Wednesday, July 22, 2009

Utah Field Guide - Lodgepole Pines and how the tiny pine bark beetle is transforming the forests of the American West

Why are the forests dying? I get this question almost every day on my raft when I'm working as a river guide. I guide on the Salmon River near Stanley, Idaho, in the Sawtooth National Recreation Area, one of the prettiest natural settings in the United States. The surroundings are gorgeous, but there's no denying it, the forests around the river are dying. Everywhere you look, you see stands of red (starting to die) and brown (dead) trees clustered together in sad, lifeless clumps.

The die-off isn't limited to Idaho. You'll see it anywhere in the American West where lodgepole pines grow. The entire Rocky Mountain Region is suffering from the blight. Including Utah. The problem is particularly apparent in the Uinta Mountains along the Mirror Lake Highway, where the trees are withering by the hundreds in almost every campground. Who's the killer? And why isn't anyone doing anything about it?

The lodgepole pine forest is being killed by the Rocky Mountain pine bark beetle (Dendroctonus ponderosae). That's right, tiny (1/2 centimeter long) beetles who burrow into the bark of the tree and kill the host from the inside out. In the Western United States and Canada bark beetles have killed 36,000 square miles of forest. Depending on the area, beetles have infested as much as 40% of the lodgepole trees in the forests, and may kill up to 80-90% of the mature trees before they're done. With 90% of the trees dead, the forests will look almost entire devoid of green, living trees.

Isn't there something we can do to stop the beetles? We'll dive into that later. But first lets get a little more familiar with lodgepole pines, how to recognize them, where to find them and why they're such an important part of Utah's mountain ecosystems.

Characteristics: Lodgepole pine trees (pinus contorta) are distinctly recognizable by their rail straight trunks and high thin crowns. Their trunks are popular for traditional fences on western
ranches and are often used to build cabins because they are so consistently straight. Historically in Utah, lodgepoles were used to support mine shafts and for railroad ties. The needles of a lodgepole pines are short (relative to ponderosa pines), about 2 inches long and grow coupled together with other needles. The needles are twisted or contorted, giving the tree its scientific name pinus contorta. The bark is thin and scaly, and ranges in color from orange-brown to gray.

Where to find lodgepole pines:
Lodgepole pines usually grow above 6,000 feet in elevation in mountainous terrain. In Utah lodgepoles pines can be found in the mountains in the northern half of the state. The Uinta Mountains have the largest and most widespread distribution of lodgepole. Stands of these trees will often be associated with a natural disturbance such as fire, or in areas where the forest has been cleared by people. Their cones need extreme heat to release their seeds. In nature this heat is only generated by wildfire, so fire is necessary part of the lifecycle of lodgepole pines. Their niche as the first species to establish after forest fires makes a "pioneer species" playing an important role in forest succession.

Now that we have a feel for what lodgepole pines look like and where they live, lets explore what's happening with the forest and the pine bark beetle.

Pine bark beetle infestation: Pine bark beetles have always been present in the Rocky Mountain environment. The populations ocilate on a boom and bust cycle, much like other insects. The most recent major infestation occurred in 1983. Beetles attack the tree by tunneling into the bark where they lay their eggs. Young larvae mature inside the tree before leaving it to find a new host for the next generation.

What makes this infestation different from previous ones is how large and widespread it is. Biologists believe there are several factors contributing to the scale of this infestation. One factor is the current make-up of the forest. Pine bark beetles only infest mature lodgepole pines. We've already mentioned that lodgepole forests tend to develop in places where there's been some disturbance, whether that be a wildfire, or a man-made, such as logging. The suppression of forest fires may be playing a role in this current cycle. Because there have been less frequent fire events overall in the American West in the last 50-100 years, there are more mature trees in the forest for the bark beetles to attack. This is a result of larger trees not being burned in fires, but also a lack of fires releasing seeds from cones. So, there is effectively more food and habitat for these beetles than during previous cycles. Another contributing factor may be a prolonged and widespread drought. The trees natural defense against the beetle is sap. Trees bleed thick, viscus sap in an effort to flush the beetles out of the their bark and prevent them tunneling into the tree. Drought conditions prevent the trees from producing as much sap, thereby reducing their natural defense system against the beetles. Warmer weather has also aided the beetles in their expansion. Week-long periods of extreme cold weather can kill entire generations of pine beetles, but a long run of warmer winters has allowed the pest to survive.

What can be done about this outbreak? Unfortunately, not much. Typically outbreaks last for one to three decades. A long period of bitter cold temperatures could cause the outbreak to collapse. But much more likely, it'll be matter a the beetles running out of food - meaning most of the trees will be dead.

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