Salma Monani
Adams County Master Gardener
Perhaps you’ve heard the proverb, "Mighty oaks, from little acorns grow." Often used as a metaphor to remind us that greatness grows from seemingly insignificant things, the saying also helps us think about oak trees, which are truly remarkable for many reasons. For one, there are over 435 species within the genus classification of Oak (Quercus). Second, fossils indicate that oak trees evolved approximately 56 million years ago. That’s millions of years before humans emerged on planet earth! Third, while they are found across five continents, over 60 percent of all Quercus species exist today in the Americas.
We are lucky that sixteen of these oak species are native to Pennsylvania. Some common species in Adams County include white oaks (Quercus alba), white swamp oak (Quercus bicolor), chestnut oak (Quercus montana), northern red oak (Quercus rubra) and pin oak (Quercus palustris). Oaks are easily recognized by their leaves, which are lobate across most of the common native species in our area, though with characteristic differences between individual species. For example, white oaks (Quercus alba) have rounded lobes, while the Northern red oak (Quercus rubra) has lobes with pointed edges. Oaks are deciduous, with handsome foliage across the seasons, from leafy green in spring and summer, and vibrant reds, yellows, and bronze in fall. Some provide a lovely color contrast in winter as they don’t drop all their leaves in cold weather.
Oaks don’t just add color to a landscape; they are a keystone species. Across the tree species in our region, hands down, oaks take the top prize for the biodiversity they foster. Hundreds of our native butterfly, moth and other insect species co-evolved with oaks over time. These insects are an integral part of the food web that attracts our beautiful backyard birds and supports our local forest animals. While all parts of the oak—from bark to leaves to roots—support wildlife, the fruit—acorns—are an invaluable source of food, providing essential protein, fat, and carbohydrates. Acorns can also be milled into flour for human consumption.
As hardwood trees oaks are indispensable to humans for building materials and even used in cider-aging barrels! Oaks also help keep our air and waterways clean as they sequester carbon dioxide, absorb atmospheric pollutants, and moderate stormwater run-off to prevent erosion.
Unfortunately, in forests across the Eastern US, including in our region, native oaks are currently experiencing what foresters call a "regeneration debt." That is, while we have older mature canopies of oaks, there are very fewer young oaks growing. There are various reasons for this, amongst which are over-browsing by deer on seedlings and changing weather conditions caused by climate change. Climate change contributes to various impacts such as other species of trees now out-competing oak seedlings in the forest environment, or older oak trees becoming more vulnerable to insects like gypsy moths, which thrive in the warming temperatures.
For those who depend on oaks for building materials, there are direct economic and cultural ramifications of the "regeneration debt." In Kentucky, for example, whiskey distillers are worried about their industry as white oak barrels are essential to the aging process, giving bourbon and rye products their distinctive flavor. Distillers like Maker’s Mark are partnering with the U.S. Forest Service, other public agencies, and landowners to help ensure the sustainability of white oaks, not only for their industry, but because they understand that native oaks are keystone species and their loss will have ripple effects on entire ecosystems.
Given the remarkable benefits of native oak trees, and the current regeneration problems in our Eastern forests, planting an oak in your backyard can be very rewarding. In your backyard setting, you can help mitigate issues like competition from other trees by planting oaks in designated areas. You can also control deer impact by ensuring that your young oak seedling is protected by a plastic guard, until it is established.
Native oaks are low maintenance as they are adapted for our environment, and once established require no watering. Many oaks have deep roots, making them extremely sturdy trees in inclement weather. Because they favor deep root systems, rarely do oaks cause pavement damage, as they don’t push up through the soil.
Some people worry that oak trees will be too big in their backyards as many do grow into "mighty trees." However, many varieties are moderate to slow growing. For example, white oaks grow about a foot a year, so it will take a long time before the trees reach their mature height of 50 to 80 feet.
Finally, given the number of oak species native to our area, there’s an oak for every type of backyard landscape. Researching which native oak species will best suit your backyard will guarantee many years of aesthetic and ecosystem benefits.
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