by Klaus Puettmann & Mike Saunders Department of Forest Resources, University of Minnesota A New Tool for White Spruce Management: Density Management Guides

Acknowledgements  This work was funded by Forest Health Funds through the Northeastern Area State & Private Forestry branch of the U.S. Forest Service.  Special thanks goes to:  Glen Erickson, N.C.F.E.S., USFS  Chris Peterson, UPM-Blandin  Mike Albers, MNDNR  Al Jones, MNDNR  Steve Katovich, S&P Forestry, USFS

Outline  Basic DMD Theory  A White Spruce DMD  Methodology & Development  Preliminary Results  Application to Management  Conclusions  Q & A

Density management can be managed through:  Planting, site preparation, # of seed trees  Release and TSI  Thinning  A cultural treatment made to reduce stand density of trees primarily to improve growth, enhance forest health, or to recover potential mortality

Density Age Density as a function of age

Diameter Age Tree size as a function of age

Diameter Density Putting those two pieces together: Diameter as a function of density

log Diameter log Density Take log of density and diameter

log Diameter log Density Lines approach a maximum line = self-thinning line self-thinning line

A White Spruce DMD: Preliminary Results

Fully Stocked Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D A Maximum Size-Density Line B Mortality Initiation Line C Maximum Stand Production Initiation Line D Crown Closure Line Management Zone White Spruce DMD for the Lake States Overstocked Understocked

Example 1: Plotting A Stand Trajectory Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D AgeDBH q TPA Age 10Age 20 Age 40 Age 30 Age 50

Stand Trajectories: Unmanaged Stands  Unmanaged stands can follow one of two general trajectories, depending on whether or not ingrowth is included in stand measurements.

Example 2: Unmanaged Stand Trajectories without Ingrowth Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D

Example 3: Unmanaged Stand Trajectory with Ingrowth Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D w/o Ingrowth w/ Ingrowth

Stand Trajectories: Unmanaged Stands (cont.)  Regardless of site quality or age, unmanaged stands of the same initial density will approximately follow the same stand trajectory.  However, the higher quality stand will move along a given density trajectory faster than a lower quality stand of the same initial density.

DMDs as Management Tools I  There are several ways that you can use DMDs for decision-making.  In the simplest case, you can use it to determine if a stand will develop to a desired minimum harvest diameter without thinning.

Example 4: To Thin or Not to Thin? Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D Let’s say we measure a stand and find that is has a density of 500 tpa and a DBH q of 4.0”.

Example 4: To Thin or Not to Thin? Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D We plot the point on the DMD.

Example 4: To Thin or Not to Thin? Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D Now assume we are managing for pulpwood and need a mean diameter of 8” at harvest. Do we need to thin?

Example 4: To Thin or Not to Thin? Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D No. This stand will have little mortality before it reaches a DBH q of 8”.

Example 4: To Thin or Not to Thin? Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D Now assume we need a mean diameter of 12” at harvest. Do we need to thin?

Example 4: To Thin or Not to Thin? Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D Yes, the stand will develop only to about 7” before it crosses the B Line and mortality begins.

Example 4: To Thin or Not to Thin? Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D We should schedule a thinning approximately when the DBH q is 7-8”.

DMDs as Management Tools II  Another way that DMDs can be used is for both scheduling and determining the intensity of a thin.

Example 5: When and How Much? Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D Reviewing the last example, we determined that our stand would grow to 7” before it crossed the B Line and mortality began.

Example 5: When and How Much? Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D At this point, we determined that we needed to thin. But how intense should the thin be?

Example 5: When and How Much? Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D Well, as we look at the graph the B Line crosses 12” at about 175 tpa.

Example 5: When and How Much? Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D Therefore, we should remove about 300 tpa.

Example 5: When and How Much? Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D This will allow the stand to develop to 11” before it crosses the B Line. We can accept the small amount of mortality beyond that.

Plotting a Thin  Low thins remove the smallest trees are from the stand, thereby increasing the DBH q after the thin.  By the same token, a high thin will reduce the DBH q and a mechanical thin will have no effect on DBH q.

Plotting a Thin (cont.)  Therefore, the type of thin will determine if the trajectory has positive, negative, or no slope, based on how it affects DBH q. Low thin Mechanical thin High thin

Plotting a Thin (cont.) Heavy low thin Light low thin  The intensity of the thin then determines the length and the amount of upward or downward slope of the lines.

DMDs as Management Tools III  DMDs can also be used for determining initial planting density.

Example 6: How many trees to plant? Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D To use the DMD this way, we have to work backwards from harvest.

Example 6: How many trees to plant? Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D Let’s assume that we want a final harvest DBH q of 10”.

Example 6: How many trees to plant? Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D By looking where the B Line crosses 10”, we estimate final density to be about 250 tpa.

Example 6: How many trees to plant? Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D Therefore, assuming that we will do only 1 thin and remove about 50% of the trees…

Example 6: How many trees to plant? Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D … initial planting density should be around 500 tpa.

Example 6: How many trees to plant? Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D If you would thin more heavily or if you accepted some mortality near harvest, planting density would increase.

Example 6: How many trees to plant? Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D Also, you may wish to plant more if you can estimate seedling mortality (before they would show up on DMD).

DMDs as Management Tools IV  Now, we can incorporate several of these applications to look at a more complex case.

DMDs as Management Tools IV  Let’s assume the following: 1.The current density is 1200 tpa (6’ X 6’) and the current DBH q is 1.5”. 2.Our minimum harvest diameter is 14”. 3.We have a budget to allow for two thins, and one may be precommercial. 4.We can accept 10% mortality in the stand before we will thin or harvest.

DMDs as Management Tools IV  So, the questions are: 1.When, in terms of DBH q, should we schedule thinnings? 2.What type of thinnings should we use? 3.Can we make some predictions of the intensity of the thinnings required?  Going to the chart …

Example 7: Planning an entire rotation Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D First, let’s plot the initial stand conditions.

Example 7: Planning an entire rotation Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D This stand should develop without much mortality until it approaches the B Line.

Example 7: Planning an entire rotation Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D At this point, the stand could be thinned, but the trees are still small.

Example 7: Planning an entire rotation Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D We could either: 1.Thin the trees now precommercially; or 2.Wait a few years until trees are larger. I chose #2.

Example 7: Planning an entire rotation Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D We wait until the stand develops to a DBH q of 6” and a density of 1000 tpa.

Example 7: Planning an entire rotation Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D At this size, a mechanical thin removing every other row is most appropriate.

Example 7: Planning an entire rotation Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D Now, the stand will develop to about 7” DBH q before crossing the B Line.

Example 7: Planning an entire rotation Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D Again, I am going to wait for the stand to develop further and accept some mortality.

Example 7: Planning an entire rotation Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D Now, at a DBH q of 8.5”, we have to thin, but… What kind? and… How intense?

Example 7: Planning an entire rotation Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D To answer these questions, we need to figure out what the final harvest density will be.

Example 7: Planning an entire rotation Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D At a harvest DBH q of 14”, there will be about tpa.

Example 7: Planning an entire rotation Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D If we thin to about 150 tpa, we would remove about 2/3 of the trees.

Example 7: Planning an entire rotation Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D This would require a very intense thin, most likely a low thin that would select for the best crop trees.

Example 7: Planning an entire rotation Density (Trees/Acre) Quadratic Mean Diameter (inches) A B C D Now, the stand should develop to a harvest DBH q of 14” w/o significant mortality.

Cautions  Although DMD are very useful, there are some cautions about their application one should be aware of: 1.No temporal component 2.Only density-dependent mortality 3.Only as good as the data that formed them 4.Should be applied cautiously outside there intended purpose

Cautions (cont.)  Our white spruce DMD should be primarily used to determine the timings of 1 st thinnings in white spruce plantations. cautiously.  Application to larger diameter stands and to natural stands should be done cautiously.

Conclusions: Where do we go from here?

Future Development I  There are several things ways we are trying to improve this DMD: 1.Finding data from more stands that will improve the accuracy of the DMD across a wider range of DBH q sizes and densities.

Future Development II  There are several things ways we are trying to improve this DMD: 2.Installing a long-term thinning study to: a)Refine placement of B and C lines b)Incorporate effects of budworm on growth as well as isolate size-density combinations most prone to budworm damage

Example: Elk thermal and hiding cover (Smith and Long, 1987)

Future Development III  There are several things ways we are trying to improve this DMD: 3.Develop a computerized version of this DMD

Example: ODMD developed by Dave Smith, Ontario Forest Research Institute