Review Comments1
R. L. Specht2
MEDITERRANEAN ECOSYSTEMS
The mediterranean regions of the world are
characterised by an annual climatic sequence in
which a hot dry summer season alternates with a
cooler wet period. Mediterranean regions,
showing this climatic oscillation, extend from
the semi-arid to the humid zone.
A wide range of plant communities may be
observed throughout mediterranean regions,
ranging from semi-arid grasslands and shrublands
to woodlands, open-forests and even tall openforests (containing the tallest trees in the
world).
The nature of the ground stratum depends on
the nutrient level of the soil - a grassy/
herbaceous ground stratum is characteristic of
rich soils, while a sclerophyllous (heathy)
ground stratum flourishes on soils very low in
plant nutrients.
It is this wide range of ecosystems which must
be considered in a discussion on the interaction
of research and management in mediterranean-type
ecosystems.
CONSERVATION OF MEDITERRANEAN ECOSYSTEMS
Any landscape is likely to be subjected to a
number of competing methods of land-use, developed
to satisfy the needs of man. Among the various
land-use alternatives may be cited:- urban
and industrial development; water supply; waste
disposal; transport; mining; agriculture and
horticulture; forestry; tourism and recreation.
The conservation of ecosystems and of associated
biota must be regarded as sharing an equal place
with the many other conflicting land-uses.
Unfortunately for the land-use planner, natural
ecosystems are often unique to the area; in
weighing alternatives, it may be impossible for
the planner to dismiss conservation reserves as a
land-use strategy which can be achieved elsewhere.
1
Presented at the Symposium on Dynamics and
Management of Mediterranean-type Ecosystems,
June 22-26, 1981, San Diego, California.
The first priority in landscape planning
should be to acquire a comprehensive and
adequate system of conservation reserves.
These reserves should be of sufficient size
and diversity to ensure adequate conservation
(for both perpetuation and evolution) of the
range of mediterranean ecosystems and their
component biota.
It is often assumed that conservation reserves
must be protected from natural perturbations such
as fire, overgrazing by herbivores, insect
plagues, etc. which have influenced ecosystems
for countless years in the past. Such decisions
may lead to relatively homogeneous, overmature
communities, often with reduced species diversity.
Heterogeneity of age classes and diversity of
landscape appear to be essential requirements for
long-range conservation and for evolution of
biota and ecosystems. Management is necessary to
attain these objectives.
As well, environmental impacts imposed on the
conservation reserve both from people within the
reserve and from adjacent land-use strategies may
need careful management techniques to conserve
the ecosystem intact.
MULTIPLE LAND USE
However, only a small percentage, say 5 to 10
percent, of the landscape will be declared as
conservation reserves. Much of the landscape
will be converted to man's immediate needs - urban
and industrial development with associated land
uses such as reservoirs, grazing, agriculture,
forestry, and mining to supply water, food, timber
and minerals. In many mediterranean landscapes,
the topography may be unsuitable for complete
conversion of the original ecosystem. Multiple
land use may be attempted in these less accessible
areas; conservation may be one of the aims of
management of these areas but it is probable that,
in the long-run, only the most resilient of the
species will survive. The objective of management
in these areas is then, not conservation, but the
maintenance of ecological stability, possibly with
a continual supply of extractable products. The
ecological stability present in the original
ecosystem may include a supply of fresh water
(with balanced nutrient-levels), a stable soil
surface, a minimum of fires. Fires become an
increasing problem when urban development impinges
on these semi-natural mediterranean landscapes.
What are the extractable products which may be
gained from semi-natural mediterranean ecosystems?
Water; fodder for grazing and browsing of
domestic animals; fuel and timber; native and
feral mammals and birds (hunting and food); herbs,
cut and dried flowers; some fruits and bulbs;
honey; possibly peat, clay and rock.
Professor of Botany, University of Queensland,
St. Lucia, Queensland 4067, Australia.
It would appear possible to maximize the
supply of one or more of these extractable
products by manipulation of the ecosystem.
Nevertheless a number of attempts to achieve
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Gen. Tech. Rep. PSW-58. Berkeley, CA: Pacific Southwest Forest and Range
Experiment Station, Forest Service, U.S. Department of Agriculture; 1982.
2
these objectives has led to instability. For
example, conversion of the deep-rooted, crown-root
sprouting, evergreen chaparral vegetation to a
shallow-rooted seasonal grassland has:(1)
Improved water flow, but with release of
nitrate ions stored in soil (Sodium ions
are released from solodic soils in
mediterranean Australia).
(2)
Increased seasonal herbage for grazing
animals, but with:− increased soil erosion during flood
periods at the end of the dry summer
season
− invasion of mediterranean weeds and
pathogens
− increased fire hazard from both
lightning strikes and man (grass fires,
often causing loss of life and property
in mediterranean Australia, may occur
every year whereas brush fires are
relatively infrequent).
The conversion of brushland to grassland may be
an extreme example of the instability induced in
an ecosystem by manipulation. It is cited to
emphasize the sensitivity of many mediterranean
ecosystems to perturbation.
ECOSYSTEM RESEARCH
In order to provide a sound basis for
management decisions, it is necessary to continue,
to strengthen, or to establish a number of
integrated projects for analysis of the structural
dynamics and functioning of representative
mediterranean ecosystems especially in response
to the effect of various environmental impacts,
for example, fire, erosion, grazing, selective
removal of plant or animal species (by harvesting
or hunting), nutrient removal by harvesting or
grazing, invasive weeds, vermin, pathogens,
atmospheric pollution, nutrient and other chemical
contamination, salination - all of which can be
simulated by controlled experimentation. Each
integrated project, investigating one or more
major environmental impact, should be planned
from an holistic (not fragmented) systems approach.
It is desirable to supplement the large projects,
which necessarily have to be limited in number,
with a series of supplementary projects intended
to solve special problems, as well as supplying
additional information for comparison and synthesis.
The aim of the integrated project is to define
the basic ecological rules operating within the
ecosystem - rules which are applicable to all
mediterranean ecosystems - and to synthesise these
rules into a relatively simple working model
which will enable the effect of an environmental
impact to be predicted.
It must be stressed that even a simple model,
as outlined in this author's paper on the
General Characteristics of Mediterranean-type
Ecosystems in the first session of this Symposium,
appears to provide a basis for national and
international predictions of the results of
management practices on mediterranean ecosystems.
The essential point is to establish the
basic ecological rules as they operate seasonally,
annually, and cyclically (over the life cycle) in
the ecosystem. In the past, ecosystem research,
which tackled the problems associated with sharp
environmental discontinuities or with ecosystem
change along environmental gradients, has
established many basic rules and is likely to
be a productive area of research in the future.
Once basic ecological rules have been established,
the best management policy can be determined in
the light of the various environmental impacts
likely to be experienced in conservation reserves
or semi-natural ecosystems (where multiple land
use is practised). The ultimate aim should be
long-term stability of the ecosystems, associated
with sustainable yield, albeit at a level below
the maximum possible (on a short-term basis).
Nevertheless, it must never be forgotten that
extremely rare events (such as volcanic eruptions,
land-slips, cyclonic storms, floods etc.) are
virtually impossible to predict and may disrupt
even the most soundly based management program.
RECONSTRUCTION OF DEGRADED MEDITERRANEAN ECOSYSTEMS
Throughout mediterranean regions, there are
many areas where these objectives of sustainable
yield and long-term stability have not been
realised. Long-term stability has been forfeited,
often unintentionally, for a relatively short
period of maximum yield. As alternate land-use
may not be possible, efforts should be made to
restore these degraded areas to their former
status of long-term stability (with or without
sustainable yield). Such reconstruction efforts
should be based on the basic ecological rules
derived from research projects such as outlined
above, rather than the empirical trial-and-error
methods which are often applied. At this stage
of our knowledge, it would be unwise to claim that
reconstruction of original ecosystems (containing
all conservation objectives) is possible. However,
long-term stability (with or without sustainable
yield) seems a valid aim.
FUTURE RESEARCH AND MANAGEMENT
Research in mediterranean ecosystems should
aim at understanding the basic ecological rules
operating within the system and how resilient these
ecosystems (and their component species) are to
environmental stress. Simple working models will
enable the effect of an environmental impact to
be predicted. Such ecosystem research, basic to
management problems, will be the major theme of the
Fourth International Conference on Mediterraneantype Ecosystems to be held in Perth, Western
Australia, August 1984.
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