Putting Crop Tree Management into Practice

Roger Monthey
Forest Stewardship Coordinator
USDA Forest Service
Northeastern Area

Forest landowner Brooks Mills visualizes high-quality veneer or saw logs in each of his crop trees, from tiny saplings to towering timbers. A longtime and vigorous advocate of crop tree management, Brooks puts his beliefs into practice on his 440-acre Tree Farm near Holden, Maine. He strongly endorses:

  • Identifying crop trees at an early age;
  • Measuring their diameter growth periodically;
  • Weeding around the trees to remove competitors, especially less desirable species;
  • Pruning side branches; and
  • Thinning the crop trees as appropriate when the crowns touch.

Brooks selects potential crop trees at 2 inches diameter at breast height (d.b.h.), snip prunes the dead branches, marks them with a spot of paint, and weeds out aggressive competition such as beech, red maple, hornbeam, and striped maple. Repeating this process every 3 to 5 years ensures that they will be good crop tree candidates when they reach 5 to 6 inches in diameter in 10 to 15 years. During a recent tour by the Small Woodlot Owners Association of Maine (SWOAM), Brooks contrasted a marked and weeded red oak crop tree of about 4 inches d.b.h. with nearby unmarked and unweeded oak saplings. The vigor and size of these latter trees paled in comparison to the crop tree.

Use of hand saw.   Use of scouring device.
Competing and/or less desirable species are removed with a hand saw (left) or girdled with a scouring device (right).

Pruning crop trees at an early age also helps develop the desired characteristics of a future veneer tree. Quality can be greatly increased if the branches are pruned off as early as possible. Brooks uses hand snips to remove branches on saplings 1–2 inches d.b.h. and a pruning saw on trees 3–6 inches d.b.h. and larger. Leaving at least 60 percent of the tree length with a live crown is essential to promote proper growth. Pruning can be continued as the crop trees grow and mature, using a polesaw or even a ladder to reach as high as allowable. Ladders come in especially handy when pruning softwoods, where longer logs are preferred.

 
Brooks Mills demonstrates proper pruning techniques.

 

 
Silky saws, which cut on the pull stroke, help ease the task of pruning (insert showing sawteeth). (Photos courtesy of SWOAM.)

In addition to weeding and pruning, Brooks thins poorer quality trees from around his selected crop trees, selling them for profit as firewood and pulpwood. Some mature trees may be harvested at the same time to make the entire operation more economical. Brooks conducts his harvests with a cable skidder and a 4 by 4 tractor with a logging winch, loader bucket, and forks. He trucks his firewood, short-length pulpwood, and logs with a 1-ton dump truck.

Over 2,000 of Brooks’ current trees have been measured for growth. His interest in tree growth and the annual rate of return on his crop trees led to his collaboration with Neil Lamson, formerly a silviculturist with the USDA Forest Service, to publish Bantic—The Brooks and Neil Tree Investment Chart (see sidebar).

 

Bantic—The Brooks and Neil Tree Investment Chart

“The Brooks and Neil Tree Investment Chart (BANTIC) is a Microsoft Excel spreadsheet that can be used to determine financial maturity of standing trees, estimate stand value, and evaluate cultural treatments. It automatically computes volume, value, and annual rate of return for trees from 10 to 30 inches d.b.h. having logs with 2, 3, and 4 clear faces. BANTIC is a very powerful tool because the user enters current local log prices, which makes the results applicable for any species in any geographic region. The user can also change the log volume table, and the spreadsheet will use those volumes in its computations” (p. 4).

Copies of the publication and program may be downloaded from http://www.fs.fed.us/na/durham/ima/pubs_maps/text/bantic/bantic.htm. Hard copies are available by contacting the Forest Service at 603-868-7693 or jamccomb@fs.fed.us.

Mills, Brooks; Lamson, Neil. 1999. BANTIC—The Brooks and Neil Tree Investment Chart. NA–TP–03–99. Durham, NH: U.S. Department of Agriculture, Forest Service, Northeastern Area State and Private Forestry. 4 p. + 1 computer disk.

Mature crop trees are the ultimate goal of Brooks’ management activities. Brooks defines a crop tree as:

  • A high valued tree species that enjoys good market demand for saw and veneer quality logs. In Maine, this applies to red oak, sugar maple, yellow and white birch, white ash, and bigtooth aspen, and can also include red maple, basswood, beech, butternut, and black cherry, as well as softwoods such as white pine and red spruce.
  • A vigorous tree in the dominant or codominant crown class.
  • A tree with a straight and relatively defect-free trunk that will produce one or more 10-foot logs with 2, 3, or 4 clear faces (preferably 12-foot or longer for softwoods).
  • A tree species best suited to the site so it will develop well.
 
Brooks Mills proudly displays examples of his hardwood and softwood crop trees.

 

The Proof is in the Numbers

A crop tree demonstration area installed at Marsh-Billings-Rockefeller National Historical Park in Woodstock, Vermont, in fall 1999 has produced sizeable results in just a few years. A total of 85 crop trees were selected on the 4-acre site—45 in the 2-acre treatment area and 40 in the 2-acre control area. The treatment consisted of a crown-touching release of 0 to 4 sides of the crop tree selected.

The selected trees were assigned any combination of three objectives—aesthetics, wildlife, or timber. The measures used to evaluate the treatment’s effectiveness vary by objective:

Objective

Measurement

Aesthetics

Increased vigor of desirable trees or increased abundance of a preferred species

Wildlife  

Increase in hard mast production or retention/formation of cavity den trees

Timber 

Increase in diameter growth

The crop trees are measured periodically to track the treatments’ effectiveness. Bob Cooke, a forester with the USDA Forest Service, recently completed a partial analysis of the diameter growth of 40 white ash and sugar maple crop trees selected for timber objectives (a more complete analysis of all crop trees is due out in 2005). Results are shown below.

Measured growth in inches of timber crop trees, 1999–2003

 

Mean Growth

 

Range of Growth

 

Treatment

Control

 

Treatment

Control

White ash

1.56

1.17

 

1.0–2.0

1.0–1.5

Sugar maple

1.14

0.63

 

1.0–1.3

0.3–0.9

The treated white ash grew an average of 36 percent more than untreated trees, while the treated sugar maple showed an 80 percent growth increase. Results like these project out to large volume gains and possibly shorter rotation lengths, and are merely an indication of how successful crop tree management can be in meeting specific forest management objectives.

Brooks’ long-term goal is to support 75–100 crop trees per acre at 20–25 foot spacing between trees. The actual number may range widely due to site conditions and other factors. USDA Forest Service publications recommend crop tree densities of anywhere from 20 to 75 trees per acre for timber objectives. However, crop trees may be selected for wildlife, aesthetics, and water quality functions as well, which could increase the number of crop trees per acre.

Brooks Mills remains determined to manage his woodlands wisely and to pass on management responsibility to his son, John, a consultant forester. Brooks summarizes his forest management objectives as follows:

  • We are building a quality forest one individual crop tree at a time.
  • We do it by cutting what everyone else generally leaves (low value trees) and leaving what everyone else cuts (high value trees).
  • High value trees should be cut when they are mature, show defects, experience a sudden slowdown in growth rate, or when their removal will help one or more nearby trees with greater potential value. This harvest will sweeten the value of the cut, and the openings created start the forest cycle again.
  • We try not to lose sight of our potential crop trees despite the surrounding forest.
  • We recognize a tree’s value as a seed source, and, as a result, may defer harvest until after regeneration is established.

Brooks Mills lives by the maxim of long-term forest management, beautifully illustrated by his existing crop trees. They stand as symbols of what his land will continue to produce in the coming years, while Brooks himself serves as a model for other landowners to practice sound stewardship.

For additional information, see the following:

Mills, Brooks. 2000. Why I believe in crop tree management. Independent Sawmill & Woodlot Management. 19: 34–36, 69, 71.

Lamson, Neil I.; Smith, H. Clay; Perkey, Arlyn W.; Wilkins, Brenda L. 1988. How to release crop trees in precommercial hardwood stands. NE–INF–90–88. Broomall, PA: U.S. Department of Agriculture, Forest Service, Northeastern Forest Experiment Station. [http://www.fs.fed.us/na/Morgantown/frm/perkey/howto/ctree.htm].

Perkey, Arlyn W.; Wilkins, Brenda L.; Smith, H. Clay. 1994. Crop tree management in eastern hardwoods. NA–TP–03–93. Morgantown, WV: U.S. Department of Agriculture, Forest Service, Northeastern Area, State and Private Forestry. [pagination not continuous]. [http://www.fs.fed.us/na/morgantown/frm/perkey/ctm/ctm_index.html].

The author can be contacted as follows:

Roger Monthey
Forest Stewardship Coordinator
USDA Forest Service
Northeastern Area
P.O. Box 640
Durham, NH  03824-0640
Phone:    (603) 868-7688
E-mail:    rmonthey@fs.fed.us