E.4 Ecosystems Changes
-although see change in diversity & spp composition
(ie Glacier Bay)
-ecosystem processes change during succession
Degradive Succession: OM degraded by detritivores &
micro-organisms (ecosystem respiration)
-usually 2o succession- follows disturb.
Autotrophic Succession: new community develops
empty habitat, starts with no OM (production)
-both 1o & 2o succession
Succession after clearing to Deciduous Forest
Ricklefs (2001) Figure 22.3
E.4.1 Six Ecosystems Changes
(Odum 1969)
1) Incr. diversity, (see last section)
2) Incr. complexity structure
- soils
- habitat structure (herbs to hemlock forest)
3) Incr. complexity function (food web and Energy flow)
-more E goes into maintenance of existing
biomass over time
i.e. maintain Hemlock forest
-less E goes into production new biomass
(i.e. herbs & moss)
E.4.1 Six Ecosystems Changes- cont’d
4) Increase biomass,
-more soil organics,
- more standing biomass (not necessarily prod’n)
5) Incr. conservation of nutrients (early to mid stages)
-early, soil leach nutrients,
-later more closed
-more N tied up biomass,
- more nutrients in living portion
Plant biomass
g/m2
Hubbard Brook deforestation exp’t, succession
reduces nutrient losses caused by disturbance
Annual Export kg/ha
Ca
K
NO3
years
6) Succession culminates to stable ecosystem (sometimes)
- maximum biomass per unit gross production
- net production tends to level off
Biomass
accumulates
in
4 phases
E. 4.2: e.g. Forest SuccessionInterplay b/w gross prod. & respiration
Systems Gross Prod (GPP)
Production
Flux CO2
NPP
Systems Resp. (R)
0
years after Dist’d
200
Succession when
Ecosystem GPP = R
GPP>R
Net Prod’n
(NPP)
GPP=R
NPP=0
0
years after Dist’d
Moves towards
GPP = R
200
P/R ratio < 1 or > 1 = succession
P/R=1 climax (stable) condition
Autotrophic Succession
GPP>R
Corel
Reef
100
eg. Fire on
Prairies
Forests
Prod 10
gC/m2/d
grasslands
Lakes
1.0
Degrative Succession
GPP < R
Heterotrophic
Oceans
0.1
eg. Drained swamp
-decomp peat
Sewage farm
Deserts
0.1
1
1:
ax R )
im P=
l
C P
(G
10
1.0
Resp. gC/m2/d
100
E.5 Ecosystems Stability
6) Stability
due to:
Lack Disturbance
-constant physical cond’n (or predictable)
Resistance (Inertia)
- ability ecosystem to maintain structure
and function
Resilience
- ability to bounce back after disturbance
Upper Reaches Sycamore Creek, Arizona
Valett et al. 1994
Sycamore Creek, Arizona – following flash flood
Valett et al. 1994
E.5.1 Example: Disturbance & Desert Stream Stability
Sycamore Creek, Arizona (Valett et al. 1994)
-interaction hydrologic linkages & ecosystem resilience
Ho: Ecosystem resilience higher when hydrologic linkages b/w
surface & subsurface increase supply N
(N limits prod. in Sycamore Creek)
- look at groundwater movement w/n piezometer
(fancy well, open at bottom only)
- determines vertical direction of groundwater flow
Up-welling: when pressure at pipe bottom > water surface,
water level in piezometer above stream surface
Down-welling: when pressure pipe bottom < surface water,
water level in piezometer below stream surface
Sycamore Creek, Arizona (Valett et al. 1994)
Relationship NO3 & vertical hydraulic gradient
Creek
Vertical Hydraulic
Gradient
NO3
ug/L
Up-wellings
Highest [NO3]
Down-wellings
lowest [NO3]
E.5.1 Example: Disturbance & Desert Stream Stability
so what?
- after flash floods devastate biotic
community
Valett et al . (1994) found
-higher [NO3] in upwelling zone
Æ highest algal growth
upwelling zones important in algal
recovery (resilience) to disturbance
-flash floods do not affect spatial
arrangement upwelling areas
– thus v. stable & upwelling zones
are resistant to disturbance
to understand organization & dynamics of many streams,
must consider structure of surrounding landscape
X-section
2
Recharge area
Sycamore Creek – hydrologic linkage
stability in geomorphology
& groundwater
ve
i
R
r
1
Up-welling
Ground water
Bedrock
1-10 km away
Which disturbance has long term effect?
1- drive tractor down stream, or 2- build sub-division 1 km away?
Disturbance
1- Tractor in Desert stream
-disturbs stream bed, but not groundwater
- same as flash flood, system recovers quickly
2- Sub-division 1 km away
-if on source area for groundwater (recharge)
- blocks or cuts off gr. Water
-stream is affected and may not recover
Landscape Ecology
-resilience & resistance can be influenced by
resource availability or may result from landscape
phenomena