Mediterranean-type ecosystems are biodiversity hotspots, but increasing temperature and changes in precipitation will have significant impacts on vegetation, as evidenced by the recent die-back of many woody species in southern California, USA, due to exceptional drought conditions. We installed flow-through chambers on three native woody plant species at Stunt Ranch, a University of California Natural Reserve System site in order to continuously measure fluxes of carbon and water at the branch-scale. Study species included Heteromeles arbutifolia, Malosma laurina, and Quercus agrifolia. We monitored fluxes from the growing season, through the annual seasonal drought period, and during extreme weather events including heat waves. Here we present the results of diurnal flux patterns before, during, and after extreme heat wave events.
Results/Conclusions
Under typical summer conditions, which include hot, sunny days, study species exhibited two peaks in carbon assimilation and transpiration during a diurnal cycle: a peak in the morning and a smaller, secondary peak in the afternoon, separated by a midday depression. During heat wave events, which generally lasted 3 days or more, this diurnal pattern changed: the morning peak of carbon assimilation was reduced and there was no afternoon peak. However, transpiration rates increased significantly. All study species returned to their pre-heat wave diurnal flux patterns and rates almost immediately after weather conditions returned to normal. Our results demonstrate that carbon gain of chaparral trees and shrubs is greatly reduced during heat waves, but latent cooling protects photosynthetic machinery from damage during extreme heat events which aids in their quick recovery.