Plant Ecology - Chapter 12 Disturbance & Succession

Succession Temporal patterns in communities Replacement of species by others within particular habitat (colonization and extinction) Non-seasonal, continuous, directional

Degradative succession Decomposers breaking down organic matter Leads to disappearance of everything, species included

Autotropic succession Does not lead to degradation Habitat continually occupied by living organisms

Two types of autotropic succession Allogenic succession Autogenic succession

Allogenic succession Serial replacement of species driven by changing external geophysical processes Examples: 1) silt deposition changing aquatic habitat to terrestrial habitat 2) increasing salinity of Great Salt Lake

Autogenic succession Change of species driven by biological processes changing conditions and/or resources Example: organisms living, then dying, on bare rock

Autogenic succession can occur under 2 different conditions In an area that previously did not support any community Primary succession Example: terrestrial habitat devoid of soil In an area that previously supported a community, but now does not Secondary succession Example: terrestrial habitat where vegetation was destroyed, but soil remained

Disturbances Relatively discreet event in time that causes abrupt change in ecosystem, community, or population structure Changes resource availability, substrate availability, or the physical environment

Disturbances Intensity, size, frequency Small disturbances of low intensity are much more frequent than large disturbances of high intensity

Disturbances Gaps Fire Wind Water Animals Earthquakes, volcanoes Disease Humans

Primary succession Volcanic eruptions Glaciers

Secondary succession Floods Fires

Rate of succession Primary - slow - may take 1000s of years Secondary - faster - fraction of the time to reach same stage

Autogenic succession begins… First community comprised of r- selected species - pioneer species

r-selected species Good colonizers Tolerant of harsh conditions Reproduce quickly in unpredictable environs Example: lichens

r-selected species Primary - colonized by seeds, spores, via wind, water Secondary - wind-dispersed seeds, seed banks

Pioneer species Carry out life processes and begin to modify habitat Extract resources from bare rock Break up/fragment rock with roots Collect wind-blown dust, particles Waste products accumulate Die and decompose Soil development begins

Continuing change Colonizers joined by other species suited for modified habitat Eventually replace colonizers Better competitors in modified habitat Less r-selected, more K-selected

More change Communities may gradually become dominated by K-selected species Good competitors, able to coexist with others for long periods of time

Stability Communities may become stabilized on some scale Reach equilibrium (dynamic) Little or no change in species composition, abundance over long periods of time Climax community End stage of succession

Will climax stage be reached? Rarely is climax stage reached quickly Slow succession most common, climax stage almost never achieved Community usually affected by some major disturbance (e.g., fire) before climax stage is reached Resets succession, forces it to start again from some earlier stage

Terrestrial succession

Relay Floristics

Predictability of Succession Deterministic- process with a fixed outcome Community restoration via succession?