Shrub expansion in tundra ecosystems: dynamics, impacts and research priorities by Myers-Smith, I, Forbes, B, Wilmking, M, Hallinger, M, Lantz, T, Blok, D, Tape, K, Macias-Fauria, M, Sass-Klaassen, U, Levesque, E, Boudreau, S, Ropars, P, Hermanutz, L, Trant, A, Collier, L, Weijers, S, Rozema, J, Rayback, SA, Schmidt, N, Schaepman-Strub, G, Wipf, S, Rixen, C, Menard, C, Venn, S, Goetz, S