Fundamental Degradation Terminology

NREM 612

StructureF

unct

ion

Initial state

Degr. state

low highlo

whi

gh

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I. Ecosystem Stability

Ecosystem stability is primarily a function of:Sensitivity & Resilience

to change.

A. Sensitivity – defined as (in Barrow 1991) “the degree to which a given environment undergoes change due to natural forces, human action, or a combination of both.”

B. Resilience – defined as (in Barrow 1991) “ the way in which the ecosystem can withstand use.”

C. Matrix of sensitivity and resilience can form the basis for land classification (Blaikie & Brookfield 1987)

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SensitivityResilience High Low

High

Low

SensitivityResilience High Low

High easy to degradeeasy to restore

Low

Think of ecosystems that would fit into each quadrat the matrix?

With a partner, fill in the tables below

hard to degradeeasy to restore

easy to degradehard to restore

hard to degradehard to restore

Sensitivity & Resilience Matrix

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SensitivityResilience High Low

High Mangrove Tidal salt marsh

Temperate forest

Low Tropical rain forestDry forestCoral reef

Herbaceous wetlandRangeland

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Stability Terminology

II. Stability terminology

A. General1. Constancy: lack of variation in some property of a system, ability of pop. to preserve its #s

2. Persistence: survival time of a system or come component of a system

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B. Terms to evaluate response to disturbance:

1. Resistance: ability to resist displacement from initial state, syn. w/ inertia

2. Resilience: ability to recover to an initial state after disturbance

3. Elasticity: speed of recovery to initial state after disturbance

4. Hysteresis: path of recovery differs from path of degradation (process or time)

5. Malleability: degree to which post-disturbance state differs from initial state

Illustrate terms in figure below:

StructureF

unct

ion

Initial state

Degr. state

new. state

low high

low

high

Stability Terminology, con’t

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II. Succession1. From Barrow 1991: “An ecosystem returns to a climax state via a series of successional stages – which are equilibrium points reached after disturbance

A. Primary succession – establishment of plants and an

ecosystem on land not previously vegetated

“from scratch”

B. Secondary succession – recolonization of previously

vegetated land following disturbance, soil remains

intact

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2. r-selected species: early-successional, adapted to disturbance, good dispersal capabilities, large #s of offspring, generalist, shorter lifespan

3. k-selected species: later-successional, better competitors, smaller # of offspring w/ higher survival rates, specialist, longer lifespan

Succession, con’t

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4. Facilitation: early successional spp. alter env. to make it more favorable for estab. of later-successional spp.

5. Inhibition: early successional spp. alter env. to make it less favorable to estab. of later-successional spp.

6. Tolerance: early spp. neither help nor hinder later spp.

Succession, con’t

StructureF

unct

ion

Initial state

Degr. state

new. state

low high

low

high

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Relationship between stability and diversityAre diverse systems more stable than simple systems?

Pimm et al. (1995)?

III. Stability-Diversity Relationship

A. Species Richness: # of different species in a particular area

B. Evenness: relative abundance of each species represented in a particular area

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Q: Which site has greater evenness?

Site 1 Site 2

Q: What is the species richness (SR) for site 1 & site 2?

SR for site 1 & 2 = 4

Site 1 = high Site 2 = low

Q: Which site do you consider more diverse?

Site 1

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C. Diversity: not just richness or abundance, but relationship between richness & abundance

Define these terms quantitatively:

s = # of species

Pi = proportion of individuals belonging to ith species

Diversity

sShannon’s Diversity Index = H’ = - Pi * lnPi

i=1

H’ ranges from ~ 1 – 3.5, usu. not > 4.5

Evenness = E = H’ ln(s)

E ranges from 0-1

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Example calculation: How to calculate H’ & E given data

Site 1 Site 2

sH’ = - Pi * lnPi

i=1

E = H’

ln(s)

Species

ni

Pi

lnPi

Pi*lnPi

Species

ni

Pi

lnPi

Pi*lnPi

E= E=

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Q: Relationship between stability and diversityAre diverse systems more stable than simple systems?

Pimm et al. (1995)?

Stability-Diversity Relationship

1. Species Diversity:

Eveness, richness, H’, etc.

2. Functional Diversity:The range and value of traits that influences ecosystem functioning; “the component

of diversity that influences ecosystem dynamics, stability, productivity, nutrient balance, and other aspects of ecosystem functioning” from Tilman, D. 2001

“Functional Diversity” in the Dictionary of Biodiversity

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Additional Materials

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D. Successional Theories

1. Clementian: holistic approach, sees succession as orderly, directional, predictable, system proceeds towards stable climax community

a. autogenic-internal

A B C D

F. Clements

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2. Gleasonian: individualistic approach, sees succession as disorderly, stochastic, unpredictable, determined by chance events, no climax community

b. allogenic-external

B

A D

C

H. Gleason

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Which theory is correct?

Relationship of succession with stability?

Relationship w/ current restoration practices?

Neither, examples for which each theory works

Gleasonian probably closer to reality than Clementian

Clements argue that climax community = evidence of stability

Gleason would discount stability altogether

Self-design – Clementian

Designer theory - Gleasonian

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II. Sustainability Terminology

A. Basic Definitions

1. Primary (1o) Productivity: increase in biomass of green plants over a given period

2. Sustainable Yield: fraction of net 1o prod removed on a continuous basis w/o destroying/ 1o prod

3. Carrying Capacity: max. # of individuals supported by a given env.

4. Sustainable Development (SD): Any activity that raises social welfare w/ maximum amount

of resource conservation & minimum amount of environ. degr. allowable w/i given econ, social, technical constraints

a. Implies anticipate & avoid rather than react & cure mentality

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a. Alpha (α) Div: w/i site or habitat

b. Beta (β) Div: from site to site or along transect, gradient

c. Gamma (γ) Div: diversity of a larger geographical unit, i.e. landscape or region; γ div. = (α & β)

Which site has highest α diversity?

Which region has highest β diversity?

Which region has highest γ diversity?

Sites 1 & 3

Region Y, higher species turnover

Region Y w/ higher total # of species