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2014

Seedling Survival after Novel Drought-Induced Germination in Ceanothus megacarpus

Amanda M. Burns Pepperdine University

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Recommended Citation Burns, Amanda M., "Seedling Survival after Novel Drought-Induced Germination in Ceanothus megacarpus" (2014). Pepperdine University, Featured Research. Paper 139. https://digitalcommons.pepperdine.edu/sturesearch/139

This Research Poster is brought to you for free and open access by the Undergraduate Student Research at Pepperdine Digital Commons. It has been accepted for inclusion in Featured Research by an authorized administrator of Pepperdine Digital Commons. For more information, please contact [email protected], [email protected], [email protected]. Seedling Survival aer Novel Drought-Induced Germinaon in Ceanothus megacarpus Amanda M. Burns Mentor: Stephen D. Davis Pepperdine University, 24255 Pacific Coast Highway, Malibu, CA 90263

Abstract Materials & Methods Study Sites

As California is experiencing what is believed to be the worst drought in 500 years, monitoring the change of vegetaon is of utmost importance. This spring we observed novel germinaon of Big Pod Ceanothus seedlings (Ceanothus megacarpus). Germinaon was novel in that seeds typically require a fire heat cue but in this parcular case, germinaon was likely due to excessive soil temperatures resulng from drought-induced canopy reducon. This is a phenomenon not well known to science as Ceanothus megacarpus seedlings 2 are typically not found between fire events. We believe this results from Fig. 1: We established sixty-seven Fig. 2: Percent shade for each 1 m quadrat Fig. 3: Volumetric water content was Fig. 4: Soil water potenal at 10 cm and 20 cm depth were 2 increased soil temperatures due to greater openings in the canopy aer adult permanent 1 m quadrats to monitor and point-quarter sampling site was esmated esmated at 12 cm and 20 cm depth using measured using a Dew Point Potenometer (Decagon WPC4) die back. With this is mind, we hypothesized that there would be higher seedling mortality using a sun fleck ceptometer (Decagon LP-80) a Time Domain Reflectometer, (TDR) quanes of seedlings adjacent to trails more exposed to sunlight than off trails. To test this hypothesis, sixty-seven 1 m2 plots, were established to Backbone Trail: Four study sites monitor seedling survival along trails and compare seedling densies to adult were selected on the Backbone stands, assessed by point quarter sampling off trails. We also measured Trail off Piuma Road near Tapia percent shade, leaf area index, volumetric water content, and soil water Park, CA. potenal. There was no correlaon found between any of these measurements Fig. 5: Ceanothus megacarpus seeds were 2 and seedling survival. However survival was correlated with maximum roong incubated at room temperature (control), Fig. 6: Max soil temperature of 1 m Fig. 7: Plant community structure >3m depth of seedlings. Dead seedlings had < 20 cm roong depths whereas 70 C for 120 min, and 120 C for 5 min. plot was determined using an from trails was quanfied using a point- surviving seedlings had > 20 cm. This corresponded to mean soil water Seed diameter was measured with a infrared thermometer. Max quarter sampling method. Both Fig. 8: Dead (n=6) and alive (n=6) C. Discussion & Conclusions temperature exceeded 70 C chaparral seedlings and adults were megacarpus seedlings were excavated by potenals of -7 MPa which is less negave than crical levels of hydraulic vernier caliper and scored as germinated matching lab incubaon treatments included in the assessment. hand to determine maximum root length. dysfuncon in C. megacarpus seedlings, -11 MPa. We conclude that severe if sufficient swelling occurred By May 2014 we observed 576 Ceanothus megacarpus seedlings adjacent to drought, fostered canopy cover, increasing soil temperatures that promoted Backbone Trail, near Tapia Park. We assume novel germinaon was caused by novel seed germinaon. We speculate that novel seed germinaon will either excessive soil germinaon verified by measured soil temperatures > 70 C and compensate for drought-induced mortality of adults by enhanced recruitment Results seed germinaon trials at 70 C. By the end of July seedling survival varied of seedlings or deplete the soil seed bank through seedling establishment between 35% and 60% amongst our four study sites. Seedling survival was not failure. associated with percent shade at each study site. Volumetric water content integrated over 20 cm depth nor soil water potenal at 20 cm were correlated Fig. 9: Percent seedling survival Fig. 13: Percent seed b b S1 100 P < 0.0001 with seedling survival. However, seedling survival was associated with roong was recorded every two weeks 100 germinaon as indicated by S2 depth in that seedlings with a root depth > 20 cm were alive whereas seedlings using sixty-seven 1 m2 permanent S3 swelling aer water S4 quadrats. Survival was higher for applicaon with treatments of 80 with roots < 20 cm in depth were recently dead (Figs. 1, 8, 17). This showed sites 3 and 4 than sites 1 and 2 80 25 C (control), 70 C for 120 remarkable correspondence to water potenal at 20 cm depth and references during June and July determine min, and 120 C for 5 min. 60 in the literature (Fig. 12). That is, water potenal at 20 cm were less negave by one-way ANOVA followed by a Significant difference was than -10 MPa at all study sites. According to the literature, Ceanothus 60 Introducon Fisher’s LSD at P < 0.05. Error determined using one way 40 megacarpus seedlings do not achieve catastrophic xylem dysfuncon (water bars represent + 1 SE, n = 4-28 ANOVA followed by Fisher’s a potenal at 90% hydraulic failure) unl -11 MPa (Pra et al. 2008). LSD at P < 0.05. n = 60 The five Mediterranean-type climate regions of the world occupy less than 5% 40 20 Furthermore, overall seedling survival rates of Ceanothus megacarpus of of the earth’s landmass yet harbor nearly 20% of all known species of vascular 35-60% is much lower than that reported in the literature where survival rates plants (Rundel and Tiszler 2007). Chaparral is the most extensive 0 exceed 80% by July aer winter germinaon (Thomas and Davis, 1989; Frazer Mediterranean-type vegetaon in California and has evolved in response to 20 25 C 70 C 120 C and Davis, 1988). protracted summer drought, Santa Ana winds, and periodic wildfires. Emerging 80 issues of climate change that intensify drought and fire are most pronounced in Fig 14: Measured soil 0 We conclude: temperatures at site 1-4 70 regions of chaparral than any other type of wildland in California. 120 • Seedling germinaon is induced by soil temperature of 70 C or higher. May June July indicate that treatment Species of chaparral shrubs classified as non-sprouters aer fire typically 60 temperature of 70 C were require a heat cue from fire to promote seed germinaon. Heat is necessary to • 100 50 Increased soil temperature in 2014 is presumably caused by canopy break through the extremely thick coat of the seed, allowing water to enter and Fig 10: Percent shade was not sufficient to crack seeds and P > 0.1 promote germinaon. reducon due to drought-induced adult mortality and leaf drop (data not promote embryo development during winter rain events. Over the last two significantly different among 40 sites 1 through 4 by one way shown). years, however, the Santa Monica Mountains have experienced one of the 80 ANOVA followed by Fisher’s LSD 30 worst droughts in recorded history. With such dry condions and high • Seedling density is highest adjacent trails where canopy breaks are common. at P < 0.05 20 temperatures, three species within the family Rhamnacea, Ceanothus 60 megacarpus and Ceanothus oliganthus, and Ceanothus spinosus have 10 • Root depth is likely the primary determinate of seedling survival. germinated prematurely without the occurrence of a fire-cue. Presumably, 40 0 severe drought has opened canopy-gaps, increasing solar radiaon reaching soil 1 2 3 4 • Survival rates of novel drought-induced germinaon are lower than surfaces, enhancing temperature, that simulates fire-promoted seed Germination Sites reported for post-fire seedlings. germinaon. 20 14 a) Due to delayed germinaon There are two subgenera of Ceanothus: Cerastes and Euceanothus. Ceanothus Fig. 15: Our point-quarter sampling of 55 observaons b) Due to persistent shade 0 megacarpus is in the Cerastes subgenus, which exclusively contains non- across sites 1-4 encountered 12 sproung species. Seedlings of non-sproung species within the Rhamnaceae only 24 seedlings, with none • We speculate that novel seed germinaon will either: 10 have been shown to be both water stress resistant (Thomas and Davis 1989, occurring in high shade, and a) compensate for drought-induced mortality by enhanced Saruwatari and Davis 1989, Frazer and Davis 1988) and drought resistant, but Fig. 11: Soil volumetric water 20 balanced occurrence in low 8 recruitment of seedlings shade intolerant, whereas sproung species are opposite (Pra et al. 2008). content varied among our four P < 0.0001 and medium shade b) deplete the seed bank by seed germinaon that study sites as indicated by one 6 Taken together, we hypothesized that Ceanothus megacarpus seedlings that a ulmately fails to establish seedlings have germinated prematurely in 2014 will have lower survival rates than way ANOVA followed by Fisher’s 15 4 previously observed in post-fire studies. This is because late rainfall promoted LSD at P < 0.05. germinaon just prior to the onset of summer drought and paral shade of b 2 adults enhance seedling mortality (Pra et al. 2008). 0 Literature Cited 10 bc Low Med High c Frazer, J.M. and S.D. Davis. 1988. Differenal survival of chaparral seedlings Levels of Shade during the first summer drought aer wildfire. Oecologia 76:215-221. Pra, R.B., A.L. Jacobsen, R. Mohla, F.W. Ewers, S.D. Davis. 2008. Linkage 10 Fig. 16: The number of between water stress tolerance and life history type in seedlings of nine 5 P < 0.0001 chaparral species (Rhamnacea). Journal Ecology 96:1252-1265. seedlings per unit area was 8 Rundel, P.W., and J. Tiszler. 2007. The Santa Monica Mountains in a global significantly higher on trails context. In Flora and Ecology of the Santa Monica Mountains. Edited by than off trail. Unpaired D.A. Knapp, Southern California Botanists, Fullerton, CA. Pages 7-27. 6 Hypotheses Student’s t-test (n = 55-67) Saruwatari, M.W. and S.D. Davis. 1989. Tissue water relaons of three 0 chaparral shrub species aer wildfire. Oecologia 80:303-308. 4 Thomas, C.M. and S.D. Davis. 1989. Recovery paerns of three chaparral shrub H1: Germinaon of Ceanothus megacarpus species aer wildfire. Oecologia 80:309-320.

without fire-cue is due to reduced shade and Fig 12: Soil water potenal -15 2 at 20 cm depth was not P > 0.5 elevated soil temperatures significantly different 0 across our four study sites On Trail Off Trail Acknowledgments Ψ as indicated by one way 90 35 ANOVA followed by -10 Fig. 17: Root lengths were This research was funded by the Naonal Science Foundaon, Research H2: Seedling density will be significantly higher significantly longer for P < 0.001 Experience for Undergraduates, REU-Site Grant, #DBI-1062721 and the Natural Fisher’s LSD at P < 0.05 30 adjacent trails versus off trails excavated seedlings that were Science Division of Pepperdine University. A very special thanks to Dr. Stephen alive versus those that were 25 Davis, Helen Holmlund, and Victoria Lekson for their generous amount of help. recently dead. Unpaired Student’s t-test (n = 6) 20 H3: Survival rates of Ceanothus megacarpus -5 15 seedlings aer novel germinaon will be low * 10 compared to survival rates reported for post- 5 0 fire seedlings (e.g. Thomas & Davis 1989) 0 1 2 3 4 Alive Dead Germination Sites Seedlings