The alpine treeline ecotone in the southernmost Swedish scandes: Dynamism on different scales

Abstract

Alpine (altitudinal) treeline ecotones are elusive, spatially heterogeneous and dynamic transitional zones between closed mountain forest and treeless alpine tundra. From a distance the may look sharp, but a closer view usually reveals a highly complex structural pattern (Kullman 1979). Thermal growth limitation is considered as the fundamental part of the mechanism that creates and maintains the treeline ecotone (Grace et al. 2002; Hoch and Körner 2003; Holtmeier 2003; Kullman 1998, 2007a, 2010a; Diaz et al. 2003; Lloyd and Fastie 2002). At finer scales, the straight thermal forcing is modulated by other agents, e.g., topography, geomorphology, wind, soil depth, species interactions, fire, herbivory, human impacts, and site history (Walsh et al. 1994; Holtmeier and Broll 2005; Gehrig-Fasel et al. 2007; Kullman and Öberg 2009; Leonelli et al. 2011; Aune et al. 2011). Among these, wind appears to have a superior role (cf. Seppälä 2004; Holtmeier and Broll 2010; Kullman 2010a).