Dissertation in forest industrial production systems: Per Nordin

Abstract

Regeneration success depends on decisions made based on factors on a regional, site, and microenvironmental level. Therefore, understanding and mapping of such factors between and within sites can guide decisions for better seedling establishment. Thus, the aim of this thesis was to find combinations of regeneration measures that result in low seedling mortality and high growth. Additionally, to explore the potential of digital tools in regeneration planning. Aims were handled using field experiments and a survey, by integrating digital tools in the analysis and experimental set-up.

Increased precipitation and decreased air temperatures between April and October during the planting year lowered seedling mortality. Planting in mineral soil also lowered the mortality rate, which emphasized the importance of planting and site preparation quality (Paper I). Selection of site preparation method was found to be of minor importance. The site preparation’s ability to create suitable planting spots was most important for seedling survival and growth. Selection of site preparation affected soil disturbance, and natural regeneration was promoted with all methods used in the experiments (Paper II). Adapting planting position choice, following site preparation, to within-site variation was valuable to decrease mortality rates and promote growth (Paper II-III). In wet conditions, elevated planting positions were advantageous compared to lower ones, but more flexibility could be applied in drier conditions. Norway spruce, Scots pine, and silver birch reacted differently to planting position choice (Paper III). Paper I-III indicated that digital tools could be used in regeneration planning. A depth-to-water-raster successfully explained seedling mortality and growth in the extreme ends of the soil moisture spectrum. Using remote sensing derived variables can be valuable for further mapping and understanding of between and within-site variation in future regeneration planning. There were no long-term negative effects on stand productivity after 30 years following site preparation. The standing volume was largest after ploughing but disc trenching and mounding also had higher standing volume than the unscarified control (Paper IV). I conclude that regeneration decisions made today, regarding species selection and regeneration method, should strive for increased precision for the benefit of the forests of tomorrow.