Page 38 - Science Course 3 (Book 1)
P. 38
Mo1-L4a: How Do Land Ecosystems Change?
In a tropical forest biome, a mature tropical forest is a climax community.
Climax communities are usually stable for hundreds of years.
Annual Perennial Shrubs Softwood Hardwood
Plants Plants and Tress- Trees
Grasses Pines
TIME
Key Concept Ecological succession in new areas of land with little
or no soil, such as a lava flow or sand dune, is
How Do Land Ecosystems Change? primary succession.
What is a climax community?
The first species that colonize new or undisturbed
land are pioneer species.
During a volcanic Airborne spores from
eruption, molten lava mosses and ferns settle
flows over the ground onto the thin soil and
and into the water. add to the soil when they
After the eruption is die. The soil gradually
over, the lava cools becomes thick enough to
and hardens into hold water. Insects and
bare rock. other small organisms
move into the area.
Lichen spores carried After many years the
on the wind settle on the soil is deep and has
rock. Lichens release enough nutrients for
acid that helps break grasses, wildflowers,
down the rock and shrubs, and trees. The
create soil. Lichens new ecosystem provides
add nutrients to the habitats for many ani-
soil as they die and mals. Eventually, a climax
decay. community develops
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