A brief tour of terrestrial biomes
Biomes tour
Topical issues for particular biomes
Reading: Chapter 2
Note that the “issues” help define the difference
between “potential” and “actual” vegetation.
Indirect
Human
impacts
Direct &
Indirect
Human
impacts
Additional Themes:
• Altering vegetation has “feedback effects” on the
atmosphere & climate - e.g. via altered albedo
(surface reflectance) and gas exchange (e.g. CO2
CH4)
Atmosphere
& Climate
?
Biosphere
?
Tundra (Arctic and Alpine)
Tundra “Polygons” caused by freezethaw dynamics
Arctic Tundra Distribution & Climate Diagrams
Alpine Tundra
(found towards the top of many mountain ranges)
Issues for Tundra:
- Warming
- Permafrost melting
- Altered hydrology (e.g. surface drying)
- Altered albedo
These factors have “feedback effects”
on climate.
Evidence for disproportionate effects of warming:
Source: NASA Goddard Institute
http://www.giss.nasa.gov/data/update/gistemp/
In response to climate change, shrub cover seems to be expanding in the Arctic .
(this can conceivably increase biospheric carbon uptake, slowing climate change)
Sturm et al. 2001 Increasing shrub abundance in the Arctic, Nature 411:546-547
Thawing permafrost in Arctic tundra – a potentially large
carbon source to the atmosphere (this adds carbon to the
atmosphere and can conceivably speed up climate change)
Science, Vol 312, pp. 1612-1613 (2006)
Aerial view of Alaska’s North Slope (coastal tundra plain –
note how much of this “terrestrial” landscape is actually
covered in water!)
Photo: John Gamon
The Barrow “Biocomplexity” project is an example of an “ecosystem
experiment” manipulating surface hydrology to see the effects on
vegetation and gas exchange
Boreal Forest (Taiga)
Boreal Forest Distribution & Climate Diagrams
Issues for the Boreal Forest:
- Warming
- Changing hydrology (altered surface moisture)
- Melting permafrost
- Disturbance:
Deforestation
Drought
Insect Infestations
Wildfire
 Altered feedbacks on climate
Deforestation
Fire in the North American Boreal Region
(fires seem to be increasing in frequency and extent)
Lightning area
Human area
Lightning fires
Human fires
300
-1
Fires (number yr )
3
400
6
-1
Burned area (10 ha yr )
4
2
200
1
100
0
0
1960s
1970s
1980s
Ignitions are for fires > 2 km2 in size
1990s
E. Kasischke
Upland black spruce fire chronosequence
in Delta Junction, Alaska (64ºN)
(this cycle affects albedo and gas exchange, influencing climate)
Photos: J. Randerson
Temperate Forest
Biome
Temperate Forest Distribution & Climate Diagrams
Issues for temperate forests:
Human impacts:
e.g. Deforestation & Land-use change
(most old-growth temperate forests have been cut)
Grassland biome (e.g. prairie)
Grassland Distribution & Climate Diagrams
Issues For Grassland Biomes:
Land Conversion to Agriculture
Drought - Water supply can limit productivity
North American Prairie
Molles
& Cahill
2008
Molles
2008
Mediterranean Climate Biome
“Mediterranean” oak woodland in California” (savanna)
Molles & Cahill 2008
Molles 2008
Mediterranean Biome Distribution & Climate Diagrams
Issues for the Mediterranean Biome:
Fire (altered fire frequency)
Human disturbance:
- altered fire
- land-use change
- pollution/nitrogen deposition
- species invasions (alters ecosystem
function & biodiversity)
California “chaparral” (scrubland vegetation, aka “matorral,” “fynbos”, etc.)
After drought, before fire
After fire
Sampling surface reflectance,
(albedo), and temperature
following fire. Note basal
resprouting of chaparral
shrubs.
Desert Biome
Cactus in North America
Euphorbia in Africa
Desert Biome Distribution & Climate Diagrams
Issues for deserts:
Drought!
(Heat)
Human disturbance
irrigation – alters hydrology, salinity
grazing (e.g. Sahel)
Savanna Biome
Savanna Biome Distribution & Climate Diagrams
Issues for Savanna regions:
Human disturbance – e.g. grazing
Dry Tropical Forest Biome
Tropical Dry Forest Biome Distribution & Climate Diagrams
Issues for the Dry Tropical Forest:
Human population pressures & disturbance
- Deforestation
- Biodiversity losses
- Lack of water
- Wildfire
Tropical Rainforest
Biome
Tropical Rainforest Biome Distribution & Climate Diagrams
Issues for Rainforests:
Human Disturbance
Deforestation
Wildfires
Conversion to pasture and agriculture
Biodiversity Loss
Deforestation – large areas of the “tropical rainforest biome” are no longer forests
Alves et al. 1997, Global Change Biology
Conclusions:
We tend to think of biomes as “static” entities in “climate space,”
when in reality they are far more dynamic, due to a combination
of natural factors (e.g. fire cycles) and direct and indirect human
impacts.
Examples of direct impacts might be deforestation or conversion
to agriculture. Examples of indirect impacts might be altered
vegetation distribution due to climate change.
These direct and direct impacts differ in relative importance for
different regions of the Earth.
Altering biomes (conversion from potential to actual vegetation)
exerts “feedback effects” on the atmosphere and climate.