Spatio-temporal properties of tree-species belts during primary succession on rising Gulf of Bothnia coastlines

This paper elucidates spatial and temporal pathways of tree-species colonization and forest development during 260 years of undisturbed primary succession on rising ground-moraine shorelines in the Norra Kvarken Archipelago, Gulf of Bothnia, northern Sweden. Four species — grey alder (Alnus incana), rowan (Sorbus aucuparia), juniper (Juniperus communis), and spruce (Picea abies) — occur commonly and form distinct belts. The earliest individuals (≥ 0.5 m) of alder were found after 20 years of succession, of spruce after 40 years, of juniper after 50 years, and of rowan after 60 years. Because of the longer time required by spruce to become dominant, the order of belts from younger to older was: alder—rowan—juniper—spruce. The belt width decreased from alder to rowan to juniper, and with increasing shore slope. We identified six successional stages by occurrence and composition, from pure alder to pure spruce, and three stages by species dominance. Spruce became dominant after 160 years of succession and forms the climax forests on these sites.