|Title||Historical development and structure of the aspen, jack pine, and oak vegetation type on sandy soils in northern lower Michigan|
|Year of Publication||1957|
|Degree||Doctor of Philosophy|
|Number of Pages||267 pp.|
|University||University of Michigan|
|City||Ann Arbor, MI|
Vegetation has existed continuously in Cheboygan county for about 11,000 years, or since the retreat of the last ice sheet. Three major climatic and vegetational periods have occurred during this time; a spruce period, extending from about 11,000 to 8,000 years ago; a pine period, extending from about 8,000 to 4,500 years agp; and a deciduous period, extending to the present. The above designations are simplifications, for different types prevailed on different habitats. The presettlement vegetation was composed of five vegetation-complexes, each of which was composed of a varying number of vegetation types. The complexes were related to habitats ranging from very wet to very dry in the following manner: bog forest, wet organic soils; swamp forests, wet-moist mineral soils; northern hardwood forests, loams; transitional forests, sandy loams and loamy sands; pine woodlands, sands. The pine woodland complex included a pine-hemlock-aspen type, a pine-oak type and a jack pine type. These three dry land types were strongly affected by settlement and remnants of them were analyzed in the present-day study. The lumbering and burning of these types converted the pine-hemlock-aspen type to a bigtooth aspen type and the pine-oak type to a red oak-white oak type. The jack pine type was not seriously affected, because jack pine was not lumbered. A statistically significant correlation was evidenced between the texture of the A2 and C horizons of the aspen soils on the one hand, and the jack pine and oak soils on the other. The aspen soils contain a higher silt plus clay content than the jack pine or oak soils, and this feature is considered important in determining the present distribution of these types. Other environmental features are certainly important but are secondary to soil texture. There is some indication that the field layer is also affected by soil texture. Pteridium aquilinum and Diervilla lonicera are more abundant on soils of finer texture, while Carex pensylvanica and Vaccinium angustifolium are more abundant on soils of coarser texture. Apart from the differences in tree cover in these forest types, the vegetation is very similar. The most prominant plants are common in all types and in several plots the dominant trees could not be determined by examination of the field layer alone. Some distinctions were evident and are mentioned below. Field layer coverage is greatest in the aspen plots, primarily because of the abundance of Pteridium aquilinum fronds of which form an almost continuous layer in most aspen stands. Pteridium is also pevalent in jack pine stands, while a layer predominated by Carex pensylvanica and Vaccinium angustifolium is conspicuous. Coverage in the oak type is smallest of the three, although here the greatest development of bare soil mosses and lichens occurs. Succession is proceeding gradually in each of these types. The aspen and oak types are being converted gradually to pine communities resembling the pre-settlement forest types. The jack pine type, on the other hand, appears stable, except where northern pin oak is prominent. In such areas the oak appears to be replacing the pine. There is no indication, however, that any of these successions are proceeding toward a beech-maple climax. Both the present-day and pre-settlement vegetation seem best described as a continuum of merging, yet stable, vegetation types. The vegetation is termed a soil moisture continuum, because it is governed primarily by soil texture and drainage. Within the sandy soil portion of the continuum the forest types are not as sharply defined as in the broad complexes, mainly because other environmental features become more important as differences in soil moisture become smaller. Finally, it is suggested that information on the dynamics and structure of the sand soil presented in this study can provide basic information which may be applied directly to enlightened forest and watershed management in these areas.