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1. Elevated light levels reduce hemlock woolly adelgid infestation and improve carbon balance of infested eastern hemlock seedlings

   https://doi.org/10.1016/j.foreco.2016.11.028  

   Brantley, Steven T. ; Mayfield, Albert E. ; Jetton, Robert M. ; Miniat, Chelcy F. ; Zietlow, David R. ; Brown, Cindi L. ; Rhea, James R. ( February 2017 , Forest Ecology and Management)
2. Physiological responses of eastern hemlock (Tsuga canadensis) to light, adelgid infestation, and biological control: Implications for hemlock restoration

   https://doi.org/10.1016/j.foreco.2020.117903  

   Miniat, Chelcy Ford ; Zietlow, David R. ; Brantley, Steven T. ; Brown, Cindi L. ; Mayfield III, Albert E. ; Jetton, Robert M. ; Rhea, James R. ; Arnold, Paul ( March 2020 , Forest Ecology and Management)

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3. High Rainfall May Induce Fungal Attack of Hemlock Woolly Adelgid (Hemiptera: Adelgidae) Leading to Regional Decline

   https://doi.org/10.1093/ee/nvab125  

   Chandler, Jennifer L ; Elkinton, Joseph S ; Orwig, David A ( November 2021 , Environmental Entomology)

   Ross, Darrell (Ed.)

   Abstract Hemlock woolly adelgid (HWA; Adelges tsugae Annand (Hemiptera: Adelgidae)) is the cause of widespread mortality of Carolina and eastern hemlock (Tsuga caroliniana Engelmann and T. canadensis (L.) Carrière) throughout the eastern United States (U.S.). Since its arrival in the northeastern U.S., HWA has steadily invaded and established throughout eastern hemlock stands. However, in 2018, anecdotal evidence suggested a sharp, widespread HWA decline in the northeastern U.S. following above-average summer and autumn rainfall. To quantify this decline in HWA density and investigate its cause, we surveyed HWA density in hemlock stands from northern Massachusetts to southern Connecticut and analyzed HWA density and summer mortality in Pennsylvania. As native fungal entomopathogens are known to infect HWA in the northeastern U.S. and rainfall facilitates propagation and spread of fungi, we hypothesized high rainfall facilitates fungal infection of aestivating nymphs, leading to a decline in HWA density. We tested this hypothesis by applying a rain-simulation treatment to hemlock branches with existing HWA infestations in western MA. Our results indicate a regional-scale decline and subsequent rebound in HWA density that correlates with 2018 rainfall at each site. Experimental rain treatments resulted in higher proportions of aestivating nymphs with signs of mortality compared to controls. In conjunction with no evidence of increased mortality from extreme winter or summer temperatures, our results demonstrate an indirect relationship between high rainfall and regional HWA decline. This knowledge may lead to better prediction of HWA population dynamics. 

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4. Property value effects of the Hemlock wooly adelgid infestation in New England, U.S.A.

   https://doi.org/10.1016/j.ecolecon.2022.107354  

   Li, Xiaoshu ; Boyle, Kevin J. ; Preisser, Evan L. ; Holmes, Thomas P. ; Orwig, David ( April 2022 , Ecological Economics)
5. Detecting Change in Forest Structure with Simulated GEDI Lidar Waveforms: A Case Study of the Hemlock Woolly Adelgid (HWA; Adelges tsugae) Infestation

   https://doi.org/10.3390/rs12081304  

   Boucher, Peter ; Hancock, Steven ; Orwig, David ; Duncanson, Laura ; Armston, John ; Tang, Hao ; Krause, Keith ; Cook, Bruce ; Paynter, Ian ; Li, Zhan ; et al ( April 2020 , Remote Sensing)

   The hemlock woolly adelgid (HWA; Adelges tsugae) is an invasive insect infestation that is spreading into the forests of the northeastern United States, driven by the warmer winter temperatures associated with climate change. The initial stages of this disturbance are difficult to detect with passive optical remote sensing, since the insect often causes its host species, eastern hemlock trees (Tsuga canadensis), to defoliate in the midstory and understory before showing impacts in the overstory. New active remote sensing technologies—such as the recently launched NASA Global Ecosystem Dynamics Investigation (GEDI) spaceborne lidar—can address this limitation by penetrating canopy gaps and recording lower canopy structural changes. This study explores new opportunities for monitoring the HWA infestation with airborne lidar scanning (ALS) and GEDI spaceborne lidar data. GEDI waveforms were simulated using airborne lidar datasets from an HWA-infested forest plot at the Harvard Forest ForestGEO site in central Massachusetts. Two airborne lidar instruments, the NASA G-LiHT and the NEON AOP, overflew the site in 2012 and 2016. GEDI waveforms were simulated from each airborne lidar dataset, and the change in waveform metrics from 2012 to 2016 was compared to field-derived hemlock mortality at the ForestGEO site. Hemlock plots were shown to be undergoing dynamic changes as a result of the HWA infestation, losing substantial plant area in the middle canopy, while still growing in the upper canopy. Changes in midstory plant area (PAI 11–12 m above ground) and overall canopy permeability (indicated by RH10) accounted for 60% of the variation in hemlock mortality in a logistic regression model. The robustness of these structure-condition relationships held even when simulated waveforms were treated as real GEDI data with added noise and sparse spatial coverage. These results show promise for future disturbance monitoring studies with ALS and GEDI lidar data. 

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