Over the course of the last 20 years, Canadian filmmaker Jean-Marc Vallée has helmed over a dozen acclaimed films – both features and shorts. Last year, he directed two actors (Matthew McConaughey and Jared Leto) to Academy Award-winning performances in DALLAS BUYERS CLUB. His newest film is WILD which is based on the powerful true story of Cheryl Strayed (Reese Witherspoon) and her life-changing solo hike along the Pacific Crest Trail. The film showcases a physical and emotional journey as Strayed seeks personal redemption and healing. Even before the movie’s release, Witherspoon’s fearless performance is already earning praise from critics.

We chatted with Vallée during a break from shooting his next movie, DEMOLITION (starring Jake Gyllenhaal and Naomi Watts), in New York City. He spoke to us about the making of WILD, the benefits of shooting in natural light and the difficulties Witherspoon faced during the shoot.

AFI: What attracted you to the story of Cheryl Strayed?

JMV: It was such an emotional book and a beautiful story. I was attracted not only to the emotional and powerful material but also the fact that it was the kind of material that allows a director to have fun with the language, the editing, the flashbacks, the shots, the landscapes, the music, the voiceover. So it was exciting to do this project, which was beautiful in its essence…and then also, again, to have fun as a director and play with music, which I like to do.

AFI: Has Cheryl seen the film?

JMV: Yeah, she’s seen the film. She was a trooper from the beginning to the end.

AFI: What was her reaction after she saw the film for the first time?

JMV: It was an emotional moment. She was in the cutting room the first time. [When] she saw it first, it was longer than the actual finished film and it was something special. You know, witnessing, watching your life being told in a film in front of you. She was happy and excited. It’s an emotional film.

AFI: Having made two biographical films, DALLAS BUYERS CLUB and now WILD, were there any similarities in the making of them?

JMV: I wouldn’t say I took from DALLAS because it was another film based on a true story. It’s just from one project to the other, one script to the other. You work on the script beforehand, shoot it, then piece it together in the cutting room. The thing that is similar with WILD and DALLAS is the way we shot it with available light, and we didn’t want flash, often no makeup.

We also shot 360 degrees and the crew was often out of the way and the actors can just be free to move wherever they want to move and we captured what they’re doing instead of being limited by spotlights, and flags and this mark and that. It was more “Ok, do what you gotta do. It’s just the space and then let’s see what will happen and we’ll be there to shoot it with the camera.”

AFI: You shoot many of your films with natural light. Were there any specific challenges with this film in working with only natural light?

JMV: No, it’s just accepting it. It’s more of a challenge for the cinematographer, who has to become humble enough to do this and to control the camera and make it happen and just capture what we see. Sometimes, of course, when we have interior scenes, the DP asks the production designer to come up with some practical lights to put in the set or some candles or whatever’s going to help when there’s not enough light. But when we choose our locations, we chose them because they [allowed us] to shoot in available light. WILD was shot outside in the wilderness and the amazing landscapes were 65 percent of the film so the challenge was to wake up very early and to capture the sunrises and then finish early at sunset and it was amazing. I would tell my kids that I was playing outside [in the] early morning to the end of the day.

Was it a challenge? Well, it was raining and raining. We were dealing with Mother Nature. Just filming amazing, beautiful landscapes like that puts you in a mode where you just want to watch it. And putting Reese in these landscapes was something I realized in the cutting room was more emotional after 60 minutes of storytelling…When you know Cheryl’s story and how she lost her mom and then you see Reese, lost with her backpack on her shoulder, just walking in the landscapes, and then you go, “Oh my God, these wide, wide shots become as emotional as a beautiful close-up of her face.” Although we shot most of the hiking with a handheld dolly on her face, a medium close-up on her face, whatever she was seeing or looking at, the audience is also looking at.

AFI: How did you prepare Reese Witherspoon for not only the emotional but also the physical challenges the role required?

JMV: I didn’t prepare her and she didn’t prepare. That was the whole idea. That was the intent. Just like Cheryl’s experience, there was no preparation. You just find yourself on a trail on the Pacific Crest Trail and you have no experience and let’s see how you do it. I didn’t want her to practice to set up a tent or a stove and she just learned as we were shooting. Again, it was like capturing. It wasn’t staged where I would say “Okay Reese, let’s stage the fact that you’re setting up the tent.” It was just, “Reese, set up the tent.” And it took like 20 minutes. So we shot for 20 minutes, different angles. But she was setting up the tent, wondering how [LAUGHS]. She was up to it. She was up to the challenge of being Cheryl.

WILD opens in theaters across North America on December 5, 2014. It features art direction by Javiera Varas (AFI Class of 2006). Read more about the film on the official Fox Searchlight website.