Succession

Ecological Succession Natural ecological restoration –Primary succession – gradual establishment of biotic communities in lifeless areas where there is no soil or sediment –Secondary succession – series of communities with different species develop in places containing only soil or bottom sediment

Primary Succession In the beginning… –No soil = no nutrients –Over time rock weathers Hundreds and thousands of years later…

Primary Succession Early pioneer plant species –Species arrive and attach themselves to inhospitable patches of weathered rock Lichens, mosses –Help form soil by trapping wind-blown soil particles and detritus Add waste and dead bodies Hundreds and thousands of years later…

Primary Succession Mid-successional plant species –Soil becomes deep and fertile enough to hold moisture –Supports the growth of herbs, grasses, and low shrubs –Creates shade which causes mosses and lichens to die –Trees replace grasses and shrubs

Primary Succession Late successional plant species –Species that can tolerate shade –Bare rock ultimately becomes a complex forest

Aquatic Primary Succession Newly created small pond Influx of nutrients via runoff

Secondary Succession Some soil remains in a terrestrial system or sediment in an aquatic system Ecosystem has been –Disturbed –Removed –Destroyed

Secondary Succession New vegetation can germinate usually within a few weeks –Seeds already in the soil or imported by wind, birds, and other animals Climax community – stability

Similarities Primary and secondary succession –Tend to increase biodiversity –Increase species richness and interactions among species Primary and secondary succession can be interrupted by –Fires –Hurricanes –Clear-cutting of forests –Plowing of grasslands –Invasion by nonnative species

Species Replacement Facilitation – one set of species makes an area suitable for species with different niche requirements –Less suitable for itself (mosses and lichens) Inhibition – some early species hinder the establishment and growth of other species –Pine needles make soil acidic Tolerance – late succession plants are largely unaffected by plants at earlier stages of succession

Succession Doesn’t Follow a Predictable Path Traditional view – Balance of nature and a climax community Current view –Ever-changing mosaic of patches of vegetation –Mature late-successional ecosystems State of continual disturbance and change

Living Systems Are Sustained through Constant Change Inertia, persistence –Ability of a living system to survive moderate disturbances Resilience –Ability of a living system to be restored through secondary succession after a moderate disturbance Tipping point –Any additional stress can cause the system to change in an abrupt and usually irreversible way that often involves collapse