Oregon State University research shows two invasive beach grasses hybridize
CORVALLIS, Ore. – Two sand-stabilizing beach grass species introduced to the Pacific Northwest from the early 1900s hybridize, raising new questions about the impacts on coastal ecosystems that non-native plants are developing for over a century.
Researchers at the Oregon State University College of Science have identified the hybrid in a paper published in Ecosphere.
Besides their ecological implications, the findings are important in the context of coastal vulnerability to the effects of climate change, including the increasing danger of flooding and erosion from storms and rising sea levels.
An OSU collaboration led by a doctorate in integrative biology. Candidate Rebecca Mostow and Professor Sally Hacker used several analytical techniques to show that the beach grasses that dominate the Northwestern dunes, Ammophila arenaria and A. breviligulata, hybridized.
A. arenaria is a European species and A. breviligulata an American species. Scientists say the hybrid’s traits lie between its parent species in many ways, but the hybrid is taller, which is especially important because the height of the shoots is an indicator of the potential for dune building.
“Understanding the genetic, ecological and demographic consequences of hybridization is essential in a system where any change in dominant grass species can have significant effects on both biodiversity management and coastal protection,” said Hacker .
Dunes make up nearly half of the combined Oregon and Washington coastline and a quarter of California. From the early 1920se century, the intentional planting of Ammophila beach grasses has been used as a tool to stabilize an otherwise changing sandy environment.
Grasses grow in stiff, sturdy clumps capable of reaching 4 feet tall. Their strong rhizome mat – the mass of underground stems – helps stabilize the sand and allows for rapid colonization. These tufts are capable of capturing sand and building dunes at rates of up to 3 feet per year.
“By the 1950s, Ammophila arenaria had spread from Mexico to Canada while building high and continuous foreshore,” Mostow said. “Halfway through this spread, in the 1930s, Ammophila breviligulata was planted in the dunes near the Columbia River. Over the next 50 years, it moved north and dominated Washington’s sandy coast. And there is no doubt that the spread of these beach grasses has had a positive impact on development by stabilizing the soil and building dunes that protect the coastline.
However, as with many introduced species, beach grasses have ecological costs for native flora and fauna. Resistant to pests and grazing, the hardy, densely growing plants have changed the dune ecology by displacing native plants and animals, including endangered pink sand-verbena and western snow plover.
OSU researchers claim that the hybrid of A. Arenaria and A. Breviligulata was found at a total of 12 sites in Washington and Oregon. The morphology of the plants – what they look like and how they are put together – is consistent with hybridization, and genotyping and genome size comparisons show that the hybrid is a first generation blend of the two introduced beach grasses which ranges overlap.
“The new hybrid areas are an ecologically important result of species introductions and invasions,” Mostow said. “Hybridization between different species can result in gene flow between parent species or produce new taxa that can alter invasion dynamics or ecosystem services. To our knowledge, the Pacific Northwest is the only place in the world where the two Ammophila species have had the opportunity to hybridize. “
A. breviligulata, Hacker notes, is better than A. arenaria at establishing its place in an ecosystem – it is more competitive – but A. arenaria builds higher dunes. Strengths and weaknesses arise from differences in density, morphology and growth form of grass and their effects on sand uptake.
“If the hybrid exceeds its parents in traits associated with dune building, which it most likely could, then its spread could affect the shape and size of the dunes and have huge scale consequences. ‘ecosystem,’ she said. “Hybridization could result in a truly invasive taxon or increase the invasive potential of either parent species.”
Felipe Barreto, assistant professor at OSU College of Science, also collaborated in this research.
The study was supported by Oregon Sea Grant, the National Science Foundation, and the Washington Native Plant Society.