The very best info I've found so far is in a book entitled, TERRAIN MODELLING, by Richard Windrow. It's published by Osbrey Modelling. With all due respect to Kalmbach Publishing Co -- ( I have most of their how-to books. ) Terrain Modelling covers, not only how to make many different types of trees, but also how to produce varing kinds of foliage such as palm leaves. I got my copy through the Military Book Club and I think Squadron Mail Order carries it. You should be able to get it through your local hobby shop, too.
I just checked-- this book has a section specifically on making conifers and pines. The photos of the ones made by the author look so real that they could be bonsai trees instead of fakes. Also, another question in this section of the Forum asks about making realistic swamps. This book shows how to do this, too.
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