Lecture6

Lecture6 - CWR5140C Ecohydrology Fall 2008 Discussion of...

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CWR5140C – Ecohydrology Fall 2008
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Discussion of Ridolfi et al. (2006) paper Focus is on the interaction between vegetation and the water table (humid to wetlands) Transpiration results in water uptake from the soil, and it is a dynamic process driven by the coupled interaction between water and vegetation.
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Examining the Ridolfi et al (2006) model ( ) V V V dt dV CC = α The “logistics” equation V = biomass V CC is the “carrying capacity” d is the water table depth
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Water table depth and carrying capacity V d V d β + = 0 ) ( > < = lim lim ) ( 0 ) ( d d if d f d d if d V CC
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Water table depth and carrying capacity
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Water table depth and carrying capacity Mesophytes: adapted to moderate levels of soil moisture without requiring uptake from the water table, curve (a). Phreatophytes: require to uptake water from the water table; become stressed when water table is either too low (d lim ) or too high (h lim ), curve (b). Intermediate: not flood tolerant, but may grow with increasing water depth, curve (c).
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Possible cases encountered Case A: d 0 > d lim , so that the water table depth is always conducive to vegetation growth and survival. Case B: d o < d lim , but plants are able to lower (through transpiration) the value of the water table depth d below the threshold limit d lim after a given time transpiring. Case C: d o < d lim , but plants are never able to lower (through transpiration) the value of the water table depth d below the threshold limit d lim after a given time transpiring.
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Equilibrium States 1 equilibrium state 1 equilibrium state 2 equilibrium states
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Discussion Dynamics will depend on the values of d 0 , d lim and the form of the V CC =f(d) curve. “Resilience” can be defined as the disturbance that can be introduced in the ecosystem that allows it to return to its equilibrium stable state (allowing restoration to be feasible). These results suggest the vulnerability of ecosystems, and particularly the conditions that would yield to unvegetated conditions.
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Questions What happens after the unvegetated equilibrium state is reached? Is there a transition process to another vegetation species that finds these conditions more favorable? SUCCESSION What happens when we consider the water balance dynamics? INVASIBILITY What era the implications of these disturbance- response dynamics in ecosystem management?
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Expanding the Ridolfi et al (2006) model n n n x x x d x x x d β + + + + = ... ) ,..., , ( 2 2 1 1 0 2 1 > < = * ) * ( 1 * * 0 ) ( i d d if i d d a e i K i d d if d i K = i j j B ij i B d i K i r dt i dB α ) (
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Two vegetation species model 2 2 1 1 0 1 21 2 2 2 2 2 12 1 1 1 1 ) ( ) ( V V d d V V V V dt dV V V V V dt dV cc cc β α + + = = = 5 10 15 20 25 0.2 0.4 0.6 0.8 1 V d Flood tolerant V1 Flood intolerant V2
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Typical Simulation Results
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0.2 0.4 0.6 0.8 1 V1 1 V2 Phase portrait for 2 species dynamics Flood intolerant Flood tolerant
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The simulation results suggests that…
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Lecture6 - CWR5140C Ecohydrology Fall 2008 Discussion of...

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