“I have read many definitions of what is a conservationist, and written not a few myself, but I suspect that the best one is written not with a pen, but with an axe. It is a matter of what a man thinks about while chopping, or while deciding what to chop. A conservationist is one who is humbly aware that with each stroke he is writing his signature on the face of his land.”

Source: The Pearl (1947), Ch. IV

Sometimes attributed to Audubon in recent years, there are no occurrences of this statement that have been located prior to 1997, and it is probably derived from the remarks of Wendell Berry:
I am speaking of the life of a man who knows that the world is not given by his fathers, but borrowed from his children; who has undertaken to cherish it and do it no damage, not because he is duty-bound, but because he loves the world and loves his children; whose work serves the earth he lives on and from and with, and is therefore pleasurable and meaningful and unending; whose rewards are not deferred until "retirement," but arrive daily and seasonally out of the details of the life of their place; whose goal is the continuance of the life of the world, which for a while animates and contains them, and which they know they can never compass with their understanding or desire.
The Unforeseen Wilderness : An Essay on Kentucky's Red River Gorge (1971), p. 33
Misattributed

From Nobel Lecture (2014)

Source: Thus Spake Zarathustra: A Book for All and None

Half-Truths and One-And-A-Half Truths (1976)

Variant translation by Pearl S. Buck: "Alas, I was born to die! How can I know what those who come after me and read my book will think of it? I cannot even know what I myself, born into another incarnation, will think of it. I do not even know if I myself afterwards can even read this book. Why therefore should I care?" (All Men are Brothers, 1933; p. xiii)
Preface to Water Margin

Source: On Writing Well (Fifth Edition, orig. pub. 1976), Chapter 6, Words, p. 36.