Ecology: Desert and Grassland

xerocoles

animals that can live in deserts

erg

sand dune region

largest desert in the world

antarctica - 5.5M square miles

also largest cold desert

5.4M arctic then sahara

xerophytes

desert plants

map of deserts

plus antarctica and arctic

area of earth w/ desert

1/3 of earth (30-33%) including polar

20% is true desert, the 33% is climactic 10in rain defn

hottest temp ever

54C in death valley and also in kuwait

desert defn

less than 10in (25cm) of rain per year

xerophyte adaptations

annuals: short lived during rains, winter annual

succulents: store water in stem so no transpiration, thick waxy cuticle resist water loss, CAM, recessed stomata;

deep roots to tap groundwater or shallow to get as much rain as possible

where do grasslands form

in areas where too little precip for forest but too much for true desert

aridity index

A = P/PET = average annual precip/potential evapotranspiration

<0.05 = hyperarid

0.05-0.20 = arid

0.20-0.50 = semiarid

generalizations about grassland plant species

grasses of multiple species and genera but mostly dominated by a few species

most with rhizomes (underground spreading stems that send up shoots and nodes and store starches up to 1/2 of biomass); wind pollination

perennial bunchgrasses don't have rhizomes and come back from base (not spreading)

will grow back after fire, grazing, wind, extreme temp

temperatures in grasslands

huge range from seasons often deep into the negs in winter (more to north), 110 to -20

grassland precipitation

24-40in

steppes often include semiarid lands 10-24in

whole range is 6-40in (generally)

grassland precipitation season

scattered thunderstorms (convective storms) in summer but most rain/snow in winter and cooler times

grassland soils

mollisols (basic, hummus rich, dark, productive, Ca/Mg)

mollisols are most common soil type in US (21.5%) and 7% of ice free land worldwide

found in W great plains and scattered rest of west

grassland growing season

typically 120-200 days

grasslands topography

flat, some rolling hills, steep canyons

grasslands fire

frequent due to summer thunderstorms

necessary to maintain ecosystem and keep back trees and shrubs, grasses have survival mechs

grasslands fauna

grazing animals like deer, elk, bison in large herds

songbirds and small burrowing mammals very common

Grassland animal adaptations

fast, colony burrowers, jumping, strong flying birds, camoflage, good vision,

tallgrass prairie

usually around 1-3m, deep roots, nearest eastern deciduous forests

precip around 25-40in, usually around 35in

Tallgrass prairie problems

most plowed and planted w/ wheat/corn; increased drainage and runoff reduces moister areas

Tallgrass prairie plants

Big bluestem (image), sand bluestem, indian grass, slough grass, switchgrass

mixed grass prairie

usually under 0.5-1.3m in height; usually around 3ft

precip around 14-25(35-65cm)

mixed with taller grasses growing in slightly wetter areas and shorter ones in drier areas

mixed grass prairie species

little bluestem grass, june grass, needle grass, dropseed grass, wheatgrass, wild rye

mixed grass prairie problems

almost entirely planted over with crops such as corn and soybean

shortgrass prairie

nearest to western deserts, cover most area of the 3 groups in N america; mostly W of latitude 100W

most less than 20in high; fewer forbs because lower rain favor grasses; can't grow bigger bc no water

precip usually around 10-15in

shortgrass prairie problems

some takeover for irrigated corn and crops; mostly just overgrazed for cattle, fenced from native grazers, invasives on ranges

shortgrass prairies species

buffalo grass, galleta grass, needle grass, grama grass, penn sedge

bunchgrass prairie

also called palouse prairie (near palouse river in WA)

found in plains N of great basin, colorado, UT, CA, WY, MT

bunchgrass prairie species

purple needlegrass, sagebrush, bluebunch wheatgrass

bunchgrass vs. typical plains grass

bunchgrass sends up new shoots from its base forming a clump

Most prairie grasses have mat-like roots that spread and produce new shoots spread out from one another

characteristics of grassland birds

lots of them (lots of songbirds)

strong fliers due to high winds, nest in tall grasses,

characteristics of small grassland mammals

many in colonies, many burrow, many hop for visibility

grassland history

during pleistocene/miocene (50-3.5MYA) mountains in N amer make grassland climate more favorable

after pleistocene ice ages, drier/warmer climate expand grasslands

savanna

tropical grassland with few uniformly dispersed trees that aren't dense enough to form a closed canopy

savanna reqs

20-50in of rain concentrated in 6-8 months followed by long hot drought where fires are common; average daily temp never drop below 64F

types of savanna

climactic savannas - classic all rain in one season and fire and drought maintain in rest of year

edaphic savannas - thin or clay soils that inhibit tropical forest growth

derrived savannas - human or elephant deforestation creates critical mass of grass to burn away tree sprouts

savanna plants

generally has a dominant grass or few grass/forb species and scattered deciduous trees

grasses: includes elephant grass which is like 10ft

trees: acacia, baobab, candelabra

savanna seasons

winter is dry starting October with strong winds, little rains, few lightning

summer is wet

neither season is very cold

savanna fires

during winter dry season

small animals in burrow, big out run, insects die, grades burn but roots ok

savanna problems

desertification, clearing for farming, poaching, overgrazing

savanna locations

brazillian horn highlands, venezualan campos, sahel (lot thicker than shown), E africa and S africa, parts of india and SE asia; N australia

temperate grasslands definition

clearly defined hot summer and cold Winters

temperate grasslands distribution

plains of US, pampas in Argentina, eurasian steppes from ukraine through balkash, mongolia and manchuria area, turkey

rainfall in temperate grasslands

moderate: 20-35in per year (more rain is taller grass)

mostly late spring early Summer

temperate grasslands soil

mollisols dark and Rich

savanna soils

rich ish but often leached

temperate grasslands fire

there is some fire in the drought season in fall or summer, but not as much or as important as savannas

temperate grasslands seasons

very hot summer and cold winter

rains in late spring and early Summer and drought for the rest of the year

trees in temperate grasslands

some riparian but basically nonexistent in actual grass unlike savanna

steppe rain

10-20in in winter (30-50cm), can be as low as 6in

steppe problems

wheat and grazing destroying it, salinization from irrigation

desert fires

uncommon, most of the time there isn't enough vegetation

flash flooding mechs

earth is hard baked so all the water just runs off immediately after it falls

desert classification systems

common: hot/subtropical, cold, semiarid, coastal

cause based: trade wind, midlatitude, rainshadow, monsoon, polar, coastal

stupid-ass far-left soinc classification: hot, warm, cold

hot and dry desert

little rain but varies; mean temps 20-25C; often over 40C; can drop into -C

plants w/ thick cuticle and sometimes CAM; small animals (lizards mostly)

include major N amer deserts of chihuahua-sonoran, sahara, australia

semiarid desert

cooler (20-25 in summer, 10C at night, cooler winters); precip 10-20in (between desert and grasslands); sort of includes steppes and more vegetated areas

gravelly in hills with hardpan bottoms

plants are larger shrubs like creosote; brickelbrush; somewhat more animals (small mammals)

cent asia, great basin, montana, mojave in some parts

coastal deserts

cool (15-20C in summers) summers and moderate winters; very little precip, often years between

cold W coastal currents block rain

atacama and namib

very dry adapted animals and plants

cold/polar deserts

cold (below freezing winter, 20C in summer); higher precip (15-25cm) mostly as snow in winter; air too cold to hold moisture

antarctica/arctic

silty soil

trade wind desert

encompasses most hot and dry deserts

found closer to the equator at less than 30 latitudes

hottest and driest; ie: sahara

midlatitude deserts

encompasses some hot deserts and most semi-arid colder ones

found towards the poles from 30 latitude

bit cooler and wetter than trade wind deserts; ie: great basin, talkamakan, gobi

rainshadow deserts

water dumped on windward side of mountains leaving adiabatic heated dry air on leeward side

monsoon deserts

sort of suss; dry but get some rain from monsoon season, mostly fall under other classification and only really found on one site

Great basin gets some monsoon, thar, can prob ignore this term

paleodeserts

places that used to be deserts but aren't anymore

ie: sand hills nebraska

the sun and deserts

lack of moisture means 90% of solar radiation hits ground vs. 40% in humid/tropical

bajada

alluvial fans merge into a gradual slope from mountains in desert to base

different names for grasslands

pampas, prairies, meadows, steppes, savannas, veldt,

list savanna types

tropical, temperate, mediterranean, montane, flooded

montane grasslands

found high up like arctic tundra but not quite

like tibetan plateau, high andes and new guinea

tropical savanna

synonymous with typical savanna

temperate savanna

sketchy term to describe any temperate grassland with sparse trees and shrubs

mediterranean savanna

savannas in mediterranean climates with interspersed trees (med, socal)

ie: oak savannas

flooded grasslands

grasslands that are seasonally/permanently flooded

ie: rann of kutch, okavango

alpine grassland

found above the treeline or polar direction from treeline but not in permafrost

mostly tussock fescue grasses where temperature never tops 50F in summer

drops 6.5C for every thousand feet up of 3 degrees?

successional grasslands

grasslands maintained by fire and grazing and disturbances that would otherwise be taken over by trees and shrubs

temperate vs. savanna

mostly by distance from equator (savanna usually between tropic of capricorn and cancer)

savannas have trees and shrubs while temperate typically little to none

climate: rains and temps

prairie

name given to US grasslands

california grasslands

used to be sagebrush steppes in owens valley and NE and stipa pulchra (purple needlegrass) bunchgrasslands through central and Socal

bunchgrasses disappeared

steppe

treeless, colder, semiarid grasslands

steppe climate

dry (10-20in); drought common summer-autumn; precipitation distributed with rain in summer and some snow in winter but dries out fast in summer rains

cold winters below freezing for 5 months; moderate summers up to around 70's (F)

steppe plants

treeless entirely; feather grasses dominant; feathery flowers, mostly stipa, avena

grasses die back in august and don't revive until spring; most plants less than <0.5m

laterite

hard soil that is clay-like and have iron and aluminum oxides; tropical soil type, low in nutrients and common in savanna

grasslands storms

strong and often short, water evaporates

gullies

large canyons from rills; form in grasslands bc grass usually break force of rain but when gone, erosion rapid into rills then gullies

climate vs. weather

weather is one day; climate is long term patterns

maritime vs continental climates

maritime more stabilized (less seasonal temp variation) and higher rainfall

continental more extreme variation and lower rainfall

intertropical convergence zone

zone around equator where hadley cells meet forcing moist air up and dumping rain

moves around by season (further N in summer)

dust bowl

1931; OK, KA, TX, CO; blow off topsoil in dark clouds across continent; drought caused and fallow fields and dryness mean easy blow away

monsoons

migration of intertropical convergence zone towards poles during their respective summers; cooler air in summers over oceans blows in as land heats into less dense hot air

vast majority of rain falls in summer season with little in winter bc reverses (called anticyclone) where cool air blows out from interior

relative humidity

humidity in air as percent of saturation for that temp

ENSO

el nino southern oscillation

heating of water off peru-chile deepening thermocline; hot air rises drawing in air and rain from E pacific

last glacial period

wisconsinian up until 1mya; interglacial period after is holocene; grasses expand after

sahara

largest non-cold desert; 3.5M square miles

large, some sandy, hot and dry, next to no rain, red sea to atlantic

US deserts

mojave: rainshadow coastal and sierra

colorado: small; around salton sink

sonoran: colorado delta through phoenix and south into mexico

painted: E of little colorado/colorado jnct in NE AZ

chihuahua: little bit into NM but mostly mex

wetting front

rain in deserts leaches down calcium carbonate down to a hardpan layer where it builds up

hardpan

layer of hard material just below surface preventing good drainage

what is sand

bits of silicon dioxide (weathered quartz); erosion resistant

loess

wind blown silt that builds into fertile formations; usually blown from deserts