Could you please show an example of your image? Is your goal to automatically extract those bush patches from the image? It would be also good if you can manually create an example of a segmentation result that can completely satisfy you.

You might try using eCognition if you have access to it. I know it is an expensive software. Here is a link: http://www.ecognition.com/ It is designed for object-based image analysis. We've used it to identify landscape-level soil features, but others have used it to identify vegetation patches or even individual shrubs.

Matt, I know of eCognition, but unfortunately I do not have it.

Lars, while I don't have a stero-pair, the reference you provided looks very helpful. thanks!