Wednesday, May 17, 2017

Ecology and Restoration of California's Coastal Dune Habitat

Much like California's deserts, a cursory glance at our coastal dune ecosystem - by the untrained eye - shows little more than a barren, windswept, lifeless place.  But the concept of coastal dunes as lifeless is far from the truth.  In fact, the unfortunate truth is that much like deserts, coastal dunes have been written off time and time again as areas in need of "improvement."  As a result, nearly all of California's coastal dune systems have been severely degraded. 

Restored dunes at Moss Landing State Beach

Highways cut through the dunes, housing developments and condominiums perch on top of them, mining operations remove sand entirely.  Invasive plants have been introduced to "stabilize" the soil: most notably, iceplants (Carpobrotus chilensis and Mesembryantheum crystallinum) and Eruopean Beachgrass (Ammophila arenaria).  These plants have been wildly successful, covering extensive dune systems to the exclusion of native species.  Invasive plants crowd out native plants, offer native wildlife very little in the way of food and shelter, and alter the structure of the entire dune system.  It is from these iceplant-covered slopes, dangerously low in biodiversity, that we have arrived at the mistaken conclusion that coastal dunes are inherently barren wastelands.

As a kid visiting the beach, my abiding memories are of iceplant: rolling dunes covered in nothing but iceplant.  Even as a curious, observant young naturalist, I could not have told you anything about native dune plants and wildflowers!  All I knew was iceplant.  I assume the experience of many California beach-goers has been the same.

Non-native Sea Rocket (Cakile maritima) blooms on restored dunes at Moss Landing State Beach, where the battle 
to eradicate introduced, invasive plants continues.

In their natural, undisturbed state, coastal dunes are fluid, moving entities that support a diverse and unique assemblage of plants and animals.  The introduction of non-native plants not only excludes native species, but also stops the development of dunes.  The thick cover of non-native plants differs from the widely-spaced growth pattern of native plants.  The dunes become immobilized, and sand builds up along the foredunes to create tall, steep slopes that effectually cut off the supply of sand to the rest of the dune field.  This eventually starves the dune field, leading to the degradation of the entire ecosystem.  As the shape and structure of the dune field changes, it becomes unsuitable for native wildlife.

Western Snowy Plover (Charadrius alexandrinus nivosus)

While coastal dune ecosystems are relatively food-poor habitats, they still support a surprising variety of life.  Insects are the most numerous group, and several rare butterflies rely on dune habitat.  Rare members of the genus Euphilotes, or Buckwheat Blue butterflies, feed exclusively on Buckwheat plants of the dunes.  Federally threatened Western Snowy Plovers (Charadrius nivosus nivosus) and endangered California Least Terns (Sternula antillarum browni) breed in California's coastal dune habitats.  Black Legless Lizards (Anniella pulchra nigra), an endangered subspecies of the California Legless Lizard, live below ground in the sand of the dunes on the southern coast of Monterey Bay and the Monterey Peninsula.  Federally endangered plants of the coastal strand habitat include Tidestrom's lupine (Lupinus tidestromii) beach layia (Layia carnosa) and Menzie's wallflower (Erysimum menziesii).

Menzie's wallflower (Erysimum menziesii)

Ecologically, there are similarities between coastal strand (coastal dune and beach habitats, collectively) and desert plant communities.  Both have sandy soils, and one of the main properties of sand is that it is porous, lacking the ability to hold a significant amount of water.  In response, both plants of the desert and coastal strand plants may exhibit long tap roots and succulent leaves. 

Like desert plants, plants of the coastal strand must adapt to survive in harsh conditions.  Challenges include excess salts in the soil (from evaporation in the desert and salt-laden sea air on the coast), high winds and abrasive sand, shifting sand and occasional burial, and lack of freshwater.  Prostrate growth forms are common in plants of the coastal strand, as this protects plants from excessive winds.  Beach Sagewort (Artemisia phycnocephala) is covered in soft, protective hairs, a natural barrier against windblown sand; Beach Bur (Ambrosia chamissonis) grows new, upright stems after it has been buried by shifting sand. 

Restored dunes with silvery Beach Sagewort and Beach Bur

Perhaps not surprisingly, quite a few genera of plants have representative species in both desert and coastal strand communities.  Beach Sagewort belongs to the same genus (Artemisia) as our familiar sagebrushes, and the genus Ambrosia, to which Beach Bur belongs, has several desert members as well.  The buckwheats, Eriogonum spp., have members in alpine, desert, and coastal strand communities.  Wildflowers such as Beach Primrose (Camissonia cheiranthifolia), Red Sand Verbena and Yellow Sand Verbena (Abronia maritima and A. latifolia, respectively) will all look very familiar to any desert wildflower aficionado. 

Beach Primrose (Camissonia cheiranthifolia)

Like the cryptogamic or cryptobiotic crusts of desert soils, a thin soil crust also forms on the surface of undisturbed coastal dunes.  This crust is caused by the moist, salty air and is critical to the development of dune vegetation.  It is imperative that this crustal layer remains intact, as it holds in place just enough moisture and substrate to create a seedbed suitable for the germination and establishment of new plants.  Just like in deserts, trampling obviously disturbs this important layer; careless activities such as off highway vehicle use severely damages the soil crust, and in turn the entire ecosystem.

Yellow Sand Verbena (Abronia latifolia)

The main difference between plants of the desert and those of the coastal strand is life strategy.  While annuals prevail in deserts, where they are able to grow very quickly, set seed and die in one short rainy season, plants of the coastal strand are largely perennial.  Cloudy days and year round fog creates a different environment from the intense sun of the desert, preventing the high photosynthetic rates required for the rapid growth of annuals.  The foggy climate of the coastal strand is far more moderate than the extremes of the desert, so even though freshwater can be in short supply, the absence of an intensely hot, dry season allows perennial plants to persist here throughout the year. 

 Beach Pea (Lathyrus littoralis)

As I mentioned earlier, as a kid I noticed little else at our favorite beaches beside iceplant (and Eucalyptus, but that's another story entirely!)  But when we began visiting a different beach, Asilomar State Beach in Pacific Grove, I noticed something different.  The dunes looked different.  There were different plants growing on them, and a neat boardwalk to walk on. 

White-crowned Sparrows (Zonotrichia leucophrys) not only breed but also can spend most of their lives in
coastal strand habitat.

I didn't know it at the time, but the Asilomar Dunes are one of the best places in Central California to see an example of dune restoration.  Development, sand mining and unrestricted use by enthusiastic beach-goers completely destroyed most of the dune system by the early to mid-1900's, and what was left was badly trampled and eroded.  Seeing how the natural state of the dunes had been so degraded, groups of people stepped in to fix the problem they had created. 

Unfortunately, these early efforts to fix the problem only compounded it.  By introducing non-native, invasive plants to stabilize the dunes, the ecosystem was drastically altered.  In the area of Asilomar State Beach, this began in the 1960's with the introduction of iceplant.  But iceplant doesn't provide food or shelter for wildlife, and by the 1970's, the iceplant had excluded virtually all native plantlife and the dunes were considered a wasteland - an idea that has persisted in many uninformed minds. 

In 1984, efforts to restore the Asilomar Dunes began with the goal of returning them to their natural "pre-European" state.  Nearby isolated remnants of native vegetation served as a guide; seeds were collected and plants were raised in a specially built nursery.  Non-native plants were removed and the dunes were dramatically reshaped, as non-native "stabilizing" plants had reshaped the entire dune system by not allowing the wind to work on the dunes in a natural way.  Native plants were planted, and a boardwalk was built to allow restricted visitor access to the area.  Today, the restoration work is on-going and showing great signs of success. 

Endangered Menzie's Wallflower, replanted at Asilomar State Beach. 
Each plant is protected from herbivory by a small wire cage.

Most people are probably as unfamiliar with our native dune habitat as I was.  The boardwalk across the Asilomar Dunes allows visitors to experience the dunes, offering an up-close close look without causing damage to the plants.  Today, 35 native plant species grow in the restored dunes, each specially adapted to the unique environment and playing a distinct role in the ecosystem.  (Many of these plants were mentioned above, including Beach Sagewort, Beach Bur, Beach Buckwheat and the sand verbenas.)

Beach Sand Verbena (Abronia umbellata)

In addition to being threatened habitat for an assemblage of unique species, coastal dunes offer an ecosystem service to the general population as well.  Coastal dunes provide a buffer against extreme high tides and storm waves.  But to be effective, the dunes need to be able to move freely as wind and waves dictate.  When they are over-stabilized by non-native and invasive plants, the dunes become immobile and much more susceptible to erosion.

Clearly, it behooves us all to protect and restore California's coastal strand, its beautiful stretches of beaches and dunes, preserving the integrity of the coast and its native habitats.  If you remain unconvinced, I invite you to pay a visit to one of California's coastal dune systems.  In central California, try the restored dunes at Asilomar State Beach, Moss Landing State Beach, or the Marina Dunes Preserve, all near Monterey.  Visitors to these special places are able to experience the dunes without trampling the vegetation; they are able to walk among the plants, butterflies and birds, to hopefully gain a deeper understanding and appreciation for coastal dunes.

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