Port Frank’s dunes EarthCache

Sand Dune Conservation A dune may be simply defined as a mound or ridge formed by the deposition of sand. These geologic landforms develop when an abundance of sand combines with wind, vegetation and geography. The major sand deposits along the eastern shores of Lake Huron were laid down over the last 3000 to 4000 years, since post-glacial Lake Nipissing began to recede.

These dunes are formed from post-glacial lake deposits which preceded the present Lake Huron shoreline. The dunes in the Pinery-Port Franks-Ipperwash complex continue to develop and evolve as erosion from the shores to the north continue to support the dune system here.

These dunes are comprised of fine sands, and as a result, they are particularly vulnerable to erosion from stormwaves and from wind. People’s indiscriminate use of dunes can damage or destroy thousands of years of geologic processes in one instant.

Lake Huron’s dune systems represent an extremely small land mass. Yet these are the areas of the lakeshore that attract thousands of people each summer. All ecosystems have a certain threshold for being able to tolerate human impacts. Dunes, in particular, have a very low threshold.

Research has demonstrated that dune vegetation is sensitive to damage by human disturbance. Dunes are vulnerable to wind erosion once the anchoring vegetation on them is damaged or destroyed. Without effective conservation measures, we stand to lose an already limited resource. To protect these fragile ecosystems, we need to become more aware, and sensitive to the vulnerability of these important coastal features and their importance to Lake Huron’s shores.

Port Frank’s dunes are not only import to conserve because they are an important ecological and economic resource, but also because of the occurrence of the endangered dune plant “Pitcher’s Thistle”. Pitcher’s Thistle is a globally rare and endangered dune plant that exists in the Pinery-Port Franks area, and likely in Ipperwash as well.

If we manage our activities correctly, we can ensure that the beaches and dunes at Port Franks remain intact for future generations, and the special habitat they provide for Pitcher’s Thistle and other important dune species can continue to be sustained.

Beach and Dune Processes

Sand is continually being eroded and deposited on the shore by waves. Storm waves will erode the beach, taking the sand offshore, and forming a sand bar. The sand bar acts as a temporary protective berm, absorbing wave energy that would otherwise reach the shore causing even more erosion. Once the storm subsides, gentle waves will gradually bring the sand from the sand bar back to the shore and re-attach it to the beach.

Once onshore, the sand is then prone to movement by wind.

While wind strength is a key factor in sand movement, the quantity of sand moved is also influenced by how long the wind is blowing from a particular direction. Wind duration is an important consideration, and knowing the prevailing wind directions at certain times of the year can help with determining management strategies for dune conservation and restoration efforts. Winds with the greatest intensity and duration on the eastern shores of Lake Huron tend to be during the late fall, winter and early spring months.

As well as wind speeds and duration, the prevailing water level plays a significant role in how much sand transportation will take place. During high water levels, more of the beach is submerged and the width of dry beach is reduced. As a result, a smaller beach area may be exposed to wind erosion. Conversely, during lower water levels, more beach is exposed and greater wind erosion of the beach is possible. Therefore, periods of dune building tend to occur during lower water levels. Periods of natural dune erosion tend to occur during high lake levels when storm waves erode the base of the dune and carry that sand to offshore bars.

What is fundamental to understand is that sand dunes and beaches must be managed as one system. Dunes depend on beach sand for their formation, particularly during low water level periods, and beaches need the sand reserve held in the dunes during high lake levels and storm events. When the wind encounters an obstacle such as a clump of vegetation, the wind speed is reduced and the sand grains fall out under gravity, resulting in sand deposition. As the sand accumulation continues, a dune is formed. Dunes form when there is an adequate sand supply and onshore winds with enough velocity to move the sand. As the dune builds, it becomes a major obstacle to the landward movement of windblown sand. In other words, the dune serves to conserve sand in close proximity to the beach system.

Sand dune grasses are plants which have specifically adapted to the dune environment. The structure of these grasses can resist sand abrasion, wind breakage and water loss. They have adapted to extreme heat (dunes can reach temperatures of 60°C in summer!) as well as nutrient deficient soil. Confronted by high winds capable of blowing seeds many kilometres away, some of these plants have evolved a dual system of reproduction. In addition to seed production, they send out horizontal root stems called ‘rhizomes’ under the surface to push up new growth short distances away. The massive underground root systems that develop provide the dune with structure, making them far more durable than they would be otherwise.

Impacts to Dunes

Beach and dune vegetation are important for capturing and anchoring wind blown sand. While beach and dune vegetation have adapted to a harsh, demanding environment, they are quite fragile to human disturbances.

The coastal plant “Pitcher’s Thistle” (Cirsium pitcheri) is a rare and endangered plant species in Canada, and has the status of being globally rare.

Although it is related to other thistles found in fields or roadsides, Pitcher’s Thistle is a separate species that is found only on the open sand dunes and low beach ridges of Great Lakes shores. Less prickly than other thistles, Pitcher’s Thistle is has distinctive blue-green leaves covered with fine white hairs that give the plant a downy appearance.

Its range is restricted to the Great Lakes, primarily along the shores of Lakes Huron and Michigan. The plant’s life cycle includes a long 5 to 8 year growth period, and once its seeds form and disperse, the entire plant dies. The plant’s thick cuticle and pale fine hairs help to protect it against water loss and the sun’s intense rays, while deep tap roots help them find water and sparse soil nutrients. By extending their stems and leaves above the shifting sands, the thistle can tolerate burial and help to stabilize the dune.

At the Pinery, and along the southern boundary of the park, Pitcher’s Thistle grows in the dunes in the interior beach ridge. This thistle has very particular habitat requirements and Pinery/Port Franks has the special physical conditions available for this rare plant to survive. The main threat to this plant is human disturbance, including trampling, destruction from ATV’s, and habitat alteration from development and building structures in dune areas.

To log this Earthcache you need to submit a picture of the sand dunes at this location and your GPS unit. Plus, answer the following educational tasks/research questions:

- Do you know how sand dunes are formed?

- Approx. how many years ago were these dunes formed?