Transcript Desertsx - Global Change Biology

The Desert Biome
and
Climate Change
Kelly Barnhart
Global Change Biology
February 16, 2016
Pictures from http://w3.marietta.edu/~biol/biomes/desert.htm
Deserts

Environmental extremes

Arid and hot

Large daily temperature fluctuations

Cold deserts

Low rainfall


Annual rainfall <250 mm (arid)
Overall biomass of plants and animals is low
(Noble and Gitay, 1996).
Desert Locations
 Most
occur between 20 and 40° latitude
 Some

found in rain shadows of mountains
Atacama desert in South America
 Some
are very far away from oceanic
moisture

Central Asian deserts
(Noble and Gitay, 1996).
Desert Locations
 Approximately
(Noble and Gitay, 1996).
30% of the Earth’s surface
(Lioubimtseva and Adams, 2004)
Why do deserts exist?

Low moisture regions
Hadley Cell
1.
Solar heating strong at equator, air rises and cools, forms
clouds and rain at equator
 Rising equatorial air spreads towards the poles and then
descends
 As the now dry air descends, it warms and creates a dry
region

Mountain ranges
2.

Rain shadow effect


Mountain ranges force moist air to rise and precipitate
Descending air on the other side warms and dries
Distance from moisture
3.

Trade Winds blow from east to west, losing moisture as
they travel
Cold ocean currents
4.

Flow 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 species
 Biodiversity
declines with increasing aridity
 Biological
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 dew
Ephemeral biota:
 migrate
into deserts
 become 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
http://www.desertusa.com/flora.html
From
https://nationalzoo.si.edu/Animals/SmallMamm
ct-fennecfox.cfm
 Nocturnal
 Live
in burrows
From
http://w3.m
arietta.edu/
~biol/biome
s/desert.htm
Evapotranspiration
 Potential
evapotranspiration is very high
 Arid
zones are where evapotranspiration
exceeds precipitation

Aridity Index (PET/P) where P = precipitation and
PET = potential evapotranspiration
 Increases
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 Nfixing organisms on the soil surface

lichens, cyanobacteria, moss, and fungi
 Rates
of decomposition are slow
 Carbon
1.
2.
takes place in two forms in desert soil:
Organic carbon in decaying plants and animals
Inorganic carbon
 Calcium
 Organic
carbonate
carbon in desert soils is generally low
(Lioubimtseva and Adams, 2004)
Predictions
 Most
deserts are likely to become hotter, but
not significantly wetter
 (moister
areas)
and drier predictions for different
 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 CO2 will favor C3 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 SalgueroGómez, 2014)
C3 versus C4 plants
 Desert
(Lioubimtseva and Adams, 2004)
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.
C3 versus C4 plants
 As
CO2 levels increase, it’s expected that plants
which use the more water-efficient and CO2efficient 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 erosion
Deterioration of properties of soil
 Loss
of nutrients, fine soil grains, water holding
capacity
 Increase in salinity and toxicity

Long-term loss of natural vegetation
 Shifts
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 security
 Generally
irreversible because it is an alternative
stable state
 Leads
to loss of biomass and soil organic carbon
 Can
seriously modify albedo as well as water
exchange and nutrient cycles
(D’Odorico, Paolo, et al., 2013)
http://www.gre
enfacts.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 land
 Increased soil salinity destroys soil structure
and reduces porosity and permeability of
soils

Reduces crop growth and yield
 Overexploitation
of land in general
(D’Odorico, Paolo, et al., 2013)
Desertification Feedbacks
 Nutrient
loss
 Salinization
 Precipitation recycling
 Dust emissions
 Shrub encroachment
 Decrease 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