Snow Damages Foothill Oaks

In the middle of February, a cold arctic storm swept through California, dumping record amounts of snow in the Northern California Sierra Foothills. Low elevation areas that may go 10 years without a trace of snow were inundated with 6 or more inches of snow. While the snow was a delight for local children, it caused tremendous damage to native oak trees. Many were broken or uprooted, which in turn resulted in widespread power outages as hundreds of lines were downed by falling limbs.

The trees most severely affected were the live oaks. Their leafy canopies tended to hold and support the snow until the weight became too great. As they broke, sharp cracks sounding like gunshots echoed through the hills. The deciduous oaks, on the other hand, were generally spared since they had not yet leafed out and the snow fell through their bare branches to the ground.

The greatest damage appeared to be at low- to mid-elevations, between 500-1500 feet. The snow tended to be fairly wet and heavy in this zone and these trees were especially vulnerable to snow damage, compared to those at higher elevations. In regions where snowfall is exceedingly rare, there is little selective pressure or adaptive advantage for trees to develop resistance to snow damage.

As summer approaches, one of the most frightening consequences of the damage is the increased threat of fire associated with this huge volume of highly combustible material. Dead, broken branches are not only much easier to ignite, they also burn much hotter than living trees, making it more difficult to control fires that do get started. The California Department of Forestry and Fire Protection has advised people to clean this material up, especially near buildings and roads, but in many steep remote areas this is clearly impossible. One can only hope the 1990 fire season will not be as bad as is currently predicted.

Aside from the increased fire danger, the damage to oak trees may have other consequences also. The total acorn production in the region should be reduced, adversely affecting wildlife species such as deer, acorn woodpeckers and squirrels which rely heavily on acorns as a food source. Conversely the gaps created by down trees in dense live oak thickets may encourage use by some bird species since these scattered openings will result in more herbaceous production and a greater number of insects. The greater amount of down woody materials should also benefit some species of amphibians and reptiles.

Although many mature trees were felled by this ìonce-in-50-years storm,î the result will not last forever. Live oaks are vigorous sprouters, and most of the trees that were broken near their bases (but not uprooted) will grow new shoots along the remaining trunk. In time, these will grow back to form a new generation of trees.

prepared and edited by John M. Harper, Richard B. Standiford, and John W. LeBlanc