Simple answer- an adventurous one.
Seriously, I think an explanation is required.
Here in the UK we don't have "Community Orchestras" as such but we have "Amateur Orchestras" The American Community Orchestra seems to be a large ensemble with more players per part than is required in a professional orchestra, but a UK Amateur Orchestra would have the same number of players as a professional orchestra except a slightly reduced number of strings, especially in the more rural locations. This reduces problems of balance, dynamics and ensemble playing. The orchestra in question recently did a concert where the programme was Beethoven Egmont Overture, The Snowstorm by Sviridov and Tchaikovsky's Manfred Symphony and the orchestra numbered 61 players. Sometimes we have to invite extra players to cover extra parts and sometimes we have too many players on a particular instrument and so we share out the concerts (usually 4 or 5 concerts each year) I run the heavy brass section and I have 4 trombones and 2 tubas on the books to call on regularly and a list of others in case of emergency.
The planned programme for the next 18 months is
William Tell Overture, Rossini
Piano Concerto No. !, Beethoven
Romeo and Juliet Suites 1&2, Prokofiev
Tintagel, Bax
Violin Concerto No. 1, Bruch
Job, Vaughan Williams
Four Last Songs, Strauss
Symphony No. 5, Mahler
Nutcracker Suite, Tchaikovsky
Checkmate, Bliss
Spartacus, Khachaturian
Firebird, Stravinsky
There would also be 2"Classical" concerts with a smaller orchestra (no heavy brass)
We share the parts around once we know who is available for which concert and that way everyone gets the chance to play different parts, if they want to. All the 4 trombonists play tenor, 2 play bass, I am the only alto player and2 of them play tenor tuba.
All the amateur orchestras I have played in have all worked in the same way.
Cheers
Stewbones43