Joey, it kinda is - think about it
Normally you have water containing DO in your pond...add an object to displace that volume (like a dead fall tree) and water spills over (stand pipe, overflow, spillway etc.) In this case the added volume comes in the form of suspended solids. Less water per volume = less DO carrying capacity.
DO is usually measured as PPM (Parts Per Million) or milligrams per liter (mg/L). In your example, the tree has displaced water from the pond, however, the DO in PPM or mg/L of the water still in the pond remains the same.
