DesertsDeserts what are deserts? relative term - transitions occurlatitudinally with more xeric thornforests and with grass savannasMojave Desert Namib DesertDeserts what are deserts? relative term - high elevationtropical mountains (paramo, etc.) areessentially “desert” likeHaleakala Crater - MauiDeserts what are deserts? relative term - high elevationtropical mountains (paramo, etc.) areessentially “desert” likeOpuntia (Cactaceae) in high Andean puna (Peru)Deserts what are deserts? subtropical arid regions where potential evaporation(>2000mm) is >> annual precipitation (<200mm)Deserts distinction between subtropical and temperate (cool or cold winter) desertsGreat BasinGobi DesertPatagonianDesertDesert Locations lie between 15o and 30ocentered on Tropics of Cancerand Capricorn on west sidesof continentsSonoran, Mojave,ChihuahuanAtacama lie between 15o and 30ocentered on Tropics of Cancerand Capricorn on west sidesof continentsSaharanNamib, AustralianDesert Locations desert climate due to subtropical highs and adiabaticwarming of dry air . . . . . . and circulation of cold currents (holding littlemoisture above the currents) along west sides ofcontinentsDesert Climate variation in amount of precipitation from semiarid to rainless desertsMojaveNamib (Skeleton coast)Desert Climate variation in seasonality of precipitationMojave - winter rains (Mediterranean!)Sonoran - light winter rains and heaviersummer rain (bimodal)Chihuahuan - only summer rain(subtropical!)Namib, Atacama - onlyfog, no rainDesert Climate soil types: counter-intuitive, but clay soils form driest habitats, sandysoils better water retention, and rocky/fissured soils provide the wettesthabitatsDesert Climate Halophytes (“salt plants”) - adaptations to salt left behind as water isevaporated at surface of soilDesert Life FormsSalt accumulators (often succulent)Salt excretorsSalicornea (Chenopodiaceae)Tamarix (Tamaricaceae) Malakophyllus (“soft leaved”) xerophytes (“arid plants”) - adaptationsto water stress by wilting under dry conditionsDesert Life FormsSphaeralcea (Malvaceae) -desert globe mallowAsteraceae - daisy family Succulents - adaptations to water stress by storing water in swollen tissueDesert Life FormsAloe - Africa Opuntia - North Americaleaves stems Ephemerals - adaptations to water stress by short lifeDesert Life FormsGeophytes (survive under ground)Therophytes (annuals, survive by seeds)Phanero.(trees/shrubs)Chamae. (nearground)Hemicrypto.(leaf litter)Crypto.(under ground)Thero.(annuals)Rainforest 96% 2% 0% 2% 0%Desert 11% 7% 27% 14% 41%TemperateDeciduousForest15% 2% 49% 22% 12%Tundra 0% 23% 61% 15% 1% Ephemerals - adaptations to water stress by short lifeDesert Life Forms Plant defenses - physical and chemicalDesert Life FormsCactaceae - New Worldspine protectedEuphorbia - Old Worldspine & toxin protectedDesert Floristics Three families species richer in deserts than elsewhere Three families species richer in deserts than elsewhereDesert FloristicsFrankeniaceaeFrankenia chilensis SaharaAfrican DesertsYellow indicates lowest photosyntheticallyabsorbed radiation SaharaAfrican DesertsWoody plants: Phoenix (date palm)and shrubs (Acacia, Tamarix,Ephedra)Tamarix - tamariskPhoenix dactylifera (date palm) - Tunisia“mustard” (Brassicaceae)Annuals: Brassicaceae; but alsoperennial herbs like grasses SaharaAfrican DesertsStem succulents: Apocynaceae(milkweed and relatives)Caralluma & Sarcostemma (Apocynaceae)EthiopiaLoranthaceae parasitic on AcaciaEthiopiaParasites: Loranthaceae Namib - western southern AfricaAfrican DesertsAfrican Deserts Namib - western southern AfricaFog desert: fog only moisture for mostof the year along coastDarkling beetle - dew specialistAfrican Deserts Namib - western southern AfricaFog desert: fog only moisture for mostof the year along coastDarkling beetle - dew specialistWelwitschia mirabilis nephelophyte - fogspecialistAfrican Deserts Namib - western southern AfricaStem succulents: Aloe (Liliaceae s.l.),Euphorbia, Pachypodium (Apocynaceae)PachypodiumAloe - quiver plantAfrican Deserts Namib - western southern AfricaStem succulents: Stapelia (Apocynaceae) -cactus mimic; Adenia (Passifloraceae)Stapelia - carrion flowerAdeniaAfrican Deserts Namib - western southern AfricaLeaf succulents: Aizoaceae -cactus mimicsLithops - living stonesDelospermumAustralian Deserts One quarter of Australia is “desert”-largest is the Simpson desertDeserts straddle Tropic ofCapricornAustralian Deserts Spinifex desert type: desert grassland dominated by Triodia grasshummocksAustralian Deserts Spinifex desert type: desert grassland dominated by Triodia grasshummocksCasuarina - desert oak - N2 fixing!Grass trees, Xanthorrhoeaceae (endemic toAustralia, 9 genera, 75 spp.)Australian Deserts Saline desert type: low vegetation dominated by salt-tolerant bluebush,saltbush, and other ChenopodiaceaeWilliams Creek - salineMaireana (Chenopodiaceae) - bluebushAustralian Deserts Mulga desert type: perhaps transitional with extreme arid woodlands butcovers 20% of Australia - dominated by Acacia anerua (mulga)Acacia aneura - mulgaSouth American Deserts Atacama - western Chile &southwestern Peru - straddles Tropicof Capricorn on Pacific Ocean edgeof South America essentially a rainless desert in theshadow of the AndesSouth American Deserts Atacama - western Chile &southwestern Peru - straddles Tropicof Capricorn on Pacific Ocean edge ofSouth America a fog desert: note moistureladen clouds over coldHumboldt current stop at edgeof continentSouth American Deserts Atacama - western Chile &southwestern Peru - straddles Tropicof Capricorn on Pacific Ocean edge ofSouth America Coastal cloud wall inPan de Azucar orographic precipitation isalways inland at higherelevations due to adiabaticeffect a fog desert: note moistureladen clouds over coldHumboldt current stop at edgeof continentTillandsia landbeckii(Bromeliaceae) - samegenus as Spanish mossSouth American Deserts Atacama - western Chile &southwestern Peru - straddles Tropicof Capricorn on Pacific Ocean edge ofSouth America rainless desert with plants(nephelophytes) adapted tocapture fog moisture as lomas(small hill) vegetationSouth American DesertsEulychnia iquiquensis (Cactaceae),Copiapoa (Cactaceae) & Euphorbialatifolia (Euphorbiaceae)South American DesertsMalesherbia tocopillana(Malesherbiaceae) -
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