Thinning

Objectives Consider basic factors in the planning of a thinning operation Know different methods of thinning

Reasons to Thin Maintain vigor of the stand Shift growth onto smaller number of trees Salvage potential mortality Early financial returns Non-timber aspects

Decisions 1.When? 2.How much? 3.Which trees?

When? Crowdedness (growing space) –Live crown ratio –Diameter growth (rings) –Density management diagram Diameter distribution Growth model Rate of return

How much? When is next action? Thinning costs Re-occupancy of growing space Type of thinning

Which trees? All previous factors Logistics Reality

Methods of thinning Low Crown Selection Geometric Free

Low thinning Trees removed from lowest crown classes Mimics natural thinning Easy to select trees Has less effect on relative density

Pre-thinning

Low thinning

Low thinning example Percent of trees removed – 49% Percent basal area removed – 28% d/D -.74

d/D [Average diameter of trees harvested] [Average diameter of stand before harvest]

Crown thinning Trees removed from upper crown classes Favor development of best trees Bulk of intermediate and healthier portion of upper crown classes remain Better financial return than low thinning Greater effect on relative density

Pre-thinning

Crown thinning

Crown thinning example Percent of trees removed – 26% Percent basal area removed – 29% d/D – 1.07

Selection thinning Thinning of the dominants Can be high-grading Can reduce potential growth Greatest financial return Greatest effect on relative density (but may not increase growth rate)

Pre-thinning

Selection thinning

Selection thinning example Percent of trees removed – 26% Percent basal area removed – 47% d/D – 1.39

Geometric thinning Usually row or strip thinning Can lead to lopsided crowns Less chance to remove damaged trees Low harvesting costs

Pre-thinning

Geometric thinning

Geometric thinning example Percent of trees removed – 29% Percent basal area removed – 29% d/D – 1.00

Thinning examples LowCrownSelectionGeometric Number of trees 49% 26% 29% Basal area 28% 29% 47% 29% d/D

Free thinning A mixture of all thinning types Often used in first entry in a very irregular, single cohort stand. Example: Slow invasion so dominants are older and very rough (low value); codominants are very dense; logging machinery access is difficult