Black Cherry Seedlings Research Articles

Predicting the height growth of oak species (Quercus) reproduction over a 23-year period following clearcutting

We resampled plots from a repeated measures study implemented on the Hoosier National Forest (HNF) in southern Indiana in 1988 to investigate the influence of site and seedling physical attributes on height growth and establishment success of oak species (Quercus spp.) reproduction in stands regenerated by the clearcut method. Before harvest, an array of physical attributes were documented for individual stems of advance reproduction. Across all surveys, the same characteristics were remeasured in years 6, 12, and 23 for all reproduction types (advance reproduction, stump sprouts, and new seedlings). In order to characterize topo-edaphic conditions, soil samples were collected and analyzed in 2011, and slope aspect, slope percent, and slope position were measured in the field. Random Forest (RF) analysis was used to determine the best physical and environmental predictors of height growth for oak species and their competitors in developing stands. Overall, advance reproduction of oak species fared poorly following harvests. Sprout-origin oak stems proved stronger competitors in developing stands, although their abundance relative to competing species was quite low. Advance and sprout origin maple (Acer spp.) stems, along with new seedlings of black cherry (Prunus serotina Ehrh.) and yellow-poplar (Liriodendron tulipifera L.), quickly overtopped oak advance reproduction and established dominance in the developing canopy. The height of stems during prior sampling periods was the best overall predictor of stem height in subsequent sampling periods. Species was also an important predictor of stem height. Comparatively, environmental variables were poor predictors of height growth of individual stems throughout the study, although more mesic aspects, greater cation exchange capacity, and greater soil magnesium saturation were associated with greater height of non-sprout origin stems from species groups other than oak or hickory in year 6. Our results suggest that overstory removal has driven stand demographics towards species favored by infrequent large-scale disturbance events such as clearcutting. Without post-harvest treatments to control competitors, oak regeneration on more mesic sites is unlikely to recruit into developing stands.

Early seedling response to group selection harvesting in a northern hardwood forest

We evaluated the immediate effects of group selection harvesting on the establishment of yellow birch (Betula alleghaniensis Britt.) and black cherry (Prunus serotina Ehrh.) seedlings in maple-dominated hardwood stands of Algonquin Provincial Park, Ontario. Group selection gaps were compared to single-tree selection cutting and uncut reference stands pre-harvest and one growing season post-harvest using a before-after-control-impact (BACI) design. The percent cover of yellow birch seedlings increased significantly more in gaps than in single-tree selection and reference plots. Black cherry seedling cover increased significantly more in gaps than in reference plots, but increased at a similar rate in gaps and single-tree selection plots. Increased soil exposure and closer seed trees resulted in increased yellow birch recruitment when harvesting occurred in the late-summer-fall. These factors had little influence on yellow birch recruitment when harvesting occurred in the winter. The proportion of black cherry in the stand overstory had the greatest influence on black cherry recruitment; however, the uneven distribution of black cherry between stands may have precluded our ability to reliably test the influence of other factors. Concomitant increases in potential competitors such as wild red raspberry (Rubus strigosus Michx.) and sedges (Carex spp.) and the continued dominance of sugar maple (Acer saccharum Marsh) in gap openings may limit yellow birch and black cherry regeneration in successive growing seasons. While continued monitoring is required, our short-term results demonstrate that fall harvesting with group selection is effective at stimulating natural regeneration of yellow birch and black cherry. Key words: yellow birch, black cherry, seedling recruitment, group selection, single-tree selection, mid-tolerant, shadeintolerant

Effects of woody debris and ferns on herb-layer vegetation and deer herbivory in a Pennsylvania forest blowdown

Disturbances create a variety of legacy types, which can influence subsequent forest dynamics. One method by which legacies may influence succession is by altering herbivore activities. For example, logging slash has been shown to be effective in preventing browsing by large herbivores. Generalizing from studies after logging, we hypothesized that windthrow slash (woody debris) would limit the ability of deer to reach or locate individual plants. Furthermore, another legacy of disturbances is the establishment of recalcitrant vegetation, such as dense fern layers, which subsequently preclude woody plant establishment. To test for potential influences of these 2 types of legacies, we examined the effects of slash and fern abundance on herb and woody community structure and deer herbivory levels within a Pennsylvania windthrow gap. Slash abundance was negatively correlated with woody diversity, richness, black cherry seedling densities, and total seedling densities, but this effect was probably not a consequence of browsing. Fern abundance was negatively correlated with woody richness, red maple densities, total seedling densities, herb diversity, and richness. Fern effects on the woody community appeared to be related to reductions in light availability. Our results contradict the findings of previous studies that show that slash piles serve as refugia from herbivores. We suggest the inconsistencies may be due to a lack of quantitative measures of slash within those studies.

Ozone uptake (flux) as it relates to ozone-induced foliar symptoms of Prunus serotina and Populus maximowizii × trichocarpa

Field studies were conducted during 2003 and 2004 from early June to the end of August, at 20 sites of lower or higher elevation within north-central Pennsylvania, using seedlings of black cherry ( Prunus serotina, Ehrh.) and ramets of hybrid poplar ( Populus maximowizii × trichocarpa). A linear model was developed to estimate the influence of local environmental conditions on stomatal conductance. The most significant factors explaining stomatal variance were tree species, air temperature, leaf vapor pressure deficit, elevation, and time of day. Overall, environmental factors explained less than 35% of the variation in stomatal conductance. Ozone did not affect gas exchange rates in either poplar or cherry. Ozone-induced foliar injury was positively correlated with cumulative ozone exposures, expressed as SUM40. Overall, the amount of foliar injury was better correlated to a flux-based approach rather than to an exposure-based approach. More severe foliar injuries were observed on plants growing at higher elevations.

Morphological plasticity in seedlings of three deciduous species under shelterwood under-planting management does not correspond to shade tolerance ranks

The morphological plasticity of tree seedlings is considered to be an important factor in shade tolerance and plant succession dynamics. However, recent studies comparing temperate deciduous species have not found the expected relationship between plasticity and shade tolerance or successional status. We measured morphological plasticity in seedlings of three temperate deciduous species of north-eastern North America, using 13 parameters associated with growth, crown geometry, branching, and leaf arrangement, as a function of a steep light gradient (0.5–43%) in young transition forests under shelterwood management. The effects of light and seedling height were investigated using variance partitioning. We studied naturally occurring seedlings of the very shade tolerant sugar maple ( Acer saccharum), and planted seedlings of shade intolerant black cherry ( Prunus serotina) and red oak ( Quercus rubra), a species of intermediate shade tolerance. Contrary to expectations, sugar maple had the lowest light-induced plasticity and did not modify its morphology except as a function of height. It also produced relatively good growth. Moreover, black cherry displayed several unexpected characteristics, such as weak growth in response to increasing light and strong plasticity at several levels, mostly light-induced. Although red oak had a low level of overall plasticity, it produced the largest height increments under these shelterwoods. The morphological plasticity we observed lends support to models of shade tolerance which include resistance to pathogens and herbivory, and the capacity to store reserves, but still need to be supported with larger, integrated studies. Our results lead us to question how useful classic shade tolerance models based on morphological plasticity are for regeneration management and silviculture. At least under the pioneer stands we studied, both black cherry and sugar maple behaved in ways opposite to what was predicted.

Modeling tree regeneration height growth after an experimental hurricane

Annual height growth rates for six species of tree seedlings were modeled during the first 10 years of cohort initiation following an experimental hurricane in central Massachusetts. Selected canopy trees in a second-growth, transition oak – northern hardwoods forest were pulled over with a winch in a 50 m × 160 m area. Regeneration height growth did not follow the species-specific patterns anticipated if the disturbance had been stand replacing. Instead, the temporal increase in shade from crown expansion and sprouting of residual trees slowed cohort development and resulted in a variety of annual height growth patterns among species. Height development was followed separately for advance regeneration and new seedlings of red maple white ash, black cherry, black and yellow birch, paper birch, and red oak. All species had increasing height growth rates for 3 years followed by either decreasing or unchanged (flat) rates except red maple and ash advance regeneration, which had increasing rates throughout the measurement period. After 10 years, black and yellow birch, and red maple are the most numerous species and compose the majority of the tallest regeneration. Red oaks, which dominated the original stand, are few and unlikely to emerge to the canopy of the new cohort.

Relative contribution of initial root and shoot morphology in predicting field performance of hardwood seedlings

Single and multiple linear regression techniques were used to explain the capacity of initial seedling root volume (Rv) and first-order lateral roots (FOLR) relative to shoot height, diameter, and fresh mass to serve as important indicators of stock quality and predictors of first- and second-year height and diameter on an afforestation site in southern Indiana, USA. This was accomplished for northern red oak (Quercus rubra L.), white oak (Quercus alba L.), and black cherry (Prunus serotina Ehrh) seedlings graded into four Rv categories at establishment. Field survival was high (85–97%) for all species. Initial diameter, height, fresh mass, and Rv provided similar predictive ability of second-year field response for absolute height (R2 = 0.59–0.77) and diameter (R2 = 0.50–0.73) for both oak species. Initial seedling Rv was a better predictor of field response than FOLR for both oak species, though not for cherry. Multiple-variable models accounted for a greater proportion of the total variation in seedling field height and diameter than did single-variable equations. The high R2 (up to 0.95) of regression models suggests field performance of these species can be reliably predicted and confirms the importance of initial seedling morphology in dictating early plantation performance.

Ecological factors controlling the abundance of non-native invasive black cherry ( Prunus serotina) in deciduous forest understory in Belgium

The relation between invasion success of Prunus serotina and type of recipient habitat was studied in a large forest in central Belgium. The major emphasis in this study was the determination of factors controlling the abundance of P. serotina in understory strata. Environmental variables measured in 34 sample plots were slope, aspect, litter depth, soil type, pH, soil compaction, soil moisture, air humidity, soil temperature and light intensity in spring and late summer. Site conditions were also expressed indirectly for 210 sample plots using Ellenberg indicator values (soil nutrients, acidity, moisture, light conditions). Plots with P. serotina had lower mean indicator values for soil moisture, reaction (pH) and nitrogen, compared to plots without P. serotina. Twenty indicator species were identified for plots in which P. serotina occurs. The species richness of the herb layer was negatively correlated with the percentage cover of black cherry in the shrub layer. The percentage cover of P. serotina saplings in different overstory types was ranked as follows: Quercus > Pinus > Fagus > logging areas. Only three variables explained significant amounts of variation in Prunus abundance: slope, light intensity at 120 cm in April and light intensity at ground level in September. We found a positive response of black cherry seedlings to light intensity between 58 and 80% of full light (April measurements at 120 cm), while saplings showed a negative response within this range. Between 21 and 47% of full light (April measurements at 120 cm), seedlings were poorly represented whereas saplings showed a quite high cover. Between 0.3 and 1.8% light (September measurements at ground level), seedlings were almost absent while saplings maintained a high abundance. The results suggest that P. serotina shows a differential response to light intensity in relation to its development stage, i.e. the species is heliophilous at the seedling stage and becomes a shade plant at the sapling stage.

Heritability of Ozone Sensitivity in Open-Pollinated Families of Black Cherry (Prunus serotina Ehrh.)

Abstract First-year seedlings of black cherry, representing 10 open-pollinated families from wild parents, were exposed in CSTR chambers to replicated treatments of 30, 60, 90, and 120 ppb ambient ozone for a 7 hr day-1, 5 day wk-1. Stem height, occurrence of leaf senescence, and visible foliar injury expressed as adaxial stipple were measured weekly during the 10 wk duration of exposure. Basal stem diameters were measured before and after fumigation. Stipple began to occur in week 1 of the 120 ppb ozone treatment, week 2 of the 90 ppb treatment, and week 4 of the 60 ppb treatment. No stipple occurred on any seedlings exposed to 30 ppb ozone. Premature leaf senescence occurred in all treatments, but sooner and more severely at higher concentrations of ozone. Relative diameter growth rates declined as ozone concentrations increased. Families differed significantly in their response to ozone treatments in severity of adaxial stipple, but not in leaf senescence or height or diameter growth. Family heritability estimates for foliar injury, calculated by treatment and week of measurement, were generally above 0.5 in the 90 and 120 ppb ozone treatments. The relative ozone sensitivity of these 10 families under CSTR conditions corresponded well with sensitivity rankings of their 27-yr-old parents, replicated in a clonal seed orchard, and growing under ambient ozone exposures. The existence of localized, heritable variation in ozone sensitivity in wild populations has obvious implications for the use of bioindicators in forest health monitoring. For. Sci. 48(1):111–117.

Leaf morphology and ozone sensitivity of two open pollinated genotypes of black cherry ( Prunus serotina) seedlings

Two black cherry families differing in sensitivity to ozone (O 3) were used to test the hypothesis that leaf morphology is related to foliar sensitivity to O 3. Two uninjured sections of leaf tissue were sampled from a single leaf collected from each of 12 open-grown O 3-tolerant and 12 O 3-sensitive seedlings. Standard histological techniques and light microscopy were used to examine 11 morphological characteristics. The O 3-sensitive genotype had significantly greater stomatal density, thinner palisade mesophyll layer and thicker spongy mesophyll layer, lower ratio of palisade to spongy mesophyll, greater leaf weight and leaf area. In addition, total leaf thickness, guard cell length, and specific leaf mass were also slightly greater for the O 3-sensitive genotype.

Foliar injury, leaf gas exchange and biomass responses of black cherry ( Prunus serotina Ehrh.) half-sibling families to ozone exposure

Open pollinated families of black cherry seedlings were studied to determine genotypic differences in foliar ozone injury and leaf gas exchange in 1994 and growth response following three growing seasons. An O 3-sensitive half-sibling family (R-12) and an O 3-tolerant half-sibling family (MO-7) planted in natural soil were studied along with generic nursery stock (NS) seedlings. Ozone exposure treatments were provided through open top chambers and consisted of 50, 75, and 97% of ambient ozone, and open plots from May 9 to August 26, 1994. Ambient ozone concentrations reached an hourly peak of 88 ppb with 7-hour averages ranging from 39 to 46 ppb. Seedlings in the 50 and 75% of ambient chambers were never exposed to greater than 80 ppb O 3. Visible foliar ozone injury (stipple) was significantly higher for R-12 seedlings than MO-7 seedlings and increased with increasing ozone exposures. For the chamber treatments averaged over all families, there was no significant difference in stomatal conductance and net photosynthetic rates, but there was a significant decrease in root biomass, and a significant decrease in root/shoot ratio between the 50 and 97% of ambient chambers. Stomatal conductance and net photosynthetic rates were significantly different between families with R-12 seedlings generally greater than MO-7 seedlings. The R-12 seedlings had a 7.5 mmol m −2 increase in ozone uptake compared to MO-7, and at the same cumulative O 3 exposure R-12 exhibited 40.9% stippled leaf area, whereas MO-7 had 9.2% stippled leaf area. Significant differences were observed in stem volume growth and total final biomass between the open-top chambers and open plots. Although R-12 had the most severe foliar ozone injury, this family had significantly greater stem volume growth and total final biomass than MO-7 and NS seedlings. Root:shoot ratio was not significantly different between MO-7 and R-12 seedlings.

Interactive effects of ozone and elevated carbon dioxide on the growth and physiology of black cherry, green ash, and yellow-poplar seedlings

Potted seedlings of black cherry ( Prunus serotina Ehrh.) (BC), green ash ( Fraxinus pennsylvanica Marsh.) (GA), and yellow-poplar ( Liriodendron tulipifera L.) (YP) were exposed to one of the four treatments: (1) charcoal-filtered air (CF) at ambient CO 2 (control); (2) twice ambient O 3 (2×O 3); (3) twice ambient CO 2 (650 μl l −1) plus CF air (2×CO 2); or (4) twice ambient CO 2 (650 μl l −1) plus twice ambient O 3 (2×CO 2+2×O 3). The treatments were duplicated in eight continuously stirred tank reactors for 10 weeks. Gas exchange was measured during the last 3 weeks of treatment and all seedlings were destructively harvested after 10 weeks. Significant interactive effects of O 3 and CO 2 on the gas exchange of all three species were limited. The effects of elevated CO 2 and O 3, singly and combined, on light-saturated net photosynthesis ( A max) and stomatal conductance ( g s) were inconsistent across species. In all three species, elevated O 3 had no effect on g s. Elevated CO 2 significantly increased A max in GA and YP foliage, and decreased g s in YP foliage. Maximum carbon exchange rates and quantum efficiencies derived from light-response curves increased, while compensation irradiance and dark respiration decreased in all three species when exposed to 2×CO 2. Elevated O 3 affected few of these parameters but any change that was observed was opposite to that from exposure to 2×CO 2–air. Interactive effects of CO 2 and O 3 on light-response parameters were limited. Carboxylation efficiencies, derived from CO 2-response curves ( A/C i curves) decreased only in YP foliage exposed to 2×CO 2–air. In general, growth was significantly stimulated by 2×CO 2 in all three species; though there were few significant growth responses following exposure to 2×O 3 or the combination of 2×CO 2 plus 2×O 3. Results indicate that responses to interacting stressors such as O 3 and CO 2 are species specific.

Temporal development of visual ozone injury on the foliage of Prunus serotina—a statistical evaluation

Ozone-induced visible injury to plants is relatively common in North America but has rarely been reported in Europe. The south of Switzerland (canton Ticino) has been identified as having high ambient ozone exposures relative to other parts of Switzerland, with accumulated annual exposures over a threshold of 40 ppb (40 nl O 3 litre −1) for daylight hours from April to September of >30 ppm×h. Ozone-induced foliar injury on black cherry ( Prunus serotina) has been observed in the area. The main purpose of this study was to establish whether seedlings of black cherry grown in three different treatments (open plots [ambient ozone concentrations], chambers receiving non-filtered [96% ambient] air and charcoal-filtered chambers [ca. 60% ambient]) showed significant differences with respect to the various aspects of ozone injury development, particularly trends in injury development, the survival probabilities, the average injury level of a tree and the proportion of trees showing any sign of injury over the summer growing season. Visual estimates of the percentage of leaves showing symptoms (adaxial stipple and leaf reddening) on a plant and the percentage of leaf area of only the injured leaves which showed symptoms of ozone injury were recorded weekly for each seedling for eight consecutive weeks. These two scores were multiplied to derive a measure of injury ( Y) which can be interpreted as the proportion of injured leaf area on a tree. This derived score was used in all subsequent analyses. In this paper we assess whether, overall, an increasing trend in the injury levels, as given by the values of Y, was evident. We have also estimated the probability F( t) that the first sign of injury (measured by Y) might occur after a given number t of weeks. The smaller the value of F( t) for a given t, the stronger the effect of the treatment (i.e. the treatment causes relatively more damage). The average injury level of a tree and the proportion of trees that showed any sign of injury over the 8-week period were also analysed. The results from the open plots, the non-filtered chambers and the charcoal-filtered chambers were significantly different. However, no statistically significant difference was found between the open plots and the non-filtered chambers.

Evaluation of ozone injury on foliage of black cherry ( Prunus serotina) and tall milkweed ( Asclepias exaltata) in Great Smoky Mountains National Park

The incidence and severity of visible foliar ozone injury on black cherry ( Prunus serotina) seedlings and saplings and tall milkweed ( Asclepias exaltata) plants in Great Smoky Mountains National Park (GRSM) were determined by surveys along selected trails conducted during late summer 1992. The incidence (% injured plants) of ozone injury on black cherry was 47% and the percent injured leaves/injured plant and average leaf area injured were 43 and 6%, respectively. Maximum severity (avg. leaf area of the most severely injured leaf) was 12%. Black cherry seedlings and saplings exhibiting ozone injury were taller than non-injured plants. When insect feeding was present, it occurred 96% of the time on plants with ozone injury. Significantly more injury ( P = 0.007) on black cherry (% injured leaves/injured black cherry) occurred in the NW section of GRSM compared with the other Park sections. Regression analyses showed no relationships in ozone injury with respect to aspect, slope or elevation. Tall milkweed was evaluated twice during August for ozone injury. The incidence (% injured plants) of ozone injury was 74 and 79% for the first and second survey, respectively. The percentage of injured leaves per plant from the first to second survey was 63 to 79%, respectively. Tall milkweeds showing ozone injury were taller than the non-injured plants. The percentage of insect-damaged plants was 50% among plants without ozone injury and 60% among ozone-injured plants. Non-injured tall milkweed had fewer flowers and/or pods than the injured plants. Mean leaf area injured increased over time, and mean maximum leaf area injured increased from 8 to 11% during the same period. Regression analyses showed no differences in ozone injury regarding aspect, slope or elevation. Our findings indicate that ozone injury is widespread throughout the Park on sensitive vegetation.

Vegetative Responses to Prescribed Burning in a Mature Red Pine Stand

Abstract We investigated the effects of low-intensity, prescribed spring surface fires at varying intervals in a widely spaced, mature red pine plantation growing on a high quality sandy loam soil in northern Lower Michigan. Measurements of overstory characteristics, as well as the composition and development of the herbaceous and woody understory, were taken in unburned plots and during the seventh growing season following a single burn, the second growing season following the last of two burns at 5 yr intervals, and the growing season immediately following the last of four burns 2 yr intervals. Except for loss of a few trees due to crown scorch early in the study when fuel loadings were high, the red pine overstory was minimally affected by fires at any return interval. Compared to unburned plots, fire had no effect on total species richness or percent cover of ground flora < 1.4 m tall, but species composition shifted; cover of mosses and lichens declined and black cherry seedlings increased at the two shortest fire intervals. Although percent cover of grasses, bracken fern, and Rubus spp. appeared to increase following fire, the clumped distribution of vegetation and interplot variability in overstory density obscured the statistical significance of these trends. Species richness and density of stems in the woody understory (> 1.4 m tall but < 10 cm dbh) declined abruptly as burning interval decreased and number of burns increased. Fewer than two woody understory species, on the average, persisted on plots burned every 2 yr, whereas nearly 12 grew on unburned plots. Postburn conditions were conducive to the re-establishment of black cherry and paper birch in the understory; density of all other major species dropped sharply after more than one fire. As time after the last fire increased, however, red maple, choke cherry, and white ash densities began to recover slowly, largely by sprouting. The significance of these findings to red pine managers in the Lake States is discussed. North. J. Appl. For. 13(3):140-146.

Sensitivity of seedlings of black cherry ( Prunus serotina Ehrh.) to ozone in Great Smoky Mountains National Park. I. Exposure-response curves for biomass : H. S. Neufeld, E. H. Lee, J. R. Renfro, W. D. Hacker & Ben-Hui Yu, New Phytologist, 130(3), 1995, pp 447–459

Sensitivity of seedlings of black cherry ( Prunus serotina Ehrh.) to ozone in Great Smoky Mountains National Park. I. Exposure-response curves for biomass : H. S. Neufeld, E. H. Lee, J. R. Renfro, W. D. Hacker & Ben-Hui Yu, New Phytologist, 130(3), 1995, pp 447–459

Managed Development of Tree Roots: II. Ultra-Deep Rootball and Root Barrier Effects on Southwestern Black Cherry

Three-year-old seedlings of southwestern black cherry (Prunusserotinasubsp. wrensvar. virens with rootballs 35 and 70 cm deep were field planted in northern California in April 1986 to compare the effects on root development of rootballs of two depths and a root barrier, which was a polyethylene casing around the rootballs of half of the trees of each treatment. Three growing seasons later, the roots were excavated to a depth of 32 cm in an area within a radius of 1 m from the tree trunks and dry weights of the exposed roots of each tree determined. There was no significant difference in root dry weights between the two rootball types. The casing, on the other hand, significantly reduced root dry weights for each rootball type.

Sensitivity of seedlings of black cherry (Prunus serotina Ehrh.) to ozone in Great Smoky Mountains National Park

summaryThe response of seedlings of black cherry (Prunus serotina Ehrh.) to ozone was evaluated in Great Smoky Mountains National Park using open‐top chambers during the growing seasons of 1989 and 1992. Two separate sets of seedlings were each exposed to various concentrations of ozone (charcoal‐filtered; 0.5 × (not used in 1989), 1.0 ×, 1.5 ×, and 2.0 × modified ambient) in two different seasons. Seasonal indices of exposure (SUM00, SUM06 and AOT40) for the 1.0 × treatments were 39.2, 1.9, and 1.62 ppm h respectively, in 1989, and 63.1, 0.9, and 0.78 ppm h, respectively, in 1992. No significant chamber effects were noted, except for reduced height growth in open plots compared with 1.0 × chambers in 1992. In both years, the 2.0 × treatment reduced total, leaf, root, and shoot‐I‐root biomass, although some of these changes were only marginally significant in 1992. Stem biomass was significantly reduced in 1989, but not 1992. Leaf area, count and weight were all highly correlated, and showed significant reductions in both years. The leaf area ratio (leaf area/total weight) was reduced in 1989, but not in 1992. Height was not affected by ozone, but diameter was reduced only in 1989. Chamber‐to‐chamber variation for biomass and leaf variates was greater in 1992, and as a result, significance levels were lower. Weibull functions were fitted to chamber means, and showed significant near‐linear declines for most components when log‐transformed data were plotted against the SUM06 and AOT40 indices. Individual Weibull models for the 1989 and 1992 data sets, and combined models over both years, were developed. Combined models were adequate for describing ozone responses for all biomass components, as determined by the likelihood ratio test. The data show‐that the two years of exposure produced similar, but not identical effects, despite large differences in initial size of the seedlings and in seasonal ozone dynamics. Leaf and root biomass were most sensitive to ozone (as determined by the slope of decrease with increasing SUM06), whereas stem biomass was least sensitive. Black cherry seedlings are shown to be among the most sensitive to elevated ozone of the 21 tree species examined to date in Great Smoky Mountains National Park.

Physiology, morphology, and ozone uptake of leaves of black cherry seedlings, saplings, and canopy trees

Patterns of ozone uptake were related to physiological, morphological, and phenological characteristics of different-sized black cherry trees ( Prunus serotina Ehrh.) at a site in central Pennsylvania. Calculated ozone uptake differed among open-grown seedlings, forest gap saplings, and canopy trees and between leaves in the upper and lower crown of saplings and canopy trees. On an instantaneous basis, seedling leaves had the greatest ozone uptake rates of all tree size classes due to greater stomatal conductance and higher concentrations of ozone in their local environment. A pattern of higher stomatal conductance of seedlings was consistent with higher incident photosynthetically-active radiation, stomatal density, and predawn xylem water potentials for seedlings relative to larger trees. However, seedlings displayed an indeterminate pattern of shoot growth, with the majority of their leaves produced after shoot growth had ceased for canopy and sapling trees. Full leaf expansion occurred by mid-June for sapling and canopy trees. Because many of their leaves were exposed to ozone for only part of the growing season, seedlings had a lower relative exposure over the course of the growing season, and subsequently lower cumulative uptake, of ozone than canopy trees and a level of uptake similar to upper canopy leaves of saplings. Visible injury symptoms were not always correlated with patterns in ozone uptake. Visible symptoms were more apparent on seedling leaves in concurrence with their high instantaneous uptake rates. However, visible injury was more prevalent on leaves in the lower versus upper crown of canopy trees and saplings, even though lower crown leaves had less ozone uptake. Lower crown leaves may be more sensitive to ozone per unit uptake than upper crown leaves because of their morphology. In addition, the lower net carbon uptake of lower crown leaves may limit repair and anti-oxidant defense processes.

Shade, leaf growth and crown development of Quercus rubra, Quercus velutina, Prunus serotina and Acer rubrum seedlings.

The study was conducted in an open field to determine the optimum irradiance for establishment and growth of two oak species and two major associated woody species. Half-sib seedlings of black cherry (Prunus serotina Ehrh.), red maple (Acer rubrum L.), northern red oak (Quercus rubra L.) and black oak (Q. velutina Lam.) were grown for two years under shade-cloth tents. Eight shade treatments (94, 70, 57, 45, 37, 27, 20 and 8% of full sunlight) with three replications each were used. Measurements were made on seedlings harvested at the end of the first and second growing seasons. In the second year, shading significantly decreased the number of leaves for all species except black cherry, but only significantly decreased leaf area in northern red oak. Shading significantly decreased average leaf size of red maple. Average leaf size of black cherry was largest in the intermediate shade treatments and decreased significantly with increased and decreased shade. Leaf weight/leaf area (mg cm(-2)) increased significantly in a quadratic pattern with decreasing shade for all four species. Leaf area ratio (cm(2) g(-1)) decreased significantly with decreasing shade for all species except red maple in the first year and black oak in the second year. Total branch development increased significantly with decreasing shade in red maple and northern red oak, whereas indeterminate branches increased significantly with decreasing shade only in black cherry, and short branches increased significantly with decreasing shade only in red maple.