Have you ever tried searching the internet for “tree year” (or “tree-year”)? And how about “wolf year”? How about “man year”?
The first just gave me results like “Tree of the year” and such.
The second “Year of the wolf” and so on.
The third tells you that “man year” means a certain amount of work.
But what if we started using these words (perhaps using “human year” rather than “man year”) for not an amount of work, but an amount of life and experience?
In other words: the number of tree years in a forest equals the sum of the ages of the trees in it. Thus, a park with of one hundred trees with an average age of 50 years has 5000 tree years. One year later, it will have gained another hundred tree years, totaling 5100.
Then it instantly becomes clear that one cannot compensate cutting down one hundred trees of one fifty years old by planting one hundred trees of one year old - you’ll lose 5000 - 100 = 4900 tree years!
And then we do not even take into account the fact that those one year old ones do not produce any acorns, provide no nesting places and so on. That means that in addition you’ll lose lots of squirrel years, nuthatch years, and so on.
What would all those computations about how many trees we had in 1900 and 2000 respectively look like when we count not just the number of trees, wolves, elephants, and people, but the tree years, wolf years, elephant years, and human years?