Imagine that someone stops you on the street and asks “How many hectares of plantations do we need for a pulp mill that produces 1 million tonnes per year of Eucalyptus pulp in Chile?” They don’t need a highly accurate result but a ballpark figure, the right order of magnitude. A Fermi estimate.

How many assumptions do we need?

- We need 4 cubic metres of wood for a metric tonne of pulp (wood density 0.5 ton/m
^{3}and 0.5 pulp yield) - Harvest age 12 years
- Productivity 25 m
^{3}/year/ha

Using 1. we need 4 m^{3}/ton x 1,000,000 ton = 4,000,000 m^{3} of wood per year. Using 2. and 3. we see that 1 ha produces 25 m^{3}/year/ha x 12 year = 300 m^{3}/ha.

Therefore we need 4,000,000 m^{3}/year / (300 m^{3}/ha) = 13,333.33 ha/year and because we need the same amount in year 1, 2, …, 12 (Harvest age) and we keep on planting forever, the total is 13,333.33 ha/year x 12 year = 160,000 ha.

If you have been paying attention, you’ll notice that we divide and multiply by the rotation (12 years) so we can simplify the calculation back to:

product conversion (4 m^{3}/ton) x capacity (1,000,000 ton/year) / productivity (25 m^{3}/year/ha) = 160,000 ha.

We know that none of those numbers is perfectly correct, but put together they give us an idea of the magnitude of the problem. We can play with them: change site productivity, conversion rate, add safety margins, etc.

Now let’s say that we read of people complaining because a Chilean company announces a 2.5 million tonnes short fibre mill in Brasil. That would need 160,000 ha x 2.5 = 400,000 ha. Massive. As a comparison, INFOR tells us that the whole Eucalyptus estate in Chile is about 900,000 ha and that’s already used by the existing pulp mills, bioenergy producers, etc.

Just from the resource access point of view, having a pulp mill that size would need increasing the country’s Eucalyptus forest estate by roughly 50%. That gives some context to the speculation about the reasons for the investment in Brasil.