I am measuring trees for a project and am trying to determine why the tree is larger in the evening?

Answer 1

The tree feed during the day.This is because the tree gets the sunlight which heats up the tree and this causes the moisture to flow upward and through the branches to the leaves.when this happens,it causes the branches and leaves to perk up which gives it the appearance of being larger.At night,the moisture settles to the lowest point and the next day,it starts all over again.

Answer 2

A tree's actually size, based on industry standards, does not fluxuate between night and day. Assuming the tree is in a growth stage rather than receeding into a dormant stage, the tree is continually growing, but from night to day, or visa versa, there is such an minute change, that it cannot be measured by normal means.
Timber industry and federal/state research stardards for measuring tree size are based on the diameter of a tree at breast height (4.5 ft from ground) and the tree's height.
From your question, I can assume that you're speaking of the tree in its entirety, crown and all. The only larger/smaller growth that could be noticed is an obtical illusion that is experienced by the differences in light, barometric pressure, etc.
Sorry if this was no help...

Answer 3

Assuming you are speaking of the tree's girth measured at D.B.H. (Diameter at Breast Height; 4.5 ft. from the ground), the tree will fluctuate throughout the day (just as your weight will fluctuate throughout the day). Trees will thin out during the afternoon when the tree is most active and water is being moved up the stem (trunk, bole) and out into the branches and leaves through capillary action. When the water gets to the leaves, it escapes the leaves (evaporates) or is broken apart and used in the energy production cycle (photosynthesis). At night, after the sun has set, the water in the tree will settle in the tubular cells of the tree's trunk (xylem and phloem) as the leaves have closed their exit and entry ports (stomas). Since nothing can get out of the tree, the water pressure pushes back down in association with gravity and thus, back into the trunk. This happens during "leaf on" season (spring, summer, some of fall) for deciduous trees and to a greater or lesser degree all year long for coniferous trees. During the "leaf on" or growing season, a tree will swell and thin everyday and build new cell layers faster than during the end of the season when the tree's growth production begins to slow down. This cycle produces the common growth rings of the tree. the lighter colored rings being the faster grown summer wood and the darker colored rings being the slower grown winter wood (although, these rings aren't grown in the winter, just towards the end of the growing season).