Deep Freeze

6/16/2017 (Permalink)

DEEP FREEZE

When heavy ice and wet snow coat tree limbs, the layers can be thick enough to break branches, twist limbs and crack tree crowns. Such an ice storm blanketed southern Missouri’s Mark Twain National Forest in 2009, snapping miles of telephone poles, limbs and trees.

After an ice storm or blizzard has passed through a forest, the first order of business is unblocking roads, especially roads that lead to residences, then clearing roads for larger vehicles. “We make sure people are safe first of all,” says Douglas Oliver, the Forest Service district ranger responsible for Mark Twain National Forest’s Poplar Bluff Ranger District. Then, trees are cleared from ditches, and workers ensure there aren’t hazardous trees or limbs dangling over recreation areas.

Similar to hurricane cleanup, timber may need to be salvaged before it rots and becomes worthless — or a breeding ground for pests. When the chainsaws stop, Oliver says, salvage teams have reported hearing swarms of insects boring into the downed wood. Such sheer volume of hungry insects can threaten nearby stands of surviving trees, likely weakened from the ice or wind.

Beyond insects, weakened, still-standing trees are vulnerable to disease and other physiological decline. At Mark Twain National Forest — where tornadoes and a 100-year flood have also occurred in the last five years — many surviving trees are more susceptible to ailments such as oak decline, which has afflicted red and black oak in the eastern U.S.

The summer after an ice storm or blizzard also can bring another danger. The layer of downed tree material can increase wildfire risk if conditions are extremely dry. Such a well-fueled fire could create catastrophic conditions to the point of soil sterilization, Oliver says.

The May 18, 1980 magnitude 5.2 earthquake triggered a major pumice and ash eruption of the volcano. Credit: U.S. Geological Survey

In ice- and snow-damaged areas, trees that sustain light to moderate damage can begin to regenerate within a few years as the forest ecosystem as a whole recovers, but after the worst storms, enough biomass may cover the ground that new seedlings from natural seed banks can’t break through. After the cleanups in the Missouri forest, Oliver says that occasionally forest managers will do supplemental planting — especially if a silviculturist determines the need for more pines, for instance — but many times replanting isn’t necessary, as the forest regenerates on its own in subsequent decades.