White pine reserve shelterwood (UMN-CFC)

Stand Information

Evening silhouette of white pine shelterwood stand

State or Province:

Minnesota

Nearest city or town:

Cloquet

Describe the location:

T49N R17W 4th PM Sec. 31 NE ¼ NE ¼: Cloquet Forestry Center just east of University Road

Landowner:

UMN - Cloquet Forestry Center

Cover-type:

Pine

MN ECS Native Plant Community System:

Fire Dependent

Plant community or habitat classification and growth stage:

FDn33a

Forest Health Threats:

Deer

Estimated year of stand origin:

1910

Additional information about stand origin:

Seed trees originated apx 1910. Stand was thinned 1962, 1972, and 1994

Site Index:

feet

for species:

white pine

Silviculture System:

Shelterwood

Brief silvicultural objective:

To reserve mature white pine for legacy and open growing space for a new cohort of white pine.

Soils:

188C—Omega loamy sand, 2 to 12 percent slopes

Stand area:

22 acres

Treatment area:

7 acres

Overview

This case study seeks to determine the success of maintaining mature white pine for reserve and aesthetic value while regenerating white pine with a shelterwood harvest. In an attempt to maximize white pine regeneration, the prescription for the shelterwood harvest included utilizing full tree and random skidding in late fall to maximize brush breakage and soil surface disturbance to limit understory competition and prepare the seed bed.

Silviculture Objective(s)

Reserve white pine canopy trees as legacy and seed trees. Regenerate second cohort of white pine with target of 700 stems/acre. The target stems/acre was not designated at the time of prescription but collected during case study preparation from the Wisconsin Silviculture and Forest Aesthetics Handbook section on white pine.

Pre-treatment stand description and condition

Stand establishment and management history:

Natural regeneration 1910-1911, Thinned 1962, 1972, 1994.

Pre-treatment species composition:

Red pine, white pine, scotch pine, jack pine, white spruce, balsam fir, maple, paper birch, and aspen.

Pre-treatment growth and stocking:

Across the entire 22.6 acre stand (including volume from the reserve shelterwood), the pre-harvest cruise suggested that there were a total of 484 cords of standing volume, or roughly 21.4 cords per acre (Author’s note: this seems like a low volume per acre for a mature, high-quality red pine stand). Of this, 68% was red pine, 19% white pine, and less than four percent each of white spruce, aspen, paper birch, balsam fir, red maple, and jack pine.

In the white pine reserve shelterwood area, plus a 50 foot wide road buffer on the east edge, only the reserve trees were measured. This measurement suggested an estimated basal area of 52.7 ft²/ac, which seems more appropriate than the 21.4 cds/ac number listed above . Of this, 77% was white pine, 17% red pine, and less than four percent each of balsam fir, aspen, white spruce, paper birch, and jack pine.

Pre-treatment forest health issues:

Scattered white pine blister rust.

Landowner objectives/situation:

A majority of the pre-European settlement white pine was harvested around 1910, when much of the Cloquet Forestry Center (CFC) forest was cut over. Unfortunately, it is not known what percentage of the pre-harvest acreage would have been in a white pine cover type, though it is thought to be less than the percentage of red pine.

The purpose for reserving the white pine in this prescription was to maintain as much of the mature white pine component as possible in the CFC forest. At the time of treatment, the CFC had only 23 acres dominated by white pine across the total 3400 acres. CFC forester managers decided that where opportunities existed to maintain or increase the volume of white pine they would be taken. Given the anticipated seed rain from the reserved trees, white pine was expected to become the dominant regeneration component in the treatment area. It was also thought that both reserve trees and future canopy trees would contribute to increasing the overall seed level on the forest to, potentially, add additional acres to the CFC white pine type.

Silviculture Prescription

No harvesting until October – prescription stated the reason for this was that the temperature would be colder and brush more brittle to create more breakage and allow for two growing seasons before competition control is needed.

Full tree skidding – to maximize brush breakage, to maximize soil surface disturbance (seed bed preparation), to minimize slash debris on area, for aesthetics, fire consideration, seed surface exposure.

Random Skidding – Skidder operators were instructed to skid over the entire sale area to cause as much breakage to understory brush, yet minimize damage to advanced conifer regeneration.

Harvest before soil freeze up – to allow maximum soil disturbance. For seed bed preparation and possibly increase tree stress by damaging surface feeder roots of the seed trees, stress can be beneficial in producing seed.

What actually happened during the treatment

Treatment was implemented as prescribed November 3, 2003 - November 21, 2004. White pine regeneration started within a few years after harvest but was experiencing heavy levels of herbivory from white-tailed deer. In 2013, systematic bud-capping of rough one individual per 36 ft² was started to help ensure an adequate number of seedlings could grow past browse height (roughly 4-5 ft tall). As of 2017, there was a minimum average stocking of 1583±1880 white pine seedlings per acre (see below for more detail); many of these are considered free-to-grow but some budcapping continues.

Post-treatment assessment

Prior to harvest in 2004, each reserve tree in the white pine reserve shelterwood area, plus a 50 foot wide road buffer on the east edge, was measured (no evidence could be found of a post-harvest cruise). This measurement totaled a basal area per acre of 52.7 ft²/ac. Of this, 77% was white pine, 17% red pine, and less than four percent each of balsam fir, aspen, white spruce, paper birch, and jack pine.

In 2017, twelve 20BAF variable radius plots for basal area were sampled. This cruise calculated a mean basal area of 95 ft²/ac (CV = 61%). Of this, 64.9% was white pine and 35% were other species (See Table 1). The relatively high coefficient of variation for both the stand basal area and regeneration illustrate the stand is quite variable with patches dominated by mature trees and patches dominated by regeneration.

Table 1. Basal Area of reserve trees calculated from twelve 20BAF variable radius plots.

	White Pine BA	Other Species BA	Total BA
Mean (ft²/ac)	61.7	33.3	95
StdDev	56.9	54.8	57.9
CV (%)	92.2	164.6	60.9
% of total	64.9	35.0

In 2017, twelve 1/500th acre plots for were sampled for regeneration data (Seedlings > 12" tall and < 4"dbh). This sample calculated a mean stocking level of 2708 seedlings/ac (CV = 75%). Of this, 58.5% was white pine and 41.5% were other species (see Table 2). (Author’s note: a layer of heavy snow covered the ground and, likely, some seedlings. Thus these figures likely underestimate actual seedling stocking.)

A visit to the stand in December of 2015 revealed some lesions on many of the white pine seedlings’ limbs. It is thought that these were caused by a summer hail storm. They do not appear to be causing mortality though it is unknown whether or not these will limit growth.

Table 2. Seedling regeneration (in Trees per acre [TPA]) (Seedlings > 12" tall an < 4"dbh) derived from twelve 1/500^th acre plots.

	White pine	Other Species	Total
Mean (TPA)	1583	1125	2708
StdDev	1880.9	1150.6	2038.9
CV (%)	118.8	102.3	75.3
% of total	58.5	41.5

Plans for future treatments

Continue to budcap select white pine seedlings to ensure that at least 700 white pine seedlings/acre grow past the deer browse level. If seedling height growth stagnates, canopy trees will be assessed as to whether or not the overwood white pine should be harvested to fully release the advanced regeneration.

Costs and economic considerations

2004 Harvest value/ac.: $2793. 2004 Reserve tree value / ac.: $573

Summary / lessons learned / additional thoughts

For the objective of maintaining current white pine seed crop trees and promoting future potential seed crop trees this prescription is currently deemed to be successful. Very few of the reserve trees have succumbed to windthrow or other mortality agents. The estimated seedling density of 1583 white pines per acre (likely an underestimate due to snow cover during sample) suggest that the future canopy will be primarily composed of white pine. This density also suggests that pre-commercial thinning and pathological pruning may need to happen to reduce incidence of white pine blister rust, which is not currently observed in any seedlings.

Although seedling density was not quantitatively monitored between 2004 and 2017, it is suspected that it took some time (> ten years) to reach at least 700 seedlings per acre. Three factors may have shortened this window of recruitment: 1) higher levels of ground scarification, 2) earlier herbivory protection, or 3) matching the harvest/scarification year to a mast cone crop in the seed trees. Understory competition from hazel and other shrubs does not seem to be limiting seedling recruitment across the stand, though some patches of high-density hazel exist.

This prescription would also be considered successful if heterogeneous stand structure for wildlife habitat or carbon accumulation was the primary management objective. The current stand structure is both vertically heterogeneous with high levels of canopy biomass in the crowns of the reserve trees and good understory biomass in the understory from both trees and shrubs. This biomass is also horizontally heterogeneous with many of the reserves being in patches and understory developing in patches.

If one’s primary objective was white pine timber production and economics, the time observed to adequate regeneration density, thought to be at least ten years in this case study, is probably too long. Ideas listed above could have shortened the recruitment window. Additionally, understory light availability could have been increased by reserving fewer white pines would have needed to be reserved or by a return entry to harvest a portion of the reserved trees. Removing the currently reserved canopy trees would allow a manager to recoup the full economic value of the standing timber, the basal area of which has nearly doubled since the 2004 harvest.

Photographs