Quantifying Microstegium vimineum Seed Movement by Non-Riparian Water Dispersal Using an Ultraviolet-Marking Based Recapture Method

Daniel R Tekiela,Jacob N Barney,Mark Van Kleunen

doi:10.1371/journal.pone.0063811

Abstract

Microstegium vimineum is a shade tolerant annual C4 invasive grass in the Eastern US, which has been shown to negatively impact species diversity and succession in hardwood forests. To date, empirical studies have shown that population expansion is limited to <1 m yr−1, which is largely driven by gravity dispersal. However, this likely does not fully account for all mechanisms of population-scale dispersal as we observe greater rates of population expansion. Though water, both riparian and non-riparian water (i.e., ephemeral overland flow), have been speculated mechanisms for M. vimineum dispersal, few studies have empirically tested this hypothesis. We designed an experiment along the slopes of a Southwest Virginia hardwood forest to test the role of non-riparian water on local seed dispersal. We developed a seed marking technique by coating each seed with an ultraviolet (UV) powder that did not affect buoyancy to aid in situ seed recapture. Additionally, a new image analysis protocol was developed to automate seed identification from UV photos. Total seed mobility (summation of individual seed movement within each transect) was positively correlated with precipitation. Over a period of one month with 52.32 mm of precipitation, the maximum dispersal distance of any single recaptured seed was 2.4 m, and the average distance of dispersed seed was 0.21±0.04 m. This is the first quantitative evidence of non-riparian water dispersal in a forest understory, which accounts for an additional pathway of population expansion.

Highlights

Because the sessile nature of the plant kingdom, the dispersal of viable propagules is crucial in determining the spatial distribution, demographics, and spread of most plant species [1]
Non-riparian water dispersal has previously been suggested in the literature to partially account for M. vimineum local population expansion, but has never been empirically tested
We demonstrated that non-riparian water dispersal does move M. vimineum seed in a hardwood forest understory, and likely contributes to local population expansion

Summary

Introduction

Because the sessile nature of the plant kingdom, the dispersal of viable propagules is crucial in determining the spatial distribution, demographics, and spread of most plant species [1]. In the context of invasive species, spatial spread is a defining character: invasiveness is ‘‘produc[ing] reproductive offspring in areas distant from sites of introduction (approximate scales: .100 m over ,50 years for taxa spreading by seeds and other propagules; .6 m/3 years for taxa spreading by roots, rhizomes, stolons or creeping stems)’’ [2] Though this definition is related to long distance dispersal, it shows how critical effective dispersal is to the success of invasive species. Population expansion is the result of numerous local dispersal events that are important to characterize to understand demographic rates, as well as design effective management strategies [3]. Our aim was to explore one poorly understood mechanism of population expansion in Microstegium vimineum, one of the worst invasive species of the Eastern United States

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