Naturespeak 

"Mountain Pine Beetle

An unwelcome newcomer to Whistler

By Jack Souther,

Whistler Naturalists

Below our camp, high in the Ilgachuz Range, the Chilcotin Plateau spread out like a giant patchwork quilt – the different shades of green reflecting the ages of trees within the vast forest of lodgepole pine that covers much of central British Columbia. Here and there the pattern was broken by the geometric outline of a cut-block or the irregular footprint of a past forest fire. But within the living forest the reddish-brown skeletons of dead trees were alarmingly common.

On our first helicopter flights inland from Bella Coola we saw only clumps of a few dead trees, a year later larger patches of an acre or two, and finally, when I was wrapping up my five-year study of the Ilgachuz Range volcano, the plateau was scarred by stands of dead forest a kilometre or more across.

That was 10 years ago. Since then those reddish-brown patches have spread and coalesced like a cancer until today the dead, beetle-killed, forest in central B.C. covers an area almost four times the size of Vancouver Island.

The damage wrought by the Mountain Pine Beetle ( Dendroctonus ponderosae ) is out of all proportion to the size of the creature itself. Only 3 or 4 mm long, the tiny bug begins its cycle of destruction in late summer by boring through the thin outer bark and chewing out egg chambers in the soft cambium beneath. They bring with them spores of the Bluestain Fungi which discolours the wood and reduces the timber value of infected trees. Once established, the early arrivals release pheromones to attract more beetles and an orgy of reproduction ensues.

Their voracious, grub-like larvae, plus the fungal infection, girdle and kill the tree. By the time the dying tree begins to redden, the generation of beetles that killed it is long gone. The larvae mature and fly off as adults in search of the next unlucky host.

Lodgepole pine is the tree of choice, particularly mature trees more than 25 centimetres in diameter. In B.C. decades of successful fire suppression have resulted in vast uniform, monocultures of these susceptible trees. With nothing to interrupt their dispersal the beetles can quickly wreck havoc on a whole forest. And according to local forester Don MacLaurin, the beetle has not only arrived in Whistler, it has adapted to our younger forests and is now attacking immature trees. Controlling their spread by cutting and burning infected trees is going to involve some tough decisions and a lot of co-operation from property owners.

Apart from forest fires, and the resulting diversity of tree ages and species, the only effective natural control of these bugs is cold. According to the Canadian Forest Service it will take two consecutive winters of extreme cold to kill enough larvae to halt the present epidemic. So far this sure isn't one of them! If the trend continues I question how long the stands of lodgepole pine on the benchlands of the Sea to Sky corridor can survive.

Upcoming events

Saturday, March 1 — Monthly Bird Count. Meet Michael Thompson at the bottom of Lorimer Road at 8 a.m.

Thursday, March 27 — Monthly Speaker Series; Killer Whales. John Ford will be at Millennium Place talking about Orca behaviour and biology

For more information on the Whistler Naturalists, contact Veronica Sommerville at: whistlernaturalists@canada.com

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