2010 ice storm: Tree damage requires immediate study

By Glenn Patrick Juday, Professor of Forest Ecology and Director of the Tree Ring Lab, UAF School of Natural Resources and Agricultural Sciences, and researcher at Bonanza Creek Experimental Forest since the 1970s.

Alaska experienced a historic warm weather anomaly Nov. 22-24, 2010. Much of the Alaska boreal region and even parts of the Arctic experienced a steady rain, which totaled nearly 10 percent of the annual water budget at Fairbanks International Airport. At one point the freezing level was at 6,000 feet elevation, an exceptional mass of warm air for the Arctic only a month from the winter solstice, and unprecedented since at least the mid-20th century. During much of the rain/ice event the precipitation was not supercooled water, which freezes on contact, but ordinary rain. But as the freezing level varied during the course of the storm, many locations received freezing rain that led to the buildup of an ice layer on tree branches. Even during the ordinary liquid rain period some cold surfaces with high mass (the ground, tree trunks, etc.) quickly froze the water that touched them and formed a frozen layer.

On Dec. 16 I traveled with Brian Charlton, research technician for Bonanza Creek Experimental Forest to look at the effects of the rain/ice event. We drove Bonanza Creek Road to the base of the bluff and out the ridge road. I took 140 pictures. Some trees were coated with 0.5 to 1.0 cm of ice on what were the uppermost fine branches of the crown. Snapped upper branches are widespread. Some snapped tree tops can be seen, but mainstem breakage is relatively light to moderate for such an event. Some large tree boles are heavily ice coated. The Bonanza Creek Road is heavily obstructed, although not blocked, by bent tree crowns.

Overall, at this point we can say that the event was (1) widespread, (2) spatially patchy and variable, (3) disproportionate in its effect on tree species.

(1) Widespread. The weather system that caused the late November rain was general across northern mainland Alaska, from Anchorage to at least the south slopes of the Brooks Range (Bettles station), and from eastern interior Alaska (Eagle station) to western Alaska stations such as Nome. Damage to trees can be seen (patchily) from Fairbanks to well beyond BCEF to the west. Reports are still being collected, but there is no reason to believe that the effects were confined to a small area.

(2) Spatially patchy and variable. Within the transect examined (Parks Highway/Bonanza Creek Road) patches of one to several acres of severe tree bending and snapped tree tops are common, but larger areas of heavy to light ice coating with only light amounts bending are present. While a majority of the forest landscape contained trees with only snow and light ice in tree crowns and branches, damaged trees are well distributed within the region. In general, damaged trees are more severe and widespread the higher the elevation.

(3) Disproportionate effect on tree species. Where heavy ice coating occurred, Alaska birch are disproportionately bent or snapped compared to spruces or aspen, and by a large margin. Canopy dominant white spruce, within the area examined, are relatively free of obvious major damage, but breakage and bending can be observed. Some areas of light to moderate aspen damage occurred.

The November 2010 ice storm killed and severely damaged trees across a large cumulative area. Growth of surviving damaged trees will be reduced for years to come. The ability of trees to defend themselves against insect attack has been reduced. In the recent past major insect outbreaks, which further kill and damage trees, have occurred following such mechanical tree damage under appropriate weather conditions. Foresters need a quantitative estimate of the amount of tree death, reduction in tree growth, and insect and disease events that will follow this event, particularly now that biomass energy projects have created a significant demand for wood. Measurements can also assist forest health, wildland fire, and wildlife habitat management.

Two major research facilities particularly suitable for the needed work are available in the Bonanza Creek Experimental Forest, a state-owned property leased by the USDA Forest Service in the process of being transferred to the University of Alaska. (1) The Densmore Tree Regeneration Installation (DTRI) is one of the oldest and largest forest regeneration experiments in boreal North America, and was established by direct appropriation from the Alaska Legislature in 1985 following the Rosie Creek Fire. Measurements of effects in DTRI will represent forests managed for wood production. (2) Effects of the ice storm in forests of natural origin can be measured in the network of seven hectare-scale Reference Monitoring Stands (RMS) covering the main Interior Alaska forest types. In a cooperative project with USGS the RMS and DTRI were geo-registered at high precision in 2007 and 2008, and enhanced monitoring activity was carried out in the hectare reference stands, including digital photos at permanent photo points three times yearly and close scale aerial photos. These will allow the effects of the ice storm to be definitively identified compared to all other changes. Finally, the UAF Tree Ring Laboratory has an extensive set of tree growth measurements that allow the background level of tree growth to be determined, so the departure from “normal” conditions can be quantified.

My goals are to measure the level of tree death and damage and establish new reference stands in damaged areas as needed, measure tree growth in 2011 and 2012 and calculate the quantitative effect of the ice storm in reducing growth, and to monitor damaged stands for insect and disease problems in 2011 and 2012.

I believe that we need to be able to document the effects of this powerful and potentially decisive warm weather anomaly. Environmental change in our part of the world is unfolding and in fact accelerating and in my opinion this event is simply a requirement for research to adapt.

(Above photos of the icy trees in Bonanza Creek Experimental Forest were taken by Glenn Juday.)

Related reading:

November ice storm could put trees in Alaska in peril for years, Fairbanks Daily News-Miner, Jan. 9, 2011, by Jeff Richardson