- Author: Kat Kerlin
Reposted from the UC Davis College of Agricultural and Environmental Sciences news
Redwood Trees Have 2 Types of Leaves, and They Do Totally Different Things
Quick Summary
- Redwoods have two types of leaves, one to make food and the other to absorb water
- Study is first to estimate whole-crown water absorption in a large, mature tree
- Leaf types shift places on the tree depending on if environment is wet or dry
- Findings can help scientists monitor trees' adaptability amid a changing climate
Redwoods are among the most well-studied trees on the planet, and yet their mysteries continue to surprise and delight scientists and nature lovers.
Scientists from the University of California, Davis, discovered that redwood trees have two types of leaves, and those leaves have completely different jobs, according to a study in the American Journal of Botany. Together, these functionally distinct leaves allow the world's tallest trees to thrive in both wet and dry parts of their range in California, without sacrificing water or food.
Division of labor
The peripheral leaf spends its working hours making the tree's food — converting sunlight into sugar through photosynthesis. Its colleague, the axial leaf, does almost nothing to help with photosynthesis. Instead its specialty is to absorb water. In fact, the study found that a large redwood can absorb up to 14 gallons of water in just the first hour its leaves are wet.
How does that compare to other trees? Scientists don't know. This is the first study estimating whole-crown water absorption in a large, mature tree. Because large redwoods have over 100 million leaves, this absorption record may prove hard to beat.
In wet forests, photosynthesis can be inhibited by films of water covering leaf stomata when they get wet. For redwoods, the different leaf types allow the trees to get wet and still be able to photosynthesize. The peripheral leaves have a waxy coating that slows water absorption but may help them continue photosynthesis throughout the wet season.
“I'd be surprised if there weren't a lot of conifers doing this,” said lead author Alana Chin, a Ph.D. student in ecology with the UC Davis Department of Plant Sciences at the time of the study. “Having leaves that aren't for photosynthesis is in itself surprising. If you're a tree, you don't want to have a leaf that's not photosynthesizing unless there's a very good reason for it.”
Trading spaces
The study also found that leaves can shift their “office space” along the tree depending on whether the environment is wet or dry.
In the wet, rainy north coast, the water-absorbing leaf type is found on the tree's lower branches, leaving the upper, sunnier levels to the photosynthesizing leaf type. That dynamic flips for redwoods in their southern range: The water-collectors live among the tree's higher levels to take more advantage of fog and rain, which occur less often in the drier environment.
To arrive at their findings, the authors collected shoot clusters from six redwood trees at five forest locations stretching from wet Del Norte County to the dry Santa Cruz Mountains and exposed them to experimental fog. They estimated the water absorption potential for seven additional trees — including the tallest living tree — and took samples at varying heights.
They then compared the anatomy and measured photosynthesis of the peripheral and axial leaves to understand their function. They also developed a physics-based causal model that allowed them to determine the leaf traits that regulate absorption rates.
Amid all the findings, Chin is most excited to have found an easy and effective way to indicate redwood trees' ability to access fog. Researchers can monitor how and if redwoods are adapting to climate conditions and a future, drier world by simply looking at the visible waxes covering the two types of leaves — something that could be captured on a cell phone camera and shared by other scientists or even members of the public.
Superlative species
Redwoods are renowned for their resilience in the face of many natural threats and inspire numerous superlatives: They are among the planet's biggest, tallest, oldest trees. They have tannin-rich heartwood, fire-resistant bark and pest-resistant leaves. This new finding is another example of their ability to respond to environmental conditions, like drought and water stress.
“The cool thing here is their ability to thrive under all these circumstances and adjust themselves to these different environments,” said Chin, who grew up near the redwoods in Mendocino County. “That things like this can be happening right under our nose in one of the best-studied species out there — none of us assumed this would be the story.”
Study co-authors include Paula Guzman-Delgado, Jessica Orozco, Zane Moore and senior author Maciej Zwieniecki of the UC Davis Department of Plant Sciences, as well as Stephen Sillett, Lucy Kerhoulas and Marty Reed of Cal Poly Humboldt, and Russell Kramer of Dipper and Spruce LLC in Washington.
The study was funded by the National Science Foundation and a Katherine Esau Fellowship from UC Davis.
Media Resources
- Alana Chin, UC Davis Plant Sciences, alanaroseo@gmail.com. Chin is currently based in Switzerland. (Please note time difference for interview requests.)
- Kat Kerlin, UC Davis News and Media Relations, 530-750-9195, kekerlin@ucdavis.edu
- Author: Ed Perry
Although many coast redwoods (Sequoia sempervirons) appear to grow well in some parts of the San Joaquin Valley, the UCCE Master Gardeners are often contacted for help diagnosing redwoods with dead branches that seem to be dying.
It's important to remember that coast redwoods are native to the coasts of Central and Northern California. In this environment, the trees are shaded by each other and experience significant cooling from fog. They also receive moisture from fog drip and high rainfall. In their native forests, redwoods grow with large amounts of forest litter over their roots.
While coast redwood trees are susceptible to some serious diseases, they are most often injured or killed by abiotic (non living) problems. High soil salinity caused by excess sodium (alkaline soil), and toxicity caused by high concentrations of specific ions such as boron and chlorides will stunt their growth and cause their leaves to turn yellow and “burn.” They grow poorly in heavy soils that are too wet, or in dry, compacted soils with poor drainage. Coast redwoods are also susceptible to iron deficiency, especially in high pH soils. They may be injured by freezing temperatures, especially in dry soil. Because they are adapted to a cool, moist environment, they will develop brown and scorched leaves during our hot and dry summers, especially if they're not adequately watered. Drought stressed trees may then be attacked by bark beetles.
In dry or compacted soils the trees grow slowly and their trunks develop a distinct taper. Under ideal soil and moisture conditions, such as along portions of the California Coast, the trunks will be nearly the same diameter from the base of the tree to several feet high. Some brown foliage in the interior of the tree is normal. In fact, it is normal for the oldest leaves to turn yellow, then brown, and finally drop from the tree in late summer and early fall. It is also normal for short twigs to turn brown and fall. New growth at the ends of branches indicates that the branches are alive and healthy, despite some dieback of twigs and leaves.
As mentioned, coast redwoods are susceptible to some diseases. In Stanislaus County, redwoods infected by Botryosphaeria canker (Botryosphaeria dothidea), crown rot (Phytophthora sp.) and Armellaria root rot (Armillaria mellea) have been identified. However, these diseases are relatively uncommon on redwoods here. If you're trying to diagnose a redwood problem, be sure to consider soil and water-related problems first.
Redwoods are forest trees. We have cultivated them for use in non-forest landscapes as street and park trees, and as specimen trees. These conditions are not always favorable to their growth or long term establishment. They grow best with shade, cool root systems, abundant mulch, and continual moisture that is relatively salt free. If you can create some of these conditions in the landscape, redwood culture and disease management will be much less problematic.
Ed Perry is the emeritus Environmental Horticultural Advisor for University of California Cooperative Extension (UCCE) in Stanislaus County where he worked for over 30 years.
- Author: Carlin Starrs
The UC Center for Forestry's Whitaker's Forest was recently featured in a video put together by the Cornell Outdoor Education program during a recent trip to climb trees and help collect cones as part of an ongoing research project. To learn more about this exciting experience, check out the video on Cornell's website.
- Author: Jennifer Baumbach
It's been over a week since we successfully completed our annual Wreath Workshop at the Buck Mansion in Vacaville. I just wanted to share with you some pictures of the prep days and then the actual workshop. I also wanted to recognize the hard work the Master Gardeners do to make this such a great event. It might entice you to sign up for the workshop in December 2014. I will take RSVP's starting in November.
Traditionally, the workshop is held the first Saturday of December. Participants pay a fee and get greens, a wreath frame, paddle wire, a bow and delicious refreshments for a fee. It's a great way for residents to kick off the holiday season and a lot of fun (work!) for the UCCE Master Gardeners of Solano County.
Oh, and note the wreaths. They are all made from the same exact materials, but each an individual, wonderful creation.
- Author: Ann King Filmer
Millions of trees, including tanoaks, coast live oak, California bay laurels, and many other forest species have been killed by sudden oak death in coastal areas of central and northern California, and Oregon. The pathogen, Phytophthora ramorum, was first linked to the massive tree death in the mid-1990s.
David Rizzo, professor in the Department of Plant Pathology at UC Davis, and his research team are studying how the coastal forest ecology is changing since sudden oak death appeared, and why coast redwoods (Sequoia sempervirens) are subsequently so much more susceptible to fire.
It is the presence of the sudden oak death pathogen in forests that poses heavier fire risks for redwoods.
“If redwoods didn’t live in forests affected by the disease, they could withstand fires just fine,” says Margaret Metz, a postdoctoral research scholar working with Rizzo.
According to Rizzo, “The disease likely created more fuel for wildfires as dead tanoak branches fell. The loss of the oaks also would have decreased the amount of shade, drying out the forest and turning it into a tinder box, one not even redwoods could survive.”
A real key, though, is the finding that dead tanoaks, still standing, carry flames high into tree canopies, scorching the crowns of adjacent redwood trees. It’s this crown injury that is believed to have caused so many redwood trees to die in a number of fires that occurred in 2008.
Rizzo, noting that an increase in fire severity is resulting from climate change and global movement of species, says, “There may be all sorts of consequences, among them, dead and dying coast redwoods.”
Additional information:
- California's iconic redwoods in danger from fire and infectious disease. National Science Foundation report on Rizzo group’s work, August 2013
- The effects of sudden oak death and wildfire on forest composition and dynamics in the Big Sur ecoregion of coastal California. General technical report
- Ecology research article, Ecological Society of America
- California Oak Mortality Task Force website