For those interested in seeing a partial view of a full-grown Joshua tree’s (Yucca brevifolia) root system, read this post. This plant grows along Alamo Road about 5 miles northwest of my property. It predates the road by at least 100 years or so, but just happened to be on the edge of the easement when Alamo Road was widened to its current alignment. I’ve noticed this large and beautifully-shaped 16 foot (5 meter) tall tree for years as I drive past it. Although the basally flared trunk was clipped a few times by the county road grader, it’s mostly been unbothered by the road maintenance activities – until now that is.

Heavy late summer rains and flooding about 6 weeks ago have eroded quite a bit of the embankment back toward the tree’s root system, undermining and exposing it to the sun and the air. As monocot plants, Joshua trees have a fibrous root system like palms and grasses do, as opposed to the woody, branching one of dicot trees. The tangled mat of pencil-thick roots extends laterally about as wide as the tree’s crown does – about 6 to 8 feet radially in all directions and 3 to 4 feet deep. I placed my shadow into the second image to show a bit of scale for the size.

This is a good illustration of how roots do not necessarily need to be huge in order to effectively anchor a large plant to the ground. Thousands of small roots are about as useful as fewer, thicker roots are. Plus the fibrous root systems of yuccas and other monocots are not as prone to heaving sidewalks, cracking foundations, or breaking water or sewer lines as the thick, massive underground roots of large trees like pines, oaks, maples, or eucalyptus, for example. With dicot trees like those, the roots start small and over time can massively increase in diameter, buckling nearby buried or surface objects. Joshua tree roots, while dense, never get thicker in diameter than about 1/4 inch (6 mm), and as such they tend to leave those things intact.

The future of this Joshua tree is uncertain. Continued erosion will eventually topple it, and it’s also in danger from the activities of the road grader and repair work. Also, exposing the root ball to drying from the sides like this (which would normally not occur) will place the tree under extra stress, so that will probably take a toll too. I hope that it will continue to live, but it may be destroyed by either one of these forces before too long. Therefore, if nothing else, I wish to use the tree’s plight to help educate people before it disappears. Wish the tree luck!

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Note: This post was originally made on Facebook on October 15, 2013, five years before I also published it as a blog post. Since I regularly get asked about Joshua tree root systems from people looking to buy one, including those who want other yucca species as well, I figured that this would be illustrative of the appearance and morphology of those roots. The tree is still present in October 2018, and has not been eroded away much worse, been impacted by the road grader, or dehydrated to death. So far, so good….