Range expansion and population dynamics of co-occurring invasive herbivores

Preisser, Evan L.; Lodge, Alexandra G.; Orwig, David A.; Elkinton, Joseph S.

doi:10.1007/s10530-007-9123-z

Cited by 56 publications

(47 citation statements)

References 33 publications

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“…The experiment took place in Cadwell Forest (Petersham, Massachusetts, USA), a research forest managed by the University of Massachusetts. Although this location is south of the current northern range limit of both HWA and EHS (Preisser et al 2008), repeated surveys of the forest itself have found neither insect (J. Elkinton, unpublished data). Because HWA and EHS occur in forests to both the north and south of Cadwell Forest, we were given permission to carry out our experiment.…”

Section: Experimental Designmentioning

confidence: 95%

“…In light of research showing that landscape-level hemlock health has not declined as quickly as initially predicted (Preisser et al 2008), we hypothesized that for HWA-infested eastern hemlocks, the benefit of EHS co-infestation (reduced HWA density via exploitative competition) outweighs the resourcerelated costs of EHS presence. We predicted that plant growth should be highest in the control, but that plant growth in the HWA þ EHS treatment should be greater than in the HWA-only treatment but less than in the EHS-only treatment.…”

Section: Introductionmentioning

confidence: 92%

“…The high degree of HWA-induced hemlock mortality led to widespread fear that HWA would rapidly extirpate hemlocks from its invaded range (Orwig and Foster 1998), a prediction that appears generally accurate (reviewed in Ward et al 2004). In New England, however, hemlock mortality appears to be occurring much more slowly than predicted (Preisser et al 2008). Although HWA overwintering mortality undoubtedly plays a role in reducing hemlock losses in the north (Parker et al 2002), another potential (but nonexclusive) explanation involves the recent rapid range expansion of a second introduced hemipteran, the elongate hemlock scale Fiorinia externa (EHS).…”

Section: Introductionmentioning

confidence: 99%

“…Although EHS can reduce hemlock growth and may be capable of killing already-stressed trees (McClure 1980a), this insect is generally considered far less dangerous than HWA. The gloomiest predictions of hemlock mortality were made in the mid-1990s; since then, however, research assessing changes in insect density and forest health in 142 southern New England hemlock stands from 1997 through 2005 found that HWA densities have substantially declined and many hemlock stands still appear relatively healthy (Preisser et al 2008). The same survey found dramatic increases in both the invaded range and stand-level density of EHS, which was present in 22 out of 79 sampled Connecticut stands in 1997 but had spread to all 79 stands by 2005.…”

Section: Introductionmentioning

confidence: 99%

“…The same survey found dramatic increases in both the invaded range and stand-level density of EHS, which was present in 22 out of 79 sampled Connecticut stands in 1997 but had spread to all 79 stands by 2005. The rapid rise of this second invasive herbivore, coupled paradoxically with an apparent decrease in the rate of hemlock mortality, led to the suggestion that EHS might somehow be altering tree mortality rates through its interactions with HWA (Preisser et al 2008). Assessing the importance of the HWA-EHS interaction requires an understanding of the nature and consequences of this interaction for both invasive herbivores and their shared hemlock host.…”

Section: Introductionmentioning

confidence: 99%

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Exploitative Competition Between Invasive Herbivores Benefits a Native Host Plant

Preisser

Elkinton

2008

Ecology

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Abstract. Although biological invasions are of considerable concern to ecologists, relatively little attention has been paid to the potential for and consequences of indirect interactions between invasive species. Such interactions are generally thought to enhance invasives' spread and impact (i.e., the ''invasional meltdown'' hypothesis); however, exotic species might also act indirectly to slow the spread or blunt the impact of other invasives. On the east coast of the United States, the invasive hemlock woolly adelgid (Adelges tsugae, HWA) and elongate hemlock scale (Fiorinia externa, EHS) both feed on eastern hemlock (Tsuga canadensis). Of the two insects, HWA is considered far more damaging and disproportionately responsible for hemlock mortality. We describe research assessing the interaction between HWA and EHS, and the consequences of this interaction for eastern hemlock. We conducted an experiment in which uninfested hemlock branches were experimentally infested with herbivores in a 2 3 2 factorial design (either, both, or neither herbivore species). Over the 2.5-year course of the experiment, each herbivore's density was ;30% lower in mixed-vs. single-species treatments. Intriguingly, however, interspecific competition weakened rather than enhanced plant damage: growth was lower in the HWAonly treatment than in the HWA þ EHS, EHS-only, or control treatments. Our results suggest that, for HWA-infested hemlocks, the benefit of co-occurring EHS infestations (reduced HWA density) may outweigh the cost (increased resource depletion).

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Section: Experimental Designmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Exploitative Competition Between Invasive Herbivores Benefits a Native Host Plant

Preisser

Elkinton

2008

Ecology

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When a foundation crumbles: forecasting forest dynamics following the decline of the foundation species Tsuga canadensis

et al. 2017

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Abstract. In the forests of northeastern North America, invasive insects and pathogens are causing major declines in some tree species and a subsequent reorganization of associated forest communities. Using observations and experiments to investigate the consequences of such declines are hampered because trees are long-lived. Simulation models can provide a means to forecast possible futures based on different scenarios of tree species decline, death, and removal. Such modeling is particularly urgent for species such as eastern hemlock (Tsuga canadensis), a foundation species in many northeastern forest regions that is declining due to the hemlock woolly adelgid (Adelges tsugae). Here, we used an individual-based forest simulator, SORTIE-ND, to forecast changes in forest communities in Central Massachusetts over the next 200 yr under a range of scenarios: a no-adelgid, status quo scenario; partial resistance of hemlock to the adelgid; adelgid irruption and total hemlock decline over 25 yr, adelgid irruption and salvage logging of hemlock trees; and two scenarios of preemptive logging of hemlock and hemlock/white pine. We applied the model to six study plots comprising a range of initial species mixtures, abundances, and levels of hemlock dominance. Simulations indicated that eastern white pine, and to a lesser extent black birch and American beech, would gain most in relative abundance and basal area following hemlock decline. The relative dominance of these species depended on initial conditions and the amount of hemlock mortality, and their combined effect on neighborhood-scale community dynamics. Simulated outcomes were little different whether hemlock died out gradually due to the adelgid or disappeared rapidly following logging. However, if eastern hemlock were to become partially resistant to the adelgid, hemlock would be able to retain its dominance despite substantial losses of basal area. Our modeling highlights the complexities associated with secondary forest succession due to ongoing hemlock decline and loss. We emphasize the need both for a precautionary approach in deciding between management intervention or simply doing nothing in these declining hemlock forests, and for clear aims and understanding regarding desired community-and ecosystem-level outcomes.

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Chronic impacts of invasive herbivores on a foundational forest species: a whole‐tree perspective

Wilson

Schaeffer

Hickin

et al. 2018

Ecology

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Forests make up a large portion of terrestrial plant biomass, and the long-lived woody plants that dominate them possess an array of traits that deter consumption by forest pests. Although often extremely effective against native consumers, invasive species that avoid or overcome these defenses can wreak havoc on trees and surrounding ecosystems. This is especially true when multiple invasive species co-occur, since interactions between invasive herbivores may yield non-additive effects on the host. While the threat posed by invasive forest pests is well known, long-term field experiments are necessary to explore these consumer-host interactions at appropriate spatial and temporal scales. Moreover, it is important to measure multiple variables to get a "whole-plant" picture of their combined impact. We report the results of a 4-yr field experiment addressing the individual and combined impacts of two invasive herbivores, the hemlock woolly adelgid (Adelges tsugae) and elongate hemlock scale (Fiorinia externa), on native eastern hemlock (Tsuga canadensis) in southern New England. In 2011, we planted 200 hemlock saplings into a temperate forest understory and experimentally manipulated the presence/absence of both herbivore species; in 2015, we harvested the 88 remaining saplings and assessed plant physiology, growth, and resource allocation. Adelgids strongly affected hemlock growth: infested saplings had lower above/belowground biomass ratios, more needle loss, and produced fewer new needles than control saplings. Hemlock scale did not alter plant biomass allocation or growth, and its co-occurrence did not alter the impact of adelgid. While both adelgid and scale impacted the concentrations of primary metabolites, adelgid effects were more pronounced. Adelgid feeding simultaneously increased free amino acids local to feeding sites and a ~30% reduction in starch. The cumulative impact of adelgid-induced needle loss, manipulation of nitrogen pools, and the loss of stored resources likely accelerates host decline through disruption of homeostatic source-sink dynamics occurring at the whole-plant level. Our research stresses the importance of considering long-term impacts to predict how plants will cope with contemporary pressures experienced in disturbed forests.

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Range expansion and population dynamics of co-occurring invasive herbivores

Cited by 56 publications

References 33 publications

Exploitative Competition Between Invasive Herbivores Benefits a Native Host Plant

Exploitative Competition Between Invasive Herbivores Benefits a Native Host Plant

When a foundation crumbles: forecasting forest dynamics following the decline of the foundation species Tsuga canadensis

Chronic impacts of invasive herbivores on a foundational forest species: a whole‐tree perspective

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