Find further information on the Conservation of Freshwater Ecosystem Values (CFEV) Program and its data at www.dpipwe.tas.gov.au/cfev.
TitleSaltmarsh naturalness score
CustodianWater and Marine Resources Division, Department of Primary Industries, Parks, Water and Environment
CreatorSteve Carter, Environmental Dynamics
DescriptionAn index which rates the relative ‘naturalness’ or condition of saltmarshes based on a selection of input variables.
Input data
Lineage
The saltmarsh condition assessment was conducted by integrating data collected from aerial photographs (sometimes in conjunction with other spatial data) using expert rule systems to produce an overall Naturalness score (N-score). Information on expert rules systems can be found in Appendix 3 of the CFEV Project Technical Report. Figure 1 illustrates all the inputs that were either directly or indirectly used to generate the N-score for saltmarshes, indicating those variables that were calculated using expert rule systems.
Figure 1. Flow-chart outlining data used in the saltmarshes condition assessment to derive a Naturalness score (N-score). Note: variables were combined using expert rule systems where indicated.
Variables used in the condition assessment for saltmarshes were limited to those that could be detected from aerial photographs. Creating the N-score for saltmarshes involved multiple cascading levels of expert rule systems. These were focused around the idea that impacts can be from within the saltmarsh or from the adjoining land. Adjacent lands are those considered to be within 100 m of the saltmarsh.
The final step in the saltmarshes condition assessment is described in more detail here. The N-score was calculated for saltmarshes using the outputs from two expert rule systems which described the impacts within and impacts adjacent to saltmarshes. The definition table is shown below (see ‘Assigning values to ecosystem spatial units’). Impacts within saltmarshes was considered to have a greater influence on the final N-score than impacts adjacent to saltmarshes.
The size (area) of the saltmarsh (big ≥20 ha, small ≤10 ha) was used as a context for the condition assessment as impacts adjacent to saltmarshes are generally going to have greater effect on smaller saltmarshes than larger ones.
Date createdJanuary 2005
Scale and coverage1:25 000; Statewide
Column headingSM_NSCORE
Type of dataContinuous but has been converted to categorical format (see Table 2).
Number of classes3
Assigning values to ecosystem spatial units
An N-score (0 = poor condition – 1 = good condition) was assigned to saltmarshes spatial units as SM_NSCORE using the expert rule system shown as a definition table in Table 1. A context was set to take into account the size of the saltmarsh area (i.e. whether the saltmarsh is big (≥20 ha) or small ≤10 ha). An example of applying the rules is that if the saltmarsh area has a HIGH score for impacts adjacent to saltmarshes and a LOW score for impacts within saltmarshes, and the saltmarsh is big, then assign a score of 0.3). Using fuzzy logic enables input data and output results to be continuous rather than categorical as implied here (i.e. inputs and output data can range on a continuous scale between 0 and 1, and the process of executing the expert rule system will determine its membership as being HIGH or LOW) (refer to Appendix 3 of the CFEV Project Technical Report for more information on expert rules systems).
Table 1. Expert rules system definition table for the naturalness sub-index for saltmarshes.
Impacts adjacent to saltmarshes (SM_IMADJ) | Impacts within saltmarshes (SM_IMWIN) | Naturalness score (SM_NSCORE) where Area (SM_AREA) = Big | Naturalness score (SM_NSCORE) where Area (SM_AREA) = Small |
H | H | 1 | 0 |
H | L | 0.3 | 0.3 |
L | H | 0.7 | 0.5 |
L | L | 0 | 0 |
The saltmarshes spatial data layer has the continuous naturalness data categorised according to Table 2. The categorical data was used for reporting and mapping purposes.
Table 2. Naturalness categories for saltmarshes.
Category | Min to max values |
Low | 0 to 0.6 |
Medium | >0.6 to 0.85 |
High | >0.85 to 1 |
CFEV assessment framework hierarchy