Signs of spring are all around us, but there are still some interesting discoveries to be made about the past season. Early spring is a perfect time to learn about the winter diet of white-tailed deer. We may think that deer are basically grazers as we see them placidly feeding in fields, like cows and horses. But that would be wrong. Cows, horses–and bison, to include an example of a wild species–are strict grazers and consume grasses, forbs, and other non-woody plants year-round. Deer are browsers rather than grazers. Although they feed on the same kinds of low-growing vegetation as grazers during the growing season, in winter they switch to the twigs, buds, and bark of woody plants. The deer you see in the lead photo (not my shot, but I couldn’t find a good attribution for it) are eating the twigs of a cedar sapling.
Deer do not have upper incisors, so in order to remove a twig they clamp it between their lower incisors and their tough upper palate. A jerk of the head suffices to yank the twig off, enabling it to be macerated by the molars and then swallowed. Rough breaks like those shown on apple in the photo below indicate that deer were feeding on the small twigs.
This contrasts with the sign left by rabbits and hares, which also depend on woody browse for winter food. Rabbits have both upper and lower incisors, and they make sharp, angled cuts like the ones shown in the next photo of multiflora rose.
The browsing preferences of deer vary in different regions. Some of their favorites in the northeast are sugar maple, ash, dogwood, striped maple, northern white cedar, and hemlock. In the next photo you see a sugar maple branch that was browsed by deer. The animals are not equipped to chew on larger branches, so they limit their browsing to the small twigs and buds at the branch tips. In mature forests these only become available if trees or large branches fall, which is exactly what happened in this case.
Hungry deer will eat everything they can reach, and unrelenting feeding often leaves browse lines like the one on northern white cedar in the photo below. This doesn’t affect the overall health of the stand, but browsing can have adverse effects on the growth of smaller trees.
The ash seedlings in the next photo show the excessive lateral branching patterns that result from heavy browsing. During each growing season the young trees form new twigs and buds, but each winter the new growth is eaten by hungry deer. The stunted trees are never able to outgrow the reach of the deer and eventually die.
Deer found a hemlock sapling at the edge of a field, and you see the result in the next photo. It’s hard to see the hemlock against the background because so many of the small twigs have been eaten, but if you follow the main stem up from the bottom center of the photo you’ll see how much foliage is missing.
Overbrowsing makes a difference in the appearance of forests. In the next photo you see a woodland that has been heavily impacted by winter deer feeding. The lack of understory trees makes it easier to walk through this kind of forest, and its cleaner appearance may be more appealing. But this forest is in trouble.
In the next photo you see a much healthier woodland. The spaces between the large trees are filled with young and medium-sized saplings, and these are the ones that are ready to fill gaps when larger trees die or fall.
Without a multi-aged understory, forests have limited ability to regenerate. When large trees die, there are no young trees ready to fill in the gaps. It’s true that there are seeds in the soil that will germinate quickly once openings are formed, but the delay in regrowth may allow invasive species to get a foothold. Signs of deer browsing tell us much more than the mere presence of hungry animals. There are larger lessons to be learned, and nature is ready to share them if we are willing to pay attention.