Community analysis of redbay (Persea borbonia) and swampbay (P. palustris) ecosystems

Background/Question/Methods

Redbay and swampbay are evergreen broadleaf tree species in the Lauraceae native to the southeastern United States. Their taxonomic status has been debated with some authors placing both species in one largely defined “redbay”. Since 2003 extensive mortality has occurred in both species due to Laurel Wilt Disease (LWD), a fungal infection spread by a non-native ambrosia beetle.  Little has been published on the ecology of these species, and with their recent mortality and uncertain future due to LWD, it is important to document the characteristics of their communities. Our objectives were to (1) determine if redbay and swampbay are associated with different communities, (2) identify distinct communities where these species occur, and (3) determine if any communities have higher importance of redbay/swampbay and are therefore at higher risk.  We analyzed data collected by the Carolina Vegetation Survey between 1998 and 2012 to describe stand characteristics of redbay and swampbay communities in the Carolinas. To test for differences in bay communities, we ran a Multi-Response Permutation Procedure. We used cluster analyses, species indicator analyses, and ordination to group 452 plots into distinct communities. We then tested for differences in importance among communities using the Kruskal-Wallis test.

Results/Conclusions

Redbay and swampbay communities were significantly different in species composition. Redbay was almost exclusively limited to maritime coastal forests, whereas swampbay had a larger geographical range. We identified seven unique vegetation groups: (1) maritime forest; (2) deciduous hardwood forest; (3) baldcypress/water tupelo swamp; (4) mixed hardwood swamp; (5) longleaf pine woodland; (6) sweetbay/loblolly bay/pond pine forest; and (7) pond cypress/holly depression. Redbay/swampbay had the highest importance and basal area in the mixed hardwood swamp group, while they had the lowest importance/basal area in longleaf pine woodlands. Due to its limited geographical range, redbay has a higher risk of being extirpated by LWD than swampbay.