An Inventory and Comparative Study of Bees, A Keystone Ecological Group in the Endangered Coastal Prairie of Louisiana

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Much of Louisiana's coastal prairie has been converted to rice and sugarcane cultivation. USGS is inventorying bee populations in these areas to explore how effective restoration efforts have been.

 

Louisiana’s coastal prairie grassland types

Louisiana’s coastal prairie grassland types

Science Issue and Relevance: The coastal prairie of Louisiana is near extirpation and much of the original 1 million ha that once covered the southwestern part of the state has been converted to rice and sugarcane cultivation. Removal of native grazers, disruption of hydrology, alteration of historical fire regimes, and agricultural/urban development has drastically changed the landscape. Approximately 3,500 ha of this rare ecosystem remain in the state. While a few ungrazed patches occur on railroad right-of-ways, most occur on private ranches where it has been heavily grazed. Several attempts to restore this rare grassland have met with varying results. Efforts to determine restoration success and remnant quality have primarily employed vegetation metrics, hydrology, nutrient cycling in the soil, and recruitment of grassland animals such as birds and insects. Of these measures, insects have been the least utilized, despite the fact that they are excellent ecological indicators. High species richness, large numbers of individuals, short generation times, and a high number of functional guilds make insect populations very sensitive to environmental change. Among insect groups, pollinators have recently received significant attention. Of the insects providing this keystone ecosystem service, bees are the principal pollinators of both wild and cultivated plants.  Native bees have never been studied in south Louisiana.

Bee pollinating a flowering coastal prairie plant

Bee pollinating a flowering coastal prairie plant

Methodology for Addressing the Issue: This project explores the bee fauna of Louisiana’s coastal prairie in four grassland types with varying levels of disturbance: ungrazed remnant prairie, grazed remnant prairie, restored prairie, and old fields. Bees are collected monthly by passive trapping and hand netting. Plant community factors such as species richness, alpha diversity, average height and the abundance of floral resources are also documented at each site. An important product of this research is the creation of a list of native and non-native bees occurring in southwest Louisiana that can serve as baseline data for future monitoring efforts and the detection of long-term changes. Additionally, factors that influence bee habitat quality and provide refugia for bee diversity will be explored. Development of best management practices for pollinator habitat requires an understanding of the effects of grazing, mowing, harrowing, prescribed burning, the use of pesticides, etc. Management also affects the abundance and diversity of flowering forbs and available nesting sites, both critical for pollinator use. Effects of spatial landscape features such as habitat patch size, distance between patches, existence of corridors, and distance from agricultural fields can be used to create decision support models designed to determine conservation priorities. Finally, determining recruitment of bee species to restored habitat will provide a valuable assessment of past restoration efforts.

Future Steps: Restoration efforts by multiple partners will use this sampling methodology to identify candidate restoration sites and to monitor habitat health over time at both restorations and remnants. Best plants for creating pollinator habitat will be identified for plant material efforts.