UNEP Islands Web Site
EXPLANATION OF ISLAND INDICATORS
General comments on indicators
- Coastal Index
- Sea level rise risk Indicator
- Isolation Indicator
- Threat Indicator
- Natural Protection Indicator
- Ecosystem Richness Indicator
- Species Richness Indicator
- Endemism Indicator
- Special Features Indicator
- Invasive Species Indicator
- Urbanization Indicator
- Human Threat Indicator
- Economic Pressure Indicator
- Protected Area Coverage Indicator
- Reliability of Data Indicator
- Human Impact Index
- Terrestrial Conservation
- Marine Conservation Importance
comments on indicators
One aim of this island directory is to classify islands by various
criteria, and to make comparisons between different islands or areas as
a basis for facilitating inter-island cooperation and sharing of solutions,
and identifying conservation importance. Given the large number of
islands, the diversity of their characteristics, and the inadequacies in
the data, it seems important to show as clearly as possible the bases on
which indicators have been calculated, and the weightings that are given
to different objective and subjective factors. To do this, the series
of simple numerical indicators developed for the Review of the Protected
Areas System in Oceania (Dahl, 1986) have been refined and expanded to
adapt them to the needs of a world island list. These include indicators
for the nature and isolation of the island, for features of conservation
interest, for risks to that conservation interest, and for the feasibility
of conservation action, and are incorporated in the island entries and
the various tables. They make it possible to reduce, or at least
to make more consistent and explicit, the subjectivity of judgements as
to relative island significance and conservation importance. They
also can help to identify islands with particular characteristics.
While this approach using numerical values reduces the chances of personal
bias or the drift in judgement that can occur between the beginning and
the end of a long analysis, it does have its weaknesses. First among
these is the tendency to see the numbers as having more accuracy or weight
than is actually the case. The indicators only reflect present information,
and can be expected to change as more data become available. A low
overall indicator including a low reliability of data rating can easily
reflect a lack of information rather than a lack of conservation interest.
At the same time, the system of indicators can be updated rapidly when
Users of this directory are cautioned not to place too much weight on
these indicators without first studying their derivation to ensure that
they are appropriate to the intended use of the information. Small
differences between indicators should not be considered important, since
there are too many uncertainties in the database, and some indicators are
derived from what are essentially subjective judgements. Where particular
uses require other selection criteria, it is not difficult to modify the
content and weighting of the indicators for such other uses.
The indicators of conservation importance are explained in broad catagories,
since the numerical ratings in the island entries are based on data that
are still too incomplete for fair inter-island comparisons. Rankings
in the tables, however, are based on the calculated numerical values.
Despite these weaknesses in detail, the indicators do give a good overall
picture of conservation needs and relative importance of islands, and should
prove a useful tool in sustainable development planning if used wisely.
A coastal index as one measure of insularity is calculated by dividing
the length of the shoreline by the land area.
level rise risk
The risk to the island from sea level rise due to climate change is
evaluated as the percentage of the land area less than 5 metres above sea
level, divided by 10 to give a single digit.
To measure the isolation of the island from potential sources of colonization,
the square roots of the distances to the nearest equivalent or larger island,
the nearest island group or archipelago and the nearest continent are added
to give an index of isolation. Where one of these does not exist,
the next higher distance is repeated, except in the case of small satellite
islands close to much larger land masses. See table of more
One point is given for each of the major categories of large scale
catastrophic threats to the island environment:
--- cyclones (hurricanes or typhoons);
--- volcanic eruptions;
--- earthquakes, tsunamis (tidal waves), landslides, etc.;
--- severe drought;
--- susceptibility to major fires;
--- high risk of oil spills.
This is a measure of the risk of natural or human catastrophes that
could threaten human welfare, seriously damage the economy, and endanger
endemic species or protected areas, thus increasing the importance of adequate
(Scale: 0 to 6)
The natural protection afforded to the island by its condition or situation
is rated by giving one point each for:
a) remoteness (at least 200 km) from the nearest island
or other land area;
b) not presently inhabited;
c) few or no introductions of predatory or competitor species
such as feral animals, european rats and aggressive weeds.
(Scale: 0 to 3)
The ecosystem richness is measured as the number of terrestrial or
marine ecosystem types or biomes, based where possible on an existing classification
or estimated from the island description and structure. For the terrestrial
measure, less than 5 ecosystems or biomes is typical of impoverished low
coral islands, 5 to 10 ecosystems indicates some distinct vegetation types,
10 to 25 ecosystem types would be found on high islands with some habitat
diversity and differentiation of biomes with altitude, 25 to 40 ecosystem
types shows considerable diversity of habitats, and more than 40 biomes
and ecosystems approaches continental areas in richness.
A separate marine rating is based on a count of the marine ecosystems
in the coastal zone to 100 metres depth.
The numbers of species of different categories of organisms that occur
on an island are an important measure of its biological diversity.
The figures most frequently available are for terrestrial plants and/or
land birds, and these are used as the basis for the terrestrial indicator
scale. Where individual island data are not available, estimates
have been made based on figures for the country or island group.
0 = few or no species (less than 24 plants
and/or 8 land birds);
1 = poor in species (25-224 plants; 9-23 land
2 = moderate species richness (225-624 plants;
3 = good species richness (625-1224 plants;
4 = high species richness (1225-2024 plants;
5 = very rich in species (over 2025 plants
and/or 72 birds).
An equivalent indicator of marine species richness follows the
same scale as that used for terrestrial plants, based on the few categories
of organisms such as fish, corals or molluscs for which species data are
The endemism is rated both for island groups (GE) and individual islands
(IE) on the basis of the number of endemic species and sub-species recorded.
For terrestrial endemism, the scale for the indicator is as follows:
0 = no endemic species;
1 = 1 to 5 endemic species;
2 = 6 to 38 endemic species;
3 = 39 to 149 endemic species;
4 = 150 to 410 endemic species;
5 = 411 to 915 endemic species;
6 = over 916 endemic species.
For marine endemism, the following scale is used:
0 = no endemic species;
1 = 1-2 endemic species;
2 = 3-6 endemic species;
3 = 7-12 endemic species;
4 = 13-20 endemic species;
5 = 21-30 endemic species;
6 = over 31 endemic species
The two indicators permit identifying both individual islands with
endemic species restricted to that island, and islands in a group which
may share endemic species with other nearby islands.
Many islands have special features of conservation or tourism importance
that need to be highlighted in any evaluation, such as seabird rookeries,
turtle nesting beaches, marine mammal breeding areas, lakes, active volcanos,
scenic mushroom islets, caves, etc. These are listed and counted
separately for marine and terrestrial environments to produce two special
The threat represented by invasive introduced species is rated both
on the number of such species and their aggressiveness in island situations.
0 = few or no introductions
1 = some introductions (i.e. rats, common
2 = common domestic introductions (dogs,
3 = some problems with invasive species
4 = major problems with invasive species
5 = devastated by invasive species
The urbanization indicator is based on the proportion of the island
population living in urban areas. (scale: 0-9)
This indicator estimates the pressure of the local population on the
land and resources. Statistics for the percentage of the population
in agriculture, mining and fishing are divided by 30, giving a scale of
0 to 3. Some adjustments must be made for specific islands (such
as remote or uninhabited islands) where the situation is known to be different
from the country average.
This measures the level of economic development and thus of modern
development impact on the environment. The indicator is generally
calculated for each country, based on the Gross Domestic Product, GNP or
income per capita (in US$) divided by 2000, giving a scale of 0 to 9.
There are at present no statistics which would allow these average indicators
for each country to be adjusted for rural islands with less development
or for islands with urban centres or major development projects.
Area Coverage (PA)
The rating for the coverage of the land and marine areas of the island
by protected areas is rated according to the following scale based on the
percentage of surface protected:
0 = <0.5% protected
4 = 25-40% protected
1 = 0.5-4% protected
5 = 41-60% protected
2 = 5-12% protected
6 = 61-84% protected
3 = 13-24% protected
7 = >85% protected
See table of islands with protected areas.
of Data (DA)
It is important to know whether an island situation or local conservation
problem is well documented and clearly understood, or only suspected on
the basis of inadequate data. The following scale is used:
0 = no reliable
1 = poor data
(both partial and out of date);
2 = data only
partial or out of date
3 = good recent
data (within the last 10 years).
This scale favours islands with problems that are well understood,
and where conservation action can be clearly defined, over those that closer
examination may show not to have problems, or to be irremediable.
A low indicator does not mean that conservation action is not needed, but
that is should be preceded by further studies to determine the present
situation. This indicator can also be used to judge the overall accuracy
of the combined ratings.
The data for each island are summarized in three aggregated indices
to give an overall evaluation and to permit comparisons and rankings.
The Human Impact index measures the overall human pressure or impact
on the island and therefore the potential threat to remaining natural areas
or endemic species. Since it is based on
the present situation and its potential for future change, it does
not measure past changes (such as caused by former inhabitants or abandoned
mines) which no longer represent a current threat, nor
does it reflect the cumulative human impact of such past changes.
The HI index is calculated as follows: the population density (for the
island if known, or else for the country), divided by 50, is multiplied
by a population trend factor based on the growth rate that produces a reduced
figure for a declining population and a larger value for a fast-growing
population. To this figure for the demographic pressure on resources
is added the Human Threat indicator based on the percent of the population
in agriculture, mining and fishing), the Economic Pressure indicator (based
on GDP), the Urbanization indicator (based on the percentage of the population
in urban areas), the number of tourists divided by the population multiplied
by 5, the invasive species rating, and the percentage of developed plus
degraded land divided by 10. Range: 0 to 99.
HI = (density/50) x (trend/2) + HT +
EP + URB
+ INV + (devland+degraded)/10
See table of Islands by Human Impact Index
Conservation Importance (CI-T)
The Terrestrial Conservation Importance index is intended to give an
overall numerical evaluation of the significance of the land area of the
island for the conservation of nature. It
consists of the sum of a series of measures of conservation interest
weighted for their relative importance. Both measures of biological
importance and measures of their natural conservation
status have been included, since both are important for successful
conservation action, although biological factors are given the heavier
weighting. In a sense the formula tries to reflect the
kind of evaluation process used by a conservation planner or a protected
area manager in selecting a protected area. The elements of the CI
- the Ecosystem Richness (ER) indicator divided by 10 and the Species
Richness (SR) indicator, both multiplied by 2 (scale: 0 to 20 points) as
measures of the richness of natural communities;
- the percentage of the land area covered by Forest divided by 10 (up
to 10 points);
- the Island Endemism (IE) and Group Endemism (GE) indicators based
on numbers of endemic species (maximum 12 points), and the percent endemism
of plants and of land birds, divided by 10 (up to 10 points each);
- measures of threatened species, including the number of Endangered,
Vulnerable, Rare, Indeterminate or K (EVRI) plant and bird species divided
by 5 (up to 31 points in exceptional cases such as New Caledonia);
- one point each for Special Features (SpFe) of conservation interest,
such as seabird rookeries, sea turtle nesting areas or other critical habitats,
lakes, unusual geological formations or other features deserving specific
protection (generally 0 to 4 per island);
- the Vulnerability (Vu) indicator (up to 6 points); and
- the Natural Protection (NP) indicator (0 to 3 points).
CI-T = 2(ERT/10+SRT)+forest/10+IENDT+GENDT+percent
The theoretical maximum value of the terrestrial CI (for present numbers
of endangered and threatened species) approaches 100 points.
This index of Conservation Importance will thus favour islands with
greater ecological complexity and species diversity, with more species
endemism, with larger numbers of endangered and threatened species, with
more special features of conservation interest, with greater vulnerability
to natural disasters, and with better natural protection.
The terrestrial CI does not favour pristine but simple islands except
for their natural conservation status, even though such highly simplified
ecosystems may be of great scientific and conservation interest.
It also does not single out islands with critical habitats of importance
to sea birds, turtles or marine mammals. Conservation priorities
for these should be identified using other measures.
See table of Islands by Conservation Importance Index
Conservation Importance (CI-M)
The index for Marine Conservation Importance is intended to provide
an equivalent measure to the terrestrial Conservation Importance (CI-T)
index, but adapted to the special characteristics of the island marine
environment down to 100 metres depth.
Since even less data are available for coastal and marine areas of islands
than for terrestrial areas, it may not be possible at present to calculate
a viable marine indicator for many islands, but it is included here to
highlight the information needed. The index consists of:
- the marine Ecosystem Richness (ERM) indicator, divided by 3 because
of the relative importance of coastal marine ecosystem diversity, and the
marine Species Richness (SRM) indicator, both multiplied by 2;
- the marine Island Endemism (IENDM) and Group Endemism (GENDM) indicators
based on the numbers of marine endemic species multiplied by 3 because
of the relative rarity of marine endemism;
- one point for each marine Special Feature (SpFe) of conservation interest;
- the Vulnerability (Vu) indicator (up to 6 points); and
- the Natural Protection (NP) indicator (0 to 4 points).
CI-M = 2(ERM/3+SRM)+(IENDM*3)+(GENDM*3)+SpFeM+VU+NP
As with the CI-T, the CI-M favors rich and complex coastal areas with
good prospects for conservation action. It is not a good measure
to identify simple undisturbed coastal areas which maybe unique in their
own way, nor does it include any measure of the importance of marine protected
areas for fisheries management.
There can be many reasons for taking special action to protect an island,
and the above choice of measures and weightings may be debatable in particular
instances. Overall, however, broadly-based aggregate indices such
as these should help to identify and rank the different islands in terms
of priorities for terrestrial and marine conservation and sustainable development
action. Indices can also be combined, as in the table of Islands
most at risk, combining HI and CI indices.
Return to Island Directory Home
Updated 23 July 2003