DOI: 10.5061/dryad.9ghx3fft6
title: Invaders break assembly rules to beat the natives: How cheatgrass cheats

description: Understanding how some introduced plants achieve invasive status while
 most simply become naturalized is a fundamental question in invasion
 ecology. Traditional approaches comparing native and introduced plants
 have linked ruderal traits such as annual life history, high fecundity,
 and rapid growth rates to invasiveness. However, they do not explain why
 other introduced species bearing similar traits fail to become invasive,
 possibly because generic comparisons ignore local processes that drive
 community assembly. Herein, we contrasted native and introduced annuals in
 the context of local successional processes to elucidate how introduced
 annual bromes like cheatgrass (Bromus tectorum) overtake perennial
 grasslands in the intermountain western United States. We created
 disturbed plots and seeded them first with annuals representing natives,
 naturalized species, or invasive bromes. We then seeded plots with native
 perennial community dominants to examine how the different annuals
 influenced succession. Native annuals established transient populations
 that facilitated perennial establishment compared to unseeded controls,
 enabling the shift to perennial dominance. Naturalized annuals mirrored
 the natives, but invasive annuals maintained robust populations at high
 biomass that inhibited perennial establishment and impeded succession.
 Mechanistically, invasive annuals reduced soil moisture and elevated plant
 biomass, litter, and soil N. However, only litter abundance correlated
 with perennial seedling recruitment across treatments. Overall, litter
 showed a unimodal relationship wherein lower litter abundance associated
 with native and naturalized annuals appeared to facilitate perennial
 seedling establishment while higher litter levels generated by invasives
 appeared to suppress perennial establishment and inhibit succession.
 Additional experiments provided little support for the roles of pathogen
 spill-over or plant-soil feedbacks favoring the introduced bromes. The
 domination of perennial grasslands by annual bromes may be driven by
 litter buildup that allows these introduced plants to break local
 succession rules by acting as both early seral and climax species. Traits
 like litter accumulation may strongly influence invasion outcomes but are
 indistinguishable using trait comparisons lacking community context.
description: Data for this study derive from a main field experiment, an
 embedded seed fate experiment, and two greenhouse experiments. In the
 field, we primarily measured response variables that assayed plant
 community development and associated changes in soil conditions. The
 greenhouse experiments involved the same focal annual and perennial
 species used in the field experiments, but with a focus on testing for
 plant-soil feedbacks. Please see README information (included in this
 archive and within data files) in addition to the published article for
 detailed methods.
description: # Invaders break assembly rules to beat the natives: How cheatgrass cheats
 [https://doi.org/10.5061/dryad.9ghx3fft6](https://doi.org/10.5061/dryad.9ghx3fft6) ## Description of the data and file structure These data assay plant community succession via field and greenhouse experiments to test whether processes diverge between communities initiated with invasive annual bromes or native and naturalized annuals. In the files described further below, note that cases where no data were collected are indicated with a period (".") ### Files and variables #### File: FIELD\_DATA\_FOR\_DRYAD.xlsx **Description:**  DATA FROM MAIN FIELD EXPERIMENT AND EMBEDDED SEED FATE EXPERIMENT ##### Variables * **FIELD EXP TAB** YEAR: SAMPLING YEAR, 2016-2019 PLOT: EXPERIMENTAL UNIT UNIQUELY LABELED SPECIES: FOUR LETTER CODE REPRESENTING FOCAL ANNUAL SPECIES ORIGINALLY SEEDED INTO PLOT (SEE FIG. S1 FOR KEY) TREAT: ANNUAL SPECIES CATEGORY REPRESENTED BY FOCAL SEEDED SPECIES, WITH CNTL=UNSEEDED CONTROL, INVA=INVASIVE, NATU=NATURALIZED, AND NATV = NATIVE FOCAL: COVER (%) OF ANNUAL SPECIES SEEDED INTO PLOT (NOTE: TRACE LEVELS CODED AS 0.1% FOR ALL COVER VARIABLES, AND COVER OF BROMUS JAPONICUS AND B. TECTORUM LUMPED GIVEN DIFFICULTY OF SPLITTING THESE TAXA) FOCAL_T: TOTAL COVER (%) OF FOCAL ANNUALS COMPRISED OF FOCAL SPECIES SEEDED INTO PLOT PLUS COVER OF FUNCTIONALLY SIMILAR FOCAL SPECIES COLONIZING FROM OTHER PLOTS COLNZ: COVER (%) OF NATIVE AND NATURLIZED FOCAL ANNUALS COLONIZING FROM OTHER PLOTS COLNZ_MEAN: MEAN COVER (%) PER COLONIZING NATIVE OR NATURALIZED FOCAL ANNUAL SPECIES LITTER: LITTER COVER (%) N_SEEDL: NUMBER OF SEEDLINGS OF SEEDED NATIVE PERENNIALS COUNTED IN THE FIRST GROWING SEASON AFTER SOWING, 2017 AND 2018 NH4: SOIL AMMONIUM MEASURED IN 2018 NO3: SOIL NITRATE MEASURED IN 2018 SOM: SOIL ORGANIC MATTER (LOI %) MEASURED IN 2018 PH: SOIL PH MEASURED IN 2018 P: SOIL PHOSPHORUS (PPM) MEASURED IN 2018 K: SOIL POTASSIUM (PPM) MEASURED IN 2018 S: SOIL SULFATE (PPM) MEASURED IN 2018 ZN: SOIL ZINC (PPM) MEASURED IN 2018 FE: SOIL IRON (PPM) MEASURED IN 2018 MN: SOIL MANGANESE (PPM) MEASURED IN 2018 CU: SOIL COPPER (PPM) MEASURED IN 2018 CA: SOIL CALCIUM (PPM) MEASURED IN 2018 MG: SOIL MAGNESIUM (PPM) MEASURED IN 2018 NA: SOIL SODIUM (PPM) MEASURED IN 2018 CEC: SOIL CATION EXCHANGE CAPACITY (ME/100 G) MEASURED IN 2018 VWC: SOIL VOLUMETRIC WATER CONTENT (%) MEASURED IN 2018 BM_FOCAL_19: ABOVEGROUND BIOMASS (G) OF FOCAL SEEDED ANNUAL SPECIES, AS HARVESTED IN 2019 (NOTE: B. JAPONICUS AND B. TECTORUM WERE DINSTIGUISHABLE AT HARVEST AND TREATED AS SEPARATE SPECIES FOR THIS METRIC) BM_FOCAL_T_19: TOTAL ABOVEGROUND BIOMASS (G) OF FOCAL ANNUALS COMPRISED OF FOCAL SPECIES SEEDED INTO PLOT PLUS COVER OF FUNCTIONALLY SIMILAR FOCAL SPECIES COLONIZING FROM OTHER PLOTS, AS HARVESTED IN 2019 BM_PEREN_19: ABOVEGROUND BIOMASS (G) OF SEEDED PERENNIALS FROM 2018 SEEDLING COHORT, AS HARVESTED IN 2019 BM_LITTER_19: ABOVEGROUND BIOMASS (G) OF LITTER, AS HARVESTED IN 2019 LITTER_PC: PRIMARY PRINCIPLE COMPONENT BUILT FROM LITTER COVER IN THE SAMPLING YEAR (2017 OR 2018, RESPECTIVELY) AND LITTER BIOMASS FROM 2019 LITTER_PC_TX: LITTER_PC SCALED SO THAT MINIMUM NUMBER WAS &gt;0 FOR DISPLAY PURPOSES ONLY * **PSSP SEED FATE TAB** PLOT: EXPERIMENTAL UNIT UNIQUELY LABELED (REPRESENTING SUBSET OF PLOTS FROM MAIN EXPERIMENT) SPECIES: FOUR LETTER CODE REPRESENTING FOCAL ANNUAL SPECIES ORIGINALLY SEEDED INTO PLOT (SEE FIG. S1 FOR KEY) TREAT: ANNUAL SPECIES CATEGORY REPRESENTED BY FOCAL SEEDED SPECIES, WITH CNTL=UNSEEDED CONTROL, INVA=INVASIVE, NATU=NATURALIZED, AND NATV = NATIVE N_EMERG_F: NUMBER OF MARKED PSSP (PSEUDOROEGNERIA SPICATA) SEEDS WITH EVIDENCE OF EMERGENCE IN FALL 2018 COUNT N_EMERG_SP: NUMBER OF MARKED PSSP SEEDS WITH EVIDENCE OF EMERGENCE IN SPRING 2019 COUNT (EXCLUDES THOSE SCORED AS EMERGING IN FALL) N_EMERG: TOTAL NUMBER OF MARKED PSSP SEEDS WITH EVIDENCE OF EMERGENCE (FALL 2018 COUNT PLUS SPRING 2019 COUNT) P_EMERG: PROPORTION OF TOTAL MARKED PSSP SEEDS (OF N=20 PER PLOT) WITH EVIDENCE OF EMERGENCE (FALL 2018 COUNT PLUS SPRING 2019 COUNT) N_SURV_SP: NUMBER OF MARKED PSSP SEEDLINGS FROM FALL SURVING UNTIL SPRING 2019 COUNT P_SURV_SP: PROPORTION OF MARKED PSSP SEEDLINGS FROM FALL SURVING UNTIL SPRING 2019 COUNT (N_SURV_SP/N_EMERG_F) N_RECOV: NUMBER OF MARKED PSSP SEEDS WITH NO EVIDENCE OF EMERGENCE (FROM FALL OR SPRING) THAT WERE RECOVERED FOR LAB INSPECTION N_PYREN: NUMBER OF RECOVERED PSSP SEEDS WITH SIGNS OF INFECTION BY THE PATHOGEN PYRENOPHORA SEMENIPERDA (NO RECOVERED SEEDS HAD SIGNS OF FUSARIUM INFECTION) D_PYREN: FOR PLOTS WITH RECOVERED PSSP SEEDS, INDICATES DETECTION OF INFECTION BY THE PATHOGEN PYRENOPHORA SEMENIPERDA (1=DETECTED, 0=NOT DETECTED) #### File: GREENHOUSE\_DATA\_FOR\_DRYAD.xlsx **Description:**  DATA FROM GREENHOUSE EXPERIMENTS FOCUSED ON PLANT-SOIL FEEDBACKS (PSF) ##### Variables * **PSF EXP1 TAB - FEEDBACKS OF FOCAL ANNUALS ON THEMSELVES** ROUND: FIRST OR SECOND GREENHOUSE GROWTH PERIOD (TRAINED SOIL FROM EACH ROUND 1 POT WAS USED TO GROW CONSPECIFICS IN THE SAME POT IN ROUND 2) SPECIES: FOUR LETTER CODE REPRESENTING FOCAL ANNUAL SPECIES PLANTED IN POT (SEE FIG. S1 FOR KEY) TREAT: ANNUAL SPECIES CATEGORY REPRESENTED BY PLANTED FOCAL SPECIES, WITH INVA=INVASIVE, NATU=NATURALIZED, AND NATV = NATIVE SOIL_TYPE: LIVE=FIELD SOIL USED IN THE MAIN EXPERIMENT; INERT=POTTING SOIL CONTROL USED TO TEST FOR BROAD CHANGES IN GROWING CONDITIONS BETWEEN ROUNDS POT_ID: UNIQUE ID FOR EACH POT NPLANTS: NUMBER OF PLANTS SURVIVING UNTIL THE END OF THE ROUND MASS_1: SHOOT BIOMASS (G) OF FIRST PLANT WEIGHED AT THE END OF THE ROUND MASS_2: SHOOT BIOMASS (G) OF SECOND PLANT WEIGHED AT THE END OF THE ROUND MASS_3: SHOOT BIOMASS (G) OF THIRD PLANT WEIGHED AT THE END OF THE ROUND MASS_MEAN: MEAN SHOOT BIOMASS (G) PER PLANT AT THE END OF THE ROUND * **PSF EXP2 TAB - FEEDBACKS OF FOCAL ANNUALS ON NATIVE PERENNIALS** SPECIES1: FOUR LETTER CODE REPRESENTING FOCAL ANNUAL SPECIES GROWN IN POT IN ROUND 1 TO TRAIN SOIL (SEE FIG. S1 FOR KEY) TREAT: ANNUAL SPECIES TYPE REPRESENTED BY FOCAL SPECIES PLANTED IN ROUND 1, WITH BRTE=BROMUS TECTORUM (INVASIVE) AND NOT=EITHER NATURALIZED OR NATIVE SPECIES SPECIES2: FOUR LETTER CODE REPRESENTING NATIVE PERENNIAL SPECIES GROWN IN TRAINED SOIL IN ROUND 2 (SEE FIG. S4 FOR KEY) POT_ID: UNIQUE ID FOR EACH POT MASS2: SHOOT BIOMASS (G) OF NATIVE PERENNIAL PLANT WEIGHED AT THE END OF ROUND 2 ## Code/software No specialized code/software needed.