Want to conserve a significant proportion of the insect, bird and plant diversity on your property? Then don’t mow that hedgerow! We can make a positive impact on the diversity of their environment by fostering semi-natural areas in our human landscape. That means preserving hedgerows. Native hedgerows provide shelter and food for insects, amphibians, small mammals, songbirds, wildflowers and raptors. They increase the proportion of beneficial insects available to protect crops, provide shelter for insect-eating birds that patrol fields, and rich hunting for raptors. Cedar waxwings enjoy the fruits that ripen in established hedgerows.

So what makes a hedgerow? A continuous strip of shrubby vegetation with an undisturbed understory. If you stop mowing the edge of a yard or field a “spontaneous hedgerow” will arise. In the San Juans these hedgerows are often made up of native shrubs and wildflowers such as serviceberry (Amalanchier alnifolia) with its bright white spring flowers; Nootka rose (Rosa nutkana) with its fragrant pink blooms in May and June and charming yellow fall leaves; and native Pacific crabapple (Malus fusca), a favorite with birds when its sprays of fruit ripen in the fall.

The value of hedgerows goes beyond direct habitat value. They also provide a proportionally large amount of “edge” between different kinds of habitats, and they act as “green corridors” allowing animals (and, more slowly, plants) to move between different habitat patches. Providing more edge and corridors attracts species that profit from using multiple habitats for foraging, nesting and refuge. It sustains greater species diversity and higher genetic diversity. By creating networks of otherwise isolated habitat fragments, hedgerows can prevent species loss by connecting small populations into a larger breeding population (a metapopulation).

Hedgerows also bar the drift of contaminants generated by vehicle exhaust, road dust, pesticides and herbicides applied to adjacent fields, and help degrade toxic chemicals in runoff water. They do this by slowing the movement of water so that sediments settle around shrubs and trees. Microbial communities in the root mass can then break down some contaminants. Plants can even accumulate heavy metals, and keep them from traveling further downstream. Like all plants, hedgerow species absorb CO2 during photosynthesis, so roadside hedgerows help manage unburned hydrocarbons from car exhaust.

Despite their many benefits to wildlife and people, hedgerows are not protected in the San Juan Islands, and are routinely sacrificed when roads are mown or properties are developed and landscaped. It is a particular loss when old hedgerows are destroyed. If your field isn’t blessed with a hedgerow yet, you can either let one develop spontaneously, or plant some native woody species to give it a head start. Take a look at neighboring hedgerows to see what will work best in your area.

Madrona Murphy and Russel Barsh work for the non-profit conservation lab Kwiaht. Their research this summer includes sampling insect diversity in farmland. They are looking for volunteers to help collect seeds of hedgerow species so that in future plants from locally adapted species will be available to the public. For more information contact Madrona Murphy, (madrona.blue@gmail.com, 360-468-2808).