Winter Dormancy and Desert-Adapted Trees

Mon, September 29, 2014 11:51 AM | Danielle Corral

Although temperatures are just beginning to subside in Arizona, several tree owners contacted us because their trees looked like they were dying. In most cases, the tree has gone into dormancy. We thought we’d explain winter dormancy and what you can expect your tree to do--and what you can do to see if your tree is still alive.

Many desert-adapted trees are deciduous, meaning they lose their leaves seasonally. Trees shed their leaves because they stop producing food (photosynthesis) due to environmental changes such as cold weather, not enough light, or extreme drought. The tree remains alive by living off its store of carbohydrates in its roots. Dormancy is the tree version of hibernation, where everything slows down--metabolism, energy consumption, and growth. Leaves require energy to maintain and, therefore, are shed during dormancy. A chemical called abscisic acid is produced in terminal buds (where the stem connects to the leaf) that signals the leaf to break off and suspends tree growth. 

Often, when customers plant their trees in the fall or when fall approaches, leaves begin to fall off or in the case of Desert Willows--one of the tree types available through the Shade Tree Program--the tree stops blooming and flowers fall off.  During the summer, desert-adapted trees such as the Desert Willow or the Willow Acacia (pictured right) are in full bloom but when the cold weather approaches, their branches look bare and dead (as pictured below).  

A simple way to tell if your tree is still alive is to test the flexibility and color of its twigs. Supple twigs that bend easily without breaking or still have green just under the bark are likely still OK. Twigs that break or snap or are brown under the bark may be dead. If you can’t tell, wait. A living tree will begin to sprout and produce new leaves when the conditions are appropriate. A dead tree will still be dead no matter how long you wait; it won’t get any “deader.”  So when in doubt, wait for spring.

If you are concerned about your tree or have a question, please post it on our forum under “Ask the Arborist…” and our volunteer Arborist Erik will answer it. 

 

References:

Erik the Arborist, on our forum:  http://vpaaz.org/STForum

http://www.aridzonetrees.com/AZTimes%20Horticultural/Cold%20Hardiness%20of%20Desert%20Trees.htm

http://www.horticultureunlimited.com/landscape-plants/desert-willow.html

http://www.wildflower.org/plants/result.php?id_plant=CHLI2

http://www.gardenguides.com/92697-desert-willow-trees.html

http://www.sciencemag.org/content/171/3966/29.abstract

http://www.mnn.com/local-reports/illinois/local-blog/how-do-trees-get-through-the-winter

http://desertswest.blogspot.com/2010/03/desert-willow-and-blue-skyskywatch.html

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