Ecosystem RestorationEcosystem Restoration

Repaying the Ecological DebtRepaying the Ecological Debt

Conceptual issuesConceptual issues

After manipulation of a natural system, After manipulation of a natural system, have three choices:have three choices:

Ecosystem RestorationEcosystem Restoration

RestorationRestoration – bring back to pre-disturbance – bring back to pre-disturbance conditioncondition

RehabilitationRehabilitation – partial replacement of original – partial replacement of original ecosystemecosystem

EnhancementEnhancement – alternative ecosystem – alternative ecosystem

Note: to understand above scenarios of recovery Note: to understand above scenarios of recovery have to consider two biological factors of have to consider two biological factors of colonizationcolonization and and successionsuccession

Colonization and SuccessionColonization and Succession

- Both are ecosystem changes with time- Both are ecosystem changes with time

1.1. ColonizationColonization – arrival of new species in an – arrival of new species in an empty patchempty patch

Colonization of “bare” areas based on MacArthur Colonization of “bare” areas based on MacArthur and Wilson theory of island biogeography and Wilson theory of island biogeography CONSIDER CONSIDER DENUDED PATCHESDENUDED PATCHES AS AS ISLANDSISLANDS

Ex. Clear-cuts, strip mine are islands in a “sea” of Ex. Clear-cuts, strip mine are islands in a “sea” of mixed deciduous forestmixed deciduous forest

Time (t)

Spe

cies

(s)

Seq

G = ____ = colonization rate∆S

∆t

S = Seq (1-e -Gt)

1. Number of species depends on colonization rate (G)

2. G starts out high, gets smaller and smaller

3. Colonization rate based on two relationships

inhospitable terrain

“islands”

(clear-cut, toxic waste site, strip mine)

Spe

cies

sou

rce

(mai

nlan

d, d

ecid

uous

fore

st)

▲ Longer distance from source (mainland) = lower # of species

inhospitable

terrain

Larger patches = higher probability of being “hit” by propagules

▲ Increased size/area = increased # of species on islands

Seq

Factors Affecting Colonization RatesFactors Affecting Colonization Rates

Proximity to source

Kind of organism (vagility)

Reproductive rate (r- vs K-selection)

Air, water currents (rafting)

Residual disturbance, toxics

Competition

Habitat diversity and quality

Generalist/Specialist

Immigration Extinction

Note: once reach equilibrium dynamics become interactive = succession

Time (t)

Spe

cies

(s)

Seq

Non-interactive Interactive = succession

SuccessionSuccession

• Orderly change in community composition over time

• Usually follows colonization especially studied in plant communities

• Two models– relay floristics– initial floristics

Relay floristics

Crop Weeds | Grassland | Shrubland | ForestA

band

onm

ent

Years

Spe

cies

Initial floristics

Crop Weeds | Grassland | Shrubland | ForestA

band

onm

ent

Years

Spe

cies

Implications for Reserve Design

better worse

A

B

C

D

E

F

Significance to restoration of altered ecosystems

• Relay floristics – ongoing process based on external input

• Initial floristics – happens all at once based on internal input

▲Might have to manage system to help recovery- stock fish- soil stabilization with annual plants- etc.

Tionesta Natural Area,

Allegheny National

Forest, PA

Photo by R. Grippo