[Math] Why is ‘something per hectare’ denoted with a negative exponent ( $ha^{-1}$)

Question

Quick question…. why is it that something per hectare is shown as having a negative exponent, $ha^{-1}$?

For example, on this page:
http://www.ipcc.ch/ipccreports/sres/land_use/index.php?idp=12

1 tonne per hectare is shown as (t $ha^{-1}$).

I did some searching and can't find a good explanation. Any ideas?

Answer 1

This is because something to the power of $-1$ is equivalent the following;

to $$\frac{1}{t}=t^{-1}$$

and for example

$$\frac{1}{t^3}=t^{-3}$$

So it should make more sense now as it is $$\frac{something}{hectare}$$ in your example , or as I said above, $$something(hectare)^{-1}$$