Michigan's forests over ten thousand years

TitleMichigan's forests over ten thousand years
Publication TypeJournal Article
Year of Publication1956
AuthorsSpurr SH
JournalThe Michigan Alumnus Quarterly Review

As we look over our present forests in the light of this history--much of it newly unraveled with the aid of radioactive carbon dating and pollen analysis techniques--much of the seeming meaninglessness of the trees disappears and a definite pattern emerges. In southern Michigan, spruces, tamarack, and other northern species grow in bogs. Weather studies in such bogs tell us that here the winter temperatures are ten to fifteen degrees colder than on surrounding uplands and here the growing season is up to two months shorter. Clearly, the spruces persist today where the local climate approximates that of Canada--and that of Michigan when spruce was the dominant vegetation eight thousand years ago. Jack and red pines are still the dominant vegetation on the sand plains in the central part of the Northern Peninsula. On such sites, the coarse sands create extremely dry growing conditions, while the flat surfaces gather the winter cold--witness the common winter temperatures reported from Cadillac and Pellston. Here we have the cold, dry growing conditions characteristic of most of Michigan six thousand years ago when the lakes were shrunken to half their present size. As the weather moderated but remained dry, oaks and other hardwoods from the south moved north into Michigan. Oaks have remained the dominant vegetation in lower Michigan, where the climate is mild, and have kept their foothold to the north on the warmer south-facing slopes--local spots where the climate is milder than elsewhere in the same localities. During the warm dry climate of three thousand five hundred years, agricultural Indians settled the area, often burning the forests and causing the replacement of woods by prairies in some southern parts of the state. Fire and grazing have helped maintain the oak forest. If the spruces, the pines, and the oaks are relics of the past and persist where local climates give them competitive advantages, then the beech, the maples, and basswood represent the climates of the present--of the past few thousand years. Where the local climate is average for the region, these are the species that are gradually taking over the forest in the absence of fire, heavy logging, and other severe disturbances that actually change the climate near the ground, where the trees must begin their life. Each minor fluctuation of the climate, however, changes the balance of the forest. The warm trend of the past hundred years has effectively prevented the natural reseeding of aspen in the Lower Peninsula (our popple stands are composed of sprouts from the roots of trees that seeded in during colder and wetter days), and have inhibited the natural reseeding of spruces, firs and pines, the valuable timber species of the northern forest. Chaning climate is clearly a matter of concern to the silviculturist--the practicing woods forester. Only by learning the past can we interpret the present and predict the future. Michigan has only a short past--eleven to thirteen thousand years since it was covered with ice--and what we have learned about Michigan's forests over the past thousand years should aid us much in understanding our natural resources and in planning for their wise use.