The Hydrological Effects of Beetle Kill
Beetle Kill and Water
By Emily Krall
For the many people of Steamboat Springs, a hike through the Routt National Forest evokes a sense of belonging and familiarity. Recently, however, this forest has transformed into a new landscape consumed by the mountain pine beetle epidemic. Along with the pines, the beetles have robbed us of our favorite views and the very idea that Routt forests will continue to serve us in the ways we remember. It is important to be aware that these changes will have positive and negative impacts on the environment we know.
Any hiker can see that the forest is packed with fuel and massive forest fires are a possibility. Fire is a natural process, essential to regenerate a healthy forest. The impact of a fire is entirely dependent on the conditions; some fires are fairly insignificant while others are devastating. A low-temperature fire will not damage soils and is helpful to regenerate vegetation. A high-temperature fire will have more serious effects because it penetrates the soil.
Fires affect the watershed in many ways. A hot-burning fire will create hydrophobic soils caused by a waxy substance derived from plant material burned during a hot fire. The waxy substance penetrates into the soil as a gas and solidifies after it cools, forming a coating around soil particles, making the soil impermeable to water, and thus increasing run-off, depositing sediment into streams, and causing erosion on the land. It will take time for the forest to recover to normal soil conditions, capable of circulating water and supporting plant life. After hot-burning fires, our watersheds may become overwhelmed by sediment deposits and gravel streambeds will be choked with slit. But remember, fire is natural in the ecosystem, and some scientists believe that this reset is essential in renewing aquatic habitats.
Even without a major fire, we can expect the pine beetle to cause changes in the water. Normally, our pines contribute to important aspects of the water cycle called evapotranspiration and interception. As water makes its way from the earth's surface to the atmosphere, some is used by plants and converted into vapor through leaves. In a properly functioning watershed, these plants, or evapotranspirators, are in balance with nearby streams. Interception refers to the water, often in the form of snow, literally intercepted by the tree on its path to the ground. The water is not absorbed by the tree, it is merely a resting point. Interception will not be greatly affected by beetle-kill because dead trees still have surface-area to catch water.
Once the pines are dead, they no longer use water or transpire it into the air. Instead, this water rushes towards the nearest stream. The lack of evapotranspiration will impact water differently depending on whether it is a dry or a wet year. In a wet year, once the soil is saturated, the excess flows away in streams, recharging the ground water and raising the water table. During a dry year, the soil may never reach saturation and less water reaches the streams. Since dead pines don't use any water, more is available for recharging streams and ground water during dry years.
Erosion and sediment deposition in our streams will affect the many riparian species that make-up an aquatic ecosystem. Sediment build-up has the potential to clog tributaries, and change the course of the flow. Trout prefer to spawn in shallow riffles that could be flooded and entrenched by increased run-off. In places where sediment clogs the stream gravel, trout may not be able to spawn. A decreased trout population could negatively impact other riparian species by diminishing food sources for heron, river otters, and other predators that keep watersheds healthy. This is called a positive feedback cycle because an initial cause triggers a series of effects that exacerbate the cause. Ecosystems are fragile and small changes can disrupt all life forms, quickly generating big problems.
As individuals, there are many things we can do to improve the conditions of a watershed. If you have a streamside area laden with dead pines on your property, you can take positive measures. Plant water-friendly trees and shrubs such as cottonwoods and alders. These woody plants can compensate for the evapotranspiration lost from dead pines. Smaller plants, such as sedges and willows, can help keep soil moist and increase bank stability to prevent erosion. Allow beavers to build in the watershed to help filter excess sediment and dissipate flood flows.
What does this hydrologic change mean for the people of Steamboat Springs? No one can predict perfectly how life in the Yampa Valley may change with changes in the hydrologic system. Every piece of the forest is different and can react in various ways and many predictions are hypothetical. Informed citizens are at an advantage, though, to make predictions and preparations for the future. It is our responsibility to learn the facts and explore new options. Perhaps someone will develop a creative way to use extra water productively to benefit our community in the sixty to eighty years it takes the forest to regenerate. While we have lost the battle to the beetle, we have a unique opportunity to use new information to be innovative with our water.
Works Cited
Oliver, Chadwick D., and Bruce C. Larson. Forest Stand Dynamics. Hoboken, NJ: John Wiley and Sons, 1996.
Poppleton, Jayla R. "A Good Intention Gone Wrong." Headwaters (2008): 19-23.
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