Chapter 5: Disturbance January 29

Disturbance Disturbance – short-term physical or biological events that significantly alter ecosystems OR, any relatively discrete event in time that disrupts ecosystem, community, or population structure and changes resources, substrate availability, or the physical environment Fire, wind, landslide, floods, ice, avalanche, volcano, pests/disease, humans

Succession Succession changes in physical and biological conditions that follow disturbances Primary succession – starting with a lifeless surface Secondary succession – when an existing ecosystem is partially destroyed by disturbance

Primary Succession

Secondary Succession

Facilitation

Succession Successsional change is characterized as either –Autogenic – endogenous factors OR –Allogenic – exogenous factors

Succession Models Clementsian Model – seres are highly predictable sequences controlled by facilitation Tolerance Model – pioneer species move in first Inhibition Model – chance factors related to seed dispersal determine occupation Random – no facilitation or inhibition Chronosequence approach – patches

Fire Every ecosystem on the planet has a natural fire return interval → Time between two successive fire events at a given site or an area of a specified size –Chaparral – 3 to 5 years –Southern yellow pine – 5 to 15 years –Grasslands, cool deserts – 10 to 20 years –Mixed conifer-oak forest – 60 to 75 years –Deciduous forest, Temperate rainforest, Boreal forest – 100 years –Warm desert, Wetlands– 100 to 200 years –Rainforest – 800 years –Tundra – 1000 years

Fire Southern pines evolved to be fire dependent during the last ice age Humans arrived 10,000 BC Native Americans burned: –To prevent catastrophic fires –Eliminate underbrush –Hunting purposes –Religious purposes –Control mosquitoes and snakes near villages

Fire Ground fire – Surface fire – Crown fire -