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Disturbances & Succession

• Objectives – Overview of:

• Disturbances (natural and anthropogenic) • Ecological succession

– Implications for forest management

– First, take-home points, things you learned, etc. from reading assignments

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• Disturbance – Mix of large, infrequent and small frequent events – A given disturbance is the result of numerous,

interconnected factors – Natural disturbances are not “bad” – Disturbances characterized by type, size, severity,

intensity, frequency, timing, etc. • Disturbance Regime

Disturbances & Succession

Disturbances & Succession

• Disturbance Regime − Spatial and Temporal Components

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100 year flood 30 year fire return interval

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• Disturbance - Fire

Disturbances & Succession

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Disturbances & Succession

• Disturbance - Fire

Crown Fire Surface Fire

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Disturbances & Succession

• Disturbance - Wind

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Disturbances & Succession

• Disturbance – Diseases, Insects, and Pathogens (DIPs)

Disturbances & Succession

• Other important natural disturbances

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Flooding Earthquakes Volcanoes

Disturbances & Succession

• Natural disturbances are not “bad” − Renew ecosystems and diversify landscapes − Integral part of ecosystem structure and

function that results in ecological succession • Humans have modified disturbance

regimes, and the actual disturbances − Anthropogenic disturbances can be a serious

threat to ecological integrity

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Disturbances & Succession

• Disturbance – Invasive Species

Psidium cattleianum

Pennisetum setaceum

Quadrastichus erythrinae

Feral Pigs

Feral Cattle

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Disturbances & Succession

• Disturbance – LULCC

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Disturbances & Succession

• Ecological Succession

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Disturbances & Succession

• Succession - Models

Initial Floristic Composition Model Relay Floristics Model vs.

Disturbances & Succession

• Species occurrence during succession: – Who can get there and establish

• Dispersal and colonization – Who can survive and reproduce

• Competition and other biotic interactions

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Disturbances & Succession

• Succession – Stable vs. Alternative Steady States

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Disturbances & Succession

• Succession – Primary vs. Secondary

Primary Succession Secondary Succession

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Disturbances & Succession

• Succession – Primary

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Disturbances & Succession

• Succession – Secondary

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Disturbances & Succession

• Succession – Gap Phase Dynamics

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Disturbances & Succession

• Succession – Facilitation

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Disturbances & Succession

• Succession – Structure

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Disturbances & Succession

• Succession – Ecosystem Processes

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Disturbances & Succession

• Succession – Ecosystem Processes

• Implications of disturbances for management • Natural, often desirable, and inevitable

– Historical frequency, severity, and scale modified – Large disturbances largely beyond control – Small disturbances easier to control, but often not a

good idea to do such, at least over long time periods

• To manage and conserve forests, we must: – Understand ecological role of natural disturbances

» Anticipate their occurrence » ***Emulate them, where possible, in management 24

Disturbances & Succession

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Disturbances & Succession

• Implications of succession for management – Ecosystems are characterized by change

• Physical, chemical and biological

– Succession does not always follow same pattern • Alternative stable states; variability in rate & duration

– Change in structure → change in function • Beneficial or detrimental; manage for beneficial

– Foresters constantly manipulate succession to optimize growth of desired species (ENFD)

• Requires theoretical and/or empirical knowledge