Hey, cool picture. How did you done this?

Well, just simply apply a lenght map to your hair material. The length map does the obvious- change the length of strands according the its value.

You see the gradient bar under the hair? This is the lenght map applyed to the lenght channel. Later in this tutorial you will see another object behind the hair. That will illustrate additional settings in the material channels.

Allright, now where's the beef?

In the material dialog, put a new gradient ramp map for the lenght channel. Because we want the lenght to decrease along the objects surface, we need gradient to change along the UV coordinate. We also need it to go from white (long) to black (short) colors.

Push the render button and enjoy your results.

Ofcourse you can do a lot more with the lenght channel.

Let's see some examples - but belive me, once you discovered the possibilities, you will surely find new ways and usages for this powerfull function.

Let's change the gradient's properties a little bit. Keep it on the white side constant, and apply in the last 3rd part the decrease to blaxk. Fairly simple- or?

This picture illustrates very well how different color densities affect the hair lenght.

Following the mentioned Sasquatch tutorial, you can create a bar like this with corresponding proportions to your models as a guide for your length map.