I'd never really thought about length as a determining genre element. I have many short poems by Shakespeare or Donne or later poets, but only a very few Anglo-Saxon exemplars, and a few fifteenth-century contributions by "Unknown" grace my shelves from the medieval period. Is this an idiosyncracy of the sort of material I work with, or is there really a paucity of short poetry surviving from the Middle Ages?
And if there is plenty of shorter poetry, where would I go looking for it? I can think of the Carmina Burana. Perhaps collections of marginalia. Any other particular instances of fairly short poetry from the period (one or two pages or less)?