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In terrestrial ecosystems, a large portion (20-80%) of the dissolved Si (DSi) in soil solution has passed through vegetation. While the importance of this "terrestrial Si filter" is generally accepted, few data exist on the pools and fluxes of Si in forest vegetation and the rate of release of Si from decomposing plant tissues. We quantified the pools and fluxes of Si through vegetation and coarse woody debris (CWD) in a northern hardwood forest ecosystem (Watershed 6, W6) at the Hubbard Brook Experimental Forest (HBEF) in New Hampshire, USA. Previous work suggested that the decomposition of CWD may have significantly contributed to an excess of DSi reported in stream-waters following experimental deforestation of Watershed 2 (W2) at the HBEF. We found that woody biomass (wood + bark) and foliage account for approximately 65% and 31%, respectively, of the total Si in biomass at the HBEF. During the decay of American beech (Fagus grandifolia) boles, Si loss tracked the whole-bole mass loss, while yellow birch (Betula alleghaniensis) and sugar maple (Acer saccharum) decomposition resulted in a preferential Si retention of up to 30% after 16 yr. A power-law model for the changes in wood and bark Si concentrations during decomposition, in combination with an exponential model for whole-bole mass loss, successfully reproduced Si dynamics in decaying boles. Our data suggest that a minimum of 50% of the DSi annually produced in the soil of a biogeochemical reference watershed (W6) derives from biogenic Si (BSi) dissolution. The major source is fresh litter, whereas only ~2% comes from the decay of CWD. Decay of tree boles could only account for 9% of the excess DSi release observed following the experimental deforestation of W2. Therefore, elevated DSi concentrations after forest disturbance are largely derived from other sources (e.g., dissolution of BSi from forest floor soils and/or mineral weathering).

Although understanding of nitrogen cycling and nitrification in forest ecosystems has improved greatly over the past several decades, our ability to characterize spatial patterns is still quite limited. A number of studies have shown linkages between canopy chemistry and N cycling, but few have considered the degree to which these trends can provide an indicator of forest N status across large, heterogeneous landscapes. In this study, we examined relationships among canopy chemistry, nitrogen cycling, and soil carbon:nitrogen ratios across 30 forested stands in the White Mountains of New Hampshire. Plots included a range of species (sugar maple, red maple, American beech, yellow birch, paper birch, red spruce, balsam fir, eastern hemlock) and were broadly grouped into two disturbance categories: those that were historically affected by intensive logging and/or fire and those that experienced minimal human disturbance. Across all plots, rates of net N mineralization and net nitrification were correlated wi...

Preferences for foraging in particular tree species have been well documented in a variety of bird species, but underlying reasons remain little investigated. Understanding the causal bases for such patterns of habitat use can help to elucidate mechanisms of habitat selection and, therefore, community organization and structure. I experimentally tested the hypothesis that fine-scale foliage structure of two deciduous tree species influences the foraging behavior of three small, insectivorous bird species. On sugar maple (Acer saccharum), with its orbicular leaves elevated above the branch, Black-throated Blue Warblers (Dendroica caerulescens) and American Redstarts (Setophaga ruticilla) captured prey predominantly from lower leaf surfaces, whereas Black-throated Green Warblers (Dendroica virens) captured prey predominantly from upper leaf surfaces. In contrast, on yellow birch (Betula alleghaniensis), with its oblong-ovate leaves held within the plane of the supporting branch, all three bird species captu...

Oribatid mites (Acari: Oribatidae) are the most diverse arthropod group in forest litter and soil, and they make significant contributions to decomposition as microbial grazers and saprophages. As is true for all the hyperdiverse soil taxa, the determinants of their diversity and species composition are virtually unexplored. This experiment tests whether heterogeneity of the litter habitat is a determinant of their local diversity, and whether litter composition is a determinant of their species composition. At a single site of temperate deciduous forest at the Coweeta Hydrological Laboratory in the mountains of North Carolina, USA, natural litterfall was excluded from a series of 42 1-m2 plots and, for three consecutive years, replaced with treatment litters that varied in their composition and complexity. Plots of pure yellow birch (Betula alleghaniensis), sugar maple (Acer saccharum), and red oak (Quercus rubra) litter comprised the monotypic or simple litter treatments. Two complex litters included a ...

Permanent plots in old-growth hemlock-northern hardwood forests of Mich- igan's upper peninsula have been remeasured over periods of 16-32 yr. A gradient from hemlock (Tsuga canadensis) to sugar maple (Acer saccharum) dominance is associated with increasing soil pH and calcium. Secondary species include yellow birch (Betula al- leghaniensis) and basswood (Tilia americana). From 1962 to 1994 hemlock increased in basal area and dominance in most plots. Sugar maple showed little overall change, while basswood and especially yellow birch showed sporadic but often large declines in basal area. Birch populations declined due to lack of recruitment, and sugar maple and basswood may be subject to similar decline; only hemlock showed a fairly stable size structure. Mortality rates were lowest for hemlock (0.3%/yr) and highest for yellow birch (1.6%/yr), corresponding to canopy residence times of 357 and 61 yr, respectively. Stem maps allowed assessment of neighborhood influences on growth and mortality. Growth and mortality rates were negatively correlated for all species. Growth rate was influenced by tree size and site conditions for all species, but hemlock and sugar maple growth rates were also affected by size- and distance-weighted indices of neighbor influence. Old-growth stands several centuries old continue to undergo compositional change related to both stand history and current population interactions. Yellow birch and basswood are probably maintained by significant disturbances and will decline under a disturbance regime of small gaps. Hemlock may be the ultimate competitive dominant in most sites but may require well over a mil- lennium without major disturbance to displace sugar maple.

Species composition of temperate forests vary with successional age (i.e., years after a major disturbance) and seems likely to change in response to significant global climate change. Because photosynthesis rates in co-occurring tree species can differ in their sensitivity to environmental conditions, these changes in species composition are likely to alter the carbon dynamics of temperate forests. To help improve our understanding of such atmosphere-biosphere interactions, we explored changes in leaf-level photosynthesis in a 60-70 yr old temperate mixed-deciduous forest in Petersham, Massachusetts (USA). Diurnally and seasonally varying environmental conditions differentially influenced in situ leaf-level photosynthesis rates in the canopies of four mature temperate deciduous tree species: red oak (Quercus rubra), red maple (Acer rubrum), white birch (Betulapapyrifera), and yellow birch (Betula alleghaniensis). We measured in situ photosynthesis at two heights within the canopies (top of the canopy at -20 m, and in the sub-canopy of the same individual trees at -14-16 m) through a diurnal time course on 7 d over two growing seasons. We simultaneously measured a suite of environmental conditions surrounding the leaf at the time of each measurement. We used path analysis to examine the influence of environmental factors on in situ photosynthesis in the tree canopies. Overall, red oak had the highest photosynthesis rates, followed by white birch, yellow birch, and red maple. There was little evidence for a substantial midday depression in photosynthesis. Instead, photosynthesis declined throughout the day, particularly after 1600. Diurnal patterns of light reaching canopy leaves, leaf and air temperature, and vapor pressure deficit (VPD) contributed to diurnally varying photosynthesis rates. Large differences in these parameters through the growing season partly led to the seasonal differences observed in photosynthesis rates. Path analyses helped to identify the relative contribution of various environmental factors on photosynthesis and further revealed that species-specific sensi- tivities to various environmental conditions shifted through the season. Red oak photo- synthesis was particularly sensitive to air temperatures late in the season when air tem- peratures were low. Further, red maple photosynthesis was particularly sensitive to high VPDs through the growing season. Incorporating data on the physiological differences among tree species into forest carbon models will greatly improve our ability to predict alterations to the forest carbon budgets under various environmental scenarios such as global climate change, or with differing species composition.

We studied how an enriched CO2 atmosphere, in a fully crossed design of light and nutrients, influenced 1 st-yr seedling growth in six New England deciduous forest tree species. The species, in the order of increasing shade tolerance, were gray birch (Betula populifolia), ash (Fraxinus americana L.), red maple (Acer rubrum L.), red oak (Quercus rubra L.), yellow birch (Betula alleghaniensis Britton), and striped maple (Acer pensylvan- icum). Elevated CO2 environments significantly stimulated the seedling growth of all six species. Generally this was more pronounced in low light. The greatest stimulation was found under the condition of low light and high nutrients. However, individual species responded differently to elevated CO2 levels. Among the three early-successional species, gray birch, ash, and red maple, a significant increase in seedling growth under elevated CO2 conditions was found only with high nutrients. The three late-successional species grown under elevated CO2 conditions (red oak, yellow birch, and striped maple) showed a greater percentage increase in seedling growth in low light than in high light. Thus, for the early-successional species, the degree of enhancement of seedling growth by elevated CO2 levels was more sensitive to nutrient levels, while in the late-successional species the enhancement was more sensitive to the level of light. Moreover, species with large seeds (e.g., red oak) exhibited a greater response to elevated CO2 levels under low light than species with small seeds (e.g., gray birch). The results emphasize the importance of plant species as well as other environmental resources in modifying the response of plants to elevated CO,. Considering the light and nutrient environment observed in forest gaps of various sizes, the results of the present experiment suggest seedling regeneration in New England deciduous forests may be altered in a future high CO2 environment.

Fully cold-acclimated dormant twigs from provenance collections of red oak (Quercus rubra L.), yellow birch (Betula lutea Michx. F.), black walnut (Juglans nigra L.), and wild black cherry (Prunus serotina Ehrh.) were collected in winter 1975. Stem sections from latest season's growth were evaluated for freezing of a deep supercooled fraction of their stem H20 which froze anomalously at their killing temperature. Results show that all trees within each provenance collection have low temperature freezing points for stem H20 between -38? and -470C. Generally no correla- tions were found in simple linear regression analyses comparing the low temperature freezing points with average annual minimum temperature or latitude for each geographic seed source. All trees throughout the natural ranges of the species investigated are capable of attaining a freezing resistance in the vicinity of -40'C. Additional analysis on red oak demonstrated a 25% decrease in the amount of deep supercooling H20 for northern versus southern samples.

Increasing the proportion of yellow birch (Betula alleghaniensis Britton) in the northern hardwood type should also increase the economic return from management. Under current market prices the stumpage value of yellow birch is about double that of sugar maple (Acer saccharum Marsh.), the next most valuable species in the type. The use of yellow birch for veneer accounts for most of its high value. In upper Michigan about 30% of the net volume of this species is sold as veneer compared to only 7% of the volume of sugar maple. The proportion of yellow birch stems in the old-growth northern hardwood stands is seldom over 12% (Lake States 1935). In this type it is most commonly found as single trees on the edge of small openings or occasionally in small groups where the more tolerant species have died out or been destroyed by a catastrophic type of disturbance. Yellow birch seldom occurs as a pure stand except on relatively small areas that have been opened and mineral soil exposed, such as by windthrow, light burns, or abandoned clearings. However, in the hemlock-yellow birch sub-type (Soc. Amer. Foresters 1954), which occurs on mesophytic sites, yellow birch commonly makes up 25% or more of the stand basal area. In secondgrowth stands the percentage is usually less, the amount seeming to vary with the soil moisture conditions and species association. Some regeneration studies have been made in the north central and northeastern portions of the botanical range of yellow birch, but very little work has been reported in the Lake States, which are in the western portion. Although the general silvical requirements of this species are fairly well known, particularly as the tree reaches the larger size classes, little information is available on the early stages of establishment and growth in the Upper Peninsula of Michigan. The reasons for the lack of sufficient yellow birch reproduction after cutting in other regions are generally considered to be the relative intolerance of the species (Baker 1949, Graham 1941), browsing by animals, and more specific seedbed requirements than its competitors. A study was begun in the Upper Peninsula of Michigan in the fall of 1952 to determine (1) the influence of seedbed conditions on the regeneration of yellow birch, and (2) the relative importance of physical and biotic factors on the establishment and early growth of yellow birch seedlings. In the area selected for study, all seedbearing trees except yellow birch and a few white pine and hemlock were cut during the winter of 1952-53, and the area was disked in the fall of 1953. This paper summarizes the changes that occurred during four growing seasons after disking and discusses results of special studies on the factors affecting the early growth of yellow birch.

Islands have long been recognized as having faunas with unique properties. Beginning in 1950 the Quetico-Superior Wilderness Research Center, by giving support and making available its facilities, made it possible for us to conduct investigations on the small mammals found on the islands in Basswood Lake, Lake County, Minnesota. This paper reports on three years' work in which we have attempted to ascertain the status of the natural populations on these islands. The study was set up to determine (1) whether or not the islands of Basswood Lake would show relatively complete isolation throughout the year with water in the summer and ice in the winter serving as effective barriers to ingress and egress and (2) to determine some of the characteristics of the small mammal populations on these islands. Basswood Lake is typical of the large lakes along the Ontario-Minnesota boundary. These lakes lie in rock-bound basins formed by the glaciers of the Pleistocene Epoch (Zumberge 1952). The upland is characterized by numerous low bedrock hills and knobs which are covered with a very thin mantle of glacial drift (Thiel 1947). Interspersed among these hills are numerous swamps and small lakes. The original dominant vegetation of this area was composed primarily of conifers. The characteristic trees of the upland forest were the red and white pines, white spruce, balsam fir and white birch while the swamps were filled with black spruce, tamarack, white cedar and black ash. Deciduous trees such as aspen, balsam poplar, red maple, pin cherry, yellow birch and mountain ash were found throughout the area, but except where there had been some disturbance, they formed only a small part of the vegetation (Rosendahl and Butters 1928). The present vegetation shows the effects of heavy logging, burning and reburning. The destruction of the original forest was followed by the rapid growth of aspen and white birch which, at the present time, form the dominant part of the flora. The islands, for the most part, were affected less by these destructive forces than the mainland.

Yellow birch seedlings were grown under heavy (86%) shade, moderate (72%) shade, and full sun. Shaded seedlings grew more in height and leaf area, but those in full sun accumulated more dry weight. Shaded seedlings were also more efficient photosynthetically near the end of the growing season than unshaded seedlings. Percentage dry weight was greater in leaves and stems of shaded seedlings and greater in roots of unshaded seedlings.

Previous studies (Kittredge, '34; Grant, '34; Daubenmire, '36) have indicated that over much of Wisconsin and southeastern Minnesota the regional climax is a type dominated by sugar maple, Acer saccharulm,2 and basswood, Tilia americana. Southeastward there is a transition to a type richer in species, in which beech, Fagnis grantdifolia, is especially prominent; northeastward to another type in which, in addition to beech, hemlock, Tsuga canadensis, and yellow birch, Betula ilntea, are added; northwestward to a spruce-fir climax; and southwestward to the oak forest which fringes the great plains grassland. The purpose of the present study was to add to the knowledge of the maple-basswood type by investigation in northwestern Wisconsin, a region where no work of this type had as yet been done. The prime objects were two: first, an intensive study by precise methods of stands as nearly virgin as could be found; second, measurement of significant habitat factors in an attempt to explain local relations between forest types and environment. The field work was done in the summer of 1935.

This investigation compared the mycofloral populations inhabiting the organic and mineralized soil horizons, and evaluated the effect of catastrophic vegetational disturbances on their species composition, in selected upland forests in northern Wisconsin. Eight forests, part of the conifer-hardwood complex, were included in the study: three of them served as virginal reference stands, four represented secondary successional communities occupying areas that experienced severe forest fires, and one was a yellow birch forest that became established on a clear-cut area. Sample populations, obtained by the dilution plate method, were isolated from each detectable horizon in each stand. In general, the highly organic layers, especially the litter and fermentation horizons, pos- sessed the greatest number of fungal propagules as well as the greatest species diversity. With increasing depth, both the density and diversity decreased rapidly. Although many of the species were present in more than one horizon, most of them exhibited maximum densities and fre- quencies in only one of them. Thus, the populations colonizing each horizon could be charac- terized by a somewhat specific combination of prevalent species. The relatively low similarity coefficients derived from comparisons between the populations in the horizons within a stand substantiated the view that there were distinct populations. Ordination of the coefficients suggested that the soil profile could not be visualized as an edaphic dine which elicited a soil microfungal continuum. Since most of the predominant species in any specific horizon differed from those residing in overlying horizons, the establishment of a characteristic mycoflora could not be attributed to differential survival of propagules that percolate from horizons above.

A 2—year study of basal area change of six tree species was conducted with vernier growth bands in the northern conifer—hardwood sub—formation in north—central Wisconsin. Curves of basal area change per unit of stem circumference satisfactorily expressed differences in initiation of stem expansion, rate and duration of growth, and winter shrinkage for various species and crown classes. Seasonal growth for all species and crown classes was represented by a sigmoid curve beginning with a short period of slow basal area increase in early spring and ending with a longer period of declining growth rates leading to relative stability through late summer and fall. Winter shrinkage, most marked in basswood, began in early winter and often exceeded total summer growth by midwinter. Recovery was complete by early spring. Hemlock began rapid growth earlier and ceased growth later than any other species studied. Basswood began and ceased growth later than sugar maple, white and yellow birch, and trembling aspen. Timi...