Why cut back native plants on the dune?
Updated: Aug 8, 2020
Concerning the naupaka and pohuehue (Beach Morning Glory) trim-back areas:
UH Sea Grant and Maui County Planning specialists have been so kind over the years to repeatedly explain to us why it is important to trim back and contain the naupaka and trim back the other native plants on occasion. We want to make sure that message gets to all of our new crew members as well as to inquiring onlookers. So here goes with a Q&A format with questions from volunteers to us and UH Sea Grant.
"Naupaka helps build the dune! Right?" Actually the answer is ‘no’. Naupaka at our beaches in South Maui blocks sand accretion. It also robs space and light from the more desirable beach vines and native grasses that do help grow the sand dunes. We don’t remove it completely because it is a solid native beach plant that is important in its place, on the top and backs of the dunes.
"Does naupaka grow that quickly in nature?" No, in nature there is not the passive irrigation from our parks/ houses/ condo’s that cause the plants to grow so large. In nature it will grow low and tight to the ground, with small leaves.
"Why can’t we just lightly trim back the naupaka?- why do we have to severely cut it back?" You could cut it lightly but you would have to do it every few weeks. It comes back strong so we cut the height to encourage lateral growth and we thin it to discourage migration towards the beach or towards the park, homes, pathways on the back dune areas. (The other reason is that our time window for cutting in seabired nesting sites is short because of the returning sea birds, so the ‘cut’ has to last until the next season.)
"How often do we have to trim it out to maintain the size and shape that are best for our beaches and dunes?" Usually once or twice per year. In sea bird sanctuary areas we trim it back between Jan and March, and in other areas without sea birds we trim back other times during the year.
"How do the sand dunes grow in relation to the beach plants?" Trade winds blow sand up the beach where it is captured by the beach vines and grasses. The root systems of the vines and grasses allow them to grow right up above the blown sand where they continue to capture more and more sand. When large waves from storms hit, they take some of that beach and dune sand back offshore and form shallow sand bars that cause the really big waves to break further offshore. Those shallow sand bars help save our beaches from the damaging impact of the big waves. After the storm passes the small ocean waves return and they wash the sand from the bars back onto the beaches. From there the trade winds complete the cycle and blow the dry sand onto the same dunes again where the vine and grass roots return. (Tip- if you want to watch the sand being washed out to sea you have to be on the beach for the very first of the storm waves- those are the ones that take the sand. The larger but later waves then break further offshore on the newly formed sand bars.)