Posts Tagged: urban heat islands
It's only right that our University of California Cooperative Extension (UCCE) San Bernardino County Master Gardener ‘Trees for Tomorrow' team of volunteers are our featured ‘Spotlight' Master Gardener volunteers for September, 2021. They provided vital education to Redlands residents receiving gratis trees through a multi-partnership grant obtained by Inland Empire Resource Conservation District Manager Mandy Parkes.
It's an honor and privilege to recognize UCCE San Bernardino County Master Gardener Project Leader Debbie LeDoux and her dedicated team of 'Trees for Tomorrow' volunteers: Zhibo (Sandy) Anderson; Consuelo (Connie) Davis (pictured); Pam O'Connell; Gail Sefl; and Husam Yousef. These dedicated Master Gardeners were tasked with helping residents select, plant and care for drought, heat, and pest tolerant trees. (Species including Chilopsis linearis 'Bubba', and Pistacia x 'Red Push' were selected due to their excellent performance in our University of California/United States Forest Service research project as 'climate-ready' trees able to withstand harsh conditions related to our changing climate.) Working with a team of California Climate Action Corps volunteers, civic leaders, Common Vision Coalition, and other groups, nearly 100 trees were planted in yards and parks lacking the preferred 25% tree canopy cover.
Trees can cool urban heat islands by 50 degrees Fahrenheit or more during spring and summer, creating welcome oases in hot inland communities. With spring 2021 temperatures so high they broke previous records on multiple dates, the project is especially timely and necessary.
In addition to proper tree selection, trees require the right long-term care. Master Gardeners will continue to provide advice on irrigation, pruning, fertilizing and pest control to residents receiving trees long after the trees are planted. This is critical since an average urban tree lives less than 20% of its potential lifespan due largely to poor care. The long-term engagement of Master Gardeners with residents is as important as is selecting the right species.
UCCE Master Gardeners are all volunteers, giving of their time and talents to enhance the quality of life for individuals and families who call San Bernardino County their home. Each Master Gardener is required to complete a rigorous 18-week training class complete with exams, class projects, and lots of participation! Due to COVID-19, volunteers had to master key horticultural concepts during the first ever all on-line training class. Only recently have they been able to meet fellow Master Gardener graduates and, in some cases, the Redlands residents they mentored through the tree canopy enhancement project. They truly exemplify community spirit and all it takes to successfully work together under adverse conditions. Kudos to each and every one of you from Master Gardener Coordinator Maggie O'Neil and myself! You are creating a cooler, greener and healthier environment for our children's children.
I asked the honored Master Gardeners their thoughts on the project. Here's what they had to say:
“The Redlands tree canopy project was the best volunteer project ever. In the midst of Covid-19, horrific politics and way too many good byes, it was a truly joyous experience. The legacy of being a part of the group that promoted healthy sustainable trees, knowledge of how to plant and care for them, tips on maintaining their health and beauty was the absolute best. For me as a Master Gardener, it was so much fun. I loved the site walks and getting to help our participants select the perfect sustainable trees for their properties. What started as a one-on-one visit often expanded to an enlarged group of neighbors and extended family. I got to give out many handouts and publications and promote our excellent Master Gardener program. I got to share our helpline email and phone numbers. I love the fact that I have been asked to revisit sites to see how great they are doing (once to make sure the tree did not look funny!). I receive emails every now and then asking me questions and showing me pictures of "Our Trees.” So much fun, Janet. Thank you. By far the coolest project ever! Pam O'Connell
There are a few things that really made an impact on me.1) It was rewarding to attend the Zoom presentation you developed that provided education to various professionals on the importance of planting sustainable trees. I found it to be open and inclusive allowing for good interchange of ideas and concerns.2) There are many beautiful trees that are sustainable.3) Reaching out to the community to offer beautiful, sustainable trees was a worthwhile way to show how various organizations can work together to benefit the community while trying to improve our environment.4) When dealing with homeowners that belong to an HOA, additional time and communication may be needed to assist them in obtaining approval for trees from their HOA's. Connie Davis
"I see tree planting efforts similar to what a trend of the future is to combat climate change and increase awareness of the importance of trees and tree canopies in our neighborhoods. Not only that but I see this project expanded to other cities in the county of San Bernardino. The continuity of this project is so valuable so that we can see the positive impact on the environment and the well-being of San Bernardino residents in the coming decades. I see this important work being organized and well-coordinated by involving the appropriate stakeholders at all stages of the planning project. It is about time to give back what we have taken for tens of years!" Husam Yousef
It was rewarding to see local homeowners excited about planting trees and grateful for the program providing them. Gail Sefl
THANK YOU ALL! Janet Hartin and Maggie O'Neill
I've been interested in surface temperatures of various living and non-living surfaces in our inland Southern California cities with increasingly hot urban heat islands for some time. Results are in! Use of dark asphalt, synthetic turf,
What can you do?
Take care of your trees, shrubs, groundcovers, and lawns, which cool the environment substantially. In the same experiment, the coolest scenario was the surface temperature of a lawn growing in the shade of a mature tree. Remember that, through transpiration, living plants cool the environment while non-living surfaces do not.
If you're tired of your high maintenance lawn, think about alternative groundcovers that have similar effects (see suggestions below). While cool season lawns like tall fescue and ryes are high water-requiring plants, warm season lawns like Bermuda, zoysia, and buffalograss are more drought-resistant. Our studies have found that it's not the lawns and groundcovers that waste the water, it's the uneven coverage (low distribution uniformity) of most sprinkler systems, coupled with not applying the right amount of water at the right time. This holds true for even the most drought-resistant native and non-native groundcovers irrigated via sprinklers, as well.
Plant drought-tolerant groundcovers
There are dozens of groundcover species that are both drought and heat-tolerant suitable for California gardens.
Here are just two examples:
Creeping thyme (Thymus serpyhllum) They are both drought resistant and do well in the heat. Fragrant flowers add a special touch to a meandering path to a secret backyard garden (below left).
Rosemary (Rosmarinus prostratus) Some rosemary species are low-growing groundcovers. It is great for rock gardens, growing to only 6 inches tall. It produces purple flowers in the summer and attracts pollinators and can be used for culinary purpose (below right).
trees cool urban heat islands
• Your trees come first! If there just isn't enough water to go around, your lawn and flowers should be sacrificed instead. Trees are our most valuable landscape resource and take years to maximize their benefits (shade, cooling, habitat/ecosystem enhancement, carbon dioxide storage, etc.).
• Spread and maintain 2-4” of mulch around garden plants and trees (3-4” for wood chips, 2” for pebbles, decomposed gravel, etc.) keeping it a few inches away from tree trunks.
• Water early in the morning when soil evaporation is minimal.
• Control weeds. They compete with other plants for water.
• Avoid fertilizing. Nitrogen increases growth and the need for more water.
• Don't plant new plants during the summer when temperatures are highest. Even drought-resistant native and non-native plants need regular watering their first season.
Do you have Spring Fever? If you have adequate space, why not leave a legacy to your children's children by planting a tree? When the right species is planted in the right location with the right care, landscape trees can be enjoyed for 100 years or more. Landscape trees cool urban heat islands, absorb carbon dioxide, filter toxic chemicals from soil preventing them from polluting our waterways, reduce soil and water erosion, reduce internal energy needs and related costs, provide habitat, and beautify neighborhoods.
Spring is a much better times to plant a container landscape tree in California than is summer. Trees incur far less stress if they've been in the ground several weeks rather than having to immediately adapt to high summer temperatures. Cooler weather allows plants to establish roots in their new ‘home' before the harshness of summer sets in. (Deciduous bare-root fruit trees, on the other hand, should be planted during the winter when they are dormant.) Choose recommended species for your climate and micro-climate.
Choose trees based on your Sunset climate zone (more precise than USDA zones for California since they include impacts of high temperatures as well as low temperatures) and your microclimate (shade, soil conditions, space, etc.). Four of my favorite search engines that allow one to search by multiple criteria (size, water needs, flower color, ecosystem functions, pest susceptibility, etc.) are: Inland Valley Garden Planner: https://inlandvalleygardenplanner.org/; Cal Poly, Pomona: https://selectree.calpoly.edu;California Native Plant Society: http://www.cnps.org/cnps/grownative/lists.php; and WUCOLS IV (Water Use Classification of Landscape Species): http://ucanr.edu/sites/WUCOLS
Avoid circled, girdled roots. Remember to inspect the root system of container trees. Avoid purchasing specimens with severely circled and girdled roots. Root pruning will not solve the problem and the resulting tree is much more prone to failure later. This occurs because the upper portion of the tree continues to grow and expand while the root system lacks the breadth and architectural strength to support the tree. Many times a tree will look fine for several years and - seemingly - very suddenly topple in winds that otherwise it could sustain with a more adequate root system. Only when the tree falls does the owner actually notice firsthand that the root system is the same size it was when the tree was planted years before!
Check drainage before you plant. Dig a hole where you are planning on planting the tree, fill it with water, and make sure it completely drains within 24-hours. If it doesn't drain, don't plant a tree there. In some cases, trees are carefully selected based on species and location only to perish ten or more years later due to poor drainage and water-logged soil. Trees often die in these situations due to a lack of aeration setting them up for disease-causing fungal pathogens.
Planting the tree. Dig a hole at least 2-1/2 times the width of the container (in clay or compacted soils make the hole at least 4-5 times wider) up to two inches shallower than the depth of the tree in the container to compensate for settling. Use a shovel or trowel to roughen the soil on the sides of the hole to encourage root growth into the native soil. Remove the tree from the container along with any loose soil that covers the lower part of the trunk. Carefully place the tree in the planting hole, keeping the trunk flare (the area where the trunk widens and connects with the roots) 1-2 inches above the existing grade. Gently fill the hole with the same soil that was removed. Do not add soil amendments or compost, another common cause of circled and kinked roots. Irrigate the tree immediately after planting through the entire root system and slightly deeper. Keep in mind that soils with appreciable clay content absorb water more slowly than sandier soils and need to be watered longer but less often. Water newly planted container trees often through their establishment period, even if they are drought tolerant species. Recently transplanted trees have a small volume of roots that dry out very quickly. Water newly planted trees regularly through the first season. Trees in sandy soils require more frequent watering than do trees in heavier soils. (After trees are fully established, irrigation frequency should be reduced but more water should be added during each irrigation.)
Avoid staking trees unless necessary. Stake trees only if they were staked at the nursery and/or if they are planted in a wind-prone area. Remember to loosen ties on nursery stock before they girdle the trunk. Gently secure any tree requiring staking with two opposing flexible ties on the lower half of the tree, allowing the tree to gently blow in the wind to encourage lower trunk strength. Avoids taking trees tightly, restricting flex. As the tree matures, remember to loosen ties and aim for removing stakes entirely if the tree is self-supporting.
Pruning. Avoid heavy pruning at the time of planting. Remove only broken branches, crossed branches and suckers at the base of the tree.
Fertilizing. Most trees have received adequate nutrition in the nursery and do not need fertilizer at the time of planting.
Mulching. Apply a 2-4 inch layer of mulch three or more inches away from the tree trunk. Organic mulches such as woodchips and compost should be applied and maintained at a depth of 3-4 inches to prevent weed seeds from sprouting. Inorganic mulches (gravel, pebbles, etc.) should be maintained at 2-3 inches. In fire-prone areas, organic mulches near the urban/forest interface should be avoided. Remember to irrigate below the mulch.
For more information on tree planting and care and all other home gardening and landscape topics, contact the UCCE San Bernardino County Master Gardener Helpline at email@example.com
Our population of urban trees is shrinking! You can help turn this around by protecting your own trees and by planting new ones recommended for your climate and the conditions around your home. For more on this topic, please revisit my February blog for specific selection and care recommendations: https://ucanr.edu/b/~ZuB.
In addition, please encourage your city to plant a wide range of recommended species today for a healthier tomorrow. Why is this so important? Many of our current street trees are in the 11th hour of their lifespans. While some that were planted decades ago are simply aging naturally, in other cases, they are perishing prematurely due to poor selection and care. This leads to a downward spiral; trees not adapted to the climate they're planted in and not receiving proper care are much more susceptible to invasive pests (shot-hole borers, etc.) and diseases than are healthy, well- chosen and maintained trees. Even the loss of one front yard shade tree can significantly reduce shade, increase the surrounding temperature, and diminish energy savings.
Another reason we're losing our trees is due to the negative impacts of urban heat islands (UHIs) which shorten the lifespan of many species of trees dramatically. Some trees (even many natives!) just aren't able to withstand the higher temperatures (sometimes exceeding 20 degrees) they are subjected to due to UHIs.
What are urban heat islands and why should we care? Urban heat islands are caused by reradiated heat from paved concrete and (especially) asphalt surfaces.
And, our cities are growing and expanding. Very few Southern California residents reside in rural areas. Instead of living near pastures, field-filled crops, and forests that cool the surrounding area through evapotranspiration, the vast majority of us reside in warmer urban city centers. Conditions we expect our city trees to endure in 2021 are very different from even 20 to 30 years alone, let alone decades ago.
The good news is that, through proper tree selection and care, we can be a part of the solution. In fact, trees offer many benefits that offset the impacts of UHIs. Cities with larger tree canopies are a testament to this fact and have fewer adverse impacts from UHIs than do cities with low tree canopies. Trees reduce the impact of UHIs by shading parking lots, buildings, and vehicles), deflecting the sun's radiation, and cooling the atmosphere through evapotranspiration. Trees also absorb and store carbon which lessens the impacts of pollution from fossil fuels. A well-tended mature landscape tree can absorb 40 tons of carbon over its lifespan.
The solution? Augment our current urban tree palettes with heat, drought, and pest-resistant native and adapted non-native species. A case in point of a native tree in trouble is our beautiful Joshua trees (Yucca brevifolia) which are dying off in their namesake National Park and seeding 500 or more feet higher elevation than parent plants. Planting trees that withstand UHIs today is crucial for tomorrow.
We are well on the way to identifying landscape tree species that can remain healthy under adverse urban conditions. In our study examining the performance of 12 species of underplanted but promising landscape trees, several candidates are standing out for their heat, drought, and pest resistance.