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these spatial models do not provide sufficient
functionality to represent complex landscape-
ecological systems satisfactorily. Moreover the creativity
of the modeller is confined. In an ideal situation
landscape modellers in search of appropriate analytical
tools and spatial modellers lacking an ecological
background interact to produce a seamless coupling
between the two modelling steps.
Test site
mu] rorem
Survey e Y
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Processing J Landscape-ecoiogical model
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| Y
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Digital landscape model Spatial model
Instrumentation
Fig. 1. Process of conceptual and concrete landscape
modelling.
So far only conceptual models have been dealt with.
The next step is the construction of a concrete or digital
landscape model according to the specifications
originating from the conceptual spatial model (fig 1).
The specifications concern the implementation of the
spatial model with some data structure, and the
surveying and processing of the actual data, eg. digital
photogrammetry.
2 HYBRID SPATIAL MODELLING:
'FIELDS IN OBJECTS'
Crucial in the development of a monitoring system is
the specification of a spatial data model, which enables
a proper representation of all features of interest. In
spatial information processing two major approaches
exist for the conceptual representation of spatial
systems, the field and object respectively.
A (physical) field is a feature which is contiguously
distributed over space and time. In a field the strength
of the interacting forces is a function of the position
within the field and the resulting pattern can also be
expressed in terms of position dependent field values.
Examples of terrain features with a field characteristic
ate relief and groundwater table and the gravity field.
Also the electromagnetic radiation emitted or reflected
by the earth surface and detected by human vision and
remote sensing techniques is a field. For the
lepresentation of fields several data structures are
available retaining a contiguous character, e.g. TIN,
contour models and rasters.
215
As opposed to the field approach, the object-structured
approach applies to discrete terrain features. The object
approach assumes that the Earth's surface is populated
with spatially interacting discrete units. Each unit or
object has its own behaviour. The pattern resulting
from these processes can be expressed by the spatial
distribution and the state of the objects. Evident objects
are individual plants or animals, but also less tangible
spatial units like plant communities can be considered
as objects.
Many landscape-ecological concepts use
discrete spatial units to structure a landscape pattern.
Kotliar and Wiens (1990) term their elementary units
patch and define it as 'a nonlinear surface area differing
in appearance from its surroundings'. Zonneveld (1989)
introduces the term ‘land unit' for 'an ecological
homogeneous tract of land at the scale of issue’. All
methods guiding the landscape ecologist in
determining appropriate objects for the landscape
under study have in common that the object has to be
internally homogeneous in some respect and externally
heterogeneous. Consequently, in the object approach
spatial variation is modelled at the objects’ boundary.
Two opposite approaches for the spatial modelling of
natural landscapes have been introduced, the field and
object respectively. Because natural landscapes often
show both continuous and discrete variation in space
and time, they are not properly represented in only one
of the two alternatives. In order to be able to describe
continuous and discrete variation simultaneously, a
hybrid terrain description allowing the location of fields
in an object is suggested. For example the distribution
of solitary shrubs in a varying herbaceous vegetation
can be modelled this way.
There is, however, no practical application yet
of this hybrid approach known to the authors. This is
surprising, because many landscape-ecologists
recognise the existence of both discrete and gradual
transitions in one landscape type. Moreover there is a
strong analogy between the approach of fields in
objects and the landscape-ecological concept of
patches in a matrix (Forman and Godron, 1989). in this
concept non-patch areas are called matrix when the
following three criteria are met:
1. relative to the patchy area the non-patch area
is more extensive,
2. the non-patch area is highly interconnected,
and
3. controls many of the dynamics in the
landscape.
Consider again the example vegetation, where shrubs
form patches. Due to the criterium of more or less sharp
boundaries around patches obviously not the whole
landscape has to be patch covered. In the example the
rest-area or non-patch covers the herbaceous
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996
