Developing Old-Growth Structure

At the time of European settlement, old-growth forests covered approximately 80% of the state of Massachusetts. Recent work by Tony D’Amato, a PhD candidate at UMass Amherst, has confirmed that only 1,119 acres of old-growth forest remain in the state. This acreage represents 1/10th of 1% of Massachusetts forests – much lower than the 80% covering the pre-colonial landscape. If we are going to provide for the habitat needs for the full array of species that are native to Massachusetts, then it is important to look at how we might be able to provide old-growth characteristics in our woods.

Tony’s work is providing information into the differences between old-growth forests and our current “second-growth”? forests. Knowing these differences gives us insight into how we can approach the management of our forests.

Old-growth forests provide a special and very rare habitat in Massachusetts as they have a structure that is unlike our current forests. In particular, old-growth forests have more dead wood on the ground- approximately three times as much. Those dead and down trees are also much larger than we currently find in our forests. In addition, old-growth forests also have more, large standing dead trees. The structure found in old-growth forests provide habitat for a wide range of organisms, including salamanders, lichens, beetles, and interior forest dwelling birds.

There are two critical components to creating forests with old-growth characteristics. The first is the development of large trees that can then become large standing dead trees and eventually large down logs. Large trees can be created by letting the forest develop at its own pace, which may take waiting until the trees are around 150 years old. You may also create larger trees by thinning the woods to increase growth rates.

The second critical factor in developing old-growth characteristics in your woods is natural disturbance. The development of large trees alone will not result in the full suite of structures found in old-growth forests. Many of the structures found in old-growth forests are the result of tree death through natural mortality or disturbances. As a result, your woods need to experience natural disturbances such as wind and ice storms and insects and diseases to allow for the creation of standing dead trees and large, down logs. In addition to creating dead wood, these disturbances also create gaps in the forest allowing for new growth and the development of a diversity of vegetative layers in your forest.

Allowing natural disturbance to shape your woods may conflict with your other landowner objectives. Leaving large down trees will mean that you are forgoing the economic return of the timber. In addition, natural disturbance can be messy for those landowners who enjoy the neat appearance of their woods. Although unsightly, natural disturbance is how our forests have evolved and therefore is a crucial component to developing old-growth characteristics.

The size of the area with old-growth characteristics will influence the types of species that are attracted to the habitat type. The property’s landscape position is also an important consideration. Is the property in the middle of development or is it surrounded by other forests? Ten acres is a good estimate of the minimal amount of woods necessary to have an effect on salamander, lichens, and insects. For species such as interior forest birds, hundreds of acres are necessary.

Like any landowner objective, managing for old-growth structure is not for everyone. Developing old-growth structure will take time, decades. The property will likely be in different ownership during the time it takes to develop old-growth structure. It is therefore important to consider the future of your land. As with any decision about your woods, know your options and the likely impacts before making a decision.