Forest Stewards

Acorns: Science & Mysteries

Penn State Forest Stewards series article – written by Jim Finley, Professor Emeritus, Forest Resources Management, Center for Private Forests at Penn State.

Oaks are economically important tree species in Pennsylvania and across the East. Acorns, or mast – a word derived from old English which means “forest food,” are important to wildlife. Oak-borne mast production varies from year to year. Much research has sought to predict masting years, when big acorn crops occur, and shed light on what leads to poor years – or early acorn abscission (detachment) – like you may have seen this season.

Science and Mysteries of Acorns - Pennsylvania Forest Stewards article

Oaks separate into two groups, popularly referred to as red and white, and learning to identify the difference between the two groups is easy.

Red oaks – e.g. Northern red oak, pin oak, scarlet oak, and black oak – have small “bristles” on the lobes and tips of their leaves. White oaks – e.g. white oak and rock, or chestnut, oak – lack these bristles, and have rounded leaf lobes.  (CFC note: the image above is of a white oak.)  There are other differences that are more difficult to recognize, such as acorn structure and wood anatomy.

The Process of Creating an Acorn –
and the Trials of 2020

Both red and white oaks produce female and male flowers on the same tree, unlike ash which has male and female trees. The process of producing an acorn starts late in the growing year when the male flowers form as the tree’s growth slows toward the end of summer. That is the end of the first year (year 1) in the process. Then, in the second year (year 2), as the tree comes out of dormancy, female flowers form in the axil of the leaf stem and the twig and remain dormant. As the spring leaves begin to unfold, the male flowers emerge and are very apparent as rather-long, drooping, greenish-yellow catkins. These appear about two weeks before the much smaller female flowers emerge.

White Oak Acorn Production

For the white oaks, as the male and female flowers emerge in year 2 as described above, pollination and fertilization should happen. The pollen from the male flower, which is wind-disseminated, lands on the style, which is part of the female flower. When this happens, the pollen initiates the development of a pollen tube that transfers male cells into the ovule to complete fertilization and the process of acorn formation should start in earnest. For this to happen, it is ideal to have warm days and cool nights. 

If temperatures are not right, fertilization may fail, and the female flowers will abort, which results in low acorn initiation. Alternatively, if temperatures become too hot or drought conditions occur, white oak acorns may abort, which is likely apparent in mid-June to mid- to late-July; perhaps that is the reason for reported early acorn drop this year. The other big threat to white oak acorns is late spring frosts, which also happened this year, and would again remove the fertilized flowers.

Trees and Dry Conditions

Penn State Forest Stewards series article – written by Allyson Muth, Interim Director, Center for Private Forests at Penn State.

Many areas across the northeastern US are experiencing dry and drought conditions, Pennsylvania included. As of July 28, two-thirds of Pennsylvania was in an abnormally dry to moderate drought condition. Yet, tallied across the state, we are very close to the total predicted rainfall for an average year to date. Depending on where you look in Pennsylvania, the regions are somewhere between 25% below, to as much as 26% above annual precipitation. These numbers don’t sound like they would result in two-thirds of the state be in abnormally dry conditions. So, how does that work?

PAFS article tree health during drought

Climate Change

Climate change models for Pennsylvania have consistently predicted the pattern that we’re seeing this summer. Less frequent, but more intense rainstorms, with extended drought periods occurring between those large rain events. The result is highly variable and uneven conditions across the state. Conversations with landowners in the south central region have shared their recent 4-inch rain storm events and subsequent flooding. In many other Pennsylvania regions, rains came early, and we’ve entered a dry summer period with rather infrequent rain events.

Pennsylvania is known for its waterways – over 86,000 miles of streams, creeks, and rivers. We usually have ample water during the growing season. We rarely have the water conservation requirements that the US West and Midwest implement to conserve water for human consumption. But when it’s this dry, do we need to worry about the trees?

Contributing Factors

Healthy, established trees can normally withstand relatively long periods of drought, so long as there are intervening months or years that are more favorable. However, recently planted trees, or trees with small soil footprints (rootprints?) are more susceptible to decline under these dry conditions. 

Forest Resilience in a Changing Climate

Penn State Forest Stewards series article – written by Jim Finley, Professor Emeritus, Forest Resources Management, Center for Private Forests at Penn State.

So far for most Pennsylvanians, Winter 2020 has been a non-event. Depending on where you live, temperatures are considerably above normal and snowfall below normal. Individual perspectives might lead to interpreting these two statistics as either positive or negative. No snow equals no shoveling. Warm temperatures equal more time outside. Or, no snow equals no sledding or skiing. Warm temperatures equal more ticks.

Thinking more broadly than personal values or needs; Is this winter’s weather a harbinger of a future driven by climate change? If so, how will Pennsylvania’s forests respond?

PA Forest Stewards - Jim Finley on Climate Change 2020

For sure, weather is fickle. Mark Twain purportedly said, “Climate is what we expect, weather is what we get.” It seems something is happening to the climate and, whether you attribute it to human activities or just unexplainable variation, Pennsylvania’s forests are facing challenges.

Forest Resilience in a Changing Climate

Aldo Leopold, a 20th century mid-western conservationist, and author of The Sand County Almanac and many other writings about our relationships to the land and natural systems, was a keen observer of change that others seemed to miss. He wrote, “One of the penalties of an ecological education is that one lives alone in a world of wounds. Much of the damage inflicted on the land is quite invisible to laymen . . . in a community that believes itself well and does not want to be told otherwise.” Simply, he was saying that the more one knows about ecology, the more apparent change is and that many will neither see nor believe that it matters. Many resource professionals as well as laypeople are seeing change in many areas of our environment. As Leopold suggests though, many of these changes and linkages may not be obvious to less than “keen observers.”

Disturbance and change are part of natural systems. Resilience is the ability of a system to recover after disturbance, which determines its ability to persist and function over time. The degree and extent of a disturbance logically affects the capacity of a natural system to recover. For example, in a typical winter, forests often experience damage from wind and ice. Most commonly this is local damage and a few trees experience broken limbs and some trees tip over. The ability of the forest to function across a larger landscape continues unabated – some trees benefit from increased light and growing space from the loss of their neighbors – the forest almost ignores the event.

Woods not Lawns for Water Quality

Penn State Forest Stewards series article – written by Jim Finley, Professor Emeritus, Forest Resources Management, Center for Private Forests at Penn State.

It’s January and perhaps your thoughts are already turning toward summer activities. For many Pennsylvanians, mowing and maintaining lawns is either a larger or small part of their summer routine. Lawns, as we know them, are part of American culture and history(1). An Internet search on lawn maintenance suggests creating the perfect lawn is a major industry very dependent on labor and chemical inputs.

Annually we spread millions of tons of insecticides, herbicides, fungicides, and fertilizer around our homes to have the envy of the neighborhood – a perfectly green lawn(2). Interestingly, as interest in organic foods increases, there is a disconnect about using despised chemicals where our children and pets spend quality time. At the same time, water quality suffers as excess nutrients from lawns and agricultural fields are one of the largest sources of non-point pollutants impacting water quality in our streams, rivers, lakes, and the Chesapeake Bay.

Penn State’s Center for Turfgrass Science estimates that Pennsylvanians maintain about 2 million acres of grass (about 7% of the state’s surface area), and 1.4 million acres of this are home lawns (about 5% of the state). About two-thirds of Pennsylvania is in the Chesapeake Bay watershed and contains an estimated one million acres of lawns. 

Pennsylvania has set a goal of converting 10,000 acres of these lawns to woodlands or meadows. This seems like a small target and maybe you can help by learning how to convert lawns to woodlands and meadows by participating in a Penn State Extension Winter Workshop series entitled “The Woods in Your Backyard: Learning to Create and Enhance Natural Areas Around Your Home.” This webinar-based education program will use a full-color, 108-page publication by the same title to guide you through the process of developing and implementing projects to enhance your land’s natural resources. Register by Saturday, 18 January 2020 via the link above, or call 877-345-0691.

A principle focus of the workshop series is to learn about what happens to the rain and snow that falls on your land. There is a very strong link between land use and our water resources. Buildings, pavement, lawns, fields – human changes to the landscape – have affected natural water movement and water cycles Water now moves across the land and into streams in different ways and carries with it nutrients and pollutants.

Interestingly, most lawns are very poor at absorbing water – in fact, they are only a little better than pavement! Your lawn, because of grass root structure and soil compaction, can only absorb about 2 inches of water per hour compared to a forest that can handle 14 inches or more in the same time frame. In the ideal scenario, water does not move across the land – instead, it should move into the soil.

Some Litter Is Necessary

Penn State Forest Stewards series article – written by Jim Finley, Professor Emeritus, Forest Resources Management, Center for Private Forests at Penn State.

Well once again, Pennsylvania’s forests are a mess – full of litter. Following the annual spectacular display of colors, fallen leaves, twigs, and branches “litter-ly” despoil our forest floors with layers of brown discarded leaves. What a mess!

2019-11 PAFS article Jim Finley on leaf litter

Depending on your awareness of litter’s value and your aesthetic sensibilities it can result in different appreciation levels. If you are a gardener, you would welcome, collect, compost, and hoard tree leaves. If your taste leans toward green grass lawns, you may abhor fallen leaves. Either way, you will likely gather them up; however, there are some who want to leave them in situ and mow them into increasingly smaller pieces to foster quicker decay hoping they will benefit that lawn.

Forests full of fallen leaves are a gift trees give to themselves. No one rakes or mulches them; nonetheless, they do slowly disappear. Estimates are that a mature hardwood forests produce an estimated 2,000 and 3,000 pounds per acre of litter annually. While most of this (about 70%) is leaves, it also contains twigs and branches, which may be partially decomposed prior to falling. It is amazing that through natural decomposition processes, tons of leaves contribute to forest vitality and health in so many ways.

 

Scouting for deer browse

Penn State Forest Stewards series article – written by Dave Jackson, Forest Resources Educator, Penn State Extension and Matt Russell, Associate Professor/Extension Specialist, University of Minnesota

Many woodland owners take to their woods in October to begin scouting for deer season. A good way to learn more about where white-tailed deer might be found is by understanding what they’re eating. A deer’s diet consists of a variety of crops, herbaceous and woody vegetation, fruits, and nuts. A healthy diet will consist of a variety of different foods. A deer requires an estimated 6 to 8 percent of their body weight daily in forage to stay healthy. For a 150-pound deer, that’s up to 12 pounds of food every day!

PAFS series - Dave Jackson on Deer Browse

Too much browsing pressure, eating twigs and young shoots, from deer can kill or limit the growth of tree seedlings, a fact that foresters and woodland owners know very well. Over decades, deer populations can greatly impact the look of woodlands. Knowing which tree seedlings are growing in your woods and which ones are browsed can give you more details on a deer’s diet.

In Pennsylvania, tree species that rank high on a deer’s list include a number of hardwood trees. Red and white oaks are two of the primary hardwood species that deer prefer to browse, while blackgum, hickory, and yellow poplar are also very high on the preference list. As you move north, species like maple (red and sugar), white ash, and basswood become more preferred species where they are more abundant.

While deer prefer these tree species, they also avoid certain plants. Deer will start by browsing the most preferred or palatable trees first. If there are high populations of deer in an area, preferred plants will see more browsing which can lead to other plants, that deer don’t prefer, taking over.

So what does it mean if deer are browsing beech seedlings/sprouts? Likely that deer are getting desperate and other food sources are limited. Evidence of high deer populations can be seen in a woodland that is dominated by beech brush, striped maple, black birch, black cherry, mountain laurel, ferns (primarily hayscented and New York) and invasive exotic plants. Deer avoid browsing these plants because they are not as digestible compared to other vegetation.

More evidence of deer browse impacts is the presence of a browse line on all understory trees, where there are no green branches until about five or six feet up. Another sign may include the presence of seedlings that are severely hedged and not able to grow above 1-foot in height, as well as understories dominated by species that deer avoid. Deer do not readily eat species like ferns, striped maple, beech, ironwood, mountain laurel, blueberry, and spicebush. As a result, we see these species dominating the forest understory in many areas.

To have a healthy woodland, tree seedlings need to develop into healthy, mature trees. As an example, consider a browse-sensitive species like oak. First, it can take over thirty years for an oak tree to produce acorns. Second, acorn crops only occur every two to five years and truly “bumper” crops much less often. In these good crop years, acorns can make up the majority of a deer’s diet in the late fall. If oaks can never make it from acorn, to seedling, to sapling, to healthy mature tree, the habitat quality for deer can suffer in the long term as oaks are replaced by other, potentially less desirable, species.

Knowing which species are being browsed can also give you insight into which methods can be used to protect seedlings. Although costly, fencing can be constructed around individual trees or larger areas several acres in size. Protecting tree seedlings ensures that you have healthy trees for the future while steering deer towards other food sources.

You may also consider harvesting additional antlerless deer. The Pennsylvania Game Commission’s Deer Management Assistance Program (DMAP) helps landowners meet their forest management goals by allowing hunters to harvest additional antlerless deer from a property during the regular hunting seasons.

Areas with low deer browsing pressure provide diverse wildlife habitats. They support healthy understories, preparing the forest for future replacement following natural tree mortality or planned timber harvests. Habitat repeatedly damaged by over-browsing continues to decline, losing its ability to support additional deer and other wildlife. It is important to reach a proper balance between desired habitat conditions and deer populations.