o_19ko2dt161ng2j4e1tgnoqv1s45a.pdf

APPLYING THE IUCN RED LIST CATEGORIES IN A FOREST SETTING
transparency and introduce some certainty about how the evaluation took place. The guidelines
are full of rules of thumb that are applicable at a general level. However, more specific rules
of thumb may be defined for groups of related taxa or unrelated taxa either with shared life
forms, biological or ecological traits, habitat preferences or geographical ranges.
There are numerous points in the Red List process where decisions on interpretation make a
considerable difference to the assessment and where rules of thumb may be particularly useful;
the interpretation of the main definitions in particular:
1. Generation length/Mature individuals – estimating the average age of parents and when
age at effective reproductive maturity is particularly influential for species exhibiting
wide ranging values (e.g. for trees between 100 years). The interpretation of
these definitions influence estimated population size and the estimated timeframe by which
population declines are judged (Criteria A, B, C & D).
2. Location/Subpopulation/Severely fragmented – defining subpopulations that exist in
almost complete isolation from incoming genetic influence or locations that may be
potentially influenced by a single event is a relatively subjective judgement, especially
for lesser known species. These definitions influence population status estimates (Criteria
B, C & D).
3. Extent of occurrence (EOO)/Area of occupancy (AOO) – measuring EOO and AOO
is entirely subject to the scale of measurement and influence distribution estimates (Criteria
A & B). The guidelines recognise that the scale used should be appropriate to the biological
aspects of the taxon, the nature of threats and available data. Clearly rules of thumb are
called for here.
4. Population reduction/Continuing decline/Extreme fluctuations – depend on
judgements as to whether a decline is part of a natural fluctuation or a more serious
extinction process (Criteria A, B & C). Assessors also must consider whether the trend
will continue.
Developing a common understanding of the spirit of the definitions and how they should be
interpreted or defining rules of thumb within a group of assessors or a network may significantly
speed up and simplify the evaluation process. Using proxy data provides a special case. Where
specific habitat types harbour a number of endemic species, it may be possible to share estimates
of habitat loss among relevant species. Inferences of decreasing habitat extent or quality are
acceptable for criteria A and B. Quantifying the reduction of specific habitat types at a national
level through a consensual approach may facilitate the assessment of diverse species. However,
careful attention should be paid to assessing the habitat-specificity of the species in question
and the impact of forest loss and fragmentation on those species, as well as whether other
criteria may apply. Proxy data should not be used to carry out bulk assessments of large
numbers of species without giving thought in each individual case to whether the species
might be more or less prone to extinction and deserve more detailed assessment.
The other alternative is to give species a category of ‘data deficient’. The problem with this
category is that it is a hold-all for assessments suffering diverse data limitations and has no
application in conservation prioritization. More compelling support for pursuing a path of
assigning threat categories wherever possible is provided by the hundreds of resource managers,
who are making decisions on conservation priorities every day.
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