Randall J. Schaetzl

Tree uprooting: review of impacts on forest ecology

This paper reviews the ecological effects of tree uprooting. In many forests, disturbance by uprooting is the primary means of maintaining species richness and diversity. Treefall may be due to exogenous factors or it may be endogenously created, although the former predominate. The canopy gap formed by downed trees is often vital to community vegetation dynamics and successional pathways, by providing high light niches (gaps) for pioneer species, by encouraging release of suppressed, shade-tolerant saplings, and through recruitment of new individuals. Nutrient cycling may be affected by uprooting as subsoil materials are brought to the surface, via additions of woody debris to the forest floor, through exposure of bare mineral soil, and by changes in throughfall chemistry. The influence of the resultant pit/mound microtopography on understorey herb distribution is largely due to microclimatic and microtopographic variation. Tree seedling distribution, however, is related to microtopography primarily through differences in soil morphology, nutrition, and moisture content of mound and pit sites.

Origin and Evolution of the Great Lakes

This paper presents a synthesis of traditional and recently published work regarding the origin and evolution of the Great Lakes. It differs from previously published reviews by focusing on three topics critical to the development of the Great Lakes: the glaciation of the Great Lakes watershed during the late Cenozoic, the evolution of the Great Lakes since the last glacial maximum, and the record of lake levels and coastal erosion in modern times. The Great Lakes are a product of glacial scour and were partially or totally covered by glacier ice at least six times since 0.78 Ma. During retreat of the last ice sheet large proglacial lakes developed in the Great Lakes watershed. Their levels and areas varied considerably as the oscillating ice margin opened and closed outlets at differing elevations and locations; they were also significantly affected by channel downcutting, crustal rebound, and catastrophic inflows from other large glacial lakes. Today, lake level changes of about a 1/3 m annually, and up to 2 m over 10 to 20 year time periods, are mainly climatically-driven. Various engineering works provide small control on lake levels for some but not all the Great Lakes. Although not as pronounced as former changes, these subtle variations in lake level have had a significant effect on shoreline erosion, which is often a major concern of coastal residents.

EFFECTS OF TREETHROW MICROTOPOGRAPHY ON THE CHARACTERISTICS AND GENESIS OF SPODOSOLS, MICHIGAN, USA

Summary This study examined the pedogenic effects of pit and mound microtopography, formed by tree uprooting, in a Spodosol (Haplorthods) landscape. Most soils in treethrow pits were Entic Haplorthods or Spodic Upidsamments whereas mound soils usually classified as Typic Udipsamments, suggesting that degree of profile development is: Undisturbed ≥ Pit > Mound. Given that pit and mound soils are substantially younger than pedons on “undisturbed” sites, rates of pedogenesis are thought to be: Pit > Undisturbed > Mound. Strong pedogenesis in pits was explained by: 1. greater water contents in the upper sola, which may facilitate weathering processes, 2. thicker O horizons, which may lead to increased production of organic acids, and 3. greater insulation by thick litter and snow cover, which reduces the incidence of soil freezing. In winter, mound soils may develop impermeable layers of concrete soil frost that impede infiltration of snowmelt waters, whereas pit soils remain unfrozen or acquire only a porous, granular frost layer. Thus, saturated flow of snowmelt within pits is relatively unrestricted, resulting in maximal leaching and profile differentiation.

Proisotropic and proanisotropic processes of pedoturbation

Because pedoturbation processes (soil mixing) occur in all soils in varying degrees during the curse of their evolution, mixing processes should be assessed within the larger context of soil genesis. Soils may be viewed as evolving along two pedogenic pathways that operate concurrently: a progressive pathway that includes processes, factors, and conditions that promote ordered, differentiated and/or deep profiles; and a regressive pathway that promotes disordered, simplified, rejuvenated, and/or shallow profiles. Pedoturbative processes that disrupt, blend, destroy, or prevent the formation of horizons, subhorizons, or genetic layers, such that simplified profiles evolve from more ordered ones, are proisotropic and function within the regressive pathway. Pedoturbative processes that form or aid in the formation and maintenance of horizons, subhorizons, or genetic layers and/or promote increased profile order are proanisotropic and function within the progressive pathway. Ten forms of pedoturbation are recognized. Hypothetical and real examples of how proisotropic and proanisotropic mixing processes affect soil profiles are presented. The examples demonstrate that both the form of pedoturbation and the texture of the parent material largely determine whether the ensuing morphology of a soil expresses order or disorder. A particular form of pedoturbation may produce a disordered profile in one soils or polypedon, but a more ordered profile in another. This can be true not only for different soils on a landscape, but also for the same soil at different times during its evolution. Homogeneous or heterogeneous geologic deposits may be pedologically organized, or reorganized, via proanisotropic pedoturbation to express profile order and in certain cases may produce spatial patterning and microrelief. Surface stone pavements and armored surfaces, subsurface stone lines and stone zones, and upper profile biomantles can thus be formed.

Longevity of treethrow microtopography: implications for mass wasting

Abstract This study examines and compares methods of dating pit/mound microtopography formed by tree uprooting, and provides 14 C evidence for the longevity of these landforms. Microtopography can often by dated by reference to known meteorological phenomena, or within certain age constraints, by dendrochronologic means. We used 14 C analysis of buried wood and charcoal in treethrow mounds in Michigan and Wisconsin, U.S.A. to arrive at estimates of the geochronometric ages of treethrow mounds. Results indicate that mounds in these areas often persist for more than 1000 years, which are two to five times longer than published estimates by less reliable methods. The longevity of treethrow mounds in these regions is ascribed to (l) sandy, porous soils which minimize runoff, (2) a continuous mat of forest litter and vegetation cover, (3) surface concentrations of gravel which may act as an “armor”, (4) large initial size of the features, and (5) soil freezing. Implications are that rates of mass movement due to uprooting may be substantially less than studies from other regions suggest.

Lithologic discontinuities in some soils on drumlins : Theory, detection, and application

This paper discusses the importance of lithologic discontinuities in pedologic and geologic research, reviews the primary methods used to detect them, and examines some soils in northern Michigan that exhibit varying degrees of evidence for lithologic discontinuities. Although many different parameters have been used successfully to detect discontinuities in soils, those involving immobile and inert components offer the best likelihood of success, and these data are best reported on a clay-free basis. Parameters involving acquired (pedogenic) characteristics or the mobile element (plasma) of soils should be avoided. Six Typic Eutroboralfpedons, formed on drumlins, were the primary focus of this study. Obvious-to-subtle evidence exists for lithologic discontinuities within the lower sola of these soils. Frequently, a weakly expressed stone line exists at or near the discontinuity. In this geologically young landscape, the origin of the discontinuity is presumed to have been glaciosedimentologic rather than pedologic (i.e., formed by bioturbation, surface creep, or eolian additions to near-surface horizons). Depth functions involving clay-free particle-size data, especially for coarser (coarse sand and fine gravel) fractions, were the most consistent indicators of the discontinuity. Mean particle-size data and heavy versus light minerals were also somewhat useful in discriminating between the two materials. This study may be the first of its kind to use measures of sand grain sphericity (e.g., mean feret diameter, compactness, and shape factor) to identify discontinuities in soils, although the utility of these indices in detecting discontinuities was mixed. The data underscore the need for multiple lines of evidence in the detection oflithologic discontinuities in soils and cautions that they are not all geologic/sedimentologic in origin.

COMPLETE SOIL PROFILE INVERSION BY TREE UPROOTING

Treethrow pits and mounds in sandy Spodosols were examined to determine their internal soil horizonation. Treethrow mounds were found to contain either (1) nearly intact, yet inverted soil profiles above otherwise undisturbed soil horizon sequences, or (2) more typical mixed and random horizonation. Soil profile inversion, emphasized here for the first time, is initiated by treethrow on steep slopes which produces overhanging root plates. Subsequent fire burns the trunk, eliminating all support and allowing the plate to overturn. Charcoal within buried A horizons of mounds supports this hypothesis. On gentle slopes, soil slumps off a more vertically-inclined root mass, resulting in a haphazard arrangement of horizons. This arrangement occurs regardless of the presence or absence of fire, and results in the typical contorted horizonation often reported for treethrow mounds. [Key words: Spodosols, treethrow, pedoturbation, fire, Michigan.]

Effects of slope angle on mass movement by tree uprooting

Abstract An examination of 189 well-delineated mounds and pits in sandy soils of northern lower Michigan, all presumably formed by tree uprooting, was used to determine the effects of slope angle on morphology and volume, and to assess the potential importance of uprooting to mass movement. Slopes ranged from zero to 54%. Data indicate that mound and pit volumes increase with increasing slope angle, suggesting that on gentle slopes more of the disturbed soil wastes off the mound, back into the new pit. Mounds are often elongated in the downslope direction on steep slopes. Based on regression analyses, slopes of ⇌47° are generally sufficient for all mound soil to slump or wash off in a downslope direction, rather than into the upslope pit. Thus, on steep slopes pit volumes provide a better representation of root plate volume. Pit depth can also be used as a surrogate for rooting depth on steep slopes where infilling from the mound is minimal.

Regional-scale relationships between climate and strength of podzolization in the Great Lakes Region, North America

Abstract Along a 300 km transect in northern Wisconsin and the upper peninsula of Michigan, the areal coverage of Spodosols and spodic horizon development increases markedly from south to north. This study elucidated those aspects of climate that promote podzolization in this region, through an examination of the geographic correspondences between Spodosol development and soil climate. Climatic data (1951–1991) from 21 sites along this transect were processed by a hydrologic model developed to output data on (1) soil temperatures for 0.05 and 0.5 m depths for 20 minute intervals, including data on soil freezing, (2) snowpack thicknesses under forest cover, and (3) daily water fluxes, runoff, and soil water contents at several depths. Spodosols dominate the landscape in areas where soil frost and freeze-thaw activity are minimal and where soil temperatures rarely exceed 16–17°C. Podzolization is strongest where snowpacks are thickest — an association that holds at both regional and meso scales. Thick snowpacks inhibit soil frost and allow large fluxes of snowmelt water to infiltrate into already moist profiles. This type of flux (slow, steady, cold water) may be particularly effective in the podzolization process. In the southern part of the transect, where Spodosols are rare, snowmelt fluxes are 1/3 as large as in the northern “snowbelt” areas. The southern areas also have a small autumn infiltration peak that usually reaches to ≈ 0.3 m depth; this flux is absent in areas of strong podzolization. Mean soil water contents are low and fluxes of water into the soil are small along the entire transect during summer, underscoring the belief that the bulk of pedogenesis (i.e., translocation), in Spodosols in the study area, occurs during snowmelt.

EFFECTS OF WINTER WEATHER CONDITIONS ON SOIL FREEZING IN SOUTHERN MICHIGAN

We examined climatic and (modelled) soil-temperature data from five winters in southern Michigan to ascertain the spatial variability in soil-freezing and freeze-thaw cycles at 5 cm. The five winters chosen for study (1951–1952, 1952–1953, 1953–1954, 1976–1977, and 1979–1980) represent the extremes of weather (e.g., cold and snowy, warm and dry) for the 1951–1980 period. We chose this study area because it lies on an ecotone between the cold, snowy climates of southern Canada and the warmer climates of the Ohio Valley where persistent snowpacks are rare, and because virtually no data on soil freezing exist for this area. Soil freezing in winter in southern Michigan is more dependent on snowpack persistence and thickness, especially in mid-winter, than on air temperatures. Here, even in warm winters, soils freeze to 5 cm, provided that snowpacks are thin or absent. Conversely, in even the coldest winters, soils rarely freeze where deep snows accumulate. Thus, freezing is least frequent, and in some years n...