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Comparative Nocturnal Thermal Budgets of Large and Small Trees

Turrell, F. M., Austin, S. W.
Ecology 1965 v.46 no.1-2 pp. 25-34
Citrus, grapefruits, heat exchangers, heat transfer, leaves, microclimate, orchards, shade, trees, winter, California
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.