Hi Pjort,
I agree with Götz here in that you could try increasing the value for the “Large triangle removal treshold” from the default value of 10 to some high number like 100 or 200 or even higher. You can check which value you need to use by using the “Advanced selection tool” and changing the value of the “Edge Threshold multiplier”.
If you change this parameter from the default value to for instance 50 and press “Select large triangle”, RC will only select the large triangles. Set this parameter to a number at which RC is unable to select any triangle for that size. Then use that size for the unwrap tool and fill it in in the “Large triangle removal treshold”.
After unwrap has finished, use Sweet mode to check if your large triangles (i.e. removed vegetation areas) now also show up as checkered boxes.