Environmental Engineering Reference
In-Depth Information
even results in a complete reversal of water fl ow direc-
tion. Such activities have a large impact on wetlands
downstream. The straightening of the Upper Rhine
along the French-German border has led to the loss of
87% of the characteristic fl oodplain woodland, on both
the German and French sides.
Changes in groundwater fl ows are less obvious but
can potentially also have major effects on landscapes.
The most obvious effects occur when the water regime is
changed. Lowered water tables during the dry season
lead to increased mineralization of organic matter and
hence increased nutrient availability. In low-productive
wetlands, this results in a substantial increase of non-
characteristic ruderal plants at the cost of typical species
that are less competitive (Grootjans
et al
. 1985 ). Changes
in water chemistry are more insidious but can have
similarly large impacts. A groundwater abstraction
facility does not necessarily lead to lowered water levels
in a nearby groundwater-fed mire because surface water
or rainwater may replace the groundwater. In the long
run, however, the increased infl uence of nutrient-rich
surface water (
eutrophication
) results in increased
plant productivity, whereas a replacement with acidic
rainwater leads to
acidifi cation
of the top soil (van
Diggelen
et al
. 1994). Both processes result in completely
altered vegetation composition but it may take up to
several decades before the effects are clearly visible or
discernable. The relative importance of these processes
depends to a high degree on the local situation.
both in space and in time. In what follows, we explore
these issues briefl y.
5.5.1 Landscape-scale restoration
as a process
Any restoration project should start with a defi nition
of the problem and an analysis of its causes. At a land-
scape scale, there is hardly ever only one single problem
with only one cause, but rather a multitude of prob-
lems triggered by a multitude of factors and kept going
by a multitude of actors. Different stakeholders also
tend to differ in their perceptions, and specifi cally, their
choice of a reference to use as a yardstick to measure
the degree of degradation and the effects of restoration
activities against. Landscape actors such as farmers,
tourists and conservationists may have entirely differ-
ent views about what 'nature' is, or should be, ranging
from production-oriented and arcadian landscapes to
wilderness (Swart
et al
. 2001 ; see Chapter 1 ). Addition-
ally, stakeholders may have confl icting commercial,
political or legal interests leading to different prefer-
ences for alternative restoration options.
Another typical characteristic of landscape-scale res-
toration programmes is that there is much time needed
to complete the actions. Larger programmes typically
involve many years to even a few decades, and during
that time actors may vanish or appear, public policies
may change, budgets may increase or decrease and so on
and as a result the fi nal situation may deviate dramati-
cally from the original plan. Planning and managing
such processes in a changing world requires, on the one
hand, clear priority setting to minimize risks of failure
and disappointment, and, on the other hand, fl exibility
to use unexpected events and opportunities to maximize
or optimize possibilities as the programme goes forward.
Numerous schemes for setting priorities have been
developed, but there is not a universally agreed
approach to this. Landscape-scale restoration in many
cases still depends on actions taken at the individual
patch scale. Deciding on priority actions depends on an
initial assessment of within-patch conditions and a
consideration of the landscape context. Correct diag-
nosis of what, if anything, is currently wrong is an
essential fi rst step. Further considerations include the
degree of threat, the feasibility of the management
required, the likelihood of it succeeding, and the rela-
tive value of the different patches or remnants being
considered (Cramer & Hobbs 2002; Hobbs
et al
. 2003 ).
5.5
LANDSCAPE-SCALE RESTORATION
Human impact on landscapes has been enormous,
throughout the world, and has in most cases resulted
in large biodiversity losses. To reverse further declines
and especially to make ecosystems more robust against
disturbances, it is unavoidable to enhance spatial rela-
tions (Grootjans
et al
. 1996 ; Hobbs & Norton 1996 ).
This implies that restoration of complete landscapes
gives the best chances for long-term survival of self-
sustaining ecosystems.
Like any restoration programme, projects at the
landscape scale consist of several phases. These are
often derived from the concept of systematic conserva-
tion planning (Margules & Pressey 2000), but there
are a few inherent differences as compared to 'classical'
small-scale restoration projects. These differences arise
from a much more explicit inclusion of
stakeholders
other than conservationists, and with scale differences,
