The MCE equation shown below was applied to the data to determine what areas are susceptible to the spread of Hemlock Woolly Adelgid.
MCE equation: Constraints*(Weight1Criteria1 + Weight2Criteria2 + Weight3Criteria3 + Weight4Criteria4)
So Susceptibility to Spread = Temperature constraint*((0.1136)+(distance from roads)+(0.0753)*(road size)+(0.5502)*(distance from HWA)+(0.2612)*(temperature))
In order to determine the weights of each criterion that would be included in the multi-criteria evaluation, a pairwise comparison table was used and is shown in Table 3. Distance from current Hemlock Woolly Adelgid was determined to be the most significant factor in determining future spread since it will most easily spread to Hemlocks in close proximity to affected trees. The second most important was temperature since this factor determines what range the species can survive in. Third and fourth most important were the distance from roads followed by road size.
Table 3: Pairwise comparison for Hemlock Woolly Adelgid Spread
| |
Pairwise Ranks |
|
|
|
Individual Ranks |
|
|
|
Total Weights |
W*Sum |
CV |
| |
Distance From Roads |
Road Type |
Distance From HWA |
Temperature |
Distance From Roads |
Road Type |
Distance From HWA |
Temperature |
|
|
|
| Distance From Roads |
1 |
3 |
1/7 |
1/5 |
0.0750 |
0.25 |
0.0852 |
0.0442 |
0.1136 |
1.5143 |
2.9871 |
| Road Type |
1/3 |
1 |
1/5 |
1/3 |
0.0250 |
0.0833 |
0.1193 |
0.0736 |
0.0753 |
0.9036 |
5.0059 |
| Distance From HWA |
7 |
5 |
1 |
3 |
0.5251 |
0.4167 |
0.5966 |
0.6623 |
0.5502 |
0.9222 |
4.9049 |
| Temperature |
5 |
3 |
1/3 |
1 |
0.3751 |
0.25 |
0.1989 |
0.2208 |
0.2612 |
1.1832 |
3.8229 |
| Sum |
13.33 |
12 |
1.6762 |
4.53 |
1 |
1 |
1 |
1 |
1 |
4.5233 |
|
Consistency Ratio:
λ = (2.9871 + 5.0059 + 4.9049 + 3.8229) / 4 = 4.1802
CI = (4.1802 - 4) / (4 - 1) = 0.0601
CR = CI / RI = 0.0601 / 0.9 = 0.06678
Since the value was less than 0.10, the pairwise logic was considered to be consistent.
After the MCE model yielded susceptibility to spreading, this layer was multiplied by Hemlock Density using the raster calculator tool to determine the vulnerability of Eastern Hemlock to the spread: Vulnerability= (Hemlock Density)*(Susceptibility to Spread).
Further spatial analysis was then conducted to determine the difference in spread between the two climate scenarios using the raster calculator tool to subtract one climate scenario from the other. In addition, Moran's I was used to confirm the presence of hot spots of vulnerability and the Optimized Hot Spot tool was used to identify these hot spots. The complete process used for the analysis is outlined in a flow chart in Figure 3.
Figure 3. Steps for MCE model process
The areas with the greatest vulnerability are where Eastern Hemlocks are most likely to be affected by Hemlock Woolly Adelgid.
