Intermediate Silvicultural Treatments

1. Intermediate Silvicultural Treatments

2. Summary of Intermediate Stand Treatments • Thinning • Release • Improvement cutting • Sanitation and Salvage • Fertilization • Pruning

3. How intermediate treatments fit into a silvicultural system Components of even-aged silvicultural systems Stand Initiation

4. How intermediate treatments fit into a silvicultural system

5. Textbook Chapters by Topic • Thinning: Ch 17, 18, 19 • Release Treatments: Ch 16 • Improvement, Sanitation and Salvage: Ch 22 • Pruning: Ch 20

6. Thinning

7. What is Thinning? • Defined by Nyland as: “A treatment to increase the diameter increment of residual trees, improve stand quality and health, and increase stand level production by cutting excess and potential mortality trees without permanently breaking the crown canopy”

8. When we thin a stand… • We are reallocating growing space to the residual trees • Which residual trees you choose depends on your objectives

9. Why do we manage stand density through thinning and other intermediate treatments? • Increase dbh growth, maintain larger crowns and higher vigor • Reduces rotation length • Improve average tree quality and value • Provide intermediate income • Reduce volume losses to mortality • Improve resistance to insect disturbances • Increase seed production • Enhance wildlife food production and availability • Improve aesthetics, by creating a more open, park-like appearance

10. Effects of Thinning on Individual Growth • Thinning increases diameter growth • By allocating more growing space to residual trees, they are able to capture more above and belowground resources 1969 1979 1959

11. Effects of Thinning on Individual Growth • Species and canopy position influence magnitude of diameter growth response

12. Effect of Thinning on Stand Growth • Thinning recovers the yield in potential mortality trees and excess growing stock • Increases total realized sawtimber yield over an even-aged rotation • Net Volume Yield = Final Harvest Volume + Volume Removed in Previous Thinnings • Improved growth on residual trees compensates for the increment lost from cut trees • Ensuring full net production in stands with adequate residual stocking

13. Effect of Thinning on Stand Growth

14. Effect of Thinning on Stand Growth

15. Effect of Thinning on Stand Growth

16. Effect of Thinning on Stand Growth

17. Effects of Thinning • Four major factors influencing long-term growth following thinning: • Timing of each thinning • Crown condition and position of residual trees • Post-thinning spacing and its influence over crown vigor and development • Interval between successive thinnings

18. Timing of thinning effect diameter growth responses Early thinning can yield increased diameter growth when compared to later or no thinning

19. Timing of thinning and site quality impact cumulative stand yield

20. Period of post-thinning growth increase vary due to spacing and a tree’s competitive position.

21. Potential Negative Effects of Thinning • Damage residual stems and site • Reduce tree quality due to increase limb retention and epicormic branching • Increased danger of wind and ice damage due to sudden exposure • Initial post-thinning stress may increase insect attack and disease losses • Tends to reduce total biomass production • Temporarily increase wildfire hazard due to increased fuel load

22. What is epicormic branching?

23. Methods of Thinning • Low thinning • Crown thinning • Selection thinning • Geometric thinning • Free thinning

24. Methods of Thinning: Low Thinning • Low thinning • Trees are removed from the lower crown classes • Must be very heavy or done early and frequently to appreciably increase growth of upper crown class trees • Most applicable in stands which nearly all trees are merchantable

25. Methods of Thinning: Low Thinning • Low thinning intensities • Grade A (very light): remove overtopped • Grade B (light): remove overtopped and intermediate • Grade C (moderate): remove overtopped, intermediate, and some co-dominant • Grade D (heavy): remove overtopped, intermediate, and most codominant • Other names for low thinning: • Thinning from below • German

27. Methods of Thinning: Crown Thinning • Crown thinning • Removes trees from upper crown classes to favor the best trees in those classes • Removes mostly co-dominant trees, but intermediate or dominant trees interfering with desired residuals also removed • Unlike low thinning, no matter how lightly applied, principle cutting is made in the upper crown classes • Can provides greater income than low thinning • Other names for crown thinning • Thinning from above • French

29. Methods of Thinning: Selection Thinning • Selection thinning • Removes dominant crown class trees in order to favor the growth of trees in lower crown classes • Trees favored in crown and low thinning are likely to be cut in selection thinning • If incorrectly applied, leads to high-grading and reductions in residual stand growth and quality • Most commonly used to remove poorly formed dominant trees • Applied in some two-layered stands to remove taller layer • Repeated selection thinning is only appropriate for shade tolerant and negatively geotropic conifers

30. Methods of Thinning: Geometric Thinning • Geometric thinning • Trees to be cut are chosen strictly on the basis of spacing or pattern with no regard to crown class • This results in removal from all crown classes and retention of trees in all crown classes • Most appropriate where there is little differentiation in crowns or in tree quality • Usually applied only as a first thinning in young stands or plantations

31. Methods of Thinning: Geometric Thinning • Row thinning removes strictly by rows in a plantation • Every fifth row is common practice • Provides easy access for large machinery • Provides no improvement in stand quality

32. A geometric thin performed by removing every 5th row in a 14-year-old slash pine plantation in Georgia. Photo Credit: David Moorhead, UGA, Bugwood.org

33. After 5th row thinning with thin from below in leave rows in a 14-year old stand. Initial Basal Area = 140 square feet per acre, Residual Basal Area = 70 square feet per acre.

34. Methods of Thinning: Geometric Thinning • Strip thinning (or corridor thinning) cuts trees in a strip of set width • Applied most commonly for precommercial thinning in young overcrowded natural or direct seeded stands • May use heavy mower or drum chopper in seedling stands

35. Aspen stand, 15 ft wide machine corridor, first summer post-harvest.

36. Methods of Thinning: Free Thinning • Free thinning • Objective is to select the best trees, regardless of canopy position, and release them • Differs from area-wide thinning methods (e.g. low or crown) in that residual density or spacing across the site need not be uniform • Typically, a set number of crop trees are released (e.g. 50 or 100) • Number of crop trees should be sufficient to fully stock the stand at the end of the rotation

37. Thinning Regimes • Whether to thin? • When to thin? • How much to thin? • What thinning method do we use? Often tough questions. Objectives, economics, growth rates, and current stand conditions will drive the decision.

38. Timing of Thinning - When do we thin? Merchantability • To avoid capital investment, a commercial operation is desirable rather than pre-commercial • Southern pines: • Commercial thinning tends to be possible at about age 12, depending on site quality and initial density • Upland hardwoods: • Commercial thinning occurs later than for conifers due to slower diameter growth in dense stands and higher minimum merchantability requirements

39. Timing of Thinning - When do we thin? Objectives • Pulpwood: thin late or preferably not at all • Sawtimber: concentrate growth on best trees as soon as possible • Density must be sufficient to encourage self pruning to at least 17 feet • Wildlife: in general, thin early, frequently, and heavily from below to increase light levels in the understory and increase growth of shrubs, grasses, and forbs.

40. Timing of Thinning - When do we thin? Site Quality • Thinning can occur earlier on more productive sites • May chose to thin only on sites of medium to high productivity

41. Timing of Thinning - When do we thin? Live Crown Ratio • Best simple indicator of tree vigor and ability to respond to thinning

42. What is Live Crown Ratio?

43. Timing of Thinning - When do we thin? Live Crown Ratio • Critical threshold for crown ratio of overstory trees may dictate when thinning occurs Example for southern pines • First thinning, attempt to keep most potential crop trees at least above 35% LCR; • 40-45% is better for a high growth rate, but this slows self pruning • For older stands, seek to keep LCR above 30% (higher for more diameter growth)

44. How much do we thin?Choosing a Residual Density Objectives • Pulpwood: maintain high residual density (light or no cut) • Sawtimber: lower residual density to keep diameter increment higher • Density should be high enough to maintain good self pruning • Wildlife or grazing: low density to encourage understory vegetation

45. How much do we thin?Choosing a Residual Density Live Crown Ratio • If crowns are small, thin lightly and frequent Site Quality • More flexibility in residual density is possible on good sites • Productive sites can carry higher density without losing vigor, yet openings close rapidly

46. Stand Density and Stocking Quantitative tools for determining how much we should thin • Stand density is an absolute measurement based on basal area or number of trees per acre • Stand density reflects the degree of crowding of stems within a stand • Stocking is a relative term that relates a given stand density to a management objective • Because size-density relationships influence the amount of available growing space in a stand • Two stands with equal stand density may not have an equivalent stocking • Example: 100, 4 inch trees do not occupy an equal amount of growing space as 100, 18 inch trees

47. Simple Measures of Stand Density • Trees per acre • Simple, but does little to describe size-density relationships as it only accounts for the number per area • Basal area per acre • Basal area is a combined measure of both, number of trees and their size • Widely used because it is: • Simple to measure via point sampling • Highly correlated with volume and growth of even-aged forest stands • Works well for single species plantations

48. Stocking • Stocking Chart for Upland Hardwoods (Gingrich 1967) • A graphical tool to allocate growing space on a relative basis for upland hardwood stands in the Central Hardwood Forest Region

49. Properties of the Upland Hardwood Stocking Chart Average Maximum Density (A-Line) is set at 100% Stocking Shows the upper limit of a fully stocked stand

50. Properties of the Upland Hardwood Stocking Chart Area between the A-Line and B-Line indicates that a stand is fully stocked A similar level of merchantable volume produced within the range of full stocking