Naturally Speaking
Now is not a good time to pick out a Christmas tree. There are too many yellow leaves. Evergreen trees, like deciduous trees, lose their leaves, except evergreens drop some of their older leaves and retain the younger ones for a year or longer.
White pines, for example, keep their leaves (called needles because of their shapes) for two-to-three years. Needles produced in 2015 will not die and fall off the tree until 2018. The time when pine needles yellow, then turn brown, and eventually drop off is about the same time deciduous trees are dropping leaves. That's usually late September through October.
Right now pines, and many evergreen trees, have dying, yellowing, browning needles, as well as bright green, healthy needles. Within a few weeks all those old, dead needles will be on the ground under the pine trees.
Because the leaves are needle-shaped, they usually drop directly below the tree and don't blow around like leaves from broadleaf trees. That's beneficial to the pines because the decomposing needles help to make the soil beneath pines more suitable for pine tree growth.
So wait a few weeks (you would anyway) to select this year's Christmas tree. If there are still dead needles on that special tree, shake them off.