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One-year-old, cold-hardened, container-grown yellow birch (Betula alleghaniensis Britt.) seedlings were exposed to cold treatments after being pretreated with a simulated winter thaw. Freezing injury to roots and shoots was assessed by relative electrolyte leakage and triphenyltetrazolium chloride reduction. Growth characteristics were also determined after 60 days under greenhouse conditions. Relative electrolyte leakage and triphenyltetrazolium chloride reduction measurements showed that roots became increasingly damaged with decreasing cold-treatment temperatures. However, plants pretreated with thaws showed significantly lower stem increment, shoot length, and leaf area in response to the cold temperatures than did the unthawed plants. Variation in these growth parameters was also significantly correlated with both root and shoot freezing injury parameters. Cold hardiness under different thaw pretreatments was assessed using the highest freezing temperature that caused significant injury, referred to as the critical temperature. For seedlings without the thaw pretreatment, shoot and root critical temperatures were estimated as –52.5 and 23.8°C, respectively. Following 12 days of thaw, these temperatures increased to –24.08°C for shoots and –13°C for roots. Twelve days of thaw, or growing degree-day (>4°C) accumulations greater than 66 during a thaw, could sufficiently deharden roots and shoots such that they would be susceptible to freezing damage at ambient temperatures commonly encountered in the Canadian Maritimes. We also observed that root pressure declined significantly with increasing root freezing injury. Sufficient root pressure is required for springtime refilling of xylem embolisms caused by winter cavitation of the vessels in this species. Weak root pressure caused by freezing injury would represent a risk of shoot dieback and tree decline due to the remaining embolisms reducing water flow to the developing foliage. The rapid reduction of shoot cold hardiness may also indicate the threat of late-spring frosts to this species. These induced changes are especially important under climate change scenarios that suggest increases in winter temperatures and changes in seasonality in eastern Canada.Key words: climate change, cold hardiness, electrolyte leakage, growth, root pressure, TTC reduction.

Phenotypic plasticity enables tree saplings to change their morphology according to their environment to grow toward a better light micro-habitat. Therefore, processes of crown development could be expected to vary as a function of light. The objectives of this study were to (i) evaluate the effects of position and light availability on shoot growth within the crowns of understory saplings of sugar maple (Acer saccharum Marsh.) and yellow birch (Betula alleghaniensis Britton.); (ii) develop a new vigour index for shoots; and (iii) evaluate the possible factors relating to branch mortality in the crown of sugar maple saplings. The results revealed that there is a clear branch position effect on shoot growth in the crown for yellow birch saplings and that it is partly related to the presence of two types of shoots. Dead branches were located at the bottom of the crown of sugar maple saplings; they were smaller in size, had wider angles and had lower indexes of vigour than live branches found nearby. Preliminary results obtained on the vigour index indicate that it is a potentially useful tool for predicting the growth and vigour status of a branch.Key words: shoot growth, branch position, light availability, branch mortality, sugar maple, yellow birch.

The ontogeny and ultrastructure of ectomycorrhizae synthesized between Betula alleghaniensis (yellow birch) and Pisolithus tinctorius, a broad host range fungus, were studied to determine the structural modifications in both symbionts during ectomycorrhiza establishment. A number of stages, including initial contact of hyphae with the root surface, early mantle formation, and mature mantle formation, were distinguished. Interactions between hyphae and root hairs were frequent. As a paraepidermal Hartig net developed, root epidermal cells elongated in a radial direction, but wall ingrowths were not formed. Repeated branching of Hartig net hyphae resulted in extensive fine branches and the compartmentalization of hyphal cytoplasm. Nuclei and elongated mitochondria were frequently located in the narrow cytoplasmic compartments, and [Formula: see text] thickenings developed along walls of cortical cells in primary roots.

The objective of the study was to determine genetic differentiation of populations of yellow birch (Betula alleghaniensis Britton) along ecological gradients in Michigan and the Appalachian Mountains. Seeds were collected from populations in each of six physiographic regions of Michigan and in the northern and southern Appalachian Mountains. Seedlings were grown in a common garden in southeastern Michigan. First-year height of progeny, seed weight, initial germination, and germination percentage for 141 yellow birch trees in 30 populations were determined and compared.Significant differences were found among the six Michigan regions for all characters. Strong south–north clinal trends of decreasing height, increasing seed weight, earlier initial germination, and increasing total germination were revealed. Comparisons between physiographic regions showed that tall seedlings were produced by relatively light, late-germinating seeds. Within each region, however, seedlings from earlier germinating seeds tended to exhibit greater height growth. Significant differences were found among populations within a given region for specific characters. In the Appalachian Mountains, southern populations had taller progeny and lighter and poorer germinating seeds than northern populations.Regressions relating each character to 13 site variables were computed. Variation in total height and initial germination were interpreted as the result of differences in the length of the growing season associated with changes in elevation, terrain type, and aspect. Variation in seed weight was associated with differences in the length of growing season and soil moisture regimes.

Natural variation was studied in 47 morphological attributes of yellow birch and sweet birch collected from adult trees along five elevational transects in the Appalachian Mountains. Populations of one or both species were analyzed from 30 locales extending from southern North Carolina to northern Vermont and New Hampshire. The major objectives of the study were (1) to test for differences in foliage, fruits, bark, and pollen among species and among populations; (2) to determine if patterns of variation associated with latitude could be strengthened by elevational adjustments; and (3) to determine the degree of similarity in patterns of variation for the two species.The results indicated considerable within-population variation and significant differences among populations and species. However, few morphological characters showed consistent trends in size, shape, or pubescence with changes in elevation and latitude. Where relationships were consistent, they were not particularly strong as indicated by linear correlation coefficients (few exceed 0.70). These findings are in contrast to earlier studies demonstrating a strong relationship of growth periodicity to elevation and latitude of seedling populations grown in a uniform garden.Preliminary evidence suggests that expression of morphological variation may be greater in the less extreme portions of the species latitudinal and elevational distributions.

The objective of the study was to elucidate the patterns of phenology of growth initiation and cessation among diverse sources of yellow birch (Betula alleghaniensis Britton) and sweet birch (B. lenta L.) along latitudinal and elevational gradients in the Appalachian Mountains. Fruit was collected from parent trees of both species, encompassing a range of 9° of latitude and 3000 ft (914 m) of elevation, and was sown in the greenhouse. The resulting seedling populations were grown in a uniform garden located in southeastern Michigan, where they were analyzed for differences in leaf flushing and growth cessation associated with latitude and elevation of the seed source. Under the conditions of the experiment, northern populations flushed earlier than southern populations. The absence of differences in leaf flushing among populations from different elevations suggests that environmental factors in addition to temperature regulate the initiation of growth. Populations of high latitudes and high elevations ceased growth earlier than populations from low latitudes and low elevations, indicating that populations from shorter growing seasons adapted by ceasing growth earlier. Sixty-seven percent of the variation in the phenology of shoot growth among seedling populations of both species was associated with latitude and elevation of the seed source; the rest was attributed to local variations in topography and resulting microclimates.Observations of parent trees in situ and of half-sib seedling progeny in the uniform garden revealed that individuals of yellow birch exhibit an earlier phenology than individuals of sweet birch from the same field sites. This appears to be an important feature of niche differentiation and a function of the adaptation of yellow birch to colder climates.

Analysis of leaves from several crown positions of a single yellow birch (Betula alleghaniensis Britton) indicated that particular short-shoot leaves from the middle and lower inside crown were more uniform than those from other crown positions. The short-shoot leaves typically occur in pairs. Each pair consists of two distinctly different leaves, termed here the A and B leaves. The A leaf is consistently larger, with more veins and teeth and a more inequilateral base than the B leaf. Because of their relative uniformity, lower inside crown A leaves would be useful as "standard" leaves for among-tree and among-population comparisons. Late leaves, borne on long shoots in exposed portions of the upper crown, were smaller than the short-shoot leaves in all dimensions. Principal components and canonical variates of the short-shoot leaves from the lower and middle inside crown exhibited the most compact and least variable groupings of all of the leaf types. The first canonical variate separated the leaves of the lower and middle crown from those of the upper crown. The second canonical variate separated A and B leaves. Observations of emerging leaves indicated no systematic differences in position of the A and B leaf.

A yellow birch stand was divided into five age classes (1–5, 6–10, 11–20, 21–40, and >40 years old) to evaluate variations in spectral properties of leaves during the growth of yellow birch. Shade leaves of 1 to 5 year-old seedlings absorb significantly less, while they reflect and transmit significantly more than shade leaves of the other age classes in the 390–725 nm wavelength range. Absorptance differences are more striking in the green and the yellow between 501 and 590 nm (0.067–0.091) than in the orange and the red between 591 and 700 nm (0.041–0.054) and the violet and the blue between 401 and 500 nm (0.017–0.020).

A new family Tripterosporaceae is introduced by the description of three species of a new genus, Tripterospora, similar in several characteristics to Podospora (Sordaria) but clearly separable by the production of globose, non-ostiolate ascocarps and of ascospores which lack gelatinous secondary appendages and sheaths. In T. longicaudata Cain sp. nov., the type of the genus, and in T. brevicaudata Cain sp. nov., early development of the ascocarp is seen to be from a coiled and twisted ascogonium as in many members of the Ascohymeniales, with the ascogonia scattered on the aerial mycelium. Ascospores in all three species are two-celled, the upper cell dark and ellipsoid with a circular germ pore at the apex, the lower cell hyaline. Descriptions and illustrations are given for the known species: T. longicaudata, isolated in pure culture from dung and from swiss chard plants in Ontario; T. brevicaudata, also observed only in pure culture, obtained from a living branch of yellow birch in Connecticut, and from tomato seed in Ontario; and the third, described by Griffiths as Pleurage erostrata, collected on dung in Ontario and Manitoba.

Cylindrosporium sp., isolated from dead yellow birch roots, inhibited the growth of another fungus isolated from mycorrhiza and dead roots. Growth rate of the former increased while that of the latter decreased with increased temperature above the optimum for rootlet, development. Twenty-four species of fungi were isolated from mycorrhiza. Seedlings grown aseptically in soil and in agar were inoculated with fungi isolated from dead and dying rootlets and from mycorrhiza, but none of the organisms displayed sufficient virulence to cause birch dieback. The optimum temperature for development of potted seedlings was about 18.5 °C. Increases or decreases of 2 °C. or more from the optimum for yellow birch development resulted in increased rootlet mortality, decreased frequency of mycorrhiza, and a thinner mantle of hyphae in mycorrhiza, followed by reduction in foliage vigor. Normal rootlet mortality of 6% in a 55-year-old yellow birch stand was increased to 19 and 60% by raising soil temperature 1° and 2 °C, respectively, above the normal during one summer. Soil moisture was not lowered a statistically significant amount by a 5 °C. increase until the sixth day following rain. Mycorrhiza existed on residual living roots in about the same proportion as on undisturbed root systems. The possibility that birch dieback may be the result of soil temperature increases is discussed. It is suggested that cutting practices in hardwood stands should remove all yellow birch trees or prevent increased temperatures in soil occupied by residual birch.

Well-marked differences, involving both the patterns of moisture movement and storage, have been found to separate the water relationships of yellow birch, Betula lutea Michx., in various stages of deterioration. The cumulative results of injection studies, root excavations, and an extended survey of the trends in moisture distribution in the species over a prolonged period, suggest that the locus of action of the disease is, in the first instance, in the roots, and that excessive rootlet mortalities in apparently healthy trees constitute the initial indication of a diseased condition in the species.

Disease symptoms found in nature on yellow birch (Betula alleghaniensis Britt.) infected by Diaporthe alleghaniensis R. H. Arnold, were induced by inoculation of seedlings and saplings with mycelium or conidia. On vigorously growing yellow birch plants, cankers, dead shoots, blackened necrotic petioles and mid-veins of leaves, and leaf spot developed during the inoculation year, and dieback occurred the next spring. Spore tendrils of the Phomopsis state of the pathogen were found on the most recently killed parts of the plants from May until early July. Initial symptoms were most severe on young tissues, and inoculation of shoots caused more damage to seedlings than inoculation of older tissues. The pathogen persisted in the host for several years without symptom expression, or in healed-over cankers. Initial symptoms were more severe on unshaded than on shaded seedlings, but shading increased the ultimate severity of the disease. Soil temperature and soil moisture did not influence artificial infection and subsequent development of the disease. There was evidence that the fungus produces a wilt-inducing agent. The disease was not found in nature on white birch (Betula papyrifera Marsh.), but seedlings were infected artificially. The probable course and importance of natural infection of yellow birch is discussed.

In 1967 yellow birch, Betula alleghaniensis Britt., and white birch, B. papyrifera Marsh., developed extremely large seed crops in Ontario. Foliage was dwarfed or missing in the heavily seeded portions of tree crowns. Buds did not develop on the terminal portions of most branches, and in 1968 branches died back to the point where buds were available for growth. Terminal growth and diameter growth were reduced for both species in 1967, and terminal growth by yellow birch continued at a reduced rate in 1968. Terminal growth and bud production were inversely related to the amount of fruiting. Similar conditions prevailed on some yellow birch in 1970.Yellow birch was more seriously affected, and in most mature stands dieback averaged 20 to 50 cm. White birch was not affected to this extent; however, some trees in most mature stands suffered extensive dieback.

Diaporthe alleghaniensis R. Horner Arnold, sp. nov., is described and illustrated in both the ascigerous and conidial (Phomopsis) states, and the cultural characters are given. This is the first species of Diaporthe described on the host Betula alleghaniensis Britt. It is distinguished morphologically from known species of Diaporthe by the narrow cylindrical ascus with truncate apex and by the narrow cylindrical-ellipsoid ascospores with variable position of the single septum. It is a facultative parasite of yellow birch (B. alleghaniensis) on which it causes an annual bark canker and foliage disease. The symptoms of the disease are described and illustrated.

Movement of rubidium86 and calcium45 injected into the trunks of yellow birch and white pine was followed with a newly-developed portable scintillation counter. Maximum rate of upward movement of the rubidium86 in the xylem of yellow birch approximates one foot per minute along a narrow channel spiralling upward (usually dextrally) from the point where the isotope was first introduced. Movement in decadent yellow birch was very slow with an apparent increase of permeability of the bark tissue as indicated by lateral diffusion of the isotope. In October no upward movement was discerned in healthy trees but rather an active downward translocation in the phloem.

Ascospore discharge and conidium release of Nectria galligena Bres. from cankers on yellow birch (Betula alleghaniensis Britt.) were investigated under field conditions and were related to prevailing rainfall, relative humidity, and temperature. Release of conidia was associated with splashing rain whereas ascospores were discharged during or after rain. Conidia were trapped only from May through August during the period of active growth of the host, and showed a peak in May and June. In contrast, ascospores were trapped on rainy days throughout the year, including mid-winter when temperatures were around the freezing point. Maximum ascospore discharge occurred in August and September. In the laboratory, ascospores were discharged as wetted perithecia began to dry out. Both relative humidity and temperature affected the rate of perithecial drying and thus the rate of release and duration of discharge of ascospores. The results are discussed with respect to environmental conditions that prevail in eastern Canada during winter.

In plate culture, Cryptosporiopsis sp. inhibited growth of 31 basidiomycetes isolated from decay in coniferous and deciduous trees; an ascomycete, the Dutch elm disease fungus; and a phycomycete, the potato late blight fungus. In liquid malt extract medium, Cryptosporiopsis sp. produced a substance highly inhibitory to Fomes fomentarius (L. ex Fr.) Kickx, the fungus most commonly associated with decay in living branches of yellow birch, Betula alleghaniensis Britt. Growth of F. fomentarius was also inhibited markedly by the presence of Cryptosporiopsis sp. in sterile yellow birch wood. In unsterile, peeled logs of balsam fir, Abies balsamea (L.) Mill., the amount of decay was significantly reduced in those treated with an application of a water suspension of mycelial fragments of Cryptosporiopsis sp. In unsterile, unpeeled logs there was also less decay in those treated with the mycelial suspension of Cryptosporiopsis sp.; however, the difference between the treated and untreated logs was not significant.

A study of the surface microflora of mycorrhizal and non-mycorrhizal roots of yellow birch seedlings has revealed distinct quantitative and qualitative differences. Higher bacterial counts and distinctly greater numbers of actinomycetes and of methylene-blue-reducing, sugar-fermenting, ammonifying, and fluorescent-pigment-producing bacteria were found on the former. The percentage incidence of bacteria growing optimally in a simple mineral–glucose medium was greater on normal roots whereas bacteria requiring complex nutritional factors appeared to be relatively more numerous on the mycorrhizal surface. Species of Pythium, Fusarium, and Cylindrocarpon predominated on, and Mycelium radicis (?) was absent from, normal roots, whereas, on mycorrhizal roots, Penicillium and other rapidly growing fungi as well as Mycelium radicis (?) were numerous and Pythium and Fusarium species absent. These results are discussed in relation to the nutrition of mycorrhizal and non-mycorrhizal roots.

Rates of apparent photosynthesis and dark respiration of 4-year-old yellow birch (Betula alleghaniensis Britt.) seedlings, grown in full light and shade (13% of full light), were measured with an infrared gas analyzer. Measurements were made periodically throughout the growing season, using either attached branches or entire seedlings. Effects of light intensities from 0 to 4500 ft-c on photosynthetic rates were studied, and comparisons made between young and old leaves and between photosynthetic rates in normal (300 p.p.m.) and saturating (1245 p.p.m.) CO2 concentration.The photosynthetic apparatus of yellow birch was found to adapt poorly to shaded conditions. In saturating light, the rate of apparent photosynthesis of young leaves of shade-grown seedlings was only half that of sun-grown seedlings; for old leaves the reduction was even greater. As a result, shade-grown seedlings had a lower photosynthetic capacity in saturating light despite their larger leaf area. In low light intensities, leaves of sun- and shade-grown seedlings had nearly the same rates of apparent photosynthesis. Rates of respiration of shade-grown seedlings were one-half those of sun-grown seedlings.When seedlings were exposed to light intensities comparable to those in which they were grown, their photosynthetic rates correlated with their dry matter production.When the CO2 concentration was raised to 1245 p.p.m., photosynthetic rates of leaves of sun- and shade-grown seedlings increased by the same relative amount. It is concluded that the poor adaptation of yellow birch to shade results from a reduction in content of carboxylating enzymes rather than changes in chlorophyll content or resistance to CO2 diffusion. Adaptations of yellow birch are contrasted with those of sugar maple (Acer saccharum Marsh.).

The stem tissues of yellow birch (Betula alleghaniensis Britton) saplings, with wavy bands of stained xylem parallel to the annual rings and depressions in the xylem at the xylem–phloem interface (stem pitting), were studied microscopically. The bands of stained xylem consisted of abnormally formed parenchyma (parenchymatous wood) interspersed with collapsed cells. Rays in the affected areas showed increases in both cell numbers and cell size, often being indistinguishable from adjacent parenchymatous wood. Aggregate rays were associated with stained bands as well as with stem pitting in the xylem and corresponding protrusions of the phloem.

Trichocladium canadense n. sp. is described from 20 Canadian isolations made from wood of sugar maple, yellow birch, beech, trembling aspen, and western hemlock.