Current status of naturalized temperate Asian bamboos in the United States: An on-going survey

Background/Question/Methods

The number of temperate Asian bamboos available in ornamental horticulture in the U.S. has increased linearly in the past 20 years.  Among these commercially available species, running bamboos have attracted concern because of their rapid production of extensive rhizomes and potential for naturalization.  Consequently, many temperate running bamboos have been loosely termed “invasive” in a national early detection and distribution network (EDDMaps.org).  In initiating a systematic survey of the extent and range of bamboo naturalizations (and potential invasions) within the U.S. we investigated reports of large, non-native bamboo infestations as a means to objectively evaluate the ecological status of these new introductions.  We sampled bamboo stands in Connecticut, Hawaii, Maryland, New York, North Carolina, Oregon, Pennsylvania, South Carolina, Virginia, and Washington.  At each locale we measured LAI, incident PAR, and estimated the bamboo stand’s areal extent using ground surveys or aerial photographs.  We sampled and compared genetic diversity within and amongst stands using amplified fragment length proteins (AFLP’s), which were also used to confirm species identification.

Results/Conclusions

Persistent populations of bamboos consist predominately of members of the genus Phyllostachys.  We found infestations of P. aurea and P. nigra in Kauai County, Hawaii that are extensive (e.g. > 5 ha) and could be conservatively classified as invasions, while populations of P. aurea in North Carolina, South Carolina, Virginia and Maryland are much smaller but are nonetheless persistent.  P. aureosulcata is prevalent in frost prone New England (e.g. CT, PA, NY), whereas Sasa palmata and Pseudosasa japonica are more common in OR and WA (but also in PA).  In all locales Phyllostachys frequently inhabits stream edges and riparian areas, whereas Sasa and Pseudosasa occur in forest understories.  We found little, if any, genetic diversity within populations, indicating that bamboo spread has been mainly through vegetative propagation.  Our findings confirm (and expand upon) recent anecdotal reports of bamboo naturalizations in temperate and sub-tropical forests.  Data for all stands sampled here were entered into EDDMaps.org, an open-source database.  Although ornamental bamboos are increasing in species diversity and availability in the U.S., naturalized species are so far restricted to only a few genera.  Clumping taxa (e.g. Fargesia, Thamnocalamus) could be readily substituted in horticulture for aggressive running bamboos.