Mmm, not sure they are using 'SpeedTree' to place foliage.
With regard to the visual problem, they appear to be using some kind of mask - note the grey edges:

Shame I know nothing about textures and modelling - sniff.
With regard to the visual problem, they appear to be using some kind of mask - note the grey edges:

Shame I know nothing about textures and modelling - sniff.