A couple issues that have headlined the news across the state in recent years have had to do the mountain pine beetle (MPB) Dendroctonus ponderosae, and Sudden Aspen Decline. Unfortunately there are many misconceptions about both these issues.
First of all the mountain pine beetle is native to Colorado, and plays a very important role in the natural ecosystem of our forest. MPB often kill large numbers of trees that are not growing vigorously due to old age, over crowding, poor growing conditions, drought, fire or mechanical damage, root disease and other causes.
Currently more than one million Coloradans live in proximity to 6 million acres of forest at high risk to wildfires. Over the last hundred years we have created a forest that the state of Colorado that has never seen before, due to fire suppression. We have created a weak, overcrowded, old forest that is now susceptible to mass beetle attacks. Our forests need diversity in age and structure. This will result in a healthy forest that will be more resilient and, thus, less vulnerable to the MPB. Most mature Colorado forests have twice as many trees per acre as those forests which are most resistant to the MPB. Essentially, the MPB epidemic is Mother Nature’s way of taking care of itself. The MPB has stepped in and taken the role that fire used to play in keeping diversity in the age and structure of our forest.
This leads us to Sudden Aspen Decline (SAD). Rapid mortality of aspens has been observed across much of SW Colorado since 2004. Adding to the concern, regeneration appears to be sparse especially in our stands at lower elevations.
There are approximately 3.6 million acres of aspens in Colorado, more than any other western state. Aspens are generally considered to be mature at 100 years of age, in the wild, 20 years of age for a landscape specimen. The average age of Colorado’s Aspen stands is about 120 years. Over 70% of our Aspen stands are over 110 years, and less than 2% of our stands are 70 years old or younger.
There are two primary factors associated with the SAD. The first factor is the drought we have struggled through. In 2002 Colorado had its lowest precipitation rate in more than a century receiving only 60% of the average rain and snow. The second factor is the lack of stand diversity and the fact that most of the aspens in Colorado are generally older. Drought and stand maturation, followed by secondary factors of disease and insects caused further decline and mortality within our stands on a wide spread scale.
In Conclusion, the MPB and SAD are moving into the Roaring Fork Valley probably more rapidly than we all would like to believe. These problems will have drastic impacts on our national forest and our residential landscapes. One thing we need to be conscious about is the health of the plant material in these areas. A healthy tree is the best defense against the MPB & SAD. To keep your Aspen, Pine, and Spruce healthy and resistant, we recommend spring fertilization on all your trees that have been planted for more than a year (use Fertilome Tree and Shrub Food or Fox Farm All purpose food) Also, on trees that have high value in your landscape we recommend a systemic insecticide, applied as a soil drench treatment in spring and fall. Bayer’s’ Tree and Shrub Protect and Feed or Tree and Shrub Insect Control have been shown to have good results.