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Research Poster

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As California is experiencing what is believed to be the worst drought in 500 years, monitoring the change of vegetation is of utmost importance. This spring we observed novel germination of Big Pod Ceanothus seedlings (Ceanothus megacarpus). Germination was novel in that seeds typically require a fire heat cue but in this particular case, germination was likely due to excessive soil temperatures resulting from drought-induced canopy reduction. This is a phenomenon not well known to science as Ceanothus megacarpus seedlings are typically not found between fire events. We believe this results from increased soil temperatures due to greater openings in the canopy after adult die back. With this is mind, we hypothesized that there would be higher quantities of seedlings adjacent to trails more exposed to sunlight than off trails. To test this hypothesis, sixty-seven 1 m2 plots, were established to monitor seedling survival along trails and compare seedling densities to adult stands, assessed by point quarter sampling off trails. We also measured percent shade, leaf area index, volumetric water content, and soil water potential. There was no correlation found between any of these measurements and seedling survival. However survival was correlated with maximum rooting depth of seedlings. Dead seedlings had < 20 cm rooting depths whereas surviving seedlings had > 20 cm. This corresponded to mean soil water potentials of -7 MPa which is less negative than critical levels of hydraulic dysfunction in C. megacarpus seedlings, -11 MPa. We conclude that severe drought, fostered canopy cover, increasing soil temperatures that promoted novel seed germination. We speculate that novel seed germination will either compensate for drought-induced mortality of adults by enhanced recruitment of seedlings or deplete the soil seed bank through seedling establishment failure.

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