Impacts of introduced Rangifer on ecosystem processes of maritime tundra on subarctic islands

• Published in: Ecosphere
• Main Authors: Ricca, Mark A, Miles, A Keith, Van Vuren, Dirk H, Eviner, Valerie T
• Other Authors: Peters, DPC
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: eScholarship, University of California 2016
• Subjects: Alaska; Aleutian; alternative state; caribou; irruption; isotope; mineralization; nitrogen; plant; Rangifer tarandus; reindeer; soil; Ecological Applications; Ecology; Zoology; Archipelago; Subarctic; Tundra
• Online Access: https://escholarship.org/uc/item/4vt8f0g8; https://escholarship.org/content/qt4vt8f0g8/qt4vt8f0g8.pdf; https://doi.org/10.1002/ecs2.1219

Introductions of mammalian herbivores to remote islands without predators provide a natural experiment to ask how temporal and spatial variation in herbivory intensity alter feedbacks between plant and soil processes. We investigated ecosystem effects resulting from introductions of Rangifer tarandus (hereafter "Rangifer") to native mammalian predator- and herbivore-free islands in the Aleutian archipelago of Alaska. We hypothesized that the maritime tundra of these islands would experience either: (1) accelerated ecosystem processes mediated by positive feedbacks between increased graminoid production and rapid nitrogen cycling; or (2) decelerated processes mediated by herbivory that stimulated shrub domination and lowered soil fertility We measured summer plant and soil properties across three islands representing a chronosequence of elapsed time post-Rangifer introduction (Atka: ∼100 yr; Adak: ∼50; Kagalaska: ∼0), with distinct stages of irruptive population dynamics of Rangifer nested within each island (Atka: irruption, K-overshoot, decline, K-re-equilibration; Adak: irruption, K-overshoot; Kagalaska: initial introduction). We also measured Rangifer spatial use within islands (indexed by pellet group counts) to determine how ecosystem processes responded to spatial variation in herbivory. Vegetation community response to herbivory varied with temporal and spatial scale. When comparing temporal effects using the island chronosequence, increased time since herbivore introduction led to more graminoids and fewer dwarf-shrubs, lichens, and mosses. Slow-growing Cladonia lichens that are highly preferred winter forage were decimated on both long-term Rangifer-occupied islands. In addition, linear relations between more concentrated Rangifer spatial use and reductions in graminoid and forb biomass within islands added spatial heterogeneity to long-term patterns identified by the chronosequence. These results support, in part, the hypothesis that Rangifer population persistence on islands is facilitated by ...