Removing exotic annual grasses from coastal dunes: effects on native solitary ground-nesting bees

Graduation Date

2010

Document Type

Thesis

Program

Other

Program

Thesis (M.S.)--Humboldt State University, Biology, 2010

Committee Chair Name

Michael Mesler

Committee Chair Affiliation

HSU Faculty or Staff

Keywords

Solitary bees, Vulpia bromoides, Humboldt State University -- Theses -- Biology, Restoration, Propane torch, Coastal dunes, Megachile wheeleri, Pacific Ocean--Humboldt Bay, Aira, Invasive species, Radiant heater

Abstract

A great effort has been made in the last few decades to restore and preserve coastal dunes in northwest California. The restoration effort has largely focused on removal of invasive plants, with little study on how invasive plant removal affects native pollinators. I studied how exotic annual grass removal at Lanphere Dunes affected the native ground-nesting leafcutter bee (Megachile wheeleri). I compared two thermal removal methods for eliminating exotic annual grasses: treatment with a radiant heater and treatment with a propane torch. Heat penetration into the soil was low under both treatment methods, and there was no difference in adult emergence of leafcutter bees among treatment types. When remaining nest cells containing dead bees were examined to assign a cause of death, there was no evidence that mortality was due to heat treatment. It remains unclear whether exotic annual grass removal has an effect on quality or abundance of leafcutter bee nesting habitat over the long term. Areas treated with the propane torch for 2 consecutive seasons showed significant reduction in exotic annual grass cover, but not biotic soil crust cover, which is possibly correlated with leafcutter bee nesting success because it affects soil texture and structure. No significant relationship, however, could be established for the density of leafcutter bee nests and the percent cover of exotic annual grasses or biotic soil crust. While it was unclear whether thermal treatment of exotic annual grasses reduced or increased nesting habitat over the long-term, it was clear that the most efficient and effective method of exotic annual grass removal, the propane torch, caused no immediate increase in mortality of leafcutter bees, one of the dunes' most important pollinators.

https://scholarworks.calstate.edu/concern/theses/zw12z785q

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