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Red Pine
Article #305 February 2020
By Bill Cook

Red pine has long been a fast-growing, attractive, and relatively disease-free forest tree species.  While many natural stands exist, most red pine was planted.

     A great deal of Michigan’s red pine was planted by the Civilian Conservation Corps, mostly in the 1930s.  Michigan had one of the largest CCC programs in the nation and a lot of red pine was planted to reforest lands that had been cutover and burned. 
     Red pine was selected because the seeds were readily available and fairly easy to extract and work with.  Nevertheless, it was a quite a task to grow seedlings in nurseries.  The process was rather involved, especially for the technology of the times.  A visit to the CCC Museum near Higgins Lake explains all this. 
     Fast-forward to more recent times and much of that red pine has been managed by the Michigan DNR, federal government, and industry using a prescribed thinning regime.  Researchers developed these protocols after the optimistic and hopeful CCC-ers, and others, had planted thousands of acres of red pine. 
     Red pine growth patterns have a bit of an antagonistic relationship between site occupancy and rapid growth.  The best spacing will close the canopy, exclude most competing vegetation, and begin self-pruning.  All this is good.  However, attaining enough diameter to justify a commercial first thinning is also important.  Too close together, and the canopy will close before that first pulpstick appears.  Too far apart, and stand-wide growth will suffer and stem form will be branchy for too long.  Small and few knots is one objective. 
     Spacing recommendations, usually about 6 by 8 feet or 6 by 10 feet, found the sweet spot, assuming a future thinning would happen to keep the trees growing at full speed.  Too often, that first thinning didn’t happen or was done too late. 
     Red pine is remarkably sensitive to shade.  Once the canopy closes, diameter growth drops dramatically.  However, height growth continues.  So, abandoned and unthinned stands consist of tall, skinny trees that are stressed from too little sunlight and the subsequent loss of sugar production through photosynthesis. 
     As lower branches die, the living crowns of trees can drop to ten percent of the height of the tree, or less.  At this point, the plantation (or natural stand) is a lost cause.  Even if thinned, the crown ratio will not recover, and the gaunt lollipop trees will be even more subject to wind breakage. 
     With long-unmanaged stands, it is often best to clearcut and start over.  One of the worst things that can be done to a red pine stand is a failure to thin.
     While relatively pest-free, red pine does have a few health concerns worthy of mention, in addition to benign neglect (lack of management). 
     Stressed red pine are an invitation to bark beetles, wood borers, and other pests.  Especially in drought years, bark beetle populations can explode killing much of a red pine stand.  Sawfly larvae enjoy munching on younger trees, particularly when they’re shaded. 
     Oddly, the good deed of thinning red pine stands can result in punishment by a fungal disease called “Heterobasidion root disease”, or HRD (H. irregulare).  Rather pernicious, HRD can invade recently cut stumps.  Once in a stand, the pathogen will spread through root systems.  Pockets of dead and dying red pine appear. 
     Diplodia shoot blight and Sirococcus blight will disproportionately impact multi-storied stands, which are sometimes created for species diversity or other good reasons.  Understories of red pine, under or near mature red pine can have high mortality rates.  
     Scleroderris canker is another enemy of red pine.  A more virulent European strain can cause stand mortality.  However, that strain is not yet known to be in Michigan. 
     On the habitat side, young plantations provide excellent cover from weather and predators for many animal species.  However, once canopies close and shade eliminates most of the understory, species diversity drops for a period of time.  However, this cloistered habitat is preferred by a handful of wildlife species, which adds diversity at the community level in a landscape dominated by hardwoods and aspen. 
     Traditional red pine management guidelines were built around the goal of maximizing the commercial growth for forest products.  As goals change over time and with new ownerships, opening-up red pine stands now comes with certain risks of disease.  Many red pine stands have been lost through development of human infrastructure or converted to other forest types.  However, red pine remains one of Michigan’s most common and beautiful tree species.

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Mature red pine stand. 

 Unthinned red pine where interior trees are beyond recovery. 


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