This is a 24-acre jack pine stand near Norris Camp in Beltrami Island State Forest, in northern Minnesota. It was clearcut between mid-November and late December, 2007. Slash was scattered across the site. Some scarification occurred during logging. All paper birch, spruce, balsam fir and unmarked red pines were reserved from harvest. In 2010, half of the stand was burned. Half was not burned. This is a retrospective case study initiated by Skylar Werner during her internship. Data collection and analysis were completed by permanent staff after the completion of the internship.
Achieve natural jack pine regeneration by distributing cone-bearing slash throughout the site while clearcutting.
Pre-treatment stand description and condition
Stand establishment and management history:
Natural origin stand.
Pre-treatment species composition:
Mature jack pine, quaking aspen, red pine, paper birch and balsam fir. Unfortunately, we didn't collect data on other vegetation prior to treatment.
Pre-treatment growth and stocking:
Timber volume was estimated at 30 cords/acre. The jack pine was advertised at 30% sawbolts. Red pine was advertised at 40% bolts.
Pre-treatment forest health issues:
Heterobasidian root rot is documented within a mile of this site.
The purpose of the burn was:
The purpose of the burn was to expose mineral soil seedbeds on 20-40% of the prescribed burn area, and reduce slash by 60-70%, in an effort to promote fire-dependent plant species, particularly blueberry, bearberry and other ericaceous shrubs, while regenerating jack pine.
Figure 1: Aerial photo of the treatment area with regeneration plots designated
Harvest mature timber and regenerate jack pine by scattering slash. After two years, burn slash on half the stand to favor growth of blueberries, bearberries and other ericaceous shrubs by exposing mineral soil over 20-40% of the ground surface and reducing slash by 60-70%. Allow the other half to grow without burning as a control comparison.
What actually happened during the treatment
Figure 2: Firefighter ignites grass and shrubs with a drip torch.
The burn took place in September 2010 with ground ignition by drip torch. A strip-head fire technique was used. The burn was successfully contained to the intended area.
Mineral seedbed and slash consumption assessments weren't documented after the burn.
Regeneration, as measured in Summer 2016:
Figure 3: Shrubs and trees on the burned site in 2016
111 jack pine regenerants per acre; (<1” dbh and under 1’ tall)
2,165 seedlings per acre; (<1” dbh & over 1’ tall); 12% jack pine, 18% balsam poplar, 70% quaking aspen
55 jack pine saplings per acre; (1-3” dbh)
Intense competition with alder, beaked hazel, red raspberry, juneberry, willow, and choke cherry.
Jack pine regeneration was concentrated near the south and north ends of the stand. Lowbush blueberry (Vaccinium angustifolium) occurred in the 1 meter subplot of the species/area plot, indicating it is present at a fine scale. Wintergreen (Gaultheria procumbens) and round-leaved shinleaf (Pyrola rotundifolia) occurred in the 32 meter subplot (moderately fine scale). Bearberry (Arctostaphylos uva-ursi) occurred in the 1024 meter subplot, indicating it is present at a coarse scale.
Figure 4: Shrubs and trees on the unburned species/area plot in 2016
443 regenerants per acre; 12% jack pine, 88% balsam fir
1,942 seedlings per acre; 74% jack pine, 14% balsam poplar, 8% balsam fir, 4% black spruce
443 saplings per acre; 75% jack pine, 12.5% balsam fir, 12.5% balsam poplar
Lowbush blueberry occurred in the 1 meter subplot (similar to the burned plot). Wintergreen occurred in the 16 meter plot (a bit finer scale than on the burned plot). We found no pyrolas or bearberry.
Some competition with beaked hazel, willow, and red raspberry
Total jack pine density on the burned plot was 425/ac. Total jack pine density on the unburned plot was 1822/ac.
We tallied 60 species on the species/area plot for the burned plot. That's 12 fewer species than on the unburned species/area plot. Thirty-two species that were present on the unburned plot were missing from the burned plot. Five of those species are non-native. Twenty species were found on both plots, but at a coarser scale on the burned plot, suggesting a lower density. Seven species were found on both plots at the same scale. Fifteen species occur at a finer scale in the burned plot than in the unburned. None of those were among the target species (blueberry or ericaceous shrubs). Nineteen species appeared in the burned plot that weren't in the unburned plot, including bearberry (a target species).
*Minimal aspen regeneration occurred on the unburned site, but not within our plots. Aspen regeneration was concentrated around two regeneration plots on the burned site. Scattered red pines exist on both sites, but not in our plots.
Plans for future treatments
Continue monitoring. Supplemental jack pine seeding or planting may be considered for the burned area.
Does prescribed slash burning affect the climate? It releases carbon dioxide, a greenhouse gas, from the woody fuels that are burned. However, unburned fine and medium fuels are quick to decay and release carbon dioxide, anyway. Burning releases it faster, but the difference is likely only a matter of a few years. Coarse woody debris that becomes charred during a prescribed burn can be protected from decay for a matter of decades, perhaps 100 years, thus resulting in long-term carbon sequestration. Preserved coarse woody debris can have a positive sustained effect on moisture retention and available soil nutrients on the site.
Phenolic compounds can leach from the foliage of living ericaceous shrubs. Once released in the soil, they can bind up available nitrogen, which can reduce seed germination and initial growth of pine seedlings. Activated charcoal can absorb phenolic compounds, reducing the allelopathic effect (https://link.springer.com/article/10.1007/s11104-006-9074-7). Some literature suggests charcoal remains active for about 100 years, suggesting an effective minimum fire rotation where ericaceous shrubs are a concern. Fire also causes top kill on ericaceous shrubs, temporarily interrupting the leaching activity.
Summary / lessons learned / additional thoughts
A more accurate appraisal could be made if we had been able to establish the species/area plots and collect data prior to burning, and then compared it with data collected from those respective plots after burning. Since that's not possible, we can compare the two plots with the assumption that they were similar prior to burning, but with the awareness that making assumptions devalues the study's scientific merit.
In the experience of local foresters, prescribed burning is generally not necessary for regenerating jack pine in this landscape. Clearcutting with a good distribution of the slash usually produces good results.
Burning caused jack pine density to fall from 1822/ac to 425/ac. That statistic would likely have been much different if the burn had been accomplished immediately after logging, and not delayed until after seeds had germinated. The low jack pine seedling density on the burned site is bordering on being insufficient, but the stand may fill in more over time. Lower stocking may be preferable if wildlife habitat is your first priority. However, such a dramatic loss of an important timber species is significant and may not be satisfactory for timber production goals.
A net loss of 12 species due to burning suggests a significant loss in species richness, but losing five non-native species is probably good. We also saw fire effect the apparent loss of 33 species and the apparent gain of 19 new species. The synecological score for moisture decreased from 2.3 to 2.1, which might be expected after a fire, perhaps reflecting the loss of some species that have a high moisture demand. The score for light decreased from 3.7 to 3.6, perhaps due to a post-fire increase in shrubby vegetation that shaded out some smaller stature species that have a high demand for sunlight. The synecological coordinates for nutrients and heat remained constant.
Regarding the goal of encouraging blueberries and ericaceous shrubs: Blueberries were conserved at the same density. Bearberry and round-leaved shinleaf (target species) apparently increased after burning, but wintergreen decreased. Fire seemed to increase overall shrub density.
Harvey was a staff forester at the MNDNR Northwest Region headquarters in Bemidji, MN. His primary focus was Ecological Land Classification and applications in silviculture. Prior to 2008, he was primarily involved in the timber program. He worked for the Minnesota DNR since he graduated from the University of Minnesota in 1978. Harvey passed away in July of 2022.