THE FORBIDDEN ECOSYSTEM
CONIFER PLANTATIONS AND BIODIVERSITY
Written by: Mike Meriwether
Anyone who has driven through Michigan has likely noticed the plantation type conifer plantings that dot the landscape. Many were planted years ago (60) by the CCC under the State and Federal reforestation programs. Extensive additional acreages have been planted by individual landowners in co-operation NRCS, FSA, Conservation Districts and local Extension offices.
There are all kinds of conifer plantations in Michigan and they range from one acre to several hundred acres in size. They are of different ages, in different growing conditions and subject to varying management practices. There are plantations of red, white, jack and scotch pine, larch, Douglas fir, balsam fir and mixtures of all. They have been established for a variety of purposes including Christmas trees now abandoned, soil stabilization, wind breaks, reforestation, and wildlife. Most of these plantings exist on abandoned farm lands, hill sides, and lower productive agricultural lands.
What impact has plantation establishment had on wildlife habitats, on ecological diversity and or landscape diversity? Many wildlife biologists, ecologists and others viewed with alarm all the plantations growing on Michigan’s abandoned hills and agricultural fields. They felt (and many still do) that these areas create thousands of acres of “wildlife deserts”. The terms biological deserts and monoculture are commonly used to describe conifer plantings especially red pine. In fact agencies such as the MDNR, NRCS and the USFS became so enamored with their own verbiage that policies discriminating against the establishment of red pine began to filter into the conservation community.
After 20 years of planting thinning and observing the development and dynamics of the plantations here in Antrim County, I have discovered some unique attributes within our conifer plantations. Let’s take a close look at red pine the forbidden ecosystem.
Red pine grow well in sandy soils, it competes well and grows fast. It is drought resistant, and relatively free of major pest problems. The first 10 years young plantations struggling up through the grass and brambles have little effect on resident wildlife. Cottontails, meadowlark, vespar sparrows, mice and voles, grasshoppers, turkey, deer and raptors continue to use the area.
As the plantation begins to occupy the site the field takes on more of the characteristics of a thicket. While it is true, conditions within the stand become unfavorable to some wildlife, others prosper from the new habitat. At 10 to 15 years of age the plantation is much like an overgrown field but with considerably better cover. There are still plenty of islands of herbaceous ground cover and trees are close to the ground. Snowshoe hare and cotton tail rabbit couldn’t ask for a better home. They are soon joined by the towhee, robin and purple finch. Ruffed grouse begin utilizing the edges and song sparrows are common. Deer and bear love these plantations and begin using them every day.
By the time the plantation has grown to 20 to 25 feet in height, significant changes have taken place on the site. The crowns have closed shutting out the light and the lower limbs have begun to die. The traces of old field plants beneath the trees are nearly gone. Openings, however, are often created by blow-downs, storms, planting mortality, and insect damage. Thus, a variety of cover conditions can exist. It is at this stage of development that the plantation contains its greatest variety of wildlife. Rabbits and ruffed grouse occupy edges and the openings in summer and seek dense cover in winter. White-tail deer retreat to plantations for winter protection and hide their fawns in the summer. The gray fox and the red squirrel appear on the seen. Towhees nest in the openings and sing from the tops of the conifers. The purple finch, morning dove, the robin, and the veery, the black-throated, green, the myrtle, Nashville, magnolia and chestnut-sided warblers add song and color. Where sufficient ground cover exists or blow-down occurs, the slate colored junco is at home. Wood peckers exploit the dead limbs for insects.
Red pine and Scotch pine over 20 feet in height provide the white-tail deer with ideal winter cover. Often the snow is only a third of the depth outside. If the plantation is wide enough, the force of the wind is considerably reduced. On stormy winter days, deer and other wildlife retreat to the depths of the pine plantation. In fact, they prefer pines to the hardwood-hemlock forests for bedding. Scotch pine furnished food for deer and some studies have shown that they prefer the terminal whorls of Scotch pine over white cedar (Cornell University).
Exceptional habitat for wildlife begins to wane as the plantation continues to mature. It’s been 30 years plus or minus. More and more of the lower limbs and undercover disappear. Rabbits now use the area only for travel lanes. The gray fox and the red squirrel, the white footed mouse and the deer are the principal mammalian inhabitants. The birds of the thicket along with the veery and junco are gone. Only birds of the canopy, the black throated green warbler and the blue jay remain. Now for the first time the Blackburnian warbler, characteristic of older conifer growth, appears. Conspicuously few or absent, except in winter, are the chickadees and woodpeckers, since no suitable nesting sites occur. It is this stage where diversity is least and many view the area as a biological desert. Poor management or lack of management has lengthened the amount of time the plantations exists in this state. Often overstocked and stagnant these plantations are not void of diversity but do lack the thriving communities that once existed in them.
It is at this point that red pine begins another transformation. Around age 30 +/- these plantations become commercially attractive and thinning them is recommended. It is interesting to note that many of the plantations planted in the CCC days have been thinned at least once and likely two or three times. Revenues to the State and federal governments have been significant. Perhaps the economics of red pine can be discussed in another article.
First thinning within pine plantations commonly consist of row thinning. Removing 1/3 or every 3rd row is the typical recommendation. Shortly after this fist thinning hardwood species, shrubs and herbaceous plants begin to invade the edges, landing areas and skid trails. If managed properly the plantations will receive periodic thinning at 10 to 12 year intervals. Each thinning changes the dynamics of the plantation.
After a second thinning, advancing hardwood and shrubs are persistent in the under-story. As hardwood begins to invade the under-story, rabbit and deer begin finding forage again. Ruff grouse and wood cock find acceptable breeding and rearing habitats, and song birds re-introduce themselves to the site. The plantation is now 40 – 45 years of age.
At age 55 – 60 the plantation is thinned again. At this time tree diameters have increased and larger diameter trees add additional diversity. Well established hardwoods exist in the under-story, now we have a multitude of wildlife using the under-story and canopy dwellers using the over-story. Rich diversity has returned to the stand. Rabbit, coyote, fox, deer, squirrel, grouse, woodcock, and bear make up the list of game species utilizing the plantations. The vertical diversity attracts resident song birds and neo-tropical birds alike.
Now managers have some decisions to make. Do we thin a 4th and possibly 5th time allowing tree diameters to exceed 20 inches? This decision will further the stands development toward a hardwood forest in most cases but may influence tree marketability. Is this best for resident wildlife? Do we leave a residual density of pine? And if so at what density is best for diversity? Keep in mind, pine both red and white can live up to 300 years! Do we clear-cut the pine and re-plant thus starting the cycle all over again?
Much is yet to be learned regarding conifer plantations and their contribution long term to our ecology. Most state and federal plantations and many private plantations are aging and removal at around the 16 inch diameter mark is often the rule. Although some sites are converted back to pine, many times the better quality sites are left to convert to hardwood, more on this in part II. Across the landscape red pine plantations and other conifer plantings have offered landscape diversity. They have acted as replacements for our disappearing conifer swamps and have jump started the successional process on abandoned agricultural lands. Lastly, in the case of red pine, wood products have played a significant role creating jobs and revenues for individuals and governmental agencies throughout the State.
I not sure if there is another artificially established ecosystem that offers more diversity over time or has had a greater impact on wildlife populations than the conifer plantation. Can you think of one?
BIRDS AND MAMMALS KNOW TO UTILIZE PINE PLANATIONS AT VARIOUS STAGES OF DEVELOPMENT
Cottontail Vespar sparrow Junco
Deer Towhee Woodpeckers (many)
Meadow Vole Robin Blue Jay
Red Squirrel Purple finch Blackburnian warbler
Bear Meadow Lark Black Poll Warbler
Hare Ruffed Grouse American Redstart
Fox (gray) Song sparrows Bobolink
Fox (red) Morning Dove Canada Warbler
White footed mouse Veery Gray Catbird
Raccoon Black Throated Warbler Grosbeak
Coyote Chestnut sided Warbler Whip poor will
Bobcat Green Warbler Wood thrush
Black Squirrel Nashville Warbler Pine Warbler
Magnolia Warbler Oven bird Indigo Bunting
Red eyed Verio Hawks (many) Owls (many)
Woodcock Chickadee Wild Turkey
Not a complete list.