Here is an answer from a mathematical and not biological point of view. It seems like moose cows breed more or less annually annualy from age 3 to 11. So I assumed that each female produces 2 females during her life, that is has calfs every other year and half are female; I assume they die at age 11. I'm ignoring all other factors, but just trying to give a perspective on how these things work.

With the above parameters, here is the female population every 10 years:

Year 1: 2

Year 11: 20

Year 21: 164

Year 31: 1277

Year 41: 9931

Year 51: 77181

Year 61: 599847

The point is that these processes are exponential, that is they grow pretty fast.