Hi Jo, That's not easy to give detailed instructions for. I tend to get into a rhythm when I work; so my mind is concentrating on the output, not the steps. But here it goes.
I start with a single population, say a pine object. I right click in the preview window somewhere near the center for the 'copy coordinates'. I paste these into the populations coordinate input. This moves the population to where it is needed. I resize it to cover the necessary area. I change the density to something which will populate quickly; I am only interested in seeing how the objects scale looks.
Now I adjust the min and max scales. Add a distribution shader to set altitude and slope constraints. Press the generate population to see how this looks. Looks ok.
It's time to add a second population. I want it to cover the same area and use the same distribution shader. Basically the same population as the first, but with oaks.
It would be easy to cut and paste the coverage size and the other parameters. Except highlighting the first populations values to copy them then trying to paste these into the second populations values does not work. The paste does not put the copied value into the input of the second population.
So I open the first population in a floating window from the node network. Then I open the second in the object tree (upper right white area). Now I just enter the values to correspond to the values of the first population.
I use Windows Vista Home Premium 32 bit on a Pentium 4 HT with 4 GB of ram. To me this is merely inconvenient. I could just copy and paste the original population node group and connect the new nodes and change the object. But this interrupts my normal 'flow' of doing things.
I hope this helps, but sometimes for me logic is a field of poppies with little birds singing sweetly in the haze.