Unproductive land is being turned back to nature in rewilding project

The video discusses the transformation of a site from farmland harvested in 2019 to a habitat left to benefit local wildlife. Grazing animals like horses, Catelyn, and pigs are introduced to prevent the area from becoming a dense woodland, instead creating a mosaic structure that supports diverse wildlife.

Why is it important to leave the site alone for the benefit of local wildlife?

What are the potential consequences of allowing the area to turn into a woodland?