DesertsDesertsDeserts 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)