An aggressive hatch of Douglas-fir tussock moth caterpillars is threatening trees, both in national forests and in Santa Fe.

Vladimir Kokorin / Getty Images. There are many coniferous trees that have single needles directly and singly attached to the twig. These attachments can be in the form of wooden "pegs" (spruce ...

Dave Powell/USDA Forest Service (retired) / Bugwood.org. All spruce trees have sharp-pointed needles that are often 4-sided or diamond-shaped in cross-section and have four whitish striped lines.

Evergreens like pine, spruce, fir, arborvitae, and hemlock only retain the newest years’ needles (2 or more years), and naturally lose their inner (oldest) needles on established trees each year.

White fir and red fir trees are dying at a fast clip in the Lake Tahoe Basin, the U.S ... But as the summer progressed, the orange-hued needles seemed to spread from tree to tree.

Two Christmas tree experts explain how to choose between the many types of fir, pine, and spruce. If you're going to buy a live Christmas tree this year, there's a good chance it will be a fir.