ARBORETUM NEWS (NATURALISTSNOTES)

Late Fall Woodlands

SUNDAY, NOVEMBER 27, 2011

In just two days, from Friday’s almost 60 degrees, sunny and only a light south breeze, we have gone through a day of rain to today’s mid 30 temperatures with a 15 to 25 mile an hour north wind. The sharp contrast in weather makes for a different experience when walking in the Arboretum’s late fall woodlands.

First, might I ask the obvious, does the term “fall” to name the season more properly known as “autumn” have to do with the falling of leaves? I suspect so. So why do leaves fall? One reason leaves fall is to reduce the leaf surfaces during the “dry season” of frozen temperatures when water is scarce because it is frozen. Cold air is often dry, lower humidity, and frozen soil provides little water for roots to absorb. Also, leaves fall to reduce possible broken branches from accumulation of wet, heavy snow during winter storms. There are probably other reasons, too. In any case, now there are leaves covering most of the forest floor.

The leaf cover and the absence of leaves in most of the native deciduous trees and shrubs in some cases help to identify some of the leafless trees and shrubs. Now you can see to the tops of the dominant big oaks, while in summer with all the leaves on the trees your view to the forest canopy is blocked by a sea of green leaves. The leaves of these big trees are often out of reach during summer, but now you can find them by looking down at the ground. Assuming you match the correct fall colored leaf with the tree you are trying to identify, you can compare leaf, bark, tree size and shape with a tree field guide to make an identification.

To identify the large open grown, largest diameter trees in Wingra Woods, look among the leaves below them and select the oak like leaves. You can be pretty sure it is an old red or black oak if a majority of the oak like leaves have points. It is more likely a white oak if most of the leaves below the tree have rounded tips. Bur oaks tend to be in drier locations, often near the edges of the woods.

Similarly in Gallistel Woods there are many maple leaves under foot. By examining the leaves under the smooth bark, tall maples, you can make a good guess at which is a sugar maple or a red maple. One problem with this method of identifying trees after their leaves have fallen is that some leaves decompose rather quickly while others, like oak leaves, persist much longer. Birch leaves, for example, are relatively small, fall earlier than many other types of leaves and decompose quickly. Fortunately the bark of the birch trees is rather distinct. Just from examining the bark you can identify white or paper birch, yellow birch and river birch.

The bark of a tree can be a major factor in identifying the tree. Black cherry is known for its dark, burnt potato-chip appearance. Shagbark hickory on older trees has a very shaggy bark with long strands of peeling bark hanging off the trunk. Hackberry has a very rough, warty-growth with ridges that looks cork like, but is tough.

Nuts are another way to identify trees in the fall and it is often easier to do so after the leaves have fallen and the nuts are more visible or after the nuts have fallen and are under foot. Its large fruit easily identifies the black walnut, with a hard green sheath around a hard inner sheath that contains the edible nut. The shagbark hickory can be identified by its hard nut, which is eaten by several of the forest animals. A common sound in the fall woods is that of a squirrel gnawing on one of these hard nuts.

In general the late fall woodlands are rather quite. The usual bird calls are those from the mixed species feeding groups of Black-capped Chickadees, White-breasted Nuthatches and accompanying woodpeckers, usually Downy, Hairy or Red-bellied Woodpeckers. Since these non-migratory, resident birds do not maintain territories and are not attracting mates at this time of year, there is very little bird song. On a calm day the dominant sound is the swish of your foot steps in the leaves, but on a windy day, like today, the dominant sound is the wind rustling the leaves and moving the tree branches.

The overall feeling on a late fall walk through the Arboretum woodlands today is lets seek some shelter from the wind and the cold. The squirrels hole up in cavities high in the trees or in their leafy nests. The chipmunks are sheltered under ground in their holes. Most birds seek shelter in the evergreens or dense bushes. Only the larger, hardier animals and birds, such as Turkeys, Raptors, Crows are likely to be out and about today. Somehow the plants know, certainly the animals and birds know and so do we know that frost and snow, with frozen ground, will be visiting us soon!

Levi Wood
UW Arboretum Naturalist

Located between Lake Wingra and the West Beltline Highway at 1207 Seminole Highway, the University of Wisconsin-Madison Arboretum features the restored prairies, forests and wetlands of pre-settlement Wisconsin. This 1,260-acre arboretum also houses flowering trees, shrubs and a world-famous lilac collection. Educational tours for groups and the general public, science and nature-based classes for all ages and abilities, and a wide variety of volunteer opportunities for groups, families and individuals are available.