Thawing Regimes for Freezer-Stored Container Stock

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1 Report: Reserch Report Thwing Regimes for Freezer-Stored Continer Stock Roin Rose nd Dine L. Hse Project leder nd ssocite director, Nursery Technology Coopertive,Oregon Stte University, Deprtment of Forest Science, Corvllis, Oregon Three thwing regimes were pplied over 6-week period to frozen Douglsfir (Pseudotsug menziesii (Mir.) Frnco.), western lrch (Lrix occidentlis Nutt.), nd ponderos pine (Pinus ponderos Dougl. ex Lws.) continer stock: (1) rpid thw followed y cold storge, (2) slow thw, nd (3) freezer storge followed y rpid thw. Seedlings were outplnted to 3 sites in northcentrl Wshington. A susmple of seedlings ws evluted for root growth potentil (RGP) t the time of outplnting. Seedling performnce ws ssessed fter the first nd second growing sesons. Although there were significnt differences mong species, thwing regime did not ffect seedling growth or survivl fter 2 growing sesons nor did it ffect RGP. The results indicte tht seedlings cn tolerte vritions in thwing prctices tht my occur due to wether or other circumstnces eyond control. However, it is noted tht it my e est to keep seedlings in freezer storge for s long s possile in order to prevent storge molds. Tree Plnters Notes 48 (1/2): 12 17; Freezer storge of continer seedlings, lthough n ccepted prctice in the nursery industry, is still reltively misunderstood technique in some forest nurseries nd reforesttion orgniztions. Reserch nd experience hve shown tht freezer storge cn e vlule mngement tool to successful reforesttion progrm. Freezer storge gives the nursery greter flexiility y llowing for lifting during lte utumn nd shipping the following spring. This results in more lnced work lod t the nursery nd n effective surge uffer etween nursery nd field production (Hee 1987). Colomo nd Cmeron (1986) found tht freezer storge of continer lck spruce Pice mrin (Mill) B.S.P. llows mngers to sfely dely udset of lte-sown crop, therey reching minimum cceptle height, without the risk of winter dmge ssocited with outdoor storge. Furthermore, freezer storge is more suitle for periods in excess of 2 months, ecuse crohydrte depletion nd Person Eduction, Inc. All rights reserved.

2 2 Tree Plnters Notes storge molds cn e prolem with long-term cold (2 F) storge (Ritchie 1982, 1984). Freezer storge is often necessry to mintin crop dormncy when lte-seson plnting is required in snowed-in units, especilly for stock to e plnted to high-elevtion sites. Odlum (1992) noted tht lck spruce seedlings kept in frozen storge hd greter susequent root nd shoot growth thn those wintered outdoors, especilly for those outplnted t lter dte. Ritchie (1984, 1989) found tht the rte of dormncy relese in reroot Dougls-fir Pseudotsug menziesii (Mir.) Frnco seedlings ws sustntilly retrded y freezer storge compred to those left in the nursery ed resulting in n expnsion of the plnting window nd higher, more uniform, physiologicl qulity. Likewise, Lindström nd Stttin (1994) found tht freezer-stored seedlings of Norwy spruce (Pice ies (L.) Krst.) nd Scots pine (Pinus sylvestris L.) hd greter tolernce to freezing in the spring thn those tht were stored outdoors. A concern with freezer storge is the thwing process. One thwing method commonly used is to llow the stock to thw very slowly t tempertures just ove freezing over period of severl weeks. Another method is to plce seedlings in n re with mient tempertures for severl dys prior to outplnting. The stndrd thwing prctice for Weyerheuser nurseries is to spred seedling pllets out nd llow them to thw t mient temperture (10 to 15 F) for 3 to 5 dys (re-root seedlings) nd for 10 to 15 dys (continer seedlings) (Hee 1987). Whether thwed rpidly or slowly, field foresters prefer to hve the stock thwed just prior to outplnting. However, chnging wether conditions or other circumstnces eyond control cn result in thwed stock eing held for severl weeks in cold storge prior to outplnt. Hee (1987) noted tht it is est to plnt seedlings s soon s they hve thwed, ut lso noted tht they cn e held in cooler storge fter thwing for up to 4 weeks without detriment. The ojective of this study ws to exmine the effects of 3 thwing regimes on the susequent qulity of 3 species of continer-grown conifer seedlings outplnted to 3 sites. The thwing regimes were designed to simulte circumstnces typiclly encountered with frozen stock. The null hypothesis ws tht there would e no differences in seedling field performnce for ny of the species due to thwing tretment. Person Eduction, Inc. All rights reserved.

3 Spring Mterils nd Methods Dougls-fir, western lrch (Lrix occidentlis Nutt.), nd ponderos pine (Pinus ponderos Dougl.) continer stock (1-yer-old Styro-8) were used in this study. For ech species on ech outplnting site, seedlings were from the sme seedlot. Seedlings were grown nd freezer stored under stndrd nursery prctices. Seedlings were shipped frozen to the Levenworth District of the Wentchee Ntionl Forest in lte Mrch to erly April 1995, depending on the expected dte of plnting for ech site. Three thw schedule tretments were pplied over 6-week period s follows: 1. Seedlings were plced under rpid thw (5 dys t 7 C = 44.6 F) 6 weeks efore expected outplnting, then held in cold storge (1 C = 33.8 F) until outplnting. 2. Seedlings were plced in cold storge for slow thw (6 weeks) efore outplnting. 3. Seedlings were kept in freezer storge ( 2 C = 28.4 F) until 1 week efore outplnting, when they were plced under rpid thw. Telog temperture recorders (Model 2103, Telog Instruments Inc., Victor, NY) were plced with seedlings in ech thwing tretment. Becuse there were limited numer of Telogs ville nd ecuse Telog dt cnnot e exmined until it is downloded to computer, dditionl digitl temperture proes were plced with the seedlings nd monitored weekly. Seedlings were outplnted to 3 sites on the Wentchee nd Oknogn Ntionl Forests in north-centrl Wshington s follows: Twisp District, Oknogn Ntionl Forest; high-elevtion (1,372 m = 4,500 ft) dry site. The slope is 10 to 40% with northestern spect, with light slsh nd vegettion. All 3 species were plnted on June 1, Levenworth District, Wentchee Ntionl Forest; low-elevtion (610 m = 2,000 ft) dry site in re urned y 1994 wildfire. Annul precipittion is 53 to 76 cm (20 to 30 in). Soil is sndy to cly lom. Person Eduction, Inc. All rights reserved.

4 4 Tree Plnters Notes The slope is 60% nd the urned trees (vg. dh = 10 cm = 4 in) were left stnding. Dougls-fir nd ponderos pine were plnted on April 20, Nches District, Wentchee Ntionl Forest; high-elevtion (1,219 m = 4,000 ft) temperte site. The slope is 15% with western spect. Dougls-fir nd western lrch were plnted on My 31, Seedlings were outplnted t out the sme time tht the site ws scheduled to e opertionlly plnted. Becuse of lte-winter conditions, the 6-week thwing period ws extended y 7 to 10 dys for seedlings plnted on the Twisp nd Nches Districts. For ech site, ll seedlings were plnted on the sme dy. Seedlings were plnted t spcing of m (= ft). Initil height nd survivl were mesured nd recorded 2 weeks fter outplnting nd gin t the end of the first nd second growing sesons (Septemer 1995 nd August 1996). In ddition, dmge/vigor ssessment (incidence of rowse, chlorosis, etc.) ws recorded for ech seedling. In ddition to the outplnted seedlings, susmple of 15 seedlings of ech species/tretment from the Levenworth nd Twisp sites were sent to Interntionl Pper s Lenon fcility shortly fter seedlings were outplnted (tht is, fter tretment) nd evluted for root growth potentil. These seedlings were potted nd llowed to grow in greenhouse for 3 weeks, then evluted for the numer of seedlings with new roots. The experimentl design consisted of split-plot design with 5 locks, 2 or 3 species per site (whole plots), 3 thw tretments (suplots), nd 10 seedlings in ech lock/species/tretment for totl of 450 seedlings on the Twisp site nd 300 seedlings on the Levenworth nd Nches sites. All seedlings were leled nd rndomly plnted within lock. An nlysis of vrince (ANOVA) ws performed on ll dt to determine if thw tretment hs significnt effect on susequent seedling performnce. Differences mong men vlues for species nd tretment were determined using Fisher s protected lest significnt difference procedure. Sttisticl Anlysis Softwre (SAS Institute 1989) ws used for ll dt nlyses. Person Eduction, Inc. All rights reserved.

5 Spring Results It took out 5 dys to ccomplish the rpid thw (tretments 1 nd 3) nd out 3 weeks for the slow thw (tretment 2) (figure 1). As would e expected, there were significnt differences in field performnce mong species on ech site (figures 2 nd 3). However, there did not pper to e ny meningful differences mong thwing tretments. During the first seson, there were significnt tretment y species interctions for oth height nd growth on the Levenworth nd Nches sites (figure 2). However, despite the sttisticl significnce etween tretments, the differences in first-yer verge height nd growth my not e significnt from reforesttion perspective, s the differences re smll (1 to 3 cm =.4 to 1.2 in) nd the rnking does not follow ny pttern with regrd to the tretments. For exmple, tretment 1 Dougls- Degrees F Levenworth stock Tretment 1 Cold Storge 32 3/14/95 4/22/95 Note: Telog did not cpture initil rpid thw or ws not with seedlings t time. Nches/Twisp stock 5/30/95 Degrees F Tretment 2 32 Slow thw (lst hlf) Slow thw Nches/Twisp stock Levenworth stock 30 3/14/95 4/22/95 5/30/95 45 Tretment 3 40 Degrees F 35 Figure 1 Output from Telog temperture recorders showing the thwing process of ech tretment. 30 Cold storge Rpid thw Levenworth stock Rpid thw Nches/Twisp stock 4/10/95 5/5/95 5/30/95 Person Eduction, Inc. All rights reserved.

6 6 Tree Plnters Notes 16 Twisp site Levenworth site Nches site Growth (cm) c c c c c d T1 T2 T3 c c Height (cm) c d c d d DF PP WL DF PP DF WL Figure 2 Totl seedling height nd growth fter the first growing seson in the field (1995). On ech site, rs with different letters re significntly different t the 0.05 level. Person Eduction, Inc. All rights reserved.

7 Spring Growth (cm) Twisp site Levenworth site Nches site T1 T2 T c c c 40 Height (cm) DF PP WL DF PP DF WL Figure 3 Totl height nd growth fter two growing sesons (1996). Although species differed significntly, there were no significnt differences etween thwing tretments. On ech site, rs with different letters re significntly different t the 0.05 level. Person Eduction, Inc. All rights reserved.

8 8 Tree Plnters Notes fir hd the gretest height on the Levenworth site, wheres tretment 3 Dougls-fir hd the gretest height on the Nches site. Similrly, tretment 3 ponderos pine hd the most growth on the Levenworth site wheres tretment 1 western lrch hd the most growth on the Nches site. During the second growing seson, there were no significnt differences mong thwing tretments for totl height, sesonl height growth, or totl height growth on ny of the 3 sites (figure 3). Survivl verged 77% on the Twisp site nd 96% on the Levenworth site regrdless of species or tretment. On the Nches site, survivl ws not influenced y tretment ut ws very poor for Dougls-fir (23%) compred to western lrch (83%). Thw tretment hd no effect on root growth potentil. Discussion We found tht thwing regime did not ffect susequent seedling field performnce. In similr study, Cmm nd others (1995) reported tht there were very few differences etween white spruce (Pice gluc (Moench) Voss) nd Engelmnn spruce (Pice engelmnnii Prry) seedlings plnted either directly from the freezer or fter 9 dys of thwing. The ltter roke ud 3.3 dys erlier thn those plnted directly from the freezer ut hd less uniform udrek. Height, shoot, nd root mss did not differ fter 3 months of growth. Cmm nd others (1995) suggest tht suitle on-site opertionl protocol for rpid thwing might e to ly frozen undles on the ground t mient temperture overnight. Additionl possile enefits to this pproch tht they mention include reductions in hndling costs, secondry storge fcilities, nd losses cused y refrigertor filure (Cmm nd others 1995). The ide of long, slow thw hs een to llow norml physiologicl processes to fully resume prior to plnting. However, this my not e necessry ecuse recovery of wter potentil fter thwing spruce seedlings took hours, not dys, once ice crystls left the roots (Cmm nd others 1995). As result, these uthors recommend ginst the prctice of slowly thwing seedlings for up to severl weeks efore shipping to the plnttion site ecuse fungi (Botrytis spp.) often proliferte on seedlings held ove freezing in the drk for extended periods. Another Person Eduction, Inc. All rights reserved.

9 Spring study showed tht stedy-stte respirtion rtes increse significntly during thwing nd hence hve the potentil to gretly deplete crohydrte reserves, especilly over time (Lévesque nd Guy 1994). On the other hnd, Odlum (1992) stted tht rpid thwing of stock cn result in dmge or mortlity ttriutle to shoots rpidly rising to mient thw temperture, while seedling plugs remin frozen, due to their higher wter content. Thus, folir trnspirtion without wter vilility from the roots results in desicction. Odlum recommended tht stock e thwed slowly s descried y Koistr nd others (1989); seedlings re first exposed to 5 C until completely thwed. Our findings do not suggest the need for this. Conclusions Despite ssertions in the literture of dmge to seedlings cused y either rpid or slow thwing, the results of our study indicte tht continer seedlings cn withstnd vritions in thwing regimes, s we descried, without ny detrimentl effect to their susequent field performnce. However, mngers concerned with post-storge fungl infection should consider using short thwing intervls. Literture Cited Cmm EL, Guy RD, Kuien DS, Goetze DC, Silim SN, Burton PJ Physiologicl recovery of freezer-stored white nd Engelmnn spruce seedlings plnted following different thwing regimes. New Forests 10: Colomo SJ, Cmeron SC Assessing rediness of lck spruce continer seedlings for frozen storge using electricl impednce, oscilloscope squre wve nd frost hrdiness techniques. For. Res. Note 42. Loction: Ontrio Ministry of Nturl Resources, Ontrio Tree Improvement nd Forest Biomss Institute: 6 p. Hee SM Freezer storge prctices t Weyerheuser nurseries. Tree Plnters Notes 38(2): Koistr C, Ostfew S, Lukinuk I Cold storge guidelines. Victori, BC: British Columi Ministry of Forests. Person Eduction, Inc. All rights reserved.

10 10 Tree Plnters Notes Lévesque F, Guy RD Chnges in respirtion rtes of white spruce nd lodgepole pine seedlings during freezer storge nd thwing nd reltionship to crohydrte depletion. Poster presented t Annul Meeting of the Americn Society of Plnt Physiologists. Portlnd, OR. July 30 August 3, Lindström A, Stttin E Root freezing tolernce nd vitlity of Norwy spruce nd Scots pine seedlings: influence of storge durtion, storge temperture, nd prestorge root freezing. Cndin Journl of Forest Reserch 24: Odlum KD Mye or mye nots of frozen storge. Pper presented t OTSGA continer workshop, 1991 Octoer 1 3; Kirklnd Lke, ON. Loction: Ontrio Tree Seedling Growers Assocition nd Ontrio Ministry of Nturl Resources. Ritchie CA Crohydrte reserves nd root growth potentil in Dougls-fir seedlings efore nd fter cold storge. Cndin Journl of Forest Reserch 12: Ritchie GA Effect of freezer storge on ud dormncy relese in Dougls-fir seedlings. Cndin Journl of Forest Reserch 14(2): Ritchie GA Integrted growing schedules for chieving physiologicl uniformity in coniferous plnting stock. Forestry 62 (Suppl.): SAS Institute SAS/STAT User s Guide, Version 6, Fourth ed. Cry, NC: SAS Institute. 846 p. Person Eduction, Inc. All rights reserved.