Red Willow

Red willow is a riparian native.

Of the few native species that share the same designation of ‘red willow’, Salix lasiandra, is likely the most common locally. However, it has a few other common names, including shining willow and Pacific willow. For those acquainted with it, recognition is easier than nomenclature. It is not a problem though, since red willow is rarely an intentional choice.

Red willows, including less common species, grow wild in local riparian situations. They sometimes sneak into home gardens, particularly if irrigation is generous. Their rampant growth is susceptible to spontaneous limb failure. Pruning can compensate for structural deficiency of young trees. However, trunks typically succumb to decay within thirty years.

Mature trees are mostly less than thirty feet tall, typically with low branches, and possibly with a few elegant trunks. The gray or light brown bark is finely furrowed. The deciduous foliage has a slight sheen, and then turns brownish yellow prior to autumn defoliation. Its narrow leaves are about three inches long. Twigs are yellowish or green rather than red, as it implies.

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. 

Limb Failure Of Spontaneous Nature

Riparian trees notoriously shed limbs spontaneously.

Winter storms sometimes break limbs or topple trees. Such damage is no surprise during winter because that is when almost all windy weather happens here. Early storms during autumn might be more damaging because deciduous trees are less aerodynamic prior to defoliation. Nonetheless, falling trees and limb failure are typically associated with wind.

That is why spontaneous limb failure is such a surprise when it happens, typically during pleasantly mild or warm weather of spring or early summer. It is more likely without wind than with it. Humidity, although atypical here, is a contributing factor. Healthy trees within riparian situations or lawns are more susceptible than distressed trees in drier situations. 

Particular types of trees are more susceptible to spontaneous limb failure as well. Valley oak, coast live oak, sweetgum, carob, some pines and various eucalypti may shed limbs after an unusually rainy winter or an increase of irrigation. Riparian trees, such as willow, cottonwood, box elder and sycamore are notorious for shedding big limbs unexpectedly.

Spontaneous limb failure occurs if limbs are unable to support their own increasing foliar weight. Bloom can add significant weight too. Warmth promotes the vascular activity that increases foliar weight. Humidity and insufficient air circulation inhibit evapotranspiration (evaporation of foliar moisture), which typically compensates for increasing foliar weight.

As the terminology implies, spontaneous limb failure occurs suddenly, and often without warning. It is therefore potentially very dangerous. It is common among limbs that exhibit no prior structural deficiency. Even experienced and educated arborists who are familiar with vulnerable tree species can not identify and mitigate all potentially hazardous limbs. 

Arborists often suggest pruning to limit the weight of trees that are innately susceptible to spontaneous limb failure. However, limbs that are already sagging from their own weight are risky to engage. Most damage occurs in spring and early summer. Fruit trees that are too productive can succumb to the weight of fruit as it ripens through summer or autumn.