Arroyo Seco Seedlings and Erosion Issues

September 19, 2012  •  2 Comments

Oak seedlings in Arroyo Seco In an earlier post, I documented erosion in Arroyo Seco and some of the plant life growing along the sides and in the creek bottom. This is an update to that post.

I'm on record as stating that newly planted trees do not need to be watered as much as most people claim. The seedlings along Arroyo Seco are a good test of my assertion. Last year, after the acorns dropped in the fall, we had sufficient rain for acorns to sprout. I took pictures of some of the seedlings and wondered how successful they'd be. Some of them met their demise because of the mowers. The mowers tend to mow from the curb up until the drop off into the creek bed. That area is also the place where the seedlings would otherwise be best off, because downward growing roots are perpendicular to the surface and grow far away from the area that dries up from evaporation. Unfortunately, they don't fare well against lawn mowers. They can survive by resprouting at their bases, and the oaks that grow around here are actually pretty good about that. I didn't spend much time looking for plants that had survived that way. At this time of year, I think they're more likely to hunker down for the year and come up again in the spring. So I'll look again in the spring and carefully examine them to distinguish whether they are 2012 plants or 2013 plants.

Bur Oak Seedling

Most of the seedlings I saw were bur oaks, like the one, above. Some were shumard oaks, like the one, below. I didn't see any live oak seedlings, but I also didn't look very hard. 

Shumard Oak Seedling All our local oaks send a main root down deep into the soil when they sprout. Then they send a sprout up above the soil and unfurl a handful of leaves. Vertical growth is minimal for the first year. The plant concentrates on the portion below the soil. A surprising amount of girth is added to the root during the first year. This is not exactly a tuber, but it serves a similar function. The plant can tap into the moisture reserves of the thick root if it gets dry.

As I stated earlier, most of the seedlings along the top were mowed down. But there were plenty along the steep edge:

Seedlings along embankment and in the creek bed:

Oak seedling in creek bed In the middle of the creek bed is not the best place for trees to grow up. Well, good for the tree, but bad for erosion. Objects in the center of the creek will force water flow to the edges. Then you get a situation like this where a concrete channel under an intersection dumps silt in the middle of the creek causing the creek to go to either side, thus eroding the edges.

Silt accumulating in the center forces erosion on the edges There are places where the soil has eroded from around the base of grasses, which are typically thought of as good erosion control plants.

Soil eroded from beneath an oak and grass

But enough about erosion. The rest is simply a gallery of interesting plants along the arroyo.

Viola sp. Some sort of violet.

Commelinantia anomala Commelinantia anomala Commelinantia animal growing among violets and horse herb.

Other miscellaneous plants:

Neptunia pubescens var. microcarpa Ragweed and Four O Huh? What's this last one? The time of day is wrong, but that is a Four O'clock plant and a ragweed plant growing together. Maybe I'll get another picture when the four o'clock flowers are open (not 4 o'clock).

 


Comments

Victor's Pictures
You could very well be right.
Bob Jacobson(non-registered)
I wonder if the plant growing with the 4 o'clock (in the the bottom Arroyo Seco photo) is actually an amaranth (genus Amaranthus) as opposed to a ragweed (genus Ambrosia). It looks more like the former to me although a close-up photo would be needed to confirm this.
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