After Two Decades Of Failure, New Generation Of Western Sycamore, White Alder Saplings Survive Their First Year

A piece of wood

Western Sycamores and White Alders are two of the most common tree species in Eaton Canyon, the former of which being considered a keystone species. Both of these tree species are also considered ‘relic’ species as they no longer exist across the Los Angeles Basin at the extent they did during the ice age 11,000 years ago. Today, their habitat is limited to the canyon floors where water is more regularly available. Both of these tree species require lots of water and cool summers to get through their infancy. With climate change making summers in Pasadena 7.2°F hotter than they were 100 years ago, there is no longer any such thing as a “cool summer” locally. Even worse, these higher temperatures mean increased rates of evaporation which dry up the creek faster than it normally would. Between 2006 and 2022, it is believed that there were no successful Western Sycamore or White Alder saplings at all below the first waterfall at Eaton Canyon.

All of that appears to have changed, however.

A field with a mountain in the background
Western Sycamores (yellow trees) huddle on the wash floor where there is enough water, avoiding the slopes

Since October 2022, weather stations around lower Eaton Canyon have reported between 73.06″ and 78.78″ of rainfall. This is currently the second wettest 24-month period on record, and there are still 6 months remaining in the water year. Records go back to 1909.

In spring 2023, something happened at Eaton Canyon that hadn’t been seen since 2019; creekside tree saplings. Winter 2023, despite its huge rains, lacked significant flash flooding in the canyon to destroy the wash. Thousands of Western Sycamore and White Alder tree sapling sprouted alongside the creek and began to grow. The worry, of course, was that summer 2023 was going to be too hot and dry for these saplings to survive just like every other summer of the past 2 decades had been. Indeed, July 2023 was record hot with more afternoons over 95°F than any other July on record. As a consequence, many of these young saplings began to perish especially in the lower wash where the creek had begun to dry up.

A pile of green grass
Muddy creekside depressions like this are a nursery for native tree saplings

As Tropical Storm Hilary took aim at Southern California in late August 2023 and community members began sandbagging their homes, climatologists awed at the sheer rarity of such an event. The California Current is typically far too cold to support tropical entities making landfall in Los Angeles County, but in 2023, the perfect combination of ingredients made it happen. A midsummer deluge was certainly going to have an impact on Eaton Canyon, especially now that we had an entire new generation of tree saplings fighting for survival alongside Eaton Creek. The deluge came, no saplings died to flash flooding, and the creek was rejuvenated.

A large mountain in the background
Eaton Canyon soaked at the height of summer 2023, precisely what these new trees needed

As of March 31, 2024, another winter of soaking rains without extensive flash flooding has kept these young tree saplings alive. Now, they have made it a full calendar year and have a much better chance of making it to adulthood. A repeat of 2023’s tropical storm Hilary is unlikely, but with the trees having developed some form of a root system, they will be better equipped to handle the drought and heat coming this summer.

A young White Alder emerges from decaying Mule Fat

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