Shoreline erosion has become an increasing problem for Hawaii. Nearly 25% (17 miles) of Oahu’s beaches were lost during the 20th century. Even greater losses have been reported on Maui. While it would be nice to blame something sinister and faceless like climate change, the reality is that the problem has been caused primarily by beach-loving people like many of us. Homeowners with beachfront property have built as close to the beach as possible. Once the natural shifting of the shoreline occurred, they constructed seawalls, with or without permits, to protect the stability of their homes. While seawalls may have protected their homes, the scouring action of the waves working at each end of the wall caused the neighboring properties to be more severely affected by the erosion. Of course, the neighbors then constructed seawalls to protect their properties and so on. The next thing you know, the entire beach is a line of walls and the sand is gone. This is a big problem, particularly for a state whose largest industry is tourism with a primary focus on beach activities.
So what does all of this have to do with trees? Plenty. It’s not just homes that become destabilized. Beaches, such as Baldwin Beach Park on Maui, have had to be closed temporarily to protect beachgoers from tumbling trees. Once the trees are removed, the beaches are reopened, but with less shade and beauty than before. Somehow tree stumps don’t have quite the same ambience as the waving coconut palms in tourist brochures.
While arborists may not be able to prevent shoreline erosion, we can learn from it. Naturally exposed root systems provide a glimpse into the below-ground structure of trees. I had the opportunity to work on a property with shoreline erosion problems in early 2006. One ironwood (Casaurina equisetifolia) in particular caught my eye. This tree, measuring eighty feet (80’) in height, looked as though it was growing on stilts because so much of its root system was exposed. I thought I would share the photos with my fellow arborists so we can all learn together. In case you’re wondering about the fate of this tree, it has been reduced to a 5’ high stump but not poisoned so that it can continue to help stabilize the shoreline for as long as possible. The owner has been instructed to maintain it as a shrub by shearing it regularly to prevent the growth of large watersprouts.
Advertiser Staff, Erosion closes popular Maui beach, The Honolulu Advertiser,July 29, 2006, http://the.honoluluadvertiser.com/article/2006/Jul/29/ln/FP607290351.html .
Mike Leidemann, Advertiser Staff Writer, Beach erosion ‘widespread’, The Honolulu Advertiser,August 6, 2006, http://www.honoluluadvertiser.com/apps/pbcs.dll/article?AID=/20060806/NEWS01/608060345
Coastal Erosion and Beach Loss in Hawaii, Facts about beach erosion and the Coastal Lands Program at DLNR, http://www.soest.hawaii.edu/SEAGRANT/CEaBLiH.html
A version of this article was first published in the Western Arborist around Winter or Spring 2006.