Objective 4:To apply the models to determine and compare the worst case and best case scenarios for spread of Hemlock Woolly Adelgid and vulnerability of Eastern Hemlock
The model developed was also applied to different climate scenarios in order to evaluate spread under high and low climate change schemes. This analysis focused on the RCP4.5 and RCP8.5 climate schemes for 2011-2040. The first layer showing mean winter temperatures from the Representative Concentration Pathway 4.5 for 2011-2040 was based on a scenario which incorporated a combination of long-term greenhouse gas emissions, land use, land cover, and short-lived species that would lead to a stabilization of radiative forcing at 4.5 Watts by the year 2100 (Thomson et al. 2012). This scenario would be representative of the best case scenario for the future spread, as emissions would be lower and climate change less drastic, allowing for a more limited spread. RCP8.5, or Representative Concentration Pathway 8.5, was similar to 4.5 but represented a scenario in which radiative forcing is stabilized at 8.5 Watts by 2100, instead of 4.5 (Thomson et al. 2012). This high emissions scenario was hypothesized to lead to a more extensive northward spread of Hemlock Woolly Adelgid spread due to warmer winter temperatures.
The previously developed multi-criteria evaluation model was applied using distance to roads, road size, distance from HWA, and the RCP4.5 mean winter temperature layer to produce the susceptibility to spreading under RCP4.5:
Suitability = Temperature constraint*((0.1136)+(distance from roads)+(0.0753)*(road size)+(0.5502)(distance from HWA)+(0.2612)(RCP4.5 mean winter temperature)).
This created an output showing areas where the Hemlock Woolly Adelgid were most likely to spread under the RCP4.5 climate scenario.
The model was then used again with the RCP8.5 temperature data to produce the second susceptibility to spread:
Suitability= Temperature constraint*((0.1136)+(distance from roads)+(0.0753)*(road size)+(0.5502)(distance from HWA)+(0.2612)(RCP8.5 mean winter temperature))
Both suitability outputs were compared to determine the extent of the effect different climate change projection scenarios would have on the spread of Hemlock Woolly Adelgid and consequently the vulnerability of hemlock groves in Eastern Canada. This comparison was conducted by subtracting the susceptibility of spread under RCP4.5 from the spread under RCP8.5 using the raster calculator tool:
Difference in spread = Suitability RCP8.5 - Suitability RCP4.5