Distribution data for
Rhododendron and bilberry are
available via the
National Biodiversity Network
Gateway. Although the coverage for bilberry is likely to
be good at the 10km square level, it is too common to have been
recorded in greater detail. Similarly, coverage for
rhododendron is probably less consistent, even at the 10km square
level, because non-native species have not been consistently
recorded. Unfortunately data at 10km square level is not
sufficient for establishing detailed impact or identifying areas at
risk.
The distribution data, together with a number of other datasets,
such as altitude, weather and landcover were fed into a ‘Maxent’ model to create modelled
distributions of the species with a precision of 1km2 or
better. In order to be able to test the fit of the models,
they were developed using a random selection of half of the data,
and tested with the other half. The distributions developed
produced a fit of 94% for Rhododendron and 93% for
bilberry.
These models can then be used to look at the likelihood of
co-occurrence of the two species. Different thresholds can be
chosen for different purposes, for example to guide inspections or
control measures – the map on the left shows a threshold where the
predicted probability of both Rhododendron and bilberry is
greater than or equal to 30%. Threshold maps are important to
help make decisions on where control measures are most important,
and depending on the control chosen, where that control might be
sensitive.