Using herbaria records to examine the spread of the invasive woody plant Frangula alnus

Background/Question/Methods

Invasive non-native species have negative effects on biodiversity and human health, and create serious problems for natural resource management.  The seriousness of these threats has led to substantial research on their ecology and evolution, yet the processes that govern invasion are still not fully understood.  Analysis of herbaria records can be an important tool to study these processes, allowing for an examination of patterns of the spread of invasive plants.  I collected herbaria records to investigate the rate of spread and pattern of establishment for the invasive shrub Frangula alnus (Glossy Buckthorn) in space and in time.  F. alnus is a perennial woody species of concern to land managers throughout northeast North America.  Accession records were collected from online databases of herbaria throughout North America and from direct requests to herbaria curators, resulting in ~600 records of F. alnus covering a temporal range from ca. 1880-Present and a spatial range broadly covering the entire invaded range in northeast North America.  I addressed unequal sampling effort by comparing temporal and spatial patterns F. alnus accessions to a randomized null model created using F. alnus accession records and to the patterns of common native plants with similar ecological characteristics.

Results/Conclusions

The results suggest novel hypotheses regarding the initial introduction of F. alnus into northeast North America.  Previously it has been reported that F. alnus was likely first introduced in southern Ontario (near London), however my examination finds that initial introductions appear to have been greatly separated geographically, ranging from southern Ontario to coastal New York and New Jersey.  Such large spatial separations may be the result of multiple introductions by humans, a hypothesis that will be addressed in future research.  Additionally, the results indicate that the rate of spread of Glossy Buckthorn was initially very small, then increased rapidly during the early stages of its invasion, and leveled off to a relatively constant rate more recently.  These results are placed in context of an examination of the reported lag-time between the introduction of F. alnus and its rapid spread throughout its current range.  In future research, these rates of spread will be incorporated into a demographic model of F. alnus to inform rates of dispersal.