Wyoming Big Sagebrush Transplant Survival and Growth Affected by Age, Season of Planting, and Competition

ABSTRACT Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis [Beetle & A. Young] S. L. Welsh) has decreased from its historic prevalence across the sagebrush steppe in part because of its interaction with invasive annual grasses and the increased wildfire frequency. Restoration of this species is vital to the ecosystem; however, traditional seeding methods such as broadcast or drill seeding have low success rates. Seedling mortality is associated with harsh weather conditions such as freezing temperatures in the winter and extreme temperature and soil moisture conditions during the summer drought. Transplanting sagebrush has greater success by overcoming the bottleneck of early seedling mortality. We tested how sagebrush transplant survival and size (canopy volume) are affected by age at the time of planting (10 classes, 6–24 wk), planting season (fall versus spring), and invasive annual grass competition (low/high) with a randomized factorial design over 2 yr. Survival was lower for age classes under 10 or 12 wk (in yr 1 and 2, respectively) but relatively similar from 12 to 24 wk. Fall-planted transplants had lower survival but increased canopy volume compared with spring-planted transplants. Survival and canopy volume decreased with competition with annual grasses. Our results suggest that land managers should consider planting younger transplants than previously thought and controlling invasive annual grasses before planting sagebrush transplants to increase long-term survival and canopy volume.


Introduction
Restoration of Wyoming big sagebrush ( Artemisia tridentata Nutt.ssp.wyomingensis [Beetle & A. Young] S. L. Welsh) is necessary to maintain ecosystem resilience and provide habitat for a large number of wildlife species including the imperiled greater sage-grouse (Centrocercus urophasianus).There is a large effort across the field of rangeland ecology to restore sagebrush habitat; however, traditional seeding methods (broadcast and drill seeding) ✩ This work was supported by the USDA Agricultural Research Service .The EOARC is jointly operated by the USDA-ARS and the Oregon State University Agricultural Experiment Station.USDA is an equal opportunity provider and employer.Proprietary or trade names are for information only, and do not convey endorsement of one product over another.
have low success rates ( Lysne and Pellant 2004 ;Knutson et al. 2014 ;Davies et al. 2018 ).There are several reasons for such low success rates.Sagebrush seed is only viable for 1-2 yr and has specific requirements for emergence ( Wijayratne and Pyke 2012 ;Brabec et al. 2015 ).Sagebrush seedlings do not compete well with invasive annual grasses, and seedlings may not establish in years of low or erratic precipitation ( Shaw et al. 2005 ;McAdoo et al. 2013 ;Shriver et al. 2018 ).The use of sagebrush transplants or outplantings is often the most successful method for restoration ( McAdoo et al. 2013 ;Pyke et al. 2020 ), especially in highly competitive introduced grasslands ( Davies et al. 2013 ).Sagebrush transplants often have greater success by overcoming the bottleneck of early seedling mortality ( James et al. 2011 ;Davidson et al. 2019 ).
Seedlings are vulnerable to abiotic factors, such as freezing temperatures in the winter and extreme temperature and soil moisture conditions during summer drought ( Fenner 20 0 0 ; Copeland et al. 2022 ).Conditions that promote successful sagebrush transplant restoration need further research and development to restore sagebrush habitat.Restoration of Wyoming big sagebrush is made more difficult by the invasion of exotic annual grasses in the sagebrush steppe.Annual grasses such as cheatgrass ( Bromus tectorum L.), ventenata ( Ventenata dubia [Leers] Coss.), and medusahead ( Taeniatherum caput-medusae [L.] Nevski) are highly competitive, change nutrient cycling processes, deplete the soil water content, and consequently decrease biodiversity ( Melgoza et al. 1990 ;Knapp 1996 ;Norton et al. 2004 ;Davies 2011 ;Bansal and Sheley 2016 ).They are also often associated with an increase in the frequency of wildfire ( Whisenant 1990 ;D'Antonio and Vitousek 1992 ;Meyer et al. 2008 ).Historically, lower-elevation Wyoming big sagebrush plant communities had a fire return interval of approximately 50−100 + yr ( Whisenant 1990 ;Miller et al. 2011 ;Rau et al. 2011 ;McIver and Brunson 2014 ); with the invasion of annual grasses, the fire return interval for plant communities dominated by annual grasses has decreased to < 10 yr in some cases ( Whisenant 1990 ;Miller et al. 2011 ).Wyoming big sagebrush is not adapted to frequent fire and cannot withstand aboveground combustion ( Brabec et al. 2015 ).Natural recovery of big sagebrush is difficult because sagebrush only establishes in large numbers during rare, favorable years.Natural establishment is made more difficult following wildfire due to its inability to resprout, its short-lived seedbank, and competition with invasive annual grasses ( Dettweiler-Robinson et al. 2013 ;Mata-González et al. 2018 ).
Although restoration using Wyoming big sagebrush transplants generally has a higher success rate than seeding, transplant survival is highly variable ( Dettweiler-Robinson et al. 2013 ;Pyke et al. 2020 ).Seed source, site characteristics, and method of planting are associated with a wide range of transplant success ( McAdoo et al. 2013 ;Brabec et al. 2015 ;Davidson et al. 2019 ).Furthermore, sagebrush transplant success likely varies by planting season, but disagreement exists over whether spring or fall plantings are more successful ( Monsen et al. 2004 ;Clements and Harmon 2019 ).According to some studies, fall plantings can be successful in areas with mild winters that allow for root development over the winter months ( Wirth and Pyke 2011 ;Shaw et al. 2015 ).In environments with harsher winter conditions, a spring planting could have more favorable results ( Shaw et al. 2015 ).
Age of sagebrush transplants at time of planting has the potential to affect transplant survival and growth; however, this has not been thoroughly researched.Traditionally, transplants are often grown out in a grow room or nursery for 6 mo to a year before being planted in the field ( Fleege 2010 ;Moore 2015 ;Shaw et al. 2015 ;Clements and Harmon 2019 ).The cost to grow and plant transplants is much greater than seed-based restoration.If shorter growing times (i.e., decreased transplant age) do not reduce survival, restoration practitioners would save time and money.
Our study examines the effects of age of transplant at planting, season of planting, and competition from invasive annual grasses on Wyoming big sagebrush transplant vigor (as measured by shrub canopy volume) and survival after a 1-and 2-yr postplanting growth period.We hypothesized that sagebrush transplant canopy volume and survival would increase with transplant age at time of planting, suppression of invasive annual grasses, and spring (versus fall) planting timing.

Site description
The field site was located at the Northern Great Basin Experimental Range (NGBER; 119 ˚42 35.9"W, 43 ˚29 22.0"N) outside of Riley, Oregon, United States at approximately 1 400 m elevation in a formerly Wyoming big sagebrush steppe community type with annual grass (cheatgrass) invasion.The site had 0−2% slope, a Gochea sandy loam soil ( USDA NRCS 2021 ) and identified as a Sandyloam 10-12 PZ Ecological Site (R023XY213OR).Annual precipitation at the site averages 294 mm, mostly falling from October to March.The average annual temperature is 7.5 °C with July being the warmest month (19.6 °C) and December being the coldest (−2.8 °C; Great Basin Weather Applications 2021 ).
Climate data were obtained from a US Climate Reference Network site, approximately 3.5 km from the field site at the same elevation and similar flat topographic position ( Diamond et al. 2013 ).Soil probes (Em50 Data Logger; Decagon Devices Inc.; Pullman, Washington, United States with 5TM sensor; Campbell Scientific Corp.; Edmonton, AB, Canada) were used at the site to record hourly soil moisture and temperature at varying depths (5,10,15,20,25 cm below the surface) and in two locations.
The site selected for this study had been previously disturbed and contained mostly invasive annual grass (cheatgrass) and annual forb species with some interspersed native shrubs and grasses.Each year, transplants were planted in a competition location where invasive annual grasses were allowed to emerge, or a reduced competition location that had competing vegetation removed via herbicide (see Study Design section later).
The first and second planting years generally had below-average precipitation and above-average temperatures with yr 2 having drier and hotter conditions than planting yr 1 ( Table 1 ).Soil moisture was generally higher in the reduced competition location for a longer duration into the summer months compared with the competition location (see Table 1 ).

Study design
The study was a completely randomized 10 × 2 × 2 factorial design repeated in two planting years.The study treatments were transplant age at time of planting (10), planting season (fall or spring), and two levels of annual grass competition (competition and reduced competition).The transplant seed source was the Columbia [River] Basin biotype of Wyoming big sagebrush (BFI Native Seeds, Moses Lake, Washington, United States).Ten age classes of transplants were used (6, 8, 10, 12, 14, 16, 18, 20, 22, and 24 wk of age).Seeds were sown every 14 d starting on May 1, 2019 for the first-yr fall cohort; October 2, 2019 for the first-yr spring cohort; May 18, 2020 for the second-yr fall cohort; and October 12, 2020 for the second-yr spring cohort.Transplants were grown in an indoor climate-controlled grow room (16−22 °C) under high-intensity lights with a 12-h light/dark cycle.Transplants were grown in cone-tainers (Ray Leach "Super Cell Classic" cone-tainers, Stuewe & Sons, Inc., Tangent, Oregon, United States) with a 3.8-cm diameter at the top and 21-cm depth, filled with a 50/50 mixture of soil collected from the field site that had been sifted to remove weed seed, and a potting soil mix (MiracleGro Seed Starting Potting Mix 0.03[N]-0.03[P]-0.03[K];Scotts Company LLC; Marysville, Ohio, United States) and watered as needed.Transplants are often hardened by leaving them outside or in cold storage before planting to provide an adjustment period and allow the transplants to acclimate to the colder temperature ( Généré et al. 2004 ;Overton 2012 ;Brabec et al. 2015 ).Our transplants were not hardened before planting.
A different 40 × 25 m planting site was used each year.Sites were adjacent to one another and homogenous in soil type, plant community, and microclimate.Sites were burned each year (September 26, 2019 andSeptember 15, 2020) to clear existing vegetation and ensure invasive annual grasses would reestablish.Any remaining vegetation was hand cleared using a combination of shovels, rakes, and hand pulling.Both sites were fenced to exclude rabbits.Each site each year was then split into two planting

Table 1
Weather data for critical growth periods during yr 1 and yr 2 of the study.Temperature data ( °C) and precipitation data are compared with the 40-yr average  for the field site.Soil moisture (m ³/m ³ Volumetric Water Content) is reported for the 5-cm depth moisture probe for the no-competition landscape and the competition landscape ( Great Basin Weather Applications 2021 ).At the time of planting, transplants were randomly assigned to 1-m 2 plots within each planting location (i.e., completely randomized design).Given the spatial design of the experiment, individual plots could not be randomly assigned to competition treatments, and therefore results for this factor with limited randomization should be interpreted with caution.In each season and year, 20 replicates per age class in the reduced competition treatment and 10 replicates per age class in the competition treatment were used.Each transplant was planted using a planting bar (Jim-Gem Speedy Dibble Tree Planting Bar; Forestry Suppliers, Inc.; Jackson, Mississippi, United States) that created an approximately 21-cm deep hole.The transplant was placed in the hole and, using a garden trowel, soil was pressed firmly against the roots to prevent air pockets.

Vegetative measurements
Before planting, transplant root and shoot height were recorded to the nearest mm for a randomly selected subset of 25 plants in each age class; these plants were discarded after measurement.Transplant survival and surviving shrub volume were measured approximately 1 yr following planting in the summer (August 2020 and 2021) and again 2 yr post planting for the first-yr cohort only.Shrubs were considered alive if any green tissue remained and if, when bent, the transplant did not break.Canopy volume was used as an index of transplant vigor ( Miglia et al. 2007 ;McAdoo et al. 2013 ) and was calculated by measuring the maximum height (ground surface to tallest point), the major diameter (maximum diameter of shrub), and minor diameter (diameter of shrub perpendicular to major diameter).Volume was calculated using a commonly used shrub canopy volume formula, V = 2/3 π H ([Ma- , where H is the plant height ( Thorne et al. 2002 ).Vegetative cover, litter, and bare ground were estimated at each location in each planting year (June 2020 and 2021) with linepoint intercept every 1 m along four evenly spaced 25-m transects ( Herrick et al. 2009 ).In planting yr 1 in the reduced competition planting location, cover was 90% ± 2.6% bare ground, 6% ± 2.6% cheatgrass, 4% ±1.3% annual forbs, 0% native perennial forbs, and 0% perennial grass cover.The competition planting location had 15% ± 2.3% bare ground, 78% ± 5.6% cheatgrass, 7% ± 3.5% perennial grass cover, and 0% annual or perennial forb cover.In planting yr 2 in the reduced competition planting location, cover was 92% ± 2.3% bare ground, 2.6% ± 0.5% native perennial forb, and 5.3% ± 4% perennial grass, 0% cheatgrass or annual grass, and 0% annual forb cover.The competition planting location had 28.8% ± 2.3% bare ground, 53.3% ± 7.5% cheatgrass, 4.4% ± 0.5% perennial grass, 4.4% ± 0.5% native perennial forb, and 8.8% ± 2.3% annual forb cover ( Fig. 1 ).

Statistical analyses
The effects of transplant age, planting season, competition, and their interactions on survival by August were analyzed with separate binomial generalized linear models each planting year in the nlme R package ( Pinheiro et al. 2021 ).When quasi or complete separation were suspected, the brglm R package Firth bias correction function (a penalized likelihood method) was used to reduce bias ( Heinze and Schemper 2002 ).Analysis of variance was used to model treatment effects on transplant volume with the fixed effects of age, season of planting, competition, and their interaction.For first yr transplants only, 2 yr post planting, we tested for the effects of age, planting season, competition, planting year, and interactions on survival and volume with separate repeated measures models (survival: binomial distribution, volume: normal distribution, random effect for year, R package nlme, Pinheiro et al. 2021 ).A two-sided t -test was used to determine differences between transplant root length and shoot height between planting yr 1 and 2 and between age classes and season of planting.Volume data were log transformed to improve assumptions of the statistical models and to increase model fit.When significant treatment or interactive effects were found, means were separated using the emmeans R package (Tukey Honest Significant Difference method; Lenth 2020 ).All treatment means are reported with their associated standard errors.Differences were considered significant at P ≤ 0.05.All analyses were conducted in R software version 4.0.2 ( R Core Team 2020 ).

Survival
Transplant survival in planting yr 1 was affected by the interaction between age class and planting season ( P = 0.004; Fig. 2 ; Appendix S1, available online at doi: 10.1016/j.rama.2023.09.005 ) but not by competition ( P = 0.08).Generally, age classes 6 wk and 8 wk had the lowest survival compared with the other eight age classes.Age class 6 had 7% ± 5% survival in the fall and 42% ± 10% in the spring, and age class 8 had 58% ± 10% survival in the fall and 46% ± 10% in the spring planting.The other eight age classes had relatively higher survival rates ranging from 62% to 78% survival in the fall and spring plantings, with the exception of age classes 16 and 18 in the fall planting with 40% and 33% survival, respectively.Yr 1 spring-planted transplants had about 1.5-fold higher survival than the fall-planted transplants across both competition and reduced-competition locations (see Fig. 2 ).Competition transplants in planting yr 1 averaged 60% ± 0.04% survival, and reduced-competition transplants averaged 67% ± 0.03% survival (data not shown).
Transplant survival in planting yr 2 was low with only 12.7% ± 0.2% of all transplants surviving.Transplant survival in yr 2 was affected by age class ( P < 0.001; Fig. 3 A ; see Appendix S1), planting season ( P < 0.001), and an interaction between planting season and competition ( P = 0.003; Fig. 3 B ). Similar to planting yr 1, in planting yr 2, age classes 6 and 8 wk had the lowest survival with age class 6 having 0% survival in both planting seasons and age class 8 having 1.7% survival in both planting seasons.Age class 10 also had comparatively low survival with only 5% ± 2.8% survival across planting seasons.The other seven age classes ranged from 10% to 28% survival across planting seasons.In yr 2, reduced competition transplants exhibited greater survival for the spring planting (competition and planting season interaction P = 0.003) and competition transplants had no difference in survival between planting seasons (see Fig. 3 B ).
Two yr following yr 1 planting, yr 1 transplant survival was generally higher in spring-planted transplants (age class and planting season interaction P < 0.001; see Appendix S1) and generally higher in reduced competition transplants (age class and competition interaction P = 0.02, Fig. 4 A−4C ).There was no difference in survival from yr 1 to yr 2 post planting; only 5% of transplants that survived yr 1 died, 80% of which were competition transplants (data not shown).

Volume
Volume of surviving transplants in planting yr 1 was highly variable by treatment.Volume for planting yr 1 transplants was not affected by age ( P = 0.12) but was greater in fall-planted transplants with 3.4 × greater volume than transplants planted in the spring ( P < 0.001); Fig. 5 A ; see Appendix S1).Competition ( P < 0.001) generally decreased transplant volume in both planting seasons in planting yr 1 with 54-fold greater volume in reduced competition transplants compared with competition transplants (see Fig. 5 B ).
Volume of surviving transplants in planting yr 2 was affected by competition ( P = 0.004; Fig. 6 A ; see Appendix S1), with reduced competition transplants being ninefold larger than competition transplants (see Fig. 6 A ). Surviving shrub volume was also Two yr following planting, planting yr 1 transplant shrub volume was affected by the interactions between year and planting season ( P < 0.001; Fig. 7 A ) and year and competition ( P < 0.001; see Fig. 7 B ), planting season and age at planting ( P = 0.002; data not shown), and a three-way interaction among age, season, and competition ( P = 0.02; see Fig. 7 C and Appendix S1).Shrub volume overall increased 11-fold from the first to second yr following planting (see Fig. 7 A and 7 B ), and reduced competition transplants were at least 11-fold larger than competition transplants after 2 yr (see Fig. 7 B ). Transplants planted in the fall had 1.6 × greater volume than transplants planted in the spring (see Fig. 7 A and 7 C ).The three-way interaction indicates that older transplants planted in the fall and in the reduced competition landscape exhibited the largest volume compared with the other treatment combinations.

Root length and shoot height
Age class and planting season did not affect root length and shoot height in the first or second planting year.Mean root length was 180 ± 1.8 mm across all age classes, planting seasons, and years.Shoot height, however, did differ between years ( P < 0.001; see Appendix S1).

Discussion
Our study is the first to indicate that sagebrush transplants may not need to be grown for an extended period of time (24 wk or greater) before being transplanted in the field.Transplants ranging from 12 to 24 wk of age had comparable within-planting-year survival and transplant vigor (canopy volume) in both years of the study, suggesting that restoration practitioners could reduce growout time before planting, relative to the traditional 24 wk ( Fleege 2010 ;Moore 2015 ;Shaw et al. 2015 ).Previous research indicates that sagebrush transplants have highly variable success, with survival rates ranging from 15% to 80% ( Jacobs et al. 2011 ;Dettweiler-Robertson et al. 2013 ).Survival in planting yr 2 of our study falls below this range (12.67% survival), likely attributable to abiotic conditions (see later discussion); however, survival rates in planting yr 1 were comparable with the literature and even exceeded previously reported survival rates in some age classes and planting seasons (see Fig. 2 ).By reducing grow-out time, land managers could save a substantial amount of time and expense on sagebrush transplant restoration projects.Quantifying the exact cost saved is difficult because of differences in growing procedures, availability and cost of seed, etc.If transplants were grown for 12 wk in a grow room or greenhouse (compared with the traditional 24 wk), the labor cost to successfully plant transplants could be reduced with greenhouse labor costs potentially being cut in half.By reducing growing costs, the use of sagebrush transplants becomes a more favorable restoration option.
In our study, spring-planted transplants had higher survival in both years, which contradicts some previous work (e.g., Clements and Harmon 2019 ); however, even slight differences in climatic variables between field sites could elicit different results ( Barnett and McGilvray 1993 ).Previous studies have shown that fall plantings may be more favorable in milder climates and spring plantings may be more favorable in colder climates ( Wirth and Pyke 2011 ;Shaw et al. 2015 ).Our field site had average or belowaverage temperatures immediately following the fall plantings (see Table 1 ), which could explain why our transplants had higher survival in the spring planting compared with fall planting.Additionally, our transplants were not hardened before planting, which could have led to decreased survival for the fall-planted transplants.Although survival was higher for spring-planted transplants in the present study, volume was greater for fall-planted transplants, suggesting that a fall planting may result in increased transplant vigor.Alternatively, at time of measurement, the fallplanted transplants had been growing for a longer period of time compared with spring-planted transplants, potentially leading to increased volume.Our data suggest that spring planting may be a better time to plant because it may increase chances of survival as opposed to a fall planting.Although there was an increase in volume for fall-planted transplants, the major determinant of volume for older age classes was competition with annual grasses, not season of planting.
Competition played a significant role in the success of sagebrush transplants.Two growing seasons post planting, survival was affected by com petition, indicating that com petition with invasive annual grasses does decrease long-term survival, which is consistent with previous research ( Davies et al. 2020a ).Given the spatial design of the experiment, however, individual plots could not be randomly assigned to competition treatments, and therefore results for this factor should be interpreted with caution.Previous studies have shown that by decreasing competing herbaceous vegetation, sagebrush transplant survival and growth increased ( Austin et al. 1994 ;Schuman et al. 1998 ;McAdoo et al. 2013 ;Brabec et al. 2015 ;Davies 2020a and2020b ).In the sagebrush steppe, smaller transplants are less likely to survive winter thermal extremes and summer drought as supported by low survival for small size classes in our analysis and previous work ( Fenner 20 0 0 ).This suggests that smaller sagebrush may be more negatively impacted by annual grass competition.Increased transplant vigor in transplants not competing with annual grasses could result in more resilient transplants ( Cook and Child 1971 ;McAdoo et al. 2013 ).Larger sagebrush shrubs will also reach maturity sooner and start producing seed earlier than smaller shrubs ( Young et al. 1989 ;Innes 2019 ), indicating that competition with invasive annual grasses could influence the sagebrush seedbank.
Year-to-year weather variation, especially precipitation, can greatly affect survival and volume of transplants ( Barnett and McGilvray 1993 ).In our study, transplants from planting yr 2 had fivefold lower survival and 10-fold lower volume than transplants from planting yr 1.There are several possible reasons for this difference.Precipitation in the second yr of the study was lower than the 40-yr average, especially during the spring growing season (March−June; see Table 1 ).The site received 42% of the Figure 7. Mean volume (cm 3 ) of surviving transplants from planting yr 1 after 1 and 2 yr of growth as a function n of A, the interaction between planting season and yr, B, the interaction between competition with cheatgrass and yr, and C, the three-way interaction among planting season, age, and competition after 2 yr of growth.Significant differences for A and B are denoted by differing lowercase letters.long-term average precipitation during March−June in the second yr, compared with 93% of the long-term average precipitation in the first yr.In the second yr, average daily temperatures in the spring growing season were 2 °C ± 0.7 °C greater than the long-term average (see Table 1 ).The above-average temperatures likely led to an increase in evaporative losses in the soil, and abnormally low precipitation decreased the soil moisture content in yr 2 (see Table 1 ).Additionally, soil moisture was higher during the planting process in the first yr ( ≈0.146 Volumetric Water Content [VWC] m 3 /m 3 for the fall planting and 0.229 VWC m 3 /m 3 for the spring planting; see Table 1 ) than the second yr ( ≈0.032 VWC m 3 /m 3 for the fall planting and 0.174 VWC m 3 /m 3 for the spring planting; see Table 1 ), which could have created water stress at time of planting in yr 2.
The transplants grown for the second yr of the study also had shorter shoot height compared with the first yr despite the transplant care protocol being the same in both years, perhaps due to slight differences in watering or light exposure that could have influenced growing rates.Even though second-yr transplants had reduced shoot heights, they still met the minimum required shoot height (5 cm) for transplanting according to previous work ( Dettweiler-Robinson et al. 2013 ;Brabec et al. 2015 ).Additionally, these transplants, due to their reduced shoot height (i.e., compared with planting yr 1) but comparable root length, exhibited a high root-to-shoot ratio.Many plants in arid and semiarid regions have evolved a high root-to-shoot ratio to increase resource capture and decrease water loss in a precipitation limited environment ( Fernandez and Caldwell 1975 ;Mata-González et al. 2017 ).For this reason, the reduced shoot height is unlikely to be a contributing factor to decreased survival in the second yr.

Management Implications
With increasing frequency and size of wildfires in low to midelevation sagebrush communities, there is an increasing need to re-store sagebrush.Although transplants are more costly compared with seeding, transplants have a higher success rate, making this technique a favorable restoration option for land managers, particularly for localized high priority areas (e.g., critical sage-grouse habitat).Our data suggest a less costly alternative to traditional sagebrush transplant grow-out protocols, which would reduce the cost of using sagebrush transplants in restoration projects; specifically, growing sagebrush transplants for only 10 or 12 wk compared with the traditional 24 + wk.
This study indicates that spring planting may promote higher survival compared with fall planting.Competition with invasive annual grasses also greatly reduces sagebrush transplants' vigor and decreases long-term survival, suggesting that removal of competing herbaceous vegetation will increase transplant restoration success.Year-to-year variation in weather can also strongly affect transplant survival and canopy volume.All of these factors add to the ecological knowledge around sagebrush restoration and contribute to improving the success of sagebrush transplanting.Further studies should follow to confirm the results of this study, especially in different climate conditions to help land managers form a better understanding of sagebrush restoration options.

Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figure 1 .
Figure 1.Side-by-side comparison of the reduced competition location (left) and competition location (right) taken in summer 2020.

Figure 2 .
Figure 2. Mean survival of sagebrush transplants from planting yr 1 as a function of the interaction of age and planting season in the first yr of the study.Significant differences are denoted by differing lowercase letters.

Figure 3 .
Figure 3. Mean survival density of transplants from planting yr 2 as a function of A, age at time of planting and B, the interaction between planting season and competition.Significant differences are denoted by differing lowercase letters.

Figure 4 .
Figure 4. Mean survival density of transplants from planting yr 1, two yr following planting as a function of A, the interaction between planting season and age, B, the interaction between age and competition, and C, the interaction between planting season and competition.Significant differences are denoted by differing lowercase letters.

Figure 5 .
Figure 5. Mean volume (cm 3 ) of planting yr 1 transplants A, by planting season and B, competition transplants and reduced competition transplants.

Figure 6 .
Figure 6.Mean volume (cm 3 ) of transplants from planting yr 2 as a function of A, competition with cheatgrass and B, the interaction between age and season.Significant differences in B are denoted by differing lowercase letters.