Forest ecosystems across northern latitudes frequently experience nutrient limitations, particularly regarding available soil nitrogen. As forest managers seek sustainable methods to enhance timber production and lock away atmospheric carbon, biochar has emerged as a promising soil additive. Derived from heating organic biomassBiomass is a complex biological organic or non-organic solid product derived from living or recently living organism and available naturally. Various types of wastes such as animal manure, waste paper, sludge and many industrial wastes are also treated as biomass because like natural biomass these More under oxygen-restricted conditions, this carbon-rich material is celebrated for its ability to persist in ground layers for centuries. Beyond carbon storage, biochar can alter physical and chemical soil properties, such as increasing water retention, decreasing acidity, and promoting microbial activity. However, most research evaluating biochar performance has centered on agricultural crops or young tree seedlings in greenhouse pots. Field trials examining mature, established forests remain remarkably scarce, leaving foresters uncertain about whether surface applications of biochar translate to meaningful timber growth.

To address this gap, researchers Kjersti Holt Hanssen, Jogeir Stokland, and Rasmus Astrup conducted a five-year field experiment published in the journal GCB Bioenergy. The team targeted two middle-aged, sixty-year-old Scots pine stands situated on medium-quality podzolic soils in southeastern Norway. They established replicated experimental plots to compare four distinct soil treatments: an unfertilized control, pure wood biochar applied at two point five metric tons per hectare, standard mineral nitrogen fertilizer supplying one hundred fifty kilograms of nitrogen per hectare, and a combined treatment featuring biochar pre-loaded with the identical nitrogen dosage. The biochar utilized was produced via high-temperature pyrolysisPyrolysis is a thermochemical process that converts waste biomass into bio-char, bio-oil, and pyro-gas. It offers significant advantages in waste valorization, turning low-value materials into economically valuable resources. Its versatility allows for tailored products based on operational conditions, presenting itself as a cost-effective and efficient More of Norway spruce wood chips. By measuring tree heights, trunk diameters, and core samples over five full growing seasons, the scientists tracked changes in overall standing volume, basal area, and annual ring formation.

The findings revealed a distinct divide between treatments containing added nitrogen and those without. Over the five-year observation period, plots receiving pure biochar showed no statistical boost in tree growth compared to the unfertilized control. Five years post-application, the modeled standing timber volume reached two hundred fifty-four cubic meters per hectare in control plots and two hundred fifty-two cubic meters per hectare in pure biochar plots. Corresponding basal area measurements were similarly matched at twenty-five point five square meters per hectare for both groups. Annual ring analysis confirmed that tree growth in pure biochar plots closely tracked the control group, exhibiting a gradual decline characteristic of aging pine stands. The lack of response indicates that biochar alone cannot overcome the primary growth bottleneck in these boreal soils, where accessible nitrogen remains the ultimate limiting factor for plant productivity. Furthermore, surface-applied biochar resides initially within the upper organic layer, taking considerable time to migrate downward where active tree roots reside.

Conversely, treatments supplying nitrogen produced strong growth surges. Plots treated with mineral nitrogen reached a standing volume of two hundred sixty-four cubic meters per hectare, while the nitrogen-enriched biochar plots reached two hundred sixty-five cubic meters per hectare. Both nitrogen-bearing treatments expanded basal area to over twenty-six square meters per hectare. When examining annual tree ring growth, both treatments stimulated increased wood deposition beginning in the second year and peaking during the third year after application. During that peak third year, annual ring growth increased to one hundred thirty-seven percent for nitrogen alone and one hundred fifty-seven percent for nitrogen-enriched biochar relative to control levels. Although the nitrogen-enriched biochar delivered a brief advantage in that single year, the cumulative five-year growth response between the two nitrogen treatments was essentially identical. This demonstrates that pine trees take up nitrogen rapidly regardless of whether it arrives in traditional fertilizer granules or embedded within a biochar framework.

While biochar did not act as a direct growth stimulant on its own, it caused no negative impacts on tree health or timber development. Consequently, forest managers can safely deploy biochar as a carbon sequestration tool without worrying about compromising forest productivity. To fully capture how biochar interacts with varied forest environments, future trials must examine different application rates, younger tree stands, and longer timeframes across diverse soil types.

Source: Hanssen, K. H., Stokland, J., & Astrup, R. (2026). Effects of biochar and nitrogen‐enriched biochar on tree growth in Scots pine stands. GCB Bioenergy, 18(9), e70148.