Immediate effects on the beetle community after intensive fertilization in young Norway spruce (Picea abies) stands

Abstract: New intensified forest management measures are needed in order to meet the increasing demands of bio products. Intensive fertilization has large potential to enhance wood production in already existing forests. By repeatedly fertilizing young stands of Norway spruce, stem volume growth can increase by up to 350 %. Higher levels of forest exploitation are usually associated with loss of biodiversity and new forest management measures should therefore be carefully evaluated before implemented on larger scale. This study examines the immediate effects of intensive fertilization on the beetle community in an intensive managed forest area in southern Sweden. The results show that fertilized stands had 51% more individuals and 23% more species than unfertilized stands. Even though the total abundance and total species richness did not differ statistically between treatments, the results indicate a trend for short term positive effect at stand scale. The results also suggest that there is a difference in the response between functional groups of beetles based on their nutritional ecology. Herbivorous beetles were significantly more abundant and had higher species richness in fertilized stands, likely favored by the enhanced nutrition availability. It was particularly species that primarily foraging on other plant species than trees that differed in abundance between treatments. Predator beetles were also significantly more abundant in fertilized stands and may have been indirectly affected by greater number of potential prey. Cambium consuming beetles showed a significantly higher species richness in fertilized stands. This result is hard to interpret and may have been interfered by the effects of pre-commercial thinning that was performed in one stand during the monitoring period. The results from this study suggests that the beetle community is immediate affected by fertilization. Long term effects and the implication of large scale application should be evaluated before this management measure is applied on national scale. As this study is part of a large scale and long term experiment, future implications for beetle biodiversity and assemblage composition will be monitored.