Introduction
Successful seed production in dioecious plants requires that potential mates shed pollen and have receptive stigmata at the same time. Because exposing delicate reproductive organs such as stigmata and anthers to desiccation can be stressful in times of drought, deferring anthesis until conditions are better could be adaptive (1-3). Garrya elliptica (Coast Silk Tassel) is a dioecious wind-pollinated shrub to small tree locally common in Maritime Chaparral and Oak Woodland along the coast of California and Oregon (X). No pollinator is needed in the case of G. elliptica, so flowering is not constrained to times when a pollinator is present. Flowering could hypothetically vary according to soil moisture in an individual plant's root zone.
Most Fort Ord soils are Loamy Sands with a plant available water capacity of about one inch per foot of soil profile. Since most plants get most of their water from the upper 18" of soil and some evaporation and runnoff could be expected, I chose two inches of precipitation as the threshold for soil moist enough to trigger normal growth activity in shrubs and trees in the Fort Ord area. In practice, this threshold seems to work (me checking with a shovel and observing new growth in chamise, coffeeberry, manzanita, oak, black sage, and silk tassel). However, this hypothesis will also be tested using buried moisture sensors.
Hypothesis: Flowering in Garrya elliptica is sensitive to soil moisture.
Test: If flowering in Garrya elliptica is sensitive to soil moisture then flowering should begin later in years where significant rains come later.
Q1: When did the soil profile become moist in the Fall each study year?
Based on personal experience, the soil profile at Fort Ord is not moist in the Fall until 2" of rain has accumulated. However, this will be tested over a three year period (Fall 2024 until Spring 2028) in soil of typical Garrya elliptica habitat on the former Fort Ord. Until then, an estimate can be made using rainfall data from the Monterey Airport.
During the Water Year 2022-2023 Fort Ord had accumulated 2 inches of rain by November 9, 2022
During the Water Year 2023-2024 Fort Ord had accumulated 2 inches of rain by December 20, 2023
In the Fall of 2022 Fort Ord soil profile was wet 41 days earlier than in the Fall of 2023.
Q2: How long after the soil profile is wet will Garrya elliptica anthesis begin in the study area each year?
Addressing Q1 Directly Using Buried Moisture Sensors
On October 11, 2024 two Irrometer WATERMARK 200SS sensors (A) were installed at 8" and 24" soil depths approximately two meters from a pair of male Garrya elliptica in a stand of Maritime Chaparral dominated by Adenostoma fasciculatum and two species of Arctostaphylos (A. pumila and A. tomentosa) on the former Fort Ord (see associated observations below). The preparation and installation of the sensors was as recommended by Irrometer () except that the sensors were positioned horizontally, in order to more correctly measure moisture at the two precise depths, instead of vertically as illustrated in the specifications sheet.
*Garrya elliptica* iNat Observations in Study Area
Fort Ord Garrya elliptica https://www.inaturalist.org/observations?place_id=163575&taxon_id=53399
Fort Ord known females https://www.inaturalist.org/observations?place_id=163575&taxon_id=53399&term_id=9&term_value_id=10
Fort Ord known males https://www.inaturalist.org/observations?place_id=163575&taxon_id=53399&term_id=9&term_value_id=11
iNaturalist observations of the same *Garrya elliptica* over time: (incomplete. Will continue as spreadsheet)
@asauble Jan 3, 2023 Male Fully flowering https://www.inaturalist.org/observations/145778755
@fredwatson Jan 8, 2023 Male Fully flowering https://www.inaturalist.org/observations/146171533
@hkibak Jan 13, 2024 Male Incipient flowering https://www.inaturalist.org/observations/196636265
@fredwatson Jan 9, 2023 Male Fully flowering https://www.inaturalist.org/observations/146243108
@hkibak Jan 12, 2024 Male (presumed) Budding https://www.inaturalist.org/observations/196477795
@hkibak Apr 11, 2020 Male fully flowering https://www.inaturalist.org/observations/41975327
@hkibak Jan 13, 2024 Male flower budding https://www.inaturalist.org/observations/196789187
@yerbasanta Feb 18, 2023 flowering https://www.inaturalist.org/observations/149279041
@hkibak Jan 16, 2024 female flowering https://www.inaturalist.org/observations/196996047
References (#) and Footnotes:
(A) https://www.irrometer.com/pdf/403.pdf
(B) https://www.inaturalist.org/journal/hkibak/86783-fort-ord-national-monument-precipitation-water-year-2024
(X) Freeman, D. C., McArthur, E. D., & Harper, K. T. (1984). The Adaptive Significance of Sexual Lability in Plants; Atriplex canescens as a Principal Example. Annals of the Missouri Botanical Garden, 71(1), 265–277. https://doi.org/10.2307/2399070
(X) Kemal Kazan, Rebecca Lyons, The link between flowering time and stress tolerance, Journal of Experimental Botany, Volume 67, Issue 1, January 2016, Pages 47–60, https://doi.org/10.1093/jxb/erv441
(X) Fiona Tooke, Nicholas H. Battey, Temperate flowering phenology, Journal of Experimental Botany, Volume 61, Issue 11, June 2010, Pages 2853–2862, https://doi.org/10.1093/jxb/erq165
(X)Thomas F. Daniel 2012, Garrya elliptica, in Jepson Flora Project (eds.) Jepson eFlora, https://ucjeps.berkeley.edu/eflora/eflora_display.php?tid=26460, accessed on January 14, 2024.
(X) Jepson Video https://www.youtube.com/watch?v=LFVGFzBwczw
