SINGAPORE — Some countries have strategic oil reserves; others stockpile rice or wheat. The island nation of Singapore has emergency reserves of imported sand.

The sand is there to secure Singapore’s insatiable demand for concrete, a reminder of its vulnerability as a nation without a hinterland to supply it with vital resources.

The government is now being forced to tap its sand hoard after its usual supplier, Indonesia, abruptly banned exports in February, citing the impact of a recent Singaporean construction boom on Indonesian beaches and island environments.

The ban touched off the latest in a string of disputes between Singapore and its neighbors over water, land reclamation, satellite concessions, corporate takeovers and the flight patterns of the Singapore Air Force, just to name a few.