation crew brought down several dead or dying eucalypti, part of a growing grove of stumps amid trees that have found the park a great place to flourish.
Flourish may be an understatement. Actually, eucalyptus trees tend to dominate the soil wherever they grow. According to Mike Marika, the city's park arborist, eucalypti are particularly adept at negative allelopathy, the "inhibition of the growth of one plant by another, usually through chemical compounds released into the soil environment." In other words, they literally try to stop other trees from growing around them.
They're also tolerant of higher levels of salinity than most trees, which explains why so many found purchase beside the fragile sandstone cliffs that give Sunset Cliffs park its name.
Recently fallen tree at Grape Street Dog Park
Problem is, like the cliffs themselves, eucalypti tend to fall apart unpredictably, throwing branches and in some cases toppling over in high winds, or by caprice. Several instances of this were recently witnessed at Grape Street Dog Park, including branches up to 20 feet long and approximately a foot in diameter.
Eucalypti boast dense, resinous wood, so when they fall, they fall hard. While decades-old trees, grown from seed, may possess great durability, young trees do not, and according to Marika, can grow exceedingly fast, up to ten feet per year. Furthermore, eucalypti may grow from root sprouts, producing trees that tend to be less structurally sound. He says this is the case with many eucalyptus trees found around city parks, a result of many of the so-called "nuisance" trees being felled decades ago.
"The trees were cut down, the brush removed, the wood was hauled away, and the root stumps were forgotten about," he says, "only to sprout back, forming weakly attached, poorly structured trees prone to failure at an unpredictable time." He adds, "These maturing trees should be pruned biannually or at least looked at by someone who is familiar with their growth and nuances."
Granted, eucalypti aren't alone in requiring such attention. Just as many park resources are routinely used to trim palm trees (another nonnative species), and during a recent spate of high winds, Marika says a number of ficus, pine, and silk oak also lost branches.
As for the recently cut trees at Sunset Cliffs, parks district manager Daniel Daneri speculates the recent cuttings may be due to a beetle called the longhorn borer, which also hails from Australia and thrives on the eucalyptus, with infestation leading to a greater chance of collapse and lost limbs.
Exacerbating this problem, according to information provided by the Statewide Integrated Pest Management Program at UC Davis, is that such beetles tend to be attracted by "Freshly cut wood, dying limbs, and trees suffering from stress, especially drought stress."
Like the drought we're in. Marika says longhorn borers aren't typically found so near the coast, though their presence in the region has been documented for years.
Daneri says park supervisors have the authority to cut noticeably dead or dying trees. In fact, the Sunset Cliffs Natural Park Master Plan, issued in July 2005, calls for the "eradication of exotic invasive plants and a revegetation program for restoring native vegetation."
Which means, eventually, the eucalyptus trees of Sunset Cliffs should disappear altogether. As long as the stumps don't grow back.