On sand, ecological succession is

The correct option is "psammosere".

Ecological succession is the progressive series of changes in the species structure of an ecological community over time. When succession starts on a newly exposed or undeveloped substrate, it is referred to by specific names depending on the nature of that habitat:
1. Psammosere: A succession that initiates on sand or sand dunes.
2. Halosere: A succession that starts in saline water or soil (salty environment).
3. Xerosere: A succession that initiates in extremely dry areas (like bare rocks).
4. Hydrosere: A succession that starts in a water body (like a pond or lake).

Since the question asks about ecological succession on sand, it is termed a psammosere.