2. Geologic and Edaphic Factors Influencing Susceptibility of Forest to Environmental Change

Scott W. Bailey

There is great diversity in the structure and function of the northern forest across the 20-state portion of the United States considered in this book. The interplay of many factors accounts for the mosaic of ecological regimes across the region. In particular, climate, physiography, geology, and soils influence dominance and distribution of vegetation communities across the region. This chapter provides a review of the ecology of the northern forest, emphasizing the role of geology and soils. The chapter begins with descriptive material reviewing the physiog- raphy, bedrock geology, and soils of the various provinces that constitute the northern forest. The distribution of vegetation communities and the role of climate, while of prime importance in defining the ecology of the region, are given limited coverage here as these are discussed more thoroughly elsewhere in this volume (see Chapters 1 and 3). However, to the extent that climate and vegetation are important -forming factors (Jenny, 1941), their characteristics in each province are summarized here. As the historical vegetation, which developed prior to large-scale anthropogenic alterations of the landscape in the last 150 years, is more 28 S.W. Bailey germane to the distribution of soil types than current vegetation patterns, long-term climax vegetation or potential natural vegetation (Kuchler, 1964) is listed here. In the second portion of the chapter, particular attention is paid to the important resource of the soils, upon which our forests grow. Perhaps the single most important factor in determining the health and productivity of the forest, soils integrate many of the same influences that result in distribution of a variety of ecological types across the region. Distribution of major soil types is reviewed, highlighting the important differences in soil-forming factors and processes among soil taxonomic types. In particular, characteristics of each that most affect forest nutrient cycling, and which might be most dynamic in a changing environment, are highlighted. Finally, efforts to predict distribution of soils susceptible to nutrient depletion are reviewed. Nutrient depletion is perhaps the aspect of environmental change that is most associated with soil processes and is the subject of much recent study. Opportunities for advancement of the methods used to evaluate this phenomenon are suggested.

Ecological Regions

The United States Department of Agriculture (USDA) Forest Service has adopted a hierarchical classification system for mapping ecological regions at multiple scales (McNab and Avers, 1994). At the highest level of classification, the domain, are broad climatic regions, such as Polar, Humid Temperate, Humid Tropical, and Dry. The entire northern forest region lies within the Humid Temperate Domain. At the second level of classification, four divisions occur in the northern forest. The Warm Continental, Hot Continental, Subtropical, and Prairie Divisions delineate broad differences in climate, primarily temperature and precipitation. Two divisions in this region are in mountainous terrain, characterized by altitudinal zonation of vegetation; the letter "M" designates these units (see Fig. 2.1 in the color insert). Broad distinctions within the northern forest region are best illustrated at the third level of the classification system, the province. The following is a breakdown of the study region at this level of detail, highlighting factors responsible for the distinction of ecological units at this scale.

Laurentian Mixed Forest Province The Laurentian Mixed Forest occurs on flat to moderately hilly areas in the northern part of the region (see Fig. 2.1 in color insert). This province, which constitutes 22% of the region (Table 2.1), is characterized by 2. Geologic and Edaphic Factors 29

Table 2.1. Area of Ecological Provinces in the Northern Forest Region Svmbol Province Area (ha) Area (%) Laurentian Mixed Forest 37,656,021 New England-Adirondack 10,938,240 Mixed-Coniferous Forest-Alpine Meadow Eastern Broadleaf Forest (Oceanic) Central Appalachian Broadleaf-Coniferous Forest-Meadow Eastern Broadleaf Forest (Continental) Southeastern Mixed Forest Outer Coastal Plain Mixed Forest Lower Mississippi Riverine Forest Prairie Parkland (Temperate) Total northern hardwood forests (American beech [Fagus grandifolia Ehrh.], yellow birch [Betula alleglzaniensis Britton], sugar maple [Acer saccha- rum L.]). Lesser forest types include spruce (Picea spp.)-fir (Ahies spp.) in Maine and Minnesota, Appalachian oak (Quevcus spp.) forests in southern New York and adjacent Pennsylvania, and aspen (Populus spp.)-birch (Betula spp.) and mixed pine (Pinus spp.) forests in the upper Midwest. Mean annual precipitation ranges from 530 mm in northern Minnesota to 1270 mm in coastal Maine and portions of the Allegheny Plateau of Pennsylvania and New York. The frost-free growing season is relatively short, ranging from 100 to 160 days. The age, structure, and composition of bedrock, as well as its influence on forests, is quite varied within the Laurentian Mixed Forest. In Maine, bedrock ranges from deformed but unmetamorphosed sedimentary rocks in the northeast to high-grade metasedimentary rocks in the southwest. Variable contributions of plutonic rocks, mostly granitic, as well as volcanic rocks also occur throughout Maine. The northern New York and Vermont portion is underlain by an assortment of unmetamorphosed sedimentary rocks, including carbonates, shale, and sandstone, their metamorphosed equivalents of marble, schist, and quartzite, as well as gneiss and amphibolite. The influence of Appalachian deformation, metamorphism and igneous activity is less prevalent in the Allegheny Plateau of southern New York and adjacent Pennsylvania. Here, bedrock is slightly deformed sandstone, siltstone, and shale, with lesser amounts of limestone, conglomerate, and coal. Slightly deformed sandstone, limestone, and dolomite characterize the Michigan portion of the forest. In western sections of the province, highly deformed and metamorphosed rocks, associated with the Canadian Shield, dominate, including felsic to mafic plutonic and volcanic rocks, their metamorphic equivalents gneiss and amphibolite, as well as quartzites, and banded iron formation. 30 S.W. Bailey

Direct influence of bedrock on forest processes such as nutrient- and water-cycling, is minimal in portions of the Laurentian Mixed Forest where thick surficial deposits blanket the bedrock surface. However, in areas of shallow surficial deposits, bedrock influence may be great, depending on topography, bedrock composition, and degree of water flow through bedrock pores or fractures. In the only unglaciated portion of this province, in southwestern New York and adjacent Pennsylvania, bedrock influences the texture and mineralogy of surficial deposits ultimately derived from saprolite. Indirect influence of the bedrock is important in all glaciated areas, as primary mineralogy, and to a certain extent texture, of surficial deposits is dependent on the bedrock origin of the . Surficial deposits in this province are nearly all of glacial origin, deposited during the final retreat of the continental glacier at the close of the Wisconsinan Stage, approximately 10,000 to 15,000 years ago. Minor areas of glacial deposits from earlier stages, up to 550,000 years old, are found in southern portions of the province adjacent to the limit of the Wisconsinan advance. Glacial deposits result from a variety of deposi- tional modes, resulting in a variety of configurations and textures. Unsorted, unstratified ground moraine, or till, is the most common glacial deposit in this region. The till tends to be relatively thin (meters to tens of meters thick) in eastern portions, while it is up to hundreds of meters thick in some portions of the upper Midwest. Stratified drift, including outwash plains, kames, and eskers of lesser areal extent are common in most regions, while large sandy outwash deposits dominate some parts of Michigan. Lacustrine deposits, ranging from clays to stratified and , are common in some low-lying portions, for example, east of Lake Champlain in Vermont and in northern Minnesota. Marine clays are found in east central Maine and the Saint Lawrence Valley. These were deposited when sea level was higher, due to land subsidence under the weight of the continental glaciers. Recent surficial deposits include in river valleys and organic accumulations common in wetland basins throughout the region. These range greatly in size and frequency, with large deposits common in extreme eastern Maine and especially in northern Minnesota. The only unglaciated portion of the Laurentian Mixed Forest occurs in southwestern New York and adjacent portions of Pennsylvania. This area is underlain by residuum in the most stable landscape positions, primarily gently sloping plateau tops. dominates steeper slopes, whereas alluvium is found in lower slope positions. The Laurentian Mixed Forest and its mountain analog, the New England-Adirondack Province, are the only forest provinces in the study region with a predominance of Spodosols (Fig. 2.2 in color insert; Table 2.2). In this province, these are found in a large variety of parent materials and landscape positions. Several other soil orders dominate certain parent materials or more limited portions of the landscape. Table 2.2. Distribution of Dominant Soil Orders bv Ecological Province (Areas in Hectares) - Soil Order Laurentian New Eastern Central Eastern Southeastern Outer Lower Prairie Mixed England- Broadleaf Appalachian Broadleaf Mixed Coastal Mississippi Parkland Forest Adirondack Forest Broadleaf- Forest Forest Plain Riverine (Temperate) N Mixed- (Oceanic) Coniferous (Continental) Mixed Forest Coniferous Forest- Forest 8 Forest- Meadow oz Q. Alpine 0 Meadow Spodosols Water Total S.W. Bailey

Inceptisols are common, especially in wetter portions of the landscape and in finer parent materials. For example, while sandy to sandy parent materials are most prevalent, are common in some northeastern areas where lower metamorphic grade has resulted in large areas underlain by phyllites. Entisols are found in sandy stratified drift and alluvium. In low-lying basins in the cooler and wetter parts of the province, in Maine and Minnesota, large deposits of decaying organic matter accumulate, resulting in formation of large areas of Histosols. Most of the province is in the frigid temperature regime, with cryic soils in the Aroostook Hills of northern Maine and mesic soils at lower elevations of the Allegheny Plateau of New York and Pennsylvania. regime is xeric, udic, or aquic, largely dependent on texture and landscape position.

New England-Adirondack Mixed Forest-Coniferous Forest-Alpine Meadow Province This mountainous province is characterized by vegetational zonation, primarily with altitude, but also with latitude. Northern hardwood forests dominate lower elevations and latitudes, whereas spruce-fir forests are found at higher elevations and northern reaches of the province. Small areas of alpine tundra are found above timberline on the highest mountains of Maine, New Hampshire, Vermont, and New York. The climate is characterized by an abundance of precipitation, which is evenly spaced throughout the year. Frost-free growing season is the shortest in the northern forest, ranging from 80 to 150 days. Most of the province is underlain by an extremely complex assortment of igneous and highly deformed metamorphic rocks. A large variety of compositions are represented, including slates, phyllites, schist, gneiss, marble, quartzite, granitic plutons, rhyolite, and amphibolite. In north- western Maine, metasedimentary rocks are less deformed and at lower grade. Anorthosite, a relatively uncommon lithology on Earth, underlies large areas in the central Adirondacks. The Catskills and Tug Hill Plateau in New York differ from the rest of the province in that bedrock consists of only slightly deformed sandstone, conglomerate, siltstone, and shale. Because surficial deposits are thin and composed primarily of material of local origin, bedrock has a relatively large influence on forest processes in this province. Where topography and fracture patterns are favorable, large amounts of water may exchange between bedrock and surficial deposits, yielding an influence of bedrock on composition of groundwater and surface water. Whereas bedrock type varies greatly over short distances, the mineralogic composition of glacial deposits may also vary greatly, reflecting differences in directions and efficacy of glacial and deposition, as well as differences in lithology of bedrock source areas (Hornbeck et al., 1997). 2. Geologic and Edaphic Factors 33

Physiography includes glacially scoured, maturely dissected mountains and peneplains with scattered monadnocks. Surficial deposits are pre- dominantly thin, stony till with some stratified drift and lacustrine deposits, primarily in the larger valleys. Spodosols underlie 76% of the province (Fig. 2.2; Table 2.2), a larger proportion than any soil order in any of the provinces. Much of the remainder is underlain by Inceptisols, which are more common further south, at lower elevations, and on finer, less acidic parent materials. Most of the province is in the frigid temperature regime, with cryic soils at the highest elevations and some mesic soils in the larger valleys in the southern portion. Soil moisture regimes are udic and aquic.

Eastern Broadleaf Forest (Oceanic) Province Eastern Broadleaf Forest provinces cover 48% of the study region. This extensive type is subdivided into three provinces based on topography and climate. The eastern portions have an oceanic influenced climate, whereas a continental influenced climate dominates western and interior portions. In between, in the central Appalachians, lies a mountainous province characterized by altitudinal zonation of vegetation communities. The Oceanic Eastern Broadleaf province is a transitional forest with northern hardwoods dominant in northern portions and oak-hickory (Cavya spp.) dominant in the south. Oak-pine types are scattered throughout, especially in areas dominated by Entisols. The mixed mesophytic community is a component of the glaciated portion of the Allegheny Plateau in northwestern Pennsylvania and northeastern Ohio. Abundant precipitation is spaced evenly throughout the year, with winter snowfall ranging from none in the south to 2.5 m in the north. The frost- free growing season ranges from 120 to 250 days. Bedrock geology is varied and complex in this province, which was heavily influenced by metamorphism, igneous activity, and subse- quent sedimentation associated with closing of the Iapetus Ocean and opening of the Atlantic basin. The region from southern New England, south through eastern Pennsylvania and Maryland, is characterized by a highly deformed assemblage of metamorphic rocks with varying amounts of igneous rocks, primarily granites. Sandstones, siltstones, arkose, and basalt fill Mesozoic basins, such as the Connecticut Valley and the Newark Basin. The Hudson Valley includes a variety of siliciclastic rocks and carbonates in the valley, with metasediments and metavolcanics in eastern portions, bordering the Taconic Mountains. Toward the western part of the province, in western Pennsylvania, Ohio, and West Virginia, are slightly deformed sandstones, siltstones, and shales, with lesser amounts of limestone and coal. There is a broad range of surficial deposits underlying this province, reflecting differing processes of coastal and inland settings, as well as 34 S.W. Bailey differing glacial history. Approximately the northern half of this province is glaciated, whereas sections in southern Pennsylvania, Maryland, West Virginia, and southeastern Ohio are not. Thin till is the dominant surficial deposit in glaciated portions, although there are large areas of stratified drift, composed of sands and gravels, as well as marine clays, especially in southeastern New England. Glaciolacustrine deposits and alluvium of recent origin dominate the Hudson Valley of New York. Unglaciated portions are underlain by residuum in the most stable landscape positions, primarily gently sloping plateau tops. Colluvium dominates steeper slopes while alluvium is found in lower slope positions. Dominant soil taxa reflect a diversity of parent materials as well as the broad range in climate and vegetation types (Table 2.2). Inceptisols are dominant in glaciated areas, with Entisols in alluvium and some stratified deposits, and lesser areas of Alfisols in parent materials influenced by carbonates and lacustrine deposits. Ultisols are common in unglaciated portions, especially in more stable landscape positions. Alfisols are found in lower landscape positions and areas influenced by base-rich parent materials. Inceptisols are found in more acidic, steeper portions of the unglaciated Piedmont and Allegheny Plateau. Soil temperature regime throughout the province is predominantly mesic, with udic and aquic moisture regimes.

Central Appalachian Broadleaf-Coniferous Forest-Meadow Province Forest vegetation varies with altitude in this province. Oak forests and mixed oak-hickory-pine types occupy the lowest elevations. Northern hardwood forests are at moderate elevations, whereas the southern extension of the spruce-fir forest is found at the highest elevations. Precipitation is abundant and well spaced throughout the year. On average, the eastern Valley and Ridge is noticeably drier than western portions, as it lies in the rain shadow of the Allegheny Mountains. Twenty to thirty percent of the annual precipitation falls as snow. The frost-free growing season varies from 120 to 180 days. Parallel narrow ridges and valleys characterize the eastern portion of the province, yielding to maturely dissected mountains and plateaus of the western and southern portions. Bedrock consists of folded sedimentary rocks, including shale, siltstone, sandstone, chert, limestone, and coal. The bedrock has an important influence in this province by determining the chemistry, mineralogy, and texture of soil parent materials. Surficial materials are derived from saprolite in this unglaciated region. Residuum is found in the most stable landscape positions, primarily gently sloping plateau tops. Inceptisols are primarily found on steeper slopes and are the most common soil order in the province (Table 2.2). Substantial areas are 2. Geologic and Edaphic Factors 3 5 underlain by Ultisols, primarily in residuum on plateau summits. Lower landscape positions develop Inceptisols on more acidic parent materials and Alfisols in calcareous parent materials. Soil temperature regime is mesic, with udic and aquic moisture regimes.

Continental Eastern Broadleaf Forest Province Within the Continental Eastern Broadleaf Forest province, there is an east to west transition in vegetation types that corresponds to a longitudinal gradient in moisture excess (precipitation minus evapotranspiration). Northern hardwood forests are found at the eastern end of this province, in New York, northwestern Ohio, and southeastern Michigan. In the central parts of the province, in Michigan, Ohio, and Indiana, there is a transition from northern hardwood forest to oak-hickory forest with some oak savanna and minor bluestem prairie. Continuing west, oak savanna dominates southern Wisconsin with bluestem prairie becoming dominant further west, in the Minnesota portions of the province. The southwestern portions of the province, in southern Illinois and Missouri, are dominated by oak-hickory with some pine, oak-gum (Liquidambar spp.)-cypress (Taxodium spp.) in lowlands, and increasing proportions of prairie toward the west in Missouri. Average annual precipitation varies from 635 mm in northern Minne- sota to 1270 mm in the southern portions of the province. Moisture excess is less in this province than in other provinces in the subject region, approaching zero in the west. Frost-free growing season varies from 120 days in northern Minnesota to 200 days in southern Missouri. Bedrock geology may have little direct influence on the forests of this province due to the great thickness of surficial deposits in most regions. However, an important indirect influence is on the mineralogy of surficial deposits. Most of the province is underlain by slightly to undeformed sedimentary rocks, including limestone, dolomite, sandstone, and shale. Igneous rocks, primarily granite, are found in northern Minnesota. The Ozark Highlands of Missouri are underlain by a variety of igneous rocks, including granite, gabbro, rhyolite, and andesite. Metamorphosed volca- nic~and sediments, associated with the Canadian Shield, are found only in the northern Minnesota portion. Most of the province is level to gently rolling till plains, with till thickness up to 100 m or more. The till is mantled by in portions of the province, especially southern Wisconsin and southern Illinois. A lake plain, underlain by glaciolacustrine deposits from Lake Agassiz is found in northern Minnesota. Outwash deposits, some of great extent, are common, especially in the northern parts of the province. The portions in Missouri and southernmost Illinois, Indiana, and Ohio are unglaciated, maturely dissected plateaus, with steep to rolling hills. Sandstone bluffs are characteristic of the unglaciated portion of southern Illinois. Soils in 3 6 S.W. Bailey the unglaciated portion are derived from residuum, colluvium, and alluvium, typical of unglaciated regions. However, owing to the proximity to the southern extent of glaciation, loess deposits are common in the unglaciated portion. In this region, loess is characteristically cherty, especially in Missouri. With a wide variety of climate, parent materials, vegetation, and age characterizing the soils of this province, it is not surprising that a large variety of soil orders are found, each dominating different conditions. Alfisols are the dominant soil order, with substantial areas underlain by Mollisols. These two orders are characteristic of portions of the province with till or lacustrine deposits influenced by calcareous parent materials. Entisols are found on outwash and alluvial deposits. Ultisols are typical in more mature portions of the unglaciated terrain. Orders of lesser extent in this province include Spodosols, primarily in Michigan, Inceptisols, common in the Erie and Ontario lake plains, and Histosols in northern Minnesota. Soil temperature regime is mesic with a udic moisture regime.

Temperate Prairie Parkland Province The Temperate Prairie Parkland in the western portion of the subject region represents a transition from the deciduous forests of the east to the open prairie of the Great Plains to the west. Bluestem prairie is the dominant vegetation with interspersed forested tracts. Oak-hickory forests are common along stream channels. Northern floodplain forests are found along a few rivers, notably the Minnesota and Red. Mean annual precipitation varies from 460 to 1015 mm, with minimal excess over potential evapotranspiration. Frost-free growing season varies from 11 1 to 235 days. The Prairie Parkland, with the exception of the Osage Plains in southwestern Missouri, is glaciated, level to gently rolling till plain. Bedrock geology includes granite, gneiss, and metavolcanic rocks in Minnesota, with sedimentary rocks, including sandstone, shale, limestone, dolomite, and some coal in the remainder of the province. Till deposits are quite thick, blanketed with loess in some areas, and interspersed with lesser areas of glaciolacustrine and recent alluvial deposits. Loess and residuum are the dominant soil parent materials in the Osage Plains, similar to the unglaciated portions of the Continental Broadleaf Forest. Mollisols, reflecting the dominance of prairie vegetation, are dominant, with substantial areas of Alfisols. Entisols are found primarily in alluvial positions, whereas Vertisols enter the study region primarily in this province, in westernmost Minnesota. Soil temperature regimes range from frigid in northern Minnesota, to mesic in most of the province, and thermic in southwestern Missouri. Soil moisture regimes include ustic, udic, and aquic. 2. Geologic and Edaphic Factors 37

Southern Ecological Provinces Three ecological provinces, which together only account for 3% of the study area, are found along the southern border (Table 1.1). These provinces, which include the Coastal Plain Mixed Forest, Southeastern Mixed Forest, and Lower Mississippi Riverine Forest, are of much greater extent to the south. Climate is warm and moist, moderated by the marine influence, with a frost-free growing season ranging from 185 to over 250 days. The Coastal Plain Mixed Forest, dominated by oak, hickory and pine, is found on Long Island, New York, southern New Jersey and Maryland, and Delaware. With the exception of Long Island, which is composed of sands at the terminal moraine, this province is an unglaciated, flat to weakly dissected alluvial plain interspersed with marine terraces and . Ultisols and Entisols are the dominant soil orders (Table 2.2), with mesic to thermic temperature regimes, and xeric, udic, and aquic moisture regimes. These soils formed in unconsolidated marine silts, sands, and gravel. The Southeastern Mixed Forest barely extends into the study region in central Maryland. This province, dominated by southern species of oak, hickory, and pine, is rooted in thick saprolite deposits developed from schists, phyllite, and gneiss. Soils include nearly equal proportions of Ultisols, Inceptisols, and Alfisols in the thermic temperature regime. In extreme southeastern Missouri, the Lower Mississippi Riverine Forest also barely extends into the study region. Oak-hickory and southern floodplain forest, composed of oak, gum, and cypress, grow in a dissected alluvial plain of marine and alluvial sediments. Entisols are the dominant soil order, with some Alfisols and Vertisols. Temperature regime is thermic, with udic to aquic moisture regime.

Soils

Although susceptibility to environmental change is not a criterion of soil taxonomic systems, taxonomic units provide a convenient framework for examination of the potential effects of global change issues on the soil resource. The American taxonomic system is based on differences in dominant genetic processes ( Staff, 1996). These distinctions result from fundamental differences in parent material age, texture, and composition. These factors, along with climate, topography, and vegeta- tion, result in differences in how water and nutrients move through the soil profile, as well as on the development and distribution of organic matter and cation exchange sites. In sum, these influences and processes result in general differences in nutrient content and flux rates between taxonomic units. Following is a review of this subject by taxonomic order, highlighting potential for environmental change in each. 38 S.W. Bailey

Alfisols Accumulation of translocated in a subsurface horizon (the argillic horizon) and increasing base saturation in the are the defining characteristics of an . These soils form under many climatic regimes, but are most extensive in humid and subhumid temperate regions on relatively young, stable surfaces. Till, loess, and alluvium are typical parent materials. In humid temperate climates, Alfisols are found on most landscape positions except very steep slopes, alluvial floodplains, and very poorly drained depressions. A prerequisite to Alfisol development is of carbonates, which act as a flocculent, preventing clay translocation. Braunification, the release of the milder flocculent, iron, results in deposition of clay in the B-horizon. Deposition may also result from depletion of percolating waters as they are soaked up by peds, swelling of voids, slowing of percolating waters, sieve action of clogging fine pores, and by higher base saturation lower in the solum. Conditions for translocation may be relatively rare, occurring only during intense rains following prolonged drought (Buol et al., 1997). In general, Alfisols are considered to be more highly developed than Tnceptisols but less developed and less weathered than Ultisols. Ciolkosz et al. (1989) highlight the apparent anomoly that in central New York, - 12,000-year-old Alfisols are found, which are younger than the -1 8,000- year-old Inceptisols of southern New York and northeastern Pennsylva- nia. Carbonates in glacial deposits have enhanced development of Alfisols compared with the coarser, carbonate-free deposits to the south. With higher base saturation at depth, Alfisols are generally more nutrient rich than Ultisols. In New York, Cline (1949) considered forest soils to represent a chronolithosequence from unleached Mollisols (Udolls) to moderately leached Alfisols (Udalfs) to most leached Spodo- sols (Haplorthods). Organic matter loss from clearing or farming may degrade Mollisols to Alfisols. Changes in climatic patterns might alter clay translocation and deposition processes. Acidification of soil waters, resulting from atmospheric acid deposition or intensive forest manage- ment might accelerate soil development or even speed the transition of Alfisols toward Ultisols.

Entisols Entisols, which exhibit the least soil development of any of the soil orders, are characteristic of mountainous and sandy regions. They form on young surfaces in recent deposits such as alluvial floodplains, deltas, and areas of active loess or deposition. They are also typical of recently exposed surfaces, such as on steep slopes, where or other forms of rapid erosion have removed surficial material faster than 2. Geologic and Edaphic Factors 39 pedogenic horizons can form. Entisols are also found in older deposits, such as sand dominated by the quartz, where exception- ally resistant to have limited development. Nutrient content of Entisols may vary widely. Many Entisols have very low cation exchange capacity due to low clay and organic matter content. On the other hand, high cation exchange capacity is typical of alluvial deposits. Thus, the ability of an to meet nutrient demands of various forest types is largely dependent on the parent material and mode of deposition. Forest vegetation is important in stabilizing landforms; removal may accelerate erosional processes, resulting in Entisol formation on land- scapes that otherwise are characterized by other soil types. Artificial drainage or drying climatic trends may promote oxidation of water- saturated soils, accelerating pedogenic development in floodplains. Forest management may also promote Entisols through changes in vegetative cover. In Wisconsin, conversion of stands from hemlock (Tsuga spp.) to aspen resulted in degradation of the spodic horizon in less than one hundred years, converting Spodosols to Entisols (Hole, 1976).

Histosols Overall, Histosols comprise a small portion of the region's soils (Table 2.2), yet they are very widely distributed. Histosols form where production of organic matter exceeds mineralization, usually under saturated water conditions, which impedes decomposition. They develop in a variety of climates and substrates, although maritime climates and relatively impermeable substrates favor their formation. They are especially typical of glaciated regions, where glacial deposits include depressions and blocked drainage ways, and of the lower coastal plain where high water table and tidal inundation promote development. Although generally confined to depressions and low-lying areas, in extreme eastern Maine, where precipitation is high and frequent fog limits evapotranspiration, Histosols extend above depressional basins and even climb gentle slopes. Also, cooler temperatures and high precipitation at high elevations promotes development in mountainous regions. Cation exchange capacity, derived from carboxyl, phenolic, and other functional groups in organic matter, may be quite high in Histosols. Exchange capacity may be quite sensitive to changes in pH due to the variable charge nature of the organic matter. Depending on hydrologic position, some Histosols are located in zones of groundwater discharge, where dissolved and exchangeable cations reflect the weathering regime of underlying unconsolidated mineral deposits or bedrock. At the opposite extreme, Histosols in ombrotrophic bogs may be completely dependent on 40 S.W. Bailey atmospheric deposition for water inputs, in which case, pore waters and exchangeable cations are likely to be dominated by hydrogen ion. Decomposition of organic matter is controlled by a number of interrelated factors, such as moisture content, temperature, composition of organic matter, acidity, and microbial activity. Therefore, changes in climate, hydrologic flow patterns, or vegetation communities might be expected to change the nature of Histosols.

Inceptisols Inceptisols are generally considered to be immature soils, not having formed diagnostic subsurface horizons necessary for other orders. On the other hand, horizonation is too advanced to qualify as Entisols. Subsurface horizons of Inceptisols closely resemble parent material, with some development of structure and deposition of illuvial organic matter to distinguish B-horizons from similar C-horizons. These soils occur on young geomorphic surfaces, steep slopes subject to deposition, churning, and erosion, and depressions where water saturation limits development of spodic or argillic horizons. They are found in a wide range of climates and parent materials. Although many pedogenic processes may be at work, none predominates in an . In acid parent material, Inceptisols in depressions tend to be more leached, with lower base content and higher exchangeable aluminum than soils in surrounding areas. In base-rich landscapes, Inceptisols in depressions tend to have higher base status than surrounding landscape positions (Buol et al., 1997). In some regions, Inceptisols are on unusually resistant parent materials; low weathering rates limit the amount of clay produced, impeding formation of an argillic horizon. In regions where Inceptisols are interspersed with other soil orders, they are generally more productive than the others. With a wide range of parent materials, climates, and landscape positions, it is particularly difficult to generalize about the susceptibility of this soil order to environmental change. Base-poor Inceptisols, such as Dystrochrepts may be relatively sensitive to acidification and nutrient depletion, whereas Eutrochrepts may be relatively insensitive. Taxa with high organic matter (Haplumbrepts) and wetter moisture regimes (Aque- pts) may be more sensitive to climatic or vegetative changes that alter organic matter decomposition or hydrologic regime.

Mollisols Mollisols are defined by a deep, dark, relatively fertile A-horizon and higher base saturation in the subsoil. Most are found under grassland vegetation, while forested examples include poorly drained Mollisols of lowland hardwoods and relatively uncommon well-drained examples 2. Geologic and Edaphic Factors 4 1 within the udic moisture regime (Udolls). Severe, relatively dry winters, a moist spring, and droughty summers with occasional thunderstorms and tornadoes typify the climate where Mollisols dominate the landscape. Large annual inputs of organic matter through root turnover of deep- rooting prairie vegetation, partial decay of litter inputs during the dry growing season, reworking of organic matter by active soil faunal communities, and illuviation of organic colloids are among the processes responsible for development of thick, dark A-horizons. are slightly leached, with a high base status, resulting from younger or more base-rich parent materials. Mollisols on older surfaces and in moister climates show deposition of clay coatings on ped faces lower in the B-horizon. At the forest-prairie boundary in Wisconsin, Mollisols occur on topographic positions that favor spread of fire, namely ridgetops and windward slopes (Buol et al., 1997). Forests were much more widespread in the Midwest until about 5000 years ago, when climate changes brought a great expansion of the prairie and likely also of Mollisols (Ruhe, 1969). As this soil order is dependent on a relatively narrow range of climate and vegetation, changes in quality and distribution might be expected in the event of future changes in climate and in response to present and future changes in vegetative cover brought about by agricultural and silvicultural management.

Spodosols Spodosols are defined by eluviation of organic matter and iron, with or without aluminum from surface horizons and accumulation (illuviation) in the subsoil, the spodic horizon. The variably expressed albic or E-horizon is a zone of accumulation of resistant minerals and insoluble products of decomposition. Spodosols characteristically form in cool, humid climates under forest vegetation. Coniferous trees, notably hemlock are known for their capability of promoting spodic development (Buol et al., 1997). Leaching of carbonates and dominance of exchangeable cations by hydrogen and aluminum in the A-horizon are prerequisite to mobilization of organic matter and, with it, of iron and aluminum. Illuviation of clay may be a precursor to podzolization in finer parent materials. Throughfall may be the major source of mobile organic matter for mobilization of aluminum and iron (Malcolm and McCracken, 1968). As throughfall quality is highly variable, dependent on species composition, this may explain the relative intensity of Spodosol formation with differing vegetative communities. Removal of hemlock from mixed hemlock- hardwood forests in northern Wisconsin resulted in fading of the spodic horizon (Milfred et al., 1967). The half-life of the spodic horizon after removal of hemlock may be a short as 100 years (Hole, 1975). Management activities that change species composition might result in changes in the intensity of podzolization processes. 42 S.W. Bailey

In a transect of Spodosols and Inceptisols in Wisconsin and Michigan, Schaetzl and Isard (1996) found that Spodosols dominate the landscape in areas where the snowpack is thickest, limiting soil frost and allowing large snowmelt runoff events to infiltrate the soil. They hypothesize that the bulk of podzolization occurs during the snowmelt period. Thus, climatic changes that affect patterns of snow accumulation and melt might result in changes in Spodosol development.

Ultisols Worldwide, areas between the limit of glaciation and the equator, in humid temperate to tropical climates, are dominated by Ultisols. Parent materials and landscapes are older than in glaciated areas, resulting in a longer period of weathering and soil development. A long frost-free season and an abundance of rain also contribute to deep weathering by promoting leaching over a long portion of the year. These soils are acidic to great depths, where the parent material is siliceous crystalline or sedimentary rock relatively poor in bases. On older surfaces, even soils developed in carbonate parent materials may be acidic to great depths. Weatherable minerals in the solum have been converted to secondary clays and oxides. Ultisols are defined by low base saturation at depth, in association with pronounced clay accumulation in subsurface argillic horizons. There is more emphasis of in situ clay formation through advanced weathering in Ultisols as compared with argillic horizons in Alfisols that are more the result of clay translocation. Ciolkosz et al. (1989) emphasize the distinc- tion between parent material Ultisols and genetic Ultisols. Parent material Ultisols have low base status that is inherited through low base parent materials and show less development than genetic Ultisols. As in Alfisols, clay translocation is the dominant process in parent material Ultisols. Parent material Ultisols typify many of the Ultisols found just south of the limit of glaciation, formed in unglaciated parent materials that were affected by severe erosion and frost-churning during periglacial periods. These soils contrast with well-developed Ultisols of the Piedmont, for example, which formed due to longer periods of weathering in older, more stable positions. Clay accumulation in these soils occurs deeper in the profile, in a thicker horizon, and in amounts that cannot be accounted for by translocation alone. Although extensive leaching leads to a severe loss of bases in Ultisols, the pattern of base concentrations decreasing with depth suggests that biocycling successfully counters the leaching process. These soils of low fertility may be dependent on uninterrupted biocycling by forest vegetation for maintenance of organic matter and nutrient content. Cutting of native forests often leads to a major loss of fertility in Ultisols of tropical climates. To a lesser extent, the same concern holds for temperate region Ultisols. 2. Geologic and Edaphic Factors 43

Vertisols Vertisols form through seasonal drying of a soil profile that is rich in clay, predominantly 2:l expanding clays. The resultant seasonal shrink-swell cycles lead to alternating periods during which large vertical cracks characterize the upper portion of the soil profile. Vertisols occur in climates with a dry season of variable timing and intensity. They are characteristically alkaline, resulting from parent materials such as calcareous sediments and basic igneous. Small areas in the northwest and southwest portions of the study area exhibit Vertisols. Overall, this is not an important soil to the northern forest.

Sensitivity to Soil Nutrient Depletion

A particular global change issue involving dynamics of forest soils, that potentially could alter the health and productivity of the northern forest, is base cation nutrient depletion. In recent years, atmospheric acid deposi- tion and intensive forest management practices have led to concerns about potential for nutrient depletion from forest soils (Federer et al., 1989; see Chapter 8). The theoretical basis for these changes is well founded. Empirical studies have documented these processes in laboratory settings. However, extreme spatial variability in forest and difficulty in maintaining consistency in collection techniques limit the ability of sampling programs to detect temporal changes. A primary issue in determining the regional extent of this problem is whether mineral weathering rates, which are notoriously difficult to measure in the field, are high enough to replace base cations lost to forest regrowth and leaching (Federer et al., 1989). Mass balance studies, where weathering rates have been relatively well constrained, have documented net depletion of base cations, presumably derived from exchangeable soil pools, at the small watershed scale (Bailey et al., 1996; Likens et al., 1996). Several studies have documented decreases in soil base nutrient pools (Johnson and Todd, 1990; Joslin et al., 1992; Knoepp and Swank, 1994). However the causes and extent of these changes on a landscape basis are subject to great debate. Landscape and regional estimates of the extent of this phenomenon must be based on models of spatial patterns in deposition and soil processes.

Methods to Rate Sensitivity to Nutrient Depletion

The distribution of bedrock lithologies can tell much about the spatial distribution of areas sensitive to nutrient depletion. Table 2.3 lists the rock types found in the study region by generalized lithology. Within each Table 2.3. General Lithology and Characteristics of Bedrock in the Northern Forest Region and Generalized Influence on the Acidity, $ Nutrient Content, and Texture of Soil Parent Materials General Type Lithology Characteristics Acidity Nutrients Texture Sedimentary Sandstone Cemented sand particles, typically mostly quartz Acidic Low Coarse Sedimentary Pelite Cemented slit and clay particles Acidic Low to moderate Fine to medium Sedimentary Limestone/ Cemented calcium and magnesium carbonate particles; Basic High Fine to medium marble marble is recrystallized Igneous Mafic Dark-colored rock crystallized from a melt; contains Slightly Moderate Medium plutonic amphiboles, pyroxenes or olivine acidic to coarse Igneous Granitoid Light-colored rock crystallized from a melt; composed Acidic Low Coarse primarily of quartz and feldspars Igneous Syenite Light-colored rock crystallized from a melt; con~posed Acidic Low to moderate Coarse primarily of feldspars with little or no quartz Igneous Anorthosite Light-colored rock crystallized from a melt; composed Slightly Moderate Medium primarily of plagioclase; may be recrystallized acidic to coarse F Metamorphic Slate Metamorphic equivalent to pelite; mineral crystals too Acidic Low to moderate Fine to medium . small to be seen with naked eye Metamorphic Phyllite Metamorphic equivalent to pelite; micaceous minerals Acidic Low Fine to medium barley large enough to be seen with naked eye r Metamorphic Mica schist Coarse-grained metamorphic equivalent to phyllite with Acidic Low Medium muscovite and/or biotite mica to coarse Metamorphic Sulfidic schist Coarse-grained metamorphic equivalent to phyllite Very Low Medium with iron sulfides acidic to coarse Metamorphic Calcareous Coarse-grained metamorphic rock with carbonates Neutral Moderate to high Medium schist at lower grades to calciun~silicates at higher grades to coarse Metamorphic Metasand- Recrystallized sandstones; quartz-rich varieties referred Acidic Low Coarse stone to as quartzite Metamorphic Gneiss Granitoids and sediments in which minerals have Acidic Low Coarse separated into distinct bands during metamorphism Metamorphic Amphibolite Recrystallized mafic rocks composed primarily of Slightly Moderate to high Medium hornblende and plagioclase acidic to coarse Metamorphic Ultramafic Primarily of iron and magnesium silicates such as Basic Low to high Fine to medium talc and serpentine Color Plate V

Map Un* Pmvinw MwUniI Prminw 1212 humtlul fiwt . 222 E..tm hdlulForut. ContM.l IM212 kEnpmMdbndrk - Zll loumY.Om Mlwd *,.,I I221 Unm hdlutFaut .0-lc 232 OvUCwWWnMMfiM M221 cemd~o@rhhnWadlut- U. LamMU~mwlr.Forrt CO~I~~Y.FOMMY~W

Figure 2.1. Ecological provinces of the northern forest region (after Keys el a\., 1995). ~olorPlate VI

Dominam Soil Ordan urn* Iwm IRock

Figure 2.2. Dom~nantsoil orders of the northern forest reglon (after Quandt and Waltman, 1997). 2. Geologic and Edaphic Factors 45 category, based on typical mineralogy and fabric, the general tendencies of the bedrock's influence on acidity, nutrient content, and texture of soil parent materials can be predicted. Norton (1980) categorized susceptibility to acidification based on generalized bedrock type. While this method is useful for comparing regions, it is of limited usefulness at finer scales. Local variation may be expected due to the transported nature of many parent materials, which may not reflect local bedrock; the highly variable age of landscape surfaces, resulting in parent materials of greatly differing age and degree of alteration from bedrock sources, and the variability in topog- raphy, thickness, and permeability of surficial deposits which affect the efficacy of weathering reactions. Models useful for predictions at scales from the landscape to the management unit must account for these factors. An important limitation to classification schemes based on lithology, which has received relatively little attention, is that variability in mineralogic content of even narrowly defined lithologies may vary greatly. As an example, granites, coarse-grained igneous rocks composed of quartz, feldspar, and lesser amounts of amphibole and mica, are considered to form acidic, coarse-grained parent materials (Table 2.3) with low weathering rates and relative sensitivity to nutrient depletion. The Conway granite, which underlies large areas in central New Hampshire, is a good example. It is composed of quartz, microcline, and biotite (Billings, 1956), relatively slowly weathering silicate minerals (Table 2.4). Soils derived from this rock would be expected to be relatively

Table 2.4. Range of Base Cation Nutrient Content and Weathering Rate for Primary Minerals Commonly Found in Forest Soils. Nutrient Contents Are Midrange Examples for Minerals that Exhibit Solid Solution. Weathering Rates, Based on Laboratory Studies at pH 5, in Log Units (keq[m2s]-I), Were Compiled by Sverdrup and Warfinge (1995) Mineral Ca (%) Mg (%I K (%) Weathering Rate Calcite 40 -8 to -10 Dolomite 22 13 -8 to -10 Olivine 14 -12 to -13.5 Garnet 8 5 -12 to -13.5 Diopside 19 11 -12 to -13.5 Chlorite 11 -12 to -13.5 Epidote 18 -12 to -13.5 Plagioclase 7 -13.5 to -15 Hypersthene 11 -13.5 to -15 Augite 17 5 -13.5 to -15 Hornblende 5 3 -13.5 to -15 Actinolite 9 5 -13.5 to -15 Serpentine 26 -13.5 to -15 Biotite 8 8 -13.5 to -15 Microcline 14 -15 to -16 Muscovite 10 -15 to -16 46 S.W. Bailey poor in base cations and sensitive to acidification, true to the general prediction. On the other hand, granitic rocks of the nearby Highlandcroft Pluton typically contain about 25% plagioclase, 8% hornblende, and 3% calcite (Billings, 1956), faster weathering silicates and a very fast weathering carbonate (Table 2.4). Forested sites influenced by this rock might be relatively base-rich and well buffered from acidification. Advancement of models to determine sensitivity was made by Warfinge and Sverdrup (1992) with development of PROFILE, a model which takes into account major nutrient-cycling processes and uses information about soil mineralogy to estimate weathering rates. This method has been used to map critical loads of atmospheric pollutants relative to soil and surface water acidification in several European countries. It has also been used to evaluate discrepancies between lab- based and field estimates of soil weathering rates (Sverdrup and Warfinge, 1995). A disadvantage of this method is its extensive site-specific data requirements. Additionally, soil mineral content is modeled based on a bulk element analysis. This does not take into account variations in mineral chemistry, inherent in soil parent materials, which may be critical in determining weathering stoichiometry and rates. Many minerals are solid solutions of two to four end-members; weathering rates can vary by several orders of magnitude depending on chemical composition (Table 2.4) (White and Brantley, 1995).

Potential for the Next Generation of Models

Opportunities to improve models of susceptibility to nutrient depletion will come through incorporation of a better understanding of spatial patterns of mineralogic composition of soil parent materials and better knowledge of mechanisms and locations where weathering reactions occur in the landscape. Extensive soil surveys to determine spatial patterns in mineralogy are extremely expensive, while estimates of mineralogic composition based on bulk element composition may be misleading. However, mineralogic composition of bedrock formations is often relatively uniform within map units. Furthermore, there is a wealth of data on bedrock chemical and mineralogic composition in the geologic literature. By better understanding how bedrock sources are sampled and incorporated by surficial deposits, we might be able to best predict spatial pattern in parent material composition. One effort using this approach is in progress for soils developed in glacial till (Hornbeck et al., 1997). Further progress might be accomplished by development of methods which consider the properties of a larger portion of the soil than is traditionally studied. Soil mineralogy and chemistry protocols are performed on only the fine-earth fraction of the soil-that portion that 2. Geologic and Edaphic Factors 47 passes a 2 mm sieve. These techniques have largely been developed for study of agricultural soils, which, due to the limitations of cultural practices, are centered mostly in relatively rock-free portions of the landscape. In contrast, forested soils, typically located on steeper upland portions of the landscape unsuitable for agriculture, frequently contain high amounts of rock fragments, termed "skeleton". A further reason for ignoring these coarse fragments is that the rates of many reactions, including weathering, are dependent on surface area. Thus, fine particles are considered to be more reactive than coarse particles. For example, the specific surface area of colloidal clay ranges from about 10 to 1000 m2 g-l compared with 0.1 m2 g-' for fine sand. The specific surface area of gravel and pebbles, even where they make up the majority of a soil, is negligible. Yet, Bailey and Hornbeck (1992) found that pebbles in forest soils derived from glacial till contained highly weathered interiors. Fractures and zones of secondary alteration allow water to percolate into seemingly impervious pebbles. Ugolini et al. (1996) found that the skeleton of forest soils in Tuscany, derived from sandstone, contained more weatherable minerals than the fine-earth fraction, and contributed significantly to the soils' overall cation exchange capacity as well as available and total nutrient content for a number of nutrients, including nitrogen. Yet another reason why specific surface area may not be important is that biologically mediated weathering may not differentiate between particle size, rather focusing on nutrient content of minerals and their susceptibiltiy to direct weathering by exuded organic acids. April and Keller (1990) documented extensive alteration of primary minerals in the rhizosphere compared with bulk soil. Minerals in direct contact with roots were most highly altered. Jongmans et al. (1997) documented direct weathering of feldspar and hornblende grains by mycorrhizal hyphae. Finally, a better understanding of the role of bedrock weathering must be incorporated into models. In many regions, as stated previously in the review of ecological provinces, reactions in bedrock may influence forest nutrient cycles. For example, in areas of crystalline bedrock, such as granite-schist terrain in central New Hampshire, effective hydraulic conductivity of bedrock may be in the same order of magnitude as that of glacial till. Local zones of concentrated bedrock fractures may have conductivity a few orders of magnitude higher than till (Tiedeman et al., 1997). In this case, in landscape positions where groundwater flows from bedrock into surficial deposits, weathering products derived from mineral decomposition within bedrock may be delivered to soil and the rooting zone of the forest. Johnson and Todd (1998) found that nutrient flux measurements overpredicted calcium depletion from forest harvesting for an unglaciated site on Ultisols developed in calcareous bedrock. They suggest that deep rooting and bedrock weathering could account for this discrepancy. 48 S.W. Bailey

References April R, Keller D (1990) Mineralogy of the rhizosphere in forest soils of the eastern United States. Biogeochem 9: 1-1 8. Bailey SW, Hornbeck JW (1992) Lithologic Composition and Rock Weathering Potential of Forested Glacial-Till Soils. USDA Forest Service, Northeastern Forest Experiment Station, Radnor, PA. Bailey SW, Hornbeck JW, Driscoll CT, Gaudette HE (1996) Calcium inputs and transport in a base-poor forest ecosystem as interpreted by Sr isotopes. Water Resour Res 32:707-719. Billings MP (1956) The Geology of New Hampshire Part 11-Beduock Geology. Concord: New Hampshire State Planning and Development Commission, Concord, NH. Buol SW, Hole FD, McCracken RJ, Southard RJ (1997) Soil Genesis and Classijication. 4th ed. Iowa State University Press, Ames, IA. Ciolkosz EJ, Waltman WJ, Simpson TW, Dobos RR (1989) Distribution and genesis of soils of the northeastern United States. Geomorph 2:285-302. Cline MG (1949) Profile studies of normal soils of New York. I. Soil profile sequences involving Brown Forest, Gray-Brown Podzolic, and Brown Podzolic soils. Soil Sci 68:259-272. Federer CA, Hornbeck JW, Tritton LM, Martin CW, Pierce RS, Smith CT (1989) Long-term depletion of calcium and other nutrients in eastern US Forests. Environ Mgt 13:593-601. Hole FD (1975) Some relationships between forest vegetation and B horizons in soils of Menominee tribal lands, Wisconsin, USA. Soviet Soil Sci 7:714-723. Hole FD (1976) Soils of Wisconsin. 62. Wis Geol Nat Hist Surv Bull 87, University of Wisconsin Press, Madison, WI. Hornbeck JW, Bailey SW, Buso DC, Shanley JB (1997) Streamwater chemistry and nutrient budgets for forested watersheds in New England: variability and management implications. Forest Ecol Mgt 93:73-89. Jenny H (1941) Factors of Soil Formation: A System of Quantitative . McGraw-Hill, New York. Johnson DW, Todd DE (1990) Nutrient cycling in forests of Walker Branch Watershed, Tennessee: roles of uptake and leaching in causing soil changes. J Environ Qual 19:97-104. Johnson DW, Todd DE (1998) Harvesting effects on long-term changes in nutrient pools of mixed oak forests. Soil Sci Soc Am J 62:1725-1735. Jongmans AG, van Breeman N, Lundstrom U, van Hees PAW, Finlay RD, Srinivasan M, Unestam T, Giesler R, Melkerud PA, Olsson M (1997) Rock- eating fungi. Nature 389:682-683. Joslin JD, Kelly JM, van Miegroet H (1992) Soil chemistry and nutrition of North American spruce-fir stands: evidence for recent change. J Environ Qual 21: 12-30. Keys JE, Carpenter C, Hooks S, Koenig F, McNab WH, Russell WE, Smith ML (1995) Ecological Units of the Eastern United States-First Approximation. 1:3,500,000. USDA Forest Service, Atlanta, GA. Knoepp JD, Swank WT (1994) Long-term soil chemistry changes in aggrading forest ecosystems. Soil Sci Soc Am J 58:325-331. Kuchler AW (1964) Potential Natural Vegetation of the Conterminous United States. American Geographic Society, New York. 2. Geologic and Edaphic Factors 49

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Robert A. Mickler Richard A. Birdsey John Horn Editors

Responses of Northern U.S. Forests to Environmental Change

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