Worship the forest that you make.
There is a real life parallel for you: the ancient Amazon. Exactly what you describe happened there. Whether the ancient Amazonians disappeared because of European diseases or at some earlier point (like the Mound Builder civilization) is still not known, I do not think. But they were there in great numbers, and their descendants are hunter gatherers much like the pygmies.
For more than 8,000 years, people lived in the Amazon and farmed it to
make it more productive. They favored certain trees over others,
effectively creating crops that we now call the cocoa bean and the
brazil nut, and they eventually domesticated them. And while many of
the communities who managed these plants died in the Amerindian
genocide 500 years ago, the effects of their work can still be
observed in today’s Amazon rainforest.
“People arrived in the Amazon at least 10,000 years ago, and they
started to use the species that were there. And more than 8,000 years
ago, they selected some individuals with specific phenotypes that are
useful for humans,” says Carolina Levis, a scholar at Wageningen
University who helped lead the study. “They really cultivated and
planted these species in their home gardens, in the forests they were
managing,” she said.
That cultivation eventually altered entire regions of the Amazon, the
study argues. Levis and her colleagues found that some of these
species domesticated by indigenous people—including the brazil nut,
the rubber tree, the maripa palm, and the cocoa tree—still dominate
vast swaths of the forest, especially in the southwest section of the
“Modern tree communities in Amazonia are structured to an important
extent by a long history of plant domestication by Amazonian peoples,”
says the paper.
So too your ancients. They revere the forest and they manage the forest. The forest is not a wild thing. It is the place they live and they work to keep it a nice place to live. And just as the Amazon today, what appears to be a wild forest is actually akin to an overrun garden - with evidence of the ancient gardeners if you know how to look.
The linked article is more about the forest but you can read about ancient Amazonian agriculture here: https://en.wikipedia.org/wiki/Terra_preta They had a system for enriching the soil with charcoal and pottery shards. The soil enrichments those ancients made persist to this day and are still valued as soil amendments.