Introduction to the guidance manual
10. Attributes for species interest features
Assessing favourable condition for species interest features
could be by direct means (e.g. measures of species population size)
or via indirect means (e.g. extent/condition of suitable habitat).
These are complementary, and a balance (section 10.3) should be
struck for any particular feature having due regard to both needs
and practicalities.
10.1 Indirect measures
The use of direct measures is expected to be the norm, but for
many species (especially cryptic and/or poorly known species, such
as many invertebrates) it is very difficult to make reliable
estimates of population size; in some cases (e.g. wood-boring
beetles), population assessment may even destroy the species'
habitat. Even where quantitative assessments can be made (e.g.
birds), populations may fluctuate widely on a seasonal, annual or
longer-term basis; defining appropriate target/limit values may be
problematic if the population dynamics of the species are unknown.
Given that management for notable species is normally undertaken by
managing the habitat, rather than directly managing the species, it
is normally appropriate to include habitat attributes within
conservation objectives for species interest features where the
habitat needs of the species are known.
10.2 Direct measures
Notwithstanding the foregoing remarks, some direct measure of
a species feature is clearly highly desirable, as over-reliance on
habitat attributes could lead to misleading conclusions. The
relationships between habitat condition/extent and associated
species are often poorly-known. If condition assessment for species
relied solely on habitat attributes it would be possible for the
habitat to be in apparently favourable condition, but for the
associated species to have declined to the point of extinction.
Species may also be influenced by factors other than habitat
condition/extent, e.g. disturbance, as in relation to bat
roosts.
10.3 A balance of approaches
The solution is to use a combination of approaches, tailored
to the particular interest feature. The following principles are
advocated:
- In general, attributes for species interest features should
include both assessments of habitat extent/quality and assessments
of the species population where data exist through recording
schemes, or can be easily and reliably obtained without significant
costs or delays.
- Quantitative assessments of population size should only be used
when:
- the species population can be counted or measured reliably,
e.g. most birds, some vascular plants, some invertebrates
(butterflies and dragonflies); and
- meaningful targets/limits can be set which take population
fluctuations into account; and
- assessment methods avoid significant additional costs, time, or
generating a need for higher competencies of local staff.
- Where quantitative assessments cannot be used, conservation
objectives should generally incorporate species presence/absence,
i.e. for a species feature to be in favourable condition the
species should usually be recorded at least once during a 6-year
reporting cycle.
- Some habitat attributes should be used, provided the habitat
requirements of the species are broadly known – if necessary,
further work should be undertaken to establish this.
There will be a gradient in the balance of attributes from
groups where the habitat attributes will predominate and where
presence/absence of the species may be the most that can be
expected to be monitored, through to groups where species
population data will predominate and where only major changes of
habitat may be worth recording. Most species interest features are
likely to lie between these two extreme positions and, for these,
population data and habitat attributes will both be important. When
assembling evidence of feature condition, the use of relevant
'contextual' information on species populations, collected through
existing recording schemes or specially commissioned surveillance
schemes outwith CSM methods should always be considered.
For certain species, disturbance or predation are major
factors affecting populations, and conservation objectives should
include attributes relating to minimising these factors. There is
obviously a cross-over here to the management plan for the
site.