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California trees are suffering under climate change and invasive pests

Branch die-back in a Chinese flame tree because of invasive shothole borer infestation. (Photo: Beatriz Nobua-Behrmann)
Trees are facing stress from a variety of pressures in California, including climate change and exotic invasive pests, reported Jeanette Marantos in the Los Angeles Times

“There are lots of invasive pests everywhere because of global warming and the movement of plant materials in general,” said Philippe Rolshausen, UC Cooperative Extension subtropical tree specialist at UC Riverside.

Yellowing leaves, a thinning canopy and branch die-back are symptoms that the tree is sick. UC Master Gardeners, headquartered in UCCE county offices across the state, can provide free help, the article said.

Marantos listed possible reasons for common tree symptoms:

Yellow leaves: May be due to a lack of nutrients. A sudden jolt of fertilizer isn't the best solution. Homeowners often remove the best fertilizer and mulch for trees — their own fallen leaves.

Thinning canopies and branch die-back: May be the result of a soil-born disease, such a phytophthora, caused by excessive water. “Homeowners have a tendency to over-irrigate a tree that's not doing well, but soil-borne diseases actually thrive in wet soils, so that's making things even worse,” Rolshausen said. “Trees don't like standing water on their root systems because they can't breathe.”

Huanglongbing of citrus: Invested trees send up shoots of bright yellow leaves. Eventually, new leaves get twisted and mottled and the fruit stops ripening. The disease was first spotted in Southern California in the late 1990s and has since been detected in Los Angeles, Orange, San Bernardino and Riverside counties, according to a map prepared by University of California Agriculture and Natural Resources.

The Times article also recommended the UC Integrated Pest Management Program website to learn how to diagnose and control tree insects and diseases.

Posted on Monday, March 2, 2020 at 8:59 AM
Focus Area Tags: Yard & Garden

Can harvesting Christmas trees help the forest?

California forests are overstocked with conifers, and California residents want to decorate their homes during the holiday season with Christmas trees. The smart harvest of Christmas trees can kill two birds with one stone, according to UC Cooperative Extension forestry advisor Susie Kocher. Kocher spoke to Capital Public Radio reporter Ezra David Romero about the prospect of thinning the forest by taking home trees.

Smart harvest of Christmas trees can help thin the forest. (Photo: USDA)

"It's a great win-win solution," Kocher said. "You get the public out in the forest, you do good work reducing the density of trees."

Kocher, who lives in Lake Tahoe, holds a family Christmas tree harvest party every year. With $10 permits from the Lake Tahoe Basin Management Unit, they trek through snow to select their trees. This year the management unit sold 2,000 permits. Kocher believes the program could be ramped up to further benefit forests.

“By removing some of the smaller trees, we are doing some of the work,” Kocher said. If left in place, the small trees grow larger, and more human resources, equipment and funds are needed to remove them. Moreover, the income from permit sales can be used for other forest-thinning projects.

However, some foresters are skeptical that harvesting Christmas trees is a realistic solution to management of California forests.

“It's great to have the masses come up during the holiday season full of mirth and cheer,” said Joseph Flannery with the Tahoe National Forest. “But I don't think there's the infrastructure in place to really make a dent in the hazardous fuels reduction needed.”

This story was also covered for KTVU Fox Channel 2 in the Bay Area by Lisa Fernandez. 

“You need a 4-wheel drive, and yes, you trudge through snow,” Kocher said. “It's not for everyone. But for those who want that adventure, it's super fun. I do it because I don't think there's a substitute for a real tree in the house. And we always turn it into a family party.”

Besides, she said, “I feel good about removing excess small trees.”

Posted on Thursday, December 6, 2018 at 3:05 PM
Focus Area Tags: Environment

Cities in California inland areas must make street tree changes to adapt to future climate

Many common street trees now growing in the interior of California are unlikely to persist in the warmer climate expected in 2099, according to research published in the July 2018 issue of the journal Urban Forestry & Urban Greening.

“Urban foresters in inland cities of California should begin reconsidering their palettes of common street trees to prepare for warmer conditions expected in 2099 due to climate change,” said the study's co-author, Igor Lacan, UC Cooperative Extension environmental horticulture advisor in the Bay Area.

Common trees in Coastal California cities appear to be better suited to withstand the 2099 climate.

Urban foresters in inland cities of California should begin reconsidering their palettes of common street trees to prepare for climate change.

“Our research shows that some trees now lining the streets of cities like Fresno, Stockton and Ukiah are likely to perform poorly in 2099,” Lacan said. “Those cities need to look at the conditions – and trees – now found in El Centro, Barstow and Fresno respectively.”

To reach these conclusions, Lacan and co-author, professor Joe McBride of UC Berkeley, used space-for-time substitution. They compared the most common street tree species in cities representing each of the 16 California climate zones with trees in cities that currently have climates that approximate the expected warmer conditions in the 16 cities 80 years from now.

For example, Eureka can expect a climate like Berkeley's today; Fresno's climate will resemble the climate of El Centro today. (Find the complete list of cities below.) The corresponding cities were determined with climate predictions from Cal-Adapt, which synthesizes California climate change scenarios to reach a consensus view of the magnitude of climatic warming.

Igor Lancan, UC Cooperative Extension urban horticulture advisor. (Photo: Evett Kilmartin)

“We used the mid-range models,” Lacan said. “It's very reasonable to say the warming predicted by the model we used is already ‘baked in,' regardless of any mitigation efforts. While we should take measures to prevent even greater warming – mostly by reducing the use of fossil fuels – this study aims to help adapt California urban forests to the warming that can be reasonably expected to occur.”

Lacan said he and McBride were surprised to find that coastal cities and their warm equivalents contain most of the same common urban tree species, while the warm equivalents of inland cities seemed to lack most and, in some cases, all of the common trees there today.

“It's really a sharp distinction,” Lacan said. “Perhaps they were lucky, but coastal cities are better positioned for the climate of 2099 than the inland cities.”

Climate zone

City

Corresponding city
(approximates climate
in 2099)

1

Eureka

Berkeley

2

Ukiah

Fresno

3

Berkeley

Santa Ana

4

King City

Stockton

5

Santa Maria

Santa Ana

6

Santa Monica

King City

7

San Diego

Santa Ana

8

Santa Ana

Burbank

9

Burbank

Fresno

10

Riverside

Barstow

11

Yuba City

El Centro

12

Stockton

Barstow

13

Fresno

El Centro

14

Barstow

El Centro

15

El Centro

Furnace Creek

16

Susanville

Barstow

For a copy of the complete research report email Igor Lacan, ilacan@ucanr.edu.

Posted on Friday, August 3, 2018 at 8:38 AM
Focus Area Tags: Environment

This BOG in the Heart of UC Davis Is a Treasure

The Biological Orchard and Gardens (BOG) sign features floral and insect designs. It's located by the Mann Laboratory, UC Davis campus. (Photo by Kathy Keatley Garvey)

"A bog is a wetland that accumulates peat, a deposit of dead plant material—often mosses, and in a majority of cases, sphagnum...

The Biological Orchard and Gardens (BOG) sign features floral and insect designs. It's located by the Mann Laboratory, UC Davis campus. (Photo by Kathy Keatley Garvey)
The Biological Orchard and Gardens (BOG) sign features floral and insect designs. It's located by the Mann Laboratory, UC Davis campus. (Photo by Kathy Keatley Garvey)

The Biological Orchard and Gardens (BOG) sign features floral and insect designs. It's located by the Mann Laboratory, UC Davis campus. (Photo by Kathy Keatley Garvey)

Colorful BOG garden in the early spring: among the flowers are tidy tips, desert bell, and European red flax. (Photo by Kathy Keatley Garvey)
Colorful BOG garden in the early spring: among the flowers are tidy tips, desert bell, and European red flax. (Photo by Kathy Keatley Garvey)

Colorful BOG garden in the early spring: among the flowers are tidy tips, desert bell, and European red flax. (Photo by Kathy Keatley Garvey)

A mini-meadow of tidy tips, Layia platyglossa, with tall phacelia, Phacelia tanacetifolia. (Photo by Kathy Keatley Garvey)
A mini-meadow of tidy tips, Layia platyglossa, with tall phacelia, Phacelia tanacetifolia. (Photo by Kathy Keatley Garvey)

A mini-meadow of tidy tips, Layia platyglossa, with tall phacelia, Phacelia tanacetifolia. (Photo by Kathy Keatley Garvey)

A male Valley carpenter bee, (Xylocopa varipuncta) forages on  phacelia. (Photo by Kathy Keatley Garvey)
A male Valley carpenter bee, (Xylocopa varipuncta) forages on phacelia. (Photo by Kathy Keatley Garvey)

A male Valley carpenter bee, (Xylocopa varipuncta) forages on phacelia. (Photo by Kathy Keatley Garvey)

A yellow-faced bumble bee (Bombus vosnesenskii) sips nectar from  phacelia. (Photo by Kathy Keatley Garvey)
A yellow-faced bumble bee (Bombus vosnesenskii) sips nectar from phacelia. (Photo by Kathy Keatley Garvey)

A yellow-faced bumble bee (Bombus vosnesenskii) sips nectar from phacelia. (Photo by Kathy Keatley Garvey)

Size comparison! A honey bee is  dwarfed by a male Valley carpenter bee, Xylocopa varipuncta. (Photo by Kathy Keatley Garvey)
Size comparison! A honey bee is dwarfed by a male Valley carpenter bee, Xylocopa varipuncta. (Photo by Kathy Keatley Garvey)

Size comparison! A honey bee is dwarfed by a male Valley carpenter bee, Xylocopa varipuncta. (Photo by Kathy Keatley Garvey)

Many species of bees--as well as butterflies and other insects--are drawn to the blanketflower, Gaillardia. (Photo by Kathy Keatley Garvey)
Many species of bees--as well as butterflies and other insects--are drawn to the blanketflower, Gaillardia. (Photo by Kathy Keatley Garvey)

Many species of bees--as well as butterflies and other insects--are drawn to the blanketflower, Gaillardia. (Photo by Kathy Keatley Garvey)

Posted on Wednesday, June 6, 2018 at 3:59 PM
Focus Area Tags: Agriculture, Economic Development, Environment, Innovation, Natural Resources, Yard & Garden

UC study seeks street trees that can cope with climate change

The changing climate predicted for California – including less rain and higher day and nighttime temperatures – is expected to cause chronic stress on many street tree species that have shaded and beautified urban areas for decades.

Realizing that popular trees may not thrive under the changing conditions, UC Cooperative Extension scientists are partnering with the U.S. Forest Service in an unprecedented 20-year research study to expand the palette of drought-adapted, climate-ready trees for several of the state's climate zones.

“The idea is to look at available but under-planted, drought-tolerant, structurally sound, pest resistant trees for Southern California that do well in even warmer climates,” said Janet Hartin, UCCE horticulture advisor in San Bernardino County.

Hartin, a 34-year veteran advisor, said the project is her first to stretch to 20 years; it will likely extend past her tenure with UCCE.

“I'd like to retire in five or six years,” she said. “But I'm very excited about being a pioneer in a study that will continue with my successors. I think it's important for our children and our children's children, as well as for the environment.”

At the end of 2019, with three years of data on tree health and growth rates, the scientists expect to be able to publish the first results and make them available to arborists, urban foresters and residents throughout the regions of the study.

Twelve tree species were selected for each climate zone in the comparative study, with several area parks used as control sites. Hartin and her Southern California research collaborators – UCCE advisors  Darren Haver of Orange County and Jim Downer of Ventura County – worked closely with UC Davis plant biologist Alison Berry, UC Davis research associate Greg McPherson and USFS research urban ecologist Natalie van Doorn to select promising species.

They looked for trees that are already available at local nurseries, but are underutilized. The trees in the project exhibit drought tolerance and disease resistance, plus produce minimal litter. The researchers also sought trees that would provide ample cooling shade for a long time – ideally 50 years or longer.

The varieties come from areas around the world with climates similar to California. Two trees planted in replicated plots at the UC Riverside Citrus Field Station are native to Australia, two are native to Oklahoma and Texas, one is native to Asia and two are non-native crosses of other trees. Three of the trees are native to California: the netleaf hackberry, Catalina cherry and island oak.

“Trees are a long-term investment,” Hartin said. “A tree will live 50, 70, 90 years. The proper selection is very important to help ensure longevity.”

Making the long-term investment with the proper selection yields considerable returns. In a warming world, trees are natural air conditioners.

“Urban areas create heat islands, with dark asphalt surfaces reradiating heat. Cities can be 10 to 20 degrees warmer than the surrounding environment,” Hartin said.

Other tree benefits include soil health and stability, wildlife habitat and aesthetic beauty.

Following are a sampling of trees that are part of the comparative study:

Acacia – A 20-foot-tall, 20-foot wide evergreen that is drought resistant, and withstands moderate irrigation.  Native of Australia.

Palo verde is a drought-resistant tree. (Photo: Bri Weldon, flickr, CC BY-SA 2.0)
Blue palo verde – A tree that reaches about 25 feet in height, the Blue palo verde is drought resistance and lives 50 to 150 years. Its trunk, branches and leaves have a blue-green hue. Native to the southwestern U.S. and Mexico.

Brazilian cedarwood – A native of Brazil and Paraguay, the deciduous tree grows to 50 to 65 feet. The tree produces pale yellow tubular flowers in the spring.

Catalina cherry – Native to the chaparral areas of coastal California, the Catalina cherry grows to 30 feet high. The evergreen tree tolerates drought when mature. It produces sweet purple-to-black edible fruit.

Chinese pistache – A deciduous tree with beautiful fall color. Grows to 35 feet tall, 30 feet wide. Drought resistant, but tolerates moist soil. Native to central and western China.

Desert willow – Growing to 30 feet tall and living 40 to 150 years, the desert willow tolerates highly alkaline soil and some salinity. A deciduous tree, it boasts large pink flowers all summer that attract hummingbirds and other wildlife. Native to the southwestern U.S. and northern Mexico.

Escarpment live oak – Native to west Texas, this tree is cold hardy and drought tolerant. Typically evergreen, it can be deciduous in colder climates.

Ghost gum – Very tall at maturity and drought tolerant. An Australia native.

Indian laurel – Commonly called a ficus, this is a 35-foot-tall, 35-foot-wide tree at maturity that is drought resistant and tolerates highly alkaline and saline soils. Shade potential is high. Native of Asia and Hawaii.

Ironwood – A southwestern and northern Mexico native, Ironwood is semi-drought resistant once mature and tolerates alkaline soil. Ironwood, which grows to about 33 feet tall, can live 50 to 150 years.

Island oak – This tree is native to five of six California off-shore islands. Drought tolerant, it grows to nearly 70 feet tall when mature.

Maverick mesquite – Native to the southwestern U.S. and northern Mexico, this tree does well in full sun and is drought resistant once established. The tree grows to 35 feet tall. The Maverick mesquite is a thornless variety.

Mulga – A versatile and hardy tree that grows 15 to 20 feet in height, the mulga – a Western Australia native – tolerates hot and dry conditions. The leaves are evergreen and the tree has yellow elongated fluffy flowers in spring.

Netleaf hackberry – A California native, the netleaf hackberry grows to 30 feet. Its deep root systems and heat resistance makes the tree idea for urban conditions.

Climate-ready trees planted in 2016 at the UC South Coast Research and Extension Center.

Rosewood – Native to southern Iran, Indian rosewood grows to 65 feet tall, and 40 feet wide. Evergreen. Semi drought resistant and intolerant of alkaline soil.

Shoestring Acacia – Evergreen and 30 feet tall when mature, shoestring acacia is drought resistant and thrives in slightly acidic to highly alkaline soils. Native to Australia.

Tecate cypress – A native of Southern California and Mexico, the Tecate cypress is very drought tolerant. Its foliage is bright green. Young trees are pyramidal in shape, becoming more rounded or contorted with age.

Partners in the tree study are Los Angeles Beautification Team volunteers, LA Parks and Recreation team, Chino Basin Water Conservation District, and Mountain States Wholesale Nursery.

Funding and other support is provided by LA Center for Urban Natural Resources Sustainability, ISA Western Chapter, Britton Fund, USFS Pacific Southwest Research Station, and the UC system.

Posted on Wednesday, April 18, 2018 at 11:35 AM
Tags: climate change (96), Earth Day (6), Janet Hartin (7), trees (10)
Focus Area Tags: Environment

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