Thinning is a woodland management practice where a proportion of the trees are deliberately removed. This can be done for several reasons.
Thinning will give the remaining trees more light and space, stimulating them to grow faster and put on more girth, and therefore improving your crop and timber yield.
It can also be done to help manage invasive species, to enable pheasant shoots and to benefit wildlife, as woodlands with natural light allow more flowering plants to grow, which in turn attract insects, birds and other wildlife.