Posted on by tonytomeo

Redwoods & Gravity

Physics are dangerous!

Sequoia sempervirens, coastal redwood is the Official State Tree of California, and the tallest species of tree in the World. One large specimen can contain more lumber than many acres of Douglas fir (really). While some trees ensnare kites, redwoods collect satellites. Redwood lumber can be delivered anywhere in western North America simply by aiming a tree in the direction of delivery while cutting it down. Redwood shadows reach Japan at dawn and New England at dusk. The moon is covered with craters because it could not dodge the growing redwoods while orbiting over California. You can see for yourself how tall redwoods are just by looking in this direction from wherever you are in the World. Unfortunately though, not all of the debris that falls from the huge canopies of redwoods burns up in the atmosphere on its way down. Such huge canopies generate a lot of debris. Almost all of it is finely textured foliar debris. Some is twiggy detritus. The worst of it are significant branches. The descent of most of such branches is slowed by lower branches and foliage that they encounter on their way down. However, the lowest branches of some canopies are very high up, and falling branches resume acceleration after falling past them. Also, some falling branches fall outside of their canopies. Even branches that weigh only a few pounds can be extremely dangerous. Many falling branches weigh many pounds, and some are as big as trees. The fallen branch in the picture above is only several feet long and about three inches wide, (and happened to fall through the only three inch wide plank in a pedestrian bridge. The replacement plank needed to be custom cut.) I am annoyed by this relatively minor damage, but also relieved that it was not worse.

Posted on by tonytomeo · 4 Comments

Sudden Limb Failure Jeopardizes Safety

Entire trees can also fall unexpectedly.

Windy weather sometimes breaks limbs from trees, or blows entire trees over. Evergreen trees are innately more susceptible to such damage than deciduous trees are. Wind can blow more easily through deciduous trees while they are bare through winter, when most wind occurs. However, deciduous trees are now more susceptible to sudden limb failure. 

Sudden limb failure, or spontaneous limb failure, is a result of gravity rather than of wind. It is actually more likely without wind, during mild or warm weather, particularly with high humidity. It consequently has potential to be more hazardous than limbs that blow down. More people go outside among trees during mild weather, and fewer expect falling limbs. 

Sudden limb failure occurs if limbs become unable to support their own increasing foliar weight. Warmth accelerates vascular activity, which sustains foliar growth. High humidity and a lack of wind inhibit evapotranspiration (evaporation from foliage), which otherwise helps to alleviate excessive weight. Developing fruit can also cause sudden limb failure.

In the wild, willows, poplars, sycamores, and perhaps a few other riparian trees regularly and naturally exhibit partial sudden limb failure. Limbs that fracture and sag onto soil, but remain partially attached to their original tree, can generate roots and grow as new trees. Although their strategy is practical for them, it is unacceptable within refined landscapes. 

Several native and exotic trees of chaparral climate are quite susceptible to sudden limb failure within or adjacent to irrigated landscapes. Since they are not accustomed to such abundant moisture, they overindulge. Mature wild trees are more likely to exhibit sudden limb failure after an unusually rainy and warm winter, or if rain continued late into spring.

All native oaks, particularly valley oak and coast live oak, are susceptible to sudden limb failure. So are Monterey pine and Monterey cypress. Carob, sweetgum, various elm and various eucalypti are exotic species that are notorious for such behavior. Evergreens are more unpredictable, since their new growth is less obvious among their lingering foliage.