Landscape Ecology

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What is landscape ecology?

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"The study of landscapes-its spatial patterns and how they develop" (Urban et al. 1987).

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Central concepts of landscape ecology

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1.Ecological processes
2.Spatial pattern / Landscape heterogeneity
3.Scale –spatial and temporal
4.Role of humans
5.In reference to an organisms or processes

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Community

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An association of interacting populations, usually defined by the nature of their interactions or the place in which they live (Ricklefs1990).

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Most community definitions include characteristics related to:

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1.Composition of multiple populations
2.Environmental and composition homogeneity
3.Interactions between species

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landscape

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Can be consider a spatially heterogeneousarea." The landscape is a function of 1) structure,
2) function and
3) change (Turner 1989).

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ecosystem

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The biotic component and its environment treated together as a functional system of complementary relationships, and transfer and circulation of energy and matter." (Whittaker 1975)

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Landscape ecologists focus on 5 key areas:

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1.Pattern of patches on the landscape
2.Interchange of energy, materials, nutrients, and organisms between patches
3.Disturbance (natural and human-caused) and other landscape changes
4.Effects of spatial and temporal scale
5.Design and management

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Why has Landscape Ecology emerged as a distinct area of study?

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Broad-scale environmental issues.
Realization of the importance of scale in ecology.
Technological advances-remote sensing, geographic information systems, increased computing power

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Configuration:

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Specific arrangement of spatial elements

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Connectivity:

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Spatial continuity of a habitat or cover type across a landscape

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Corridor:

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A relatively narrow strip of a particular type that differs from adjacent areas on both sides

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Edge:

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That portion of a cover type near its perimeter

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Fragmentation:

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Breaking up of a habitat into smaller disconnected parcels

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Heterogeneity:

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Quality or state of consisting of dissimilar elements

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Matrix:

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Background cover types within a landscape

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Scale:

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Spatial or temporal dimension of an object or process, characterized by both grain and extent

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Grain

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finest level of resolution

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Extent

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size of the area or time frame assessed

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What happens when you increase grain size

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smaller patches are no longer visible

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what happens when you increase extent

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you often find more patches and more patch types

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broad or course scale

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Broader scales give context; they encompass the process of interest//shows a large area

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Fine scale

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shows pattern in a small area, & there is less difference between map and ground observations

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Definitions of scale

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resolution, grain and extent

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what is hierarchy theory?

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Hierarchy theory helps us to understand the linkages among scales in both time and space

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Causes of landscape pattern

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Environmental conditions
Secondary succession as driven and affected by the biotic processes such as: mortality-natality (birth-death), dispersal, reproductive strategy, disease, herbivory, competition, etc
Disturbance and stress: human-caused and natural
•Data and map resolution
–Spatial and temporal grain and extent
–Thematic resolution: # of classes

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biotic components that cause landscape patterns

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species interactions--Mutualism (++), Commensalism (+0), Predation, Herbivory, Parasitism (+-), Amensalism(0-), competition (- -)

Soil formation

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major disturbances resulting in landscape patterns

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fire, herbivory, human activities, climatic variations

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what is a disturbance

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Disturbance: “A relatively discrete event along time that modifies landscapes, ecosystems, community, and population structure and changes the substrate, the physical environment and the availability of resources" (Pickett and White 1985 as quoted by Farina (1998, p.51)).

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stress

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Stresses are less discrete, and include drought, herbivory

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important components of disturbance and stress

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•Disturbance is part of natural ecosystems (Pickett 1980)
•Disturbances change resource availability, alters environmental conditions, and favors one species over another
•Disturbance does not depend on a presumption of stability (Levins and Lewontin 1985)
•A portion of the heterogeneity in the landscape at any one time is caused by disturbance (Bormann and Likens 1981)
•Management involves contending with and using disturbanceApproaches

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define disturbance

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Results in ecosystem functional change-consider any factor that results in “significant” change in function to be a disturbance

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what is considered to be a significant change caused by a disturbance

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change outside of the Historical Range of Variability (HRV)-an event occurring outside of the normal range for a system

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levels of hierarchy

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broad, focal, fine

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frequency

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how often

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intensity

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measure of strength of the disturbance

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residuals

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species that can survive disturbance

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return intervals

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how often does the disturbance occur

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Why do people want to model landscape change?

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1. Develop estimates of Historical Range of Variation(HRV)
2. Predict future changes in landscape composition,configuration, etc.
3. Strategic planning
4. Scenario assessment
Cumulative effects assessment (similar to scenarioassessment but often with more narrow scope.
6. Determine major causes of landscape change
7. Develop land management goals for monitoring
8. Determine where knowledge gaps exist

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Deterministic model-

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always end up at same point which is
predetermined by model assumptions. Time-step
successional models are deterministic with respect to
succession.

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Stochastic model-

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at least a portion of the model has a
random probability included within which allows model to
come to varying endpoints, must "run" model several times
to determine characteristics of outcome (mean, variance,
range etc.).

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Mechanistic model-

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a mechanistic models attempts to represent dynamics in a manner that is consistent with real world phenomena, the term implies that the parts are arranged to explain the whole system

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Process-based model

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implies that the model components are specifically developed to represent specific ecological processes3

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Empirical model-

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a model that is designed to explain an existingdata set, may not involve an explanation as to why things arehappening. Most models have empirical components includedwithin them which are used to parameterize the model

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Whole landscape models

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models of landscape
phenomena, in aggregate, for the landscape as a whole

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Distributional landscape models

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models the distribution of
landscape area for different elements (i.e. cover types)

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Spatial landscape models-

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spatially explicit, models the
location and configuration of landscapes

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Model components

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1.initial configuration
2.birth, death and change functions
(succession, disturbance)
3.output configuration

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Driving factors of landscape change

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1.time-step functions
2.bio-geo-chemical processes
3.stochastic events (probability functions)

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Steps in Building a Model

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1.Define the problem
2.Select the model type
3.Develop model
4.Computer implementation
5.Parameter estimation
6.Model evaluation (sensitivity analysis)
7.Experimentation, application, refinementExamples

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Examples of modeling approaches

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1. Conceptual models
2. Distribution models

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How does VDDT work?

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For each PVT the model tracks the proportion of all pixelsin each successional class (cover type and structuralstage) over time.
-Using the pathways and probabilities defined for that PVT,the model simulates the probability of each pixel beingaffected by one of the disturbance types, and if a disturbance does occur within a specified time period, themodel moves the pixel to the appropriate class.
-To initialize, each polygon is randomly assigned an agewithin the range of ages possible for that successionalclassVDDT

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What are some spatially explicit models

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TELSA(Tool for Exploratory Landscape Scenario Analysis): Spatial explicit model that uses a VDDT approach in predicting disturbance and succession.
SIMPPLLE(Simulating Patterns and Processes at landscape Scales) spatially explicit expert system model, includes spatial context.

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How do we choose a model?

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•What do we want the model to predict?
•What is the required resolution (temporal & spatial) andconfidence of the outputs?
•Does the model need to have a spatial component or is adistributional model adequate?
•What are the data input requirements?

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Synergistic effects

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The effects of an earlier disturbance on the response to another disturbance,it may be of the same or different type of disturbance

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Ecological and physical processes affected by landscape pattern

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•Movement and persistenceof organisms
•Movement of disturbance
•Cycling and/or movement of energy and nutrients
•Micro-climate
•Rates and patterns of succession
•Habitat suitability (organisms often need 2 or more types of habitatin close proximity)
•Edges act as filters/amplifiers for transfer of organisms, nutrients, energy, disturbance etc
•Human use

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Some effects of fragmentation?

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Changes in patch distribution, size and characteristics
–Fewer patches less total area of habitat
–Smaller patches
•Less interior habitat
•More edge habitat
–Increasing isolation of residual habitat patches

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What do landscape ecologists mean when they refer to “equilibrium”?

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Much of our ecological theory and practice depends on the existence (at least theoretically) of a single, stable equilibrium
•Steady-state mosaic
•Multiple or Non-equilibrium models
–Multiple stable states
–Catastrophe
–Chaos

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Equilibrium?

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Initially, ecologists viewed landscapes as a closed and self regulating system that possessed stable equilibrium. However, a shift from this viewpoint occurred that suggests if equilibrium is observed it may only appear at certain spatial and temporal scales.

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What is landscape composition?

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One of the most simple description of a landscape
•Absolute (area) or Relative Abundance (percentage) of different patch types.
•Patch type may be defined in terms of:
–land-use type (forest, agricultural, urban)
–cover type with varying levels of thematic resolution, e.g.
•Low resolution: coniferous forest, deciduous forest, shrubland
•Medium resolution-overstory species: ponderosa pine, Douglas-fir, lodgepolepine
•High resolution-cover type/structural stage: sapling, pole, mature, old growth (over-mature)

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Shifting steady-state mosaic

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A shifting steady state mosaic model has two
important components that determine the
characteristics of the equilibrium state:
• the temporal component
• the spatial component
Vegetation present at individual points on the landscape changes, but the proportion of the landscape in each seral stage is relatively constant, that is, is in equilibrium when considered over a large area or long time period

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What occurs when a community’s composition is stable

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the distribution of species within it
continually change through time due to mortality and recruitment of individual
plants but the composition remains fairly constant.

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Turner et al. (1993)
theorized that
equilibrium depended
on two parameters

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Temporal parameter
(T): ratio of
disturbance interval
to the recovery time
– Spatial parameter
(S): ratio of size of
the disturbance to
the size of the
landscape

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Why characterize landscape composition
and spatial pattern?

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To compare one landscape with another
To capture the "essence" of the landscape in a
few simple words or quantitative measures
In monitoring

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What can we measure in a landscape to characterize the composition and pattern of vegetation?

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area of each cover type, pattern??

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Approaches to Defining Disturbance

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Biomass mortality-the loss of living biomass used as baseline
•Resource availability-a sudden increase in the available resources
-Human value assessment-use the value of the resources to humans as baseline

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What is meant by the term “disturbance regime"

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refers to the temporal and spatial dynamics of disturbances over a longer period of time. It includes the following characteristics
Frequency
Intensity
Residuals
Return interval
Rotation period
Severity
Size

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Continuity of a disturbance

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The uniformity of severity of the disturbance across the entire affected area

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Rotation period

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Mean time needed to disturb an area equivalent to the studyarea

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What is meant by the term “Biological diversity” or “Biodiversity”?

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5Biological diversity is the variety of life and its processes; and includes the variety of living organisms, the genetic differences among them, and the communities and ecosystems in which they occur (Keystone Report 1991).

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Many Species Diversity Indiceshave been developed to account for the variation in both the number of species and the distribution among species. In most cases they have two components:

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1) richness
2)equitability (abundance)

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Spatial scale of measurement varies:
point diversity
alpha diversity
beta diversity
gamma diversity

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point diversity -sample point
alpha diversity-(within community)
beta diversity-(turnover of species along a
gradient between alpha and gamma)
gamma diversity-(between community, across the
landscape

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Landscape diversityresults from two superimposed influences:

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1) the vegetation pattern of distribution of communities along gradients of
environmental conditions, limiting
factors and resources, and
2) the patterns of disturbance and
recovery within the communities
along the gradients

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What does the evenness indices account for?

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subtracts out the influence of richness in the equation.

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Which indices sensitive to rare species?

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Shannon Wiener indices

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What are diversity indices useful for?

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measure temporal changes of a landscape
Care when using landscape diversity indices to compare between landscapes due to inherent differences
All info related to patch type, and individual patches is lost during calculations.

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Diversity measures used

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relative richness, evenness, patchiness, diversity

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metrics that describe in more detail the compositionof the landscape.

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1.Patch area(patch number, patch density,
total patch type area, core area)
2.Patch perimeter(edge density, total patch
length, edge contrast)
3.Patch shape(perimeter to area ratio,
elongation index, shape indices, fractal
dimension)
4.Intra-patch type distances(nearest
neighbor, proximity)

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Mean Proximity Index

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considers both the patch sizeand
distance from a focal patch to other patches of the same
type that have an edge within a given search radius.
Mean Proximity Index = (sum) of patch area / squared distance to
the nearest patch of the same type within a given search
radius.

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Mean nearest neighbor

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neighbor is the corresponding average
between each patch and its nearest neighbor of the same
type.

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Nearest neighbor and proximity indices were developed
to

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characterize the distribution of a single patch type on
the landscape.
2. These indices have ecological applications related to
fragmentation, dispersal of propagules and migration of
species.

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Fractals are used in landscape ecology as an

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index of shape. We are primarily interested in the relationship of lines that enclose areas. Dash line is more than a line but not yet a square.

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Commonly used metrics related to edge include:

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Perimeter-area ratio(Farina 1998)= patch perimeter /
patch area
This metric varies with both changing patch shape and
increasing patch size.
2. Elongation index(L:W ratio) (Forman 1995)
= 1: (Length/width)
range > 1, value increases as patch becomes more
elongated
3. Shape index(M&M 1995)
vector = p / 2 (x area of patch)
raster = 0.25 p / (area of patch)
ij
ij
0.5
0.5

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Edge contrast

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contrastis sometimes used to quantify the functional aspects of edge. The general approach is to assign a rank to a patch type edge (Ordinal ranking). The difference at the boundary between adjacent patches can then be roughly quantified.

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The ecological function of shape can be estimated by 4
easily measured attributes of the patch shape

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elongation (width:length ratio),
convolution, interior, and perimeter.

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Patch density

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Number of patches / 100 ha)-useful
when comparing landscapes of different size

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how do you calculate patch perimeter

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Calculated by
counting edge pixels in raster systems and geometry in
vector systems

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Shape index

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related to actual area of patch and converts to what the perimeter should be if it were a square or circle. as shape moves beyond square or circle the number gets larger

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what does the metric relative richness calculate

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number of cover types present as a percent of the total number of possible cover types.

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what does the metrics diversity or relative evenness provide

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refers to how evenly the proportions of cover types are distributed.

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what does 1) richness
2)equitability (abundance measure

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Species Diversity Indices have been developed to account for the variation in both the number of species and the distribution among species.

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two ways to measure diversity

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Mean of relative richness, evenness and patchiness and Shannon-Wiener diversity index