These two plants belong to an ocean plant community wherein they provide a classic environmental struggle between two competing genera.  Hudsonia tomentosa and Arcostaphylos uva-ursi (beach heather and bearberry) both strive to colonize seemingly identical sites at the expense of their rival. The contest becomes more interesting with the realization that each genus thrives under conditions that weaken its opponent.  This set of opposing growing criteria allows new battle lines to form seasonally and throws a wild card into the equation of dominance and ultimately survival for the plants involved.  The plant with the temporary upper hand will press its advantage by crowding out its neighbor by growing under or over the weakened plant. Victory is measured by increased growth for the winner or a gain in total biomass for the individual plant, or more importantly, the genus as a whole.

The battlefield is the land-facing side of the primary dunes through the secondary dune flats.  It is the portion of the sand dune immediately away from the ocean but not yet thick shrub or forest.  These areas are more stable than the ocean (or bay) side of the primary dune and get some protection from the dune windward side.  The primary dune protects the plants from outright washing away and keeps the roots of colonizing plants from salt water immersion, which is fatal to our combatants.  Even with the dune protection, the factors of salt-laden air combined with fierce sun and drought with nutrient poor sand, allow only a few plants to tolerate an ocean exposed site.  Beach heather and bearberry both adapt well to colonize the broad, mainly flat areas of the back dune. The plants increase by spreading rooting branches and rootstock. Growth gains are not just important in a direct competitive sense, but also in the production of flowers and later seed. The increase of seed production may not produce dividends on the immediate site but rather on other uncolonized or empty sites. The plant with the first few struggling plants to take hold has a better chance to monopolize the bare ground and propagate its genus further in anticipation of the inevitable future battles.

click photo to enlarge

click photo to enlarge

The Hudsonia-Arcostaphylos Association

The wild card factor concerns the ability of both plants to respond to moving sand.  Hudsonia adapts well to sand covering its crown and grows roots along the entire stem length, forming a newly layered root system. Beach heather likes and actually needs occasional sand covering to produce a rejuvenating effect and in years in which the sand covers the heather, it increases.  Likewise in years with no or little sand movement, the crown of the plant becomes open at the center and in time the wood becomes weak and brittle.  In the presence of many years of stable sand, Hudsonia wood becomes old (lignified), and old thick wood roots poorly.

In contrast Arcostaphylos prefers a more stable sand substrate and detests heavy loads of shifting sand. Bearberry can take some sand covering as all beach plants do, but it is much more successful in areas where the sand does not move a great deal. As a result of every ocean storm new circumstances can change the local growing conditions.

If one wants to watch this struggle, north eastern seaboard dunes have typical associations of these plants. On eastern Long Island the dunes in and around Amagansett and Hither Hills State Park provide excellent examples of this plant behavior.

Dune Plants Homeindex.htmlshapeimage_2_link_0
Dune Plant Survival & Supremacyplantsurvival.htmlshapeimage_3_link_0
Perennials & Grasses - Woody PlantsPerennialsGrasses.htmlshapeimage_4_link_0
Carex pensylvanicaCarexpensylvanica.htmlshapeimage_5_link_0
Beach PlumBeachPlum.htmlshapeimage_6_link_0
Comptonia peregrina (Sweet Fern)SweetFern.htmlshapeimage_7_link_0
Hudsonia-Arcostaphylos Associationshapeimage_8_link_0
Winter SeasonWinterSeason.htmlshapeimage_10_link_0