De or het duinbeplanting?

The correct Dutch article is:

de duinbeplanting

Rule Words ending in -ing: almost always de. See the rule

How to use duinbeplanting

the duinbeplantingde duinbeplanting
this duinbeplantingdeze duinbeplanting
that duinbeplantingdie duinbeplanting
our duinbeplantingonze duinbeplanting
your duinbeplantingjouw duinbeplanting
every duinbeplantingelke duinbeplanting
which duinbeplanting?welke duinbeplanting?
a big duinbeplanting / the big duinbeplantingeen grote duinbeplanting, de grote duinbeplanting