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Title: Geomorphology and Ecology:


1
Geomorphology and Ecology
  • Jim Heffernan
  • November 15th, 2006

2
What is Ecology?
  • Ecology is the study of the interactions between
    organisms and their environment
  • Physical and chemical features
  • Temperature, nutrients, etc.
  • Biotic features
  • Predators, competitors, prey, etc.
  • Different levels of organization
  • Individuals
  • Populations
  • Communities
  • Ecosystems

3
Organismal Ecology
  • How do organisms survive, grow, and reproduce?
  • Behavior
  • Foraging, reproduction, etc.
  • Physiology
  • Maintenance of homeostasis (temp, water, ions)
  • Acquisition of resources (food, light, etc).

4
Population Ecology
  • What determines species abundance?
  • External controls
  • Resources
  • Conditions
  • Internal dynamics
  • Demographics
  • Boom-bust cycles

www.air-and-space.com
5
Community Ecology
  • What determines the composition of the biotic
    community?
  • Biogeography and species diversity
  • Species interactions
  • Competition, mutualism, etc.

6
Ecosystem Ecology
  • Patterns of energy and material flow through
    ecological systems
  • Nutrient cycling and biogeochemistry
  • Food webs and energy transfer
  • System of interest includes biotic and abiotic
    components
  • Ecosystem is a scale-free concept
  • Anything that can be bounded
  • Lakes, watersheds, tree boles

7
Landscape Ecology
  • Effects of spatial pattern on ecological
    processes
  • Often evaluates broad scales
  • Regional to continental
  • Emphasizes role of humans
  • Not scale defined
  • beetle-scale
  • Relevant to all sub-disciplines of ecology
  • Behavior to biogeochemistry

8
An Interdisciplinary Boom
  • Recent Special Issues in Geomorphology
  • Geomorphology and Ecosystems (2005 Binghamton
    Conference, In Press)
  • Linking Geomorphology and Ecology (2006)
  • Interactions between Wood and Channel Forms and
    Processes (2003)
  • Biogeomorphology (2002)
  • Formation of new Biogeosciences section of ESA
    (2004)
  • New journals Biogeosciences, JGR Biogeosciences
  • Why Ecology and Geomorphology? And why now?

9
Why Ecology and Geomorphology?
  • Geomorphology
  • The study of landforms
  • Distribution in space
  • Changes over time
  • Processes that act on/generate landforms
  • Feedbacks between landform and these processes
  • Ecology
  • The study of interactions between organisms and
    their environment
  • Distribution in space
  • Changes over time
  • Processes that generate these patterns
  • Feedbacks between organisms and the environment

10
Why Ecology and Geomorphology?
  • Levels of integration
  • Disciplinary
  • Influence of landforms on distribution of
    organisms
  • Influence of organisms on the development of
    landforms
  • Epistemological
  • Borrowing approaches
  • Integrative
  • Potential for reciprocal interactions and
    positive feedback

11
Common origins of Ecology and Geomorphology
  • Early figures in natural history and geography
  • Von Humboldt
  • Lyell and Darwin
  • Separation during the formation of modern
    disciplines
  • Early-mid 20th century
  • Maturation from descriptive to process based
    science
  • 1950s and 60s

12
Geomorphic controls on organisms
  • Distribution of soil nutrients, moisture,
    temperature
  • Elevation
  • Aspect
  • Particle sizes and sorting in soils and sediments
  • Movement and dispersal
  • Channels as corridors
  • Sightlines
  • Erosion and mass wasting as disturbance
  • Hillside and channel slope
  • Different organisms respond to landform at
    different scales

13
Coupling of geomorphic and ecological processes
  • From the vary small to the very large
  • Molecular to global
  • Bidirectional
  • Effects of geomorphology on organisms
  • Effects of organisms on geomorphology

14
Effects of organisms on geomorphic processes
  • Weathering
  • Provides nutrients to plants, microbes
  • Organisms secrete weathering compounds (acids,
    enzymes)
  • Roots break up particles
  • Oxidation of the atmosphere
  • Organisms influence the development of
    overburden

15
Effects of organisms on geomorphology
  • Organisms influence the distribution of erosive
    forces
  • Rain splash and canopies
  • Infiltration and runoff
  • Channel roughness
  • Stream discharge and ET

16
Effects of organisms on geomorphology
  • Organisms influence the resistance of land
    surface
  • Plant roots and biofilms
  • Soil organic matter

17
Effects of organisms on geomorphology
  • Animals
  • Modification of landform
  • Direct agents of sediment movement
  • Distribution of plants
  • Grazing

18
Effects of organisms on geomorphology
19
Problems with space and time
  • Scale
  • What is the appropriate scale of observation?
  • Equilibrium
  • Does it exist?
  • Contingency and context
  • i.e. history matters, and so does the
    neighborhood
  • Non-linearity
  • Self-organization and catastrophic change

20
Shared solutions
  • A combination of approaches
  • Theory and Modeling
  • Observations
  • Time-series
  • Comparative
  • Experiments
  • Microscale
  • Macroscale
  • Hierarchical framework integrates these
    approaches

21
Hierarchy in ecology and geomorphology
22
Hierarchy in ecology and geomorphology
Steady Time
Graded Time
Cyclic Time
23
Hierarchy in ecology and geomorphology
  • At plot scale (.1km2) fire is a disturbance
  • At landscape scale, equilibrium includes patches
    of various ages

24
Self-Organization
  • Geomorphic stability
  • interactions of force and form
  • Equilibrium is internally determined
  • i.e. self-organized
  • Negative feedbacks
  • Positive feedbacks?

25
Alternative Stable Statesaka Catastrophe Theory
  • Multiple equilibria generated by self-reinforcing
    feedbacks
  • Catostrophic changes
  • change in conditions
  • in response to disturbance
  • Hysteresis
  • Examples
  • Lakes
  • Clear-Turbid
  • Coastal Ocean
  • Coral Reef-Algae Beds
  • Terrestrial
  • Woodland-Grassland
  • Grassland-Shrubland
  • Desert Streams?

Ecosystem State
Conditions
From Scheffer et al (2001)
26
Desert Stream Ecosystems
  • Severe hydrologic disturbance
  • Flash floods
  • Drying
  • Coarse, bare channel sediments
  • Interactions between surface stream and sediments

Sycamore Creek, AZ
27
Ciénegas in SW Streams
Upper Santa Cruz River, AZ
ca. 1870
Monkey Spring, AZ
From Hendrickson and Minckley 1984
  • Historically, many SW rivers and streams
    supported densely vegetated wetlands (ciénegas).
  • Sediment and pollen records indicate persistence
    throughout the Holocene (Martin 1963)
  • Region-wide erosion and incision at the end of
    the 19th century
  • Catastrophic loss of vegetation
  • Interactions among grazing, drought, floods (Graf
    1988)
  • Relict ciénegas in locations where grazing minimal

28
Wetland development in Sycamore Creek
  • In 2000, USFS eliminated grazing from Sycamore
    Creek watershed
  • Response to drought
  • Dramatic increase in herbaceous vegetation
  • Wetland patches currently occupy 20 of Sycamore
    Creek

October 2001
April 2002
April 2003
April 2004
April 2006
29
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30
Wetland formation
  • What are consequences of wetland formation for
    biogeochemical processes?

31
Effects of Vegetation on Sediment Structure
  • Sampled adjacent vegetated and bare patches
    within the active channel
  • Prior to and following monsoon season of 2005
  • Fine sediments and organic matter preferentially
    accumulate in vegetated patches
  • Reduced hydrologic exchange

32
Hyporheic Chemistry
33
Effects of Vegetation on Disturbance Response
Surface
Bare Hyporheic
Vegetated Hyporheic
34
Wetland formation
  • What are consequences of wetland formation for
    biogeochemical processes?
  • What limits the establishment of ciénegas in
    desert streams?

35
Vegetation and hydrologic disturbance
36
Equil. Biomass (V)
Equil. Biomass (V)
Discharge (Q)
37
Cienéga
Vegetation
Gravelbed
Time
38
Methods
  • Established 25 sites (20 m in length) at Sycamore
    Creek
  • Vary in stream permanence
  • Surveyed 3wk intervals (October 2004-present)
  • Measure plant taxa, height at 12 points on each
    of 3 transects
  • Use height-biomass relationships to estimate
    standing biomass at each point
  • Quantified per-capita vegetation losses as

39
Peak Biomass (g AFDM/m2)
Surface water duration (yr)
y -0.62 0.14 ln(x) r2 0.78 p lt 0.005
Peak Biomass (g AFDM/m2)
Flood Survival ()
40
y -0.62 0.14 ln(x) r2 0.82 p lt 0.001
41
July 29, 2006 5.1 m3/s
r2 0.27 p lt 0.01
r2 0.44 p lt 0.005
January 2, 2005 310 m3/s
0
100
300
200
Per Capita Flood Losses ()
August 12, 2006 102 m3/s
r2 0.67 p lt 0.005
June 29, 2006 2.8 m3/s
r2 0.63 p lt 0.0001

Aboveground Biomass (g AFDM/m2)
42
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43
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44
Reinforcing mechanisms
  • Primary mechanism is density dependence of
    stabilization
  • Secondary feedback
  • Fine sediments under vegetation
  • Reduced drought stress
  • Increased production

45
  • Fine Sediments and Drought

Increasing fine sediment abundance Increasing
residence time of vegetation
46
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