This forested area is located 5 miles north of Beaver Bay, MN in a large-patchy landscape dominated by northern hardwoods, aspen, and paper birch. After several field visits together, the forester and botanist agreed to prescribe a regeneration cut timber sale. Both envisioned a stand that would contain many structural and compositional characteristics of an older growth stage but still allow for selective timber management. Many of the trees are reserved from harvest including all of the conifers and the larger, older northern hardwood tree species like black ash, basswood, sugar maple, and the mysterious yellow birch.
The harvest prescription is to remove all of the paper birch, aspen, and maple less than 14" dbh (diameter at breast height) in strips and small gaps. The harvested openings will provide room for suckering and sprouting tree species like aspen and sugar maple.
My task as the sale administrator is to make sure the logging crew implements the set of instructions written up for the sale. But of particular interest to me as one who loves silviculture (and who can't seem to find a job in it, or even utilize my Union to challenge it) is how to regenerate the elusive, yet very unique yellow birch.
The silvicultural literature out there suggests four main requirements that are necessary for yellow birch to regenerate successfully and grow into mature trees:
1. Adequate seed trees and seed to regenerate. Check.
Although it’s rare to find in Northern MN nowadays, this stand has the seed trees! Many large diameter, mature (some decadent) trees are found throughout this area. Le Magnifique!
Yellow birch typically has good seed crops every 2-3 years and this season appears to be exceptional. Upwards of 1-5 million seeds/acre can be dispersed in a good year. Most don’t take however.
These are seeds (pistillate bract) I collected today before old man blizzard explodes over the North Shore.
2. Adequate seedbed conditions. Question mark.
The literature is very consistent here. Although seed can grow and germinate on stumps, mossy logs, and decayed wood, the best conditions is exposed mineral soil. According to the USFS Silvics manual (one of the traditional i.e old school... sources of silvicultural information):
"In undisturbed stands, yellow birch can only regenerate on mossy logs, decayed wood, rotten stumps, cracks in boulders, and windthrown hummocks because hardwood leaf litter is detrimental to its survival elsewhere (45). In June most seeds germinate in compacted leaf litter that birch radicals and hypocotyls cannot pierce (10). Drying of the litter during the growing season kills most germinants. The remaining seedlings later succumb to frost damage or are smothered by the next leaf fall. Unless stands have been burned or heavily disturbed by blowdowns or logging, abundant birch regeneration is normally restricted to edges of skidroads or landing areas on well-drained sites. On less-well-drained soils, sufficient moisture remains in the leaf litter to result in adequate establishment if advance regeneration of other species is removed."
Harvesting this sale was not allowed during non-frozen ground conditions. That restriction was prescribed to ensure that soils and herbaceous vegetation would be protected. Perhaps the greatest benefit of this regulation is the protection of the shallow (fine) roots of desired reserve species. One problem with frozen ground harvesting however is that the skidding process doesn’t necessarily scarify the soil adequately enough. It appears that only the main skid trails have leaf litter removed and exposed mineral soil. One way we can get around this is to underplant yellow birch bare-root seedlings and other preferred species directly into the ground.
3. Adequate light and other environmental conditions for optimal growth (post-harvest). The literature suggests small openings or gaps from 0.1 to 0.6 acres in size. Check.
Given the nature of the felling and skidding patterns, a variety of gap sizes are present. This should allow us to try a few different regeneration strategies including different planting configurations.
4. Adequate control of and protection from competitive species including vegetation and animals. Unknown.
Rabbits, deer, aggressive raspberry shrubs, sugar maple, and other damaging agents all play a role in preventing that little yellow birch seedling from maturing into a sapling and eventually... a fully grown tree.
I get asked this question a lot. When will you know if this project’s successful? Some new forester 10 or 15 years from now will have to answer I suppose. Guessing the DMT needs more stressed out program foresters to help the ECS specialists with this too....
Now… enjoy this from the other elusive "burch"