Wood discoloration due to Fusarium dieback. Photo: Eskalen Lab / UC Riverside

By Adam Rogers
9 May 2017

(Wired) – The polyphagous shot hole borer, a brown-black beetle from southeast Asia, never gets bigger than a tenth of an inch. It breeds inside trees; pregnant females drill into trunks to create networks of tunnels where they lay their eggs. The beetles also carry a fungus called Fusarium; it infects the tunnels, and when the eggs hatch, the borer larvae eat the fungus.

Unfortunately Fusarium also disrupts the trees’ ability to transport nutrients and water. Holes where the beetle bored into the tree get infected and form oily lesions. Sometimes sugars from the tree’s sap accumulate in a ring around the hole—that’s called a “sugar volcano.” The tree dies, and the wee baby beetles fly off to continue the circle of disgusting life.

This would just be a scary story for arborists and tree-huggers, except: Fusarium dieback is on track to kill 26.8 million trees across Southern California in the next few years, almost 40 percent of the trees from Los Angeles to the Nevada border and south to Mexico. That’s more than just an aesthetic tragedy. It means that thousands of human beings are going to die, too.

I’m not just being a monkeywrenching fearmonger. Dead trees mean dead people, and scientists are finally starting to figure out why. In the 1990s, spurred by a program to plant half a million trees in Chicago, researchers started trying to quantify the value of a tree beyond the fact that one is, like, at least slightly more lovely than a poem. It’s a field of study today called ecosystem services. “I’ve been trying to quantify the impacts of trees on rainfall interception, pollutants in the atmosphere, cooling and energy used by buildings, CO2 stored and emitted,” says Greg McPherson, a research forester with the US Forest Service who conducted the latest study of SoCal’s trees. “But I think those are the tip of the iceberg.” [more]

All the Trees Will Die, and Then So Will You

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