GEOG5: The Mojave Desert Ecosystem

Monday, November 19, 2012

Mulching (Pictures)

Mulching is the process of covering up trails and roads with vegetation, thereby restoring the natural look of the landscape, promoting vegetation regrowth, and protecting the land from further invasion. The following pictures show the effects of vertical mulching (burying bundles of straw or brush into the soil and allow water to seep into the earth) in 2005 at Kern County, California (Webb 388).

Before vertical mulching:

After vertical mulching:

Works Cited:

Webb, Robert H., Lynn F. Fenstermaker, Jill S. Heaton, Debra L. Hughson, Eric V. Mcdonald, and David M. Millar, eds. The Mojave Desert: Ecosystem Processes and Sustainability. Reno, Nevada: University of Nevada Press, 2009. Print.

What can we do?

The naturally arid landscape and harsh weather conditions make it unlikely that the Mojave Desert will be naturally restored anytime soon. So scientists have begun to turn to more active methods to restore the ecosystem of the Mojave Desert.

Although attempts have been made to replant endangered plant species, continued OHV and grazing prevent long-term effects, making these ventures all but futile. If plant re-growth is to be promoted, the first step required is to regulate, or possibly even ban the damaged areas from further invasion by vehicles and livestock; providing well-maintained irrigation has also showed promising results in restoring native plant species (Lovich). Fences, barbed wire, or even straw bales that do not contain nonnative seedlings or weeds may be utilized to form barriers around protected sites (Webb 386). Another way to promote vegetation growth and also restore the natural landscape of the desert is to decompose the soil to reverse soil compaction—plowing the land can help lessen soil compaction, though it may promote soil erosion instead. Existing plants at the site must be carefully preserved, so that the roots hold the soil together and reduce the negative effects of plowing (Webb 387). The method most commonly used today to restore the desert ecosystem is called mulching; this method either covers up manmade trails with natural vegetation, or sets up stacks of straw or brush upright in the soil (Webb 389). By doing so, this process helps the soil recover and restores the natural look of the landscape, protecting it from further invasion by OHV drivers who tend to stay on clearly marked trails (Webb 388).

A study conducted by Lori Hunter predicts that up to 80% of native plants and animals may be preserved if the area of desert land used in urban development in the Mojave is compacted (Hunter). However, planning land development in the desert requires money and data, neither of which has been in abundance for the land managers who are charged with caring for the land (Webb 379). One of the most important things needed for the reconstruction and preservation of the Mojave Desert is information—more studies must be conducted to have more accurate rainfall predictions, a more complete record of historical damages done to the landscape, and a more comprehensive understanding of the relationship between global environmental changes and changes in the Mojave (Webb 169). Only when the causes and effects of environmental degradation have been assessed can we begin to take steps to reverse the damages.

Works Cited:

http://www.springerlink.com/content/pg318mg147228070/fulltext.pdf

http://www.springerlink.com/content/pyhr28ncjnt8ppuc/fulltext.pdf

Recovery Time Estimated (Chart)

The above chart shows Lovich's predictions of recovery time of desert landscapes after different types of damages. Most damages are shown to have extremely long recovery times--more active recovery methods must be implemented if the Mojave Desert is to be restored more effectively.

Works Cited:

http://www.springerlink.com/content/pyhr28ncjnt8ppuc/fulltext.pdf

Saturday, November 17, 2012

Controlled Disturbance Experiment

A controlled experiment was conducted in April of 1979 to measure the effects of motorcycles as they travel over the desert landscape. The site was near Fremont Park in the Western Mojave Desert. When the site was revisited 20 years later, without any major disturbances in the meantime, the trail was almost impossible to detect, indicating that recovery rates can be relatively fast even if disturbance rate was quite high (Web 353).

A: the site before the experiment, 1979.

B: the site several hours later, after a motorcycle passed over it 200 times (equivalent to high disturbance).

C: The site 20 years later, with regrowth of vegetation and the soil compacted by 1/2.

Works Cited:

Future prospects for the Mojave

Desert ecosystems, due to extreme conditions of weather and low fertility in the soil, are very slow to recover from even minor disturbances (Hunter). Most sites in the Mojave that have had significant damage have been predicted to take up to centuries for recovery (see chart by Lovich). An analysis of spatial development in the Mojave Desert by Lori Hunter and others showed that human development at present rates will cause significant losses in already endangered plant and animal species. Road-building and military operations also contribute to the decrease in vegetation, not only killing existing plants, but also damaging the soil, making vegetation recovery much more difficult. At present, the Mojave Desert is experiencing a “wet period,” with an increased average annual precipitation than 20 years ago (planetbiomes.org). This has helped maintain the density of vegetation in the desert. However, studies of this desert’s historic climate show that the climate of the Mojave tends to fluctuate between wet and dry periods, and in the future it is more than likely that another dry spell will hit the desert, exposing the ecosystem to further damages (Hereford and Webb). If plants are unable to regenerate, herbivores dependent on the plants for food, such as the desert rodents that rely on annuals, will also face endangerment (Hereford and Webb), and eventually some of the endemic species may cease to show themselves around the Mojave Desert landscape, either having died off or emigrated to more suitable habitats.

Works Cited:

http://www.springerlink.com/content/pg318mg147228070/fulltext.pdf

http://www.sciencedirect.com/science/article/pii/S0140196306002965

http://www.blueplanetbiomes.org/mojave_climate.htm

Historic Precipitation (graphs)

The Mojave Desert is currently experiencing a "wet period" (planetbiomes.org). The precipitation levels of the Mojave have been known to fluctuate between such wet and dry periods, causing variations in the landscape and plant growth accordingly. Though the present wet period has helped maintain the vegetation in the desert despite anthropogenic disturbances, a future dry period may result in an severe loss of native plants.

The following graphs are taken from http://mojave.usgs.gov/climate-history/.