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A Discussion of Tree Sweat

Published on 7/1/2023

Several members of the community gathered on June 21 to watch the League of Women Voters/Wabash College Green Issues movie Reflection: A Walk with Water (Bullfrog Films). The narrative of the film was a group of people walking the 200-mile length of the Los Angeles aqueduct, from Owens Valley east of the Sierra Nevada mountains to LA. Interludes about water conservation, rain generation, soil health, and water ecosystems tutor viewers to be able to see and reflect on the fragility and centrality of rainfall and water retention in all of our lives.

The LA aqueduct was opened in 1913, but by the 1920’s it had drained Owens Lake. As of 2013 (according to Wikipedia), Owens Lake is the largest single source of dust pollution in the US, despite a 2004 court order for the LA Department of Water and Power to mitigate the dust (which they have worked on).

As revealed in the film, LA receives 10-15” of rain per year, adequate to meet the needs of all of the residents. But two-thirds of the city is paved, so most of the rain runs off into the LA aqueduct and runs into the Pacific Ocean. Prior to a legal change about a decade ago, LA residents (as with much of the southwest) did not have the water rights to the rainwater that landed on their roofs. Thus it was illegal to capture rainwater. Now, however, this water can be recaptured and reused, rather than letting it run into the ocean.

The movie contained a number of interesting facts. Inland rain is mostly from tree and other plant sweat (eew?). (Ocean rain is from evaporation from the ocean.) This also means that if inland areas dry up (such as Owens Lake) and the vegetation dies, there is nothing to produce rain, and the environment spirals into a desiccated landscape.

Another interesting fact is that if soil is hotter than air it repels water, rather than letting it seep in. Healthy soil, containing bacteria and fungi, holds onto water. Tillage of fields kills the soil, which then requires the nutrients to be replenished by spraying; one specialist interviewed in the film referred to this as chemotherapy. Instead, leave the root beds. Cut off the previous crop of veggies at the level of the soil, leaving the roots. Then plant the next crop on top of these. Tree roots also provide an ecosystem for critters and fungi, to act as a sponge to soak up water, purifying it in the process.

In one scene people built a lakebed. When the rains came and filled up the lake, microorganisms proliferated, birds came, the variety of birds expanded, and the water wicked up into the surrounding landscape, greening it, similar to how a napkin placed in a glass of water will wick up the water. Healthy soil allows for this system to function well. As one of the specialists interviewed in the film said, “a flood is having more water come down than can be absorbed by the ground”. Healthy trees and healthy root beds lead to healthy soil that can act as a sponge and absorb the water, filtering it down to replenish the aquifers, rather than letting it become a flood.

We invite others to join us for viewing and discussion, for one or both of the remaining 2023 Green Issues movies, sponsored by Wabash College and the League of Women Voters of Montgomery County. Wednesday, July 19 we will show The Plastic Cup: The Official Story of the Plastic Pirates (a race with boats made from found plastic bottles). Wednesday, August 9 we will have a double header with Into the Dark (an expedition into the darkest regions of the Arctic) and Evergreen (a documentary on the building of a timber house by Wabash Religion Professor Derek Nelson, who will be present for the showing). Both movies are at Korb Recital Hall, Wabash College Fine Arts Center on Grant Avenue, at 7 pm. We hope to see many of you there!

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