Epsilon Archive for Student Projects

Abstract

Boreal forest growth is largely limited by nitrogen (N) availability, leading to intense belowground competition among trees. Most boreal tree species form ectomycorrhizal (ECM) symbioses, where fungi enhance nutrient and water uptake in exchange for carbon. Following clearcutting, early-stage ECM fungi—adapted to colonize roots quickly and access mineral N—tend to dominate. As stands mature and nutrients become scarcer, later-stage ECMs capable of acquiring complex organic N forms become more competitive and prevalent.
This thesis examines the growth, nitrogen allocation, and ECM fungal community composition of 3-year-old pine (Pinus sylvestris) and spruce (Picea abies) seedlings along a distance gradient from a mature forest edge into a 7-year-old clearcut in northern Sweden.
Seedlings increased in height, dry weight, and N uptake with distance from the forest edge, with a distinct growth threshold observed between 4 and 8 meters.
Seedlings surrounded by a root exclusion barrier were generally larger and unaffected by distance, suggesting that belowground competition for nitrogen strongly limits early seedling growth. Simultaneously, the ECM fungal community composition shifted along the same gradient: early-stage ECMs were more abundant on the clearcut, while late-stage ECMs were more abundant closer to or within the forest.
These findings underscore the influence of spatial gradients and root competition on both seedling performance and ECM community structure, with implications for forest regeneration and the management of edge effects in boreal silviculture.