Post-Fiona: Sand Dunes
There is no doubt that the pictures from across PEI following Hurricane Fiona were heartbreaking. Iconic trees and local landmarks were lost, and our world-famous sand dunes have been changed - temporarily. I think it’s important to know that this change is indeed temporary, and so coastal sand dunes are the focus of today’s PEI habitat highlight.
I think of sand dunes like a bank account: there are continual deposits and withdrawals throughout the year. Some happen on a seasonal cycle, others because of weather events. Fiona has just made a huge withdrawal, but – fortunately – our shores still have a steady and reliable income stream (offshore sand), which will be added back to the bank account over time.
Offshore currents move sediment along the Island’s coast and tides bring it ashore. Where the beach is wide enough, the sand is able to dry out and wind takes over as the driving force. (PEI’s dunes are technically described as ‘aeolian’, meaning wind-formed). As wind blows along the shore it carries sand with it. Sand grains aren’t all the same size and larger, heavier grains require a higher wind speed to move than do smaller, lighter grains. When the wind encounters an obstacle - driftwood, a rock, or a plant, for example - its speed slows and the heavier grains drop to the ground on the leeward side, forming what’s called a ‘sand shadow’ (Photo 1). You can see this on any PEI beach at any time, and it’s the start of a sand dune.
Marram Grass (Ammophila breviligulata) is extremely well-adapted to its coastal habitat. The name Ammophila literally means ‘sand-lover’, and once even a small sand shadow forms, Marram Grass will take root. It’s the keystone species of our beloved sand dunes, and without this grass the dunes would not exist. Once Marram Grass establishes, it catches more sand; the more sand it catches, the taller it grows to rise above it (Photo 2).
This process continues year over year, and even our tallest dunes have a skeleton of matted Marram Grass roots inside, holding them together (Photo 3).
Marram Grass is a bit of a paradox: both extremely hardy and extremely fragile. It’s hardy in that it thrives in a habitat with virtually no organic matter, little freshwater, constant salt spray and temperatures that can vary from 40C (104F) or more in summer to -40C (-40F) in winter. But it’s fragile in that just a few people walking over the same spot can kill it, causing the sand it was holding to blow away and creating a hole called a blow out.
It's natural to want to help our landscape recover, but often the best thing we can do is give nature the time and space it needs. During Fiona, PEI’s dunes played the ecological role they were supposed to: they buffered inland areas from the storm. We can repay this service in two ways.
First, by being mindful of where we put coastal structures such as docks and breakwaters, which can interrupt longshore movement of sand and reduce that steady, reliable income the dunes need for their bank account. And second, by staying off the dunes (including the tiny foredunes shown in Photos 1 and 2!) and leaving beach vegetation alone for now.
I don’t think that’s too much to ask to help this cool PEI habitat!