EDIT

Dominant-
Abundant-Frequent-Occasional-Rare

====

For abundance you could use organismQuantity in conjunction with organismQuantityType. Both are loosely defined, so just define the terms of your abundance scale in organismQuantityType and use the relevant term in organismQuantity. If you can restrict your terms to a more standard terminology such as DAFOR or BraunBlanquet, so much the better.
Regards
Quentin

===

http://jncc.defra.gov.uk/pdf/CSM_lowland_heathland.pdf (search in Text)

The following is a quantitative definition of
frequency, intended to assist with the assessment
of several of the heathland attributes. This
is a version of the well-known DAFOR scale which
has been adapted to the particular ch
aracteristics of lowland heathland:
•
Dominant:
the species appears at most (>60%) stops and it covers more than 50%

of each sampling unit.
•
Abundant:
species occurs regularly throughout a stand, at most (>60%) stops and

its cover is less than 50% of each sampling unit.
•
Frequent:
species recorded from 31-60% of stops.
•
Occasional:
species recorded from 11-30% of stops.
•
Rare:
species recorded from up to 10% of stops.

====

http://www.durhambiodiversity.org.uk/wp-content/uploads/2012/07/Coalfields-and-Lowlands-Project-Botanical-Surveys-Second-Report.pdf

===

http://aquaticcommons.org/4608/1/MPalmer.pdf (DAFOR rating (Dominant-
Abundant-Frequent-Occasional-Rare) http://aquaticcommons.org/4608/