Background insect herbivory increases with local elevation but makes minor contribution to element cycling along natural gradients in the Subarctic

Research output: Contribution to journalArticle

Abstract

Herbivores can exert major controls over biogeochemical cycling. As invertebrates are highly sensitive to temperature shifts (ectothermal), the abundances of insects in high-latitude systems, where climate warming is rapid, is expected to increase. In subarctic mountain birch forests, research has focussed on geometrid moth outbreaks, while the contribution of background insect herbivory (BIH) to elemental cycling is poorly constrained. In northern Sweden, we estimated BIH along 9 elevational gradients distributed across a gradient in regional elevation, temperature, and precipitation to allow evaluation of consistency in local versus regional variation. We converted foliar loss via BIH to fluxes of C, nitrogen (N), and phosphorus (P) from the birch canopy to the soil to compare with other relevant soil inputs of the same elements and assessed different abiotic and biotic drivers of the observed variability. We found that leaf area loss due to BIH was ~1.6% on average. This is comparable to estimates from tundra, but considerably lower than ecosystems at lower latitudes. The C, N, and P fluxes from canopy to soil associated with BIH were 1–2 orders of magnitude lower than the soil input from senesced litter and external nutrient sources such as biological N fixation, atmospheric deposition of N, and P weathering estimated from the literature. Despite the minor contribution to overall elemental cycling in subarctic birch forests, the higher quality and earlier timing of the input of herbivore deposits to soils compared to senesced litter may make this contribution disproportionally important for various ecosystem functions. BIH increased significantly with leaf N content as well as local elevation along each transect, yet showed no significant relationship with temperature or humidity, nor the commonly used temperature proxy, absolute elevation. The lack of consistency between the local and regional elevational trends calls for caution when using elevation gradients as climate proxies.

Details

Authors
Organisations
External organisations
  • University of Copenhagen
  • Umeå University
  • Geological Survey of Denmark and Greenland, Copenhagen, Denmark
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Soil Science

Keywords

  • carbon cycling, fast cycle versus slow cycle, insect herbivory, nutrient cycling, space-for-time substitution, Subarctic mountain birch forest
Original languageEnglish
Pages (from-to)11684-11698
Number of pages15
JournalEcology and Evolution
Volume10
Issue number20
Publication statusPublished - 2020 Oct 1
Publication categoryResearch
Peer-reviewedYes