When working with Bryce, thinking “outside the box” is a skill we have to adopt early on and never let go of.
If I were attempting a tree like the examples shown above I would use Boolean Operations to accomplish it.
Step 1: Create a pine tree in the tree lab that resembles the top part of your desired tree. In the Attributes, enable this tree as a Positive. Save the material you used as the trunk in your Library.
Step 2. Create a Cube. Enable this Cube as a Negative. Place this cube at the base of your tree so that it can hide the roots. Group the tree with the cube and it should create a cut off such that the roots are no longer visible in the render.
Step 3: Now we need to create the look of the extended limbless trunk. One could use a column of metaballs, which can then be grouped and then be collapsed so that it becomes a true single mesh object . I’d export then re-import this model as an obj. Just line up the top of your metaball column with the new apparent base of your pine tree. Apply the same material to the extended trunk as you did the trunk of the pine tree, and the result should look quite decent.
Perhaps an even easier trunk could be made by using one of the tapered cylinders in the Additional Primitives. Either way, this tree can be done.
There could potentially be some slight inconsistency at the point where the original tree becomes joined with the faux trunk, but these are relatively minor considerations. I think one could make it less noticeable by cutting off the trunk of the original tree a little higher up well above where the roots are. By cutting away more of the original trunk you can hide the “seam” within the branches so that the extended trunk remains smooth looking all the remainder of the way down.
The new dual trees we have in Bryce 7 libraries show how the basic idea of gluing trees together can create new levels of naturalistic complexity. In theory, one could create almost any form of vegetation, though it may require some cleverness and multiple steps, still it can be done all within Bryce.
It helps to keep in mind that the creators of Bryce didnt necessarily have the opportunity to fully flesh out every tool. Often, Bryce’s available tools get part of the way there but not the rest, at least not in a direct sort of way. However the magic of Bryce for me is all the incredible stuff it can do indirectly, things you will not find in any manual.
What I’m saying is dont be NICE with Bryce. Start ABUSING the tools to see what surprises they may offer. Abuse boolean modeling by making booleans of trees…abuse the DTE to generate source images you can then export and apply as textures in Bryce or yet other programs…abuse cloud mats to make falling water or abuse a giant volumetric cube to create a hazy environment instead of always relying on the Sky Lab provided haze. Find unconventional uses for the available tools, and dont let the lack of a straightforward process put you off of your goal. Bryce is a riddle.
Once years ago I got into a rather heated discussion with another long time Bryce user about Bryce’s tool set. This person was kindly explaining to me how to “properly” use certain tools especially in the way of lighting. The idea was that the developers had a certain thing in mind when they introduced these tools so I would be wise to use the tools in the proper way. My argument was that if I only use the tools in the manner the developers intended, then the only results I will achieve will be those the developers intended for me to achieve, and since that is not the look I want, I must do things my own way.
Bryce provides enough options that if you dont want to, you dont have to use any of the “tools.” You can create your own sunlight with radials or domes, your own atmospheres with volumetric cubes and spheres, and lots of other stuff without ever entering the Sky Lab. 99% of the time the skylab haze is just fine, but one day you need a different more accurate haze model than the one the skylab provides so you build up your own atmosphere with fuzzy and volumetrics, and the result might end up more realistic than what the skylab would have done.