MOJAVE DESERT PLANT COMMUNITEIS

Pine Juniper Woodland inhabits the high elevations of the Mojave Desert between 4000 to 6000 feet elevation. These isolated forests are part of the “Sky Islands" surrounded by the hot dry desert of the lowlands. Some of the plants were stranded here in the small pockets of cooler& moister areas after the retreat of the last ice age. This area receives 6 to 15 inches of precipitation a year. Frosts are common in winter (it can snow), as are high winds & low humidity. Soils tend to be rocky & thin. California Junipers & Joshua Trees mix at lower elevations while Pines are found higher up.

· Castilleja subinclusa

· Cercocarpus ledifolius

· Ephedra viridis

· Juniperus californica

· Mahonia fremontii

· Opuntia chlorotica

· Pinus monophylla

· Prunus fremontii

· Purshia species

· Quercus turbinella

· Penstemon eatonii

Sagebrush Scrub is another plant community found at high elevations (3500 to 6000 feet) in the Mojave Desert. Sagebrush Scrub dominates in highland areas that are too dry or the soil too poor to support Junipers & Pines. This plant community has much in common with the Sagebrush Scrub plant community’s characteristic of the neighboring Great Basin Floristic Provence. Many plants are found in both regions. This area receives between 3 to 10 inches of precipitation annually. Frosts are common in winter, & it is windy year round. Soils can be deep heavy clay or rocky. Many plants here are important forage for grazing animals.

· Artemisia spinescens

· Artemisia tridentata

· Castilleja subinclusa

· Cercocarpus ledifolius

· Chrysothamnus nauseosus

· Coleogyne ramossissima

· Eriogonum fasciculatum polifolium

· Grayia spinosa

· Krascheninnikovia lanata

· Stipa speciosa

Joshua Tree Woodland these woodlands are found from 2000 to 5000 feet in elevation. Joshua Trees grow above the hotter & dryer low elevations dominated by Creosote Bush Scrub. Many plants from both Sagebrush Scrub & Creosote Bush Scrub are often present growing with the Joshua Trees. This area receives between 4 to 10 inches of precipitation annually. Strong winds, summer heat, & winter frosts are common, with wide swings in temperature from day to night. Soil types vary widely. This is one of the most important plant communities in the Mojave having high biodiversity.

· Calochortus kennedyi

· Encelia actonii

· Ephedra nevadensis

· Ericarmeria lineraifolia

· Eriodictyon californicum

· Nolina parryi

· Opuntia basilaris

· Opuntia echinocarpa

· Platystemon californicus

· Prunus fasciculata

· Salazaria mexicana

· Salvia dorrii

· Tetradymia spinosa

· Yucca baccata

· Yucca brevifolia

· Yucca schedigera

Creosote Bush Scrub grows from below sea level up to 4000 feet elevation, it is the dominant plant community encountered in the Mojave Desert. Widely spaced shrubs fill the landscape, & it is rich in annual wildflowers. Creosote Bush Scrub is also found in the Sonoran Desert of California, but there the species mix is different. This area receives between 1 to 6 inches of rain a year. Winter frosts, summer heat, & strong drying winds are common. Soils range from clay to well drained & rocky. Creosote Brush Scrub does not grow on saline & poorly drained soils.

· Achnatherum hymenoides

· Ambrosia dumosa

· Asclepias erosa

· Atriplex hymenelytra

· Cassia armata

· Encelia frutescens

· Eriogonum inflatum

· Isomeris arborea

· Krameria erecta

· Larrea tridentata

· Lepidium fremontii

· Lycium andersonii

· Machaeranthera tortifolia

· Oenothera deltoides

· Opuntia ramossisima

· Phacelia tanacetifolia

· Psorothamnus fremontii

· Sphaeralcea ambigua

Saltbrush & Shadscale Scrub is a specialized plant community that grows from below sea level to 5000 feet on poorly drained saline soils. Shrubs in the Chenopodiacea (Spinach family) are dominant. The combination of high salinity, alkalinity, & poor drainage precludes other plants from growing. This is an arid area that receives between 2 to 10 inches of rain a year. Saltbrush / Shadscale Scrub are found adjacent to both Creosote Bush Scrub & Alkali Sink Scrub. The shrubs here are perfectly adapted to their hostile soil conditions having little competition.

· Atriplex canescens

· Atriplex confertifolia

· Atriplex lentiformis

· Atriplex polycarpa

· Atriplex spinifera

· Sporobolus arioides

Alkali Sink Scrub can occur from below sea level to 5000ft elevation. This plant community grows on highly alkaline or saline soil with poor drainage. Often surface water is present but it is often saline & its flow restricted. Only the most specialized plans can grow here. This area receives between 1 to 10 inches of precipitation annually. All the plants here have evolved similar ways to remove excess salts. Alkali seeps are often islands, completely surrounded by other plant communities. The Alkali Sink Scrub unexpectedly shares many similarities to the Coastal Salt Marsh vegetation (this is an example of convergent evolution).

· Allenrolfea occidentalis

· Distichlis spicata

· Juncus acutus ssp. leopoldii

· Salicornia subterminalis

· Sarcobatus vermiculatus

· Suaeda torreyana

Riparian plant communities grow near water (rivers, lakes, & springs) or in washes. The Mojave, Armagosa, & Colorado are the largest of the areas rivers, which support large portions of this plant community in Mojave Desert. In riparian areas trees & shrubs are often fast growing & dense. Many plants serve to stabilize stream banks, thus riparian forests are important areas for wildlife. Washes tend to be dry between rare flood events, & the plants here are adapted to drought. Plants in wash habitats have deep taproots to reach groundwater which allows them to survive long periods without much water from surface runoff.

· Baccharis salicifolia

· Chilopsos linearis

· Populus fremontii

· Prosopis glandulosa torreyana

· Prosopis pubescens

· Salix exigua

· Salix laevigata

· Typha species

Rocky Outcrops are a niche habitat, where specialized plants have little competition on the rocks. Many of these plants are only found on these rock outcrop “islands”. The rocks chemical composition plays a large role on what grows on them. Many times limestone carbonate rocks (& soils) often host endemic plants. Plants growing on the rocks are accustomed to perfect drainage. Boulders, crevasses, & scree slopes provide a multitude of microhabitats.

· Agave utahensis var. nevadensis

· Brickelia arguta

· Chaelanthes parryi

· Echinocactus polycephalus

· Echinocereus englemanii

· Echinocereus triglochidatus var. mojavensis

· Eucnide urens

· Ferocactus cylindraceus

· Yucca schidigera

· Dudleya saxosa

Sand Dunes are found at various elevations below 5000 feet. Sand dunes usually form in large valleys or basins that are surrounded by mountains. Shifting sands make it hard for plants to take root. Other threats include getting buried or being sandblasted. While the surface is bone dry, sand actually holds moisture if it is deep enough. In deep sand the bottom layers are often moist & act as a reservoir for plant roots tough enough to reach it. Just like any other isolated & specialized habitat, this one is filled with unique plants. Plants play an important role in stabilizing & shaping the dunes.

· Abronia villosa

· Baileya pauciradiata

· Hesperocallis undulata

· Oenothera deltoides

· Petalonyx thurberi

· Pluraraphis rigida

· Swallenia alexadrae

· Tiquilia plicata

THE MOJAVE DESERT

The Mojave is the hottest, driest, & smallest desert in North America. It lies south of the Great Basin & east of both the Transverse & Peninsular mountain ranges. This desert ranges between -282 below sea level to 5000 feet elevation. The Transverse Mountain Ranges & Sierra Nevada Mountains create a rain shadow (the mountains block the rain clouds). This makes the Mojave very dry with most areas receiving less than 6 inches of precipitation a year. Eastern areas experience more summer Monsoons than western areas. However as a whole the Mojave Desert region receives more rainfall in the winter than in the summer. This Mediterranean climate influence also helps separate the Mojave from the Sonoran Desert. The Sonoran Desert experiences less cold winter, warmer average temperatures, & more summer rainfall than the Mojave Desert. This unique climate & a high diversity of habitats have created a wide variety of plants. The Mojave Desert hosts shares some plants that are also found in the neighboring Great Basin & the California Floristic Provinces. This fact further contributes to the high species diversity common to the region. In many places a large proportion of the plants are annuals (that is they only live for one growing season). Their strategy is to persist as a dormant seed waiting for the perfect conditions to sprout & grow. The Mojave Desert is relatively young being only 10,000 to 15,000 years old. Many of the plants are recent colonizers from the south moving north as the climate warmed up & dried out after the last Ice Age.

INDICATOR SPECEIS

Creosote Bush (Larrea tridentata) is the indicator of the Desert Floristic Provence as it is found in the Mojave, Sonoran, & Chihuahuan Deserts (all are part of the larger desert Floristic Provence). The Mojave Desert is home to several unique large woody Yuccas. The Joshua Tree (Yucca brevifolia) & the Mojave Yucca (Yucca schidigera) are considered the primary indicator plants for the Mojave Desert.

ENDEMIC PLANTS

There are many unique ecosystems in the Mojave which are home to nearly 50 plants found nowhere else in the world. Some plants only grow on specific soil types often where little else will grow. Many of the endemic plants are specialized for a niche habitat. Unfortunately many of these plants are naturally rare or endangered by anthropogenic (human created) causes.

PLANTS & THE LANDSCAPE

A Floristic Provence is a geographic area with a relatively uniform composition of plant species. Adjacent Floristic Provinces do not have a sharp boundary, but rather a blurred one. Instead there are transitional areas in which many species from both regions overlap.

PLANT COMMUNITIES

Proximity to the ocean, slope aspect, exposure, surface water, & elevation are the primary factors affecting the local climate. These factors create groupings of plants that grow on the Earths surface that are noticeably different from each other. Plant communities often have one or more dominate species that are common to that area. These are the Indicator Species.

ELEVATION EFFECTS ON VEGETATION

The atmosphere is like a blanket. At low elevation the insulating blanket of air is thick, while at high elevations it is much thinner. This means that the higher up we move in elevation the colder it gets. In addition high elevation areas tend to be wetter than low elevation areas.

SOIL AFFECTS ON PLANT COMMUNITIES

Soils have a great affect on what type of plants grow on them. The majority of plant nutrients come from the soil. Soil texture & drainage are important factors in the soils ability to retain moisture. Availability of ground water & organic content are also important factors.

SOIL AFFECTS ON PLANT COMMUNITIES

Some soils are hostile to plant growth, even toxic. Some plants exploit this niche. They evolve certain mechanisms to cope with the difficulties. The successful plants are rewarded with having little competition.

SLOPE ASPECT

Slopes that face north cast more shadow to the earth below. North slopes also have more shade. Southern slopes are exposed to the most intense sunlight. This difference in sunlight intensity makes north slopes moister & cooler. Southern slopes are hotter & dryer. The plants growing on a sunny slope are different from those on a shady one.

INDICATOR SPECIES

An indicator species is any organism that characterizes the environment in which it lives. Many times these species are the Dominate or Climax species. Dominant species are the most common species on a region. Climax species are often the largest & most complex.

ENDEMIC PLANTS

Plants that are found nowhere else in the world except in their local area are known as Endemic. Often times endemic plants are highly specialized to live in a special niche in the environment. Many of these plants are threatened or endangered.

NATURALIZED PLANTS (WEEDS)

Naturalized plants are plants that are not native to a particular area but grow there as if they were native (sometimes even better). These plants often have no natural enemies in their new home & can aggressively outcompete native species. Non native species increase the potential for fire.

SUNSET CLIMATE ZONES

Sunset Magazine developed a climate zone system that provides a more realistic picture about a local climate than the standard USDA climate zones. Sunset zones factor in all climatic conditions. The zones are organized from coldest to warmest zone 1 being the coldest & zone 24 being the warmest.