The answer to 'why is my tree brown patches' is that the tree is likely suffering from a disease or pest infestation. Brown patches on a tree's leaves or bark can be a sign of various issues, such as fungal infections, insect damage, or nutrient deficiencies. These problems can cause the tree's foliage to turn brown and die off in certain areas.
If you notice brown patches on your tree, it's important to inspect it closely and identify the underlying cause. This may involve looking for signs of pests, such as insects or larvae, or examining the leaves and bark for signs of disease. Once you've identified the problem, you can take the appropriate steps to treat the tree and prevent the issue from spreading.