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Abronia umbellata ssp. breviflora |
Pink sand verbena (
Abronia
umbellata ssp.
breviflora) is a short-lived perennial in the Nyctaginaceae
family that is native to the Pacific Coast.
Individuals of this species only reproduce by seed and many individuals
act as annuals, flowering and dying in their first year of growth.
Given their placement on dynamic dune
systems, most populations are obliterated during winter storm events but seeds
persist and are able to reestablish in the following years.
This pattern leads to highly variable
populations (in both size and distribution) from year to year, but shows that a long-lived,
persistent seed bank is possible and necessary for survival.
Historically found in widespread populations between
British Columbia, Canada and Northern California, the species is now sparsely
distributed throughout the range.
Pink
sand verbena was thought to be extinct in the northern part of its range
until 2 plants were found on Vancouver Island in 2000 and another two plants
were found in Washington in 2006.
Existing
populations are geographically isolated to the extent that there is little
possibility of genetic exchange.
The
greatest threat to the verbena habitat is competition with invasive European
beachgrass (
Ammophila arenaria),
which has become widespread throughout pink sand verbena’s range and easily outcompetes
native forbs.
The beach grass was
introduced to the U.S. coast in the early 1900s and, once established, began
stabilizing foredunes and disrupting the dynamic, hummocky dune habitat that pink
sand verbena thrives in.
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Staff collected sand for substrate analysis |
Research has been conducted since the mid-1990s about
methods for reintroduction.
In extensive
seeding experiments, over 3.8 million seeds have been distributed across more than 23 Oregon
Coast sites.
The sites that had the most
successful plant establishment rates were ones where the beach grass
populations had been disturbed by bulldozing the top layer of sand and
vegetation off the dune.
Following
reintroduction in 1997, population numbers were steadily increasing until
2010.
Population surveys by IAE began in 2000
and have extended across lands owned by the US Forest Service, the Bureau of
Land Management, the State of Oregon, and private land owners.
In
2012, monitoring occurred at nine populations near Bandon, Coos Bay,
and Florence. Researchers found that the number of plants at several
sites had increased since the previous year.
Oregon's
largest population of pink sand verbena occurs on the Coos Bay North
Spit and is entirely a product of seeding efforts. Seed was collected
from a population in Port Orford in the mid-1990s and was spread across
an area identified as ideal sand verbena habitat in 1997. Seeding at
the site resulted in a population of over 185,000 plants in 2011. In
addition, a trip was taken to Floras
Lake and the survey crew discovered 67 plants (8 reproductive) at the
site,
which hasn’t had plants documented since 2006.
This site was last seeded in 2000, so the current population could
indicate a small, but long-lived seed bank.
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A mat of pink sand verbena sprawls across the dune on the Coos Bay North
Spit. Now the largest population in Oregon, this is entirely a result
of seeding by IAE and its partners. |
The pink sand verbena produces flowers June through
September, but the surveying and monitoring window is limited due to protection
of the western snowy plover’s nesting habitat.
The western snowy plover is a small shorebird that has been listed as
threatened at the federal level.
It is
native to the beaches of the Pacific Coast, but has experienced a drastic
decline in numbers over the past several decades, primarily due to habitat
degradation and destruction.
The state
of Oregon recognized the decline and has included the plover on the state threatened
species list since 1975.
The Pacific Coast population of snowy plovers
inhabits the same area in which pink sand verbena is found, and their
population decline has coincided with the decline of the verbena and several
other native beach species.
According to
the
Western Snowy Plover Recovery Plan
there used to be 20 nesting sites along
the Oregon Coast, but that number has dwindled to just seven areas that are consistently
used.
One of the steps taken to work
towards delisting the species is restricting access to known breeding areas during
the nesting season, typically between March and late September.
Ideal nesting sites such as dune-backed
beaches, sand spits, and sparsely vegetated dunes with active sand movement
coincide with ideal habitat for pink sand verbena populations.
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Western snowy plover and chick. Photo source: www.duneguide.com |
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