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In the Wake of the Flood by Interpreter Eric (March 2024)

In my recent articles about our Western Sycamore trees (Platanus racemosa), I've often lamented the absence of new saplings sprouting from fallen seeds, painting a somewhat bleak picture for the future of these iconic trees that make our park so unique. Well, I am thrilled to report that this past year has proved me wrong! Immediately after the 2023 flood waters receded, the newly excavated creek banks seemed lifeless; however, hidden amongst the gravel and debris were the promises of life yet to come. 

Plants growing among rocks.

On a breezy September morning, I went out for a quick walk along the edge of the creek to observe what was starting to grow, expecting to notice a mixture of the usual invasive species like palms, eucalyptus, and stinkwort. As I combed the shoreline, looking at all the little green sprouts poking up, I found myself pleasantly surprised to see quite a bit more diversity. There were tons of cottonwood and willow saplings, tule, watercress, Spotted lady's thumb (new to me!), and American nightshade amongst many other species. 

And then, there was something else that caught my eye... A small plant jutting out from the rocks with some vaguely familiar leaves. I crouched down to inspect a bit closer. The light green leaves felt velvety to the touch with three finger-like lobes reaching towards the sky. It was a baby sycamore, sprouted from a seed! Once the initial excitement began to subside after finding this baby tree growing nonchalantly on the bank of the creek, I started to glance around the nearby wildlife with a new perspective. I continued along the edge of the creek with a pep in my step, and within a few feet, I spotted another one. This one was a bit smaller, but it still had that same fuzzy texture and three fingers pointing up at the sky. Another. And another! Within a few minutes of exploring throughout a 40-foot section along the creek side, I had found 20 or so baby sycamores. 

A map with marked points, possibly trail markers or points of interest, near roads and parkland.

Since then, we have been going out with a GPS navigator and recording all the baby sycamores we can find. We have found around 200 growing along the creek so far, with some big swaths of creek yet to be explored. 

Once I was able to fully process this exciting discovery, I found myself flooded with various intriguing questions. Why are they growing this year? Why didn’t they grow last year? Will these young trees survive and grow into adult trees? Have sycamores been happily sprouting in the park, but just not surviving their first years only to die before being noticed? How can we ensure that these ones really do survive?! I only know one thing for sure—I am not an expert! But I do have some ideas.

First of all, let's recall the great flood of 2023! Sycamores have a very specific ecological niche where they are able to thrive. Much of lower Sycamore Grove Park can be described as a Sycamore Alluvial Woodland. The key word here is "alluvial," referring to the ephemeral quality of the soil, which is constantly recharged with silt, clay, and gravels (alluvium) from up stream. A good example of another alluvial system would be at the beach. Each time the tide rises and falls, the beach itself changes. Sands are carried away by the currents, meanwhile new sands are being deposited. Driftwood drifts onshore and spends an afternoon up there until it is carried away once again. In our case, instead of constant waves pounding the beach, we have periodic flooding events that rearrange the stream channel, sending logs and gravel downstream and then replacing it with organic material from upstream. Unlike the constantly changing beaches, these floods happen on average every 10 or so years, which (hopefully!) gives the newly enriched soil time to send up some hardy enough trees to withstand the next flood. 

Various cut plant stems with budding leaves in a plastic container filled with perlite, possibly for propagation.
Two pictures of baby sycamores – one of the newest cuttings in pearlite, one of the success from last years cuttings.

There is also the convergence of another big factor that I believe is playing a role in this large-scale recruitment of baby sycamores. With such a big year of rain came an equally huge snowpack in the Sierra mountain range. While that snow began melting as temperatures finally warmed up late last spring, California's water ways were gushing with water. The draught was declared to be over, allowing the Department of Water Resources to be able to take advantage of the surplus of flowing water. The South Bay Aqueduct pulls water from the Bethany Reservoir, fed by the Delta, and carries that water via man-made canals over the Altamont Pass, along the northwest edge of Lake Del Valle and off to Santa Clara, delivering water along the way. Because of this influx of excess water, our Arroyo Del Valle (and the Mocho Creek that flows through Livermore) has been continuously flowing all year, supplied by delta water via the aqueduct. Normally, even after such a big rain fall, the arroyo would have ceased flow by late summer. 

Plant pots with soil, some with young plants and leaves, scattered on the ground with pine needles.

The purpose of this unnatural flow is to 'recharge' the aquifers or ground water for human water consumption, but raised ground water levels can also be beneficial for any shallow rooted plant. One of the biggest hurdles to overcome when planting container-grown sycamores into the park is supplying them with ample water for their first few years, at least until they are able to establish an effective deep root system. I have to assume that this easy access to water through what would have otherwise been a hot dry summer had a large impact on the success of these saplings.  

We are excited to continue to keep an eye on these young trees! As I write this article in December 2023, while walking along a stretch of creek to check on the progeny, I saw their tiny three-fingered leaves starting to take on the characteristics of yellow and orange leaves preparing to drop soon. It's time for the sycamores to patiently wait out the winter months until the warmer weather wakes them up again. If we are lucky, these young trees will be taking this time to continue growing out their root systems, and then in June or July they will open their patient leaf buds, reaching up little fuzzy hands to soak up some delicious California sun once again. 

Smiling person in a green hoodie and cap, standing before a tree with sunlight filtering through the foliage.


Note from the Author: 

We are still collecting cuttings and learning how to grow a new generation of trees to be planted into the park. Here are some successes from last winter's cuttings, and a new batch from this year!