Mixed Species Silviculture Objectives 1 Understand stratification of
Mixed Species Silviculture
Objectives 1. Understand stratification of mixed species stands 2. Understand role of height growth patterns 3. Understand role of shade tolerance 4. Understand some different ways of managing mixed species stands
Number of trees Diameter Distribution DBH
Different Inherent Height Growth Patterns 1. 2. 3. 4. Sigmoidal Linear Asymptotal (tall) Asymptotal (short)
Height Growth Patterns Age
Shade Tolerance • A species cannot survive under itself • A species cannot survive under a more shade tolerant species
Shade Tolerance Shade intolerant Ps Shade tolerant Light
Stratification • Height growth patterns • Role of spacing
Spruce and aspen
How to Manage • Single cohort (even-age) • Layercake • Thin in all layers • Multi-cohort?
Layer Cake • Take off layers by height stratum • Layers become more shade tolerant • Plays out (even-age management)
Differentiation Within Stratum • Vigor classes within stratum • Differentiation less strong in lower strata • Layer cake approach is often combined with thinning in lower strata
Yield • Volume of mixed species will not exceed a pure stand of the most shade tolerant species • Monetary yield will almost always exceed either species
Yield TOTAL 100% 50% 0% 100% A 0% B 50% A 50% B 0% A 100% B
Yield TOTAL 100% 50% 0% 100% A 0% B 50% A 50% B 0% A 100% B
Yield 6 m 3 TOTA L 3 m 3 0 m 3 100% A 0% B 50% A 50% B 0% A 100% B
Mixed Portfolio • Keep options open • Values keep changing
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