Demand-driven fertilization (BAG) effects on stream water chemistry : a study in the Undersvik high-yield experimental forest

Sammanfattning

Forests have a vital role in the transition to a bio-based economy and the mitigation of climate change since they are carbon sinks and provide sustainable wood products. Despite Sweden's long tradition of forest management, which has historically seen forest stock doubling at the same time as harvesting practices have become more sustainable, current trends indicate a nearing of national capacity for wood production. This challenges the forest industry, which now faces the need to enhance biomass production efficiently and innovate in silviculture to meet rising demands without compromising environmental and sustainability standards. This report aims to explore Behovsanpassad gödsling (BAG), or demand-driven fertilization in English, as a possible solution. BAG aim to increase growth rates while minimizing nitrogen leakage—a primary concern with conventional fertilization methods that risk eutrophication and biodiversity loss. The main focus of this thesis lies on investigating and analysing the effects that this silvicultural measure has on the stream water chemistry. This was done through utilizing data in the form of water samples from streams where BAG fertilization has been performed in the catchment area at the new operational-scale experiment at Undersvik (Project start in 2020). Water was also sampled from nearby streams without BAG influence, and from locations further downstream from the BAG treatments to see if any effects were propagated further downstream. Initial findings suggest no statistically significant impact of BAG on water chemistry in terms of nitrogen leakage, compared to reference sites. However, observed peaks and extreme values in chemical compounds indicate potential localized, short-term effects of BAG treatment. In conclusion, we can say that at this point in the Undersvik study, BAG presents a promising alternative to conventional fertilization. To judge whether BAG has potential for reduced environmental impact, longer-term studies of water chemistry and other aspects including biodiversity and forest growth are needed to fully understand the benefits and limitations.