Design of Natural Reserves
According to designations set up by IUCN, there are 6
categories of protected areas, with different
restrictions on use in each category:
Category I – a) strict nature reserves – no harvesting,
recreational use, or other access, principally for
scientific research, and b) wilderness areas –
preserving the natural condition. Both exclude
mechanized transportation and have limited access.
Category II – National parks – area managed for
ecosystem protection and recreation. No harvesting
or extractive use.
Category III – Natural monuments – managed to
protect some natural or cultural feature (e.g.
Carlsbad cavern). Generally more limited in area
than either Category I or II.
Category IV – Habitat/species management area –
protected for conservation by active intervention. A
specific habitat or species is usually the underlying
interest.
Category V – protected landscape/seascape – the
interaction of people and nature has produced an
area with distinct character deemed worthy of
protection.
Category VI – managed resource protected area –
protected mainly for maintenance of biological
diversity with sustainable harvest/removal of a
resource.
Note that these management categories apply to both
terrestrial areas and to marine reserves. The number
of protected areas has
grown since the first
ones were designated
in 1872 (Yosemite and
Yellowstone National
Parks, U.S.)
There is a parallel set of designations, classifying
areas as biosphere reserves, Ramsar wetlands
(named for Ramsar, Iran, where the convention was
signed), and/or World Heritage Sites. Sites may be
in any of the earlier categories and fit in one or more
of these designations.
If there are to be one or more protected areas to
achieve maintenance of biodiversity in a habitat type,
how should we design the area(s) to be protected?
There are a set of rules, initially proposed as
comparisons of better and worse strategies by Jared
Diamond. These are ‘old’ rules, but act as a starting
point…
1. The larger the reserve, the better. There will be
more species at equilibrium in a larger reserve, and
a lower extinction rate. The species most likely to
be endangered by isolation in limited preserves are
the most 'K-type' species. These species typically
have smaller carrying capacities and lower potential
growth rates (r). The larger park, by favoring
numerically greater equilibrium population sizes,
may best insulate endangered species from chance
demographic extinction, Allee effects, genetic drift,
and inbreeding depression due to small population
size. The larger park may also protect species with
large habitat requirements and minimize edge
effects.
2. One large preserve is better than a number of
smaller reserves with the same total area (??).
The species likely to be endangered by restriction
to the reserve(s) are, additionally, likely to be those
with the poorest dispersal capabilities, or those
with largest home range requirements. If dispersal
is the problem, these are species unlikely to be
rescued by renewed immigration from nearby
'islands‘. Species with minimum home range
requirements may not have enough area in small
reserves; even though they can move between
reserves, they cannot maintain minimum viable
populations in any of them.
2. (cont.) – the other side of the question…
Unique habitats/biotas with specific environmental
requirements may be best met by preserving multiple
isolated areas.
Effects of natural catastrophes need to be considered.
Many conservation biologists claim that a single large
reserve is dangerous (putting all your eggs in one
basket).
This design criterion is more controversial than any of
the others. Simberloff (Simberloff and Abele 1976,
1982) presented what became known as the SLOSS
(Single Large or Several Small) controversy. Given
what we know about species-area curves, why is there
a controversy?
If several small reserves duplicate the habitat variation
present in the large reserve, a larger number of species
is preserved by the single large preserve.
However, if there is habitat heterogeneity among the
small preserves, then the answer is not clear. Different
species may accumulate in different small preserves,
and in sum the total number of species present can
exceed the number in a single large reserve.
The kind of reserve favoured depends on: 1) the slope
of the species-area curve. The steeper it is the better
the larger reserve; and 2) the number of species shared
among smaller reserves. The larger the shared
proportion the better the larger preserve.
Other factors may also become important
considerations. For example:
Population management considerations. Area is not
the sufficient answer for species whose populations
fluctuate widely in size. In that case, the larger the
area the larger the management problem. This is a
management problem faced by African big game
parks. Elephants seem to go through a 50 year
population 'cycle', and during at least part of it are
remarkably capricious and destructive.
Ease of access. In tropical forest areas if there are
roads or major rivers that permit access, a reserve is
more likely to be subject to poaching or logging.
Another problem: the tendency for a large preserve to
be 'nibbled' at the edges for alternative uses in the
belief that 'there's still plenty left'.
Finally, there are frequently edge effects. Multiple
small reserves have relatively less core and more
edge.
If only small reserves are available should
conservation be abandoned?
80% of California's 1700 rare plant species are from
three habitat types available only in small patches:
valley grassland, coastal scrub, and serpentine mixed
chaparral.
The most diverse patches of tall grass prairie are
almost all very small, in a range around 2 ha. High
quality patches, e.g. along railroad rights-of-way or
odd corners between agricultural fields have, for
various reasons, not been grazed, plowed, or
otherwise disturbed.
There is a legislative problem with these kinds of
small patches, at least in the U.S., with aggressive
protection for rare species: the area cut-off for
regulatory protection is 4 ha.
Size of preserved area is a far more serious problem
for large mammals. Less than 22% of parks around
the world will, on a probabilistic basis, support their
largest mammalian carnivores (10-100kg) for a
century, and none of these species are expected to
persist for 1000 years (at least in the parks alone).
3. If small reserves are necessary, they should be
arranged spatially to maximize immigration
rates among reserves. The preferred way of
achieving this end is to position the reserves as
closely as possible and by protection of smaller,
natural area stepping stones between them, or by
protecting linking corridors. These arrangements
maximize the probability of 'rescue effects'.
You’ve heard about corridors before. What may
not be evident is the width of corridor required to
encourage movement by the large mammals
among linked preserves, none of which are
sufficiently large alone…
Species
Location
Minimum Corridor
Width(km)
Wolves
Minnesota
12.0
Wolves
Alaska
22.0
Black Bears
Minnesota
2.0
Mountain Lions California
5.0
Bobcats
South Carolina
2.5
There is a modern approach that arises from this. It is
called hierarchical reserve design. Core areas are
highly protected; surrounding them are buffer habitats
with less protection. Core areas may be connected by
corridors. The buffer areas reduce edge effects.
3. (cont.)
Another important concept is the minimum dynamic
area. If smaller reserves are necessary, a minimum
size should be an area that accommodates a complete
disturbance regime, i.e. includes areas at all stages of
a disturbance mediated succession. This might be
achieved within a combination of core and buffer
habitat areas.
The minimum viable population concept (MVP for
short) may also be important in setting minimum
reserve sizes. MVP is the subject of another lecture.
4. Reserves should be as nearly circular as possible.
Round preserves minimize dispersal distances
between habitat patches within a preserve, and thus
act to maintain or rescue populations which may be
fragmented within a reserve. It minimizes the
'peninsula effect‘.
The effect shows in reduced diversity of species at
the end of elongated peninsulas, e.g. the diversity of
mammals in southern Florida and heteromyid
rodents along Baja California.
Circular preserves also maximize the core:periphery
ratio.
heteromyids
There are broad criteria used to evaluate reserve
designs:
1.Comprehensiveness (extent) – inclusion of features
important in conserving the full diversity of
species,
2.Representativeness – choosing the ‘appropriate’
variation in including the various features and
species,
3.Adequacy – is enough preserved to permit features
to persist for an extended period? The ideas of
dynamic areas and minimum viable populations are
important here.
4. Efficiency – Achieve the conservation goals using
cost (or even area) minimization. This should also
minimize management and conflict costs.
5. Flexibility – There may be many differing ways to
achieve conservation goals. The best plan is one
that permits adjustment/expansion with little
disruption.
6. Risk spreading – this was covered under the
SLOSS controversy: avoid potential catastrophe to
the entire reserve system.
7. Irreplaceability – make sure to consider whether
there are other possible inclusions that could
achieve the same goal. If not…
8, 9, 10. Connectivity, Area shape, and Reserve
fragmentation. All are part of the ‘rules’ you’ve
already seen.
With all these rules and suggestions for strategic
factors in decision making, biodiversity protection
typically uses one of 3 approaches: 1) protect
umbrella species, 2) protect areas with high species
richness, or 3) protect functioning ecosystems. Very
often reserves are based on the presence of some
charismatic species (e.g. buffalo – Wood Buffalo
National Park) or a habitat specialist (spotted owls).
How successful are conservation decisions based
upon single, impact species?
Species from the Columbia plateau, Washington
Charismatic species
Habitat specialist
In A the x axis indicates how many occurrences of the charismatic
species are protected, the Y axis the percentage of species conserved. In
B it is habitat specialists chosen for protection.
When decisions have been made about what species
to protect, how do you determine what areas to
protect?
The procedure is called gap analysis.
1. Identify on separate maps the distribution of the
species and those areas already under protection.
2. Overlay those maps to determine which species
are present in already protected areas (and with
sufficient representation), and which are not.
3. Those not represented are called gap species.
Overlay maps of gap species distributions to
identify where new protected areas are needed.
An example of gap analysis applied to Hawaiian
finch species – numbers identify distribution areas
for the species.
Practical examples (and problems):
One major area is human impact at the boundaries of
reserves. There are a number of approaches to mix
human culture, economics, and biological concerns.
One approach views the boundary as a filter.
Management and enforcement sets the way the filter
functions.
In the tropics economics and government policy limit
manpower and enforcement. In Brazil there are 29
nature reserves (in addition to production (i.e.
multiple use) reserves and large areas set aside for
indigenous peoples) in which there are 23 guards
deployed.
On average, that means each guard is responsible for
6053 km2, which can be compared to standards in the
U.S. In the U.S. there are 367 nature reserves
covering 326,721 km2, but 4002 guards, so that on
average each is responsible for 82 km2. In practice,
only a small fraction of Brazilian reserves have any
guards (31%), so that most reserves have no
protection. Further, the guards do not carry arms or
have the power to arrest violators.
So, how can reserves be designed to minimize
damage under those conditions?
1. Designing reserves to protect the Amazon basin
Peres and Terborgh (1995) suggest the sitting of
reserves to minimize access, and thus damage from
logging or poaching. Most reserves have been set
alongside water courses or roadways to ease access.
That, of course, is exactly the wrong approach when
the objective is protection of biodiversity and
habitats. The maximum distance potential violators
are likely to travel into the interior of a reserve from
points of access is about 10km (this is a different
view of 'edge effects'). Very large fractions of current
reserves are accessible according to the 10 km
criterion.
Most of the inaccessible area lies in the largest
reserves. Many habitats and species remain
unprotected. Is there a more efficient way to achieve
protection in Amazonia?
Peres and Terborgh suggest setting reserves along
watershed divides, minimizing access by navigable
rivers, and where roads don't provide access to
internal areas. In the Brazilian rainforest, most access
is by navigable rivers. If new reserves are targeted
for headwaters areas, access can be further limited.
Defensibility can be maximized with lower costs.
How can products be moved out of a protected area?
Only on navigable rivers? A single post, placed at the
boundary of the reserve along the river access, with
the power of enforcement, can guard a reserve.
Larger areas may have multiple river accesses, and
would need protection at each access point.
Posts at each end
Of a reserve area
Single guard post
Another problem, peculiar to Brazil, is that where
reserves are bordered by rivers, there are frequently
settlements, native and otherwise, across the rivers
from the reserves, with no easy way to supervise
access from the settlements. Nevertheless,
commercial harvest from reserves can be controlled.
2: protecting the Cape Floristic Region of South Africa
Here we consider the systematic design and selection
of reserve areas. There should be obvious ways to
select fragments which remain pristine or nearly so
to maximize the number of species which are
protected. However, codifying this fairly apparent
goal in a systematic way has rarely been attempted.
One approach to ‘rules’ was developed by Margules
et al. (1988):
1.Select all fragments containing species which only
occur in that fragment. This ensures that rare species
are included first.
2. Starting with the rarest species not represented by
fragments already selected, select from among all
fragments on which it occurs, those contributing the
maximum number of additional, previously
unrepresented species.
3. Where 2 or more fragments contribute an equal
number of previously unrepresented species, choose
the one which contains the least frequently occurring
additional species.
4. Where criterion 3 doesn't end up selecting a
fragment (2 or more are equal in all comparisons)
then, to avoid subjective bias, choose the first
fragment in the list among them.
What happens when you want to include habitat
types in your scheme to select fragments? Fragments
include a number of different habitat types. Rules are
fairly similar, but come at species preservation by
first ensuring that each habitat type is included. The
rules then are:
1. Select the fragment from each habitat type which
has the greatest number of species in the taxon used
to develop the strategy. If all species are included
using only the most diverse fragment in each habitat
type, then stop.
2. Select a 2nd fragment in each habitat type which
adds the most new species. If no fragments of some
habitat type add new species, skip any further
additions of that habitat type. If all species are
included, then stop.
3. Continue selecting additional fragments in each
habitat type not yet fully represented using the
criterion of rule 2 until all species are included.
It is this approach that was used to protect fynbos in
the Cape Floristic Province. Grid lines divide the
region into 3km by 3km squares, and species lists
were developed for each square.
Part of the concern for fynbos is the development of
agriculture in the region, the increasing urbanization,
and the effects of alien species in the area. Towns are
the very dark areas, alien vegetation is dark grey, and
cultivated lands are pale grey. White indicates land
remaining largely in native vegetation.
Vertebrate species can also be incorporated into
decisions. Table 14.2 (text) indicates presence/absence
for vertebrates at locations in fynbos…
And here’s the distribution of the vertebrate species
across 3 types of fynbos:
Modern conservation strategies try to use
communities, instead of just species, to establish
optimum reserve designs. One example of this
approach is the Multiple Species Conservation Plan
for southern California (Hierl, et al. 2008).
What are the general principles that should already be
clear: 1) extent, 2) representativeness, 3)
fragmentation and 4) endangerment.
Here is a diagram of the area studied:
The community types identified as most endangered
were: coastal sage scrub (high endangerment,
underrepresented within the reserve relative to the
region, and moderately fragmented), freshwater
wetlands, and coastal habitats (both have high
fragmentation, moderate endangerment and
representativeness, and low areal extent).
While these particular communities are particular to
the study area and high urban development in the
region, the ideas underlying the identification and
potential conservation actions are more general.
Are there general approaches to design?
A Synthesis of Modern Reserve Design Models:
A number of reserve design approaches were
summarized by Williams et al. (2004) based upon
different objectives. These 4 approaches can be
shown graphically (2 slides on) and described:
1) Identify a reserve core that contains all species,
then add buffer around it, minimizing total cost of
land to acquire; may promote connectivity and
compactness of the reserve (image b in figure).
2) Highly connected and tightly clustered set of minireserves; summed distances between pairs is
minimized and connectivity achieved by selecting
adjacent pairs of cells (image c in figure).
3) Tight clustering achieved by minimizing the
summed distances between selected pairs AND
minimizing the total diameter of the reserve (image d
in figure).
4) Compactness is achieved by minimizing total
perimeter length (image e in figure).
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