Unit 3: Terrestrial Vegetation and Succession

Climax Community

Vegetation formation resulting after many years of development.

Succession

Non-essential, directional, and continuous pattern of colonization and extinction on a site by populations of species.

Facilitation

Monoclimax; one climax community that all stands of vegetation move towards; successional mechanism.

Successional Mechanism 

Each species in the sequence modifies the environment to make it more suitable for the next species; it doesn’t account for variation.

Facilitation example:

Glacial moraines on Glacier Bay.

Moraine

Glacially formed accumulation of unconsolidated glacial debris (soil and rock). 

What’s happening in Glacier Bay?

Glaciers have been retreating more rapidly, and grinds up what is underneath; then succession begins; multiple stages of vegetative growth until climax community is reached. S

What is the Climax community for Glacier Bay?

Spruce Hemlock Forest.

Tolerance

Later species outcompete earlier ones; earlier species don’t grow environment for later; chance event. 

Tolerance Sequence of Species

Can’t be predicted; result from colonizing ability, reproductive rates; later species are fewer, less mobile, slower growth rates, higher competitive abilities.

Tolerance example:

Sand Dunes

What is the climax community for sand dunes? 

Oak-Hickory forest. 

Inhibition

Opposite of facilitation; each species inhibits colonization of later; a force is required for each succession to proceed; competition not a driving force.

Allogenic force

Abiotic, force outside of the system.

Autogenic force

Force inside the system.

Inhibition Example:

Rocky Intertidal and the algae that reproduce year round vs. only in the fall.

What did the study of rocks and algae find?

Not based on surface area, but more-so on the rock turnover rate.

What are the most important factors in biomes? 

Precipitation and Temperature. 

Temperate Deciduous Forest

Eastern N Americas, N Europe, Japan, China; cold winters; wet and dry; abundant understory; familiar animals.

Coniferous Forest

Boreal forest: Northern tier of forested areas, aka taiga; Canada and Russia; spruce, fir, aspen, and birch; cold areas with long winters.

Coniferous Food Web

Many predators: lynx, wolverine, bobcats, otters, herman; Tiny prey: squirrels, bunnies, voles.

Temperate Rain Forest 

Western edge of N and S America; very wet; considerable seasonal variation; mixture on conifers and deciduous trees.

Temperate Rainforest Food Web

Very diverse

Tundra

Strong winds and harsh environments; Alpine areas north of boreal forest; low precipitation and permafrost; low biological diversity; simple vegetation.

Tundra Food Web

Most herbivores, ox, sheep, elk, voles.

Grasslands

Middle of continents, adequate precipitation; occasional droughts; tall-grass and short prairies; natural fire is very good.

Grassland Food Web

Bison; insects most abundant.

Savanna 

Grasslands with scattered trees. Less rainfall; spring time is burning season; organisms more abundant but less diverse; fire is very important. 

Shrubland

Short, densely branching shrubs; long and dry summers; mild and rainy winters; fire and drought important.

Shrubland Food Web

Deer, coyotes, jackrabbits.