I find that just waiting for the wind to drop cures my shimmering tree problems...

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Paul...

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I would imagine that because the trees (leaves) are made of hundreds (thousands?) of complex pixels, the graphics card/processor has a really hard time trying to catch up with the ever changing scenery, especially when banking an aircraft, (the very worst set of conditions for the screen!).
Win 8.1 64-bit. DX11. Advent Tower. Intel i7-3770 3.9 GHz 8-core. 8 GB System RAM. AMD Radeon HD 7700 1GB RAM. DVD ROM. 2 Terra Byte SATA Hard Drive. Philips 17" LCD Monitor. Saitek Cyborg X Fly-5 Joystick. ...and a Briggs and Stratton Petrol Lawn Mower.