Day 28: Invader plants grab hold faster than we thought

 

Kudzu. Credit: Forest & Kim Starr, U.S. Geological Survey and Bugwood.org

Once invasive plants enter the picture, they tend to make even quicker work of spreading than we thought.

Curtis Daehler, a botanist at the University of Hawai’i in Honolulu, has reported in the open access journal PLoS ONE this week that plants that aggressively took up residence in Hawaii did so on the order of five to 14 years — instead of half a century or longer, as was previously believed. 

Foresters and ecologists worry about invasives because they crowd out native vegetation, sabotage biological diversity and deprive animals of food sources they’ve evolved to use. The examples are numerous; Invasive.org, a cooperative project of the U.S. Forest Service, the U.S. Department of Agriculture and other partners, lists hundreds. Kudzu is a poster plant for the problem, as is tamarisk (saltcedar) on the banks of rivers in the West. Efforts to control the spread of invasive species cost the federal government more than $100 billion a year. 

Cecropia obtusifolia (left) and Falcataria moluccana are examples of early plantings in the Manoa Valley that became invasive. Credit: E. Caum, December 31, 1922.

Daehler examined historical planting records for Hawai’i's Lyon Arboretum dating back to 1920 to identify 23 plants that have since become invasive pests on the islands. Then, he used the arboretum’s annual reports to determine the lag times between initial plantings of the would-be invaders, and their first recorded spread. 

“Among 23 species that eventually became invasive pests, the average lag time between introduction and first evidence of spread was 14 years for woody plants and 5 years for herbaceous plants,” he wrote.

Daehler acknowledges that plants might spread more slowly in temperate climates, where winters stall them. Still, the news throws cold water on a cause that already seems daunting; just scan the sides of any highway in the eastern US.

To top it off, an Arizona researcher issued a warning earlier this month that — unless we curb our collective yen for imported produce, and get realistic about the risk of imported invasions — the problem is likely to keep on … well, spreading.

Charles Perrings, an environmental economist at Arizona State University in Phoenix, told attendees at the American Association for the Advancement of Science meeting in Chicago last week that the cost of controlling invasives equals 53 percent of agricultural Gross Domestic Product in the United States, 31 percent in the United Kingdom and 48 percent in Australia. His estimate gets steeper for developing nations, putting Brazil in the red, agriculturally speaking, and South Africa nearly so. 

Perring recently published a four-volume treatise called “Ecological Economics,” in which he proposes a solution: thinking locally and acting globally. More specifically, he’s calling for “measures to ‘internalize’ the external costs of trade – to confront exporters and importers with the true cost of their actions.”

But there is also an opportunity for grassroots action: when it comes to produce, buy local. In most cases, shopping at a local farmer’s market reduces the overall carbon footprint of our food. It supports healthy local economies and bolsters our food security. As my own locally-bought honey and blueberries prove, less distance between the farm and the table often translates into better freshness and taste. Finally, by buying from nearby farms, we can reduce the chance that our eating habits will encourage unwanted — and expensive — guests.

Sources: The PLoS study (on Hawai’i invasives), and a Eurekalert press release (Arizona perspective)