Methods

    The initial variables used to perform the site suitability analysis were elevation, slope, and proximity to streams.  

    Upon inspection of the DEM, we noted that all of the specimens were located between 280 and 300 meters above sea level.  We used the reclassify tool to reclassify the DEM, and assigned a value of “1” to locations that fell within the afore-mentioned elevation range; all other locations were assigned a value of “0”.  Similarly, after noting that all of the specimens were located in relatively flat bottom lands with slopes between 0 and 8 degrees, we again used the reclassify tool to reclassify the slope layer (which we created from the DEM using the slope tool), and assigned a value of “1” to all locations with slopes between 0 and 8 degrees; all other locations were assigned a value of “0” (Figure 2).  

                            


                                            a.                                                                              b.
                                   
                               Figure 2. (a) Reclassified DEM layer and (b) reclassified slope layer

    Next, we used the euclidian distance tool to produce a raster layer depicting distance from streams in ten 10-meter classes.  We set the maximum distance to 100 meters.  The results revealed that 15 specimens were within 40 meters of a stream.  Of the remaining 2 specimens, 1 was 60 meters away from any stream, and 1 was 100 meters away.  Based on these observations, we once again used the reclassify tool to reclassify the euclidean distance raster layer, and assigned a value of “2” (most suitable) to cells located between 0 and 40 meters from a stream, and a value of “1” (somewhat-suitable) to cells located between 41 and 100 meters from a stream (Figure 3).

      

          














                                    a.                                                                                                                           b.

Figure 3. (a) Map depicting euclidean diastance away from the streams and (b) reclassified euclidean distance layer.

    Once we had reclassified all the layers, we used the raster calculator to produce a suitability map containing 4 classes of suitability values.  Locations that were most suitable received a value of “4”, and locations least suitable received a value of “1”.  The map revealed that the locations of 15 specimens were within the “4” range; the remaining 2 specimens were located within the “3” range (Figure 4).  

Figure 4.  Site Suitability Map

    After inspecting the site suitability map, it became apparent that large portions of the site which did not contain any young trees received suitability values of “4” (most suitable).  We noticed that the 17 specimens were clustered in a narrow, roughly north-south trending line along one of the streams.  However, we also noticed that young trees were largely absent in areas that received suitability values of “4” surrounding a second stream.  This fact suggested that some undetermined variable other than elevation, slope, or proximity to streams was causing recruitments to occur along one stream but not the other.  

    Based on evidence we uncovered in a previous study, we decided to add “proximity to Cheseboro Road” as a fourth variable to the suitability analysis equation.  Cheseboro Road runs along the north-south trending stream, around which most of the trees were clustered.  We digitized the road based on the aerial photo used as the base layer.  We used the euclidean distance tool to produce a raster layer depicting distance from the road in ten 10-meter classes, with the maximum distance set to 70 meters.  The results revealed that 16 of the specimens were within 20 meters of the road.  The remaining specimen was 70 meters from the road.  Based on these observations, we used the reclassify tool to assign values of “2” to cells located less than 30 meters from the road, and values of “1” to cells located between 31 and 70 meters from the road.

    We again used used the raster calculator to produce a suitability map.  This time we added our fourth variable (proximity to road) into the equation.  The resulting map revealed that cells with the highest suitability values clustered around the road, rather than the streams (Figure 5).  

                    Figure 5. Site Suitability Map with proximity to Chesebro Road included.