California Landscape Design

Climate Ready Trees for California Communities

Why do we need to know about climate-ready trees? In the field of arboriculture, climate change has been extensively researched. If you ask an old tree, it already knows the climate is changing rapidly. 

Trees are the plants in our landscapes that live the longest. As responsible designers, some elements of our designs should take our landscapes into the future. Trees—those majestic, whimsical, lovely actors—can help do that for us. Trees have to contend with stressors that have become critical factors in their ability to thrive or even survive. These stressors include heat, drought, high winds, salinity, pests and disease, and delayed dormancy (lack of winter chill), to name a few. We need to select tree types that can cope with conditions those trees might experience in 20, 40, even 75 years. Our designs should consider using tree species that will be able to thrive in the predicted climate of the coming years.

UC Davis, in collaboration with arborists, foresters, growers and others, have a 20 year-long field study/evaluation identifying and testing the resilience of specific tree species to climate change stressors. Some are quite attractive, require minimum maintenance, and will pose little hazard to people or infrastructure. Most of these trees are unfamiliar to many of us in landscaping, but what that can mean to you is a new recommended tree palette to use, new opportunities!

TREE SPECIES FOR INLAND VALLEY CALIFORNIA
Australia:
Acacia aneura, Mulga
Acacia stenophylla, Shoestring Acacia
Eucalyptus papuana, Ghost Gum
Southwest US - drought tolerant:
Chilopsis linearis
, Desert Willow
Parkinsonia x 'Desert Museum', Desert Museum Palo Verde
Prosopis glandulosa x 'Maverick', Thornless Honey Mesquite
Oklahoma/Texas/Western US - deciduous:
Celtis reticulata
, Netleaf Hackberry
Ebenopsis ebano
, Texas Ebony
Maclura pomifera 'White Shield', White Shield Osage Orange
Quercus canbyi, Canby's Oak
Asia:
Dalbergia sissoo, Rosewood
Ulmus propinqua, Emerald Sunshine Elm

TREE SPECIES FOR COASTAL SOUTHERN CALIFORNIA
Australia:
Acacia aneura, Mulga
Corymbia papuana, Ghost Gum
Southwest US - drought tolerant:
Acacia willardiana, Palo Blanco
Hesperocyparis forbesii, Tecate Cypress
Prunus ilicifolia ssp. Lyonii, Catalina Cherry
Quercus tomentella, Island oak
Oklahoma/Texas/Western US - deciduous:
Celtis reticulata, Netleaf Hackberry
Prosopis galndulosa ‘Maverick’, Maverick Mesquite
Quercus fusiformis, Escarpment Live Oak
Asia/South America:
Dalbergia sissoo, Rosewood
Cedrela fissilis, Brazilian Cedarwood
Other:
Pistacia ‘Red Push’, Red Push Pistache

TREE SPECIES FOR INLAND SOUTHERN CALIFORNIA
Australia:
Acacia aneura, Mulga
Corymbia papuana, Ghost Gum
Southwest US - drought tolerant:
Acacia willardiana, Palo Blanco
Hesperocyparis forbesii, Tecate Cypress
Chilopsis linearis ‘Bubba’, Desert Willow
Quercus tomentella, Island oak
Oklahoma/Texas/Western US - deciduous:
Celtis reticulata
, Netleaf Hackberry
Prosopis glandulosa ‘Maverick’, Maverick Mesquite
Quercus fusiformis, Escarpment Live Oak
Asia/South America:
Dalbergia sissoo, Rosewood
Other:
Pistacia ‘Red Push’, Red Push Pistache
Parkinsonia x 'Desert Museum', Desert Museum Palo Verde

Diversity

You’ve most likely noticed that the lists are comprised of trees from different areas of the world. That’s to diversify the susceptibility of trees to pests and diseases from specific places. 

Smart tree selections for climate ready trees also can work for us when choosing trees for diversity. Species diversity is a helpful concept for maintaining the health of the urban forest. It is our most effective defense against catastrophic loss from a global onslaught of pests and diseases. Threats to our trees are increasing, and will continue to do so. Problems for particular trees increase when we design with an over reliance on certain species (I know, we all do it in our designs). We as designers need to change it up a bit! 

Think of the loss of all those American Elms to Dutch Elm disease. Even our native trees aren’t immune, we are all witnessing the devastating effects of SODS (Sudden Oak Death Syndrome). And the Gold Spotted Oak Borer is threatening our native oaks, again. There are many other threats knocking at the door, causing massive tree losses in the US Midwest, East Coast, and all over the globe. These new threats will eventually make their way to California. We are better designers when we are aware that there are new dangers for our urban forests and young trees. With this in mind, we can try and design for the approaching problems.

Tree Sources 

By no means are these lists of all the trees that might check all the boxes. They are the winners of this specific contest - there were also tree species failures that didn’t make the grade. These specific trees have, however, been evaluated over long periods of time under rather rigorous testing and proven their worthiness.

Many of these trees can be found in the wholesale nursery trade and all will become more available the more we use them! APLD sponsors carry many of these trees: Devil Mountain Wholesale Nursery, Bamboo Pipeline, Ogawa Mune (Native Sons), Urban Tree Farms, Village Nurseries. Support them! And please ask them to carry species you are interested in if they don’t have them. They won’t carry what they don’t know anyone wants. We can have an effect on what the nurseries carry.

Mountain States Wholesale Nursery—a large southwest wholesale nursery (and APLD sponsor) that is a source for many of our local wholesale nurseries—was a sponsor for these Climate-Ready Tree Studies.

Overwhelming information? These tree people have been evaluating smarter tree selection for decades, now it’s our job to use that information in our landscape design. We can add to our list of concerns in our landscapes; our tree health increasingly depends on informed tree selection. 

Links

You can access details and pictures about these trees using the following links:
climatereadytrees.ucdavis.edu › northern-california-central-valley-trees
climatereadytrees.ucdavis.edu › southern-california-coast-trees

And a great easy-to-understand power point about the subject:
www.streettreeseminar.com/pdf/2016/ClimateReadyTreesforCACommunites-Downer.pdf

by Marcia Jimenez Scott
Landscape Designer and ISA Certified Arborist

My reality as a landscape designer is quite different from many California landscape designers out there. 

I am fortunate to live in a place that DEMANDS I know something about the local trees and realize their importance in the landscape. In the Sierra Foothills, I live with 60 foot trees surrounding me. Trees are the local ‘weeds’, the sources of many risks, and the inspiration for unlimited opportunities. Some of my clients have 200 trees and others have 200 year old trees. The paranoia here is of wildfire - we know if there is a fire, it will be in the trees. And the trees are everywhere. But, the trees here help create the magic that make the Sierras Foothills a beautiful place.

Trees form the basis of many of my daily thoughts. I wake up to views of Ponderosa pines and drive through canopies of black oaks. I imagine design solutions while considering the trees that dominate the landscape here. I stare up at the tree canopies and feel my stresses disappear; for me, the trees truly are magical.

I was introduced to the field of arboriculture by a landscape design colleague 10 years ago. She opened my eyes to a world filled with these awesome life forms. After 20 years in the landscaping trade at that time, I figured I had the ‘plant thing’ around here pretty well harnessed (how naive I was!). As I explored the world of arboriculture I realized I should have started my tree schooling when I was a child! 

One of my goals is to increase the moments of intersection between landscape designers and arborists. We share common interests and knowledge, and we can complement one another in so many ways. United, we can be an effective force working for the health of our planet.