Hallett_avena-erodium.csv

Dataset to accompany the paper “Rainfall variability
maintains grass-forb coexistence” by Lauren M. Hallett, Lauren G. Shoemaker, Caitlin
T. White and Katharine N. Suding in Ecology Letters (manuscript number ELE-00234-2019.R2)

Experimental overview

In fall 2014 we established four rainfall treatments in
a random-block design, with plots arranged in a single row from east to west.
Blocks were replicated four times for a total of 16 plots. Early-season
rainfall in this system is thought to primarily affect recruitment, whereas
late-season rainfall primarily affects growth. To isolate the effect of drought
on periods of recruitment versus growth, our rainfall treatments consisted of
early-season fall dry, late-season spring dry, consistent dry, and a consistent
wet control. Dry treatments were achieved using 6.4 m x 5.2 m cold frame
rainout shelters with clear polyethylene retractable roofs. We erected the
roofs shortly before rainfall events, and removed them afterward to minimize
their effect on solar radiation. Following the first germinating rains, we
experimentally created our rainfall treatments by applying the roofs in some
seasons and not others, with a goal of reducing precipitation by 50% during
target seasons. To create early-season fall dry we applied roofs during storms
from Oct-Jan, for late-season spring dry from Feb-Apr, and for consistent dry
from Oct-Apr.

Within each main plot we manipulated the seeding density
and ratio of the dominant grass Avena barbarta to the dominant forb Erodium
botrys to assess the recruitment and growth dynamics of each species when
it was rare versus common. Prior to treatment implementation, we reduced the
extant seed bank by removing the existing vegetation and upper ~3 cm of top
soil. We seeded at two total densities on a log-scale: low (320 seeds/m2)
and high (similar to observed stem densities, 3200 seeds/m2). At
each density we manipulated the seeding ratio of Avena to Erodium to
capture a range from rare to common (0:10, 1:9, 5:5, 9:1, and 10:0 Avena:
Erodium). This yielded a total of 10 25 x 25 cm subplots per main
rainfall plot for a total of 160 subplots.

We measured initial recruitment by counting stems by
species in December, and we measured fecundity by counting species' seed
production in the spring. To account for differences in phenology we measured Erodium
fecundity in late March and Avena in late April. Both species retain
evidence of seed production following seed release Erodium retains its
sepals and Avena its spikelets). Consequently, we measured fecundity
toward the end of seed production and multiplied each indicator by accordant
seeds produced (5 seeds are produced per Erodium flower head and 2 per Avena
spikelet).

Column metadata

shelterBlock: The block in which rainfall treatments
were grouped, values range from A-D.

plot: The rainfall manipulation plot, values range from 1-16.

subplot: The vegetation manipulation subplot nested within
rainfall treatment. Names are a combination of density (D1 or D2), and the
ratio of Avena to Erodium.

treatment: The rainfall treatment. Values include
consistentDry (shelters blocked storms throughout the year), fallDry (shelters
blocked storms in the fall), springDry (shelters blocked storms in the spring),
and controlRain (no shelters).

density: The seeding density treatment. Values include Low
density (320 seeds/m2) and High density (3200 seeds/m2).

ERprop: The proportion of Erodium seeds added.

AVprop: The proportion of Avena seeds added.

ERseedin: The number of Erodium seeds added per 25
x 25 cm subplot.

ERstem: The number of Erodium stems that recruited
in December per 25 x 25 cm subplot.

ERseedout: The number of Erodium seeds produced
per 25 x 25 cm subplot.

AVseedin: The number of Avena seeds added per 25
x 25 cm subplot.

AVstem: The number of Avena stems that recruited
in December per 25 x 25 cm subplot.

AVseedout: The number of Avena seeds produced per
25 x 25 cm subplot.