Pine beetles: Before and after
September 2, 2011
GRAND LAKE, Colorado – It is amazing that the mountain pine beetle, which is only from one-eighth to one-third inches long, can cause such extensive damage in the lodgepole pine forests of Colorado. The beetle is also called the Black Hills beetle or Rocky Mountain pine beetle and has the scientific name Dendroctonus ponderosae. This beetle will impact ponderosa, limber, and bristlecone pine trees, but the lodgepole pine is the most susceptible.
I worked as a supervisory park ranger naturalist in Rocky Mountain National Park for 15 summers. I often told visitors that many of the lodgepole forests would die off or be burned in our lifetime. Many visitors were shocked by this remark. I told them that the trees were getting old and were being stressed. This would increase the probability of disease, beetles, or fire. Even though I was fully aware that I was telling the visitor what would eventually happen, I have been surprised at the speed of the event and the total area of Colorado that has been impacted. A United States Department of Agriculture Forest Service website is dedicated to this epidemic. (Do a Google search for USDA pine beetle.) A map on that site will show the amazing growth of the problem from 1996 to 2009.
Panoramas of Grand Lake show the impact of the beetle. The first panorama was taken June 11, 2006, from the hillside in front of the Grand Lake Lodge. Grand Lake, the largest and deepest natural lake in Colorado, is on the left and Shadow Mountain Lake is on the right. The purpose of the panorama was to illustrate a topic in my book, “Colorado Mountain Passes.” On Aug. 25, I returned to Grand Lake and reshot the panorama to illustrate the incredible change in the environment caused by the pine beetle in the Grand Lake area. A Google Earth search for Grand Lake also shows the enormity of the outbreak. To say the least, it has been shocking.
The first indication that Colorado was to experience an outbreak was in 1996, though scientists were aware of infestations in the early ’60s. Aerial surveys have estimated that nearly 4 million acres (6,250 square miles) of Colorado lodgepole have been impacted. Summit and Grand counties have probably seen the worst of it. It is estimated that the Vail area will loose 80 percent of the lodgepole trees in the next few years.
Lodgepole pines grow from 6,000 and 11,000 feet in elevation in Colorado. As a species, lodgepole pines are often the first tree to grow back into an area after fire, logging, or major windstorms. It is believe that some of the vast forests of lodgepole in the West may be due to all the logging and fires that occurred as the West was settled more than 100 years ago. Most lodgepole forests in Colorado are between 100 and 300 years of age.
Lodgepole is a sun-loving tree that will not grow in the shade of other trees. The tree shades the forest floor and cannot even grow in its own shade. Spruce and fir can grow in that shade and under the right circumstances can replace the lodgepole as the dominant species. Spruce and fir can grow in their own shade and will perpetuate that forest, unless it is burned. That fire provides the lodgepole the environment they need to return.
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They are often called a fire species because the serotinous cones are protected by a wax that melts and releases seeds only when exposed to fire where the temperature is between 113 and 140 degrees Fahrenheit (45-60 Celsius) and the fire duration is under 12 minutes. Many of the Rocky Mountain lodgepole pine cones may not open at maturity without fire because they are sealed shut by the resinous material between the cone scales. When lodgepoles reforest because of fire, that fire also kills the pine beetles and mistletoe that can infect the tree, giving lodgepoles a better chance of long term survival.
The best way to maintain a lodgepole forest is to allow it to burn, or by clear cutting. This allows sunlight to reach the forest floor. Since the trees are sun lovers they do not have branches on the lower part of the tree. This makes it difficult to pump water and nutrients to the upper part of the tree. Drought conditions and changing temperatures in Colorado may also be impacting the trees. The tree becomes stressed and the ideal conditions for disease and insect infestations are created. (The impact of global warming on these infestations is not fully understood.)
The female beetle lays her eggs under the bark of the lodgepole. The pine beetle larvae eat the inner bark as they develop and that stops the flow of water and nutrients to the upper parts of the tree. There is also a blue-stain in the wood that is created by a fungus carried into the trees by the female beetle. Some researchers believe that the fungus clogs the xylem, or water conducting tissues of the tree, which also leads to the death of the tree. Lodgepole will die within a few months of being hit by large numbers of beetles.
What naturally kills the beetle? Research has shown that cold temperatures can kill the beetles, but the conditions need to be almost perfect. During the winter the beetle is in the larvae stage and actually build up alcohols in their bodies that act as an antifreeze to protect the larvae. That alcohol is at its lowest point in early fall and late spring. If the temperatures drop to negative 13 Fahrenheit to negative 31 Fahrenheit the larvae may die. No one seems to really know what temperatures, for what length, and at what time of year are best for controlling the beetle. In addition, the exposure of the hillside and the depth of snow may impact this scenario.
Historically, populations of pine beetles vary over time. Pine beetles are common in North America and have probably been in our lodgepole ecosystems almost as long as lodgepole pine has existed. There is scientific evidence that the beetles and their epidemic are not at all new. Researchers have found that the level of carbon-13 in a tree’s exuded sap will increase with an epidemic. Working with amber fossils as old as 90 million years, they found an increased presence of carbon 13. These researchers also suggest that insects like the mountain pine beetle may have created two of the world’s largest amber deposits.
Visitors to Colorado forests need to be concerned with a new threat to their safety. The Forest Service recently estimated that 900 miles of trail, 3,200 miles of road, and 21,000 acres of developed recreation sites are in infected lodgepole areas that could create hazards for visitors. Don’t camp under or near red or dead trees! Other problems involve threats to power lines, buildings, other manmade structures, and water sources.
Rick Spitzer, a local photographer, is also a former high school biology teacher, park ranger and technologist. He is the author of ‚”Colorado Mountain Passes: the State’s Most Accessible High Country Roadways,” which is for sale at The Bookworm of Edwards for $23.95.