Using landscape classification within
complex, heterogeneous systems
Carola Cullum and Kevin Rogers
Centre for Water in the Environment
University of the Witwatersrand
Traditional Landscape Classification
• Assumes that landscape units and classes
are homogenous
– Average value applies over whole area
– Units are replaceable within classes
– A reference site represents a whole class
– Can extrapolate knowledge between units
– Can upscale/ downscale in a nested hierarchy
– Samples can represent the whole system
BUT ... landscapes are heterogeneous,
complex and dynamic
• Every location is unique
– History, neighbours, context
– Heterogeneity matters!
• Not noise or complication
• May be as /more important than general trends in
determining outcomes
• Complexity
• Locations change through time
Heterogeneity, complexity and
dynamics mean that…
• Average values do NOT apply equally over a
whole unit / class
• Reference sites and samples do NOT represent
the whole class equally well
• It is difficult to
– Extrapolate between units
– Upscale/ downscale
• Units change –definition issues
AND... Many different classifications/maps
are possible
• Many ways of carving up the world
– Soil? Veg? Geology? Combination?
• We need to decide
– Why are these particular units useful?
– What factors define the units?
– At what spatial and temporal scales?
– Why are the similarities that define classes of units
important?
Does heterogeneity, complexity, dynamics, lack
of a priori classification structure….
Mean we have to
• Measure everything at every location?
• Have multiple models and maps for every
purpose?
• Have different management plans for
every piece of land?
We need some practical solutions!
Our framework for landscape classification
can help ...
• For water-controlled ecosystems
– Many ecological patterns coupled to
water distribution in time and space
• Captures repeating landscape
patterns
– Catenas, drainage networks …
• Wide range of applications
– Integrates diverse disciplines,
terrestrial and aquatic,
science and management
Landscape hierarchy informs
definition of landscape units
• Based around catchments
• Guides choice of
– Scales
– Attributes to define units
and classes of units
• Factors associated with water
distribution
• Vegetation, Soils, Topography....
PHYSIOGRAPHIC ZONE
CATCHMENT
CATENAL ELEMENT
Heterogeneity demands fuzzy classes
• Landscapes do not fit neatly into predefined
categories
– Transitions, overlaps
– Not all units fit neatly into a class
• Archetypes not rules
– Archetype is an idealised style
– Degree of similarity to an archetype determines
degree of membership of a class
– All classifications not equally right or wrong
– Can assess heterogeneity within/ between classes
by mapping membership values
• Different archetypes in different settings
Landscape elements in N’waswitshaka:
Southern Granites
Physiographic zone
Geology and
landscape dissection
Catchments
Hillslopes
and
Channels
Catenal elements in CASSs of different
stream orders
1st order CASS
2nd order CASS
Catenal elements
Koppies
Woodier midslopes
Grassier toeslopes
Woodier crests
Grassier midslopes
Possible sodic sites
Grassier crests
Woodier toeslopes
Channels and banks
3rd order CASS
4th order CASS
5th order CASS
Heterogeneity in assemblages of catenal elements in 1st
order catchments in N’waswitshaka
Stream
Poss sodic site
Grassy
midslope,
woody crest
Woodier crest
Grassier midslope
Koppie
Grassier crest
Woodier midslope
Grassier toeslope
Woodier toeslope
Channel and bank
Woody
midslope,
woody crest
Where does heterogeneity matter?
• Low order catchment in N’waswitshaka
• Conceptual model for archetype
→ Hypothesised directions of water flow
Woody,
Sandy
Crest
Seepline
Grassy,
Clayey
Midslope
Clayey
banks,
gravel bed
channels
Where does heterogeneity matter?
• What matters to direction and intensity of water
flows?
– Vegetation, slope, area ++++
– Arrangement of catenal elements – boundaries
permeable?
– Geology: Dykes, koppies ...
– Humans: Roads, dams, gravel pits...
– Different arrangement of catenal elements: eg grassy crest,
woody midslope
• Outlier or new class?
How the heterogeneity approach is
different
Traditional classification
Classification under heterogeneity
paradigm
Hard boundaries
Fuzzy boundaries
Yes/No class membership
Degrees of class membership
Class is represented by….
A reference unit / sample
Archetype and range of variation
Focus on means/ similarity
Focus on variance/ dissimilarity
Inflexible classes – one size fits all
Flexible – adapt to incorporate new
learning
Thank you!