DOI: 10.5061/dryad.dr7sqvb9w
title: Relationships between flowering phenology and community composition in an experimental restoration of northwest prairies

description: Phenology, the timing of biological life cycles, is a key indicator of
 global climatic change, with numerous studies showing that species'
 phenologies are shifting in response to climate change. Despite general
 trends (e.g., warming causing earlier arrival of spring events such as
 leaf-out and flowering onset), studies repeatedly reveal that phenological
 changes tend to be species-specific and thus may alter species
 interactions. Less studied is the potential feedback between biotic
 interactions and phenology and the impacts on species’ fitness. To
 understand the consequences of shifting phenology for species and
 communities, we need to quantify how phenology and competition interact to
 affect species’ fitness. Here, we studied the potentially interacting
 effects of species’ phenology and competition on plant fecundity (as a
 proxy for fitness). We sowed seeds of various species combinations to test
 how variation in competitor species richness, identities, and densities
 affect the phenology and fecundity of an annual wildflower, Clarkia
 purpurea, using an unconventional experimental design to encourage public
 engagement with the experiment. We found that C. purpurea’s flowering
 phenology varied with competitor identity and competitor species richness,
 that fecundity was negatively correlated with competitor density but not
 species richness, and that the strength of competition tended to vary by
 competitor identity but appeared unrelated to the relative phenology of
 the competitor. These findings offer unique evidence that competitive
 interactions may impact plant phenology and fecundity in complex ways and
 could influence species’ persistence and coexistence conditions in our
 changing global environment.
description: We conducted our research along the south bank of the Willamette
 River in Eugene, Oregon (44.05 ºN, 123.07 ºS, approximately 130m
 elevation). This region has a Mediterranean climate with warm, dry summers
 and cool, wet winters (12.06 ºC average annual temperature, 961.1 mm
 average annual precipitation). Historically, the research site was
 composed primarily of riparian hardwood forest and upland prairie
 vegetation before being degraded by industrial land use (e.g., railroad
 development, gravel mining, and fill deposit) starting in the mid-19th
 century. Since 1989, it has been under the management of the University of
 Oregon and is currently part of a 24-acre area designated as the
 Willamette River Natural Area (WRNA) which aims to promote habitat
 restoration, education, research, and recreation opportunities (Krueger
 2022). Drawing on our site’s history of habitat loss and its location
 within the WRNA, we aimed to conduct this experiment in a way which
 informed local restoration efforts and engaged the community in the study
 of phenology and environmental change (Fig. 2).  
 <em>Study System</em> Following
 the restoration goals specified for our site by the WRNA management plan,
 our study focused on plants native to Willamette Valley northwest
 prairies. This ecosystem type has been reduced to less than two percent of
 its pre-settlement area, consequently making it one of the most threatened
 ecosystem types nationally (Willamette Valley Oak and Prairie Cooperative
 2020). Prior to the onset of our experiment, the dominant plant species at
 the research site were non-native shrubs (primarily <em>Rubus
 armeniacus</em>), grasses, and forbs. To prepare for sowing our
 experiment, we mowed, covered the site with plastic (i.e., solarized) to
 reduce the existing seedbank, and used spot torching to remove remaining
 plant material. We then sowed seed of nine annual prairie forbs species of
 restoration interest: <em>Collinsia grandiflora</em> (COLLIN),
 <em>Plectritis congesta</em> (PLECON), <em>Plagiobothrys
 figuratus</em> (PLAFIG), <em>Clarkia purpurea</em>
 (CLAPUR), <em>Collomia grandiflora</em> (COLLOM),
 <em>Madia sativa</em> (MADSAT), <em>Gilia capitata
 (GILCAP), Epilobium densiflorum (EPIDEN)</em>, and
 <em>Navarretia squarrosa (NAVSQU)</em>. Although these species
 are relatively common species of northwest prairies and may have been
 historically present at our site, they were not abundant (or likely
 present at all) in the immediate area of the study, which is heavily
 invaded by non-native species. We used annuals as their short life cycles
 are conducive to short-term experiments asking questions about competitive
 interactions, phenology, and fecundity. We selected annuals that are
 commonly used for restoration in our region and vary in their respective
 flowering phenology (Fig. S3). This allowed us to answer our question
 regarding competition between species with different flowering times and
 created an extended spring/summer flowering display along the pathway,
 thereby drawing public interest in the experiment.
 Experimental Design We created two
 experimental planting areas: a 30m-long planting strip and a 20m-diameter
 planting circle, each consisting of plots varying in composition, density,
 and richness of species against which <em>C. purpurea</em>
 would be competing (Fig. 2 a-c). Although not extensively discussed here,
 it is worth noting that this experiment was designed to test the study’s
 ecological questions while also engaging the public in questions of
 phenology, species coexistence, and climate/environmental change (Fig.
 2d). The planting strip contained 16  plots of annual prairie plant
 monocultures as well as one 10 density gradient plot with <em>C.
 purpurea</em> and <em>C. grandiflora</em> and four
  reduced competition plots containing <em>C. purpurea</em>
 growing without immediate neighbors (Fig. 2c). The “reduced competition”
 plots help for fitting competition models (Hart <em>et
 al.</em> 2018). The additional purpose of the planting strip was to
 display the species in monocultures, roughly in order of flowering times,
 for public education. The planting circle featured multiple rings of
 varying species richness: monocultures, two-species plots, three-species
 plots, and a center core containing all nine of our study species (Fig.
 2b). The multispecies plots contained <em>C. purpurea</em>
 with different unique combinations of our study species. Seed quantities
 for each species were estimated by weight to try to obtain an equal number
 of germinants of each species (at a target density of 300 plants per
 square meter, adjusting seed quantity by estimated germination rates).
 However, final densities for all analyses were based on counts of actual
 germinants. Initial seed sowing occurred in January 2023 with some
 reseeding in March 2023. Throughout the duration of the experiment, we
 manually removed weeds from the plots.
 <em>Fecundity and Phenology
 Measurements</em> To assess how competitive
 neighborhoods impact the flowering phenology and fecundity of <em>C.
 purpurea</em>, we marked 125 focal individuals of <em>C.
 purpurea</em> within the two planting areas, capturing a gradient of
 competitor density and species richness. We quantified the competitive
 neighborhood of each focal plant as the identity and number of plants
 rooted within a 10cm radius of the focal. We monitored the phenology of
 focal plants from the beginning of May at a frequency of three times per
 week prior to the start of <em>C. purpurea</em>’s flowering
 season and daily henceforth, until the end of August. <em>C.
 purpurea</em> produces bowl-shaped flowers; an open flower was
 defined as one in which all four whorls (sepals, petals, stamens, and
 pistil) were fully visible. Once the first focal plant was observed in
 flower, we visited plots daily to record the presence of open flowers on
 all focal plants. We derived first flower dates for our other eight study
 species from observations of the monoculture plots of each species in the
 planting strip. Once the <em>C.
 purpurea</em> focal plants matured and reached the end of their
 reproductive periods, we counted the number of fruits present on each
 plant. We converted these to a measure of fecundity (i.e., seed counts) by
 collecting and dissecting fruits from focal plants in backgrounds of
 varying competitor densities. To determine whether average seed-per-fruit
 counts varied based on competitor density, we then fit a linear
 regression. Since there was a significant difference between seed counts
 per fruit within the different competitor density environments (linear
 model, F2,43 = 4.57;   , we calculated mean seeds-per-fruit estimates in
 three competitor density categories (zero, medium, and high densities,
 corresponding to competitor densities of 0, &lt; 25, and &gt;= 25
 respectively). Finally, we used these estimates to convert each plant’s
 fruit count into a fecundity measurement which accounted for the density
 of its competitors. This fecundity measurement for each plant was used as
 a proxy for plant fitness since <em>C. purpurea</em> is an
 annual species.
description: # Relationships between flowering phenology and community composition in
 an experimental restoration of northwest prairies Dataset DOI:
 [10.5061/dryad.dr7sqvb9w](10.5061/dryad.dr7sqvb9w) ## Description of the
 data and file structure 
 
 ### Files and variables #### File: data_Dryad.csv **Description:**  #####
 Variables * id: unique focal plant ID (unique plant identifier) *
 first_flw: date of first flower   (format: month/day/year) * last_flw:
 date of last flower   (format: month/day/year) * density_category:
 categorical neighborhood density  (alone/medium/high) * fruit_count: total
 plant fruit count  (integer) * mortality: binary mortality    (0/1) *
 flw_length: length of flowering period   (units:  number of days) *
 fecundity: plant fecundity (seeds)   (units:  number of seeds) * N_total:
 total number of competitors   (units:  number of competitor plants) *
 Competitor: identity of competitor   (species 6-letter codes) * N_comp:
 number of competitors of Competitor identity   (units:  number of
 competitor plants of identity "Competitor")