Complex sentence: These grasses are found almost exclusively on the first line of coastal sand dunes; their extensive systems of creeping underground stems or rhizomes allow them to thrive under conditions of shifting sands and high winds, and to help stabilize and prevent coastal erosion.
Split into simpler sentences: These grasses are found almost exclusively on the first line of coastal sand dunes. Their extensive systems of creeping underground stems or rhizomes allow them to thrive under conditions of shifting sands and high winds, and to help stabilize and prevent coastal erosion.