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Preparing your Forest for Life after EAB

by James P. Engel, © 2015

Wandering through the local fields and forests as a youth I unknowingly passed by the aged remains of American chestnut trees. The remains were found in old stump fences that lined the fields I hunted. The American chestnut was once the dominant tree that filled the local forests but now only their rot resistant stumps and a few scattered root sprouts are all that remain.  I had read about the loss of the American chestnut and countless American elms that lined most town and city streets but at that time, the significance of there disappearance from the forests was lost to me.

I am fortunate to not have lived during that period in time, when the American chestnut succumbed to chestnut blight and I was born just after most of the American elm died from Dutch elm disease. I do recall seeing the huge bleached skeletons of recently dead elm trees in every local swamp. I did not grieve this loss because I had never experienced the elegant beauty of a mature American elm in leaf or the blossoming of an entire forest of American chestnut nor was I witness to their massive die off.  But now I, and everyone else now living, is faced with another loss of historic proportions, the loss of every ash tree, due to EAB (Emerald ash borer). It is hard for me to mentally and emotionally grasp what this will mean for the landscapes I have come to know on an intimate level and harder yet to envision what my woodlot and countless others will look like in a couple of decades after EAB has wreaked its havoc. I am not emotionally prepared for the significance of this change and a large part of me is in denial. I optimistically hold out hope that some miracle will occur between now and then to stave off this impending disaster.

My pragmatic side wonders what will happen to all of the young, early successional forests with a predominance of ash, what will the maple, ash swamps look like without ash? I try to envision what the future holds for this area, where ash is so dominant. What species will replace the ash trees when they are all dead? Will they become brushy thickets of exotic invaders as I fear or overgrown tangles of wild grape?

Ash has become the primary tree species in the majority of early successional habitats across the state. 
It has gained this status because of the ease by which ash is able to disperse its seeds over long distances and establish under a diverse range of conditions, from old fields, to swamps, in clay or sand, from full sun to shade. I do not know of, or foresee, any other native tree species filling this early successional role, unless it is an exotic invader.

If you are lucky enough to own a mixed species forest, where ash is just a minor component of the canopy, it can be safe to assume that the remaining species will fill the gaps created from the dying ash trees.  Maple, cherry, oak, hickory, pine and tulip will fill the void left by the ash. There should be minimal impact on the over all health, appearance and future succession of the forest and you will be spared the worst affects of EAB. But what about those forests where there are no other tree species but ash, or maybe just one other species? What will the successional trajectory look like for these forests? Is there anything you can, or should do, to help shape the future forest after ash.

If there are currently other native tree species present on site, the best potential seed crop trees should be preserved and managed to disperse their seed.  These seed crop trees will provide a seed source for natural regeneration of that particular species.  But what if you want to encourage other species not currently found on site or if there are no other valuable species now present? With no existing seed source nearby or within a reasonable distance, there is absolutely zero chance that new tree species will ever become established.  The future succession of the forest is bleak at best.

The logical step for a landowner to remedy the situation would be to plant seedlings of the desired species.
But planting seedlings has it’s own inherent limitations. Seedlings can be expensive to purchase at the scale of planting a forest. Add to this, the cost and labor involved in planting, weeding, protection from animal herbivory etc.  Mortality of bare root seedlings can be quite high for many tree species even with the best of care.   Add up all of the total costs for planting and the number of acres that can be reasonably planted is limited.

If you consider how nature has historically restored itself after large scale natural or man made disturbances, you might use these same strategies with the aid of human creativity and stewardship and adapt them to restoring desirable plant species to your forest. Historically, when agricultural fields were abandoned or natural disasters occurred to turn back natural succession, these disturbances impacted a few dozen acres at most.  A seed source for colonization was close at hand or seed was lying dormant in the soil.  Often a diversity of species remained in the adjacent hedgerows waiting to colonize the old field. The seeds of the future forest were ready and waiting to germinate and begin the successional process in earnest. All of that has changed in the last half century.  Large scale clearing for agriculture in past decades has eliminated miles of hedgerows and removed any possibility that a healthy seed source remains nearby. Invasive plants are ever present in proximity to people and human activity and any vacant land is quickly invaded and overrun by invasive plants. 

With a little knowledge of biological and horticultural processes and a little investment of your time, you can collect large quantities of seed from native trees and plant that seed to establish tree species that will help to replace the ash in your forest or to enhance species diversity, all at a fraction of the time and cost of planting seedlings.

Most plants produce an abundance of seed.  This seed is easy to collect and the seed can then be used for establishing new plants in the wild. Plants have no direct mechanism to plant their own seeds or to safeguard their progeny, instead plants compensate for these limitations by producing huge quantities of seed and inundating an area with seed to increase the extremely low probability that a few seeds will survive and develop into reproducing mature plants.  Most seed simply falls to the ground where it is vulnerable to all kinds of predators and environmental extremes. Each seed is a concentrated energy packet, it is highly nutritious and a very desirable food source for all kind of organisms from deer, to birds, rodents, weevils, bacteria and fungi. The seed remains vulnerable to predation or degradation for months on end and sometimes years until conditions are right for the seed to germinate.  Then the seed needs to be in the right environment for the seed to germinate and the seedling to survive and grow. It is a wonder that any seed ever survives to grow into a mature tree. The forests around you is a testament that this process does work and regeneration does occur, but at an extremely slow pace.

There are three basic steps to using seed to establish tree seedlings: collect the seed, clean or store the seed for future planting and planting the seed. Most tree seed matures in the fall.  Scout for trees that have an abundance of seed early in the season and monitor the tree over the summer.  Collect the seed in early September to October when the seed is mature but before the seed is dispersed from the tree.  Collect from trees that have an abundance of seed and are easy to reach from the ground.  Open grown trees in hedgerows, parks and cemeteries with low branches are good places to collect seed. Collect as much seed as you can.  Strip seed from branches by hand or lay a sheet on the ground and knock the seed onto the sheet for easy collection. Tens of thousands of seeds can be collected in just a couple hours of your time.

Clean the seed and prepare it for storage.  Cleaning is necessary to reduce bulk or remove any seed covering that may contain chemical inhibitors or contribute to decay. Separate the seed from any hulls or chaff.  For example separate hickory nuts and acorns from their husks and caps.  You can remove the wings from sugar maple samaras to reduce bulk.  Remove the pulp and skins from black cherry pits by hand macerating in water and straining though a screen to prevent mold and bacteria from growing. You can read how to treat and handle each species at the website printed at the end of this article. Most seed can be stored for future planting only until germination begins, usually the first spring after collecting.  A few species may be kept for two or more years.

Once cleaned, place seed under cold moist stratification.  This involves mixing the seed with an artificial potting mix, peat moss or other potting media moistened slightly, damp but not wet.  This helps the seed retain moisture and mimics what occurs under natural conditions outdoors.  Allow the seed to be exposed to cold outdoor temperatures (vernalization) by storing in an unheated garage or storage space but protected from rodents.

The last and very important step is planting the seed in the ground. Planting the seed in the ground does three things: it satisfies a vital requirement for the seed to germinate and grow. The seed needs to be in contact with the soil so when the root emerges form the seed it can supply the seedling with water and nutrients for sustained growth. Seed in the ground is less likely to be exposed to environmental extremes such as desiccation, freezing and heaving compared to seed lying on the soil surface. With the seed planted beneath the soil surface, the seed is many times less likely to be discovered and consumed by seed eating animals.  The shorter the time between planting and germination the higher the survival rate of the seed.  Seed can be planted anytime in the fall or over the winter with excellent survival but spring planted seed will have less time when it is vulnerable to seed predation. The trade off, is that people often have far more free time in the fall for planting than in the spring and there is a longer window of time for planting seed in the fall than there is in the spring. 

When choosing what species to plant it is wise to consider what species will do well at the current stage of succession in your forest. What tree species will be able to compete and grow within the existing plant community and the competition from those plants.  Also consider what species are adapted to your soil type, drainage conditions and sun exposure?  Place less emphasis on what species you would like to have but rather focus on what will do best.  Look to neighboring properties to get a sense of what species are growing there and which species are doing well. You can modify the species planted at a later stage when conditions in your forest change.

When planting the seed,  place the seed only ½ inch to 1 “ deep. The rule of thumb is twice the diameter of the seed.  Not too deep!  I use a short handled square ended spade to loosen the soil surface, drop a few seeds onto the loosened soil and then compress the seed and soil with your foot. My philosophy is to plant as much seed in the ground with the least amount of effort and time spent on each location. I try to cover a large area while planting a lot of seed.  The more seed planted the larger the number of surviving seedlings. You can also make smart choices of where to place the seed while planting. For example, plant seed where there are gaps in the canopy that provide more sunlight, or where there is less competing vegetation or where the seedlings will be less vulnerable to deer browsing. Good site selection will increase seedling survival.

Oak and hickory are the easiest species to establish from seed. They have large seeds that are easy to collect, with a high percentage of sound seed and they produce large seedlings. Cherry, maple, tulip and basswood are also fairly easy.  Species with tiny seed like birch, sycamore, hornbeam and pine are more challenging but still well worth the effort.  Don’t limit your introductions to just the canopy tree species.  All of the native understory tree, shrub and herbaceous species can be introduced just as easily by collecting and planting their seeds.
Unlike planting a seedling, where you have a high monetary investment in each plant, you don’t expect every seed will germinate and grow but you can take steps to increase the likelihood that a higher percentage of the seed will survive.  You increase that likelihood by planting a lot of seed, of many different species, covering a large area and repeating the seed planting over multiple years.

By introducing desirable species into your woods before your ash trees begin to die from EAB, you are working to set the stage for natural succession to occur with a more desirable outcome than would occur if you do nothing.  You’re efforts will ensure that your forest will be able to weather the devastating effects of EAB and your forest will have a new successional pathway into the future.

You can learn more about the whole process of collecting seed and growing native tree, shrub and herbaceous species at. 




this page updated Feb 25, 2015