IN SEARCH OF A RARE ORCHID

Overview

The objective of this analysis was to identify survey areas for the rare orchid species Spiranthes diluvialis in the southern Okanagan of British Columbia. A Multi-Criteria Evaluation (MCE) model was used to evaluate potential survey locations based on abiotic factors derived from a Digital Elevation Model (DEM).

 

Methodology

1. Used Structured Query Language (SQL) and the Editor toolbar to create features from BC Terrain Resource Information Management (TRIM) data necessary for the development of a Triangulated Irregular Network (TIN).
2. Created a TIN for the study area and converted the TIN to a Digital Elevation Model (DEM).
3. Calculated factors (elevation, slope, aspect) for Multi-Criteria Evaluation (MCE) analysis from the DEM.
4. Standardized the factor ranges.
5. Used an Analytic Hierarchy Process (AHP) calculator to determine weights for each factor based on botanical data specifying the relative importance of factors in determining the distribution of Spiranthes diluvialis. 
6. Used the Weighted Sum and Classification tools to apply the AHP results to develop a layer of potential survey areas.
7. Performed a sensitivity analysis with equal weighting for each factor to assess uncertainty in the MCE model and further refine potential survey locations.

 

Results

The overlay of the MCE and sensitivity analysis models produced a layer of  522 ha of suitable survey areas. True to the botanical data provided, the models identified low-slope, mid-high-elevation areas with a southern aspect as likely locations for Spiranthes diluvialis. The sensitivity analysis highlighted the sensitivity of the MCE model to the aspect factor, with the MCE model delineating survey areas at lower elevations and slopes as compared to the sensitivity analysis output. A survey of Spiranthes diluvialis in the study area should focus on the areas in red identified by both the MCE and the sensitivity analysis.