This is an experimental prescription designed to naturally regenerate red pine under red pine in the face of various economic and ecological constraints. The primary economic constraints consist of 1) the risk of losing high value trees to disturbance, such as windthrow, when retained to serve as seed trees and 2) the time available by a forester to plan and execute a non-coppice natural regeneration silvicultural system. The primary ecological constraint, in Minnesota at the time of writing (2017), is 1) pathogenic in the form of Diplodia pinea (Desm.) and/or Sirococcus strobilinus (Preuss). In some instances, the first economic constraint has caused foresters to retain lower value seed trees during the seed-tree cut. While this should not cause too much concern for the future genetics of a red pine stand it can limit the forester’s ability to conduct a profitable overwood removal sale once adequate regeneration has been secured, sometimes causing the overwood to remain indefinitely. Indefinite overwood retention causes a complete loss of the economic value of retained trees and can also cause regeneration loss, sometimes 100%, due to pathogen infection. The pathogenic threat of Diplodia and Sirococcus , both of which reside in the canopy of red pines and are moved via spores picked up by rain splashes, has caused great fear in foresters to attempt natural regeneration in red pine, regardless of the potential economic constraints.
The second economic constraint, the time of the forester, is not an idle constraint to consider. At a minimum for a successful seed tree silvicultural system with passive scarification, the forester will need to visit the stand eight times during two entries:
1 - Seed tree entry: cruise, mark boundaries/roads/removals, timber sale administration (TSA), and regeneration check
2 - Overwood removal entry: cruise, mark boundaries (roads and removals should be obvious), TSA, and regeneration check.
In essence, this is nearly the time-equivalent of two sales for one stand; although, an artificial regeneration silvicultural system requires at least five visits (cruise, mark, TSA, plant, and regeneration check).
Given these constraints, why would a forester ever consider natural regeneration in red pine? The answer: diversity at both landscape and, potentially, stand scales. As foresters we know that we should never be prescribing the same practice over the entire landscape because not all systems behave in the same way and also because it could create the opportunity for ecological and/or economic collapse if our forest resources assets are not diversified. To ward off such threats, we vary our silvicultural practices around the landscape to promote both intra- and inter-stand diversity. In this vein, we should be varying our silvicultural systems for red pine and not solely rely on artificial regeneration. This will diversify red pine forest resource for both known and unknown constraints and future scenarios.
This trial hopes to overcome these contraints by retaining a sufficient volume of high-value trees until the final entry, in a systematic spacial structure that minimizes loss of regeneration to pathogens and makes for efficient operation, allowing all three stand entries to be profitable.