Given the current rates of climate change, with associated shifts in herbivore population densities, understanding the role of different herbivores in ecosystem functioning is critical for predicting ecosystem responses. Here, we examined how migratory geese and resident, non‐migratory reindeer—two dominating yet functionally contrasting herbivores—control vegetation and ecosystem processes in rapidly warming Arctic tundra. We collected vegetation and ecosystem carbon (C) flux data at peak plant growing season in the two longest running, fully replicated herbivore removal experiments found in high‐Arctic Svalbard. Experiments had been set up independently in wet habitat utilised by barnacle geese Excluding geese induced vegetation state transitions from heavily grazed, moss‐dominated (only 4 g m−2of live above‐ground vascular plant biomass) to ungrazed, graminoid‐dominated (60 g m−2after 4‐year exclusion) and horsetail‐dominated (150 g m−2after 15‐year exclusion) tundra. This caused large increases in vegetation C and nitrogen (N) pools, dead biomass and moss‐layer depth. Alterations in plant N concentration and CN ratio suggest overall slower plant community nutrient dynamics in the short‐term (4‐year) absence of geese. Long‐term (15‐year) goose removal quadrupled net ecosystem C sequestration (NEE) by increasing ecosystem photosynthesis more than ecosystem respiration (ER). Excluding reindeer for 21 years also produced detectable increases in live above‐ground vascular plant biomass (from 50 to 80 g m−2; without promoting vegetation state shifts), as well as in vegetation C and N pools, dead biomass, moss‐layer depth and ER. Yet, reindeer removal did not alter the chemistry of plants and soil or NEE.
Environmental changes can rapidly alter standing biomass in tundra plant communities; yet, to what extent can they modify plant‐community nutrient levels? Nutrient levels and their changes can affect biomass production, nutrient cycling rates and nutrient availability to herbivores. We examined how environmental perturbations alter Arctic plant‐community leaf nutrient concentrations (percentage of dry mass, i.e. resource quality) and nutrient pools (absolute mass per unit area, i.e. resource quantity). We experimentally imposed two different types of environmental perturbations in a high‐Arctic ecosystem in Svalbard, spanning three habitats differing in soil moisture and plant‐community composition. We mimicked both a pulse perturbation (a grubbing event by geese in spring) and a press perturbation (a constant level of summer warming). After 2 years of perturbations, we quantified peak‐season nitrogen and phosphorus concentrations in 1268 leaf samples from the most abundant vascular plant species. We derived community‐weighted nutrient concentrations and total amount of nutrients (pools) for whole plant communities and individual plant functional types (PFTs). Spring grubbing increased plant‐community nutrient concentrations in mesic (+13%) and wet (+8%), but not moist, habitats, and reduced nutrient pools in all habitats (moist: −49%; wet, mesic: −31% to −37%). Conversely, summer warming reduced plant‐community nutrient concentrations in mesic and moist (−10% to −12%), but not wet, habitats and increased nutrient pools in moist habitats (+50%). Fast‐growing PFTs exhibited nutrient‐concentration responses, while slow‐growing PFTs generally did not. Grubbing enhanced nutrient concentrations of forbs and grasses in wet habitats (+20%) and of horsetails and grasses in mesic habitats (+19–23%). Conversely, warming decreased nutrient concentrations of horsetails in wet habitats (−15%) and of grasses, horsetails and forbs in moist habitats (−12% to −15%). Nutrient pools held by each PFT were less affected, although the most abundant PFTs responded to perturbations.
- Award ID(s):
- 2113641
- NSF-PAR ID:
- 10419725
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of Ecology
- Volume:
- 111
- Issue:
- 7
- ISSN:
- 0022-0477
- Format(s):
- Medium: X Size: p. 1514-1530
- Size(s):
- ["p. 1514-1530"]
- Sponsoring Org:
- National Science Foundation
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Location Yukon–Kuskokwim Delta, Alaska.
Methods We conducted an experiment where we simulated goose grazing by clipping the vegetation and summer warming by using open‐top chambers in three plant communities along a 6‐km coastal–inland gradient. We assessed plant community compositional changes following two years of treatments.
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