In contrast with reverberation, which is based on the propagation and amplification of the sound waves emerging from an instrument, sustain signifies the autonomous continuation of sound after playing an instrument. Sustain is comparatively short in stringed acoustic instruments such as the ukulele. It has a tendency to become even shorter at the higher frets. Sustain is influenced by the nature and quality of the bridge, nut, frets, fretboard and body. Hard tonewood reflects the sound waves better and ensures a longer sustain.

Sustain and the Ukulele

First of all, the ukulele is more of a percussive instrument, without much sustain. This usually results in most ukulele virtuosos playing fast to fill in the missing resonance space. My goal is quite different: pick up your favorite songs, slow them down, play them quieter and softer, and you'll get a wonderful sound. If you only play loud and fast, you will have no opportunity to savor the specific sound of a ukulele.1)

Kimo Hussey, quoted in Kemper, Peter: Wie die Ukulele die Welt erobert: Die Beatles, Jake Shimabukuro und die Folgen. Bosworth Edition. 2017: 304