Question

If i have a forest composed of 25 species of trees, each with a known abundances, how many events are there in the sample space describing the event of randomly selecting a single tree of a specific species?

Answer 1

There are 25 species of trees, each with a known abundances. The question is how many possible ways to randomly select one tree there are.
We should calculate the number of combinations. Combinations, because we select item/s from a collection. In this case, when we select only one item, the combination is also a permutation. From set of n objects we select r. In our case: n=25, r=1. 
The equation is: n!/r!(n-r)!= 25!/1!*24!=25*24!/24!=25
There are 25 different outcomes (events).