Succession and dynamics of Norway spruce communities on Gulf of Bothnia rising coastlinesSvensson, Johan
This thesis encompasses two approaches to primary succession on ground-moraine seashores undergoing land uplift, the directional succession from early stages via transitional broadleaf assemblages to late Norway spruce (Picea abies (L.) Karst.) forests, and the structure and dynamics of the old-growth, undisturbed spruce forest. A basic assumption made was that the constant and known (over the viewed time period) uplift rate provides a predictable ground age (temporal) sequence, which can be estimated by determining ground surface elevation above mean sea level. The studies were conducted within the Ostnäs (ca. 63°49’N, 20°41’E) and Sladan (ca. 63°51’N, 20°43’E) Nature Reserves in the Norra Kvarken Archipelago, coastal Västerbotten, northern Sweden. All study sites represented undisturbed successional sequences.
Main results and conclusions were the following: (;) Grey alder (Alnus incana (L.) Moench.), rowan (Sorbus aucuparia L.), juniper (Juniperus communis L.), and Norway spruce form six successional stages based on occurrence and composition, and three stages based on dominance, from early-successional alder to late-successional spruce, (ri) Spruce is able to establish after 30 to 40 years of succession, i.e. 25 to 35 cm above mean sea level. (Hi) Depth of organic layer and cover of bottom layer vegetation and litter increase, while cover of field layer vegetation decreases, with time of succession, (iv) Diversity of field- and bottom-layer types, and spruce size categories, increase to a mode during mid-successional stages, (v) Patterns of dead spruce reveal two mortality occasions - self-thinning associated with early-successional competition, and stochastic mortality associated with late-successional, old-growth development, (vij Spruce age pattern follows a positive, linear relationship with ground age, where spruce age pattern approaches one year per three years of ground age. (vii) Old-growth conditions can develop within 300 years from original site emergence above mean sea level.
The results are discussed with reference to basic concepts such as primary, secondary, allogenic, and autogenic succession, facilitation, directionality, colonization, and diversity. Consequences of the continuous landscape transformation owing to the land-uplift process are linked to the theory of island biogeography, and to the chronosequence approach to succession. It is argued that changing allogenic and autogenic factors maintain a continuous modification of the successional pathway, by affecting the lowest level of spruce establishment, hypothetically producing a curvilinear relationship between spruce age and ground age. Finally, some applications to forest management are elucidated.
Keywordsground age; land uplift; Picea abies; primary succession; structure; tree age; tree-species belt
Published inActa Universitatis Agriculturae Sueciae. Silvestria
2002, number: 239
Publisher: Department of Forest Ecology, Swedish University of Agricultural Sciences