Hemlock Woolly Adelgid in New England Forests: Canopy Impacts Transforming Ecosystem Processes and Landscapes

Eastern hemlock (Tsuga canadensis) is a foundation species in eastern North American forests. Because eastern hemlock is a foundation species, it often is assumed that the diversity of associated species is high. However, the herbaceous layer of eastern hemlock stands generally is sparse, species-poor, and lacks unique species or floristic assemblages. The rapidly spreading, nonnative hemlock woolly adelgid (Adelges tusgae) is causing widespread death of eastern hemlock. Loss of individual hemlock trees or whole stands rapidly leads to increases in species richness and cover of shrubs, herbs, graminoids, ferns, and fern-allies. Naively, one could conclude that the loss of eastern hemlock has a net positive effect on biodiversity. What is lost besides hemlock, however, is landscape-scale variability in the structure and composition of the herbaceous layer. In the Harvard Forest Hemlock Removal Experiment, removal of hemlock by either girdling (simulating adelgid infestation) or logging led to a proliferation of early-successional and disturbance-dependent understory species. In other declining hemlock stands, nonnative plant species expand and homogenize the flora. While local richness increases in former eastern hemlock stands, between-site and regional species diversity will be further diminished as this iconic foundation species of eastern North America succumbs to hemlock woolly adelgid.

Section: The Response Of the Herbaceous Layer To Experimental Removalmentioning

confidence: 81%

Section: The Harvard Forest Hemlock Removal Experimentsmentioning

confidence: 99%

Foundation Species Loss and Biodiversity of the Herbaceous Layer in New England Forests

Ellison

Plotkin

Khalid

2015

“…Eastern hemlock (Tsuga canadensis L.) infested with Hemlock woolly adelgid (Adelges tsugae A.) showed an increased abundance of epiphytic microorganisms [1]. Bacteria can have parasitic, commensal and mutualistic interactions with trees [61].…”

Section: Insect Outbreaks Increase Phyllosphere Bacteria Colonizationmentioning

confidence: 99%

“…Organic input into the soil increases with outbreaks of tree-canopy defoliating insects, through insect feces, cadavers, litter and other plant material [1][2][3]. This results in high amounts of labile C and extractable N [4][5][6], which can increase mineralization rates [7,8].…”

Section: Introductionmentioning

confidence: 99%

The Abundance of Fungi, Bacteria and Denitrification Genes during Insect Outbreaks in Scots Pine Forests

Grüning

Beule

Meyer

et al. 2018

Abstract:Outbreaks of defoliating insects may affect microbial populations in forests and thereby mass balances and ecosystem functioning. Here, we investigated the microbial dynamics in Scots pine (Pinus sylvestris L.) forests during outbreaks of the nun moth (Lymantria monacha L.) and the pine-tree lappet (Dendrolimus pini L.). We used real-time PCR (polymerase chain reaction) to quantify genes that characterize bacterial and fungal abundance and the denitrification processes (nirK, nirS, nosZ clades I and II) in different forest compartments and we analyzed the C and N content of pine needles, insect feces, larvae, vegetation layers, organic layers, and mineral soil horizons. The infestation of the nun moth increased the bacterial abundance on pine needles, in the vegetation layer, and in the upper organic layer, while fungal populations were increased in the vegetation layer and upper organic layer during both outbreaks. In soil, the abundance of nirK increased after insect defoliation, while the C/N ratios decreased. nosZ clades I and II showed variable responses in different soil layers and to different defoliating insects. Our results illustrate changes in the microbial populations in pine forests that were infested by defoliating insects and changes in the chemical soil properties that foster these populations, indicating a genetic potential for increased soil N 2 O emissions during the defoliation peak of insect outbreak events.

“…Tsuga canadensis has historically been a common component in forests in the eastern U.S. although recently the species has been experiencing a decline due to Adelges tsugae (hemlock woolly adelgid, HWA)-an invasive, aphid-like pest introduced to the United States from Asia [8]. HWA can be found in 15 states along the eastern seaboard from Georgia to Maine [9].Albani et al [10] predict that HWA will continue to move northward and will be established throughout Tsuga canadensis' range in Maine over the next 30 years.…”

Section: Introductionmentioning

confidence: 99%

Projected Future Distribution of Tsuga canadensis across Alternative Climate Scenarios in Maine, U.S

Dunckel

Weiskittel

Fiske

2017

Climate change is having an impact on forest ecosystems around the world and is expected to alter the suitable habitat of individual tree species. Forest managers require resources about potential impacts of climate change at the regional scale to aid in climate mitigation efforts. By understanding the geographic distribution of changes in suitable habitat, migration corridors can be identified for conservation and active management. With the increased availability of climate projection data, ancillary Geographic Information Systems data, and field observations, modeling efforts at the regional scale are now possible. Here, we modeled and mapped the continuous distribution of Tsuga canadensis throughout the state of Maine at the regional scale(30 m) with high precision (89% of pixels had a coefficient of variation ≤ 4.0%). The random forest algorithm was used to create a strong prediction of suitable habitat for the years 2050 and 2100 from both high and low emission climate projections. The results clearly suggest a significant gain in suitable habitat for Tsuga canadensis range with a general northwest expansion.