Collaborative Research: RUI:Linking Xylem Functional Traits to Life-History Type in California Chaparral

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The climate of southern California is a Mediterranean-type, characterized by mild winters, protracted summer drought, and periodic wildfire. The dominant vegetation is chaparral, which is uniquely adapted to summer dehydration and fires. There are three strategies by which chaparral survive and persist through periodic fire: non-sprouters after fire, facultative sprouters after fire, and obligate sprouters after fire. We hypothesize that these three strategies are coupled to dehydration tolerance. We will estimate dehydration tolerance by determining the threshold in dehydration that causes the water transport system of plants to fail. This failure is caused by xylem embolism formation under severe water stress, that is, when the plumbing system (xylem conduits) of plants become blocked by air bubbles, cutting off water flow to leaves, leading to shoot death.The primary objective of our research is to elucidate the mechanisms linking xylem functional traits to life history type among diverse species of chaparral shrubs. We hypothesize that there are trade-offs among xylem embolism-resistance, xylem conductivity efficiency and xylem mechanical strength and these depend on the three life history strategies that chaparral species have in response to wildfire.Issues related to recurrent wildfire, water conservation, erosion control, urban expansion and recreation are more pronounced in regions of chaparral than in any other type of wild land in California. Results from the research will be disseminated widely to local agencies responsible for management and conservation of natural resources in the Santa Monica Mountains, and to educational groups including docents for the State Park Service and the National Park Service. The findings will allow generalizations to the broader chaparral community of California and to the other four Mediterranean-type climate regions of the world. Results from the proposed work will refine predictions of expected shifts in chaparral distribution and community structure over the next century in response to an anticipate climate change to a warmer, drier California with increased episodic Santa Ana winds and wildfire.