On forest complexity and how to manage pine plantations

We have now covered the first two of the four foundations of ecologically based forest management (context, continuity, complexity, and timing). Here, I define forest complexity, describe how and why pine plantations differ from naturally regenerated pine forests, and finally illustrate how to apply lessons learned.

Forest complexity can be defined within the context of “composition” (the mix of tree species) and “structure” (the vertical and horizontal arrangement of live and dead trees). Complexity can also be defined within the context of spatial arrangement of trees. A complex forest differs from point to point and is far from uniform or orderly. While some forest types are generally more complex than others, the general rule applies that complex forests are more biologically rich.

How about plantations? In many ways, the history of forestry begins with plantation management. Gifford Pinchot, the first chief of the US Forest Service, was trained in Europe, where even the Black Forest is really a large conifer plantation. Most natural forests were cut over centuries ago in Europe and replaced with plantations primarily managed for timber production.

Plantations are forests derived from intensive management and the planting of seedlings or seeds of usually one tree species. Those seeds or seedlings are spaced to optimize vertical growth in the early years of the plantation, with subsequent “thinning” by removing some trees to give the remaining trees more sunlight for continued growth. That is how pine trees grow straight and tall, and then put on diameter growth. But plantations differ dramatically compared to naturally regenerated forests, especially in regards to complexity of composition, structure, and spatial arrangement.

In northern Michigan, jack pine and red pine plantations are common and are most often found on dry, sandy sites that historically were fire-prone. Those plantations are easily seen through aerial imagery provided by Google Earth and the uniformity of those forests is readily observed.

Trees are generally all the same height and diameter and the spacing is nearly the same between each tree. Because light conditions in many young plantations is low, jack pine and red pine plantations are usually devoid of many other plant species. Those characteristics of plantations usually dictate wildlife, use as well. Most studies suggest that plantations provide far fewer wildlife species than do natural forests of the same type.

Research has indicated how relatively more complex natural red pine and jack pine forests are than their plantation counterparts.

That complexity is often produced by fire. As a natural part of those ecosystems, fire regenerates those forests and, for red pine, maintains them. Whereas fire in jack pine tends to be severe and kills most (but not all) trees, in natural red pine stands, fire causes much less mortality.

Unlike jack pines, mature red pines have thick bark and lack lower branches, protecting the tree from heat and reducing fire from climbing up a tree into the green foliage. Consequently, fire usually produces a broader array of flora and therefore compositional complexity in those forests, compared to plantations.

In jack pine forests that are burned, structural complexity is provided by an abundance of dead trees (snags). In red pine forests, fire provides structural complexity by producing a range of different sizes of red pines and fewer, scattered snags. Finally, in both jack pine and red pine forests, fire produces complex spatial patterns and a lack of uniformity.

But can something be done to make plantations more complex?

The simple answer is yes, many things.

For instance, one of the easiest things to do is to consider leaving some remnants of the previous forest as part of the new plantation. That was addressed as “continuity’ in the previous article.

Next, consider planting a mix of pine species, including eastern white pine. While planting may still be uniform to get trees to grow straight and tall, thinning stands irregularly can then be done to produce some spatial complexity in older plantations.

Also, snags and coarse, woody debris can easily be provided at no cost while thinning is done. Logging equipment can simply either girdle or top a selected tree and leave it in place, or cut a tree and place it on the forest floor and provide coarse woody debris.

Many lessons can be learned by studying natural forests. Observed patterns in complexity can then be applied through ecologically based forest management, even in intensively managed pine plantations.

Greg Corace is the forester for the Alpena-Montmorency Conservation District. He has spent the last 25 years publishing forest and wildlife research and conducting forest planning, management, inventory, and monitoring on public and private lands across northern Michigan. For more information, including sources used in this article, email greg.corace@macd.org or call 989-356-3596, ext. 102.