Landscape: spatial interactions - Restoration Ecology - page 32

3.2.2 Scale 3.2.4 Connectivity and corridors

Connectivity has become one of the central concepts
in landscape ecology. It was realized that patches are
not isolated entities but rather are connected to other
patches, thus enabling an exchange of matter and
organisms. The relation between such flows and the
landscape pattern is often very complex. While the
present-day structure determines actual flows, this
structure itself depends to a large degree on past
flows. The size of the flows depends on the connect-
ivity between patches, which in turn depends on the
amount of suitable habitat. Model simulations
(Gardner et al. 1989) show that in purely 'random'
landscapes c .60% of the space must be covered by
suitable habitat in order to ensure that organisms
can travel from one side of the area to the other with-
out having to leave the habitat; that is, be part of a
functioning metapopulation. In real landscapes this per-
centage can be much lower, due to the presence of
corridors , relatively narrow strips of suitable habitat
that connect patches. The above-mentioned simula-
tions showed also that presence or absence of corri-
dors makes a dramatic difference for the percolation
of organisms within a landscape. One could say that
corridors function as communication channels within
the landscape. However elegant this concept may be,
the recognition of corridors in reality is not easy and
may differ from one organism to another. Hedgerows
may be corridors for beetles, but are unlikely to be
so for ospreys. In the latter case the river that flows
through a hedgerow landscape may be the real
corridor.

There is a clear correlation between the scale at
which a process operates and its dynamics (see
Chapter 2 in this volume). Small-scale processes tend
to be more dynamic and more erratic than large-scale
processes. Traditionally landscapes are seen as the
highest practical scale that is influenced by human
activities and which humans readily perceive. In this
view they constitute the third level in the conventional
ecological hierarchy after the biosphere and biomes
and before ecosystems. Recently there is a tendency
to expand the term landscape and use it for any
spatial arrangement, depending on the view of the
organisms considered. Experimental studies (Wiens
1976) showed that fine-scale spatial structures were
highly relevant for beetle movement and suggested that
a landscape from their perspective looked entirely dif-
ferent than that from the perspective of a human being
(see also Haskell et al. 2002). In this view a landscape
is a more abstract concept and can be seen as a con-
text in which (meta)populations operate (Wiens 1976,
Allen & Hoekstra 1992). Intuitively this may seem very
obvious but in the context of restoration it implies
that scales at which the target organisms operate
and at which disturbing processes occur should be
identified explicitly. For the restoration of marsh
birds for example, it might be sufficient to flood 5 ha
of degraded wetland whereas it might be necessary to
restructure a whole catchment when the aim is to
restore specific groundwater-fed plant communities in
the same site.

3.2.3 Patches and patterns

3.3 Flows between landscape elements

All landscapes are heterogeneous. Parts of the land-
scape that are considered to be uniform are called
patches . Again, the scale of a patch depends entirely
on the point of view of the organism under study.
A part of a landscape that is a patch for an elephant
can be a highly diverse region from the point of view
of a butterfly. A group of patches is called a pattern .
Topography (e.g. elevation, slope), natural disturb-
ances (e.g. fire, flooding, storms) and increasingly also
human activities (e.g. farming, building) are the prin-
cipal causes of pattern.

3.3.1 Transport of matter

Transport of matter by wind

Large quantities of material are transported by air-
flows, especially along the edges of continents where
winds are generally stronger than in more interior areas.
Under natural conditions this is a major mechanism
for the exchange of chloride between sea and inland
areas. Rainwater analyses from different sites showed
a decrease in Cl − content from over 100 to less than