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Thursday, September 24, 2015

Shade Trees for a Changing Future Climate

Blue Elderberry tree once provided needed shade in Garden of Dreams,
 CSU Dominguez Hills

The past few years have been sobering for anyone concerned with our planet’s future.   In Southern California, the effects of four years drought can be seen in nearly every garden and wild place.  Record-breaking heat and winds have also plagued us, compounding the effects of the drought.   Climate change is happening right now – and we’d best be planning for more to come.

In 2014, we gave a talk on Climate Change and the Southern California Garden.    We discussed the climate models, their predictions for Southern California and the implications for local gardens.  Two conclusions are clear: 1) overall temperatures – and the number of high heat days (> 95° F; 35° C) – will increase in S. California over the next century; 2) the frequency of extreme precipitation years (both drought and greater than normal precipitation) are also likely to increase. For more predictions see our 2014 talk:

Our gardens must provide more shade in the future.  Hardscape features like patios, arbors and awnings are one way to create shade.  But ‘living shade’ – that provided by trees, shrubs and strategically placed vines – has additional benefits.  Plants cool the surrounding areas by evaporative cooling; that’s why the shade under trees feels cooler than the shade under a patio roof.  Plants also release oxygen, clean the air of contaminants and provide habitat for numerous creatures.  If chosen carefully, shade trees and shrubs provide colorful flowers, edible fruits and a green oasis in summer.
Toyon (Heteromeles arbulifolia) - pruned as tree
Ideally, shade-producing plants are long-lived – 50 or more years is ideal.  That means that shade trees planted now must be tough enough to thrive in the climate of 50 years and more in the future.  We’re betting strongly on California natives, including some trees and shrubs that already grow in the Los Angeles Basin.   Locally native survivors are appropriate for our soils and provide key habitat for local creatures.  So we should use the local natives when appropriate.

But the choice of trees that can survive and thrive into the future is anything but straight forward.  To learn more - and for a list of suggested trees and shrubs - see: