Unevenaged beech stand Germany Unevenaged mixedhardwood stand Michigan

Uneven-aged beech stand, Germany

Uneven-aged mixed-hardwood stand, Michigan

Uneven-aged mixed spruce/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 unevenaged 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

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