Joshua Tree Woodland
Plant Communities
Plant Associations: Joshua Tree woodland often overlaps other plant communities such as blackbrush scrub, grama-gellata grasses, sagebrush or Pinyon-Juniper woodland (Gucker, 2006). Commonly overlapping plant communities are called plant associations.
Plant communities are described by dominant or abundant plant species. Joshua Trees most often occur at relatively low densities (not very abundant) but may seem to be a dominant plant due to their visual presence (Gucker, 2006). Joshua trees are also endemic or exclusive to the Mojave desert. Because of this, Joshua Trees can be considered an important indicator plant of the Mojave Desert, but may not necessarily qualify as a dominant plant species.
The climate of the Mojave Desert can be described with cold winters, hot summers and low precipitation. Joshua Trees generally grow in areas with annual precipitation ranging between 3 and 15 inches per year (Gucker, 2006).
Environmental conditions, such as precipitation, limit the growth and distribution of plants. In Nevada Joshua Trees grow between elevations of 3,600 and 6,900 feet (Kartesz, 1988). In California, Arizona and Utah the trees have been found at elevations below 3,600 feet and up to 7,200 feet in Utah (Gucker, 2006). An general elevation range for Joshua Trees in the Mojave Desert is between 2,000 and 6,600 feet (MacKay, 2003).
Source: http://www.delange.org/JoshuaTree/Dsc00086.jpg |
Quick Info
- Joshua Trees flower during the spring.
- New branches grow after flowers drop off.
- The Joshua Tree’s average life span is about 150 years (Keith, 1982).
- One 60-foot tall tree is about 1,000 years old (Lenz, 2001).
- Joshua tree seeds are transported by small mammals and wind (Gucker, 2006).
- Joshua Trees grow in silt, loam and sandy soils (Keith, 1982) and can tolerate alkaline and saline soils.
- Joshua trees recover vary slowly after fires.
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Issues
Invasive grasses such as cheat grass and red brome blanket many areas of the Mojave Desert. The biomass produced by the grasses provides fuel for fires. Fire can be started by natural causes such as lightening or by humans. Historically, fires did not exist in the southwest deserts of the U.S. This may be because there was little biomass (plant litter) to be burned and because plants are spaced far apart (low density) (Leary, 1979).
Think of a pine forest where dried pine needles drop from trees year round and accumulate on the forest floor. This dry material provides fuel for fire and the pines have evolved to survive in this environment, and may even require fire or intense heat for their seeds to germinate or begin to grow. But in the desert there was no material on the ground, and now, because of the invasive grasses, there is fuel in between plants which can assist fire in spreading from one plant to another.
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"Fires were rare in Joshua Tree National Park until about 1965. Since the establishment of red brome and cheatgrass, fires have become more frequent and more severe.?lt;/I> (Gucker, 2006)
Visitors to Red Rock National Conservation Area (Nevada) or Joshua Tree National Park (California) may often see burnt Mojave Yucca (Yucca schidigera) or charred Joshua Trees. Joshua Trees evolved to survive in the desert, where fire was not a commonplace disturbance. After fire disturbance it may take decades or centuries for Joshua Tree Woodlands to return to conditions similar to those prior to burning (Emming, 2005).
Wildlife: Coming Soon!
Amphibeans: Coming Soon!
Birds: Coming Soon!
Insects: Coming Soon!
Mammals: Coming Soon! Coyotes
Reptiles: Coming Soon! Desert tortoise
Joshua trees provide habitat and food for many different species of wildlife, including Mammals: Ground squirrels, wood rats, jackrabbits, kangaroo rats, southern grasshopper mice,
Birds: American kestrels, common nighthawks, ash-throated flycatchers, cactus wrens, northern mockingbirds, loggerhead shrikes, and orange-crowned warblers, Scott's orioles,
Reptiles: Night lizards and desert spiny lizards, Other: Spiders, scorpions, and beetles. (Gucker, 2006)
Emming, Jan. 2005. Special conservation report: Nevadagascar? The threat that invasive weeds and wildfires pose to our North American desert biomes. Part 1: The Mojave Desert and Joshua tree woodlands. Cactus and Succulent Journal. 77(6): 302-312.
Gucker, Corey L. 2006. Yucca brevifolia. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ (2006, September 28).
Kartesz, John Thomas. 1988. A flora of Nevada. Reno, NV: University of Nevada. 1729 p. [In 2 volumes]. Dissertation.
Keith, Sandra L. 1982. A tree named Joshua. American Forests. 88(7): 40-42.
Leary, Patrick J. 1979. A study of vegetational reinvasion following natural fire in Joshua Tree National Monument: I. Preliminary report. Contribution Number CPSU/UNLV No. 019/01. Las Vegas, NV: University of Nevada, Department of Biological Sciences, Cooperative National Park Resources Studies Unit. 34 p. Unpublished report on file with: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory, Missoula, MT.
Lenz, Lee W. 2001. Seed dispersal in Yucca brevifolia (Agavaceae)--present and past, with consideration of the future of the species. Aliso. 20(2): 61-74.
MacKay, Pam. 2003. Joshua tree: Yucca brevifolia Engelm. In: Mojave desert wildflowers: a field guide to wildflowers, trees, and shrubs of the Mojave Desert, including the Mojave National Preserve, Death Valley National Park, and Joshua Tree National Park. 1st ed. Guilford, CT: Falcon Books: 159.
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