On the narrow barrier islands of the U.S. East Coast, preserving the fragile dunes is a constant battle against the encroaching waves. Hurricanes and Nor'easters wreak destruction, eroding the dunes and sometimes over-washing them. Lath fences, dune grass plantings, and salt-resistant evergreens help hold the sand in place. Sometimes heavy equipment is used to rebuild dunes. And where commercial and residential structures are built nearly to the beach: after storms, huge dredges pump sand from under the breaking waves to rebuild beaches and dunes. (Bigger and more frequent storms along with rising sea levels, both caused by global warming, may yet reshape this entire coastline.)