Brighm Young University BYU ScholrsArchive All Theses nd Disserttions 2014-03-01 Wet-Therml Time nd Plnt Aville Wter in the Seededs nd Root Zones Across the Sgerush Steppe Ecosystem of the Gret Bsin Nthn Lyle Cline Brighm Young University - Provo Follow this nd dditionl works t: https://scholrsrchive.yu.edu/etd Prt of the Animl Sciences Commons BYU ScholrsArchive Cittion Cline, Nthn Lyle, "Wet-Therml Time nd Plnt Aville Wter in the Seededs nd Root Zones Across the Sgerush Steppe Ecosystem of the Gret Bsin" (2014). All Theses nd Disserttions. 4384. https://scholrsrchive.yu.edu/etd/4384 This Disserttion is rought to you for free nd open ccess y BYU ScholrsArchive. It hs een ccepted for inclusion in All Theses nd Disserttions y n uthorized dministrtor of BYU ScholrsArchive. For more informtion, plese contct scholrsrchive@yu.edu.
Wet Therml Time nd Plnt Aville Wter in the Seededs nd Root Zones Across the Sgerush Steppe Ecosystem of the Gret Bsin Nthn L. Cline TITLE PAGE A disserttion sumitted to the fculty of Brighm Young University in prtil fulfillment of the requirements for the degree of Doctor of Philosophy Bruce A. Roundy, Chir Richrd Gill Sturt Hrdegree Bryn Hopkins Smuel St.Clir Deprtment of Plnt nd Wildlife Sciences Brighm Young University Mrch 2014 Copyright 2014 Nthn L. Cline All Rights Reserved
ABSTRACT Wet Therml Time nd Plnt Aville Wter in the Seededs nd Root Zones Across the Sgerush Steppe Ecosystem of the Gret Bsin Nthn L. Cline Deprtment of Plnt nd Wildlife Sciences, BYU Doctor of Philosophy Following wildfires, plnt mterils re direct-seeded to limit erosion nd nnul weed invsion. Seedlings often fil to estlish ecuse selected plnt mterils re not lwys well dpted to locl soil moisture nd temperture conditions. In n effort to help improve plnt mterils selection nd to evlute sites potentil revegettion, we hve worked towrd developing methodology to predict germintion nd root growth sed on site specific soil moisture nd temperture conditions. First, we chrcterized the seeded environment of 24 sgerush (Artemisi spp.) steppe sites throughout the Intermountin West to determine the wettherml time of five temperture rnges relevnt to germintion response nd therml-time model ccurcy (Chpter 1). Second, we predicted potentil germintion for 31 plnt mterils t those sme sites (Chpter 2). Third, in preprtion to predict root growth t multiple sites, we chrcterized the drying ptterns nd the ssocited plnt-ville wter for in the seedling root zone cross nine woodlnd (Juniperus spp. nd Piñus spp.) sites (Chpter 3). For ll of these studies, we determined the effects of tree reduction nd tree infilling phse t time of tree reduction. Our key findings re tht seededs generlly sum most wet-therml time t temperture rnges where the germintion rtes fit therml ccumultion models quite well (R2 0.7). The mjority of plnt mterils summed enough wet-therml time for potentil germintion t most sites during the fll, erly spring, nd lte spring. Soil drying primrily occurs from the soil surfce downwrd. Drying rtes nd Plnt ville wter ssocited with the first drying event increse with incresing soil depth. Root zone (1-30 cm) plnt-ville wter increses efore nd decreses fter the first spring drying event with incresing soil depth. Tree removl with incresing pretretment tree infilling phse generlly dded progress towrd germintion, plnt ville wter, nd wet-therml time in the seeded nd root zones of the sgerush steppe in the Gret Bsin. Becuse soil moisture nd temperture does not pper to e limiting for potentil germintion, comining germintion nd root growth models to crete more comprehensive model my llow for more roust prediction for seedling survivl. For either root growth or comined germintion nd root growth models, plnt ville wter nd wet-therml time efore the first spring drying period hold the most potentil for successfully predicting seedling survivl. Keywords: therml time, germintion, root growth, soil temperture, soil moisture, tree cutting, prescried fire, mechnicl shredding, SgeSTEP, chetgrss, wet dys, wet degree dys, woodlnd, seeded
ACKNOWLEDGEMENTS I express sincere pprecition to Dr. Bruce Roundy for providing the opportunity to conduct nd report on my doctorl reserch. I m sincerely grteful to him nd my dvisory committee for their suggestions, support, nd encourgement. I lso express pprecition to my der wife Hyl nd my children, Elizeth nd Chrles, who scrificed so much s I completed this project. I would lso like to thnk Hyl nd my fther, Morris Cline, for reviewing the erly drfts of this disserttion. I pprecite the use of the dt provided y the SgeSTEP project nd funding provided y The Gret Bsin Plnt Project. Finlly nd perhps most importntly, I would like to thnk God, our Fther, nd his Son, Jesus Christ, for ultimtely mking this experience possile.
TABLE OF CONTENTS Title Pge... i Astrct... ii Acknowledgements... iii Tle of Contents... iv List of Tles... viii List of figures... x Chpter 1: Wet Therml Time t Five Temperture Rnges in Seededs of the Sgerush Steppe Ecosystem... 1 Astrct... 2 Introduction... 4 Methods... 7 Study Sites... 7 Experimentl Design nd Anlysis... 7 Results... 11 Sites Chrcteristics... 11 Temperture Rnge Distriution nd Vrition for Sgerush nd Perennil grss, Sgerush, nd Crested Whetgrss Sites... 11 Woodlnd Removl Response... 12 Additionl Wet-Degree Dys in Response to Woodlnd Tree Removl Tretments nd Infilling Phses... 13 iv
Influence of Climte nd Site Physicl Chrcteristics... 15 Discussion... 15 Sesonl Wet Therml Time... 15 Woodlnd Removl Response... 17 Influence of Site Physicl Chrcteristics... 20 Mngement Implictions... 21 Literture Cited... 22 Tles... 30 Figures... 33 Chpter 2: Germintion Prediction of 30 Plnt Mterils using Soil Wter Potentil nd Temperture t 24 Gret Bsin Sites... 47 Astrct... 48 Introduction... 50 Methods... 52 Study Sites... 52 Therml Time Anlysis... 53 Results... 55 Sgerush nd Grsslnds... 56 Tree Removl Response... 56 Discussion... 59 v
Influence of Site Chrcteristics... 63 Conclusions... 64 Literture Cited... 66 Tles... 73 Figures... 81 Chpter 3: Spring drying nd wetting for seedling root zones in the Gret Bsin... 94 Astrct... 95 Introduction... 96 Methods... 99 Study Sites... 99 Study Design nd Tree Removl... 99 Root Zone Conditions nd Anlysis... 100 Results... 102 Effect of Soil Depth... 103 Tree Removl Response... 104 Additionl Wet dys nd Wet Degree Dys Before nd After the First Spring Drying Period... 105 Winter versus spring precipittion... 107 Discussion... 107 Tree removl response... 110 vi
Literture Cited... 113 Tles... 121 Figures... 125 vii
LIST OF TABLES Tle 1-1. Site loction informtion...30 Tle 1-2. List of woodlnd sites, yer of tretment, nd yers of soil moisture nd temperture yer dt used for post tretment nd woodlnd infilling phse nlysis...31 Tle 1-3. Sesonl wet degree dys (± SE) y temperture rnge (ᵒC) for yer since tretment in woodlnds...32 Tle 2-1. List of woodlnd sites, yer of tretment, nd yers of soil moisture nd temperture yer dt used for post tretment nd woodlnd infilling phse nlysis...73 Tle 2-2. Seedlots nd relted studies where constnt temperture germintion trils were conducted nd therml germintion equtions were developed...74 Tle 2-3. Percentge of tested instnces tht t lest 50% germintion ws predicted for different experimentl sites in the Gret Bsin...76 Tle 2-4. Fixed effects on progress towrd germintion from mixed model nlysis for sgerush nd perennil grss, crested whetgrss, nd sgerush experiments...77 Tle 2-5. Progress towrd germintion (± SE) for 31 seedlots t woodlnd sites for ech yer since tree reduction tretment...78 Tle 2-6. Fixed effects on PTG from mixed model nlysis for different yers since tree reduction for woodlnd sites...79 Tle 2-7. Fixed effects on dditionl progress towrd germintion for tree reduction tretments compred to no tree reduction 3 yr fter tretment...81 viii
Tle 3-1. List of woodlnd sites, yer of tretment, nd yers of soil moisture nd temperture yer dt used for post tretment nd woodlnd infilling phse nlysis...121 Tle 3-2. Percentge of time tht soils dried t shllower soils efore deeper soils (down), soils dried occurred t deeper soils efore shllower soils (up), or oth shllow nd deep soils dried t the sme time (even) during spring (1 Mrch to 30 June) for the first nd lst drying periods of the seson cross treted nd untreted plots...122 Tle 3-3. Site drying nd wetting conditions (± stndrd error nd ± confidence intervls) cross treted nd untreted sites...123 ix
LIST OF FIGURES Figure 1-1. Typicl therml time model illustrting dys -1 to germintion of seed supopultion s function of incution temperture...33 Figure 1-2. Precipittion nd ir temperture for sites...34 Figure 1-3. Averge precipittion nd ir temperture y seson for ech experiment...36 Figure 1-4. Wet degree dys y five temperture rnges nd sesons for sgerush nd perennil grss, crested whetgrss, nd sgerush sites...37 Figure 1-5. Averge nnul wet degree dys y seson nd temperture rnge...38 Figure 1-6. Wet degree dy estimtes y site, seson nd temperture rnge...39 Figure 1-7. Site verges of wet degree dys for second, third, nd fourth yers since tree reduction tretments for seeded temperture rnges in erly spring...41 Figure 1-8. Sesonl dditionl wet degree dys y tretment for non-optiml (top) nd optiml (ottom) temperture rnges...43 Figure 1-9. Additionl wet degree dys (tree tretment wet degree dys-untreted wet degree dys) for three woodlnd infilling phses t temperture rnges of 5 to < 10 C nd 10 to < 25 C...44 Figure 1-10. The distriution of wet degree dys for 19 sgerush steppe sites in the Gret Bsin s explined y six site physicl chrcteristics...45 Figure 2-1. Sesonl progress towrds germintion...81 x
Figure 2-2. Annul progress towrd germintion y seson...82 Figure 2-3. Sesonl progress towrd germintion y site nd experiment...83 Figure 2-4. Sesonl progress towrd germintion y seedlot nd plnt functionl group for sgerush nd perennil grss (top), crested whetgrss (middle), nd sgerush (ottom) experimentl sites...84 Figure 2-5. Sesonl progress towrd germintion y seedlot nd functionl group for the woodlnd experiment...86 Figure 2-6. Sesonl progress towrd germintion cross ll seedlots y woodlnd site for yer 2 (top), yer 3 (middle), nd yer 4 (ottom) since implementtion of tree reduction tretments...87 Figure 2-7. Additionl progress towrd germintion cross ll seedlots for tree removl methods y seson for ll woodlnd sites (left) nd Uth sites (right) for the second (top) nd fourth (ottom) yers since tretment...89 Figure 2-8. Additionl progress towrd germintion cross ll seedlots for tree reduction tretments implemented t different phses of tree infilling for the second (left) nd third (right) yer since tretment y seson...90 Figure 2-9. Additionl progress towrd germintion cross ll seedlots for ech microsite y yer since tree reduction tretment for lte spring (1 My to 30 June)...91 Figure 2-10. Cnonicl correspondence nlysis (CCA) ssociting site progress towrd germintion with erly spring (1 Mrch to 30 June) (top) nd 1 Septemer to 30 June (ottom) precipittion...92 xi
Figure 3-1. Winter precipittion (top), spring precipittion (middle), nd verge spring temperture (ottom) for four yers since tree reduction tretments...125 Figure 3-2. Dte of the first spring drying period y soil depth cross treted nd untreted plots. Yer 1 (Top) is represented y two Uth sites, Yers 2-4 (ottom) re represented y six to eight sites ech...127 Figure 3-3. Spring wet period frequency (numer of wet periods from 1 Mrch to 30 June) fter the first drying period t four soil depths for 4 yr since tree reduction tretments cross treted nd untreted plots...128 Figure 3-4. Spring wet dys (1 Mrch to 30 June) efore (top) nd fter (ottom) the first spring drying period t four soil depths for 4 yr since tree reduction tretments cross treted nd untreted plots...129 Figure 3-5. Spring (1 Mrch to 30 June) wet degree dys efore nd fter first spring drying period t four soil depths for 4 yr since tree reduction tretments cross treted nd untreted plots...130 Figure 3-6. Drying rtes for the first spring (1 Mrch to 30 June) drying period etween soil depths for 4 yr since tree reduction tretments cross treted nd untreted plots...131 Figure 3-7. Wet degree dys in spring (1 Mrch to 30 June) t four temperture rnges for four soil depths nd 4 yr since tree reduction tretments cross treted nd untreted plots...132 Figure 3-8. Spring wet degree dys for 4 yr since tree reduction tretments t the 10 to 25 C temperture rnge t four soil depths cross treted nd untreted plots...133 xii
Figure 3-9. Additionl wet dys (top) nd wet degree dys (ottom) for soil depth, tree removl methods, microsites, nd tree infilling phses the first yer fter tree reduction...134 Figure 3-10. Additionl wet dys (top) nd wet degree dys (ottom) efore (left) nd fter (right) the first spring (1 Mrch to 30 June) drying period y soil depth...135 Figure 3-11. Additionl wet dys (top) nd wet degree dys (ottom) fter prescried urning nd tree cutting efore (right) nd fter (left) the first spring (1 Mrch to 30 June) drying period...136 Figure 3-12. Additionl wet dys (top) nd wet degree dys (ottom) for the efore (right) nd fter (left) the first spring (1 Mrch to 30 June) drying period when trees were reduced y prescried urning or cutting t different phses of tree infilling...137 Figure 3-13. Additionl wet dys (top) nd wet degree dys (ottom) for efore (right) nd fter (left) the first spring (1 Mrch to 30 June) drying period for different microsites nd fter tree reduction tretments...138 Figure 3-14. Cnonicl correspondence nlysis (CCA) ssociting initil spring soil drying rte for nine Gret Bsin woodlnd sites with winter (1 Decemer to 28 Ferury ) nd spring (1 Mrch to 30 June) precipittion...139 xiii
CHAPTER 1: WET THERMAL TIME AT FIVE TEMPERATURE RANGES IN SEEDBEDS OF THE SAGEBRUSH STEPPE ECOSYSTEM Nthn L. Cline 1, Bruce A. Roundy 2, nd Willim F. Christensen 3 Authors re 1 Reserch Associte, Brighm Young University, Provo, UT, USA 84602, 2 Professor Rnge Science, Brighm Young University, Provo, UT, USA 84602, 3 Professor Sttistics, Brighm Young University, Provo, UT, USA 84602. This is Contriution Numer 96 of the Sgerush Steppe Tretment Evlution Project (SgeSTEP), funded y the U.S. Joint Fire Science Progrm nd The Gret Bsin Ntive Plnt Project. Correspondence: Bruce A. Roundy, Deprtment of Plnt nd Wildlife Sciences, 275 WIDB, Brighm Young University, Provo, UT 84602. Proposed Journl: Rngelnd Ecology nd Mngement 1
ABSTRACT Wet therml germintion prediction models hve een developed to improve plnt mteril selection for rngelnd revegettion. These models predict when the fstest germinting supopultions of seeds will germinte nd re sed on summtion of therml time when seeded soil wter mtric potentil > -1.5 MP. Models re developed y fitting germintion rtes to incution tempertures using liner nd non-liner regression. However, germintion rtes cn e highly vrile t tempertures less thn 5 C nd greter thn 25 C nd only loosely fit regression models. Previous reserch hs ssumed tht minority of therml time is spent in the seeded t these temperture rnges. We tested this hypothesis y quntifying nd compring sesonl wet degree dys (WDD mesure of therml time) of sgerush (Artemisi L.) -steppe seededs t five temperture rnges for up to 9 yr cross 24 sites. Effects of three piñon nd juniper (Pinus spp. nd Juniperus spp.) tree removl tretments nd three woodlnd infilling phses t time of tree reduction were lso compred. We summrized the influence of site physicl chrcteristics on WDD. We found tht seededs sum mjority of WDD etween 5 C nd 25 C, indicting tht therml models should work well for predicting field germintion in most cses. Seededs summed enough WDD for potentil germintion of some species t 0 to 5 C (42.5 ± 3.89 WDD in Mrch-April) nd t 25 to < 30 C (52.9 ± 6.37 WDD in My-June) on some yers nd sites. However, these exceptions mount to reltively smll percentge (12-20%) of totl WDD for these sesons. Tree infilling or removl dded WDD t 0 to < 5 C nd 25 to < 30 C on few sites, ut germintion models should still e ccurte enough to predict effects of vegettion mnipultions on germintion potentil. Winter 2
precipittion, erly spring precipittion, ir temperture, nd elevtion were positively ssocited with higher erly spring WDD. 3
INTRODUCTION Reserchers use therml-time models to predict post-dormncy germintion in rnge weed nd revegettion species to help predict seedling estlishment for rngelnd revegettion (Hrdegree et l., 1999; 2002). Therml-time models estimte germintion timing y summing progress towrd germintion s function of degree-dys ove se temperture when seeds re imied (Grci-Huidoro et l., 1982; Jordn nd Hferkmp, 1989; Roundy nd Biedenender, 1996; Hrdegree et l., 2002; McDonld, 2002; Brdford, 2002). Therml-time models re developed y mesuring percent germintion over time for rnge of constnt tempertures. Germintion rte (quntified s dys -1 to given germintion percentge) is modeled s function of incution temperture using liner nd non-liner regression for temperture rnges tht re optiml (tempertures where the germintion rte is highest), suoptiml, or supr-optiml (Fig. 1) (Grci-Huidoro et l., 1982; 1982; 1985; Covell et l., 1986; Roundy nd Biedenender, 1996; Hrdegree nd Vn Vctor, 1999; Hrdegree et l., 1999; Alvrdo nd Brdford, 2002; Hrdegree, 2006; Roundy et l., 2007; Rwlins et l., 2012). These temperture rnges vry y species nd even popultions or collections of popultions of different species. Generlly, for upper su-optiml nd optiml tempertures of 5 to 25 C, therml-time models fit constnt temperture germintion dt well (R 2 > 0.7) (Roundy et l., 2007), wheres lower su-optiml tempertures <5 C nd supr-optiml tempertures >25 C hve more vrile germintion time response (Hrdegree et l., 1999; Hrdegree nd Winstrl, 2006; Rwlins et l., 2012). If sgerush (Artemisi spp.) steppe seededs spend sustntil mount of therml time when wet (soil mtric potentil > - 1.5 MP) within the lower su-optiml nd suproptiml temperture rnges, the models my hve reduced reliility. 4
Roundy et l. (2007) defined wet therml time s the sum of hourly soil tempertures > 0 C or some other se temperture for ech hour tht the seeded hs soil mtric potentil > - 1.5 MP or some other se wter potentil over period time. Hours re converted to dys nd referred to s wet degree dys (WDD) (Roundy et l., 2007). Some plnt mterils, such s chetgrss (Bromus tectorum L.), germinte with 36 to 50 wet degree dys (WDD) (Hrdegree 1994, Trudgill et l. 2000). Common revegettion plnt mterils, such s lueunch whetgrss (Pseudoroegneri spict (Pursh) Á. Löve) nd squirreltil (Elymus elymoides (Rf.) Swezey) require n estimted 60 to 80 nd 130 to 150 WDD for 50% of seeds to germinte, respectively (Hrdegree 1994). Previous chrcteriztions of WDD t lower suoptiml nd suproptiml temperture rnges re limited (Hrdegree, 2006; Rwlins et l., 2012). Identifying site physicl chrcteristics tht most influence WDD cross the sgerush steppe my llow for future development of methods for predicting germintion where soil moisture nd temperture dt re not ville. Sgerush steppe climte in the Gret Bsin is typiclly chrcterized s hving hot, dry summers nd cold, wet winters. During the hot nd cold periods, there is evidence tht seededs of the sgerush steppe my spend time t lower su-optiml nd supr optiml temperture rnges of elow 5 C nd ove 25 C. Seededs t two crested whetgrss sites (Agropyron cristtum (L.) Gertn.) in Uth spent 22% of the fll to spring wet dys etween 0 C nd 5 C (Rwlins et l., 2012). Hrdegree et l. (1999) indicted tht night tempertures in April nd into My often reched elow 5 C nd 10 C t one site in Idho. Prediction of germintion in seededs tht spend significnt mount of time t non-optiml tempertures will require 5
therml-time models tht represent ccurte germintion timing t those tempertures, or prediction my e limited if germintion is highly vrile t these rnges. Site, seson, or nnul vritions in loclized climte or ltertions to vegettion structure such s fire or fuel-control tretments my chnge seeded WDD y ltering soil tempertures nd evpotrnspirtion (ET) (Gifford nd Shw, 1973; Gifford, 1975; 1982; Everett nd Shrrow, 1985; Dvies et l., 2007; Whittker et l., 2008). Roundy et l. (2007) found tht for chetgrss (Bromus tectorum L.), differences etween sesons hd the gretest effect on predicted potentil germintion, followed y site nd yer, while disturnce tretments hd smll ut significnt effects on predicted potentil germintion (P < 0.05). Prter nd DeLuci (2006) found tht ET nd soil-het flux were higher on post-fire plots thn on djcent ntive sgerush plots. They concluded tht the differences were due to incresed soil-wter content nd incident solr rdition on the post-fire plots. Tretments tht reduce cnopy cover nd trnspirtion my reduce soil-wter loss, especilly s the woodlnd infilling increses (Roundy et l., 2014; Young et l., 2013). However, the effects of infilling on seeded wter nd temperture dynmics re not well understood (Breshers et l., 1998). Climtic fctors such s the timing nd mount of sesonl precipittion strongly ffect seeded wter dynmics (Ogle nd Reynolds, 2004; Btes et l., 2006; 2007). Site physicl fctors such s slope nd elevtion should likewise e strongly ssocited with seeded temperture nd moisture conditions (Reid, 1973; Cntón et l., 2004; Weiserg et l., 2007; Bochet et l., 2007). Determintion of site chrcteristics, such s solr rdition, slope, precipittion, nd temperture, which ffect seeded conditions nd germintion prediction my llow us to etter select plnt mterils for estlishment. Although site chrcteristics in the 6
Gret Bsin hve een ssocited with soil wter nd tempertures t depths elow the seeded (Jensen et l., 1989; Ryel et l., 2010), seededs hve not een similrly chrcterized. Here, we ddress two questions regrding sesonl WDD t optiml nd non-optiml temperture rnges. First, in sgerush steppe communities, wht effect do site, seson, yer, woodlnd removl tretment, nd woodlnd infilling phse hve on sesonl WDD t optiml nd non-optiml temperture rnges? Second, which site chrcteristics influence seeded WDD? We quntified WDD t temperture rnges relevnt to wet therml-time models for predicting potentil germintion rtes. Also, we compred WDD y sesons, sites, yers, tree removl tretments, nd tree infilling phses. Further, we determined which climte nd site chrcteristics were ssocited with seeded WDD. METHODS Study Sites We used soil wter potentil nd temperture dt collected from soil monitoring sttions instlled cross the Gret Bsin. Experiments re designted sgerush nd perennil grss, crested whetgrss (Agropyron cristtum (L.) Gertn.), sgerush, nd woodlnds (Piñus spp. nd Juniperus spp.) (Tle 1). The nine sgerush nd perennil grss sites re descried in Roundy et l. (2007), Chmers et l. (2007) nd Blnk et l. (2007). The two crested whetgrss sites re descried in Hulet et l. (2010) nd Rwlins et l. (2012). Sgerush nd woodlnd site experiments included three nd nine sites, respectively, nd re descried in McIver et l. (2010). Dt from the Stnsury site were not included in nlyses from summer 2009 to 2011 due to wildfire. Experimentl Design nd Anlysis 7
Ech experiment ws rndomized lock nd mixed model nlysis of vrince (SAS Institute, Inc.) ws used to estimte sesonl WDD y temperture rnge nd to determine effects of specific fctors for ech experiment. At ech site of the sgerush nd perennil grss experiment, hourly verges were recorded t two soil wter mtric potentil nd three soil temperture plots tht were replicted nd untreted. We verged replicted hourly mesurements of soil wter mtric potentil nd temperture y site s ws done y Roundy et l. (2007). Sites were considered rndom locks cross the region. Fixed fctors were seson nd yer. At the crested whetgrss experiment, soil monitoring sttions were instlled in four replicte locks t ech of two sites s descried in Rwlins et l. (2012). Soil wter mtric potentil nd temperture were mesured nd verged cross three untreted replicte plots in ech of four locks t ech site. Block ws considered rndom, while site, seson, nd yer were considered fixed fctors. The sgerush experiment ws set up cross the region with ech of the three sites considered rndom lock s descried in McIver et l. (2010). At ech site, monitoring sttions were instlled within plot (rnging from 30 to 81 h) where perennil grss cover ws greter thn other res within the plot). Soil wter mtric potentil nd soil temperture were mesured under shru cnopy, or djcent to tll perennil grss, short perennil grss, nd within n interspce. Seson nd yer were considered fixed fctors. The woodlnd tretments were pplied cross the region s descried in Miller et l. (2014) nd Roundy et l. (2014). Ech of nine sites ws considered rndom lock. At ech site, three tree removl tretments were pplied to 8-20 h plots: prescried urning, tree felling (lso known s cut nd drop in plce), nd untreted. Also, mechnicl shred or mstiction 8
tretment ws pplied to the four Uth sites s descried in Roundy et l. (2014; 2014), Young et l. (2013), nd Cline et l. (2010). Within ech tretment, monitoring sttions were instlled in ech of three woodlnd infilling phses (Miller et l., 2007). The three phses of tree infilling re: Phse 1 represents community where understory vegettion is dominnt with trees present. Phse 2 represents community where understory vegettion nd trees co-dominte. Phse 3 represents community where trees re dominnt. Ner (< 3 m) ech monitoring sttion, soil wter potentil nd temperture were mesured t tree drip line, shru, nd interspce. Fixed fctors were seson, yer, tree removl tretment, nd tree infilling phse. We mesured seeded soil wter potentil nd temperture using gypsum locks (Delmhorst, Inc., Towco, NJ) nd thermocouples t 1-3 cm soil depth. Gypsum locks electricl resistnce estimted soil wter potentils down to -1.5 MP using stndrd clirtion curve (Cmpell Scientific, Inc. 1983). Mesurements were mde every minute nd hourly verges were recorded on Cmpell Scientific (Logn, UT), Inc. CR10X nd CR1000 microloggers. We mesured precipittion nd mient ir temperture with Texs Electronics, Inc. (Dlls, TX) tipping-ucket rin guge nd thermistor from Cmpell Scientific, Inc. (107 temperture proe with gill shield) t ech site. Complete precipittion nd mient ir temperture dt were not ville for sgerush nd perennil grss sites from 2002 to 2005. Also, dily mximum nd minimum ir tempertures were mesured t sgerush nd woodlnd sites only. We summed WDD for five temperture rnges for ech seson. Temperture rnges were: 0 C to less thn 5 C (0 to < 5 C), 5 C to less thn 10 C (5 to < 10 C), 10 C to less thn 25 C (10 to < 25 C), 25 C to less thn 30 C (25 to < 30 C), nd 30 C to less thn 35 C (30 to < 35 C). We did not include temperture rnges ove 35 C ecuse preliminry 9
nlyses indicted tht soils were rrely wet nd therefore WDD lmost lwys summed to zero t tht temperture rnge. Hrdegree et l. (2002) nd Hrdegree (2006) reported incresed sttisticl error in seed germintion trils t temperture rnges elow 5 C nd ove 25 C. Sesons were defined s: Erly spring 1 Mrch through 31 April, lte spring-1 My through 30 June; summer 1 July through 31 August; fll 1 Septemer through 30 Novemer; winter 1 Decemer through 28 Ferury. Dt generlly hd norml distriution nd sttisticl outliers were removed. Significnt differences mong fixed fctors were determined y the Tukey- Krmer significnce test (P < 0.05). For site nlysis t sgerush nd perennil grss, sgerush, nd woodlnd sites, we used Best Unised Liner Predictors (BLUPs) (Littell et l., 1996) to estimte verge WDD y temperture rnge. We summrized the influence of five site chrcteristics on WDD using Cnonicl Correspondence Anlysis for erly spring (Mrch-April) nd fll through spring (1 Septemer through 30 June) (PC-ORD v. 6.0, McCune nd Mefford, 2010). We only used dt from untreted plots nd dt for erly spring included yers 2008 through 2011, while dt for fll through spring included yers 2008 through 2010 The site chrcteristic mtrices included summed solr rdition (WH/m 2 ), elevtion (m), nd slope (degrees) derived from Digitl Elevtion Model (DEM) (ArcGIS v. 9.3.1 Sptil Anlyst Tool). Sites with missing dt were excluded from the finl ordintion. Row nd column scores were stndrdized y using the centering nd normlizing option (Peck, 2010). Ordintion significnce ws determined y rndomiztion nd Monte Crlo tests (P < 0.05). 10
RESULTS Sites Chrcteristics Precipittion nd temperture vried y site, seson, nd yer during the study for ll experiments (Figs. 2-3). Highest precipittion ws mesured in winter for sgerush nd perennil grss, sgerush, nd woodlnd sites in 2008, 2009, nd 2010, s well s in woodlnds in 2007. On crested whetgrss sites, precipittion verged highest in erly nd lte spring. Highest tempertures were in summer, followed y lte spring, fll, erly spring, nd winter. Temperture Rnge Distriution nd Vrition for Sgerush nd Perennil grss, Sgerush, nd Crested Whetgrss Sites Generlly, WDD verged highest for 10 to < 25 C nd second highest for the upper su-optiml rnge of 5 to < 10 C for erly spring, lte spring, nd fll (Fig. 4). As expected, the lower rnge of 0 to < 5 C hd most WDD in winter. The 0 to < 5 C rnge during the erly spring verged s high s 42.6 ± 3.89 WDD t crested whetgrss sites nd 42.1 ± 6.12 WDD t sgerush nd perennil grss sites. The 25 to < 30 C temperture rnge verged s high s 52.9 ± 6.37 WDD t sgerush nd perennil grss sites during lte spring. Becuse of lrge differences in summed WDD etween the 10 to < 25 C temperture rnge nd the other temperture rnges, we seprtely nlyzed interctions etween temperture rnge nd yer. For non-optiml temperture rnges, the interction etween sesonl WDD nd yer ws significnt for ll sesons within sgerush nd perennil grss (erly spring, F24,241=2.02, P = 0.0043), sgerush ( erly spring, F6,265=2.83, P = 0.0043), nd crested whetgrss (erly spring, F4,92=4.66, P = 0.0018) sites. Annul WDD vried y seson nd temperture rnge (Figs. 4-6). The nnul WDD t 0 to < 5 C verged s high s 52.5 ± 3.97 WDD during the erly spring, 11
49.2 ± 7.57 during the fll, nd 52.2 ± 1.31 during the winter, ll during 2010. The 25 to < 30 C rnge exceeded n verge 50 WDD for three of the nine sgerush nd perennil grss sites, while ll other estimtes did not exceed 35 WDD. Wet degree dys for the optiml temperture rnge of 10 to < 25 C vried every yer t ll three sets of sites (erly spring, sgerush nd perennil grss F4,21=2.02, P = 0.0043, sgerush F2,61.2=4.04, P = 0.0225, crested whetgrss F4,21=7.82, P = 0.0005). WDD verged s high s 235.1 ± 31.3 in the erly spring, 413.59 ± 39.9 WDD during lte spring, 58.7 ± 6.09 WDD during the summer, nd 232.3 ± 12.9 WDD during the fll. WDD did not generlly exceed 10 during the winter. In generl, WDD vried y site more t 5 to < 10 C nd 10 to < 25 C during most sesons thn t 0 to < 5 C, 25 to < 30 C, nd 30 to < 35 C (Fig. 5). Woodlnd Removl Response Averge nnul WDD were 116.3 ± 13.6, 210.0 ± 13.6, 469.7 ± 13.7, 57.0 ± 13.6, nd 29.0 ± 13.7 for the 0 to < 5 C, 5 to < 10 C, 10 to < 25 C, 25 to < 30 C, nd 30 to < 35 C temperture rnges. Generlly, verge WDD incresed y the third yer post tretment for the 0 to < 5 C, 5 to < 10 C, 10 to < 25 C temperture rnges, while WDD for the 25 to < 30 C nd 30 to < 35 C temperture rnges did not chnge (Tle 3). Becuse the tretment yer vried y sites nd most sesons hd n unequl numer of dys, we seprtely estimted verge WDD for ech seson y yer-since-tretment (Roundy et l., 2014). As with the non-woodlnd experiments, we lso seprtely nlyzed non-optiml temperture rnges from the optiml temperture rnge. Burning nd tree felling tretment comprisons t non-optiml nd optiml temperture rnges were significntly different for 11 of 17 sesons since tretment (3 yr, erly spring, 12
F2,247=28.15, P < 0.0001). Tretment plots were generlly different from untreted plots t 0 to < 5 C. Where there were significnt differences t 5 to < 10 C, treted plots generlly hd more WDD thn untreted plots during erly spring nd fll. Also, urned plots occsionlly hd more WDD thn untreted plots t 25 to < 30 C nd 30 to < 35 C during the lte spring nd summer. At 10 to < 25 C, treted plots hd more WDD thn untreted plots during the first yer fter tretment nd for erly nd lte spring for the second through fourth yer fter tretment (P < 0.05). Also t 10 to < 25 C, tree felled plots hd more WDD thn untreted plots, ut often hd less WDD thn urned plots. Due to WDD vrition mong sites (Fig. 7), we determined the verge chnge in WDD in seededs s result of tretment y compring the difference etween treted nd untreted plots t ech site (Roundy et l., 2014). Additionl Wet-Degree Dys in Response to Woodlnd Tree Removl Tretments nd Infilling Phses Tretment Response. Temperture rnge ws significnt for 12 of 17 sesons since tretment when compring non-optiml temperture rnges (P < 0.05). The interction etween temperture rnge nd tree removl tretment ws significnt for 8 of 17 sesons including erly spring (yr 4, F2,651=6.25, P = 0.0066), lte spring (yr 4, F3,613=2.9, P = 0.0343), summer (yr 1, F3,561=9.81, P < 0.0001), nd fll (yr 2, F3,587=3.52, P = 0.015). Where significnt, tree removl tretments generlly dded WDD. Most increses were oserved t the upper su-optiml rnge of 5 to < 10 C nd the optiml rnge of 10 to < 25 C. Also, dditionl WDD tended to diminish with yer since tretment (Fig. 8). Where there were significnt differences etween urning nd mechnicl tretments, urning usully dded more WDD thn cutting (P < 0.05). Most differences were found during 13
erly nd lte spring t 5 to < 10 C nd 10 to < 25 C. However, during the lte spring of the third nd fourth yer post-tretment, cutting dded 10 nd 14 more WDD thn urning t 5 to < 10 C (P < 0.05). Where mechnicl shredding ws compred to urning nd cutting t Uth sites, urned nd shredded plots t 5 to < 10 C nd 10 to < 25 C hd up to 20 nd 70 more WDD thn cut plots during erly spring. Also, urned plots hd pproximtely 32 more WDD thn shredded plots during lte spring of the second yer t 25 to < 30 C. Burning lso dded etween 5 nd 32 more WDD thn shredding in the fll nd winter t 0 to < 5 C nd 5 to < 10 C, on verge (P < 0.05). Woodlnd Infilling Phse. At non-optiml temperture rnges, the interction of temperture rnge with tree infilling phse t time of tretment ws significnt for erly spring (F6,156 = 5.15, P < 0.0001) nd lte spring (F6,133 = 11.77, P < 0.0001) of the first yer fter tretment nd during erly spring of the third nd fourth yers fter tretment cross tree removl methods. During erly spring of the second yer, effects of woodlnd infilling phse were mrginlly significnt (F6,651= 2.01, P = 0.0625). At the optiml temperture rnge of 10 to < 25 C, WDD for tree infilling phses were significntly different during erly spring nd lte spring of the third yer (ES, F2,130 = 5.72, P = 0.0042; LS, F2,135 = 4.85, P = 0.0093) nd erly spring of the fourth yer (ES, F2,115 = 6.85, P = 0.0015). Similr to non-optiml comprisons, erly spring of the second yer ws mrginl, ut not significnt (P > 0.05). Generlly, incresed tree infilling dded WDD t 5 to < 10 C nd 10 to < 25 C during the erly spring (Fig. 9), ut only occsionlly during other sesons or t other temperture rnges (P < 0.05). 14
Influence of Climte nd Site Physicl Chrcteristics The CCA indicted tht erly spring WDD ws ssocited most with erly spring nd winter precipittion, elevtion, nd mient ir temperture. The resulting ordintion ws significnt (Fig. 10, P = 0.008). Also, the ssocition etween these vriles nd the vrition mong sites for erly spring WDD (xis 1 R 2 = 0.834, xis 2 R 2 = 0.678, xis 3 R 2 = 0.420) ws lso significnt (P = 0.018). The first xis explined 44.6 % of the vriility in WDD, while ll three xes explined 49.9% of the vriility. Becuse xis 1 ccounted for most of the vrition explined y the model, we focus our discussion on its elements. Winter precipittion, spring precipittion, nd elevtion were positively correlted with xis 1, while mient ir temperture ws negtively correlted with xis 1. Except for Bridge Creek, Scipio, nd the Boulter Creek Elymus sites, WDD of woodlnd nd sgerush nd perennil grss sites were ssocited with incresing elevtion, incresing spring nd winter precipittion, nd decresing mient ir temperture. For Scipio nd Boulter Creek Elymus, s well s sgerush nd crested whetgrss sites, WDD were more strongly ssocited with incresing mient ir temperture, decresing elevtion, nd decresing spring nd winter precipittion. For Mill Cnyon High, WDD were strongly ssocited with incresing winter precipittion nd elevtion, s well s decresing mient ir temperture. Assocition of site climte nd physicl chrcteristics with WDD for Septemer through June ws not significnt (P = 0.104). DISCUSSION Sesonl Wet Therml Time The ccurcy of therml-time models for estimting germintion in field seededs depends on whether or not the mjority of summed WDD is within the temperture rnge where 15
vrition in germintion rte is miniml reltive to incution temperture. Hrdegree et l. (2002) reported incresed stndrd error in the totl germintion percentge t elow 5 C nd ove 25 C. We found miniml WDD t 5 to < 10 C nd 10 to < 25 C temperture rnges where vriility in the germintion response hs een found to e miniml, verged the most WDD dys in erly spring, lte spring, nd fll (Fig. 4). These findings re consistent with the ssumption mde y Rwlins et l. (2012) tht non-optiml temperture rnges sum smll percentge of therml time compred to more optiml temperture rnges. Despite the fct tht most WDD were summed where vrition in germintion rte is miniml, seed eds occsionlly summed sufficient WDD from 0 to < 5 C nd 25 to < 30 C for potentil germintion prediction. All four sites verged etween 36 nd 52 WDD during erly spring t 0 to < 5 C. Also t 25 to < 30 C, lte spring verged up to 52.4 ± 6.37 WDD (Fig. 6). With chetgrss needing pproximtely 40 to 50 WDD for potentil germintion prediction, wet therml time models my overestimte the time to chetgrss germintion s result of underestimting progress towrd germintion t these temperture rnges (Rwlins et l., 2012; 2012). Additionlly, fluctution in wet dys (> 1.5 MP) mong sites nd yers in the top 30 cm of the soil profile hve een found (Jensen et l., 1989; Roundy et l., 2014). In our study, differences etween sesons, sites, nd yers were generlly t the upper su-optiml nd optiml temperture rnges. However, there were occsions where WDD t non-optiml temperture rnges were sufficient for potentil germintion s result of these fluctutions. For exmple, some sites during the winter of 2010 verged s high s 45 WDD (Fig. 6). The yer 2010 hd greter precipittion during fll nd winter compred to the previous few yers 16
during the sme sesons. This increse in precipittion likely llowed for the incresed summtion of WDD. Potentil-germintion predictions my e less ccurte when sufficient WDD re summed t the lower su-optiml rnge of 0 to < 5 C or t the supr optiml rnges ove 25 C. However, Rwlins et l. (2012) found tht wet therml time models were most ccurte (75% to 95%) in predicting potentil germintion etween lte winter (21 Fe) nd mid spring (10 My), period where 26% of wet dys were t 0 to < 5 C. A possile explntion for this pprent inconsistency my e tht se tempertures (the temperture where the germintion rte is zero) for mny plnt mterils re ove 0 C nd, therefore there is miniml summed wet therml time t 0 to < 5 C. Chetgrss, lueunch whetgrss, nd squirreltil hve se tempertures t pproximtely 1.5 to 2 C (Hrdegree, 1994; Hrdegree et l., 1999; 2008). Another explntion might e tht s dy-time tempertures increse through the erly spring, the mount of wet therml time the seeded spends t wrmer tempertures produces potentil germintion response well efore sufficient wet therml time is summed t 0 to < 5 C (Hrdegree, 1994; Hrdegree et l., 2008). Woodlnd Removl Response Chnges in plnt community structure like woodlnd tree removl tretments implemented t different tree infilling phses my influence soil moisture nd temperture dynmics. Tree reduction hs een reported to increse time of plnt-ville wter during the spring y s much s 26 dys to six weeks (Btes et l., 2000; Roundy et l., 2014; Young et l., 2013). Also, Roundy et l (2014) reported n dditionl 332.1 WDD during the spring t 13 to 30 cm soil depth compred to untreted plots. Similrly, we found tht tree reduction dded WDD in the seeded generlly t temperture rnges where WDD summtion is highest for ech 17
seson. In generl, these dditions re t temperture rnges where germintion vriility is low. However, temperture rnges with more vriility in germintion response do occsionlly show incresed WDD s result of tretment (Fig. 8). For exmple, s much s 12.1 ± 2.88 WDD nd 18.2 ± 6.67 WDD ws dded in fll nd winter t 0 to < 5 C s result of tretment. These dditions re still reltively smll nd re not likely to e sufficient to influence potentil germintion predictions. However, in conjunction with site nd nnul fluctutions, tretments my result in situtions where potentil germintion predictions my e influenced t some nonoptiml temperture rnges. Roundy et l. (2014) found tht there ws little difference in plnt ville wter etween urning nd mechnicl tretments t 13-30 cm soil depth the first 4 yr fter tretment. For the seeded, we found differences in WDD during some erly springs, lte springs, flls, nd one winter for most mesured temperture rnges (Fig. 8). However, these differences were generlly spordic nd often inconsistent. Where differences etween tree removl tretments occurred, ltering the plnt community structure my hve influenced the summtion of WDD y chnging ET dynmics. Burning removes tree nd understory vegettion which llows for more incident solr rdition (Prter nd DeLuci, 2006). Incresed solr rdition could result in erly post-winter thw nd wrming of the soil surfce t lest until the understory vegettion recovers nd my explin why urned plots often hd higher dditionl WDD thn t shredded nd cut plots. Mechnicl tretments likely uffer the seeded to chnges in climte y shielding the soil surfce with tree skeleton (cutting), shredded residue (mechnicl shredding), nd residul understory vegettion. Shredded residue hs een found to decrese soil wter loss from ET nd runoff (Chung nd Horton, 1987; Enrique et l., 1999; Cline et l., 2010). Shielding of the soil 18
surfce during short durtion precipittion events my result in precipittion interception. Further, ny decomposition s result of ville nitrogen during the first few yers following tretment my occur when soil moisture is high (Buggelnl nd Rynk, 2002; Ru et l., 2007; Young et l., 2013). The resulting positive thermodynmic condition, s well s effects resulting from chnges in community structure, my explin why shredding often hs more dditionl WDD thn cutting during erly spring. In ny cse, differences etween tretments tend to diminish y the fourth yer fter tretment. Roundy et l. (2014) found tht tree reduction y fire or mechnicl methods resulted in incresed WDD where pretretment woodlnd infilling ws higher t 13-30 cm soil depth. Generlly, our nlysis of woodlnd infilling phse for the seeded ws similr to their findings t the su optiml nd optiml temperture rnges. Often phse 3 hd significntly more WDD thn phse 1 (P < 0.05) where trees were reduced. Becuse trees re ssumed to e using the mjority of plnt ville wter, phse 3 tree removl would represent lrger resource pulse ( temporry increse in ville resources) thn t lower infilling phses (Ryel et l., 2010; Roundy et l., 2014; Young et l., 2013). This resource pulse my fcilitte weed invsion (Chmers et l., 2007; Roundy et l., 2014). Weed cover hs een found to increse fter tretment where tree infilling ws greter efore tretment (Roundy et l., 2014) Although the summtion of WDD t non-optiml temperture rnges ws usully smll, the potentil for overestimting the timing of potentil germintion remins concern. Rwlins et l. (2012) found tht therml-time models frequently overestimte germintion timing. Hrdegree et l. (1999) suggested tht overestimtion in therml time models my e result of germintion rte sensitivity ner se tempertures. Rwlins et l. (2012) lso stted tht 19
progress towrd germintion my e underestimted s result of summing WDD t nonoptiml temperture rnges where germintion response is not well understood (Rwlins et l., 2012). Consequently, when climte conditions llow for summtion of WDD t the lower suoptiml or supr optiml temperture rnges, more investigtion into germintion response my improve ccurcy of potentil germintion predictions in some plnt mterils. Influence of Site Physicl Chrcteristics Btes et l. (2006) found reduction in plnt productivity nd n increse in re ground t Gret Bsin sgerush site s result of pplying mjority of sesonl wter etween April nd July s compred to etween Octoer nd Mrch. This indictes tht sites with high winter precipittion my hve more WDD during the erly spring thn sites with low winter precipittion. Our CCA nlyses cross ll temperture rnges nd 19 sites indicted tht oth erly spring nd winter precipittion, s well s elevtion nd mient ir temperture, influence erly spring WDD in the seeded. Wet degree dys t wetter, cooler sites like Underdown Cnyon High nd Mill Cnyon High tend to e positively influenced y incresing winter precipittion, incresing elevtion, nd decresing mient ir temperture. On wrmer, drier sites like Skull Vlley, Lookout Pss, nd Scipio WDD tend to e influenced with decresing erly spring precipittion, decresing elevtion, nd incresing mient ir temperture. Wetter, cooler sites hve more plnt cover thn the wrmer, drier sites (Chmers et l., 2013). Plnt production relies on sufficient WDD in oth the seeded for germintion nd in the root zone for root growth. However, frequent rewetting of the seeded my promote germintion nd lengthen wet periods in the deeper root zone soil depths. One opportunity to mke therml time models more prcticl in ppliction to revegettion projects in the Gret Bsin is to model WDD using site chrcteristics. We hve 20
identified site chrcteristics ssocited with erly spring WDD cross rod rnge of conditions in the Gret Bsin. However, our nlysis ws not sufficient to estimte WDD t sites where soil moisture nd temperture conditions re not known. An nlysis of site chrcteristics t finer scle my increse the percent vriility explined y the CCA nd my revel other importnt predictors of WDD. Mngement Implictions On verge, WDD t lower su-optiml nd supr-optiml temperture rnges re not likely to e sufficient to influence germintion s predicted y wet therml time models during the erly spring. Where germintion response for individul plnt mterils hs reltively good fit to estimted response etween 5 nd 25 C, wet therml time models my e sufficiently precise to determine the site potentil for revegettion using site specific soil climte conditions. These models my lso improve plnt mteril selection for rngelnd revegettion projects for the sgerush steppe ecosystem. Tree removl tretments should not gretly influence results of model precision s it reltes to wet therml time. 21
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Dvies, K. W., J. D. Btes, nd R. F. Miller. 2007. Short-term effects of urning Wyoming ig sgerush steppe in southest Oregon. Rngelnd Ecol. Mnge. 60:515 522. Enrique, G., I. Brud, T. Jen-Louis, V. Michel, B. Pierre, nd C. Jen-Christophe. 1999. Modelling het nd wter exchnges of fllow lnd covered with plnt-residue mulch. Ag. Forest Meteorol. 97:151 169. Everett, R. L., nd S. H. Shrrow. 1985. Soil wter nd temperture in hrvested nd nonhrvested pinyon-juniper stnds soil wter nd hrvested nd nonhrvested stnds. USDA For Ser IMRS-INT-342:1 4. Grci-Huidoro, J., J. L. Monteith, nd G. R. Squire. 1982. Time, temperture nd germintion of perl millet (Pennisetum typhoides s. & h.) I. Constnt temperture. Journl of Experimentl Botny 33:288 296. Grci-Huidoro, J., J. L. Monteith, nd G. R. Squire. 1982. Time, temperture nd germintion of perl millet (Pennisetum typhoides S. & H.) II. Alternting temperture. J. Exp. Bot. 33:297 302. Grci-Huidoro, J., J. L. Monteith, nd G. R. Squire. 1985. Time, temperture nd germintion of perl millet (Pennisetum typhoides S. & H.) III. Inhiition of germintion y short exposure to high temperture. J. Exp. Bot. 36:338 343. Gifford, G. F. 1975. Approximte nnul wter udgets of two chined pinyon-juniper sites. J. Rnge Mnge. 28:73 74. 24
Gifford, G. F. 1982. Impct wter of urning in ptterns the nd grzing soil on type. J. Rnge Mnge. 35:697 699. Gifford, G. F., nd C. B. Shw. 1973. Soil moisture ptterns on two chined pinyon-juniper sites in Uth. J. Rnge Mnge. 26:436 440. Hrdegree, S. P. 1994. Mtric priming increses germintion rte of Gret Bsin ntive perennil grsses. Agron. J. 86:289 293. Hrdegree, S. P. 2006. Predicting germintion response to temperture. I. Crdinl-temperture models nd supopultion-specific regression. Ann. Bot. 97:1115 1125. Hrdegree, S. P., T. A. Jones, F. B. Pierson, P. E. Clrk, nd G. N. Flerchinger. 2008. Dynmic vriility in therml-germintion response of squirreltil (Elymus elymoides nd Elymus multisetus). Environ. Exp. Bot. 62:120 128. Hrdegree, S. P., T. A. Jones, nd S. S. Vn Vctor. 2002. Vriility in therml response of primed nd non-primed seeds of squirreltil [Elymus elymoides (Rf.) Swezey nd Elymus multisetus (J. G. Smith) M. E. Jones]. Ann. Bot. 89:311 319. Hrdegree, S. P., nd S. S. Vn Vctor. 1999. Predicting germintion response of four coolseson rnge grsses to field-vrile temperture regimes. Environ. Exp. Bot. 41:209 217. Hrdegree, S. P., S. S. Vn Vctor, F. B. Pierson, nd D. E. Plmquist. 1999. Predicting vriletemperture response of non-dormnt seeds from constnt-temperture germintion dt. J. Rnge Mnge. 52:83 91. 25
Hrdegree, S. P., nd A. H. Winstrl. 2006. Predicting germintion response to temperture. II. three-dimensionl regression, sttisticl gridding nd itertive-proit optimiztion using mesured nd interpolted-supopultion dt. Ann. Bot. 98:403 410. Hulet, A., B.. Roundy, nd B. Jessop. 2010. Crested whetgrss control nd ntive plnt estlishment in uth. Rngelnd Ecol. Mnge. 63:450 460. Jensen, M. E., G. H. Simonson, nd R. E. Kene. 1989. Soil temperture nd moisture regime reltionships within some rngelnds of the Gret Bsin. Soil Sci. 147:134 139. Jordn, G. L., nd M. R. Hferkmp. 1989. Temperture responses nd clculted het units for germintion of severl rnge grsses nd shrus. J. Rnge Mnge. 42:41 45. Littell, R. C., G. A. Milliken, W. W. Siroup, nd R. D. Wolfinger. 1996. SAS system for mixed models. Cry NC. P. 633 McDonld, C. K. 2002. Germintion response to temperture in tropicl nd sutropicl psture legumes. 1. Constnt temperture. Austrlin J. Exp. Ag. 42:407 419. McIver, J., M. Brunson, S. Bunting, J. Chmers, N. Devoe, P. Doescher, J. Grce, D. Johnson, S. Knick, R. Miller, M. Pellnt, F. Pierson, D. Pyke, K. Rollins, B. Roundy, E. Schupp, R. Tusch, nd D. Turner. 2010. The Sgerush Steppe Tretment Evlution Project (SgeSTEP): A test of stte-nd-trnsition theory. Pge 16. USDA Forest Service RMRS- GTR-237, Ft. Collins, CO. 26
Miller, R. F., J. D. Btes, T. J. Svejcr, F. B. Pierson, nd L. E. Eddlemn. 2007. Western juniper field guide: Asking the right questions to select pproprite mngement ctions. U.S. Geologicl Survey Circulr 1321, 26 p. Ogle, K., nd J. F. Reynolds. 2004. Plnt responses to precipittion in desert ecosystems: Integrting functionl types, pulses, thresholds, nd delys. Oecologi 141:282 94. Peck, J. E. 2010. Multivrite nlysis for community ecologists: Step y step using pc-ord. Gleneden Bech, OR, USA. Prter, M. R., nd E. H. DeLuci. 2006. Non-ntive grsses lter evpotrnspirtion nd energy lnce in gret sin sgerush communities. Ag. For. Meteorology 139:154 163. Ru, B. M., R. R. Blnk, J. C. Chmers, nd D. W. Johnson. 2007. Prescried fire in Gret Bsin sgerush ecosystem: Dynmics of soil extrctle nitrogen nd phosphorus. J. Arid Environ. 71:362 375. Rwlins, J. K., B. A. Roundy, S. M. Dvis, nd D. Egget. 2012. Predicting germintion in semirid wildlnd seededs. I. Therml germintion models. Environ. Exp. Bot. 76:60 67. Rwlins, J. K., B. A. Roundy, D. Egget, nd N. L. Cline. 2012. Predicting germintion in semirid wildlnd seededs II. Field vlidtion of wet therml-time models. Environ. Exp. Bot. 76:68 73. Reid, I. 1973. The influence of slope orienttion upon the soil moisture regine nd its hydrogeomorphologicl significnce. J. Hydrol.19:309 321. 27
Roundy, B. A., nd S. H. Biedenender. 1996. Germintion of wrm-seson grsses under constnt nd dynmic tempertures. J. Rnge Mnge. 49:425 431. Roundy, B. A., S. P. Hrdegree, J. C. Chmers, nd A. Whittker. 2007. Prediction of chetgrss field germintion potentil using wet therml ccumultion. Rngelnd Ecol. Mnge. 60:613 623. Roundy, B. A., R. F. Miller, R. J. Tusch, K. Young, A. Hulet, B. Ru, B. Jessop, J. C. Chmers, nd D. Eggett. 2014. Understory cover responses to piñon-juniper control cross tree cover grdients in the Gret Bsin. Rngelnd Ecol. Mnge. x:xx xx. Roundy, B. A., K. Young, N. Cline, A. Hulet, R. F. Miller, R. J. Tusch, J. C. Chmers, nd B. Ru. 2014. Piñon-juniper reduction effects on soil temperture nd wter vilility of the resource growth pool. Rngelnd Ecol. Mnge. xx:xx-xx. Ryel, R. J., A. J. Leffler, C. Ivns, M. S. Peek, nd M. M. Cldwell. 2010. Functionl differences in wter-use ptterns of contrsting life forms in Gret Bsin steppelnds. Vdose Zone J. 9:548 560. Weiserg, P. J., E. Lingu, nd R. B. Pilli. 2007. Sptil ptterns of pinyon-juniper expnsion in Centrl Nevd. Rngelnd Ecol. Mnge 60:115 124. Whittker, A., B. A. Roundy, J. C. Chmers, S. E. Meyer, R. R. Blnk, S. G. Kitchen, nd J. Korfmcher. 2008. The effects of herceous species removl, fire, nd chetgrss (Bromus tectorum) on soil wter vilility in sgerush steppe. Pges 49 56 in S. Kitchen, R. L. Pendleton, T. A. Monco, nd J. Vernon, editors. Shrulnds under fire: Disturnce nd 28
recovery in chnging worldcedr City. U. S. Deprtment of Agriculture Forest Service Rocky Mountin Reserch Sttion, Fort Collins, CO. Young, K. R., B.. Roundy, nd D. L. Eggett. 2013. Tree reduction nd deris from mstiction of Uth juniper lter the soil climte in sgerush steppe. For. Ecol. Mnge. 310:777 785. 29
TABLES Tle 1-1. Site loction informtion. Community types: Mountin ig sgerush (Artemisi tridentt Nutt. ssp. vseyn (Ryd.) Beetle), Wyoming ig sgerush (Artemisi tridentt Nutt. ssp. wyomingensis Beetle & Young), crested whetgrss (Agropyron cristtum (L.) Gertn.), squirreltil (Elymus elymoides (Rf.) Swezey), western juniper (Juniperus occidentlis Hook.), pinyon-juniper (Pinus edulis Engelm. - Juniperus osteosperm (Torr.) Little), Uth juniper (Juniperus osteosperm (Torr.) Little), chetgrss (Bromus tectorum L.). Site Comminity Type Stte Coordinnce Elev (m) Soil clssifiction Sgerush & Perennil Grss Sites (Descried in Chmers et l. 2007, Roundy et l. 2007, Blnk et l. 2007) Underdown Cnyon High (NVU) Mountin Big Sgerush NV 39⁰ N, 117⁰30' W 2380 Fine-lomy nd lomy-skeletl, frigid Typic Hploxerolls Underdown Cnyon Mid (NVM) Mountin Big Sgerush NV 39⁰ N, 117⁰30' W 2190 Lomy-skeletl, mesic, Xeric Hplodurids Underdown Cnyon Low (NVL) Wyoming Big Sgerush NV 39⁰ N, 117⁰30' W 1960 Lomy-skeletl, mesic, Typic Hploxerolls Mill Cnyon High (UTU) Mountin Big Sgerush UT 40⁰ N, 112⁰ W 2274 Lomy-skeletl, crontic, mesic, frigid, Lithic Clcixerolls Blck Rock Cnyon Mid (UTM) Mountin Big Sgerush UT 40⁰ N, 112⁰ W 2085 Lomy-skeletl, crontic, mesic, Lithic, Clcixerolls Blck Rock Cnyon Low (UTL) Wyoming Big Sgerush UT 40⁰ N, 112⁰ W 1710 Lomy-skeletl, crontic, mesic, shllow, Petroclcic Plexerolls Brrett Cnyon (NVC) Crested Whetgrss NV 39⁰ N, 117⁰30' W 2065 Lomy-skeletl, mesic, Xereptic Hplodurids Boulter Creek (UTC) Crested Whetgrss UT 40⁰ N, 112⁰ W 1628 Fine-lomy to lomy-skeletl, mesic, Xeric Hploclcids Boulter Creek ELEL (UTS) Squirreltil grss UT 40⁰ N, 112⁰ W 1597 Fine-lomy to lomy-skeletl, mesic, Xeric Hploclcids Sgerush Sites (Descried in McIver et l. 2010) Hrt Mountin (HM) Wyoming Big Sgerush OR 42⁰ 43' N, 119⁰ 29' W 1510 Lomy, mixed, superctive, frigid, shllow Xeric Hplodurids Onqui Sgerush (OS) Wyoming Big Sgerush UT 40⁰ 11' N, 112⁰ 27' W 1675 Lomy-skeletl, mixed, ctive, mesic Xeric Hploclcids Sddle Mountin (SM) Wyoming Big Sgerush WA 46⁰ 45' N, 119⁰ 21' W 1510 Corse-silty, mixed, superctive, mesic Xeric Hplocmids Crested Whetgrss Sites (Descried in Rwlins 2012 nd Hulet et l. 2010) Skull Vlley (SV) Crested Whetgrss UT 40⁰18' N, 112⁰51' W 1524 Sndy lom, mixed (Clcreous) mesic, nd xeric Torriorthents Lookout Pss (LP) Crested Whetgrss UT 40⁰09' N, 112⁰28' W 1676 Tylorsflt fine -lomy, mixed, mesic, xerolic Clciorthids 30 Woodlnd Sites(Descried in McIver et l. 2010) Blue Mountin (BM) Western Juniper CA 41⁰ 49' N, 120⁰ 50' W 1510 Lomy, mixed, superctive, mesic Lithic Hploxerolls Bridge Creek (BC) Western Juniper OR 44⁰ 36' N, 120⁰ 9' W 840 Sndy lom, frigid Typic Hploxerolls to frigid Torriorthents Devine Ridge (DR) Western Juniper OR 43⁰ 43' N, 118⁰ 56' W 1510 Lomy-skeletl, mixed, superctive, frigid Lithic Hploxerolls Mrking Corrl (MC) Pinyon-juniper NV 39⁰ 25' N, 115⁰ 7' W 1730 Lomy-skeletl, mixed, superctive, mesic Argidic Durixerolls South Ruy (SR) Pinyon-juniper NV 40⁰ 40' N, 109⁰ 46' W 2005 Lomy, mixed, superctive, mesic, shllow Hploduridic Durixerolls Greenville Bench (GV) Pinyon-juniper UT 38⁰ 12' N, 112⁰ 47' W 1800 Lomy-skeletl, crontic, mesic Typic Clcixerepts Scipio (SC) Pinyon-juniper UT 39⁰ 16' N, 112⁰ 4' W 1755 Lomy-skeletl, mixed, superctive, mesic, shllow Clcic Petroclcids Onqui woodlnd (OJ) Uth Juniper UT 40⁰ 13' N, 112⁰ 28' W 1705 Lomy-skeletl, crontic, mesic, shllow Petroclcic Plexerolls Stnsury (ST) Uth Juniper UT 40⁰ 35' N, 112⁰ 39' W 1740 Lomy-skeletl, mixed, ctive, frigid Pchic Hploxerolls
Tle 1-2. List of woodlnd sites, yer of tretment, nd yers of soil moisture nd temperture yer dt used for post tretment nd woodlnd infilling phse nlysis. * Yers where only erly spring nd lte spring dt ws used. Tretment nd phse comprison Yer dt used for yer since tretment Yer Site treted Yer 1 Yer 2 Yer 3 Yer 4* Blue Mountin 2007 2009 2010 2011 Bridge Creek 2006 2008 2009 2010 Devine Ridge 2007 2009 2010 2011 Mrking Corrl 2006 2008 2009 2010 South Ruy 2008 2010 2011* Stnsury 2007 2008 2009* Onqui 2006 2007 2008 2009 2010 Scipio 2007 2010 2011 Greenville 2007 2009 2010 2011 Totl numer of sites 2 7 7 7 31
Tle 1-3. Sesonl wet degree dys (± SE) y temperture rnge (ᵒC) for yer since tretment in woodlnds. Dsh mrks (-) indicte temperture rnges tht hd little or no wet degree dys. Seson Yer Since Tretment 0 to < 5ᵒ C Wet Degree Dys for Temperture Rnge 5 to 10 to 25 to < 10ᵒ C < 25ᵒ C < 30ᵒ C 30 to < 35ᵒ C Erly Spring Yer 1 40.9 ± 12.9 82.7 ± 12.9 140.4 ± 12.9 1.46 ± 12.9 0.1 ± 12.9 Yer 2 45.2 ± 5.3 79.5 ± 5.3 113.4 ± 5.3 4.4 ± 5.3 0.8 ± 5.3 Yer 3 51.7 ± 2.7 87.0 ± 2.7 128.9 ± 2.7 4.3 ± 2.6 0.4 ± 2.6 Yer 4 44.4 ± 6.4 79.3 ±6.4 116.8 ± 6.4 3.9 ± 6.4 0.5 ± 6.4 Lte Spring Yer 1 3.0 ± 45.0 32.0 ± 45.0 189.8 ± 45.0 28.3 ± 45.0 3.0 ± 45.0 Yer 2 7.9 ± 16.1 40.1 ± 16.2 227.6 ± 16.2 29.1 ± 16.2 13.3 ± 16.1 Yer 3 9.4 ± 8.9 63.5 ± 8.9 274.0 ± 8.9 32.2 ± 8.9 12.0 ± 8.9 Yer 4 8.9 ± 16.9 72.9 ± 16.9 324.2 ± 16.9 16.3 ± 16.9 8.9 ± 16.9 Summer Yer 1 - - 48.8 ± 5.9 15.0 ± 5.9 11.7 ± 5.9 Yer 2 - - 15.9 ± 2.7 4.2 ± 2.7 3.7 ± 2.7 Yer 3 - - 67.0 ± 8.5 22.7 ± 8.5 16.1 ± 8.5 Fll Yer 1 30.8 ± 5.5 62.1 ± 5.5 71.7 ± 5.5 8.8 ± 5.5 6.0 ± 5.5 Yer 2 26.2 ± 4.7 54.5 ± 4.7 64.8 ± 4.7 3.7 ± 4.7 1.7 ± 4.7 Yer 3 33.9 ± 8.9 24.7 ± 8.5 88.1 ± 8.5 1.9 ± 8.5 0.7 ± 8.5 Winter Yer 1 23.8 ± 5.6 10.8 ± 6.0 3.4 ± 5.6 - - Yer 2 21.5 ± 5.8 12.2 ± 5.8 2.2 ± 5.8 - - Yer 3 42.2 ± 10.6 21.4 ± 10.6 2.1 ± 10.6 - - 32
FIGURES Figure 1-1. Typicl therml time model illustrting dys-1 to germintion of seed supopultion s function of incution temperture (Rwlins et l., 2012). These nonliner curves vry y supopultions of seeds. Temperture is divided up into generlized rnges sed on optiml germintion rte. 33
2006 2007 2008 2009 2010 PRISM 700 600 500 Precipittion (mm) 400 300 200 100 0 NVU NVM NVL UTU UTM UTL NVC UTC UTS HM OS SM SV LP BM BC DR MC SP SR GV SC OJ ST Sgerush nd Perennil Grss Sgerush Crested Whetgrss Woodlnds Averge Mx Min 25 20 Air Temperture ( C) 15 10 5 0-5 -10-15 NVU NVM NVL UTU UTM UTL NVC UTC UTS HM OS SM SV LP BM BC DR MC SP SR GV SC OJ ST Sgerush nd Perennil Grss Sgerush Crested Whetgrss Woodlnds Figure 1-2. Precipittion nd ir temperture for sites. NVU = Underdown Cnyon High elevtion, NVM = Underdown Cnyon Middle elevtion, NVL = Underdown Cnyon Low elevtion, UTU = Mill Cnyon High elevtion, UTM = Blck Rock Cnyon Middle elevtion, 34
UTL = Blck Rock Cnyon Low elevtion, NVC = Brrett Cnyon, UTC = Boulter Creek, UTS = Boulter Creek ELEL, HM = Hrt Mountin, OS = Onqui Sgerush, SM = Sddle Mountin, SV = Skull Vlley, BM = Blue Mountin, BC = Bridge Creek, DR = Devine Ridge, MC = Mrking Corrl, SR = South Ruy, GV = Greenville Bench, SC = Scipio, OJ = Onqui Woodlnd, ST = Stnsury. 35
Figure 1-3. Averge precipittion nd ir temperture y seson for ech experiment. Error rs represent ± 1 stndrd error. 36
Wet Degree Dys Sgerush nd Perennil Grss Sites 300 250 200 150 100 50 0 to < 5 C 5 to < 10 C 10 to < 25 C 25 to < 30 C 30 to < 35 C 0 Erly Spring Lte Spring Fll Winter 300 250 Crested Whetgrss Sites Wet Degree Dys 200 150 100 50 0 Erly Spring Lte Spring Summer Fll Winter Wet Degree Dys 300 250 200 150 100 50 0 Sgerush Sites Erly Spring Lte Spring Summer Fll Winter Figure 1-4. Wet degree dys y five temperture rnges nd sesons for sgerush nd perennil grss, crested whetgrss, nd sgerush sites. Error rs represent ± 1 stndrd error. 37
38 Figure 1-5. Averge nnul wet degree dys y seson nd temperture rnge. Error rs represent ± 1 stndrd error.
Figure 1-6. Wet degree dy estimtes y site, seson nd temperture rnge. Experimentl 39
designs re SP = Sgerush & Perennil Grss sites, CW = Crested Whetgrss sites, nd SG = Sgerush sites. Sites re NVU = Underdown Cnyon High Elevtion, NVM = Underdown Cnyon Middle Elevtion, NVL = Underdown Cnyon Low Elevtion, UTU = Mill Cnyon High Elevtion, UTM = Blck Rock Cnyon Middle Elevtion, UTL = Blck Rock Cnyon Low Elevtion, NVC = Brrett Cnyon, UTC = Boulter Creek, UTS = Boulter Creek ELEL, HM = Hrt Mountin, OS = Onqui Sgerush, SM = Sddle Mountin, SV = Skull Vlley, BM = Blue Mountin, BC = Bridge Creek, DR = Devine Ridge, MC = Mrking Corrl, SR = South Ruy, GV = Greenville Bench, SC = Scipio, OJ = Onqui Woodlnd, ST = Stnsury. Error rs represent ± 1 stndrd error. 40
Wet Degree Dys 200 150 100 50 0 to < 5ᵒ C 5 to < 10ᵒ C 10 to < 25ᵒ C 25 to < 30ᵒ C 30 to < 35ᵒ C 200 0 BC BM DR GV MC OJ SC SR ST Yer 2 Wet Degree Dys 150 100 50 Wet Degree Dys 0 250 200 150 100 50 0 BC BM DR GV MC OJ SC SR ST Yer 3 BC BM DR GV MC OJ SC SR ST Yer 4 Figure 1-7. Site verges of wet degree dys for second, third, nd fourth yers since tree reduction tretments for seeded temperture rnges in erly spring. Dt re verges of untreted nd treted plots. Sites re BC = Bridge Creek, BM = Blue Mountin, DR = Devine 41
Ridge, MC = Mrking Corrl, OJ = Onqui Juniper, SC = Scipio, SR = South Ruy, nd ST = Stnsury. Error rs re ± 1 stndrd error. 42
Figure 1-8. Sesonl dditionl wet degree dys y tretment for non-optiml (top) nd optiml (ottom) temperture rnges. Comprisons re within yer. 43