Arboriculture & Urban Forestry 33(3): May 2007 Arboriculture & Urban Forestry 2007. 33(3):193–201. 193 Temperature Fluctuation in Fraxinus pennsylvanica var. subintegerrima and Its Surrounding Environment A.M. Shirazi and S.H. Vogel Abstract. Temperature fluctuation (TF) in an 18-year-old Fraxinus pennsylvanica var. subintegerrima and its surrounding environment was monitored using HOBO Pro temperature sensors recording every 15 min from December 2001 to February 2003 at The Morton Arboretum, Lisle, Illinois, U.S. There were significant differences (P< 0.05) between TF in 2001, mild cold temperatures, and 2003, severe record-breaking cold temperatures. In mid-December 2001, TF range in soil 30 cm (12 in) was 4°C (39.2°F) to 4.5°C (40.1°F), sod was 3°C (37.4°F) to 4°C (39.2°F), and soil surface was 2°C (35.6°F) to 2.5°C (36.5°F), whereas canopy and mulch ranged from −1°C (30.2°F) to 10°C (50°F). The south side of the trunk had the highest fluctuation of 1°C (33.8°F) to 14°C (57.2°F) followed primarily by the west side with occasional peaks in the east. However, the west side had the highest temperature peak in mid-June. The temperature difference between south and north sides during mid-December were approximately 7°C (44.6°F). In April, the TF inside the trunk ranged from 2°C (35.6°F) to 5.5°C (41.9°F) compared with the canopy, which varied between −0.5°C (31.1°F) and 8°C (46.4°F). The west side was 2°C (35.6°F) to 3°C (37.4°F) higher in mid-July than the south, east, and north sides. On 15 February 2003, which was the coldest day recorded, the soil 30 cm (12 in) temperature (under the mulch) reached ≈−1°C (≈30.2°F), whereas sod and soil surface were ≈−2°C (≈28.4°F). Mulch and base temperature ranged from −1°C (30.2°F) to −5°C (23°F) and −2.5°C (27.5°F) to −7.5°C (18.5°F), respectively. Root core temperature was ≈−1°C (≈30.2°F), the trunk temperature range was −2.5°C (27.5°F) to −3.5°C (25.7°F), whereas the canopy was −2.5°C (27.5°F) to −7.5°C (18.5°F). The south TF range was between −0.5°C (31.1°F) and −7.5°C (18.5°F) from midday to midnight. The TF difference between south and north sides was ≈2.5°C (≈36.5°F). This freeze and thaw of the south side during winter months has been attributed to sunscald in some trees. Based on temperature observations during the coldest and warmest week, a temperature fluctuation factor (TFF), a difference between weekly minimum and maximum temperature, was introduced. During the coldest week, the TFF for canopy to trunk was 2×, trunk to root or soil was 10×, and canopy to root or soil was 20×. During the warmest week, the TFF for canopy to trunk was 2×, trunk to root or soil was 7.5×, and canopy to root or soil was 15×. The stem water content was higher throughout the year; however, the bud water content was significantly higher when approaching budbreak in April to May. In a companion study, the effect of mulch depth on TF was reexamined showing that the temperature of mulch varies dependent on the time of year. In October, 15 cm (6 in) mulch was several degrees warmer than ground, 7.5 cm (3 in) mulch, and 30 cm (12 in) mulch (P < 0.05); however, in December and February, 30 cm (12 in) of mulch was significantly warmer (P < 0.05). There are many factors other than temperature that affect tree growth and development. The dynamics of TF give a greater understanding of the role temperature plays in tree physiology as well as improving horticultural and arboricultural understanding in urban environments, resulting in improved landscape management. Key Words. Canopy; cold hardiness; HOBO Pro; mulch; root zone; sod; temperature sensor. Higher plants are ectothermic and as such are unable to main- tain a constant optimum temperature in their tissues (Fitter and Hay 1987); therefore, their growth, development, and performance are all affected by environmental factors of which none are as vital as temperature (Weiser 1970). Ability of temperate woody plants to withstand freezing temperatures is affected by temperature fluctuation (TF) within the tree and its surrounding environment before freezing tempera- tures (Levitt 1980; Sakai and Larcher 1987). Temperature fluctuation, a frequent freezing and thawing during winter in temperate woody plants, may contribute to reduced cold hardiness (Sakai and Larcher 1987) depending on the stage of dormancy (Shirazi and Fuchigami 1995) and poststress temperature (Shirazi and Fuchigami 1993). The extreme vari- ability of air and soil temperatures forces plants to adapt, tolerate, or avoid temperature extremes (Levitt 1980). In tem- perate climates, roots begin to grow after soil is thawed com- pared with milder climates in which roots grow all year round. The ability of roots to grow is dependent on species and genotype but is also affected by soil temperature, soil moisture, and oxygen availability (Kozlowski and Pallardy 1997). ©2007 International Society of Arboriculture
May 2007
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