Does a spell with split second prevent players from activating mana abilities?

Split second (CR 702.61) states that while a spell with split second is on the stack, players cannot cast other spells or activate abilities that are not mana abilities. The key phrase is not mana abilities — mana abilities are carved out as an exception and remain fully usable.

A mana ability (CR 605.1) is broadly defined as an activated or triggered ability that could produce mana and does not use the stack. Because mana abilities do not use the stack, they resolve immediately and cannot meaningfully interact with split second's timing lock anyway, which is why the rules explicitly allow them.

This means that even while your opponent has resolved a spell with split second (like Sudden Shock), you can still tap your lands, activate Llanowar Elves, or use any other mana-producing ability without restriction. You simply cannot cast spells, activate non-mana abilities, or use planeswalker loyalty abilities in response.

Concrete example: Your opponent casts Sudden Shock (which has split second) targeting your creature. You cannot cast Giant Growth to save it, but you can tap your Llanowar Elves for {G} or tap a Forest for mana — those are mana abilities and are unaffected by split second.

Note that triggered abilities will still trigger and go on the stack after the split second spell resolves normally; split second only prevents players from actively casting or activating things while it is on the stack (CR 702.61b).