Riparian Forest Canopy and Soil Nutrient Cycling Responses to the Loss of Ash (Fraxinus spp. L) from Emerald Ash Borer (Agrilus planipennis Fairmaire) Infestations in Southern Ontario
This thesis examines the ecological impacts of an emerald ash borer (EAB) infestation on riparian forest habitats in Southern Ontario. From 2010 to 2015 there was 100% mortality of white, green, and black ash the study plots, and 33% mortality of blue ash. EAB caused about a 1.5-fold increase in overall openness of the riparian forest canopy, and significantly reduced the deposition of ash leaf litter. Ash regeneration displayed a negative relationship with ash tree density; this was attributed to greater competition by herbaceous vegetation that flourished in gaps created by dead ash. Analysis of forest canopy gaps (CG plots) created by dead ash in riparian forest plots and nearby closed canopy areas (CC plots) was conducted in newly infested areas (1-3 yrs; n=9) and old infestation areas (8-10 yrs; n=5). Nutrients of both litterfall flux and soil did not vary significantly between CG and CC plots. However, N concentration of soil solution was elevated in the CG plots of the new infestation and reduced in the old infestation. Herbaceous vegetation biomass in CG canopy sites at the older infestation was about 10 times higher than CC sites, and about 6 times higher in the new infestation. Collectively, my results indicate that effects of EAB on riparian canopy structure, ash leaf litter, and herbaceous vegetation biomass are substantial. However, the effects of EAB on biogeochemical cycles (N and C flux) in soil and soil water nutrients are undermined.