The Mountain Pine Beetle and Its Affects on Snowpack Chris Giersch Winter Ecology - Spring 2010 Mountain Research Station – University of Colorado, Boulder

How do the deaths of lodgepole pines due to pine beetles affect snowpack? Hypothesis: A decrease in forest canopy will allow for increased snow accumulation Implications Rate/Amount of Melt (Boon 2007) peak water flow available growing season Animals Avalanche Risk Forest Fire Risk Since 1995, N. Central Colorado has experienced a severe infestation of bark beetles, more specifically the Mountain Pine Beetle, or dendroctonus ponderosae. The beetle damages the tree enough to cut off the flow of water and nutrients and kill the tree. Some argue that climate change is playing a factor because the lack of colder temperatures mid-winter is allowing for increased rates of beetle survival. However, others say that this has happened before and it is just part of a natural cycle such as forest fires. Being a relatively new problem, there is a lack of data on this aspect of beetle-killed lodgepole pines. Some past studies assumed that the hydrologic behavior of beetle-killed stands is equivalent to that of cleared stands. (Boon 2007) However, beetle-killed stands are actually in a transitional phase with significant variations in snow accumulation. The canopy is destroyed in beetle-killed stands as needles and then branches fall to the ground. This deterioration of the canopy alters snow interception, accumulation and melting. (X Enter X)

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Methods Site 1: C1 Sub-alpine forest SW facing aspect 30% Lodgepole Pine 70% other species SW facing aspect My original plan was to dig a trench in between two lodgepole pines, in each a live stand and a dead stand, and analyze multiple points along the trench so to give a more in depth view of changes in snow accumulation and metamorphism. During the first weekend, I attempted to find any lodgepole stands in the C1 area but only had minor luck finding only small groups scattered among other species. Limited by time, this first site served more as a trial site because I was only able to accomplish one trench in the dead stand and one pit in the live stand. Snowpack morphology was analyzed by using snowpits. First, definitive snow layers were identified and marked using a meter stick and zip ties. Next, the thickness, density, and crystal size/shape of each layer was recorded using standard snow kit equipment (including: scale, digital thermometer, meter stick, density scoop, hang lens). Finally, the temperature profile of the layers along with air, surface, and ground temperatures were recorded.

Methods Site 2: Breckenridge Sub-alpine forest E facing aspect 100% Lodgepole Pine E facing aspect During my search for a more suitable site for my second attempt, I was told that the Breckenridge area was one of the worst hit areas in the area. The site I ended up finding was more or less perfect for my research, being 100% lodgepole pine, on an east facing aspect. (One issue was the fact that it was snowing very heavily the entire time I was there.)

Site 1: C1 Increased total snow pack and therefore larger weak layers within the snowpack Similar if not slightly decreases snow density Similar snow hardness throughout the snowpack other than decreased hardness from 20-30 cm

Results - Site 1  Snowpack  Snow Density  Hardness: 20-30 cm

Site 2: Breckenridge Increased overall snowpacks Similar temperature profiles, dead stand slightly warmer Increased middle layer hardness/crust Similar snow densities, dead stand slightly more dense Similar crystal sizes

Results - Site 2  Snowpack  Temperature Profile  Middle Layer Hardness/crust  Snow Density Similar crystal sizes

Discussion  Snow Pack  and  Snow Density  and  Hardness of Mid-Layer  Temperature Profile Similar Crystal Sizes So… now to address my original question: How do the deaths of lodgepole pines due to mountain pine beetles affect snowpack? As expected, there was an increase in overall snowpack in the dead stands. This may ber caused by the decreased interception of snow by destroyed canopies. This deeper snowpack contains weak layers larger than in lesser packs which can increase the risk of avalanche. There was both an increase and decrease in snow density from the two sites. This variation may have something to do with the different aspect of each site, therefore different exposure, which compacts the snowpack more than on leeward, east facing aspects. There was both an increase and decrease in the hardness of a mid-layer from the two sites. On one hand, a destroyed canopy will allow for more solar and IR input therefore allowing for the development of crust layers, but on the other hand, a healthy canopy will drip water, snow, and ice, also causing a crust to form. A loss of canopy results in a less stable environment (ie. reduced drip energy and increased solar and IR inputs) therefore increasing the temperature profile. The crystal sizes and shapes were pretty consistent although there was some slight depth hoar development in the bottom layer of the dead stands at site 2.

British Columbia Study  Bulk Snow Density  Ave. Snowpack Temperatures Temperature gradients steepest in dead stands (Boon 2007) Canopy reduces solar, wind, and IR energy inputs, but increases drip (Boon 2007) Differences in ice layer formation Needle Layers The bulk snow density in the dead stand was less than in all other stands, although it was very close to that of the live stand. (Boon 2007) Temperature gradients in the dead stand became positive (warms to surface) after melt onset, while in the cleared and alive stands they became positive over three weeks earlier. (Boon 2007) This delay in temperature transition could imply a delay of melting therefore making the peak water flow last longer and shorten growing seasons in that area. Similar to my own findings, drip in live stands created an ice layer Several needle layers occurred that did not appear in the live or cleared stands. They affect snow metamorphism and ablation by absorbing and/or re-radiating heat and longwave radiation. (Boon 2007) They also enhance snow melt due to lower albedo and potential to increase longwave re-radiation. (Boon 2007)

References Boon, S. 2007. Snow accumulation and ablation in a beetle-killed pine stand in Northern Interior British Columbia. BC Journal of Ecosystems and Management 8(3):1–13. url: http://www.forrex.org/publications/jem/ISS42/vol8_no3_art1.pdf Received from Wettstein, C. US Forest Service, Bark Beetle Incident Management Organization. Eagle, CO. Feb. 12, 2010. Sorry, I couldn’t figure out how to remove the hyperlink from the citation.