1 DESERT VEGETATION DRY DESERT –XEROPHYTIC PLANTS –WIDELY DISPERSED –SMALL HARD-LEAVED OR SPINY SHRUBS –SUCCULENT PLANTS SUCH AS CACTUS –HARD GRASSES

2 DESERT VEGETATION DRY DESERT (cont) –MANY SPECIES OF SMALL ANNUALS MAY BE PRESENT BUT ONLY APPEAR AFTER RARE BUT HEAVY RAINS –MANY AREAS HAVE NO VEGETATION COVER DUE TO SHIFTING SANDS, SALT FLATS, ETC.

3 DESERT VEGETATION DRY DESERT (cont) –PLANTS DIFFER GREATLY IN DIFFERENT PARTS OF THE WORLD –ARIZONA DESERT HAS LARGE PLANTS SUCH AS SAGUARO CACTUS OCOTILLO PRICKLY PEAR CREOSOTE BUSH SMOKE TREE

4 DESERT VEGETATION THORNTREE SEMIDESERT –XEROPHYTIC PLANTS, TREES AND SHRUBS ADAPTED TO LONG DRY SEASON WITH BRIEF BUT INTENSE RAINY SEASON –KNOWN AS THORN FOREST, THORN BUSH, OR THORNWOODS –DECIDUOUS PLANTS –CACTUS PRESENT IN SOME AREAS

5 DESERT VEGETATION SEMIDESERT –SPARSE XEROPHYTIC SHRUBS SAGEBRUSH OF WESTERN U.S. AS AN EXAMPLE FOUND IN A WIDE LATITUDINAL RANGE DESERT ANIMALS –XERIC –ADAPTATIONS TO WATER SCARCITY

6 DESERT VEGETATION DESERT ANIMALS(cont) –MANY DO DORMANT DURING DRY SEASON –IN WESTERN US RODENTS BATS REPTILES LARGER MAMMALS OPERATE MAINLY AT NIGHT

7 WATER IN THE DESERT EPHEMERAL STREAM = a stream or portion of a stream that flows only in direct response to precipitation. INTERMITTENT STREAM = a stream that flows onlypart of the year such as during the wet season, after a heavy rainfall, or during the melt season. EXOTIC STREAM = “Introduced from another place”

8 THE MOVEMENT OF SAND THE INVOLVEMENT OF WIND –“THE PHYSICS OF BLOWN SAND” –SURFACE WINDS –TRANSPORT INVOLVES INTERACTIONS BETWEEN THE WIND AND THE GROUND SURFACE. SEDIMENT TEXTURE VEGETATION MOISTURE CONTENT COHESION

9 THE MOVEMENT OF SAND THREE MODES – DEPEND ON GRAIN SIZE –SUSPENSION VERY SMALL PARTICLES MAY BE KEPT AIRBORNE FOR RELATIVELY LONG DISTANCES \SHORT TERM SUSPENSION FOR COARSER SIZES

10 THE MOVEMENT OF SAND MODES (cont) –SALTATION A SERIES OF SHORT JUMPS –REPTATION AND REPTATION CREEP IMPACT OF SALTATING GRAINS LARGER GRAINS PUSHED OR ROLLED DOMINANT MODE IS SALTATION

11 THE MOVEMENT OF SAND THE THRESHOLD OF MOTION –GRAIN SIZE –MOISTURE CONTENT –SURFACE ROUGHNESS –SURFACE SLOPE –VEGETATION

12 THE MOVEMENT OF SAND THE BUILDING OF A DUNE –INITIATION –ACCUMULATION –ANGLE OF REPOSE –INTERNAL STRUCTURE OF A DUNE FORESET BEDS TOPSET BEDS BOTTOMSET BEDS

13 THE MOVEMENT OF SAND –INTERNAL STRUCTURE (cont) SLIP FACE CREST THE RELATIONSHIP OF DUNES TO THE WIND DIRECTION