Pink sand-verbena (Abronia umbellata) COSEWIC assessment and status report: chapter 5

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Habitat

Habitat requirements

Abronia umbellata habitat in British Columbia is restricted to upper sand beaches, just below the driftwood zone, along the outer coast. These sites are scoured by high tides and winter storms thus few plants in this zone ever persist over winter. At Clo-oose Bay, the two Abronia umbellata plants were swept away in the first winter storm in October, 2000. A similar situation occurred in 2001. Few plants are adapted to this ephemeral habitat and only scattered specimens of Cakile maritima, a European introduction, occur along this area of the beach.

The sand beach/sand dune habitat is uncommon on the outer coast of British Columbia. Only three of the beaches (at Ahousat, Clo-oose Bay and Pachena Bay) have records of former occurrences of Abronia umbellata. A number of other beaches are potential sites for the latter species since they support, or have supported, Abronia latifolia, a species with similar habitat requirements.

Over the last century the sand beach and sand dune habitat along the Pacific Coast has been radically modified by the introduction of the non-native, sand dune stabilizing grasses, Ammophila arenaria and A. breviligulata (Wiedemann 1984, Rittenhouse 1994, Buell et al 1995, Wiedeman and Pickart 1996, Pickart and Sawyer 1998). These vigorously growing, rhizomatous grasses have created heavily vegetated foredunes that exclude most natural vegetation. The foredunes are higher, steeper and more stabilized than those that previously supported native vegetation. The Ammophila species also intrude on the upper sand beaches, the natural habitat of Abronia umbellata.  

Trends

The habitat, or potential habitat, to which Abronia umbellata is restricted, has been substantially reduced over the years, especially in the U.S.A. The appearance of the introduced grass, Ammophila arenaria, and more recently A. breviligulata, has drastically altered the sand beach/sand dune habitat on many west coast beaches. The earliest records of A. arenaria in the Tofino area date back to the mid-1920’s. The longest (over 3 km) beach on the west coast of Vancouver Island has undergone unnatural foredune formation to such an extent as to render the potential Abronia umbellata habitat nonexistent. In recent years, A. breviligulata, which appears to be even more vigorous than A. arenaria on newer dunes, has also invaded the dunes. There are, however, several relatively Ammophila-free beaches such as those at Clo-oose Bay and Pachena Bay.

Protection/ownership

The most recent population of Abronia umbellata at Clo-oose Bay occurred in Pacific Rim National Park Reserve. This site is protected under the Canada National Parks Act. The ownership of the other two extirpated sites is not known due to poor locational records.