The Eucalyptus is primarily grown in California as a ornamental shade tree. It grows very fast and needs little water. But not everyone in California loves the tree. Some people don’t like the smell, and in an areas where wildfires have become a concern, it is highly combustible. Some varieties can get out of hand in wet swampy areas, and force out indigenous plant species.
|Karen Winters' rendition of a Eucalyptus (from her artistic site)|
Native only to Australia, a number of predatory bugs that specialize in using the Eucalyptus as a food source have arrived in wave. Some note that air traffic has increased from Southern California to Australia, and believe that this is the cause of the pests.
Others have become suspicious and are crying foul. Timothy Paine is one of the few researches in the State who has been active in combating all these foreign pests. He has published his suspicions.
Paine [with Jocelyn Millar and Kent Daane] finally published the paper, Accumulation of Pest Insects on Eucalyptus in California: Random Process or Smoking Gun, in the Journal of Economic Entomology…
Paine outlines the patterns. First, the introductions, which his team traced to between 1983 and 2008, were all—bar one—first detected in southern California, either in Los Angeles County or Orange County. If it was accidental—through the movement of goods or people—we would have expected more in the northern part of the state, says Paine. The Port of Oakland in the San Francisco Bay Area is one of the busiest container shipping ports in the country, rivaling the Port of Long Beach near Los Angeles. And while San Francisco’s international airport is smaller than Los Angeles International, it is also a large entry point for passengers and air cargo.
Second, the introductions have occurred in bunches: year-long periods of time when up to four insects would appear followed by lulls of several years before another wave. It’s a pattern that would be consistent with a villain making periodic trips to Australia to gather pests. Paine identifies four distinct periods of multiple species arriving: 1983-84 saw three; 1990-91 saw two; another four arrived in 1994-95; followed by three in 1998-99. The clusters then peter out with a single species in 2000, one in 2003, and two more in 2008.
Grouping the pests by their native range in Australia shows those in each cluster could all have come from the same east coast state, conceivably facilitating easier collection. Pests in the first cluster all occur together in Queensland, pests in the second in New South Wales and South Australia, pests in the third across all three of those states, while pests in the fourth bunch occur together only in New South Wales.
There are other patterns too. The blue gum and the red gum, the two eucalyptus species regarded as invasive, are particularly susceptible to the pests. Indicating the introductions are from Australia, most of the pests also seem to appear in California first before spreading to eucalyptus in other parts of the world. Seven are found only in the two locations.
The nursery-landscaping trade, the main users of the tree, raise them locally from seed, so they are an unlikely source of infestation. You can see in the comment sections, that some people have suspected local eco-nativists of sabotaging the ornamental plants in the San Francisco area.
The warning is not particularly that we will lose our imported ornamental trees. I have my own list of ornamental trees that are so common as to be weed-like, and very hard to get rid of once they get hold.
The warning is that it is easy. You do need to know a little bit about what you are doing, but it doesn’t take an expert. Probably reading the periodicals about eradicating the pest in its native range would be sufficient education as to how to import many of them.
If food crops were to become involved, accidentally or otherwise, the results could be disastrous. One of the earlier post-war successful apocalyptic-catastrophe novels, did not involve humans: it involved plants: John Christopher's No Blade of Grass.