It looks like light reflecting off small twigs and marks on the bark to me. Apart from a saw, you could try increasing the contrast in the camera (If you have this option) before you shoot silhouettes as digitals seem to retain detail in shadows more than film. Use spot metering to take a reading from light part of image eg: the sky, and keep the aperture small to avoid flareing around the branches (probably need a tripod for slower shutter speed). Exposure is a bit of an experiment though, so bracketing could be useful to get couple of goes at it. Use levels in PSP to tweak image and go very gentle on the sharpening or you get marks and lines showing that are not really there. Hope this helps and good luck with it :) Richard.

And every one said, 'If we only live,
We too will go to sea in a Sieve,---
To the hills of the Chankly Bore!'
Far and few, far and few, Are the lands where the Jumblies live;
Their heads are green, and their hands are blue, And they went to sea in a Sieve.

Edward Lear
http://www.nonsenselit.org/Lear/ns/jumblies.html