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Outbreaks by canopy-feeding geometrid moth cause state-dependent shifts in understorey plant communities.

Karlsen SR, Jepsen JU, Odland A, Ims RA, Elvebakk A - Oecologia (2013)

Bottom Line: Prior to the moth outbreak, the plots divided into two oligotrophic and one eutrophic plant community.In the spatially most widespread communities, oligotrophic dwarf shrub birch forest, dominance by the allelopathic dwarf shrub Empetrum nigrum ssp. hermaphroditum, was effectively broken and replaced by a community dominated by the graminoid Avenella flexuosa, in a manner qualitatively similar to the effect of wild fires in E. nigrum communities in coniferous boreal forest further south.Our findings reveal that the impact of moth outbreaks on the northern boreal birch forest system is highly initial-state dependent, and that the widespread oligotrophic communities have a low resistance to such disturbances.

View Article: PubMed Central - PubMed

Affiliation: Norut, Northern Research Institute Tromsø, Tromsø Science Park, P.O. Box 6434, 9294, Tromsø, Norway, stein-rune.karlsen@norut.no.

ABSTRACT
The increased spread of insect outbreaks is among the most severe impacts of climate warming predicted for northern boreal forest ecosystems. Compound disturbances by insect herbivores can cause sharp transitions between vegetation states with implications for ecosystem productivity and climate feedbacks. By analysing vegetation plots prior to and immediately after a severe and widespread outbreak by geometrid moths in the birch forest-tundra ecotone, we document a shift in forest understorey community composition in response to the moth outbreak. Prior to the moth outbreak, the plots divided into two oligotrophic and one eutrophic plant community. The moth outbreak caused a vegetation state shift in the two oligotrophic communities, but only minor changes in the eutrophic community. In the spatially most widespread communities, oligotrophic dwarf shrub birch forest, dominance by the allelopathic dwarf shrub Empetrum nigrum ssp. hermaphroditum, was effectively broken and replaced by a community dominated by the graminoid Avenella flexuosa, in a manner qualitatively similar to the effect of wild fires in E. nigrum communities in coniferous boreal forest further south. As dominance by E. nigrum is associated with retrogressive succession the observed vegetation state shift has widespread implications for ecosystem productivity on a regional scale. Our findings reveal that the impact of moth outbreaks on the northern boreal birch forest system is highly initial-state dependent, and that the widespread oligotrophic communities have a low resistance to such disturbances. This provides a case for the notion that climate impacts on arctic and northern boreal vegetation may take place most abruptly when conveyed by changed dynamics of irruptive herbivores.

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The cover abundance of individual species before (open symbols) and after (closed symbols) the moth outbreak. Cover abundances are given as mean for all plots in which a given species is present within a given community. a Crowberry birch forest, b bilberry birch forest, c low-herb birch forest. Cover abundances with non-overlapping SDs before and after the outbreak are connected by arrows. Chamae. suecicum Chamaepericlymenum suecicum
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Fig5: The cover abundance of individual species before (open symbols) and after (closed symbols) the moth outbreak. Cover abundances are given as mean for all plots in which a given species is present within a given community. a Crowberry birch forest, b bilberry birch forest, c low-herb birch forest. Cover abundances with non-overlapping SDs before and after the outbreak are connected by arrows. Chamae. suecicum Chamaepericlymenum suecicum

Mentions: The significant shifts in understorey community composition observed in the two oligotrophic communities were mainly due to large changes in abundance of a limited number of plant species (Fig. 5). The two oligotrophic communities experienced a drastic transition from dominance by dwarf shrubs (V. myrtillus, B. nana and E. nigrum) to dominance by the grass A. flexuosa. In addition, the low herb C. suecicum experienced a large decrease in cover in both communities (Fig. 5a, b). C. suecicum is defoliated by larvae at outbreak densities (authors’ observations). None of the species in the eutrophic community (Fig. 5c) showed significant changes in abundance in response to the moth outbreak.Fig. 5


Outbreaks by canopy-feeding geometrid moth cause state-dependent shifts in understorey plant communities.

Karlsen SR, Jepsen JU, Odland A, Ims RA, Elvebakk A - Oecologia (2013)

The cover abundance of individual species before (open symbols) and after (closed symbols) the moth outbreak. Cover abundances are given as mean for all plots in which a given species is present within a given community. a Crowberry birch forest, b bilberry birch forest, c low-herb birch forest. Cover abundances with non-overlapping SDs before and after the outbreak are connected by arrows. Chamae. suecicum Chamaepericlymenum suecicum
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3824357&req=5

Fig5: The cover abundance of individual species before (open symbols) and after (closed symbols) the moth outbreak. Cover abundances are given as mean for all plots in which a given species is present within a given community. a Crowberry birch forest, b bilberry birch forest, c low-herb birch forest. Cover abundances with non-overlapping SDs before and after the outbreak are connected by arrows. Chamae. suecicum Chamaepericlymenum suecicum
Mentions: The significant shifts in understorey community composition observed in the two oligotrophic communities were mainly due to large changes in abundance of a limited number of plant species (Fig. 5). The two oligotrophic communities experienced a drastic transition from dominance by dwarf shrubs (V. myrtillus, B. nana and E. nigrum) to dominance by the grass A. flexuosa. In addition, the low herb C. suecicum experienced a large decrease in cover in both communities (Fig. 5a, b). C. suecicum is defoliated by larvae at outbreak densities (authors’ observations). None of the species in the eutrophic community (Fig. 5c) showed significant changes in abundance in response to the moth outbreak.Fig. 5

Bottom Line: Prior to the moth outbreak, the plots divided into two oligotrophic and one eutrophic plant community.In the spatially most widespread communities, oligotrophic dwarf shrub birch forest, dominance by the allelopathic dwarf shrub Empetrum nigrum ssp. hermaphroditum, was effectively broken and replaced by a community dominated by the graminoid Avenella flexuosa, in a manner qualitatively similar to the effect of wild fires in E. nigrum communities in coniferous boreal forest further south.Our findings reveal that the impact of moth outbreaks on the northern boreal birch forest system is highly initial-state dependent, and that the widespread oligotrophic communities have a low resistance to such disturbances.

View Article: PubMed Central - PubMed

Affiliation: Norut, Northern Research Institute Tromsø, Tromsø Science Park, P.O. Box 6434, 9294, Tromsø, Norway, stein-rune.karlsen@norut.no.

ABSTRACT
The increased spread of insect outbreaks is among the most severe impacts of climate warming predicted for northern boreal forest ecosystems. Compound disturbances by insect herbivores can cause sharp transitions between vegetation states with implications for ecosystem productivity and climate feedbacks. By analysing vegetation plots prior to and immediately after a severe and widespread outbreak by geometrid moths in the birch forest-tundra ecotone, we document a shift in forest understorey community composition in response to the moth outbreak. Prior to the moth outbreak, the plots divided into two oligotrophic and one eutrophic plant community. The moth outbreak caused a vegetation state shift in the two oligotrophic communities, but only minor changes in the eutrophic community. In the spatially most widespread communities, oligotrophic dwarf shrub birch forest, dominance by the allelopathic dwarf shrub Empetrum nigrum ssp. hermaphroditum, was effectively broken and replaced by a community dominated by the graminoid Avenella flexuosa, in a manner qualitatively similar to the effect of wild fires in E. nigrum communities in coniferous boreal forest further south. As dominance by E. nigrum is associated with retrogressive succession the observed vegetation state shift has widespread implications for ecosystem productivity on a regional scale. Our findings reveal that the impact of moth outbreaks on the northern boreal birch forest system is highly initial-state dependent, and that the widespread oligotrophic communities have a low resistance to such disturbances. This provides a case for the notion that climate impacts on arctic and northern boreal vegetation may take place most abruptly when conveyed by changed dynamics of irruptive herbivores.

Show MeSH
Related in: MedlinePlus