Uneven-agedbeech stand, Germany

Uneven-agedmixed-hardwoodstand, Michigan

Uneven-aged mixedspruce/fir stand,Germany

Density and structure in uneven-aged stands are defined by:

• Overall density (basal area after cutting)

• Maximum diameter • Relative proportions of large and

small trees), diameter distribution or Q-value

Marking guide:•< 11” – no cutting

•12 – 16 or small sawtimber – cut 1/5 of trees

•16-23 or large sawtimber – cut 1/6

•> 24 inches or mature – remove all

Density management

• Area (e.g., 4 size classes, each covering the same area)

• Leaf area allocation (after K. O’Hara)

– Represents occupied 3-D growing space – Is related to rates of energy and material exchange

• Calculating growing space efficiency by relating tree increment to leaf area

• Growing space efficiency of trees is determined by crown class, age, or species

• Optimize structures for growth

Selection criteria in uneven-aged stands• Maturity• Risk• Vigor• Soundness• Stem form, crown size and branching habit• Species • Crown position• Release effect (of seedlings/saplings)

Single Tree Selection:

• Means: cutting single tree and growing single trees

• Only limited reduction of below-ground competition

• More diffuse light, but only limited direct light (sunflecs)

• Moderate increase in soil temperature and nutrient release

Overall, environmental conditions are fairly stable

Single-tree selection:

• Density management is a combination/compromise between good growing conditions for overstory trees and establishment of regeneration

• Continuous forest cover– Usually not limiting to germination– Limiting to growth and survival of

shade intolerant species

To ensure regeneration of shade intolerant species:• On stable sites

– Reduce overall density•Tradeoffs in growth•Longer cutting cycles

– Sort out species in pre-commercial thinning entries

– Pruning to reduce LAI

Single tree selection:

High vertical structure– Wildlife habitat– Fire ladder

Disease potential– Mistletoe

Uneven-aged mixed spruce/fir forests, single tree selection Switzerland

Group selection:

• “Homogenous” groups created by “patchy” cutting patterns

• Provides more resources (light) for regeneration cohorts– Regeneration of intermediate shade

tolerant trees• More efficient harvesting and

management of regeneration

Uneven-aged mixed spruce/fir forests, group selection, Germany

Uneven-aged mixed spruce/fir forests, group selection, Germany

Group selection:

• Resource availability driven by – Group size– Spatial layout– Size and density of neighboring trees– Slope– Aspect

• Not homogenous within group (and stand edge)

Group selection

• Resource (light, moisture, nutrients) increase within opening– Edge effect due to surrounding trees

• Higher light/temperature conditions in group improve decomposition/nutrient release within opening

• Range of conditions within group and edge (in matrix) may lead to recruitment of multiple species

Uneven-aged mixed (oak) hardwood forest, group selection, Germany

Group selection

• Trees are not necessarily naturally grouped– Cutting of immature trees

• Edge effect may reduce “ecological size” of group– Especially with irregular shapes

• Difficult to map and document– Inventory methods may have to be

modified– On ground work is complicated

• May require different access system– Changes over time

Guide to implementation of

group cutting• Determine desired number of age

classes and gap sizes• Calculate number of gaps per

acre• Based on

– density of mature trees – area in gaps

– calculate number of trees to be cut

Conversion:

• Irregular stands are easier to convert

• During Conversion– Lower residual densities– Longer cutting cycles– Lower maximum diameter– Keeping healthy trees regardless

of form or species

Ex - Uneven-aged mixed spruce/fir forests, managed with single tree selection until 20 years ago, no management since, Germany

Skidder traffic - Feller buncher traffic -

Traffic patterns on a harvesting unit

Area in skid trails following a single harvest operation

13.7 13.212.5

9.6

8.2

0

2

4

6

8

10

12

14

16

Clearcutting Shelterwood Seed-Tree GroupSelection

Single TreeSelection

% S

tand

Are

a