Comparative Nocturnal Thermal Budgets of Large and Small Trees

Abstract

Less freeze injury was observed in unprotected large citrus trees during the freezes of 1962 and 1963 than in small. Earlier observations in the Coachella Valley of southern California prompted this study of the nocturnal heat exchange of a small (3—year—old) and a large (40—year—old) grapefruit tree in two orchards of their respective sized trees. Micro—climate studies were made in these orchards during several winter seasons. Other data for heat transfer calculations have been developed from numerous sources. The heat transfer budget for calm nights showed that leaves were the principal heat exchangers and that shading by neighboring trees reduced their radiation rates to about half in large trees. Stored heat of the ground beneath, and in the woody framework inside the large trees was reflected and reradiated within the leafy crown which had highly insulating properties. The top of the crown of large trees was warmed by the inversion layer.

Thermal Conductivity of Functional Citrus Tree Wood

“…MacLean (13) (24), the specific enthalpy (H.) calculated from table II is 1.02 X 104 cal trunk-' C-1 in the former and 1.02 X 102 in the latter. If the trunks were at a maximum of 00 during daylight as on the first day and -5.6°mini-mum the following night (32) the total heat available in the trunk of the large tree was 5.7 1 X 104 cal compared with 5.71 X 102 in the small tree which while adequate in the former, is far from adequate to meet the heat demand necessary to prevent freezing in the latter (table V).…”

“…Although thermal conduction was correctly considered bv Raschke (18) to plav a minor role in the heat transfer of the plant, under the stress of nocturnal advection freezes and radiation frosts, this is not the case in subtropical plants which bear leaves and fruit during winter. The magnitude of thermal conduction in the wood, relative to its mass, is important in preventing frost damage to citrus trees (24). Therefore, we have determined longitudinal and transverse thermal coniductivity coefficients for 4 species of citrus and used these coefficients to analy)se the effects of freezing temperatures on 2 cm and 20 cm diameter trees.…”

Microclimatic Effects on Water Relations, Leaf Temperatures, and the Distribution of Heracleum Lanatum at High Elevations

“…Moen (1968) reported significant reductions in longwave irradiance at night in a clearing as opposed to beneath the forest canopy, the decrease being the result of an increase in exposure to clear skies, which emit less longwave irradiance (Gates, 1980). Both Turrell and Austin (1965) and Miller (1967) found cooler leaf temperatures at the top of tree canopies due to radiative cooling through energy exchange with clear night skies. Parkhurst and Loucks (1972) concluded that the large leaves were more susceptible to radiation frosts than small leaves for the temperatures oflarge leaves are more closely coupled to sky temperature.…”

Effect of Some Foliar Applications of Nutrients on Fruit Set and Yield of Valencia Orange Trees in Newly Grown Orchards

“…The tree canopy volume (m 3 ) was calculated at the beginning and at the end of each experimental growing season according to the equation: Canopy volume (m 3 ) =0.5236 x height x diameter square as stated by (Turell, 1965). Then, the yearly increments were calculated.…”