Succession and Stability Chapter 20 SUCCESSION Succession Gradual

Succession and Stability Chapter 20

SUCCESSION • • Succession: Gradual change in plant and animal communities in an area following disturbance. v Primary succession on newly exposed geological substrates. v Secondary succession following disturbance that does not destroy soil. Climax Community: Late successional community that remains stable until disrupted by disturbance.

Primary Succession at Glacier Bay • Reiners et. al. studied changes in plant diversity during succession. v Total number of plant species increased with plot age. v Species richness increased rapidly in early years of succession and more slowly during later stages. § Not all groups increased in density throughout succession.

Primary Succession at Glacier Bay

Secondary Succession in Temperate Forests • Oosting found number of woody plant species increased during secondary succession at Piedmont Plateau. v Johnston and Odum found increase in bird diversity across successional sequence closely paralleled increase in woody plant diversity observed by Oosting.

Succession in Stream Communities • Fisher studied rapid succession in Sycamore Creek, AZ. v Evaporation nearly equals precipitation flows generally low and intermittent. § Subject to flash floods. v Observed rapid changes in diversity and composition of algae and invertebrates. § Invertebrates found refuge because many adults in aerial stage. Ø Re-colonized after flooding.

Hypothetical Periphyton Community Succession

Mirror Lake, Yosemite National Park Lake to Meadow Succession

Mirror Lake, Yosemite National Park

El Capitan Meadow, Yosemite National Park © Dan Baumbach 2002

Ecosystem Changes During Succession • Chapin documented substantial changes in ecosystem structure during succession at Glacier Bay. v Total soil depth and depth of all major soil horizons show significant increase from pioneer community. § In addition, organic content, moisture, and N concentrations all increased. Ø Physical and biological systems are inseparable.

Ecosystem Changes During Succession

Recovery of Nutrient Retention Following Disturbance • Bormann and Likens found felling trees in Hubbard Brook substantially increased nutrient losses. v Herbicide used to suppress regrowth. § When application stopped, succession proceeded, nutrient losses decreased, and primary production increased.

Mechanisms of Succession • • Clements, 1916 v Facilitation Connell and Slayter, 1977 v Facilitation v Tolerance v Inhibition

Facilitation • Proposes many species may attempt to colonize newly available space. v Only certain species will establish. § Colonizers “Pioneer Species” modify environment so it becomes less suitable for themselves and more suitable for species of later successional stages.

Tolerance • Initial stages of colonization are not limited to pioneer species. v Early successional species do not facilitate later successional species, but do change the environment. v Species remain, leave, or establish based on tolerance to environment. v Long lived species are most broadly tolerant to a range of environmental change.

Inhibition • Early occupants of an area modify the environment in a way that makes it less suitable for both early and late successional species. v Early arrivals inhibit colonization by later arrivals. v Assures late successional species dominate an area because they live a long time and resist damage by physical and biological factors.

Mechanisms of Succession

20_25 a. jpg

20_25 b. jpg

20_25 c. jpg Why Alder?

20_25 d. jpg

Successional Mechanisms in Rocky Intertidal Zone • Sousa investigated mechanisms behind succession of algae and barnacles in intertidal boulder fields. v If the inhibition model is in effect, early successional species should be more vulnerable to mortality. § Results showed early successional species had lowest survivorship and were more vulnerable to herbivores.

Community and Ecosystem Stability • Stability: Absence of change. v Ability to resist change from original state and/or return to original state once disturbed