Hello,

Based on what I see in your images, the thinning of the upper canopy and browning of leaves in your maple tree could be due to several factors. Here are some potential causes based on information from educational sources:

Branch Cankers: Fungi such as Botryosphaeria obtuse and Valsa spp. can cause leaves on random branches to wilt, turn yellow, and then brown. Infected branches may not leaf out in spring, and cankers can be identified as brown to black sunken areas on branches.

Stem Girdling Roots: This condition can lead to water-stress symptoms like marginal leaf scorch, wilting, and sudden leaf fall. The trunk may appear sunken where it contacts the girdling root, and the tree may lean abnormally.

Verticillium Wilt: Caused by the fungus Verticillium dahliae, this disease can result in leaves turning brown from the edges and tips, wilting, and dying. It can affect one or a few branches in the canopy and may show dark streaks in the sapwood.

Sapwood Rot: Fungi like Schizophyllum commune and Cerrena unicolor can cause dead branches within the canopy and may present with small semi-circle shelf fungi along killed branches or the main trunk.

Oystershell Scale: This pest can cause foliage to turn yellow, and twig and branch dieback can occur when branches are heavily infested.

Heart Rot: Fungi such as Phellinus spp. can cause decay in the trunk, which may not show immediate symptoms in the canopy but can lead to small yellowing leaves or dead branches. More information at this link:

What's wrong with my plant? : Garden : University of Minnesota Extension (umn.edu)

Environmental Stress: Factors like drought, compact soils, flood damage, or winter injury can lead to leaves wilting and turning brown at the tips and margins, eventually affecting the entire leaf. More information at this link:

What's wrong with my plant? : Garden : University of Minnesota Extension (umn.edu)

It’s important to correctly diagnose the issue to provide the appropriate treatment. Consulting with a local certified arborist or MSU Plant and Pest Diagnostics Lab can provide a more precise diagnosis and recommendations for your situation. Additionally, you might want to consider getting a soil test to check for any nutritional deficiencies that need correcting. Details on soil testing at this link: Get Started | MSU Soil Test

TWO (2) OPTIONS

OPTION 1:

For a confirmed and precise identification of the problem, I recommend you send all your images by e-mail to the MSU Plant & Pest Diagnostics Lab. The experts there can also provide you with the best treatment options. Their email is <personal data hidden>. Please include your name. The lab will let you know if they need a sample sent. FYI, the lab may also ask for additional images.

Their website is at this link:

Plant & Pest Diagnostics (msu.edu)

Their Contact Information is at this link:

Contact Us - Plant & Pest Diagnostics (msu.edu)

This link will explain the details of submitting a sample to MSU Plant & Pest Diagnostics Lab:

Submit Samples - Plant & Pest Diagnostics (msu.edu)

OPTION 2:

You can consult a local certified arborist for a more detailed onsite assessment and personalized advice. To find a certified arborist in your Zip Code, go to this link:

Find an Arborist (treesaregood.org)

I hope this helps!