Nils Henriksson

I am a researcher at the department of Forest Ecology and Management (SLU, Umeå). As a  forest ecophysiologist, I use element fluxes to study biological processes related to forest growth and ecosystem functioning. This basis on physiological processes (like photosynthetic carbon assimilation, cellular respiration, or root and mycorrhizal nitrogen acquisition and water uptake) lets me study the functions of forest ecosystems. That means asking questions about what various plant or fungal species are doing in different environbments, how is carbon being allocated, or how is nitrogen moving between organisms. This sort of muchanistic approach is very useful in understanding a dynamic ecosystem, and it is the kind of understanding that is needed in order to adjust our forest management practices to changing environmental conditions or new management goals.

For this purpose, stable isotope techniques are very useful.  I have used stable isotope tracers (13C, 15N, 2H) to study tree carbon partitioning, competition for nitrogen within common mycorrhizal networks (CMNs), as well as tree water/nitrogen uptake strategies. I combine field experiments in various boreal forest systems (such as long-term nitrogen addition experiments and root exclusions) with laboratory or greenhouse experiments where specific processes can be targeted with a greater degree of experimental control. 

Currently, I am working on a number of projects that target different aspects of tree seedling growth, competition for soil nutrients (nitrogen) and interactions with mycorrhizal fungi. I am very interested in the limiting factors for successful forest regeneration - both in the context of corrent forestry practices and the challenges of alternative forest management practices.

I am suppervising PhD students and post-doctoral researchers who are working on each project. In the case of the PhD students, the projects listed below will be part of their doctoral theses.

Forest regeneration in forest gaps

This project is headed by PhD student Alexina Brännlund. We are combining stable isotope techniques with root isolation to remove belowground interactions with roots and fungi, to study seedling growth and nitrogen nutrition at various distances from forest edges. Poor seedling growth near large trees is a well-known phenomenon, but the evidence for the specific mechanism is lacking, and is a necessary piece of the puzzle that must be solved to develop successful clearcut-free forestry methods in many parts of Sweden.

Interactions between pine seedlings, ericaceous dwarf shrubs, and mycorrhizal fungi 

This is a greenhouse experimental study focuses on the mycorrhizal interactions between pine seedlings and the ericaceous dwarf shrub Calluna vulgaris (commonly found on Swedish pine heaths), and is led by post-doctoral researcher Jasmin Danzberger. These species belong to separate mycorrhizal groups but based on DNA sequencing results we have found a significant overlap in the fungal groups present on roots of the two plants. We are now investigating how this may affect the nitrogen nutrition of the pine seedlings.

Effects of altered soil nitrogen forms (such as after fertilization) on plant root physiology

Swedish forest growth is known to be nitrogen limited. This means that applying nitrogen fertilizer reliably leads to increased tree growth. A closer look at this effect shows that the fertilization effect is mainly a shift in allocation - more stem and foliage production but less roots. An even closer scrutiny shows that this effect has only been shown for mineral nitrogen fertilizers - not the organic nitrogen forms that are in fact dominating in most  forest soils. The PhD student Ellen Svensson is leading this project which is looking at the response of tree root to different soil nitrogen forms.

Ecophysiology of tree seedlings growing under a forest canopy

Scots pine and Norway spruce are the most abundant and commecially important tree species in Sweden. They are both conifers but have very different ecologies: Pine is a pioneer species, an early colonizer of disturbed soil and grows fast after germinating. Spruce is a late-successional species and germinated seedlings can persist for decades under a closed forest canopy, growing extremely slowly until conditions become more favorable. This difference between the species is of key impotrance when considering various clearcut-free forest management options. The PhD student Marcus Björs is establishing field experiments to improve our understanding of what physiological features allow spruce to persist under a dense shelterwood and what are the most important limitations hampering pines under such conditions.

PhD level:

Ecophysiological concepts and applications in forests (P000132, 7.5 credits) - Course leader

MSc level

Forest Ecosystem ecology - Lecturing

BSc level

Bachelor thesis course in Forestry Science/Biology (EX014/EX015, 15 credits)  - Course leader

Forest Ecology - Lecturing

Skogsskötsel och Naturvårdsbiologi (BI1416)- Lecturing

Norra Sveriges Skogar och Landskap (SV0008) - Lecturing

Praktiskt Skogsbruk (SV0006) - Lecturing