The CFEV program has defined natural condition as being the same as would have been present prior to European settlement.
The CFEV variable that rates condition is termed the Naturalness score or N-score and ecosystem features that are in good condition are given N-scores closer to 1 (high). Severely impaired sites are given scores closer to 0 (low). The CFEV database contains an assessment of condition for every ecosystem spatial unit (e.g. each wetland, each lake or each river section) dealt with by the program (results of N-score for rivers shown in map below). This is used as an input when assigning RCV.
A natural, healthy ecosystem can be degraded by a broad range of impacts. The CFEV program recognises that these will have different strengths but will all add up to give an overall amount of degradation. To reflect this, the N-score was calculated using a variety of data sets and expert rules that produce an overall assessment of condition. Different ecosystems are sensitive to different types of impacts, so the condition variables that are used in the calculation of the N-score are different for each different ecosystem theme. An example is given below, for rivers.A flow chart showing all of input variables integrated to provide an overall N-score for a river section.
Flow charts listing the different condition variables used in the CFEV condition assessments and how they are combined for all the different ecosystems can be found in the CFEV assessment framework summary.
(on the CFEV Resources page)