THE FATE OF A FOREST: In his film “Sourlands,” filmmaker Jared Fleisher, shown above, details the fight to sustain the deep woods near Hopewell. The documentary, an excerpt of which was previewed at the most recent Princeton Environmental Film Festival, will be shown in its entirety at Princeton Public Library on July 11.

It was John McPhee’s book The Pine Barrens that got filmmaker Jared Fleisher thinking about making a documentary on the Sourlands. Growing up outside of Flemington, he was familiar with the 90-square-mile bucolic woodland located in portions of Mercer, Hunterdon, and Somerset counties. And from what he has observed, there are threats to the region’s ecological balance.

“I often write about environmental issues,” said Mr. Fleisher, who is 29 and graduated from Hunterdon Central High School. “And I love the way John McPhee handles them. What makes him such a great writer is that you learn so many things, whether it be about something like geology or ecology, But these are stories about people. It’s fascinating.”

Mr. Fleisher will be on hand at a screening of the film at Princeton Public Library on Wednesday, July 11, in the Community Room. The event begins at 7 p.m.

By following the famous author’s approach of focusing on people while taking on the issues, Mr. Fleisher came up with the idea for “Sourlands.” The film is divided into three “chapters” that explore the challenges faced by those who hope to keep the Sourlands landscape unspoiled.

“We have a pretty incredible forest here in central Jersey. If you were to draw a straight line between Philadelphia and New York, the Sourlands is the largest forest we have left,” Mr. Fleisher says. “The Pine Barrens has its own unique challenges, and we have ours, plus an interesting cast of characters right here. The film is issue-based, but tied to a sense of place.”

Threats to the Sourlands come from development in the region, the overpopulation of deer, and the disruption of invasive plants that have made their way into the forest. The film’s three chapters — titled “Farmers,” “The Forest,” and “Energy,” each tell a story about the challenges. “But they are very relevant to what’s happening in the rest of the world,” Mr. Fleisher says. “Native plants are in danger everywhere. The deer population and, especially, invasive plants are problems both specific to our forest but also throughout the northeast and the world. My goal was always to tell a story first and foremost and be relevant to people right here, but also to talk about some bigger problems.”

Mr. Fleisher’s background is in journalism. “I have been writing and thinking about agriculture and energy issues for awhile,” he says. “I made my first documentary film in 2009, called The Farmer and the Horse, about young people getting into sustainable farming and using old skills. It was shown at the 2011 Princeton Environmental Film Festival.”

For the first segment of the 78-minute Sourlands, Mr. Fleisher focuses again on young farmers in New Jersey and their efforts to do organic, sustainable farming. In the final part, “Energy,” he provides some solutions to the problems faced by the Sourlands forest and many other regions of the world. “I want people to feel hopeful,” he says. “The nice thing about central Jersey is that there’s an interest in clean energy and energy technology. I also talk about practical things people can do that don’t sound totally exciting and sexy, but can really have a huge, huge impact on the amount of energy we use.”

Among the people profiled are a Sourlands man who lives in the first home in the nation to be powered by solar energy and hydrogen, with no carbon emissions. “It’s a very expensive way to achieve energy independence, but it’s a model, and he’s cutting edge, so it’s interesting to hear his thoughts,” Mr. Fleisher says. Another featured character is a Princeton man who makes home energy monitors. “So it’s not only a story about why these things are important, but also about the challenges to get started as an entrepreneur,” he adds.

The idea is to get viewers fired up about saving the Sourlands without being teachy. “In all these stories, it’s not just the issues, but the people as well,” Mr. Fleisher says. “I want it to be entertaining and interesting.”