It is vital to provide
a value when assessing impacts on nature with a view to
protecting them by long-term management . The Darnell system of evaluation is
based on the idea that impacts can be broken down into twelve generalizations, or
'principles of environmental impact'. These could be regarded as a set of working
rules which would be the first step in a conservation management. Some of these
generalizations are self-evident, but they are none the less important for that. They
are paraphrased as follows.
A Natural values and the nature of the impact
1 Natural ecosystems
are of great value to society and should not be modified
without good cause.
2 Most human intrusions
into natural ecosystems are likely to be deleterious to that
ecosystem.
3 Ecological impacts
always come in groups, i.e. natural phenomena are interrelated
and impacts are transmitted via species interactions and system connectivity.
B Impact as a function
of construction type and location
4 Each general type
of intrusion results in a characteristic suite of environmental
effects.
5 Each specific type
of intrusion induces a specific set of environmental impacts.
6 There is a regional
dimension to all impacts, i.e. mangroves are not salt marshes.
7 Each specific
location exhibits site-related values and site-related response
characteristics which need checking, i.e. field inspection.
C Impact predictability and environmental response
8 Effects of intrusion
are in part predictable, but in part unpredictable.
9 Different types of
intrusion often produce the same type of response in a system.
10 Severe or prolonged
intrusion into a natural system produces systemic stress, i.e.
total breakdown.
11 Ecosystem responses
to severe intrusion take two forms: a generalized stress
response somewhat unrelated to the nature of the stress agent, and a specific
response which is particular to the nature of the stress agent.
12 Ecosystem responses
to stress agents of various types are not well understood,
and therefore further study is needed if we are to increase our predictive capability
and eventually to minimize the ecological effects of intrusion.
However, such a procedural
progression of considerations still begs a number of
important questions, such as the following. What techniques are available for
minimizing the intrusion/development effects? How far is society prepared to go in
ameliorating the impacts or creating new environments? Is society prepared to forgo
immediate monetary gains for future benefits? What institutional mechanisms,
which, of course, are different in every country and even transcend national
boundaries required to achieve the protection desired? The difficult and vexing
questions of establishing markers for the non-consumptive value of scenic, heritage
and historical issues that are still sidestepped.
With respect to the
latter aspect, seven marker categories are presented based
on the different cultural routes taken to evaluate nature. The non-consumptive
benefits of include scenic, recreational, educational, aesthetic, archaeological,
scientific, heritage and historical benefits that are difficult to define, let alone quantify.
These overlap and intertwine, and consequently a precise definition is not possible
or, perhaps, even desirable.
Non-consumptive values
have usually been considered of secondary importance
compared with the direct consumptive and economic products of environment and
the physical, chemical and biological services that they provide. However, they are
accepted and funded by ordinary people. The range of value categories reflects the
fact that the values are intangible and can be highly personal and subjective. Often
values are placed in society through the media of literature and art, or through scenic
or visual- cultural assessments, and a positive attitude to conservation may be
activated through these doors and windows. Additionally, because there is no way of
measuring these values objectively, it is difficult to compare non-consumptive with
consumptive benefits, or one type of non-consumptive type with another non-
consumptive type in the same kind of environment. The one non-consumptive benefit
that can sometimes be quantified is that of recreation, as the number of people
participating, and what they are prepared to pay for the privilege of that participation in
the form of licence fees, equipment or travel, is a measure of sorts. Thus it is
estimated in 1980-1 that 83.2 million Americans spent $14.8 billion on observing and
photographing fish and wildlife in 1980-1.
