Numerical Analyses - Raasay

 

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Frequency of Occurrence

Only one species is currently recorded from all 100 recording units on Raasay: Sagina procumbens.

Excluding the very small area of land in NG63, which has two recording units, a further twelve species are known from all 98 recording units:

Anthoxanthum odoratum Luzula campestris
Blechnum spicant Oxalis acetosella
Calluna vulgaris Potentilla erecta
Erica cinerea Prunella vulgaris
Galium saxatile Succisa pratensis
Juncus effusus Viola riviniana

The following chart shows the frequency of taxa in bands of recording units e.g. 61 taxa are known from at least 90 recording units.  There are 630 taxa in the dataset at 18 September 2014.

 

The large number of species known from fewer than 10 recording units reflects the introduced taxa and weeds found in the limited area under cultivation, as well as the rarer native species.

The full list of plants with frequencies is available from the author.

The Richest Recording Units

Number of Taxa

Recording Units

>300

2

250-299

3

200-249

21

150-199

38

100-149

31

<100

5

Total

100

The recording unit that includes Inverarish and West Suisnish is by some way the richest with 370 taxa at 18 September 2014. Next is the square containing Raasay House with 308.  This demonstrates the importance of human influence, though a significant part of this biodiversity results from introductions.

The other major sources of high taxa counts are habitat diversity and geology with the influence of the east coast lime being apparent in the diagram below.

 

Five recording units fall below 100 taxa: Holoman Island which is very small but falls into its own 1 km square, the northwest part of Eilean Tigh which again is small and is extremely exposed, the two tiny pieces of land in NG63 and one square in the middle of the moor which is just dull.

 

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