Forestry For the Birds: Crop Tree Release with Gap Creation

///Forestry For the Birds: Crop Tree Release with Gap Creation
Forestry For the Birds: Crop Tree Release with Gap Creation 2017-04-17T16:52:21+00:00

Black throated blue warbler (Dendroica caerulescens)

Management Goals

  • Improve forest health
  • Improve timber quality
  • Enhance late-successional wildlife habitat
  • Demonstrate and teach forestry practices
  • Provide for non-motorized recreational use


Hopkins Hill Rd existed as early as 1843 when John Beebe first settled nearby Hopkins Hill and established a small farm in the forest. By 1850 Beebe had cleared 100 acres around this farm to support livestock, vegetable farming, and maple sugaring. Farming continued in this area until at least the 1870s and some level of pasturing may have extended beyond the turn of the century. After reverting to softwood forest, areas of the stand were logged in the 1940s. More recent management includes stand-wide thinning in the 1960s, and a single tree/group selection harvest in 2000. The most recent logging did not impact this part of the stand.

Stand Description

Two separate areas of the Spitzer Forest were visited during this harvest. Stand 18, near the summit of Tripp Hill, is a relatively mature hardwood stand, with rich soils (nutrient-rich and less acidic) that support species such as sugar maple, yellow birch, and scattered basswood and butternut. Stand 7, while also a mature hardwood forest, has a slightly different species mix with more beech and white ash. Being adjacent to Hopkins Hill Rd (now discontinued), this forest has also had more human intervention and receives regular visits from skiers and hikers on the NorthWoods trail system.

FFTB CTR with Gap Creation (Stands 7 and 18)

What is CTR with Gap Creation?

As the name implies, this treatment combined two silvicultural practices. Crop Tree Release (CTR) is the selection of individual trees to keep– healthy, long-lived trees that will become high-value timber in the future. Each of these crop trees is then freed from competition by removing some of the surrounding trees. This ensures that each crop tree has adequate space to survive and grow quickly (thereby increasing in value).

The other part of the treatment was Gap Creation. A canopy gap is an opening in the forest overstory ranging from 1/20th to 2 acres. In this harvest, the largest gap was around 1/4 acre; small gaps promote more shade tolerant species and maintain less extreme conditions at the forest floor (temperature, light and moisture).

Stand Data

Pre-Harvest Post-Harvest
Basal Area: 120 sq ft/ac 82 sq ft/ac
Acceptable Growing Stock (AGS) 32% 49%
Mean Diameter 11.4″ 12″
Fine Woody Material 4 piles/ac 4 piles/ac + logging slash
Coarse Woody Material 16 pieces/ac 16 pieces/ac + logging slash
Snag Basal Area 20 sq ft/ac 24 sq ft/ac

Foresters for the Birds

As a forest landowner, do you choose to grow timber or manage wildlife habitat? Audubon Vermont has developed a toolkit of assessment methods and silvicultural recommendations to do both! 

The Foresters for the Birds project provides information to foresters, and this harvest at NorthWoods is one of the first ten sites to ground-truth the management recommendations.

More info available at:


Tips For Success

  • A knowledgeable forester will be indispensable as you plan a CTR with Gap Creation! He or she will be able to tell you which trees will grow well in the future, and which trees can be harvested now; the forester will probably also be the person to mark trails and trees to guide the logger. Be sure to talk through your management goals (what you want your forest to look like in the future, influenced greatly by the type of harvesting you do now) with your forester. 
  • A forester can also help choose a logger with equipment that’s appropriate for the size and condition of your forest. Large, heavy machinery is best suited to large acreages and firm, dry ground. Small, lightweight machines or draft animals will cause less damage at lower cost on small jobs or wet soils. 
  • If wildlife habitat enhancement is one of your goals, go back in a few years and see if it worked. It might take time for the birds and beasts to make their way into your forest, but they’ll appreciate the work you’ve done!

Target Species

black-throated blue warbler

Black-throated blue warbler

these birds rely on a dense vegetation less than 6 feet tall for nesting. This layer will develop in areas under canopy gaps where saplings and shrubs will begin to grow.


white-throated sparrow

White-throated Sparrow –

Larger canopy gaps will create the edge habitat that this species prefers for nesting and foraging.



Yellow-bellied sapsucker –

with a penchant for creating nest cavities, this species will benefit from the snags (standing dead trees) and large aspens retained during the harvest.