Transcript Document

Grasslands and Tundra
Temperate grasslands
Found in areas of moderate rainfall,
typically between 25 and 75 cm per
year.
Dry seasons sufficient to exclude most
trees.
Frequent fires.
North American grasslands are
dominated by “bunch grasses.”
The North American Great Plains can
be divided into several prairie types.
They differ primarily on the basis of
the amount of rain and the time of the
dry season.
Tall-grass prairie
Mixed-grass
prairie
Short-grass prairie
Tundra ecosystems are found where
cold, hard winds and/or permafrost
prevent the growth of large woody
plants. We recognize two types of
tundra:
Arctic tundra
Alpine tundra
Arctic tundra have long winters of extreme
cold. Permafrost is common.
Arctic tundra is
dominated by lichens,
mosses, sedges, and small
woody plants.
Alpine tundra
is found high in
mountains at all
latitudes.
Conditions are
variable.
Permafrost is
rare.
Are grassland ecosystems
equilibrium systems? This is
significant in determining whether
they will return if stresses are
removed.
Some have suggested that they
may have “multiple stable
states.”
Succession
models
Population cycles are commonly seen
in tundra habitats. They can be
classified into three types:
1. 3-4 year cycles common in
microtine rodents.
2. 9-10 year cycles as shown by
snowshoe hares.
3. Longer cycles as seen in some
larger tundra animals.
Lemming population cycle
Cycle of
snowshoe
hare and
lynx.
Suggested Causes of
Population Cycles
• Herbivory hypothesis
• Food supply-predation hypothesis
• Predation hypothesis
Human impact on grassland and
tundra ecosystems has been
severe.
Grazing impact of livestock is often
due to selective herbivory.
Decreasers versus increasers
Invading species like cheatgrass
(Bromius tectorum) has replaced
native grasses over large areas.
Arctic National
Wildlife Refuge
Oil in the ANWR