The record of charcoal in lake sediments indicates that fire has always been an important ecological factor in the forest history of northeastern Minnesota. The annually laminated sediments of Lake of the Clouds permit precise dating of the charcoal peaks and record the changes in the influx of various pollen types. A detailed record of the past 1000 yr shows that the average frequency of fire is approximately 60–70 yr, with a range of about 20–100 yr. The amount of charcoal in sediments dating between 1000-500 y.a. is consistently higher than that for the last 500 yr, although the fire frequency for the two periods was not appreciably different. Pollen analysis shows no change or only short-term changes in the percentages of major pollen types following charcoal peaks.

Four cores from Lake Mendota in the Yahara River valley of south-central Wisconsin provide pollen, charcoal, and sediment-year. Derived estimates of stratigraphic evidence of a middle Holocene dry period in the northern Midwest. The lake level was lower between about 6500 and 3500 yr B.P. indicating that runoff from the upper Yahara River basin may have ceased during the drier seasons of the precipitation between 6500 and 3500 yr B.P. indicate a decrease of about 10% (down to about 700 mm) from the present precipitation value of 800 mm. A warming between 6500 and 3500 yr B.P. is also interpreted based on a change of vegetation from rich mesophytic forest before 6500 yr B.P. to Quercus savanna, with increased charcoal abundances after that time. After 3500 yr B.P., a closed Quercus forest and decreased charcoal suggest a cooler and wetter climate. The qualitative paleoecological interpretations, quantitative precipitation reconstructions based on pollen from the region (including the Lake Mendota data), and estimates of hydrologic budget based on lake-level changes, all show indications of a dry and warm middle Holocene. Evidence from a large regional array of sites also supports these interpretations.

A 2000-year accumulation of varved sediments from Hell's Kitchen Lake in north-central Wisconsin was analyzed for pollen, charcoal, and seeds. The varves provided an accurate time scale for the study. The pollen record indicates changes on two different time scales. Short-term changes lasting several decades appear to be superimposed on long-term changes lasting several centuries. The short-term changes are related to individual fires, and the long-term changes result from increases or decreases in the frequency of these perturbations. From 2000 to 1150 years ago the average interval between fires was about 100 years, and from 1150 to 120 years ago the interval increased to about 140 years. Evidence from pollen, seeds, and charcoal at Hell's Kitchen Lake suggests that at least two “moist” intervals occurred during the past 2000 years, one between 2000 and 1700 years ago and the other between 600 and 100 years ago. A third but minor “moist” period occurred about 1150 to 850 years ago. A pollen and seed diagram shows that these intervals are characterized by increased percentages of white pine pollen, hemlock pollen, and yellow birch seeds, and by decreased levels of charcoal. The “dry” interval of 1700 to 1150 years ago is characterized by increased percentages of paper birch seeds, oak pollen, and aspen pollen, along with high levels of charcoal. The times of climatic change indicated at Hell's Kitchen Lake are nearly synchronous with those based on studies of tree rings, soils, glacial activity, and other pollen studies from various regions of North America, but the direction of these inferred changes is not always the same. This result suggests that the long-wave pattern of the general circulation has been variable during the past 2000 years.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.Abstract. Measurements of canopy opening, understory light, throughfall precipitation, and understory herb response in leaf surface area per square meter in pine forests on lighttextured soils in northern Wisconsin show that the understory herb layer is more responsive to differences in throughfall precipitation determined by canopy opening than to difference in light. Canopy opening controls both the level of light reaching the herb layer and the proportion of total precipitation reaching the litter layer, but the light levels are apparently considerably above the minimum thresholds for these species. On the light-textured soils, soil-moisture recharge in the surface layers, as influenced by canopy opening, exerts the major control over the total cover of herbaceous species. Moisture content of the lower litter layers and upper soil layer, where most of the northern understory herbs are rooted, is greatly influenced by variations in throughfall determined by canopy opening.' The authors gratefully acknowledge the financial assistance of the Wisconsin Alumni Research Foundation which supported this study during portions of 1963-66.

Two reconstructed histories of the monsoon rainfall in Rajasthan show that the monsoon was weak or absent in latest glacial time. With the advent of Holocene climatic patterns, fresh water lakes formed in dune fields and the pollen rain preserved in these reservoirs provides a basis for the reconstruction of the monsoon history. The two reconstructions, separated by only 150 km, have some features in common and some striking differences. Both show maximum monsoon amounts in the early Holocene, with a roughly two-thirds decrease to the present. Both show salinization in sub-Boreal time. Both show long intervals of near complete desiccation in the last four millennia. The shorter term variations, however, are not closely parallel. These shorter term variations may be explained in terms of the behavior of the present day interannual variability.