Effect of grazing, trampling, and fecal deposition on vegetation and soil nutrients, Yukon Kuskokwim Delta Alaska, 2016

Herbivores play a key role in the turnover, gains and losses of nutrients in ecosystems. Because nutrients are often limiting, herbivores influence plant growth and chemistry, and their own resource supply. Herbivores typically affect their environment in three ways: they consume aboveground biomass, they trample soil, and they return nutrients to soil via waste materials. The relative importance of these pathways is often unexplored because it requires conducting experiments that isolate these effects. Millions of geese migrate in the spring to sub-arctic coastal wetlands where they play a key role in determining the amount and quality of forage in this habitat. We conducted two field experiments on Carex subspathacea grazing lawns in western Alaska to investigate how these individual processes (grazing, trampling, and fecal addition) influence foliage quality (C:N) and soil nutrients. We isolated goose herbivory effects with five treatments: grazing only, trampling only, fecal addition only, all three treatments combined (full herbivory), and no herbivory.

植食动物（Herbivores）在生态系统养分循环、增益与流失过程中发挥关键作用。由于养分往往为限制性因子，植食动物会同时影响植物的生长与化学组成，以及自身的资源供给。植食动物通常通过三种途径调控栖息环境：取食地上生物量、踩踏土壤，以及通过排泄物将养分返还至土壤。目前上述三种途径的相对重要性尚未得到充分探究，因为需开展能够分离各单一效应的实验。每年春季，数百万只鹅会迁徙至亚北极滨海湿地，该生境中饲草的数量与品质均由鹅类发挥关键调控作用。本研究在阿拉斯加州西部的卵穗薹草（Carex subspathacea）放牧草甸上开展了两项野外实验，以探究啃食、踩踏与粪肥添加这三类单一过程如何影响叶片品质（碳氮比，C:N）与土壤养分。研究通过五组实验处理分离鹅类植食作用的效应：仅啃食组、仅踩踏组、仅粪肥添加组、全三种处理组合组（完整植食作用组）以及无植食作用对照组。