Forest regeneration and the associated challenges seem to be gaining importance with more foresters each year, as regeneration deficiencies and the long term outcomes of aging forests become more of a concern. The following information is being shared because of a collective, mutual interest in providing adequate, desirable regeneration throughout Wisconsin’s forests. Ashland County Forest consistently grows quality regeneration; the intent of this case study is to share successes, failures, observations and thoughts on what's working for Ashland County. The quality and amount of regeneration means that northern hardwoods can establish despite browse pressure from deer.
Since 2008 we have moved northern hardwood management practices away from blanketing handbook recommendations. Using our combined knowledge, experience, silvicultural principles, handbooks, and scientific literature, we make decisions based on the stand’s current conditions, expected future conditions and desired future conditions using sound reason and judgement by considering all pertinent aspects of a given stand. We try to avoid management triggers (e.g. basal area) and prefer to view each stand as holistically as possible to identify issues and opportunities.
Pre-treatment stand description and condition
Stand establishment and management history:
County Forest History
Prior to 2007, all northern hardwood management on the County Forest was all aged, even aged management was not practiced even on poor sites or in stands that technically typed out as red maple.
From 1933 to about the late 1950’s, harvesting was by legal descriptions, had minimal marking or cutting requirements and was often loggers' choice.
In the 1960’s the first recon, compartment maps and harvest scheduling / tracking started to occur; new forest road infrastructure was also created to access the entire forest. From this time, to around the late 1970’s, marked sawlog thinnings occurred in most of the County Forest’s hardwood stands. Better quality stands with reasonable access would undergo TSI’s by girdling pulp or “cull” trees in an attempt to improve the stand. Mining Company lands that Ashland County retained the timber rights on were often diameter limit cut; these lands are now entirely County owned and part of the County Forest.
1980’s – 2007 all aged management based on Carl Arbogast's research paper was practiced; emphasis was placed on growing large trees to better meet the reverse “J” diameter distribution curve. Most hardwood stands had some degree of an Elm salvage harvest. Stands were not entered until they hit 120ft2/ac of basal area. During this time several shelterwoods were conducted but were not followed up with overstory removals.
Stand 24-12 Management History
1986: Single tree selection harvest, reducing stand basal area from 135 ft2/ac to 85 ft2/ac
2004: Stand's basal area was found to be 138 ft2/ac. Recon notes indicated heavy browse of dense sugar maple regeneration.
Pre-treatment growth and stocking:
Table 1: A breakdown of the size class by basal area. The total basal area before harvest was 138 ft2/ac and the average DBH was 11.6".
|Size Class||Basal Area (ft2/ac)|
Pre-treatment forest health issues:
Deer do live in this stand year round as three sides of it are cedar swamp deer yards. There is browse, but it is not a limiting factor based on abundance of regen in adjacent portions of the stand. Past browse damage is visible on many sugar maple stems but they have been able to grow above the deer's ability to browse them and are doing well.
Deer management unit deer densities from 2004 – 2013 average 15.6 deer/square mile. The highest densities occurred in 2007 (20 deer/sq.mi) while the lowest occurred in 2013 (8 deer/sq.mi). Historical deer densities were similar ranging from 7 deer/sq. mi in 1983 to 19 deer/sq. mi in 1989, averaging 14 deer/sq.mi from 1983-1993. This data is based on deer management unit 28 from 2013 which was the last year that data was calculated before the use of County units.
Single tree selection harvest. Cut all aspen with one or more 100" pulp sticks. Cut all balsam with two or more 100" pulp sticks. Balsam with one 100" pulp stick may be cut at the logger's discretion. Utilize all felled trees to a 4" minimum top diameter for pulpwood and a 10" minimum top diameter for saw logs. Do not cut spruce, cedar, hemlock, or pine. Sugar maple is the dominant tree species and although harvesting will allow for regeneration and release of other species sugar maple will likely remain overwhelmingly dominant. Harvesting will change the distribution of trees across size classes to more closely resemble the J curve management goal for uneven aged stands. Vertical stand structure will be improved with thinning due to the release and establishment of regeneration in canopy gaps. Logging slash and other woody debris will add to the horizontal structure and wildlife habitat value of the stand.
What actually happened during the treatment
In 2006 the actual harvest was done with the use of a hot saw and tree-length grapple skidding. In 2006 allowing such equipment to operate in this stand was a contentious decision between foresters working on the forest as some were of the opinion this type of equipment would cause too much damage. However, tree length skidding provided a bare mineral seedbed that allows yellow birch to thrive.
Residual stand density was 68 ft2/ac, down from 138 ft2/ac.
Surveys of canopy gaps have shown promising results. In gaps approximately 30 feet in diameter regeneration density was found to be 20,000 stems per acre. Approximately 8,000 saplings per acre have been able to grow out of the reach of deer and are roughly 1-2" DBH and 10-15 feet high. The remaining 12,000 stems have become suppressed by the 10-15 foot regeneration and no longer have the light resources to outgrow the deer and will remain a perpetual source of deer food. 8,000 saplings per acre is far more than needed to occupy a 30 foot canopy gap. Regeneration of 10,000 to 20,000 stems per acre is common in these gaps created by the selection harvest (figure 1). In addition, the harvest served to release sugar maple saplings about 33 years old. Small stems that were browsed prior to growing beyond the reach of deer will have browse-induced defects corrected since they occurred at a young age and were able to be released before too much damage was incurred (figure 2). In addition, yellow birch vigorously regenerated in some of the skid trails from the 2006/07 harvest as a result of the tree-length skidding (figure 3).
Other portions of the stand that had smaller gaps or were only lightly thinned resulted in minimal regeneration (figures 4 and 5).
Figure 1: Mixed northern hardwood regeneration. 10,000 – 20,000 Saplings per acre. This level of advanced regeneration is common in the County Forest.
Figure 2: Mid size canopy gap, dense sugar maple regeneration. Note the lower forking and crook of many of the stems from past deer browse. The lower crook on such small stems is not a concern as the tree will out grow this as it gains diameter.
Figure 3: Skid trail used in 2006/07 harvest. Tree length skidding provided a bare mineral seedbed allowing yellow birch to thrive. Yellow birch only accounts for about 2% of the overstory’s density.
Figure 4: Small canopy gap created in area of stand with higher residual basal area. Minimal regeneration other than ironwood.
Figure 5: Portion of the stand that was lightly thinned, no canopy gaps, leaving a higher basal area resulting in very little regeneration or ironwood. If the entire stand was marked this way it would be reasonable to think there is a regeneration problem.
Plans for future treatments
Stand 24-12 will undergo an overstory removal on roughly 60% of the stand to release the outstanding regeneration in areas with a slowly failing overstory. Areas that still have a quality overstory will continue to be managed all aged using single tree selection.
Sale establishment will occur in 2019. In the overstory removal, green tree retention will include retaining all hemlock, oak, cedar and pine. An additional 5 – 30 ft2/ac of hardwood species will be marked for permanent retention following the silvicultural handbook guidelines. Post harvest, areas in the single tree selection unit that lack regeneration will be scheduled for evaluation using code HM8 for 5 years. If regeneration is still lacking and dense sedge or ironwood appears to be the issue we will begin a herbicide treatment to control the sedge and ironwood. Harvest timing will be restricted to August 15th – March 15th to prevent burning off the regeneration in the hot summer heat while the trees are actively growing. August 15th is earlier than what some foresters would conduct an overstory removal but in other past overstory removals it has not caused an issue and provides additional acreage for non-winter harvest opportunities for area loggers as well as better stumpage prices for the County.
The decision to conduct an overstory removal in portions of this stand was not automatic. The stand was essentially cruised twice and walked a third time evaluating current and future options and what those results would yield. Determining what the overall best long term management would be for the health and productivity of this stand was not easy.
This case study was developed with support from the United States Department of Agriculture's National Institute for Food and Agriculture (USDA-NIFA), Renewable Resources Extension Act (RREA). Project #MIN-44-E02, principal investigator Eli Sagor, University of Minnesota.
Summary / lessons learned / additional thoughts
Initial stand recon of 24-12 occurred in 2004, for the 2007 harvest. Though the stand was poor to average quality, likely due to direct and indirect poor past management, the option of even age management was not considered as practicing all aged management was the standard operating procedure. This resulted in a heavy selection harvest (residual basal area 68 ft2/ac). Even today, conducting a selection harvest to 68ft2/ac is not an uncommon practice in the County Forest. The issue in stand 24-12 is that the residual trees are simply overgrown, poor quality and low vigor. Looking back, this stand should have been managed even aged in 2007 with a shelterwood harvest and subsequent overstory removal.
Thoughts to Ponder:
In the absence of extreme limiting factors like invasives and very high deer numbers, are foresters un-intentionally limiting regeneration success by not adequately creating canopy & light conditions sufficient enough to give desired species the competitive advantage over undesirable species or conditions, while still treating a stand within the side boards of acceptable management? Given the huge differences in regeneration in stand 24-12 (figures 1-3 versus figures 4 and 5), I would say that is a distinct possibility.
A lot of our management guidelines, with regard to managing northern hardwoods, are based off managing the overstory to produce the best growth and highest value products. They provide rather limited guidance on what intricate factors influence establishing regeneration, largely because they are difficult to identify, difficult to create or simply out of our control. A lot of times, factors like sedge, ironwood, deer, worms get blamed solely for poor regeneration. They cannot be dismissed, as deer exclosure results don’t lie, but a lot of times these factors get more blame than they deserve, because they are easy to identify and are known culprits foresters are looking for. In reality, we may be over looking simple subtleties that we can control, such as residual stand density levels, harvest timing and site prep, to name a few, that very well may play just as big of a role in establishing regeneration as the easy to identify culprits.
We also need to consider the historic disturbance regime, past disturbances and events. The fact that today's forests are a result of conditions from the past gets overlooked too often. We expect to get regeneration if we properly implement a accepted silvicultural treatment on a given stand and little if any consideration is given to what the conditions might have been that created the current stand. If we choose to regenerate a forest but cannot closely enough replicate the conditions (biotic & abiotic) of the past, or that are suitable for a particular species we should not expect to get the same results and the stand will begin to transition to a different species mix or cover type based off the disturbance we created and conditions at that time.
Ashland County Forest has made regeneration a priority and has made financial and work load commitments to treat stands to establish regeneration when it is lacking. Seeing this stand’s contrasting conditions and having been involved with it in 2006/2007, as well as implementing a continual sedge / ironwood treatment program, really made us take a step back and ask the question: are we really managing stands appropriately to establish adequate regeneration? Or are we managing the overstory and hoping for regeneration? As foresters, is the order of what's important with regard to managing hardwood stands changing? We believe as more of us recognize regeneration short falls, it is changing. Growing young trees is at or near the top for many of us. The point we want to make is, as our priority objectives change, our overall management strategy will likely need to be adjusted away from our historic management benchmarks to attempt to meet our objectives.