Epsilon Archive for Student Projects

Abstract

Regeneration has long been a central question in Swedish forestry. Especially in the northern boreal parts of Sweden where the ground close to large trees is devoid of any seedlings. A phenomenon that is called the gap-edge effect. To get around this problem, foresters have implemented clear-cutting, a method for harvesting trees where all trees are removed from an area. This limits the influence of the gap-edge effect as only the edge of the clear-cut area is in proximity to larger trees. While this has proven to be a reliable way to get an economic return from the timber the forest provides it also causes biodiversity losses and decreases the beauty of the landscape. As times have changed, the valuation of these last two values increased. Calls for a change in forestry practices, implementing different methods where the structure of the forests are kept largely intact after harvest are being proposed. However, implementing these clear-cut free forestry methods puts the problem of the gap-edge effect back on the map, leaving foresters scratching their heads on how to satisfy these demands while still being able to get an economic return from their forest.
This study shows that belowground competition is a big factor in the gap-edge effect. By being close to mature trees, seedlings are competing for nutrients such as nitrogen with the larger trees and the seedlings are at a disadvantage. The larger trees have a much more established network of ectomycorrhizal fungi that have taken up and keep a lot of the nitrogen from the little seedlings. These fungi act as an extended root network of the trees and there are many different species that come in many different shapes and sizes that are adapted to different conditions just like aboveground plants. As such, different species are found on the mature trees and on the seedlings. However seedlings experiencing the gap-edge effect have similar species to the mature trees. Whether this causes the gap-edge effect is still unknown, but it clearly shows that mature trees impact the growth of seedlings. As such, this study expands the understanding of how seedlings grow which with further research could unlock ways to implement new forestry methods in boreal Sweden.