County Wildife Site Criteria for Cornwall Appendices

However, it is not a significant concern. This results from the fact that it is generally onlythe larger blocks that are split into smaller polygons, while the determination of the STC iscritically dependent on the number and size of the smaller blocks. An analysis of the CoastalSaltmarsh of the Lynher estuary illustrates this:Example: The LynherIf we look at the size of block above which 99% of all the habitat is included then the STCfor blocks is 0.25 ha, for polygons it is 0.23 ha; at the 98% level it is 0.41 ha for blocks and0.30 ha for polygons. Even at the 95% level it is 0.63 ha for blocks and 0.43 ha for polygons.Clearly, there is no great difference in dealing with polygons rather than blocks.The area-block relationshipThere is a general principle that the majority of any habitat is found in a few larger blocks.There are usually a lot of small blocks of any habitat, the total area of which is relativelysmall.Example: Lowland HeathlandIf we consider all Lowland Heathland blocks of 5 ha or more then 96% of the total area isincluded, but only 57% of the total number of blocks combine to produce that area. If wetake all blocks of 1 ha or more then 99.3% of the total area is included, but only 83% of thetotal number of blocks.Accordingly, even should we take 1 ha as a STC for Lowland Heathland then 17% of siteswould be lost (while including all but 0.7% of the total area). Another example is illustratedbelow.Example: the number of blocks for area of standing freshwater for each size.Here again, the majority of the blocks are very small.Fig 1The number of tetrads containing certain areas of standing water200180160140120No1008060402000.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0Area (ha)Accordingly, it is pointless to include any reference to the number of blocks in the initialSTC guidelines, but these will be referred to later under Area of Search (AOS). Thereforethe STC will be primarily based on the total area of the resource within the county.Setting the STCThere is no simple biological rule that enables a STC to be set. We will set the STC for anuncommon habitat at about 0.1% of the total area of that habitat in the county. The 0.1%criterion has no more biological justification than it accords with current thinking on whatconstitutes an ecologically sensible site. In our opinion, this figure will generally select sitesAppendix 2 – The Selection of Local Sites by SizeCounty Wildlife Site Criteria