Sorry, but this is a pet peeve of mine: every "standard" hobby collection
I have seen or heard described is actually not oriented toward helping
preserve species. If fact, many growers have not made provisions to
protect even their own collection in the event they should die, become
incapacitated, or loose interest in that group of plants. Preserving
the species requires preservation of the genetic diversity of the
population (ie. many individuals of the same species), pollinators or
other symbiotic organisms should be considered, and a reintroduction
plan should be in hand. One may fantasize about a scenario where all
the native populations die, botanical garden collections fail, leaving
only a single, dedicated, private grower, with his collection-fortress
preserving the last of the species. But this is best left as the
fantasy. I think hobby collections serve an important function
familiarizing and educating people about plants. But this shouldn't be
confused with a conservation program. In the long run, cultivation can
only preserve cultivated plants (ie. rose hybrids, ornamental cultivars,
crop plants, etc.)
Michael Chamberland