Unformatted text preview: OUTLINE: OUTLINE: 1. Distribution of Deserts 2. Causes of Aridity 4 Major Factors 3. Desert Climate Hot and Cold Deserts 4. Desert Biome Sandy Deserts, Higher Diversity Deserts Animal, Vegetation adaptations Human impact on deserts 5. Steppe climate and biome—a brief description biome—a What percentage of the earth’s land surface is What classified as arid or semi-arid (B climates)? ~35%!
Creosote scrub—CA scrub—CA Desert (BW) and Steppe (BS)… a matter of degree Very arid …a little less arid 1.. Rainfall usually 1–10 in / yr. 1 1–10 Always a moisture deficit! 2. Scattered, unreliable, often intense rainfall events Deserts (and Steppes) can be…HOT (Subtropical ~25–35º) be HOT or COLD (Midlatitude > 35º) depending on Latitude or COLD Latitude Subtropical Deserts – Really HOT, no cold months Subtropical No cold months tells you it is subtropical in latitude What does the temp pattern tell us about latitude at this site? site? Low Seasonality = Low Latitude
Why is there a Why desert at 12°S? 12°S? Cold ocean current! Plus rain shadow and E. side STH Midlatitude Deserts – Higher seasonality w/ cold winter! Midlatitude Snow is common in mid-latitude Snow mid-latitude or high-elevation deserts high-elevation Geographic Distribution: Desert (BW) (Arid) and Steppe (BS) (Semi-arid) ~35% of the earth’s surface!
Note large latitudinal range! Desert Steppe Why are arid lands where they are? You need to know the 4 Major Causes of aridity 1. STH Cells centered 30° Subtropical Deserts Especially on East Especially side of the STH in northern Hemi, strong subsidence e.g., Sahara, Arabian Desert What causes aridity in central Asia? What Gobi 2. Continentality — Great Basin, Continentality Australian, and Gobi Deserts Another major factor causing aridity…? Another aridity…? What are some examples?
3. Rainshadow — occurs anywhere there are mountains 4. Cold Currents= surface temperature inversion→air cannot surface inversion cannot rise = no rain….and what else? rise STH Cold current Cold
Cold Currents + E. side of STH + rain shadow = Extreme Dry! An des How about the cause of aridity here? Atacama Atacama Desert
What does this image from space tell us about climate in this area? • Color – No green-vegetation green-vegetation • Clarity – few clouds, lack of moisture in ATM • No signs of lakes and rivers Where is Where driest place in N. America? What are the factors causing aridity? the hottest, Death Valley Valley example
• ~36° N • 282 ft below sea level • Ave rainfall 1.65 in/yr 0 in some years! 1. Rain shadow 2. STH 3. Cold current Pacific Pacific Harsh habitat with fragile ecosystems
Libya Libya Great Sand Dunes Great monument, CO, USA Aerial view Some of the very dry and winddriven deserts have lots of sand and little vegetation to stabilize soil Dunes are great for getting lost— lost— always changing with the wind I guess I should have guess brought the GPS… Imagine trying to use a topo map here! Desert Vegetation Vegetation helps stabilize sand and prevent dune migration Vegetation low diversity desert scrub, CA Biodiversity can range from low to Biodiversity moderate in deserts. Biomass is low Desert Plant Adaptations to Aridity Desert Any ideas? 1. 2. Saguaro National Monument, AZ Saguaro Adaptations follow two main strategies: Adaptations
Store Water Reduce water loss / Drought avoidance Adaptation: Store Water Adaptation: “Succulence” = thick, fleshy,water-holding tissue “Succulence” fleshy,water-holding Saguaro Cactus, Sonoran Desert AZ, CA, northern Mexico Largest US, lives up to 200 yrs 65 yrs old to develop first arm Barrel Cactus Barrel • Shrinks in drought uses stored water
Sonora Desert, AZ Adaptation: have no Adaptation: leaves that transpire and lose water, instead… instead… • White hairs/spines reflect radiation and provide shade Adaptation: Or, just put your roots down deep where there is groundwater! Palm Oasis, Mojave Desert - 33ºN Adaptation: wide spacing -- Less competition for H2O and nutrients Do you think deserts burn frequently? Adaptation: Long-lived seeds and “ephemeral” existence: adapts to very patchy and inconsistent rainfall patterns Anza Borrego Desert CA Ephemeral herbs blooming in a desert wash (Arroyo) just after a rain Ephemeral Adaptation: Deciduous habit, Grow leaves only after a rain, lose them after rain stops Ocotillo, Anza Borrego Desert, CA - 33ºN Summary of Desert Plant Strategies Plant 1. Store water Store succulence succulence 2. Reduce Water Loss / 2. Drought Avoidance Drought Examples: • No leaves, spines • Ephemeral existence • Deciduous—drop leaves, reduce transpiration • Deep Taproots Deep • Wide Spacing 2 most important needs: most 1. Avoid “Hyperthermia” “Hyperthermia” 2. Adapt to low H2O intake (increase efficiency, reduce loss) Camels Bactrian (2-hump): Asia-Gobi Desert (2-hump): Asia-Gobi Wild population ~1000 Dromedary (1-hump) Dromedary (1-hump) Middle East, N. Africa (all but extinct in wild) • Can go days without food & water-convert fat in hump water-convert • Reduce water lost in waste e.g., Dry feces, thick concentrated urine Camels have been and are very Camels important to desert peoples for milk, meat, and transport. Desert Fox (N. Am Deserts) Desert “Fennec” Fox (Sahara, Arabian Deserts) Adaptations: • Thick coat insulates from sun • Lg. ears radiate heat away • Light color has ___albedo ___albedo REDUCE Water loss Efficiency • Obtains all water from food No need to drink! Kangaroo Rat Kangaroo N. American Deserts REDUCE water loss Improve efficiency • Nocturnal activity (cooler) and underground dens • manufactures water from seeds and food • Specialized kidneys recycle water in urine “waterless” waste disposal “waterless” Deserts have more human activity than you might think! Cities, agriculture, and more… Where the Where the hell did I park hell did I park the camel? the camel? Humans can adapt to arid climates even easier today with technology! technology! Tucson, AZ Tucson, Major Desert Crops Major in the U.S: Cotton Nuts Citrus Grapes …and Cattle? …and Why grow stuff in the desert? Nut orchard near Tucson, AZ Nut Major human-environment interaction issue: Large scale Major human-environment irrigation for commercial crops depletes underground and aboveground (there is very little of this) water supplies Irrigation canal, New Mexico Irrigation Spray vs. Drip Irrigation Spray One major advantage of Drip: • high efficiency—less runoff + evap. Another Water guzzler: Traditional Lawn-does it fit? Lawn-does “Xeriscaping” becoming popular, use native plants Xeriscaping” Another problem: Habitat destruction and fragmentation from commercial commercial agriculture and development –Desert ecosystem is fragile! –Desert Bulldozers “conquer” Bulldozers Saguaros to accommodate urban sprawl near Tuscon Desert Tortoise Declined 90% (since 1980) habitat loss and predation by ravens… Mohave, Sonora Deserts, N. America Spend 95% time underground to escape heat Spend Can survive > 1 yr without water! Cactus Rustling Cactus Rustling Threatens Chihuahuan Desert link Cactus
By Cat Lazaroff WASHINGTON, DC, January 20, 2003 (ENS) - A booming trade in wild cactus threatens to overwhelm populations of some Chihuahuan Desert species, a new study warns. The report released today suggests that demand for desert landscaping plants may soon surpass the desert's natural supply, and leads to renewed calls for better regulation of trade in all cactus species….. Saguaros are a KEYSTONE species Provide nesting areas, perches, and food Provide (fruit) for Gila woodpecker, flickers, martins, kestrels, bats Cattle ranching in the Desert? Cattle You can’t cram a square peg into a round hole…Or can you? Are cattle turning arid habitats into shrublands? Are 70 OF 116 AZ Threatened or endangered species have cattle grazing as grazing a causal factor in their imperilment. ((Witzeman, 2001) Witzeman, Tuscon, AZ Tuscon, 1988, with grazing Same location, 1998, 10 years after grazing stopped Estimated net proportion U.S. arid land grazed by livestock ~ 85% Estimated One of the most prevalent environmental problems in this climate type. Types of federal land open to grazing: BLM lands, Nat. Forests, Wilderness, Wildlife refuges, Military bases, Nat. Monuments. Mid-Latitude Steppe, Utah Geography of Steppe Geography
1. Deep in continental interiors, far from moisture sources 2. Adjacent to deserts, a little more rain than desert 3. Many in rain shadows of high mountain ranges Steppe Subtropical Steppe (Hot) Subtropical Will be NOo climographs of Subtropical Steppe on exam. Hard to distinguish these from tropical savanna. We will focus on Mid-Latitude (cold) Steppe We Mid-Latitude Relatively simple landscapes: short grass, sparsely settled, mostly wide open spaces! Mongolian steppe Mid-latitude Steppe Mid-latitude
Cooler temps mean less evaporation in steppe than desert, and slightly less continental locations You won’t have to distinguish between Deserts and Steppes on exam Steep Temp. Curve = mid-high latitude – more rain than desert Example of Native Steppe Fauna: Bison Example Grazers: Llamas in S. American steppe (BS) Prairie Dog Prairie “KEEP OFF THE GRASS! …Damn college kids” Rodents are especially common in Steppe landscapes Prairie Vole Plains Pocket Gopher Plains Jackrabbit Where you have prey you have predators like…? like…? Red Fox Red Wylie Coyote Grazing / Pasture is major land use Grazing …better fit here than in desert …better Grasslands are adapted to grazing! Some grains in moister areas, and hay (grass) for livestock Some Wheat field in Montana steppe, lee side Rocky Mtns. Questions on today? Mesothermal (C) Climates are next. Steppe climate Madison County, Montana EXTRA SLIDES EXTRA Summary 4 Major Causes of Aridity: 1. STH Cells—esp. E. side of cell
West coast deserts 2. Cold Ocean Currents 3. Continentality 4. Rain Shadow Effect These factors can work together! One review from IMDB 10 stars out of 10: “This film is not for the passive observer. It requires patience and presence. I hear you if you don't have it; but I loved this film. I sat for minutes afterwards, stunned.” The desert movie nobody The saw (2003) ...
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This note was uploaded on 04/09/2010 for the course GEOG 1104 at Virginia Tech.