Plant a thousand seedlings for a thousand trees and you will be several hundred short in eight years. Losses compound against the number you planted, so the correction is a division by the survival share — the one place where multiplying by the loss rate gives the wrong answer.
1,200 harvestable trees at an 18% loss rate needs 1,464 seedlings in the ground — not the 1,416 that adding 18% suggests.
The example
Three planting blocks, each with a harvest target and a loss rate for that site and species.
| A | B | C | D | |
|---|---|---|---|---|
| 1 | Block | Harvest target | Loss rate | Seedlings |
| 2 | North field | 1200 | 18% | 1464 |
| 3 | Replant strip | 500 | 10% | 556 |
| 4 | Dry ridge | 2000 | 25% | 2667 |
The formula
Divide, do not multiply:
How it works
Why the division is the right move:
1-C2is the survival share. An 18% loss rate means 82 of every 100 seedlings make it to harvest.B2/(...)asks the inverse question: how many must go in so that the survivors equal the target. That is a division, not a markup.- Adding the loss rate instead —
B2*(1+C2)— understates the order every time, and the gap widens as the loss rate rises. ROUNDUP(...,0)gives whole seedlings, and nurseries sell in bundles anyway, so round the result up again to the bundle size.
Loss rate is a site number, not a species number. Keep one per block and update it from the count you take at the end of each establishment year.
Try it: interactive demo
Enter the harvest target and the loss rate for the block.
Variations
Round up to whole bundles
Nurseries ship in bundles, so convert seedlings into an order quantity.
Loss over two stages
Divide once per stage when transplant loss and field loss are tracked separately.
Pitfalls & errors
Loss rate here is cumulative over the whole rotation, not annual. A 3% annual loss over eight years is closer to 22% cumulative, and using the annual figure will leave the block short.
Count survivors at the end of year one and again at harvest. Establishment loss and long-run loss behave differently, and the two-stage variation handles them properly.
Never gross up with *(1+loss). At an 18% loss it under-orders by 48 trees per 1,200; at a 40% loss it under-orders by nearly a quarter of the block.
Practice workbook
Frequently asked questions
What loss rate should a new block use?
Does this handle staggered planting for annual harvest?
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