Invaders are coming soon to a forest near you – New Hampshire Bulletin

Forests define the New Hampshire landscape. With more than 80 percent forest, our state is the second most forested state in the Union after Maine.

This was not always the case, as historians will remind us. When European settlers arrived, they found a forest they assumed to be pristine or untouched. In some places it was a managed forest, in others it was a managed forest tended by indigenous peoples to encourage the wildlife and plants that supported their cultures. They managed the forest mostly with fire, and for centuries would regularly light fires to rid the undergrowth of shrubs and plants less favorable to wildlife such as deer, elk, and woodland caribou. The regrowing woody and herbaceous plants offered these grazing animals more food and thus larger populations of potential food.

The arrival of European settlers changed all that. They wanted land for farming. They were very industrious and managed to clear most of the trees and replace them with pastures for domestic animals and fields for crops. The legacy of all that hard work, of course, was a landscape fringed by thousands of miles of stone walls, created when the settlers discovered that beneath all the eons of fallen forest leaves, the ground covered a vast crop of boulders left behind 12,000 years ago were caused by the retreating glaciers. Stone walls were built to define property boundaries, but were often primarily a place to deposit stones, large and small, which presented an obstacle to agriculture.

After the Civil War, many farming families decided that subsistence or commercial farming was just too challenging in our rocky landscape, and tales of the deep and rock-free soils of the Midwest lured them away from the New Hampshire hills. Thus began the slow but inevitable return of most of the New Hampshire landscape to forests.

Trees in our climate are the main inhabitants of deserted land. When the mountain farms were left to their own devices, the white and gray birches, oaks and pines came first. As these trees matured, species that preferred to sprout in the shade, such as maple, beech, yellow birch, and others, re-established themselves. These forests, what ecologists refer to as the “second forest,” dominate our landscape today. Some are very old, maybe more than 200 years, but the piece of forest that has never seen sheep and later cows is very rare.

But these second growth forests are extraordinary places. They are home to an enormous variety of wildlife, plants and fungi. They are the primary filter for rainwater flowing into streams, lakes and the ground, maintaining our human presence in the countryside and in our cities.

With a few exceptions, they contain a variety of species that have been familiar to us since humans have lived here. The maples, oaks, pines, beeches, birches and other native species, as well as a variety of native shrubs, still thrive. Lost are the American chestnut and American elm, decimated by diseases accidentally brought here by trade from other continents. Today we are losing our ash trees to another invading insect from Asia.

Will we continue to recognize the forests of our future? Today’s forests have evolved in a relatively stable climate over many centuries since the last Ice Age. But the climate is changing faster than at any time in human history, and our forests can’t help but notice it.

How will they react? Species that require colder winters and cool summers (fir and spruce) are likely to die off at lower elevations as they expand northward and to higher elevations. Live oaks, which like our central New Hampshire climate, will be more common farther north. Some have worried that sugar maples will decline, but it’s too early to know for sure, and scientists are working to find out.

But one thing is almost certain. A variety of exotic invasive species from other continents, well established in the forests of our South, are rapidly moving our way.

I was just in central Pennsylvania, where the native shrubs and nonwoody plants of the forest undergrowth are rapidly disappearing. They are replaced by non-native multiflora rose, autumn olive, sea buckthorn, burning bush, Japanese honeysuckle, oriental bittersweet and others that are aggressive and mostly inedible to native wildlife. In the forests I visited, “bushing” through thickets of thorny plants has become a dangerous activity. Deer visit suburban farms to find landscape plants that are edible when the forest food is not.

These invasive plants are already present in some places in New Hampshire, but not most. That’s changing fast as birds, who often see the seeds of these invaders as a good food source, are spreading them far and wide.

My own forest in Weare is changing. Autumn olive and Japanese knotweed have been here for years but are spreading at an accelerating rate. Oriental bittersweet would suffocate the native trees if I didn’t go out and prune them back every summer. In my sugar maple bush, where the tree seedlings were once all sugar maples, there is increasing shagbark hickory, a species once rare this far north.

There’s not much we can do about this invasion other than be prepared. Taking care of our forests becomes more of a challenge if we want to conserve our native species. Eradication of exotic invasive plants is no easy task and no doubt we sometimes have to resort to the use of chemical herbicides. Deer are more likely to become a nuisance as their favorite foods are replaced by invasive species they find inedible, and they flock to our gardens and native landscapes.

If you own a wooded lot or just have a wooded house lot, it’s time to find out about the invaders that are coming or have recently arrived. Consult the UNH Cooperative Extension for lists of exotic invasive plants. Get an app for your phone to identify them. Be diligent in pulling them or killing them when you find them and you might be able to keep them at bay. Ignore them and they will take over before you know it.