Complex sentence: Decline in species diversity was exacerbated through the introduction of sea buckthorn "Hippophae rhamnoides" by the military, an attempt at dune stablisation after preparation for the Normandy landings caused widespread erosion.
Split into simpler sentences: Decline in species diversity was exacerbated through the introduction of sea buckthorn "Hippophae rhamnoides" by the military. This was an attempt at dune stablisation after preparation for the Normandy landings caused widespread erosion.