Crop Tree Management

Not a Thinning / The Process / The Goals

Crop tree management removes trees that touch the crowns of the most desirable trees; the crop trees. This usually means cutting trees from all four sides of the crop tree, unless two crop trees are adjacent to each other. Treat two adjacent crop trees as a single tree. No more than two crop trees should be adjacent to each other. If there is any doubt of whether a tree is touching or competing with a crop tree for light, cut it. Understory trees do not need to be cut because they do not compete with the crop tree for light.

A crop tree harvest allows sunlight onto all sides of the crop trees. Crop tree growth is maximized. Crop trees that were shaded on all fours sides of their crown experience a doubling of their growth rate after harvest. How crop trees are chosen and how many are chosen per acre is up to the owner. More crop trees per acre results in a heavier cut.

A thinning removes an even distribution of trees to reach a specific tree density, a crop tree cut does not. The residual stand tends to have a more clumpy distribution of trees than a thinning. This is because areas that do not have crop trees do not need to be cut. Crop tree management and can include an attempt to leave an even distribution of trees of a specified density, but that is not its primary objective. Thinning areas that lack crop trees is a secondary activity.

 

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The Process

1. Identify your goals
2. Forester walk through to evaluate the history and potential of each stand
3. Based on walk through, create realistic stand specific objectives to meet goals
4. Define crop tree selection criteria for each stand based on objectives
5. Inventory number of crop trees per acre.
6. The forester shows you, in a 100' diameter circle, the crop, cut, and leave trees. Based on this sample of the stand and the foresters recommendations, the owner decides on how many crop trees to have per acre (multiply the number of crop trees in the circle by 5). Keep in mind, the more crop trees, the heavier the cut. This activity is to ensure the owner is comfortable with the intensity of the harvest.
7. You and the forester decide on the number of crop trees per acres. This decision influences the profitability of the harvest. A light cut, with few crop trees, may not be profitable. Their are government programs to help finance these precommercial cuts. Poor quality stands often do not have the desired number of crop trees per acre. When this is the case, perhaps it is time to start a new stand. If you do not want to start a new stand, be sure to leave enough of an overstory to shade out unwanted regeneration.
8. Mark trees to be cut or mark the crop trees. Method of marking should be based on what logger is most comfortable with.
9. You can observe the rate of growth in your trees by measuring DBH at the beginning and end of the growing season. This gives you the growth for one year. This is an excellent way to observe how different factors affect the rate trees grow; factors like species, weather, crowding from other trees, and site quality.

Timber / Wildlife / Aesthetics

Timber: The goal of timber translates into growing high value trees faster. These crop trees need to have the potential to respond to increased sunlight and they need to have the potential to produce high value stumpage. The timber value of a tree is in the bottom 17' of the stem.

• Good growth potential
  • Crown in or above the upper canopy layer
  • Full and healthy crown
  • Smooth bark: Indication of fast growth
  • U-shaped forks at the base of trees are less likely to rot after a cut than V-shaped forks
  • Species: Needs to match site characteristics for optimal growth
    • Each has its own longevity and age at which growth slows
      • >20" for hemlock, yellow birch, sugar maple, and white ash
      • > 16" for paper birch, beech, and red maple
• High value potential
  • Straight stem: Avoid forks and bends in bottom 17'
  • Clean stem: Avoid branches and defects in bottom 17'
  • Fat stem: Larger trees usually increase in value faster than small trees
  • Species: Each has its own value for the region you live in

• Food
  • Mast producing trees: Oak, Beech, Birch, and Pine
    • Good growth potential for more mast production
      • One large crowned tree can produce 2-3 times the mast of a small crowned tree
      • See characteristics for timber
    • Healthy
    • High value potential not necessary
• Shelter
  • Mature conifer cover for deer wintering area
    • Holds warmth in winter
    • Low snow depth
• Other
  • Snags: Keep the snags you have and instead of cutting trees, girdle them to produce more snags
    • Provide food for insects that provide food for animals like woodpeckers
    • Provide cavities that act as shelter for birds
    • Cavities at the base of the snag (a den) shelter animals like bear
  • Multi-canopied forests support a larger variety of birds

• Favor healthy and large crowns (fits well with timber goals)
• Favor red and especially sugar maple for more brilliant fall foliage
• Favor flowering trees (shrubs) like dogwood and serviceberry
• Favor attractive paper birch
• Keep the big, old, knarly, fencerow trees
• Maintain a clear understory for a park-like appearance
• Point out trees you consider special to the forester to ensure their survival
• Consider time of the cutting: Cutting in the summer results in a browning because of dead leaves in the cut trees

(Perkey et al. 1993)

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