Temperature Fluctuation in Fraxinus pennsylvanica var. subintegerrima and Its Surrounding Environment
Authors: Shirazi A.M. , Vogel S.H. 
Published: January 2022

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.