Indicator assessment
This indicator is still under development, and is therefore not
assessed.
Background
Functional connectivity can be measured using
spatial modelling tools such as those developed by Forest Research
(Watts et al, 2005). Between 2007 and 2008, Defra and the country
conservation agencies funded further development of this modelling
approach applied to land-cover data from Countryside Survey.
In September 2008, this developmental work
produced a set of recommendations for the production of a
functional connectivity indicator for the UK (Watts et al,
2008).
The proposed indicator calculates the
likelihood that a species is able to move between semi-natural
habitat patches within the wider landscape of the UK and is based
on the effective habitat patch size and the ease of movement
between patches.
The first step is to calculate the effective
patch size. For any given semi-natural habitat occurring within a
Countryside Survey square (of 1 km x 1 km), the patch area is
calculated. The area is refined to take account of surrounding
land-use. The greater the intensity of surrounding land use, the
greater the ‘edge effect’ and the smaller the effective patch
size.
The second step is to calculate the distance
over which a typical species will be able to move between habitat
patches. This assumes a negative exponential dispersal curve (i.e.
where dispersal is more likely over shorter distances, with only a
few individuals travelling longer distances). This dispersal curve
is then refined to take account of the surrounding land-use. Again,
the more intensive the land-use, the greater difficulty a species
will have moving through it and the shorter the dispersal
distances.
The final step is to calculate the probability
of movement between the remaining effective habitat patches in each
of the sample squares. A low probability indicates that there is a
small area of semi-natural habitat in isolated fragments surrounded
by intensive land use. A high probability indicates a large area of
patches surrounded by land use types within which species
associated with the semi-natural habitat are able to move. The
indicator shows the average probability for all patches across the
sample squares for any given semi-natural habitat.
The pilot indicator is currently based on the analysis of
woodland connectivity for 10 1 km Countryside Survey squares
between 1990 and 1998 (see figure 14 (i)). There were fairly subtle
changes between 1990 and 1998 within the 10 CS squares but the
proposed indicator was able to detect change consistently,
suggesting a general increase in habitat connectivity between 1990
and 1998.
Further development planned
Defra is currently funding further development of the indicator
to incorporate a larger number of Countryside Survey sample squares
and a wider range of semi-natural habitats. The work will not only
inform the indicator but will help guide conservation policies such
as the woodland or agri-environment schemes.
Details of planned development of the habitat connectivity are
available in Watts et al (2008).
References
Watts K, Humphrey J W, Griffiths M, Quine C P
and Ray D. 2005. Evaluating Biodiversity in Fragmented
Landscapes: Principles. Forestry Commission Information Note
No.073. Forestry Commission, Edinburgh.
Watts K, Handley P, Scholefield P and Norton
L. 2008. Habitat Connectivity – Developing an indicator for UK
and country level reporting. Phase 1 Pilot Study. Defra report
WC0704 by Forest Research & Centre for Ecology and
Hydrology.