If you're not training for jumping, you'll get worse at it, not better......... the only way that cycling will be to its detriment is to take the place of specific training.

Do some box jumps, squats, jump squats, tuck jumps, etc.... you know, just google for a vertical jump training program. If that's an important performance item for you in some sport you participate in, then train for it.

Funny enough, training programs for BMX racing look a lot like the vertical jump programs.