Redwood Top Die-back

July 17, 2005

(break in the carbon series to respond to a question, what is the cause of redwood top dieback?)

Throughout the redwood region redwood tops occasionally dieback. A green live top will turn brown, lose its needles and all that remains is a brown stem and lateral branches. The tree may or may not grow another top from this persistent weak spot. The dead top will sometimes break out and the tree becomes a flat top. Trees with dead tops are prevented from growing taller unless a new top grows, regardless the tree will continue to grow in diameter.

There are different causes of redwood top dieback, along the coast the harsh salt laden winds can cause tops, especially those that stick up more prominently, to lose their needles and dieback. Between Eureka and Crescent City, in the vicinity of the Drury Bypass, bear damage is apparent. Bears do not appear to get to the top, but will shred the bark, where the tree bole is larger. If the damage is extensive, the entire tree including the top will die. In Humboldt Redwoods Sate Park just south of Scotia, evident on the Eel River side of Highway 101 are old-growth redwood where nearly every tall tree has a dead top. In this case, the highway changed the water drainage pattern and increased the exposure of the treetops to increased air movement. Increased water stress combined with desiccation may have caused the tops to die.

The most common cause of redwood top dieback is animal damage by tree squirrels, wood rats and the occasional porcupine, which can chew the bark to the cambium. If enough area is affected the flow of nutrients is disrupted and the portion above the damaged area will die. The species of squirrels most likely causing the damage are Douglas' Squirrel (Tamiasciurus douglasii), also called "Red Tree Squirrel" or "Chickaree" and to a lesser extent the Western Gray Squirrel (Sciurus griseus), also called the "California Gray Squirrel". Dusky-footed Woodrats (Neotoma fuscipes) also cause damage, in younger redwood trees, trees less than 20 feet in height. In a clump of a dozen trees, the woodrat may advance a handful of tops to die. A handful more may be lightly chewed and the balance may escape being munched altogether. You may be able to catch the tree squirrels in action as they are active during the day, but it will be harder to catch woodrats in action as they are nocturnal.

I intend this column to be a public service. Therefore, if you have any questions or topics you want me to cover, please email me at thembi@mcn.org.

Thembi Borras is a Registered Professional Forester living and working in Mendocino County, CA USA.