The potential for a hemiparasitic plant to maintain species diversity during climate change: the role of warming and critical species in a salt marsh on Humboldt Bay, California, USA

Graduation Date

2011

Document Type

Thesis

Program

Other

Program

Thesis (M.A.)--Humboldt State University, Biology: Plant Ecology, 2011

Committee Chair Name

Erik S. Jules

Committee Chair Affiliation

HSU Faculty or Staff

Keywords

California, Point Reye’s Bird’s Beak, Humboldt Bay, Climate change, Hemiparasite, Experimental warming, Salt marsh, Cordylanthus maritimus ssp palustris, Humboldt State University -- Theses -- Biology

Abstract

Salt marsh ecosystems are an extremely important part of estuarine ecosystems around the world. What might happen to these systems if predictions about climate change are realized is largely unknown. I studied the effects of warming on salt marsh plant communities in Humboldt Bay, California, USA, using open top passive warming chambers (OTCs). In addition, I subjected both the ambient and experimentally warmed plant community to the removal of a rare hemiparasitic plant. Cordylanthus maritimus ssp. palustris was previously shown to facilitate coexistence and diversity in California salt marshes by lowering soil salinity levels through an increased transpiration rate. In the event that climate change increases soil salinity through increased evaporation rates, this species could play a key role in maintaining lower salinity levels in the soil. One hundred and twenty 0.5 m2 plots were arranged on a small island in Humboldt Bay. Each plot was randomly assigned to one of four treatments, Ambient, Warmed, Removal and Warmed/Removal, such that each treatment was replicated thirty times. The study lasted from April 2009 to October 2010. OTCs increased surface temperatures by 0.5-0.6 °C, however their effect decreased over time. Warming had little effect on salinity, but it negatively affected plant species richness. Non-metric multidimensional scaling ordination (NMDS) and multiple response permutation procedure (MRPP) revealed a shift in community structure between Unwarmed and Warmed treatments from 2009 to 2010. This shift was characterized by a 40% decrease in annual plant species abundance, most likely caused by increased shading by perennial species in Warmed treatments. The results indicate that warming may significantly increase canopy height and biomass, altering richness and surface temperatures. The rare hemiparasite Cordylanthus was negatively affected by warming. Warmed treatments caused a 97% decrease in biomass and fruit set over a one year period. The Removal treatment significantly increased soil salinity from ambient conditions, but there was no effect of removal on plant community structure over the duration of the experiment. Cordylanthus is currently helping to lower salinity in Humboldt Bay's salt marshes; however if warming increases shade and decreases evaporation in salt marshes, the effects that Cordylanthus has on soil salinity could be lost. A denser community that out competes annual plants could have significant impacts on biodiversity in Humboldt Bay.

https://scholarworks.calstate.edu/concern/theses/qn59q628b

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