Don’t blame the bark beetles

ELISABETH M. BROWN

On a recent trip to New Mexico, we stayed in a house overlooking a

canyon filled with Pinyon pines. Pinyons don’t have the

Christmas-tree shape of other pines, but have a branching pattern

more typical of trees with leaves. They produce edible pinyon nuts,

otherwise known as pine nuts, in their exceeding sticky pine cones.

Pinyon pines are often found with Juniper bushes, in a community

known as Pinyon-Juniper woodland. It grows in areas so dry that no

other pine can survive. In New Mexico, we passed miles of it between

Santa Fe and Los Alamos, but something was terribly wrong. The

junipers were their usual dark green, but the pinyons were brown.

A friend confirmed that the pinyons were succumbing to a bark

beetle infestation brought on by a four year drought. Bark beetles

and other tree-eating insects are always around, part of the natural

system that prunes out weak and unfit trees. The beetles attack by

boring in through the bark; the tree’s defense is to drown them in

sap. A forester told me that if the sap runs clear from a beetle

entry point, the tree has won; if it’s cloudy, the beetle is in.

During a prolonged drought, the trees can’t produce enough sap to

repel the beetles. In that New Mexico canyon, pinyon trees on the

south-facing (drier) slope were dead. Trees on the wetter,

north-facing slope were still green.

This is tree mortality on a landscape scale: perhaps irreversible

habitat conversion looms. On the south-facing slopes more

drought-tolerant desert shrubs will eventually grow; on the

north-facing slopes, the pinyons may hang on for some time. But a

letter from friends in northern Arizona notes that junipers and even

some prickly pear cactus are dying there.

In the Southwest, this has all happened before. Around AD 1300, an

extended drought forced the Anasazi Indians (the ‘old ones’) to

abandon their cliff dwellings in New Mexico and Arizona when their

crops failed. The people and their culture vanished into the heat

haze.

The same equation holds everywhere: stressed trees plus bark

beetles equals dead and dying pines. About a decade ago, overcrowded

Lodgepole pine forests in Yosemite National Park were hit by a

widespread bark beetle infestation; this was followed a few years

afterward by massive back country fires. Now the forest is regrowing.

In southern California mountains, the drought is having the same

effect on the big Ponderosa pines near Idyllwild and Julian. After

four years of scarce rainfall, huge swaths of mountainside are

covered with dead and dying pines.

The many standing dead trees are a constant fire and safety hazard

within the mountain villages.

On the local coastline we have only one native pine: the few

endangered Torrey Pines in coastal San Diego. Like other coastal

plants, much of their water comes from ocean fogs. Perhaps these

foggy refuges protect the trees from California’s recurring droughts.

I don’t blame the bark beetles for the demise of the pinyons;

they’re just part of what a ranger described as, “the way of the

forest.”

* ELISABETH BROWN is a biologist and the president of Laguna

Greenbelt Inc.