Take a Moment to Listen to the Trees

August 21, 2013

Trees don't have heartbeats. You can't put a stethoscope up to a tree trunk and expect to hear that familiar dull thumping that gently insists, "I am alive." At least I'm pretty sure you can't, no matter what hardcore LOTR fans say, Ents do not exist! However, this doesn't mean you shouldn't try putting a stethoscope up to a tree and listening. What do you think you would hear?

Alex Metcalf knows. Okay, so I know that silver trumpety thing isn't a stethoscope, but it would be really gross for a Museum to let thousands of school children and other visitors use the same stethoscope to listen to a tree. Since we're so considerate of our visitors and we really wanted everyone to be able to listen to the inner workings of a tree, we worked with British artist, Alex Metcalf. He created a listening tree installation in our new Nature Gardens by hooking up microphones to one of our coast live oaks, Quercus agrifolia. When you put your ear up to one of the four trumpets Alex installed, you'll hear one of two things. First, there's a deep rumbling sound that is the amplified sound of the oak vibrating. If you're lucky enough, especially if you are visiting on a warm day, you'll likely also hear some tiny popping that is the sound of "water passing through the cells of the Xylem tubes and cavitating as it mixes with air on its way upwards." Xyle-what you say? You see, trees have a system a bit like our veins that moves water, dissolved nutrients, and food between the leaves, trunk, and roots. Botanists call it a vascular system and it consists of two main cell types, xylem (ZI-lem) and phloem (FLO-em). Xylem tubes are the main way trees and other vascular plants get water from roots to leaves and other parts. Alex explains, "as the leaves lose the water through evaporation the cells below the leaf become drier and they in turn pull water from the next cells below, this carries on down the tree all the way down to the roots. The water molecules cling together and form a water chain from the leaves to the roots under tension-cohesion." He continues, "The Tree Listening Project aims to provide an experience that links both science and art by engaging the public with what happens inside a tree, and to excite and inspire a keen interest in trees." Hopefully this has inspired a keen interest in visiting our Nature Gardens to listen for yourself. So go grab your bike, jump on a bus or the train, or put the pedal to the metal in your car and come on down to the Nature Gardens and hear our oak tree telling you, "I am alive!"

(Posted by: Lila Higgins)


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First Baby Oaks Sprout Up in the North Campus

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The North Campus is the proud parent of some baby oak trees!

Baby coast live oak sheltered by wallCarol Bornstein, our new Director of the North Campus Gardens, discovered a couple of oak saplings on one of her recent outdoor forays. The babies are coast live oaks, Quercus agrifolia, of which we recently planted several trees. We've also planted another species of oak, the Engelmann oak, Quercus engelmanni (we planted only three of this species). Both species reside in the section of the garden called the urban wilderness which is composed of several kinds of California native trees and shrubs.

This might be the mother oak!Oak trees provide amazing habitat value, and this is the main reason we planted them. By putting in such a  sizable stand of oaks we're hoping our created wilderness will provide habitat for a whole slough of organisms rarely, if ever, seen before in Exposition Park. In just one oak tree it would be easy to find hundreds of species of associated plants and animals and thousands of individuals (think how many birds, ants, or squirrels you find in an oak tree). One species that has already shown up with our oaks, is a tiny insect called a whitefly.

Crown whitefly nymphs on oak leaf(each nymph is only 1 millimeter long)It was once again thanks to Carol, who was out inspecting our lovely oaks, that we discovered these small insects. At first we thought they might be a scale insect, but Brian Brown, the Museum's Curator of Entomology, identified them as crown whiteflies, Aleuroplatus coronata. As adults these small white homopterous insects (group of insects consisting of aphids, cicadas, scales, etc) fly around to find a suitable location to lay their eggs. For the crown whiteflies their plant of choice is oak. What you see in the image above are the nymphs (immature forms) of the whitefly, they have no wings but are covered with white waxy secretions that make them look like little crowns. The nymphs feed on the leaf's juices by piercing and inserting their mouthparts into the leaf. They can cause damage to the plant's health if their numbers are high enough, and they can also transmit disease organisms from one tree to another (not unlike mosquitos transmit malaria).Go check out your local oaks and see what animals live on them!

(Posted by: Lila Higgins)

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New Neighbors     A pair of Bushtits, Psaltriparus minimus, just built their nest in the live oak tree behind the Butterfly Pavilion. Kimball Garrett, our resident bird expert, found the nest this Monday and promptly sent me an e-mail detailing the nest's location. As soon as I got into work on Tuesday morning, I headed out to the Butterfly Pavilion to check it out.      

Adult Bushtit, Psaltriparus minimus   Nest Hunt   Thankfully Kimball had given clear instructions to find the nest, as it was very well hidden in the oak foliage. The effort was well worth it, as it was one of the coolest nests I've ever seen in the wild. As the picture below shows their nests are woven from dry plant material and hang from branches of the tree. They are small and dainty, this one measures about seven inches from top to bottom. The small opening at the top of the nest, which is only about an inch in diameter, is just big enough for the adults to enter and exit.      

Bushtit entering nest   Bushtit Behavior After spending a good portion of my morning watching the nest, I realized I had to blog about it. But what is a blog without images, or even better some actual video footage. I ran up to my colleague, Sam Easterson's office to see if he could get some for me. Sam recorded the nest for about an hour, and we captured some interesting behaviors, including removal of fecal sacs! A fecal sac is clean, tough membrane that encloses the excrement of young birds. Not all birds produce fecal sacs, but for those that do sacs are usually produced directly after each feeding and promplty removed by the adult to maintain a clean nest interior.                Bushtit cleaning nest   Sam Easterson is a video naturalist and also our new Media Producer for the North Campus and Nature Lab exhibits. He's really into implanting cameras into natural environments, and is best known for his animal borne imaging work.

(Posted by: Lila Higgins)


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