Rainbow Mars
From back cover Tor paperback May 2000:

Hanville Svetz was born into a future Earth that matches the sorriest predictions of Greenpeace.  With most of Earth's original species extinct, Svetz travels back and forth in time retrieving them.  Svetz learns that Mars was inhabited, and how the sapient Martian species were wiped out.  He foresees that Earth could soon fall victim to the same fate.
Fiction, Time travel, Trees, Extinction (Biology), Space flight to Mars
Larry Niven
Laurence van Cott Niven — known as Larry Niven — is an American science fiction writer. His best-known work is Ringworld (1970), which received Hugo, Locus, Ditmar, and Nebula awards. The Science Fiction Writers of America named him the 2015 recipient of the Damon Knight Memorial Grand Master Award. His work is primarily hard science fiction, using big science concepts and theoretical physics. It also often includes elements of detective fiction and adventure stories. His fantasy includes the series The Magic Goes Away, rational fantasy dealing with magic as a non-renewable resource.

Niven was born in Los Angeles. He briefly attended the California Institute of Technology and graduated with a Bachelor of Arts in mathematics (with a minor in psychology) from Washburn University, Topeka, Kansas, in 1962. He did a year of graduate work in mathematics at the University of California at Los Angeles. On September 6, 1969, he married Marilyn Joyce "Fuzzy Pink" Wisowaty, a science fiction and Regency literature fan. He is an agnostic.

Source: Wikipedia