I don't hike the arboretum in winter, so the photos here are of our yard after the first heavy snowfall of the year. But I do get newsletters from the arboretum on a regular basis, and the most recent one included some information that was new to me.
"It has long been believed that fallen pine needles acidify (reduce the pH of) the soil. This isn’t the case, however. While the fresh needles are acidic, the pH is neutralized during decomposition and they have no real effect on soil acidity. A recent study from the University of Wisconsin–River Falls looked at soil pH under older deciduous and coniferous trees, including four pine species, and found no relevant effect on soil pH caused by needle or leaf litter decomposition over time."
"Sporting fragrant, perfect flowers with four unique sulfur-yellow, strap-like petals, common witch-hazel (Hamamelis virginiana), a Wisconsin native, still displayed a few flowers in December. The common name is thought to derive from the old English wych, meaning “to bend,” in reference to the plants flexible branches, and “hazel” comes from the resemblance of the leaves to those of hazels in the genus Corylus.Witch-haze flowers are fragrant, bear nectar, and produce abundant sticky pollen. They are not able to self-pollinate however, which indicates that they are insect pollinated. Though witch-hazel reproduction is not fully understood, research indicates that flies and fungus gnats play a role in pollinating the flowers in the fall before freezing temperatures. For flowers present during winter, owlet moths in the family Noctuidae, referred to as shivering moths, appear to play a role. These moths overwinter as adults, living under leaf litter, and have the ability to raise the temperature around their flight muscles by as much as 50°F by shivering, so they can fly in search of food during winter months."