Yucca Brevifolia
I had to work on some business today, entering submissions of artwork for various entities. Next was a trip to the local art supply store for a couple items I forgot. After lunch I did some drawing in my room, and then headed out to explore a little before sunset. I didn't get far, but took my time looking at the Joshua trees in detail. For those not familiar with this fantastic plant, here is some information:
The scientific name is Yucca Brevifolia; they are members of the agave family, not a tree.
As the story goes, the name "Joshua Tree" was gven by a small band of Mormons passing through in the 1950s who thought they looked like the prophet Joshua pointing them to the promised land.
They live predominantly in the Mohave Desert, but can be found in part of closely surrounding areas.
There are two species, yucca brevifolia brevifolia is larger and found in the western Mojave (including in JTNP), and yucca brevifolia jaegariana, which is smaller and found in the eastern Mojave.
Trees can grow from seeds, or from underground rhizomes that spread out from the parent tree.
Young trees can grow an average of 3 inches in their first five - ten years, while adult trees grow less than one inch per year.
The trunks are filled with a fleshy pulp that does not have growth rings, so dating Joshua Trees is highly challenging. Trees that are 30 feet tall are generally estimated to be hundreds of years old. The tallest treas reach about 49 feet. Some are believed to survive a thousand years.
Joshua Trees sometimes flower in the spring. Blossoming requires a winter freeze and adequate spring rain. Researchers believe that the freeze damages the end of the branch and triggers flowering. After a flower appears, the branch splits again. Some Joshua Trees never flower and grow straight, some have abundant, random branching.
The dead leaves dry up and fold back along the trunk and branches, offering shade to reduce the heat and loss of water due to evaporation.
Joshua Trees require the yucca moth to pollinate, and yucca moths require Joshua Trees to reproduce. The moth gathers pollen and works it into a ball which is deposited into the stigmatic tube, fertilizing the plant. At the same time, the moth lays her eggs inside the flower ovary. When the eggs hatch, they eat the fertilized seeds, but never more than 10% to allow for healthy plant populations. The trees are able to actively abort ovaries in which too many eggs have been laid.
The Shasta ground sloth used to feed on Joshua Trees, and their dung is believed to be responsible for the spread of Joshua Trees over a large range. Since the sloths went extinct around 13,000 years ago, at the end of the last Ice Age, the tree's range has shrunk by nearly 90%.
Severe drought in recent years caused the death of a large number of trees in the park. While the trees are can survive extended drought, they can not always survive damage done by thirsty rodents who chew through the bark to get to the moist inside.
The Chuilla Native American's ancestors used the leaves to weave baskets and sandals, and harvested seeds and flower buds for meals.
Want to read more? Here is a link to the park's page about Joshua Trees: https://www.nps.gov/jotr/learn/nature/jtrees.htm
As the story goes, the name "Joshua Tree" was gven by a small band of Mormons passing through in the 1950s who thought they looked like the prophet Joshua pointing them to the promised land.
They live predominantly in the Mohave Desert, but can be found in part of closely surrounding areas.
There are two species, yucca brevifolia brevifolia is larger and found in the western Mojave (including in JTNP), and yucca brevifolia jaegariana, which is smaller and found in the eastern Mojave.
Trees can grow from seeds, or from underground rhizomes that spread out from the parent tree.
Young trees can grow an average of 3 inches in their first five - ten years, while adult trees grow less than one inch per year.
The trunks are filled with a fleshy pulp that does not have growth rings, so dating Joshua Trees is highly challenging. Trees that are 30 feet tall are generally estimated to be hundreds of years old. The tallest treas reach about 49 feet. Some are believed to survive a thousand years.
Joshua Trees sometimes flower in the spring. Blossoming requires a winter freeze and adequate spring rain. Researchers believe that the freeze damages the end of the branch and triggers flowering. After a flower appears, the branch splits again. Some Joshua Trees never flower and grow straight, some have abundant, random branching.
The dead leaves dry up and fold back along the trunk and branches, offering shade to reduce the heat and loss of water due to evaporation.
Joshua Trees require the yucca moth to pollinate, and yucca moths require Joshua Trees to reproduce. The moth gathers pollen and works it into a ball which is deposited into the stigmatic tube, fertilizing the plant. At the same time, the moth lays her eggs inside the flower ovary. When the eggs hatch, they eat the fertilized seeds, but never more than 10% to allow for healthy plant populations. The trees are able to actively abort ovaries in which too many eggs have been laid.
The Shasta ground sloth used to feed on Joshua Trees, and their dung is believed to be responsible for the spread of Joshua Trees over a large range. Since the sloths went extinct around 13,000 years ago, at the end of the last Ice Age, the tree's range has shrunk by nearly 90%.
Severe drought in recent years caused the death of a large number of trees in the park. While the trees are can survive extended drought, they can not always survive damage done by thirsty rodents who chew through the bark to get to the moist inside.
The Chuilla Native American's ancestors used the leaves to weave baskets and sandals, and harvested seeds and flower buds for meals.
Want to read more? Here is a link to the park's page about Joshua Trees: https://www.nps.gov/jotr/learn/nature/jtrees.htm
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| Joshua Trees come in a wide variety of shapes, this on has a fairly straight trunk and a tight grouping of branches. |
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| This tree has some spines that are still green, poking through the protective layer of dead spines. |
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| This tree has abundant short branches. |
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| A closeup of the layer of dead spines on the branches. |
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| Dried flower stalks, some look older than others so I would guess that these are from multiple years. |
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| A closeup of the spines, which curve upward to help funnel water along the trunk to the roots. |
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| The roots of Joshua Trees are found within the top inches of soil, and fan outwards under the surface to collect rainwater that penetrates only the top couple inches of dry, packed desert soil. You can see the thin finger-like roots of this toppled tree, which is continuing to thrive. It is a misconception that fallen trees are doomed to death. |
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| A tree with wildly unpredictable branching. |
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| A few different styles of trees in one shot: a loose clump of branches in the close tree, a tight clump in the distant center, and a grouping of individual trunks with few branches in the distant right (rhizome versus seed growth). |
