will I be able to use Forest screen saver in Yosemite?

When I open System Preferences/ Desktop & Screen Saver on the OS X 10.6.8 computer, I see a list of several screen saver choices under "Apple" (they are Arabesque, Computer Name, Flurry, etc.) and a different list under "Pictures". The list under "Pictures" is Shuffle, Abstract, Beach, Cosmos, Forest, Nature Patterns, and Paper Shadow.

When I go to /Library/Desktop Pictures/ and look through the jpgs that are in that folder, only some of those jpgs are what is displayed as part of the "Forest" screen saver. When I go to /Library/Screen Savers/ the only thing I found was a "World Book screen saver.saver" file that System Preferences/ Desktop & Screen Saver told me couldn't be run on this computer. It gave me the option to delete that file and I did. That deletion did not remove the "Forest" screen saver that I like so much.

I'll answer my own question -- it depends on whether Yosemite can use the .saver filetype and version that was used under OS X 10.6.8. I guess, also whether the OS will let me add Forest.saver to its list of screen savers.

I found the Forest screen saver in the System/Library/Screen Savers/ folder. I used option-drag to make a copy of that folder in a different location on the HD. The idea is that when I install OS X 10.10 that folder won't disappear. That folder contains both the Flurry and the Forest screen savers provided by Apple.

I am hopeful that I'll be able to run it under Yosemite since the System/Library/Screen Savers/ folder still has the Flurry.saver file listed, although the version under OS X 10.9 is ver. 10.8 and that under OS X 10.6.8 is ver 10.6 for Flurry.saver. There is no System//Library/Desktop Pictures/ folder on the OS 10.6.8 computer.

I'll continue to answer my own question: Success!! Yes I can use the Forest.slideSaver jpgs within the Yosemite Screen Saver.

First, I made a backup copy of the System/Library/Screen Savers folder to another location on the OS 10.6.8 computer’s HD prior to upgrading to Yosemite. I did this by holding down the option key while dragging the entire System/Library/Screen Savers folder to another location.

The Yosemite upgrade went without a hitch, that I can see. Indeed, Yosemite is much more responsive on this 2011 iMac (w/ 8GB RAM) than Mavericks is on a mid-21012 MacBookPro (w/ 4GB RAM). I still have several applications that need to be updated to run under Yosemite, but that’s for the future.

All of the following was done under Yosemite as the OS.
A Google search for the .slideSaver file format provided a MacWorld Hint of how to create your own screensaver, intended for a previous version of the OS. This involved the use of Terminal. I am not comfortable with UNIX, so I did not follow its instructions except for learning about doing a right-click (control-click) on the file to view its contents. Worked like a charm. I was then able to Show Package Contents which enabled my viewing of the Contents/Resources/ where all of the jpgs resided. I used shift-select to only select the desired jpgs within that Resources folder and then option-drag to make a copy of the jpgs into another folder on the HD.
Within Yosemite's System Preferences/Desktop & Screen Saver one has the ability to select a folder somewhere on the HD that is the source of the images that will be used for the screen saver. I selected my newly created folder of “Forest jpgs” with Shuffle slide order checked and set it to use the Ken Burns version.
Voila! I’ve replicated the Forest.slideSaver screen saver from Snow Leopard on Yosemite.