Trees move water from below ground level to their leaves, sometime 100ft or more above ground level.
The water in the ground is warmed by geothermal activity/stored solar heat etc.
Ground water is ALWAYS at a significantly higher temperature than the local air.
Trees concentrate the heat from the ground. Tree roots transport heat from a large area underground (typically the area of the tree at ground level x thousand) and concentrate it into small diameter tubes of wood that stick out of the ground.
The result is that air temperature in forest is significantly higher than air temperature in the same region where there are no trees.
ALSO tree ring diameter is linked to the density of trees in the surrounding area.