Environmental Engineering Reference
In-Depth Information
activities in most nature reserves has probably led to less
exchange with other areas (Seifert & Fisher 2010). The
signifi cance of humans for the dispersal of rare plants to
such reserves is, therefore, likely to be very low except
when a deliberate management scheme is set up to
assure ongoing seed exchange.
there is also usually a clear correlation with other
characteristics such as connectivity or degree of
modifi cation of the remaining habitat (Table 5.3).
The present section will describe general trends in
landscape alteration in the context of the above-
mentioned scheme. The advantage of using a more
sophisticated framework over a simple fragmented
versus unfragmented dichotomy is that it enables a
more clear prioritization of conservation and restora-
tion goals. For example, restoration is much less a pri-
ority in variegated landscapes, but maintenance of the
quality of the matrix is important there to stop devel-
opments towards fragmentation. Restoring
connec-
tivity
and improving the quality of the remaining
habitat, on the other hand, should be the highest pri-
orities in the case of relictual landscapes.
5.4
LANDSCAPE ALTERATION
The concept of landscape
fragmentation
has greatly
helped to clarify targets for conservation and restora-
tion activities (see section 5.4.3), but it implies a very
simplistic and not very realistic dichotomy: a landscape
is either fragmented or not. McIntyre and Hobbs
(1999) developed the idea somewhat by treating alter-
ations of a landscape matrix as a continuum, ranging
between ' not affected ' and ' completely changed ' . They
distinguished four main classes of landscape altera-
tion, based on the percentage of suitable habitat
remaining:
intact
,
variegated
,
fragmented
and
relictual
landscapes
(Figure 5.5). These categories differ in the
amount of remaining habitat for whatever specifi c
species may be of particular concern or interest, but
5.4.1
Intact landscapes
The actual geomorphologic structures of temperate
zones of the northern hemisphere are mainly a result
of erosion and sedimentation processes during the
last glacial period. Glaciers and polar deserts were the
Intact
Variegated
Fragmented
Relictual
(a)
Habitat
Destroyed habitat
Intact
Variegated
Fragmented
Relictual
(b)
Unmodified habitat
Modified
Highly modified
Destroyed habitat
Figure 5.5
Four states of landscape alteration defi ned by degree of habitat destruction, as in Table 5.3, and modifi cation of
remaining habitat. (a) Four levels of habitat destruction, each characterized by a range of proportions of habitat destroyed. (b)
Pattern of habitat modifi cation overlying landscape patterns of habitat destruction depicted in (a). Although any combination
of destruction and modifi cation levels is theoretically possible, those considered to be typical of different destruction levels are
illustrated. (Modifi ed from McIntyre and Hobbs 1999.)
