摘要：Understanding the responses of the arctic tundra biome to a changing climate requires
knowledge of the complex interactions among the climate, soils and biological system. This
study investigates the individual and interaction effects of climate change and reindeer
grazing across a variety of climate zones and soil texture types on tundra vegetation
community dynamics using an arctic vegetation model that incorporates the reindeer diet,
where grazing is a function of both foliar nitrogen concentration and reindeer forage
preference. We found that grazing is important, in addition to the latitudinal climate
gradient, in controlling tundra plant community composition, explaining about 13%
of the total variance in model simulations for all arctic tundra subzones. The
decrease in biomass of lichen, deciduous shrub and graminoid plant functional types
caused by grazing is potentially dampened by climate warming. Moss biomass
had a nonlinear response to increased grazing intensity, and such responses were
stronger when warming was present. Our results suggest that evergreen shrubs
may benefit from increased grazing intensity due to their low palatability, yet a
growth rate sensitivity analysis suggests that changes in nutrient uptake rates may
result in different shrub responses to grazing pressure. Heavy grazing caused plant
communities to shift from shrub tundra toward moss, graminoid-dominated tundra in
subzones C and D when evergreen shrub growth rates were decreased in the model.
The response of moss, lichen and forbs to warming varied across the different
subzones. Initial vegetation responses to climate change during transient warming are
different from the long term equilibrium responses due to shifts in the controlling
mechanisms (nutrient limitation versus competition) within tundra plant communities.
