<p>  </p> <p>Invasive species are a prominent problem throughout the world due to the high economic and ecological impact they have on environments. The spongy moth, <em>Lymantria dispar</em>, is a well-known and intensely studied invasive species within the United States because of the high environmental (<em>e.g.</em>, defoliation) and economic (<em>e.g.</em>, management efforts) costs. Originally introduced in Massachusetts in 1869 their range now covers much of the Northeast and Midwest, with the potential to disperse much further. </p> <p><br></p> <p>The goal of this study is to determine how the landscape has influenced <em>L. dispar</em>’s invasion rate through least-cost resistance modeling. Resistance modeling is a technique that combines the biology of <em>L. dispar </em>and landscape connectivity to potentially explain the invasion rate. Landscape connectivity has varying effects on invasion dynamics depending on the spatial scale. Monitoring efforts for <em>L. dispar</em> have occurred at a small spatial scale throughout the entire range for many years, which now provides the opportunity to look at invasion dynamics at small spatial scales. Identifying the landscape’s influence on invasion dynamics at these scales can assist in targeting management efforts to areas that have a high likelihood of being invaded soon based on the landscape connectivity within the area. This targeted management strategy can potentially help to slow <em>L. dispar</em>’s establishment and dispersal ability and reduce management and monitoring costs.</p>

Temperate forests are an important global carbon sink. However, various environmental disturbances can impact carbon sequestration capabilities of these forests. In 2021, a record-breaking defoliation, caused by the spongy moth (Lymantria dispar L., formerly knows as the gypsy moth) occurred in eastern North America. In this study, we assess the impact of this spongy moth defoliation on carbon uptake in a mature oak-dominated temperate forest in the Great Lakes region in Canada, using eddy covariance flux data from 2012 to 2022. The forest is more than 90 years old and known as CA-TPD site in the AmeriFlux and global FLUXNET networks. Study results showed that prior to spongy moth defoliation the forest was a carbon sink with mean annual gross ecosystem productivity (GEP) of 1,367 ± 104, ecosystem respiration (RE) of 1,201 ± 145 and, net ecosystem productivity (NEP) of 197 ± 74 g C m−2 yr−1 over the 2012–2020 period. However, due the defoliation in the early growing season in 2021, GEP declined to 959 g C m-2 yr-1 and RE increased to 1,345 g C m-2 yr-1 causing the forest to became a large source of carbon with annual NEP of -351 g C m-2 yr−1. This large decline in annual NEP was a result of both reduced GEP (30%) and elevated RE (12%). However, in 2022, forest carbon fluxes recovered to pre-infestation levels, with a GEP value of 1,671 g C m-2 yr-1, an RE value of 1,287 g C m-2 yr-1, and an NEP value of 298 g C m-2 yr-1, indicating that the forest was once again a large carbon sink. This research demonstrates that major transient natural disturbances such as the 2021 spongy moth defoliation can have a significant impact on forest carbon dynamics in a future warmer climate. The extent to which North American temperate forests will remain a major carbon sink will depend on the severity and intensity of these disturbance events and rate of recovery of forests following the disturbance. / Thesis / Master of Science (MSc) / Temperate deciduous forests play an important role in carbon sequestration from the atmosphere. However, the impact of climate change, extreme weather, and disturbance events can alter the extent to which these forests sequester carbon, in some cases shifting their role from being a carbon sink to becoming a carbon source to the atmosphere. In 2021, a spongy moth infestation severely defoliated a mature oak-dominated temperate forest north of Lake Erie, Ontario, Canada, turning the forest from a carbon sink to a carbon source. Our analysis indicates that meteorological conditions during the early spring might have influenced the severity of this infestation. Specifically, the prevalence of dry and warm weather conditions enabled the moth to survive and thrive longer. This study shows the significant influence of natural disturbances on forest carbon dynamics as temperatures continue to rise due to climate change. The future role forests play in carbon sequestration will be determined by the severity of disturbance events and the effectiveness of forests to recover in the aftermath of these events.