The Desert Biome and

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The Desert Biome and Climate Change

Kelly BarnhartGlobal Change BiologyFebruary 16, 2016

Pictures from http://w3.marietta.edu/~

biol

/biomes/

desert.htm

Deserts

Environmental extremesArid and hotLarge daily temperature fluctuationsCold desertsLow rainfallAnnual rainfall <250 mm (arid)Overall biomass of plants and animals is low

(Noble and

Gitay

, 1996).

Desert Locations

Most occur between 20 and 40° latitudeSome found in rain shadows of mountainsAtacama desert in South AmericaSome are very far away from oceanic moistureCentral Asian deserts

(Noble and

Gitay

, 1996).

Desert Locations

Approximately 30% of the Earth’s surface

(Noble and

Gitay

, 1996).

(

Lioubimtseva

and Adams, 2004)

Why do deserts exist?

Low moisture regionsHadley CellSolar heating strong at equator, air rises and cools, forms clouds and rain at equatorRising equatorial air spreads towards the poles and then descendsAs the now dry air descends, it warms and creates a dry regionMountain rangesRain shadow effectMountain ranges force moist air to rise and precipitateDescending air on the other side warms and driesDistance from moistureTrade Winds blow from east to west, losing moisture as they travelCold ocean currentsFlow toward equator and cause low evaporation, precipitation, and low temperature range

(

Lioubimtseva

and Adams, 2004)

Biodiversity and Productivity

Less diverse than many other biomes but have many endemic speciesBiodiversity declines with increasing aridityBiological productivity is limited by precipitation and nutrient availability (especially nitrogen)

(

Lioubimtseva

and Adams, 2004)

Biological Specifications

Many plants and animals obtain their water from fog or dewEphemeral biota: migrate into desertsbecome active after drought (drought resistant seeds)become active from dormant life stages

(

Lioubimtseva

and Adams, 2004)

Biological Specifications

Many animals and plants have thick skins or cuticles to reduce water loss Hairs or spines reflect radiation

From https://

nationalzoo.si.edu/Animals/SmallMammals/fact-fennecfox.cfm

From http://

www.desertusa.com

/

flora.html

NocturnalLive in burrows

From http://w3.marietta.edu/~

biol

/biomes/desert.htm

Evapotranspiration

Potential evapotranspiration is very highArid zones are where evapotranspiration exceeds precipitationAridity Index (PET/P) where P = precipitation and PET = potential evapotranspirationIncreases in temperature will limit soil moisture through increased rates of evapotranspiration

(

Lioubimtseva

and Adams, 2004)

Nutrient Cycles

The main sources of nitrogen in deserts are N-fixing organisms on the soil surfacelichens, cyanobacteria, moss, and fungi Rates of decomposition are slowCarbon takes place in two forms in desert soil:Organic carbon in decaying plants and animalsInorganic carbonCalcium carbonateOrganic carbon in desert soils is generally low

(

Lioubimtseva

and Adams, 2004)

Predictions

Most deserts are likely to become hotter, but not significantly wetter

(moister and drier predictions for different areas)

The

frequency of El Niño events is expected to

increase:

more

rainy pulses to winter-rain

deserts

more

drought pulses to summer-rain

deserts

Greenhouse gases are likely to persist and will not be reduced

http://

www.unep.org

/geo/

gdoutlook

/045.asp

Predictions Continued

Likely

to be changes in community

composition of plants and animals

More intense rainfall events (pulses

)

Reduction in soil moisture and droughts are expected to lead to expansion of major deserts

Human-induced desertification may counteract any positive effects of climate change unless it is managed

Increased CO

2

will favor C

3

species

Increased desert albedo due to less vegetation cover

Potential Carbon Sinks?

Deserts

are not a major store of organic carbon in either soils or vegetation.

GCMs

do not generally

predict

dramatic changes in deserts under global warming.

If desert

regions do become significantly moister under global warming (as they did during the Last Interglacial and the Holocene Optimum

),

they have potential to take up hundreds of

gigaton

(

Gt

) of carbon in more organic-rich soils and vegetation.

Possible Effects of CO2 Increase on Deserts

(

Lioubimtseva

and Adams, 2004)

Possible Effects on Desert Plants

Likely species specific Plants are likely more resilient to changes in CO2 and precipitation than previously thought due to specific adaptations that have already evolved in response to stress and extreme/variable climate

(

Tielbörger,

Katja

, and Roberto

Salguero

-Gómez, 2014)

C3 versus C4 plants

Desert plants often use C4 or CAM photosynthesis as opposed to the normal C3 photosynthesis. Compared to C3 photosynthesis, both C4 and CAM photosynthesis are more efficient under hot, dry conditions, but are not as efficient overall, and therefore fix less carbon dioxide in a given period. As a result, growth in desert plants is very slow.

(

Lioubimtseva

and Adams, 2004)

C3 versus C4 plants

As CO2 levels increase, it’s expected that plants which use the more water-efficient and CO2-efficient C4 photosynthetic system will respond less strongly than C3 plants.C4 plants will likely decline due to competition

(

Lioubimtseva

and Adams, 2004)

Desertification

“Land degradation in arid, semi-arid, and dry sub-humid areas resulting from various factors, including climatic variations and human activities.” (United Nations definition)Soil erosionDeterioration of properties of soilLoss of nutrients, fine soil grains, water holding capacityIncrease in salinity and toxicityLong-term loss of natural vegetationShifts from perennial to annual, palatable to unpalatable, grassland to shrubland

(D’Odorico, Paolo, et al., 2013)

Desertification

Important because it affects soil productivity and global food securityGenerally irreversible because it is an alternative stable stateLeads to loss of biomass and soil organic carbonCan seriously modify albedo as well as water exchange and nutrient cycles

(D’Odorico, Paolo, et al., 2013)

http://

www.greenfacts.org

/en/desertification/

Overgrazing

(

Lioubimtseva

and Adams, 2004)

Misuse or Mismanagement of Land

Construction of irrigation systems or boreholes causing unbalanced, intensive use of the landIncreased soil salinity destroys soil structure and reduces porosity and permeability of soilsReduces crop growth and yieldOverexploitation of land in general

(D’Odorico, Paolo, et al., 2013)

Desertification Feedbacks

Nutrient lossSalinizationPrecipitation recyclingDust emissionsShrub encroachmentDecrease in vegetation cover

(D’Odorico, Paolo, et al., 2013)

References

D’Odorico

, Paolo, et al. "Global desertification: drivers and feedbacks." Advances in Water Resources 51 (2013): 326-344

.

Evans, R. D., et al. "Greater ecosystem carbon in the Mojave Desert after ten years exposure to elevated CO2." Nature Climate Change 4.5 (2014): 394

.

Lioubimtseva

, Elena, and J. M. Adams. "Possible implications of increased carbon dioxide levels and climate change for desert ecosystems." Environmental Management 33.1 (2004): S388-S404

.

Noble, I. R., and H.

Gitay

. "Deserts in a changing climate: impacts." (1996)

.

Tielbörger

,

Katja

, and Roberto

Salguero

-Gómez. "Some Like It Hot: Are Desert Plants Indifferent to Climate Change?." Progress in botany. Springer Berlin Heidelberg, 2014. 377-400

.

http://www.unep.org/geo/gdoutlook/045.

asp

http://www.greenfacts.org/en/desertification

/

http://w3.marietta.edu/~biol/biomes/

desert.htm