A floristic quality assessment and Berberis thunbergii invasion in the Little Traverse Conservancy's Offield Family Nature Preserve, Emmet Co., Michigan.

Abstract

Proper land management is dependent on understanding the composition of plant communities. Floristic Quality Assessment (FQA) is a useful method that places a numeric value, or Floristic Quality Index (FQI), on vegetation in a given area. We conducted a FQA of two adjacent mesic, hardwood forest tracts at the Little Traverse Conservancy’s Offield Family Nature Preserve in Emmet County, Michigan. We compared species richness, floristic quality indices, and tree species dominance of both tracts in order to evaluate the difference in plant community composition between the two forest tracts. We recorded 86 total species in the forest (83% native, 17% non-native). Plant species richness, the total number of different plant species present in a given area, was not significantly different between the East and West forest tracts (p=0.42). However, the FQI was significantly different between the two tracts (p=0.01). This pattern is due to different species composition between the two sites, including high quality Platanthera orbiculata (Round leafed orchid) and non-native Berberis thunbergii (Japanese barberry) in the East that were absent in the West. The mean diameter at breast height (dbh) of the dominant overstory species Acer saccharum was significantly greater in the West than the East. These differences could be indicative of different age of stands, disturbance history, or productivity. We also examined a nascent invasion of B. thunbergii in our East tract sampling plots in order to provide the Little Traverse Conservancy with baseline data for understanding B. thunbergii population dynamics at OFNP. Berberis thunbergii was distributed throughout the East forest tract, with a large concentration southwest of our sampling plots. We recommend that B. thunbergii be pulled by hand as opposed to herbicide or fire control options to minimize negative ecological impact of removal, and to prevent the spread of this noxious invader.