Nitrogen restricts future treeline advance in the sub-arctic.

Arctic environmental change has induced shifts in high latitude plant community composition and stature with implications for Arctic carbon cycling and energy exchange. Two major components of high latitude ecosystems undergoing change is the advancement of trees into treeless tundra and the increased abundance and size of shrubs. How future changes in key climatic and environmental drivers will affect distributions of major ecosystem types is an active area of research. Dynamic Vegetation Models (DVMs) offer a way to investigate multiple and interacting drivers of vegetation distribution and ecosystem function. We employed the LPJ-GUESS DVM over a subarctic landscape in northern Sweden, Torneträsk. Using a highly resolved climate dataset we downscaled CMIP5 climate data from three Global Climate Models and two 21st century future scenarios (RCP2.6 and RCP8.5) to investigate future impacts of climate change on these ecosystems. We also performed three model experiments where we factorially varied drivers (climate, nitrogen deposition and [CO2]) to disentangle the effects of each on ecosystem properties and functions. We found that treelines could advance by between 45 and 195 elevational meters in the landscape until the year 2100, depending on the scenario. Temperature was a strong, but not the only, driver of vegetation change. Nitrogen availability was identified as an important modulator of treeline advance. While increased CO2fertilisation drove productivity increases it did not result in any range shifts of trees. Treeline advance was realistically simulated without any temperature dependence on growth, but biomass was overestimated. As nitrogen was identified as an important modulator of treeline advance, we support the idea that accurately representing plant-soil interactions in models will be key to future predictions Arctic vegetation change. [ABSTRACT FROM AUTHOR]