Geomorphology and Ecology:

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Geomorphology and Ecology

• Jim Heffernan
• November 15th, 2006

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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

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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).

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Population Ecology

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

www.air-and-space.com
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Community Ecology

• What determines the composition of the biotic
  community?
• Biogeography and species diversity
• Species interactions
• Competition, mutualism, etc.

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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

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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

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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?

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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

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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

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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

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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

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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

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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

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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

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Effects of organisms on geomorphology

• Organisms influence the resistance of land
  surface
• Plant roots and biofilms
• Soil organic matter

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Effects of organisms on geomorphology

• Animals
• Modification of landform
• Direct agents of sediment movement
• Distribution of plants
• Grazing

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Effects of organisms on geomorphology
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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

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Shared solutions

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

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Hierarchy in ecology and geomorphology
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Hierarchy in ecology and geomorphology
Steady Time
Graded Time
Cyclic Time
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Hierarchy in ecology and geomorphology

• At plot scale (.1km2) fire is a disturbance
• At landscape scale, equilibrium includes patches
  of various ages

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Self-Organization

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

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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)
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Desert Stream Ecosystems

• Severe hydrologic disturbance
• Flash floods
• Drying
• Coarse, bare channel sediments
• Interactions between surface stream and sediments

Sycamore Creek, AZ
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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

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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
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Wetland formation

• What are consequences of wetland formation for
  biogeochemical processes?

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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

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Hyporheic Chemistry
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Effects of Vegetation on Disturbance Response
Surface
Bare Hyporheic
Vegetated Hyporheic
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Wetland formation

• What are consequences of wetland formation for
  biogeochemical processes?
• What limits the establishment of ciénegas in
  desert streams?

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Vegetation and hydrologic disturbance
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Equil. Biomass (V)
Equil. Biomass (V)
Discharge (Q)
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Cienéga
Vegetation
Gravelbed
Time
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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

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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 ()
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y -0.62 0.14 ln(x) r2 0.82 p lt 0.001
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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)
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Reinforcing mechanisms

• Primary mechanism is density dependence of
  stabilization
• Secondary feedback
• Fine sediments under vegetation
• Reduced drought stress
• Increased production

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• Fine Sediments and Drought

Increasing fine sediment abundance Increasing
residence time of vegetation
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