With so many fine choirs in the Rogue Valley, chorale conductor Mark Reppert knows his Siskiyou Singers need to stay well suited to be successful.

"We are thrilled to be in such a rich environment as the Rogue Valley, but there is a competitive aspect," he says. "People can choose to attend only so many concerts."

Reppert feels Siskiyou Singers' niche provides varied and interesting programs for audiences because the 60-voice choir is not limited to any particular style of music.

"We're always looking for music that is of special interest, and we have different approaches to the literature that we present," he says. "Each director has his or her preferences, and selecting music is one of the most important jobs. I think about music that is going to be lively and interesting to the choir and also to the audience. At the same time, we want to present the best quality music we can."

In keeping with this weekend's global celebration of Earth Day, the Singers will present "For the Beauty of the Earth," a program of different styles of music that apply to the Earth Day theme. Shows are set for 7:30 p.m. Saturday, April 22, and 3 p.m. Sunday, April 23, in the Music Recital Hall, 405 S. Mountain Ave., at Southern Oregon University in Ashland. Tickets are $20, $5 for students and Oregon Trail cardholders, and can be purchased online at siskiyousingers.org, at Music Coop or Paddington Station in Ashland or Grocery Outlet in Medford.

"There is tons of music from the 19th century that focuses on nature and man's relationship with it," Reppert says. "It was a time when composers and artists in general became concerned about the environment. They were the first to speak up about ways the Industrial Revolution was harming us. There is a lot to choose from for a themed concert."

Siskiyou Singers will open with the show's namesake, written by English composer John Rutter.

"Rutter wrote 'Beauty of the Earth' in 1980," Reppert says. "If the requirement for being a classic is to be a highly respected, well-known piece that stands the test of time, then this one sets the standard."

The first half of the concert is from past generations: 17th-, 18th- and 19th-century music.

"Three pieces are by German composer Felix Mendelssohn," Reppert says. "They're not from any setting, but written at different times during his career. They are songs of spring in more or less the same genre. They reflect Mendelssohn at his happiest."

Audiences can look for "The Song of the Lark," "The Nightingale" and "Praise of Spring." Written in German, the Singers will perform them in English.

Johannes Brahms' Opus 92, published later in his life, is also based on nature but draws from something more personal to Brahms and his inner world, Reppert says. The set includes "O Lovely Night," "Late Autumn," "Evening Song" and "Why?"

"We've joked about that last piece," Reppert says. "The answer comes in the midst of it, if anyone is wondering. That's all I'm going to say."

"The Nightingale" chorus is the last piece on the first half of the program and will be accompanied by flutists Lori Calhoun and Debra Harris and keyboard player Mikiko Petrucelli.

The second half of the concert showcases contemporary classics and music based on folk styles. It begins with "Now I Walk in Beauty," a Navajo tune, Reppert says, with accompaniment by Calhoun on alto recorder. Another highlight is "Sure On This Shining Night," by Morten Lauridsen, with text by poet James Agee.

"Agee's poem has been set by many composers," Reppert says, "but I love Morten Lauridsen's music. We are also doing a setting of Chief Seattle's sermon called 'This We Know.' "

Seattle was a Suquamish tribal leader after whom the city of Seattle was named and a noted orator.

The concert concludes with Bob Thiele's (as "George Douglas") and George David Weiss' "What a Wonderful World," first recorded by Louis Armstrong in 1967. Armstrong's recording was inducted in the Grammy Hall of Fame in 1999.

Projections of photography captured regionally and abroad will accompany several of the works featured, and Ed Wight will present lectures an hour before each concert.