Thirty years of seed production in a subalpine Norway spruce forest: Patterns of temporal and spatial variation

Abstract

Norway spruce seed production was studied over 30 years in a subalpine forest of the south-eastern Alps. Thirteen locations were selected along a gradient of elevation and aspect. During mast years, seed production declined on average by about 100 seeds m −2 year −1 per 100 m elevation. The increase in elevation was associated with a reduction in mast year frequency and average mast production. A complex of climatic and edaphic factors appeared to be responsible for the reduction in seed production along the elevation gradient. North-facing locations produced significantly more seeds per square metre per year than south-facing locations. This difference was probably linked with frequent water stresses on south-facing slopes. Variability in seed production within the forest was pronounced and unpredictable in low-production years. The tendency to concentrate seed crops, especially during mast years was not influenced by stand characteristics. The proportion of full seeds and the proportion of seeds which survived vertebrate predation were higher during mast years. These results are interpreted in the context of Norway spruce population dynamics.