Class Description
Short-term Covers actions that take less than a tidal cycle or repeat on a time-scale of this duration or less
Medium-term Relates to seasonal or annual changes
Long-term Progressive changes over decades or centuries, including trends and cycles

To these are added two further classes to cover non-continuous events and single actions:

Class Description
Intermittent Changes that happen episodically (e.g. storms) or infrequently (e.g. accidents)
External One off actions that, in the context of management (50-100 year time horizon), do not change with time and may, therefore, be considered constant or fixed