Time series of seed production and tree-ring width of Norway spruce (Picea abies (L.) Karst.) in southern Norway were analysed for their relationship to various climatic factors occurring during "key" stages, which a priori might be expected to show a strong climate response. The following factors combined in a multiple linear regression model were found to predict seed production (based on withheld data points) with considerable accuracy, at high levels of statistical significance: June–July mean temperature and August lowest temperature in the previous year, late spring frost and June–July precipitation of the last 2 years, and January–February lowest temperature in the current year. Tree ring width was negatively correlated with the seed production index of the current year and the lowest July temperature in the previous year and positively correlated with June-July precipitation in the current year. It is suggested that habitat constraints for seedling establishment should also be considered in a more general life-history cost theory to explain masting behaviour in forest trees.

No abstract

An epizootic of sarcoptic mange among red foxes Vulpes vulpes reached central Norway in 1976, and by 1986 it had spread to the whole country, resulting in a severe decline in the red fox population. We analyse the change in the hunting bags of the predator species red fox and pine marten Martes martes, and the prey species capercaillie Tetrao urogallus, black grouse Tetrao tetrix, mountain hare Lepus timidus and willow grouse Lagopus I. lagopus from the period prior to and during the mange epizootic. The data are gathered from publications by Statistics Norway and are based on answers from more than 5,000 hunters yearly. On the national level, the hunting bags of capercaillie, black grouse, mountain hare and pine marten were significantly negatively correlated with that of the red fox. When the time series at the national level were detrended, there were positive correlations between the hunting bags of all species without time lag, except that of pine marten, which lagged one year behind the other species. At the local level there were negative correlations between the hunting bag of red fox and those of the small game species except for willow grouse. The study confirms that the red fox is a keystone predator in Scandinavia.

In an analysis of a 50-year time series of seed production in bilberry (Vaccinium myrtillus L.) from Aust-Agder, southern Norway, both previous reproduction and weather contributed to explain annual berry production. There was a relatively regular fluctuation in bilberry production, with intervals between peaks of 2-5 years. The bilberry-production index was negatively correlated with the average bilberry production index of the preceding 3 years. Regularity in the bilberry production was commonly interrupted by unfavourable weather conditions. Depressed bilberry reproduction was associated with high temperatures during flower-bud formation in autumn, high temperatures in winters with thin snow cover, low temperatures during flowering in spring, and low or high amounts of precipitation during berry ripening in summer. It was concluded that, in Fennoscandia, climatic conditions may be responsible for the temporal and spatial synchrony in seed production in bilberry.Key words: bilberry, climate, mast, reproduction, synchrony, weather.

We investigated the relationship between flowering peaks of the mountain birch, Betula pubescens ssp. czerepanovii, and population levels of the autumnal moth Epirrita autumnata in Ammarnäs, Swedish Lapland, during 1968-2000, and in Budal, Central Norway, during 1972-2000. There was a significant correlation between the two moth series, both of which showed three well-defined population cycles during the study period. In both areas, the population growth index of the moth was negatively related to population size, but also to the number of years since the previous flowering peak of mountain birch. In the northern study area, Ammarnäs, there was an additional positive effect of the winter temperature index, probably due to increased mortality of moth eggs during cold winters. No significant relationships were found between the number of birch female catkins and larval density in the previous 2 years. Both in Ammarnäs and in an area without moth outbreaks in south-eastern Norway, birch flowering was positively related to temperatures during flower bud formation and to the number of years since the previous flowering peak. The results support the idea of a lower content of chemical defence compounds in birch leaves after a mast reproduction, though we cannot exclude the possibility that the negative relationship between flowering and moth population levels was influenced or caused by stress associated with defoliation during moth outbreaks.