Disturbance and Succession

Disturbance Disturbance - any agent which causes complete or partial destruction of the community resulting in the creation of bare space Disturbance agents: both physical and biological processes may cause disturbances, though we usually focus on physical processes - Physical - fires, ice storms, floods, drought, high winds, landslides, large waves Biological - severe grazing, predation, disease, things that inadvertently kill organisms - digging and burrowing

Wind Damage – July 4, 1999 Derecho

Wildfire – Southern California October 22, 2007

Northern California Wildfires - 2017

Intermediate Disturbance Hypothesis Disturbance maintains communities in a "non-equilibrium state" (never reach equilibrium) and by renewing colonizable space, disturbance allows the persistence of species that might otherwise go extinct due to competitive exclusion. – from Joe Connell

Rocky coast near Santa Barbara, CA

Intertidal boulder field - California

Waves, boulders and disturbance Wayne Sousa

Species diversity on intertidal boulders with different degrees of disturbance – from Sousa

Species diversity on intertidal boulders with different degrees of disturbance – from Sousa Boulder size Small Medium Large turnover chance 49% / month 9 % /month 0.1%/ month bare space most medium little diversity low - mostly Ulva high - several species low - mostly Gigartina

Tree fall in Gabon

In an ecosystem, disturbance 1) clears space and interrupts competitive dominance 2) changes relative abundance of species 3) is a source of spatial and temporal variability 4) is an agent of natural selection in terms of life history characteristics

Succession Succession is the non-seasonal, directional and continuous pattern of colonization and extinction on a site by populations of species - this definition incorporates a range of successional sequences that occur over widely different time scales and have very different mechanisms.

Types of Succssion Primary - succession on a site that has not experienced life before - extremely severe disturbance may have killed all life so no seeds or roots or individuals survive - lava flow, volcanic explosion, glacial retreat, landslides, weathering of bare rock Secondary - succession on a site that may have remnants of previous life on it - some survivors of the disturbance - fire, floods, windstorms, wave battering, severe grazing  Degradative - succession in which the substrate is decaying and being exploited by various organisms - succession of decomposers on carcass, rotting log, etc.

Body Farm – University of Tennessee FBI Forensics Class

Facilitation Succession Early species change community or ecosystem in a way that allows later species to move in and changes the system so that the early species can no longer survive there.

Retreat of Muir Glacier

Retreat of Muir Glacier – 1941 – 1950 - 2004

Retreat of Pederson Glacier – Kenai Fjords NP - 1930-2005

Succession at Glacier Bay

Glacier Bay terminal moraine

Terminal Moraine – Close Up

Early succession – Moss on bare soil

Fireweed at Glacier Bay

Dryas - herbal rose at Glacier Bay

Alder thicket – Glacier Bay

Sitka spruce seedlings

Mature Spruce–Hemlock Forest – Glacier Bay

Tolerance Succession All species arrive at start of succession, but longer lived individuals eventually outlive short lived species and grow to dominate in the succession - long lived species can tolerate shade and competition early in life.

Old Field Succession

Old field succession – bare ground

Old field succession – annual weeds

Old field succession – perennials

Old field succession – pine invasion

Old field succession – hardwood forest

Inhibition Succession First species to arrive occupies space and prevents the settlement of later arriving species - the first species are replaced only after they die.

Ulva – above and Gigartina overgrowing Ulva – right

Typical Succession In most successional sequences, all three mechanisms operate at different times in the sequence.

Henry C. Cowles (center) about 1920

Lake Michigan sand dune ecosystem

Marram grass establishment

“Blow-out” in sand dune ecosystem

Successional Species Types Early successional, pioneer, opportunist Late successional seed dispersal distance long, good short, poor growth rate fast slow reach maturity early late number of offspring high low competitive ability

The Kabetogama Peninsula

Kabetogama Peninsula

Beaver – Castor Canadensis

Beaver Dam

Pond and Bog Succession

Climax Community

Many Communities Experience Constant Disturbance or Change

Fir Wave on Mt. Coe, Baxter State Park, Maine

Fir Wave Up Close