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Leith Knowles Development of a productivity Index for Douglas-fir
Productivity Indices • Site Index (SI) • SI=MTH@40years. Independent of silviculture • Site basal Area Potential (SBAP) • Derived from sample plots. The SBAP is the value that makes the growth model BA increment best match the sample plot BA increment. The overall plot mean SBAP is calculated as the period-weighted mean over all increment periods.Independent of silviculture • Is it possible to develop one simple volume index by combining the two?
Methods TSV=a*MTH*BA TSV=a*SIb*SBAPc MAI =TSV/rotation age
What is 500 Index? • 500 index is simply the predicted MAI of a stand planted at 1500 stems/ha, thinned to 500 stems/ha by 15m MTH, and grown to age 40 years
Results 500 Index = a*SIb*SBAPc Where a=0.0971 b=1.344 c=0.0973
SBAP can be predicted from SI and 500 Index SBAP=(500 Index/a*SIb))d Where a=0.0971 b=1.344 d=1.028
Sensitivity of 500 Index to changes in silviculture • Stocking @ age 10 years (1500 stems/ha) 200 stems/ha=1% change in 500 Index • MTH at thinning (15m) 1m=1.15% in 500 Index • Final crop stocking (500 stems/ha) 100 stems/ha=6.6% in 500 Index
Conclusions • Both SI and SBAP are needed to explain site productivity • These can be combined to predict MAI for a standard regime (500 Index) • Productivity of Douglas-fir on most sites in NZ is now expressed in terms of 500 Index • 500 Index included in DF Calc V2