The Pennsylvania State University. The Graduate School. Department of Horticulture EVALUATING THE EFFECTS OF SWEATING ON BUD BREAK AND

Transcription

1 The Pennsylvania State University The Graduate School Department of Horticulture EVALUATING THE EFFECTS OF SWEATING ON BUD BREAK AND SURVIVAL AND GROWTH OF FOUR DECIDIOUS TREE SPECIES A Thesis in Horticulture by Milica Dozic 2009 Milica Dozic Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science December 2009

2 ii The thesis of Milica Dozic was reviewed and approved* by the following: Ricky M. Bates Associate Professor of Horticulture Thesis Adviser Larry J. Kuhns Professor of Ornamental Horticulture James C. Sellmer Associate Professor of Ornamental Horticulture Richard Marini Professor of Horticulture Head of the Department and Professor of Horticulture *Signatures are on file in the Graduate School.

3 ABSTRACT iii The research was conducted during the growing season of The objective of the study was to investigate the effect of sweating methods for desiccation tolerant and desiccation sensitive species of deciduous bare-root trees. Plant quality was evaluated by measuring degree of stem die back, percent bud-break and growth during the first year of establishment. Four tree species were used in this study, desiccation sensitive Washington hawthorn (Crataegus phaenopyrum Med.), Paper birch (Betula papyrifera Marsh) and Common hackberry (Celtis occidentalis L.), and desiccation tolerant Norway maple (Acer platanoides L.) (Murakami et al, 1990). Bare-root maple and birch trees and hackberry and hawthorn were planted at three different times, April, May and June. Prior to planting, the bare-root trees were subjected to three different sweating periods of 2, 4, and 8 days in growth chambers under 70º F. During sweating procedure bud swell, bud break and new root initiations were observed. After the sweating procedure, trees were planted in the field. Survival of broken buds was monitored, percent bud break, dry weight of leaves, height and caliper were measured and stem die back was evaluated. In this study the desiccation sensitive Washington Hawthorn did not benefit from any of the sweating treatments. Birch, a desiccation sensitive tree (Murakami, 1990) appeared to show a high level of desiccation tolerance. Hackberry and Norway maple did not benefit from sweating treatments most of the time. Washington hawthorn was the only species that had most of the broken buds dried after trees were transplanted in the field. New buds broke later. Percent bud break of all four species decreased with late planting in most treatment-planting time combinations. Dry weight of leaves of all species significantly decreased with late planting. Washington hawthorn suffered from

4 stem die back the most and Birch the least. Stem die back of Hackberry increased with iv late planting. Norway maple had some stem die back.

5 TABLE OF CONTENTS v LIST OF FIGURES vi LIST OF TABLES...vii Acknowledgements vii Chapter 1. INTRODUCTION AND LITERATURE REVIEW Chapter 2. MATERIALS AND METHODS Chapter 3. RESULTS.11 Section 3.1.Bud Survival after Planting.11 Section 3.2. Observational Trees Section 3.3. Percent Bud Break.22 Section 3.4. Dry Weight 26 Section 3.5. Height and Caliper.30 Section 3.6. Stem Die Back...32 Chapter 4. DISCUSSION Section 4.1.Sequence of Bud Break Section 4.2. Observational Trees...35 Section 4.3. Percent Bud Break...36 Section 4.4. Dry Weight Section 4.5. Height and Caliper.39 Section 4.6. Stem Die Back...39 CONCLUSION..42 Bibliography..44 Appendix A...46 Appendix B...47

6 LIST OF FIGURES vi Figure 1: Average Bud break survival after planting for Birch trees, planted in a) April, b) May and c) June.12 Figure 2: Average Bud break survival after planting for Hackberry trees, planted in a) April, b) May and c) June..14 Figure 3: Average Bud break survival after planting for Maple trees, planted in a) April, b) May and c) June...16 Figure 4: Average Bud break survival after planting for Washington hawthorn trees, planted in a) April, b) May and c) June.18

7 LIST OF TABLES vii Table 1. Mean bud swell, bud break and mean % of seedlings shown new root growth for observational trees of birch (B), hackberry (Hb), Norway maple (NM) and Washington hawthorn (WH) planted in April, May and June, and sweated for 8 days under 70º F in a growth chamber...21 Table 2. Mean percent bud break for birch, hackberry, Norway maple and Washington hawthorn in April, May and June. Differences between planting dates analyzed by sweating treatment performed by Duncan significant test of difference...25 Table 3. Mean Dry Weight for birch, hackberry, Norway maple and Washington hawthorn in April, May and June. Differences between months performed by Duncan significant test of difference..28 Table 4. Mean Dry Weight for birch, hackberry, Norway maple and Washington hawthorn in April, May and June. Differences between planting dates analyzed by sweating treatment, and Differences between sweating treatments analyzed by month performed by Duncan significant test of difference..29 Table 5. Mean total height and caliper of birch, hackberry, Norway maple, and Washington hawthorn planted in April, May and June. Differences between planting dates by height or caliper...31 Table 6. Mean Stem Die Back of birch (B), hackberry (Hb), Norway maple (NM) and Washington hawthorn (WH) planted in April, May and June, and sweated for 0, 2, 4, and 8 days...33

8 viii ACKNOWELEDGEMENTS In first place I am grateful to my advisor Dr. Rick Bates who gave me a chance to become PennState student. His enthusiasm and love for his work became inspiration for my academic work. His faith in me was always the source of encouragement and support. I also express gratitude to my faculty committee members Dr. Kuhns and Dr. Sellmer for their input and critical reviews. I spent couple of great years in State College and I am very proud of being part of PennState University life. I had chance to meet lots of people and become good friend with some of them. Here I would thank Magalhaes Miguel and Miriam Fererira for their friendship and encouragement. Also, I would like to thank David Despot for helpful lectures in statistics. This study is very special to me. But I know that this is especially meaningful to my parents, Petrija and Zvonimir Nikolic. I dedicate this study to my mother and father who always believed in me and gave me the strength to finish this project. At the end I would also like to thank my sweet boys, Luka and Nikola and my husband Aleksandar for their love.

9 Chapter 1 1 INTRODUCTION AND LITERATURE REVIEW Many nursery-grown woody landscape plants are harvested by bare-root methods. Harvesting and handling of bare-root woody landscape plants are very important for growers in the United States and elsewhere. There are five major steps of handling bareroot plants-harvesting, processing, storing, shipping and planting (Englert, 1993). After becoming dormant and hardy (dormancy is a state of low metabolic activity, and hardiness is the resistance to stress), plants may be dug bare-root in late fall or early winter and stored for up to 5 months under high humidity (90 98 %) in refrigerators at 34 F 40 F or in freezers at 28 F 30 F. Shipment of bare-root trees usually begins in March (Englert, 1993). After digging in fall and placing into cold storage, bare-root plants are no longer exposed to natural outdoor environmental factors that control growth and development. Rather, bare-root plants in cold storage experience constant low temperatures, absence of light and constant high humidity. Storage conditions and packaging methods affect root growth and physiological quality of bare-root plants (Webb and von Althen, 1980). Physiological processes of cold stored bare-root plants, such as carbohydrate levels, bud dormancy, root growth potential, cold hardiness and water status are affected by cold storage (Ritchie, 1987). During the process of respiration plants decrease their carbohydrate reserves. Temperature and duration of cold storage affect carbohydrate status (Ritchie, 1982). Low temperatures in cold storage decrease respiratory losses slowly. The higher temperature in cold storage the greater are respiratory losses.

10 2 Moreover, carbohydrate status may affect root growth potential. Initiation of new roots of planted bare-root trees depend on carbohydrates stored within the stem and root tissue. Exposure of roots and shoots to the storage environment reduced root growth capacity (Webb and von Althen, 1980). Root growth potential of cold-stored woody plants differs among species (DeWald and Feret, 1988; Ritchie, 1982; Ritchie and Stevens, 1979). Species such as Loblolly pine, Ponderosa pine and Douglas fir have higher root growth potential when lifted later in the fall. Woody plants can be successfully cold-stored for many weeks if chilling requirements are met prior to storage (Ritchie and Dunlap, 1980). Cold storage affects dormancy release in terms of its duration and intensity (Ritchie, 1984). Bare-root plants are subject to many stresses during the lifting to planting window. The effects of stress that plants experience are cumulative. Thus, quality of the plants is reduced over time (Englert, 1993). Desiccation is one of the major stresses during all phases of bare-root production: digging, storage, shipping, and handling by the grower. A plant s water status influences its tolerance to different stress factors during transplanting. Cold storage conditions can affect the desiccation stress (storage durations, storage temperature, and packaging methods). While in cold storage, plants should be protected from water loss, sub-optimal temperatures, loss of dormancy and disease. Physiological quality, such as root growth capacity as well as bud dormancy of cold stored hardwood trees are affected by storage temperature and packaging (Webb and Althen, 1980). To maintain plant quality during storage, desiccation sensitive species may require stem protection along with root protection (Bates and Niemiera, 1994). Desiccation tolerance of bare-root trees to handling practices is species specific. Some

11 species are desiccation tolerant, such as Norway maple (Acer platanoides), Red oak 3 (Quercus rubra) and others are desiccation sensitive, such as Washington hawthorn (Crategus phaenophyrum) (Murakami et al., 1990). One of the greatest water stresses occur right after planting (Kozlowski and Davies, 1975). Species with coarser root habits such as Fraxinus excelsior Vahl. have better desiccation tolerance than species with fine roots such as Betula pubescens Ehrh. (Insley and Buckley, 1985). Generally, any treatment that reduces water stress of plants should be beneficial. Nursery growers usually apply anti-transpirants and other film-coating compounds (Englert, 1993). The effect of rough-handling is minor when compared with desiccation; some investigations reported a decrease in survival and growth of transplanted bare-root trees (McKay et al, 1999; Yuyitung et al., 1994). Further, some studies showed different abilities of species to withstand rough-handling (McKay and Milner, 2000). The combination of desiccation and rough-handling can be detrimental for bare-root plants. The two major factors most often attributed to the survival of transplanted trees are lifting date and length of cold storage (Lindquist, 1998). Plants should be lifted when they are dormant and hardy. Early lifted plants are more sensitive to cold storage than late lifted plants (Ritchie, 1984, Lindquist, 1998). The importance of accumulated exposure to low temperature before plants should be lifted and placed in cold storage (plants lifted earlier are not exposed to low temperatures) had crucial importance in terms of bare-root plant survival (Lindquist, 1998). Plant survival and damage differed among species in terms of different fall lifting dates and length of cold storage. Field performance of Ponderosa pine seedlings was best when lifted later in the fall and worse when lifted in

12 4 the early fall (Omi et al., 1994). Douglas fir lifted early in the fall released dormancy in cold storage faster than later lifted seedlings (Ritchie, 1984). Intensity of bud dormancy during cold storage was released as rapidly as in nature (Carlson, 1985). Cold storage accelerated bud break in Sugar maple and Silver birch (Donnelly, 1973). When dormancy is satisfied in early spring (March and April), seedlings broke bud when exposed to warm conditions (Ritchie, 1987). On the other hand, extended cold storage artificially prolongs dormancy and delays normal bud-break sequence for some species. Delayed bud-break after transplanting is problematic for desiccation sensitive species (Bates et al., 1994). Establishment of transplanted bare-root trees in the spring after cold storage is influenced by numerous factors. Plants lose a significant portion of their root system during the digging process (Watson and Himelick, 1982 a). Storage conditions and packaging methods influence water loss and physiological quality of bare-root plants during cold storage (Webb and Althen, 1980). Rapid regeneration of new roots significantly affects establishment success of transplanted woody plants (Watson and Himelick, 1982 b), and carbohydrate status may affect root growth potential (Ritchie and Dunlap, 1980). The time between transplanting and bud-break and new root initiation is often termed the desiccation window. The time between bud-break and root initiation is critical for establishment and survival of transplanted trees. New root growth occurs usually with bud-break. By encouraging trees to break bud rapidly after transplanting, the desiccation window could be shortened. Successful establishment and subsequent growth, based on planting date, differs among species. McKay and Milner (2000) indicated that optimal time of planting bare-root Japanese and hybrid larch after cold storage is early spring and for a short period during

13 5 the fall. Sugar maple and northern Red oak regenerated roots earlier and grew new roots more rapidly when transplanted in early fall compared to late fall or spring (Harris et al., 2002). Late spring transplanted Norway maple had better root regeneration than early spring transplanted seedlings and Green ash and Ginkgo did not have significantly different new root growth, regardless of the transplant season (Watson and Himelick, 1982 a). When bare-root trees are properly handled during all phases of bare-root production post-transplant survival rates of most of the bare-root species are high. However, desiccation sensitive species, such as Crataegus, Rosa and Betula may show poor performance due to excessive water loss during the handling practices (Englert et al., 1993). Such species may require modified treatments during harvesting, storage and post-storage conditions. A commonly suggested procedure is sweating. This is the process of forcing species out of dormancy and into bud-break just prior the planting. Sweating usually involves holding bare-root plants under moist, humid conditions, for varying lengths of time, usually 2-7 days. While nurseries have standard recommendations of sweating procedure, there are no reports detailing optimal sweating temperature and duration of the procedure or its effect on the establishment of transplant species. Most of the studies about survival rate of bare-root trees have been concentrated on lift date, length of storage and desiccation tolerance during handling. Therefore, the objectives of this research are: 1) To determine the influence of sweating temperature, duration and timing on the bud break and survival of selected desiccation sensitive and desiccation tolerant species.

14 6 2) To document the elapsed time and sequence of bud break and new root initiation for sweated Crataegus, Betula, Celtis, and Acer species. 3) To determine the influence of planting date on the survival and growth of four falldug, cold-stored deciduous tree species.

15 Chapter 2 7 MATERIALS AND METHODS Experiments were conducted during the 2004 and 2005 growing seasons. Four different deciduous tree species were selected for the experiments. Washington hawthorn (Crataegus phaenopyrum Med.), and Common hackberry (Celtis occidentalis L.) represented desiccation sensitive species, while Norway maple (Acer platanoides L.) represented a desiccation tolerant species, and Paper birch (Betula papyrifera Marsh.) represented an intermediate desiccation sensitive species (Murakami, 1990). These species were exposed to two treatments: four sweating durations (0, 2, 4, and 8 days), and three planting times (early April, early May, and early June). Temperature was 70 F (21.1 C) ± 5 F for all sweating procedures. Treatments were replicated four times. Three-year old bare-root seedlings were obtained from the Lawyers Nurseries (Plains, MT) and were held in cold storage until shipped by refrigerated truck to State College, PA in early April (arrived on 3/31/04, except the shipment of Washington hawthorn seedlings which arrived on 4/5/04), May (arrived on 5/2/04), and June (arrived on 5/26/04, except the shipment of Washington hawthorn which arrived on 6/1/04). Norway maple (2-0) and Paper birch (2-0) were 3-4 tall, while Hackberry (1-0) and Washington hawthorn (2-0) were 2-3 tall. The portion of Hawthorn seedlings arriving in June was 3-4 tall. Seedling bundles were packed in cardboard within plastic sheeting. Roots of each bundle were packed with moistened, shredded newspaper. Upon arrival the bare-root seedlings were inspected, moistened, and placed overnight in a cooler at 42 F. The next day seedlings were sorted based on the size into sweating treatments. 96

16 seedlings of all species were sorted and sealed into three plastic bags by species, 8 containing moist sphagnum moss and placed in growth chambers for sweating at 70 F. Plastic bags containing 32 seedlings each (8 of each species) were designated as 2-day, 4- day and 8-day. Each species had 8 replications. An additional bag was assigned as observational bag containing 16 seedlings (4 of each species) were placed in growth chamber at 70 F for sweating. Sixteen seedlings were planted immediately in a field at the PennState Horticulture Farm at Rock Springs, PA. Three corresponding plots representing the three planting dates (April, May, and Jun) were planted on the 2 nd, 4 th and 8 th day after sweating. The corresponding sweating treatment trees were removed from the growth chamber and planted in the field. All planted trees were top-dressed with controlled release fertilizer Osmocote Plus ( ) at planting, in order to provide continuous nutrition during the growing season and at least up to 8 months after application. Planted seedlings were watered regularly in the absence of rain. Above procedures were repeated for each month (April, May and June). During the summer, trees were kept weed free, and irrigated as necessary. Measurements Seedlings in the observational bags were checked every two days for signs of bud swell, bud break, and new root growth. Once trees were planted in the field, time to budbreak, ratio of stem dieback, and number of buds breaking were monitored and recorded. At the end of growing season, plant survival and biomass (dry weight) were measured. On August the 17 th and 18 th total height and caliper of all seedlings were measured. Bud

17 9 swell, bud break and new root growth for observational seedlings were visually measured every other day. Bud swell was determined when buds were enlarged and rotund, just prior the time of scale separation. Bud-break was defined when bud scales started to open to reveal the enclosed leaf. Swollen and broken buds were counted along with total number of buds. Bud break was expressed in % of bud-break using the following calculation: % bud-break = # of broken buds *100/ # of total buds Survival of broken buds of planted seedlings were monitored and counted after planting until most of the buds were broken. A baseline count was conducted at the time of transplanting. Subsequent counting was performed weekly. Some of the trees that arrived for June planting already had broken bud. After planting these buds dried out and trees broke new buds. Root growth was recorded on observational trees during sweating. The appearance of new roots and trees were marked with + (present) or (not present). New root growth was reported as a percentile of seedlings with new roots. Stem dieback of field and greenhouse seedlings was measured on August the 28 th. This was visually observed and rated on a 1-10 scale, where 1 = 0 10% dieback, 2 = 11 20%, 3 = 21 30%, 4 = 31 40%, 5 = 41-50%, 6 = 51 60%, 7 = 61 70%, 8 = 71 80%, 9 = 81 90%, 10 = %. Quality of planted seedlings was measured on August the 28 th. General appearance of the canopy was measured and arbitrarily rated with Yes and No based on appearance and stem dieback.

18 All the leaves on each planted tree were collected on October 4, Leaves 10 were placed into assigned paper bags and placed in a drying oven. After drying hrs of drying, dry weight of leaves was measured. Bud break data and dry weight data were analyzed using the SPSS statistical package. Collected data were subjected to analysis of variance procedures. Treatments (species, planting date, sweating duration) were in factorial combination with 8 single seedling replications (non sweated seedlings had 4 single replications) using a completely randomized design.

19 Chapter 3 11 RESULTS 1. Bud Survival after Planting Birch Number of broken buds for Birch planted in April increased for all sweating treatments from 0 buds broken at planting to an average of 38 buds broken during the 4 week testing period, except for the 8 day sweating treatment. During the 8 day treatment 13 buds broke prior to planting (Fig.1a). All sweating treatments in May exhibited some bud break during the sweating procedure (Fig.1b). Sweated trees for all treatments had between 8 and 35 broken buds at planting. Also, none sweated trees (0 day treatment) broke some buds before planting. All treatments had a similar pattern with increased number of broken buds between planting and 4 weeks after. June sweating treatments exhibited a high degree of bud break during sweating (Fig.1c), although all trees already had broken buds at the arrival time. Bud break of sweated trees decreased between the first and second week after planting and some additional buds broke by the third week.

20 BIRCH April # of broken buds Planting day 1st week 2nd week 3rd week 0-days 2-days 4-days 8-days Time after planting # of broken buds Planting day 1st week 2nd week 3rd week Time after planting May 0-days 2-days 4-days 8-days # of broken buds Planting day 1st week 2nd week 3rd week Time after planting June 0-days 2-days 4-days 8-days Figure 1: Average Bud break survival after planting for Birch trees, planted in a) April, b) May and c) June. n=8.

21 Hackberry 13 For Hackberry, all sweating treatments increased bud break during the 4 weeks of measurements in April (Fig.2a). Number of broken buds increased from 0 at planting to more than 8 for all treatments by week 4, except for 8-day sweating treatment. Six buds broke during the 8 day sweating procedure by the time of planting (Fig. 2a). All sweating treatments in May exhibited some degree of bud break during the sweating procedure (Fig.2a). All trees had at least a few broken buds at planting. Number of broken buds generally increased during the time between planting and the third week. Some broken buds of 0-day and 2-days sweated trees had died after the first week but additional buds broke after the second week. All sweating treatments in June had some broken buds at planting. Generally, bud break in June increased after planting. Greenhouse-grown Hackberry generally followed the same pattern of bud break sequence as field trees except in June when sweating treatments decreased bud break after planting (Fig. 2c).

22 HACKBERRY April # of broken buds Planting day 1st week 2nd week 3rd week 0-days 2-days 4-days 8-days Time after planting 20 May # of broken buds Planting day 1st week 2nd week 3rd week Time after planting 0-days 2-days 4-days 8-days 20 June # of broken buds Planting day 1st week 2nd week 3rd week Time after planting 0-days 2-days 4-days 8-days Figure 2: Average Bud break survival after planting for Hackberry trees, planted in a) April, b) May and c) June. n=8.

23 15 Norway maple Bud break for Norway Maple planted in April progressed for all sweating treatments from 0 buds broken at planting to over 25 buds broken by week 4 (Fig. 3a). Seventeen buds had broken during the 8-days sweating process and were fully expanded by the time of planting. All sweating treatments in May exhibited some degree of bud break during the sweating process (Fig.3b). All trees had between 5 and 15 broken buds at planting. Number of buds breaking generally increased between first and fourth weeks after planting. All sweating treatments in June exhibited a high degree of bud break during sweating process and had at least 10 buds broken at planting (Fig.3c). Bud break generally did not increase after planting.

24 MAPLE April # of broken buds Planting day 1st week 2nd week 3rd week 0-days 2-days 4-days 8-days Time after planting # of broken buds Planting day 1st week 2nd week 3rd week Time after planting May 0-days 2-days 4-days 8-days # of broken buds Planting day 1st week 2nd week 3rd week Time after planting June 0-days 2-days 4-days 8-days Figure 3: Average Bud break survival after planting for Maple trees, planted in a) April, b) May and c) June. n=8.

25 17 Washington hawthorn For Washington hawthorn, all sweating treatments in April had no buds broken at planting except 8-days sweating treatment. 35 buds had broken during the 8-days of sweating process, but then all died after planting. No additional bud had broken (Fig. 4a). 2- and 4-days sweating treatments had similar pattern between planting and the fourth week after planting. Both sweating treatments had increased bud break one week and decreased bud break the following week. All sweating treatments in May exhibited bud break during the sweating process (Fig.4b). But, these buds had died by the second week after planting and no additional buds broke. All sweating treatments in June exhibited bud break during the sweating process (Fig.4c). Number of broken buds decreased between planting and the third week after planting and many trees dried out. Only two 0-day trees had additional bud break after the second week after planting.

26 18 HAWTHORN # of broken buds Planting day 1st week 2nd week 3rd week 4th week Time after planting April *n=2 0-days 2-days 4-days 8-days # of broken buds May 0-days 2-days 4-days 8-days 0 Planting day 1st week 2nd week 3rd week Time after planting # of broken buds *n=2 June 0-days 2-days 4-days 8-days 0 Planting day 1st week 2nd week 3rd week Time after planting Figure 4: Average Bud break survival after planting for Washington hawthorn trees, planted in a) April, b) May and c) June. n=8, unless otherwise noted *.

27 19 Birch and Norway maple benefited the most from the sweating treatments. Birch exhibited the highest degree of bud break during sweating process. Most of the Washington hawthorn broken buds during sweating process died during the couple of weeks after planting. Hackberry was very slow in terms of bud break during sweating treatments with fewest broken buds. 2. Observational trees Bud swell of birch, Norway maple and Washington hawthorn appeared after two days of sweating in April (Table 1). All species broke buds at the end of sweating. Washington hawthorn produced new root growth after two days in growth chamber. New roots of birch and Norway maple started to grow later than root of hawthorn. At the end of sweating only Birch had 100% new root growth. Hackberry did not produce new root after eight days of sweating. All four species in May had swollen and broken buds at the time we placed them in growth chambers for sweating. Number of broken buds of all four species increased over time. Only Washington hawthorn seedlings produced new root growth before sweating. New rooting among hawthorn trees increased from 50% to 100% of trees producing new roots. New roots of birch appeared after four days of sweating. New roots of hackberry and Norway maple appeared after six days of sweating. Birch and Norway maple were not monitored for bud break in June since those two species broke buds before sweating. Birch trees showed root growth at a rate of

28 20 100% before sweating. Just a few buds of hackberry broke in June during the eight days of sweating. On the other hand, number of already broken buds of Washington hawthorn decreased over time from 71 at the beginning of sweating to 39 at the end of sweating procedure. The new root growth of hawthorn trees was 100% before sweating and decreased to 75% after eight days of sweating. The seedlings of hackberry producing new roots increased from 25% after four days of sweating to 50% at the end of sweating.

29 21 Table 1. Mean bud swell, bud break and mean % of seedlings shown new root growth for observational trees of birch (B), hackberry (Hb), Norway maple (NM) and Washington hawthorn (WH) planted in April, May and June, and sweated for 8 days under 70º F in a growth chamber. Temperature 70º F Days of observation Species B Hb NM WH B Hb NM WH B Hb NM WH B Hb NM WH B Hb NM WH Bud Swell * * * * * * * * April Bud Break * * * * * * * * Roots * * * * * * * * Bud Swell May Bud Break Roots Bud Swell ¹June Bud Break Roots n=8, * missing data ¹ Bud swell, bud break and new root growth of Birch and Norway maple were not observed in June

30 3. Percent Bud Break 22 Birch Birch trees sweated for 0, 2, 4, and 8 days produced better percent bud break when planted in April compared with similar treatments planted in June (Table 2). The 4- day sweating treatment produced the highest percent bud break, 97%. Percent bud break of trees sweated and planted in May generally was similar to April trees with the exception of at least 12% lower percent bud break of trees sweated for 8-days. The 4-day sweating treatment produced the highest percent bud break, 95%. Whereas the 8-days sweating treatment produced only a 78% bud break. In addition, the control (0-day sweating) treatment produced a greater percent bud break than the 8-day sweating treatment. All sweating treatments in June exhibited lower percent bud break than April and May sweating treatments. Trees sweated for 2-days had the highest percent bud break compared with other sweating treatments, (75%), but they remained lower in bud break percent than non sweated trees. Significant differences in percent bud break were found between planting months (April-June) based on sweating treatments. Generally, June planted trees of birch, hackberry and Norway maple resulted in lower bud breaking when compared to April planted trees. April planted trees of birch, hackberry and Norway maple resulted in greater bud break. Washington hawthorn was the least responsive to planting month and sweating treatments of all species based on percent bud break. No significant difference in percent bud break was found among Washington hawthorn sweating treatments.

31 Hackberry 23 Unlike birch, hackberry had much lower percent bud break for all treatments on all planting dates. Percent bud break of all treatments in April was between 48 and 58 (Table 2). Percent bud break for the 2-day treatment was not reported since all of the trees but two were dead. Percent bud break in May was between 42 and 67 whereas in June was between 21 and 57. There was no statistical difference between planting dates within the treatments except for the 0-day treatment (Table 2). Percent bud break of 0-day in May was significantly higher than in June but did not statistically differ from percent bud break in April. Norway maple Maple trees did not benefit from sweating on all planting months since non sweated trees performed better than sweated trees in terms of percent bud break. Percent bud break of sweated maple in April was between 43 and 56 (Table 2). Only the 8-day treatment in May, in the field had percent bud break over 50. The lowest percent bud break in May was for 4-day treatment, 33%. Percent bud break decreased with sweating in June. The 0-day sweating treatment in June produced the highest percent bud break, 59% whereas the 8-day sweating treatment produced only a 35% bud break. Statistical difference in April was found between the 4-day treatment planted in April and May, and the 8-day treatment planted in May and June. Later planting produced lower percent bud break.

32 Washington hawthorn 24 Compared to the other three species, Washington hawthorn had the worst percent bud break in all treatments and planting dates (Table 2). Hawthorn planted in April produced percent bud break between 16 and 35%. Trees sweated for four days had the highest percent bud break. Bud break in May did not exceed 21% in any of the treatments. The 8-day treatment had the highest percent bud break. Similarly, bud break of sweated trees in June did not exceed 21%. Sweated trees had 17-21% bud break. Treatments did not statistically differ between planting dates (Table 2).

33 Table 2. Mean percent bud break for birch, hackberry, Norway maple and Washington hawthorn in April, May and June. Differences between planting dates analyzed by sweating treatment performed by Duncan significant test of difference. 25 Sweating Treatments (Days) Birch 0** APRIL 91a 89a 97a 90a MAY 85a 87a 95a 78ab JUNE 83a 75a 66b 67b Hackberry APRIL 58ab¹ 52a -* 48a MAY 67a 58a 52a 42a JUNE 21b 57a 56a 32a N. maple APRIL 64a 56a 54a 43ab MAY 45a 43a 33b 53a JUNE 59a 41a 45ab 35b W. hawthorn APRIL 26a 18a 35a 16a MAY 12a 14a 14a 21a JUNE 29a 17a 21a 21a ¹ n=2 *=missing data ** Values followed by different letters are significantly different within the column p<0.05

34 26 4. Dry Weight Birch, Norway maple and Washington hawthorn trees showed decreasing mean dry weight of leaves the later the planting date (Table 3). The exception was hackberry. Hackberry mean leaf dry weight for trees planted in June had greater leaf dry weight than tree planted in April. Hackberry mean dry weights were less than mean dry weights of other three species in all three months of planting. This may be due to the fact that some hackberry trees died due to rabbit browsing and the sample number was lower than the other three species. Birch had the largest mean dry weight of the leaves during all three months followed by Norway maple and hawthorn. Birch had a clear response to planting date (Table 3). There was a significant difference between April and May and April and June leaf dry weight. Early planting was beneficial for Birch trees. May and June planting did not differ statistically. Hackberry leaf dry weight did not show any significant difference between the three planting dates. Norway maple showed significantly greater leaf dry weight when planted in April than in May or June (Table 3). No statistical difference was found between May and June leaf dry weight. Late planting was also detrimental for Washington hawthorn. April planted trees had significantly greater mean dry weight of leaves than May and June planted trees. There was no statistical difference between May and June means dry weight of leaves. When treatments were included in observation and statistical analysis, we found almost no response to different duration of sweating within the same month in terms of dry weight of leaves in all four species. The only exception was hackberry planted in

35 April and Norway maple planted in June. According to Duncan test we found that 27 hackberry had significantly greater leaf mean dry weight for 0-day compared to the 4- and 8-day treatments, although half of the 0-day trees were missing (Table 4). Control trees and 2-day treated trees did not statistically differ in leaf mean dry weight. Also, Norway maple trees sweated for 4 days in June had significantly greater mean dry weight of leaves than trees sweated for 2 and 8 days. No statistical difference was found between 0-day treatment and 4-day treatment (Table 4). On the other hand, mean leaf dry weight of the same treatments of birch, Norway maple, and Washington hawthorn responded to planting time (Table 4). Dry weight of leaves decreased with late planting but not always significantly. Different planting time did not have impact on leaf dry weight of hackberry in any of the treatments but 8-days of sweating. Hackberry trees planted in June had significantly greater leaf dry weight than trees planted in April. Leaf dry weight of Birch was significantly greater in April than in June in all of sweating treatments but 2-days. Statistical difference between planting dates of 2-day sweating treatment was found between April and May planted seedlings. Two days of sweating of Norway maple produced significantly more leaf dry weight in April than in May or June. Also, eight days of sweating of Norway maple produced significantly less leaf dry weight in June than in April or May. Only 4-days sweating of Washington hawthorn showed statistical difference between different planting dates. Hawthorn planted in April had greater leaf dry weight than in June.

36 Table 3. Mean Dry Weight (grams) for birch, hackberry, Norway maple and Washington hawthorn in April, May and June. Differences between months performed by Duncan significant test of difference. April May June Species Birch 44.35g 28.84g 23.07g Hackberry 3.18g 4.08g 4.69g N. Maple 17.69g 9.03g 5.89g W. Hawthorn 14.96g 8.96g 6.76g Birch Significance April vs May * April vs June * May vs June NS Hackberry Significance April vs May NS April vs June NS May vs June NS Norway Maple Significance April vs May * April vs June * May vs June NS W. Hawthorn Significance April vs May * April vs June * May vs June NS NS, * Nonsignificant or significant at p=

37 Table 4. Mean Dry Weight (grams) for birch, hackberry, Norway maple and Washington hawthorn in April, May and June. Differences between planting dates analyzed by sweating treatment, and Differences between sweating treatments analyzed by month performed by Duncan significant test of difference. Days of sweating Birch (g) (g) (g) (g) April May June Significance April vs May NS * NS NS April vs June * NS * * May vs June NS NS NS NS Hackberry April² ¹9.03a 3.9ab ¹0.86b 1.39b May ¹ June ¹ Significance April vs May NS NS NS NS April vs June NS NS NS * May vs June NS NS NS NS Norway Maple April May June² 6.95ab 4.60ab 9.20a 3.34b Significance April vs May NS * NS NS April vs June NS * NS * May vs June NS NS NS * Washington hawthorn April May June Significance April vs May NS NS NS NS April vs June NS NS * NS May vs June NS NS NS NS NS, * Nonsignificant or significant at p=0.05 ¹ n=2 ² Values followed by different letters are significantly different within the rows, p

38 30 5. Height and Caliper Height Late planting decreased heights of birch and Norway maple planted in field (Table 5). On the other hand, late planting was beneficial for hackberry and Washington hawthorn. Significant difference was observed in heights for all four species between different months of planting. Birch and Norway maple had significantly greater heights in April than in June. On the other hand, Hackberry and Washington Hawthorn had significantly greater heights in June than in April. Caliper Late planting decreased caliper of all species grown in field (Table 5). Significant difference in caliper was observed for all species but Birch. Significant differences in caliper were found for treatments planted in April and June for all species but Washington hawthorn.

39 31 Table 5. Mean total height and caliper of birch, hackberry, Norway maple, and Washington hawthorn planted in April, May and June. Differences between planting dates by height or caliper. Species Height [inch] Caliper [mm] Birch April 49.26a 12.07a May 43.94b 9.36a June 41.84b 10.75a Hackberry April 19.96a 5.70a May 24.52b 5.75a June 26.86b 4.81b Norway Maple April 44.54a 14.94a May 42.66b 11.59b June 30.76b 9.09c W. Hawthorn April 30.53a 10.21a May 30.60b 8.60b June 35.33b 8.81ab Values followed by different letter are significantly different within the column, p 0.05

40 6. Stem Die Back 32 There was little or no stem die back among Birch trees planted in April and May. Stem die back of sweated trees increased to 2 (11-20% die back) in June (Table 6). Sweating did not improve stem die back of birch at any planting date. In contrast, Washington hawthorn suffered significant stem die back at each planting date and over all sweating treatments. Of the 12 planting date-sweating treatment combinations, an 8 (71-80% die back) resulted in more than 50% of stem die back. Hawthorn stem die back was 50% or more for all treatment combinations except for trees planted in April when stem die back was rated from 3 to 5 (21-50% die back) on the stem die back scale. Hackberry suffered significant stem die back in June. But sweating did reduce stem die back in June from 7 (61-70% die back) of controls (non-sweated trees) versus rates of 5-6 (41-50% die back) of sweated trees. Sweating treatments also appeared to reduce stem die back for hackberry trees planted in May from 3 (21-30% die back) to 2 (11-20% die back). Hackberry trees planted in April had less stem die back than trees planted later except the trees sweated for 4-days with the rated stem die back of 8 (71-80% die back). Norway maple planted in April had minimal stem die back among all sweating treatments 1 (0-10% die back) except for trees sweated for 8-days when rated 2 (11-20% die back). Stem die back increased with late planting. In June, stem die back was rated 2 (11-20% die back) among all sweating treatments. Sweating treatments slightly improved stem die back in May.

41 Table 6. Mean Stem Die Back of birch (B), hackberry (Hb), Norway maple (NM) and Washington hawthorn (WH) planted in April, May and June, and sweated for 0, 2, 4, and 8 days. Stem Die Back¹ Planting date April May June Sweating Treatment (Days) Species Species Species B B B Hb 1* Hb Hb NM NM NM WH WH WH n=8, except noted *.*n=2 ¹ Stem Die Back was rated on a 1-10 scale, where 1 = 0 10% dieback, 2 = 11 20%, 3 = 21 30%, 4 = 31 40%, 5 = 41-50%, 6 = 51 60%, 7 = 61 70%, 8 = 71 80%, 9 = 81 90%, 10 = %. 33

42 34 Chapter 4 DISCUSSION This research was designed to assist the industry in addressing cultural methods for enhancing survival and performance of nursery liners during the lifting to transplanting time. Modifying cultural practices need to result in an improvement for the industry such as higher prices, better survival, faster growth, etc. Some tree species, such as Washington hawthorn, show low survival rate and poor performance after bare-root production and transplanting, slow bud break, stem dieback and low establishment rates (Insley, 1985). Sweating procedures need to be investigated closely since there are few research-based recommendations for sweating procedures, species that benefit from the practice, or its effect on tree establishment. This research documents the difference between species which have been identified as easy and difficult to plant as bare root liners. 1. Sequence of Bud Break The results of this study indicated that all four species had similar patterns of bud break during three different months of planting except Washington hawthorn in April and May. Bare root seedlings were still dormant at the beginning of April. Eight days of sweating were sufficient for all four species to break buds prior transplanting. Number of broken buds of those seedlings continued to increase during the first and second week after transplanting and then remain the same during the observation period. Seedlings subjected to shorter time of sweating broke buds later, during the first two weeks after

43 35 transplanting. Trees sweated longer may have had more time to release bud dormancy and start bud break sooner after transplanting. It seemed that sweating gradually acclimatize dormant bare root seedlings to a new environment. Bud expansion during sweating likely triggered new root growth so transplanted trees could withstand low temperatures and occasional frosts in the field. June transplanting is considered late planting for trees. Sweating seemed a waste of time since all four species already broken some buds prior the arrival in June. Nevertheless, sweated birch and hackberry broke more buds during the observation period than non sweated trees. Bud break and survival of Washington hawthorn was difficult to explain conclusively for April and May. Buds were breaking and drying alternately after trees were transplanted in the field during the time of observation in April. This study agreed with the traditional consideration that Washington hawthorn is a species difficult to handle bare root. The biggest problem with this species is poor performance due to desiccation during bare root handling. 2. Observational trees Our research documented the difference between species in terms of bud break and new root growth during the sweating procedure. In general, the sweating procedure seemed beneficial for breaking bud dormancy leading to bud swell and bud break for all species observed in April and May. While other species in June were already having buds open prior sweating, Hackberry was the only species with just a couple of opened buds before and during sweating. Prolonging time in cold storage might deepen or extend dormancy of hackberry seedlings, and even the sweating procedure could not increase

44 36 bud break. On the other hand, warm and humid conditions of sweating forced new root growth of hackberry in June. Sweating conditions were detrimental for broken buds of Washington Hawthorn in June. Root regeneration occurred after bud swell and bud break in all species but hawthorn. The new root growth of hawthorn occurred at the time of bud swell, even as early as April. Hawthorn growth measurements such as percent bud break or stem die back after transplanting, were poor. It is questionable if hawthorn needs to be sweated since the procedure did not improve tree establishment. The recommendation against sweating could also be the case for hackberry since this species also showed high degree of stem die back, in spite of sweating treatments. 2. Percent Bud Break Although birch is sometimes recommended as a species that benefits from sweating, this study showed this species as tolerant to transplanting stresses. According to the results, sweating did not have significant impact on percent bud break of birch in any of the months. Subfreezing temperatures at the beginning of April did not harm birch. Moreover, April seemed to be the best date for planting birch, with. Birch growth decreasing when planted in June. Unlike birch, hackberry was very sensitive to desiccation stress since many buds dried out in all sweating treatments and planting dates. It seemed that April was too early for planting hackberry. Low temperatures and occasional frosts were detrimental for many hackberry seedlings. Hackberry was the hardest species to get into leaf in April probably because its buds stay dormant and hard during cold storage. Even sweating

45 37 could not force bud break. Sweating was beneficial for trees planted in June since all sweating treatments had at least 11% higher bud break than 0-days treatment. This was probably because sweating conditions forced faster new bud break after already broken buds died. Norway maple had surprisingly low percent bud break compared with Birch. Our results agreed with previous studies reported by Murakami that Norway maple is a very desiccation tolerant species. Trees sweated in April did not benefit from the sweating procedure. On the other hand, sweating improved percent bud break in May. June planting was not as detrimental for maple as for other species probably because Norway maple is a desiccation tolerant species and could withstand unfavorable conditions at a late planting date. Percent bud break of Washington hawthorn was much lower than the other three species. Sweating procedure did not have positive effect on its bud break as it was expected. There was occasional benefit from sweating in April and May but data were not conclusive. Sweating in June decreased percent bud break. 4. Dry Weight Our research documented the difference between species and how these species respond after bare-root planting on three planting dates in terms of trees growth and overall performance. Birch, Norway maple and Washington hawthorn appeared to be more vigorous, with greater leaf dry weight when planted in April, compared to June planting. On the other hand, hackberry showed poor performance at all three planting dates, with greater leaf dry weight when planted later, in May and June.

46 38 Despite the fact that Birch is often described as a desiccation sensitive species, our research found this species as very tolerant to bare-root planting during the spring months. Although late planting in June significantly decreased leaf production those trees were well established and all marketable. It seems that birch has the ability to withstand transplanting stress and recover fast since trees planted in June renew desiccated buds and perform well. This may be due to rapid root regeneration after sweating. The sweating procedure forced both bud break and new root growth of birch in all planting dates. In addition, significant difference in leaf fresh weight between April and Mayplanted birch is in agreement that this species is sensitive to planting date. Unlike birch, hackberry and Norway maple did not show a response to planting date. Moreover, hackberry had better performance when planted later, in May or June. This species was hard to grow in all three months of planting. Even in June, hackberry did not have broken buds prior sweating procedure unlike other three species. The sweating procedure was helpful for hackberry and increased leaf dry weight in May and June. However, sweating and planting in April was detrimental for Hackberry. This conclusion should be taken with reserve due to lack of data in April. Norway maple decreased leaf dry weight with late planting but not significantly. Washington hawthorn, unlike birch suffered from drying in all three months of planting. Opened buds after sweating and planting dried in most of the cases. New broken buds and consequently new leaves appeared later after planting. This may be due to slow root regeneration after transplanting. Despite slow recovery after transplanting on all three planting dates, hawthorn planted in April had significantly greater leaf dry weight than in June.