Sunday, August 1, 2010

Joshua Tree

Joshua Tree (Yucca brevifolia)

At the Mojave Desert there is a vast land area where one type of plant stands out taller than the monotonous sea of low-growing shrubs.  This plant is the Yucca brevifolia which is commonly known as the Joshua tree.  The desert sits at an elevation of six to ten thousand feet above sea level which means that it is not only dry but also cold particularly in the winter.  To compare this with our town which is located at 650 feet above sea level; every year one or two of my plants succumb to the freezing temperatures of winter. 

As we traveled through the desert, I wondered how this plant persists in this dry and cold environment.  I understand that the Joshua tree is indigenous to the Mojave Desert and it is not found anywhere else in the world (except where it is cultivated).  What then makes it a plant of this desert?  Here's what I found out to explain this mystery.  This plant in fact develops two types of root systems.  One is a storage root in the form of bulbs (4 feet in circumference) that are buried very deep - 10 to 30 feet into the ground.  This is where water is stored.  The other type is what I call the explorer-roots.  They scout for water on the shallow ground.  Water from rain or melting snow in this desert is often concentrated within the upper layer of the soil. 

The Joshua tree lives on what is necessary instead of optimum.  It maintains the minimum number and size of leaves to reduce moisture lose through transpiration.  It looks whimsical but that's because it grows very slowly; it branches only by the termination of apical growth due to flowering.  It is not there to get big fast but to live and reproduce itself. 

I guess we could learn from the Joshua tree in the way we live.  Avoid excessiveness and learn to live with what's within our means. We could learn to recognize our needs against our desires.   The Joshua tree looks very austere as compared to most trees but it sits on a hefty reservoir of water.

We had to stop to get closer to a Joshua Tree.

The Joshua tree is unique to the Mojave Desert.  Do you know of other plants that are specific to one particular region?  What characteristics do they have that allows them to adapt to that particular area? 

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