A novel hybrid beachgrass is invading U.S. Pacific Northwest dunes with potential ecosystem consequences

Invasive plants formed via hybridization, especially those that modify the
structure and function of their ecosystems, are of particular concern
given the potential for hybrid vigor. In the U.S. Pacific Northwest, two
invasive, dune-building beachgrasses, Ammophila arenaria (European
beachgrass) and A. breviligulata (American beachgrass) have hybridized and
formed a new beachgrass taxa (Ammophila arenaria × A. breviligulata) but
little is known about its distribution, spread, and ecological
consequences. Here we report on surveys of the hybrid beachgrass conducted
across a 250-km range from Moclips, Washington to Pacific City, Oregon in
2021 and 2022. We detected nearly 300 hybrid individuals, or an average of
8–14 hybrid individuals per km of surveyed foredune. The hybrid was more
common at sites within southern Washington and northern Oregon where A.
breviligulata is abundant (75–90% cover) and A. arenaria is sparse and
patchy. The hybrid displayed morphological traits such as shoot density
and height that typically exceeded its parent species suggesting hybrid
vigor. We measured an average growth rate of 30% over one year, with
individuals growing faster at the leading edge of the foredune, nearest
the beach. We also found a positive relationship between hybrid abundance
and that of A. arenaria, suggesting that A. arenaria density may be a
controlling factor for hybridization rate. The hybrid showed similar sand
deposition and associated plant species richness patterns compared to its
parent species, although longer-term studies are needed. Finally, we found
hybrid individuals within and near conservation habitat of two Endangered
Species Act-listed, threatened bird species, the western snowy plover
(Charadrius alexandrinus nivosus) and the streaked horned lark (Eremophila
alpestris strigata), a concern for conservation management. Documenting
this emerging hybrid beachgrass provides insights into how hybridization
affects the spread of novel species and the consequences for communities
in which they invade.

通过杂交形成的入侵植物，尤其是能够改变所在生态系统结构与功能的类群，因具备杂交优势（hybrid vigor）的潜力而备受关注。在美国太平洋西北地区，两种具有入侵性的筑沙丘海滩草——欧洲沙草（Ammophila arenaria，European beachgrass）与美洲沙草（Ammophila breviligulata，American beachgrass）已发生杂交，形成了新的海滩草类群（Ammophila arenaria × A. breviligulata），但目前对该杂交类群的分布、扩散及其生态影响尚不清楚。本研究针对该杂交海滩草开展了野外调查，调查范围覆盖从华盛顿州莫克利普斯（Moclips）到俄勒冈州太平洋城（Pacific City）的250公里区域，调查时间为2021年与2022年。本次调查共检出近300株杂交个体，相当于在所调查的海岸前沙丘每公里范围内平均有8~14株杂交个体。该杂交类群在华盛顿州南部与俄勒冈州北部的样点中更为常见，这些区域内美洲沙草的盖度可达75%~90%，分布广泛，而欧洲沙草则较为稀疏且呈斑块状分布。该杂交类群表现出优于亲本的形态性状，如枝条密度与株高，提示其存在杂种优势。本研究测得该杂交类群在一年内的平均生长速率达30%，且生长在靠近海滩的海岸前沙丘前沿的个体生长速度更快。此外，研究发现杂交类群的丰度与欧洲沙草的种群密度呈正相关关系，这表明欧洲沙草的种群密度可能是调控杂交发生率的关键因素。尽管仍需开展长期研究，但该杂交类群的沙沉积效应与伴生植物物种丰富度格局与亲本物种较为相似。最后，研究团队在两种被列入《濒危物种法案》的受胁鸟类——西方雪鸻（Charadrius alexandrinus nivosus，western snowy plover）与条纹角百灵（Eremophila alpestris strigata，streaked horned lark）的保护栖息地内及周边发现了该杂交海滩草个体，这对保护管理工作构成了潜在威胁。本研究对这一新兴杂交海滩草类群的记录，有助于深入理解杂交如何推动新物种的扩散，以及其对入侵群落所产生的生态后果。