Abstract
Emerald ash borer (EAB) is an alien invasive species that is spreading across Canada and the United States killing ash trees. In riparian forests where ash may be abundant; loss of ash can induce significant structural changes; including the creation of canopy gaps; changes in light penetration; expansion of ground vegetation; and alteration of soil nitrogen and carbon cycling. In 2014 and 2015, we examined the effects of EAB-caused gaps in riparian forests on soil nutrient dynamics. Two sites with different infestation timelines, a “new” site (mortality in past 2–3 years) and an “old” site (infested 10 years previous) were selected to determine temporal differences in effects of canopy gaps created by ash loss on litterfall, herbaceous ground vegetation, and soil nutrient cycling. Within both sites, plots with clustered dead ash (canopy gap plots—CG) were paired with nearby plots of full canopy and no ash (canopy closed plots—CC), and differences between paired plots determined. Total litterfall was observed at all sites but was only significant at the new infestation site. Reductions in leaf litter deposition in CG plots resulted in reduced N and C flux to the forest floor but soil C and N concentrations, and nitrogen mineralization rates, were not significantly different between CG and CC plots. Nitrate concentration in soil solution was significantly greater in CG plots compared to CC plots at the new infestation sites but showed the opposite trend at the old infestation sites. Herbaceous ground vegetation biomass was significantly greater (up to 10×) in CG plots than in CC plots. Overall, despite changes to riparian forest canopy structure and litterfall, there was no significant difference in soil nutrient cycling between EAB-induced canopy gaps and closed canopy plots after 10 years, suggesting a high resilience of riparian forest soils to EAB infestation
Highlights
The ecological function of healthy riparian forest ecosystems is governed by a dynamic relationship between biotic and abiotic components [1]
Building on the study of Kreutzweiser et al [12], in the present study we examined the impact of canopy gap formation due to ash mortality on C and nutrient fluxes to the forest floor via litterfall, development of understory vegetation biomass, and soil nutrient cycling in streamside riparian areas
Our objective was to determine if gaps created by Emerald Ash Borer (EAB) in riparian forests disrupted the nutrient fluxes and cycling in soils in canopy gap (CG—gaps caused by ash mortality) locations compared to closed canopy (CC—minimal ash present) areas
Summary
The ecological function of healthy riparian forest ecosystems is governed by a dynamic relationship between biotic and abiotic components [1]. Disturbances by invasive species can disrupt the balance of functioning riparian forests by altering important biological and biogeochemical components [2]. Mortality of ash trees in riparian forests is of great concern due to the intimate role that these ecotonal forests play in mediating the flow of energy and materials to adjacent waterbodies and potentially the functioning of headwater streams whose metabolism is intimately influenced by autochthonous subsidies from terrestrial ecosystems [7,8,9]. Studies examining the impacts of ash loss in riparian terrestrial ecosystems are generally poorly represented in the literature, in relation to soil nutrient dynamics. Matthes et al [11]
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