Fraxinus Nigra Research Articles

Gradient analysis of Larix laricina dominated wetlands in Canada's southeastern boreal forest

With the objective of understanding how vegetation was structured in four Larix laricina (Du Roi) K. Koch dominated wetlands in north-western Quebec, 186 point-centred quarters were sampled in four stands. For each point, both biotic and abiotic variables were collected and species cover was recorded. Divisive hierarchical classification analysis (Twinspan) identified nine vegetation clusters: i) Larix laricina & Spiraea alba, ii) Larix laricina & Kalmia angustifolia, iii) Larix laricina, Picea mariana & Alnus rugosa, iv) Larix laricina & Betula pumila, v) Thuja occidentalis & Trientalis borealis, vi) Abies balsamea & Betula papyrifera, vii) Fraxinus nigra & Onoclea sensibilis, viii) Alnus rugosa, and ix) Eleocharis smallii. Results of the canonical correspondence analyses indicated that the distribution of these clusters was mainly related to (i) distance from shore, (ii) shade (canopy cover), (iii) substrate nitrate concentration (in relation to the abundance of Kalmia angustifolia and Alnus rugosa), (iv) substrate pH (in relation to the abundance of Sphagnum spp.), and (v) substrate conductivity. Several characteristics of the water table also affected species distribution, including pH, depth, and carbon concentration. Further studies should address the effect of the presence of Kalmia angustifolia and Alnus rugosa on larch growth.Key words: larch, wetland, vegetation analysis, flooding, boreal forest.

Effect of Basement Sump Pump Effluent on the Growth and Physiology of Urban Black Ash and Green Ash Ornamental Trees

The effect of basement sump pump effluent discharge in proximity to boulevards and ornamental trees was studied at several sites near Edmonton, Alberta, Canada throughout the summer of 1996. The growth, leaf petiole water potentials, and gas exchange of black ash (Fraxinus nigra) and green ash (F. pennsylvanica) trees were measured at sites with and without nearby sump pump effluent discharge. Black ash trees had higher mortality, altered water relations, and significantly lower caliper increase at the site with sump pump effluent discharge compared to trees at the site without effluent discharge. Green ash trees situated away from sump pump effluent discharge had significantly greater caliper increase than trees situated near effluent discharge. Furthermore, salt injury symptoms were observed on both species of trees located at sites with nearby effluent discharge. Our results demonstrate the importance of monitoring sump pump effluent discharge and its effects on boulevard ornamental trees in areas where soils are poorly drained or contain high levels of salts. It is recommended that basement sump pump effluent discharge hoses should be positioned away from boulevards and ornamental trees.

Gradient analysis of <i>Lari× laricina</i> dominated wetlands in Canada's southeastern boreal forest

With the objective of understanding how vegetation was structured in four Larix laricina (Du Roi) K. Koch dominated wetlands in north-western Quebec, 186 point-centred quarters were sampled in four stands. For each point, both biotic and abiotic variables were collected and species cover was recorded. Divisive hierarchical classification analysis (Twinspan) identified nine vegetation clusters: i) Larix laricina & Spiraea alba, ii) Larix laricina & Kalmia angustifolia, iii) Larix laricina, Picea mariana & Alnus rugosa, iv) Larix laricina & Betula pumila, v) Thuja occidentalis & Trientalis borealis, vi) Abies balsamea & Betula papyrifera, vii) Fraxinus nigra & Onoclea sensibilis, viii) Alnus rugosa, and ix) Eleocharis smallii. Results of the canonical correspondence analyses indicated that the dis - tribution of these clusters was mainly related to ( i) distance from shore, (ii) shade (canopy cover), (iii) substrate nitrate concentration (in relation to the abundance of Kalmia angustifolia and Alnus rugosa), (iv) substrate pH (in relation to the abundance of Sphagnum spp.), and (v) substrate conductivity. Several characteristics of the water table also affected species distribution, including pH, depth, and carbon concentration. Further studies should address the effect of the presence of Kalmia angustifolia and Alnus rugosa on larch growth.

Habitat and Variability of Humulus lupulus var. lupuloides in Upper Midwestern North America: A Critical Source of American Hop Germplasm

traits, and survival status of this taxonomic variety are the subjects of this study. Native Humulus populations were typically associated with only a few tree and shrub species, notably Acer negundo L. [box elder], Crategus spp. [hawthorn], Fraxinus nigra Marsh. [black ash], F. pennsylvanica Marsh. [green ash], Populus balsamifora L. [balsam poplar], P. deltoides Marsh. [cottonwood], Prunus americana Marsh. [wild plum], P. pensylvanica L. [pin cherry], P. virginiana L. [choke cherry], Quercus macrocarpa Michx. [bur oak], Ribes spp. [wild currant], Rosa spp. [wild rose], Salix spp. [willow], Sambucus canadensis L. [elder], Symphoricarpos occidentalis Hook. [snowberry], and Viburnum opulus var. americanum Ait. [highbush cranberry]. Cone (strobilus) variations, exceeding those of leaves and vines, included size (15 mm to 45 mm long), shape (globose to ovoid-conical), and compactness (loose vs. imbricated bracts). Trait diversity of seedling progenies exceeded that of each native population from which they originated. Traits of genetically potential usefulness included dwarf plant habit, precocious cone production, early season flowering, pest repellence, frost resistance, potential drought resistance, and commercially desirable cone structure. Both native-plant and progeny populations were generally free of diseases common to commercial hops, thus offering germplasm that is compatible with institutional hop breeding programs. Persistence of native hop populations from 1989 to 1999 was problematic, with five of 11 selected study sites sustaining complete loss or serious damage. Protection of sensitive riparian habitats occupied by this genetic resource may be warranted, particularly until adequate germplasm sources are secured and reposited for further investigation and use.

POPULATION DYNAMICS OFFRAXINUS NIGRAIN RESPONSE TO FLOOD-LEVEL VARIATIONS, IN NORTHWESTERN QUEBEC

Population dynamics of black ash (Fraxinus nigra) were investigated in five stands with different exposures to spring flooding at the southwestern limit of Québec's boreal forest. Fifty-four 100-m2 plots were sampled along 25 transects laid out perpendicular to Lake Duparquet. In each plot, all black ash >5 cm in diameter at breast height (dbh) were aged using dendrochronological methods. An age–height regression was used to calculate the age of those individuals <5 cm in dbh. Stump sprouts had a significantly faster height and diameter growth rate than individuals established from sexual origin. Two stands in this study showed deficits in sexual recruitment. One stand, located on a deep organic layer, also showed recent colonization by F. nigra that may have started during the 1930s. This stand had the highest stem density, and sprouting was restricted to the younger age classes. Ordination analysis of dispersion indices characterizing the age distribution of F. nigra indicated a definite pattern toward higher sexual recruitment in plots and stands that were less exposed to flooding. In contrast, poor sexual recruitment was observed on more exposed sites. However, this situation was compensated for by abundant vegetative recruitment. Analysis of the periods of growth release and suppression of 153 trees revealed that F. nigra population dynamics are not regulated by major disturbance events. A general upward trend in radial growth and F. nigra expansion toward higher elevation sites observed since the end of the 19th century may be due to changes in Lake Duparquet's hydrological regime. Increases in the severity of flooding events may result in the decrease in seedling abundance observed in the more exposed stands. F. nigra populations were found to be resistant to long-term natural water fluctuations due to their ability to regenerate both by seeds and by sprouts.

Population Dynamics of Fraxinus nigra in Response to Flood-Level Variations, in Northwestern Quebec

Population Dynamics of Fraxinus nigra in Response to Flood-Level Variations, in Northwestern Quebec

Variations in Periodicities of the Ring Width of Black Ash (Fraxinus nigra Marsh.) in Relation to Flooding and Ecological Site Factors at Lake Duparquet in Northwestern Québec

Variations in periodicities of the radial growth response of black ash (Fraxinus nigra Marsh.) exposed to yearly spring flooding were studied in relation to hydrological fluctuations and site ecological factors at Lake Duparquet in northwestern Québec. Eight mean standardized 1880-1988 ring-width chronologies were constructed from trees growing on the floodplain, for five specific stand geomorphological landforms and three classes of elevation from the lake level. These dendrochronological series were submitted to spectral analysis based on the multi-frequential periodogram statistic. Monthly mean water discharge records of the Harricana River, and monthly mean temperature and total precipitation series collected at the Iroquois Falls weather station, all over the 1915-1990 period, were analyzed similarly. About 3.5-, 3.75-, and 7.5-year periodicities were detected in all the dendrochronological series; the 3.75- and 7.5-year components are harmonics of a 15-year periodicity that a majority of the series presented. All the ring-width chronologies, with the exceptions of the high elevation class and the stand near a bog, showed a strong biennial periodic component. A predominant 6.25-year periodicity was detected in the water discharge of the Harricana River and, to a lesser extent, in the ring-width chronologies of mid and high elevations. After an about 11-year periodicity was detected in several tree-ring and climatic series, peaks in the corresponding sine waves fitted to the tree-ring series were found to correspond to maxima in sunspot activity. Effects of geomorphological landform and elevation from the lake on the fluctuations from year to year of the radial growth of black ash were assessed by a two-way analysis of variance of the finite Fourier transform of ring-width chronologies from 46 sites, using landform and elevation as factors and sites as replicates. Significant landform effects were observed at short to longer periodicities, while an elevation environmental gradient was finely delimited. The low to high concordance levels observed in the periodicities of tree-ring series from different stands were related to ecological factors.

Comparative dendroclimatological analysis of two black ash and two white cedar populations from contrasting sites in the Lake Duparquet region, northwestern Quebec

The relationship between radial growth and climate was analyzed in two black ash (Fraxinus nigra Marsh.) and two white cedar populations (Thuja occidentalis L.) growing in contrasting sites in the Abitibi region of Quebec. An indexed mean chronology of radial growth was developed in each case. Black ash from flooded sites did not cross-date with those from unflooded sites and responded differently to climate. On the floodplain sites, black ash radial growth is directly correlated with the previous yearis August precipitation (i n 1) and with the current yearis June precipitation (i). High water levels at the beginning of the growing season also had a negative impact on the following yearis growth, whereas a high drought index during June of the preceding year (i n 1) had a positive one. Radial growth of unflooded black ash is mainly related to temperature. For those black ash not exposed to flooding, the preceding yearis August temperature (i n 1), as opposed to August precipitation, had a negative impact on the current yearis growth. A high drought index in June (i) also had a negative impact on the current yearis growth. Compared with black ash, white cedar from both xeric and mesic sites showed good between-site cross dating and had similar relationships to climate. In both cases, abundant summer precipitation, associated with cool temperature, produced maximum growth. Temperature during August of the preceding year (i n 1) was also negatively correlated with radial growth. White cedar from xeric sites also responded more intensely to drought, as revealed by the negative relationship to the JunenJuly (i) drought index. In conclusion, growth-ring analyses show the specificity of the climatic response of these two species and the filtering effect caused by different environments. Resume : Lieffet du climat sur la croissance radiale de deux populations de frŒne noir (Fraxinus nigra Marsh.) et de deux populations de cdre blanc ( Thuja occidentalis L.) a OtO OtudiOe dans des sites aux caractOristiques Ocologiques distinctes situOs dans la rOgion de liAbitibi au QuObec. Une chronologie moyenne indicOe de liaccroissement radial a OtO dOveloppOe pour chacune des situations. Les frŒnes noirs sur les sites inondOs niinterdatent pas avec ceux des sites non inondOs et montrent des rOponses climatiques diffOrentes. En plaine de dObordement, la croissance radiale du frŒne noir est positivement corrOlOe aux prOcipitations du mois diaost de liannOe prOcOdente (i n 1) et du mois de juin de liannOe courante (i). En dObut de saison de croissance, les crues ont aussi un impact nOgatif sur liaccroissement de liannOe suivante. Les conditions de

Sexual Regeneration of Black Ash (Fraxinus nigra Marsh.) in a Boreal Floodplain

-In northwestern Qu6bec, black ash (Fraxinus nigra Marsh.) is found mostly in floodplains bordering lakes and rivers. In this habitat, population dynamics are largely controlled by spring water level, and sexual regeneration is more abundant in sites less exposed to flooding. The hypothesis tested in this study is that sexual regeneration of black ash in sites slightly exposed to flooding is influenced by fluctuations of spring flood water level. The age structure of two sapling populations (<5 cm DBH) was analyzed using models assuming a constant (exponential function) and decreasing mortality (power function) with age. Both models were useful in describing the age structure of the saplings. The constant mortality model was selected and analysis of the residuals showed that the populations responded in different ways to climate during the 1914-1989 period. While regeneration is correlated with summer and annual precipitation in population A, it is correlated with winter precipitation in population B. Abundant sexual regeneration in both black ash stands suggests that moisture conditions are sufficient to assure constant sexual regeneration, which is, however, diminished during dry years.

Radial growth of Fraxinus nigra in a Canadian boreal floodplain in response to climatic and hydrological fluctuations

Abstract. Stands of Fraxinus nigra (black ash) near Lake Duparquet (Abitibi region, NW Québec) are affected each year by spring or early summer flooding. The relationship between environmental factors and radial growth was studied in 50 100‐m2 quadrats laid out in five Fraxinus‐dominated stands. Response function coefficients showed that the weather in the year before growth, i.e. in the time of bud formation, had a strong influence on radial increment. Temperatures in April of the year before (year i‐1) and May (i‐ 1) were positively correlated with growth, while precipitation in April (i‐1), May (i‐1) and June (i‐1) were negatively correlated. Climatic factors positively associated with growth during the year of bud expansion were April (i) temperature and June (i) precipitation. Redundancy analysis showed that radial growth in Fraxinus nigra responded to variation in elevation and geomorphological landform. These differences in stand location and elevation were also related to different responses to climate. The sites most exposed to flooding responded much more to the negative impact of spring precipitation, while the more elevated sites were more responsive to summer precipitation. This study showed that black ash could be used for long term reconstruction of climatic and hydrological fluctuations.

Analyse écologique des peuplements de frêne noir (Fraxinus nigra) des rives du lac Duparquet, nord-ouest du Québec

Spring and early summer flood is one of the main factors affecting the dynamics of black ash (Fraxinus nigra Marsh.) stands growing on lake floodplains in the boreal forest. The effect of flooding on the vegetation was studied in five stands on the shore of Lake Duparquet in Abitibi, northwestern Quebec. Divisive hierarchical classification analysis (Twinspan) revealed the existence of four different vegetation types: (i) black ash – speckled alder (Alnus rugosa) – bog willow (Salix pedicellaris), (ii) black ash – balsam poplar (Populus balsamifera) – ostrich fern (Matteuccia struthiopteris), (iii) black ash – pussy willow (Salix discolor) – sensitive fern (Onoclea sensibilis), and (iv) black ash – speckled alder – sensitive fern. Detrended correspondance analysis (Decorana) shows that elevation and drainage are the main factors affecting plant distribution and dynamics. Geomorphology also plays a major role in the way each stand responds to flooding. For each of the vegetation types studied, black ash shows a particular regeneration pattern and sexual regeneration tends to become less frequent with increasing exposure to flooding. Finally, the strong sexual regeneration and the youth of the populations found in the most elevated sites could be related to a possible alteration of the flood regime. Key words: Fraxinus nigra Marsh., flooding, boreal forest, floodplain, ecological gradiant, regeneration.

Presettlement Forests of the Phelps and Gorham Purchase in Western New York

SEISCHAB, F. K. (Dept. of Biol., Rochester Institute of Technology, Rochester, NY 14623). Presettlement forests of the Phelps and Gorham Purchase in western New York. Bull. Torrey Bot. Club 117: 27-38. 1990.-Forests of the Phelps and Gorham Purchase in western New York were of two major types. Beech/Maple Forest, primarily on the Till Plains of the Central Lowlands Province, averaged 32% beech (Fagus grandifolia), 18% sugar maple (Acer saccharum), 12% basswood (Tilia americana), and 11% white oak (Quercus alba). The Allegheny Plateau portion of the tract supported Hemlock/White Pine/Northern Hardwood Forest averaging 19% beech, 12% sugar maple, 11% hemlock (Tsuga canadensis), 11% white pine (Pinus strobus), 10% white oak, and 9% red and black oak (Q. rubra and Q. velutina). Secondary community types of the Allegheny Plateau included beech/maple/white pine/ hemlock, oak, oak/hickory (Carya), and pitch pine (Pinus rigida). Those on the Till Plains were principally beech/maple/hemlock/basswood and silver maple (Acer saccharinum)/black ash (Fraxinus nigra)/elm (Ulmus).

Leaf development and morphology in ash: influence of gamma radiation

Under the stress of long-term exposure to gamma radiation at dose rates ranging from 1.83 to 62.48 mGy/h, planted saplings of black ash (Fraxinus nigra Marsh.) responded in a variety of ways. These were compared with naturally growing black ash trees and saplings and with green ash (F. pennsylvanica Marsh.). With increasing dose, development time shortened, the number of leaflets decreased, and phyllotaxy changed from opposite to helical. The LD50 (lethal dose to 50% of exposed plants) (acute, seed germination) was 98 for F. nigra and 174 Gy for F. pennsylvanica. In black ash, the long-term LR50 (lethal dose rate to 50% of exposed plants, in milligrays per hour) has leveled off at approximately 14 mGy/h, while the accumulative LD50 (total accumulated lethal dose to 50% of exposed plants, in grays) continued to increase with additional irradiation, and after 11 years of irradiation was over 900 Gy. Plantation black ash is surviving, and even thriving, at a dose rate of 15.6 mGy/h, which may be a stable survival dose rate. Leaves in the two species are similar, with more leaflets per leaf on later developed nodes. Leaf size increased with total accumulated dose. Green ash is surviving at the highest dose rate at which it has been found (5.93 mGy/h). The frequency of morphological changes, most of which are teratological (e.g., apparent fused leaves, alternate or missing leaflets, chlorophyll mottling and sectoring, abnormal venation, irregular leaves), increased with radiation dose. In locations with severe winters, stresses during the winter dormant period are very important to survival. It is proposed that some of the features that enable ash to survive in a "harsh" environment may help it to tolerate the stress of gamma irradiation better than other species.

Tree dynamics in an old-growth, deciduous forest

In 1926, all trees (⩾ 10.2 cm dbh) were measured, tagged and mapped in a 20.6 ha, old-growth oak forest within the extensively farmed Tipton Till Plain of Indiana. All trees (⩾ 10.0 cm dbh) within the central 8.5 ha of this forest were measured, tagged and mapped again in 1976. Stand density and basal area increased by 93.9 and 30.8%, respectively, to 320 stems ha −1 and 31.0 m 2 ha −1. Density of Ulmus americana and Acer saccharum increased most; the largest density decreases were of Quercus rubra and Fraxinus americana. Basal area increases were greatest for Q. rubra, A. saccharum, and Q. alba. The most important species in 1926 were (in order of decreasing importance value, IV) [IV = (relative density + relative basal area)/2] Q. rubra, F. americana, Q. alba, Q. macrocarpa and U. americana. In 1976, Q. rubra, U. americana, A. saccharum, Q. alba and F. americana were the most important. Nearly half (46.9%) of those trees measured in 1926 had died by 1976; however, mortality varied by species, size-class and size-class within a species. Species with low mortality (⩽ 25%) included A. saccharum, Aesculus glabra, Carya spp. (except C. cordiformis), Celtis occidentalis and Quercus spp. (except Q. rubra). Species with high mortality (⩾ 75%) included Fagus grandifolia, Ulmus americana, U. rubra, and Fraxinus nigra. The majority of ingrowth trees within a 5 m radius gap of dead dominant or codominant trees were U. americana (30% of total), followed by A. saccharum (20%). No species had greater than 50% of its ingrowth within a 5 m radius of the dead trees. Diameter growth of surviving trees varied greatly among species, size-class and size-class within a species. Q. rubra and F. americana had greatest average diameter increases after 50 years (21.8 and 18.4 cm dbh, respectively). Mortality was relatively low and diameter growth high in the 50.0–69.9 cm diameter class for all species combined. The rotated-sigmoid curve, rather than the negative exponential, appears to best describe the size-class distributions of all species in 1976. An analysis of the size-class distribution of all species suggests that early and mid-seral species such as Gleditsia triacanthos, Juglans nigra, and Quercus spp. are gradually being replaced by more tolerant, late seral and climax species such as Acer saccharum, Aesculus glabra, Carya ovata and others. Despite the old-growth appearance of this forest much structural and compositional changes have been taking place.

Biomass Equations for Six Commercial Tree Species in Quebec

Six commercial species were sampled throughout Quebec and prediction equations of ovendry masses for the total above-ground tree and its components white cedar (Thuya occidentalis L.) and eastern hemlock(Tsuga canadensis (L.) Carr.). The deciduous species are: red maple (Acer rubrum L.), white ash (Fraxinus americana L.), black ash (Fraxinus nigra Marsh.), and beech (Fagus grandifolia Ehrh.). The components expressed in ovendry masses are: the total tree, the stem, the merchantable stem, the wood and bark of the merchantable stem, and the crown. A nonlinear model is used with the diameter at breast height and the total height as predictors. Key words: Biomass, prediction equations, eastern white cedar, eastern hemlock, red maple white ash, black ash, beech.

Consumption of Leaf Litter by Lumbricus terrestris (Oligochaeta) on a Michigan Woodland Floodplain

The consumption rate of leaf litter by Lumbricus terrestris (Oligochaeta) was studied from April through May 1981, on a Michigan woodland floodplain. Feeding chambers containing earthworms and leaf litter, which excluded soil microfauna, were placed on the floodplain. After 4 weeks, earthworms consumed leaves equivalent in amount to 93.87o of the total annual leaf fall. The mean consumption rate was 11.0 mg dry weight leaves g-1 live weight earthworms d-1 for a 4-week period with a maximum rate of 14.3 mg. The consumption rate of leaf litter by L. terrestris reported herein was similar to rates reported in other studies. INTRODUCTION Few studies have been conducted on the role of soil macroinvertebrates in leaf litter breakdown in wetland areas, particularly floodplains. It has been hypothesized that a woodland floodplain may serve as a temporary storage area for detritus such as leaf litter before it enters the stream or river (Merritt and Lawson, 1979; Cummins, 1980). In a Michigan woodland floodplain, Merritt and Lawson (1979) found that several groups of macroinvertebrates were involved in leaf litter breakdown (e.g., Gastropoda, Isopoda, Insecta, Diplopoda); however, earthworms appeared to be the most important group. The importance of earthworms in leaf litter degradation is welldocumented for several types of forest and agricultural lands (Kurcheva, 1960; Raw, 1962; Edwards and Heath, 1963; Van Rhee, 1963; Satchell, 1967; Edwards and Lofty, 1972; Lofty, 1974); however, less is known about their importance in floodplain soils. The objective of this study was to determine the rate at which Lumbricus terrestris (Linn.) consumed leaf litter in a Michigan woodland floodplain. MATERIALS AND METHODS Research was conducted on a point bar of the Augusta Creek floodplain located in the W. K. Kellogg Research Forest (Kalamazoo Co.), southwestern Michigan. At this location, Augusta Creek is a third-order channel (ca. 10 m width, 0.7 m depth). The floodplain is heavily forested and contains numerous species. Some of the major tree and shrub species are black ash (Fraxinus nigra Marsh.), green ash (F. pennsylvania Marsh.), basswood (Tilia americana L.), dogwood (Cornus spp.) and black cherry (Prunus serotina Ehrh.). The dominant lowland herbaceous vegetation consists of jewelweed (Impatiens capensis Meerb.), wood nettle (Laporta canadensis (L.) Wedd.), running strawberry (Euonymus obovatus Nutt.), skunk cabbage (Symplocarpus foetidus (L.) Nutt.) and iris sp. The soil of the point bar is poorly drained Adrian muck (Terric Medisaprist) which has high soil moisture and organic content most of the year. Green ash leaves were collected from the ground in early spring, air-dried and weighed in 10-g packs. A 3 m2 experimental plot, dominated by skunk cabbage, was chosen for its homogenous composition. In each of six rows, six holes were dug (27 cm apart, 18 cm deep) in the plot. The excavated soil was hand-sorted to remove large debris and steam heated to 55 C for 30 min to eliminate soil fauna. Thirty-six perforated plastic feeding chambers (22 cm high x 20 cm diam), each lined with 50 ,tm

Four Decades of Secondary Succession in Two Lowland Permanent Plots in Northern Lower Michigan

Two 0. 1-acre lowland permanent plots in northern lower Michigan were compared for changes since 1938 in community structure and population dynamics. One was on wet sandy soil with Populus tremuloides dominant in 1938, and was severely affected by a storm in 1940. The other was on wet organic soil with Thuja occidentalis, Picea mariana and Abies balsamea present and was unaffected by the 1940 storm. In the conifer plot basal area continuously increased, whereas species richness and density peaked ca. 30 years after logging and burning and declined to a low in 1981. In general, survivorship was highest for trees already established in 1938, and numbers of recruits as well as their diameter growth and survivorship decreased as stand age increased. As a result, 85%o of the 1981 population of conifers was present in 1938. The present population of trees was most strongly influenced by conditions at the time of establishment at least 50 years ago, and events since then have been of minor importance. In contrast, a storm in 1940 destroyed the overstory aspen of Plot 6, causing an initial decrease in basal area, temporary increase in species richness, and shift in dominance from trees to shrubs. Eleven years later, the basal area had returned to prestorm levels, largely because of increases in Alnus rugosa. By 1981 Fraxinus nigra had increased in number; Acer rubrum, Populus tremuloides, Abies balsamea and Betula papyrifera had larger dbh but low density because of high mortality and low recruitment. In 1981, 41 years after the storm, the plot was still dominated by a dense shrub layer of Alnus rugosa and Ilex verticillata.

Succession in deciduous swamp communities of southeastern Michigan formerly dominated by American elm

Fifty-six permanent sample plots were established in deciduous swamp communities of south-eastern Michigan where Ulmus americana was dominant before introduction of the Dutch elm disease. Plots were also established in old fields where elm seedlings were present. The purpose of the study was to determine the composition of the overstory, understory, and seedling layers in deciduous swamp forests and to provide a base line for determining the fate of young seedling and sapling elms, and the rate and nature of succession in the deciduous swamp communities. The major overstory species in the three swamps studied were Fraxinus nigra, Acer rubrum, and Betula alleghaniensis. These species were also dominant in the understory along with smaller numbers of Carpinus caroliniana, Ulmus americana, Tilia americana, and Fraxinus pennsylvanica. In the next generation the communities will be much as they are today. The overstory dominants are also strongly represented in the seedling layer. Ulmus americana was more abundant in this layer than in the understory. Therefore, Ulmus has not been eliminated from the deciduous swamps but makes up about 10 to 15% of the understory and seedling layers. Old fields and other open upland areas are much more important habitats for regeneration of Ulmus than swamp communities. Indications are that unlike Castanea dentata, Ulmus americana will be perpetuated for generations by seeds from young elm trees; however, the average life span of the species will be drastically reduced.

Embryo Immaturity and Dormancy of Black Ash1

Abstract The seed of black ash, Fraxinus nigra Marsh., borne in a single samara, normally ripens in the autumn. At that time the seed contains an embryo which is both immature and dormant. In order to overcome this dual delay to germination, the seed can be matured in moist peat moss for 18 weeks at 21° followed by after-ripening for 18 weeks at 4°. Treatment at warm temperature matured the embryo, whereas the subsequent cool temperature after-ripened the dormant embryo. During maturation the embryo length doubled, the dry weight tripled and the cotyledons showed visual evidence of differentiation. On the other hand, for dormancy to be overcome a metabolic shift in the embryo occurred during the cool period to provide the active metabolism needed by a germinating seed. This was reflected by a 5 percent per week increase in the respiration capacity of the embryo and a reduction in the amount of oil in the seed.

Range Extension of Black Ash, Fraxinus nigra Marsh., in Manitoba

Range Extension of Black Ash, Fraxinus nigra Marsh., in Manitoba