Sugar Maple Seedlings Research Articles

Conifer Presence May Negatively Affect Sugar Maple’s Ability to Migrate into the Boreal Forest Through Reduced Foliar Nutritional Status

The discipline of ecology suffers from a lack of knowledge of non-climatic factors (for example, plant–soil, plant–plant and plant–insect interactions) to predict tree species range shifts under climate change. The next generation of simulation models of forest response to climate change must build upon local observations of species interactions and growth along climatic gradients. We examined whether sugar maple (Acer saccharum) seedlings were disadvantaged with respect to soil nutrient uptake under coniferous canopies, as this species would need to migrate northward into conifer-dominated forests in response to climate change. An experimental design was applied to 3 sites, forming the largest possible latitudinal/climatic gradient for sugar maple in Quebec (Canada) and isolating the effect of conifer presence on its seedling’s nutritional status. We tested whether: (1) both soil and climate and (2) presence of conifers affected foliar nutrient levels of sugar maple seedlings. Climate and soil (through pH) strongly affected nutrient availability for sugar maple seedlings and predicted 63.7% of their foliar nutrient variability. When controlling for site effects, we found a significant negative effect of conifers on foliar Ca and Mg levels of maple seedlings, which can adversely affect their overall health and vigour. When considering projected modifications of the forest environment due to climate change, we suggest that northward migration of sugar maple will be negatively affected by the presence of conifers through reduced foliar nutrition.

Effects of Invasive Amur Honeysuckle (Lonicera maackii) and White-Tailed Deer (Odocoileus virginianus) on Survival of Sugar Maple Seedlings in a Southwestern Ohio Forest

Invasion by Amur honeysuckle (Lonicera maackii) and browsing by white-tailed deer (Odocoileus virginianus) in eastern deciduous forests negatively affect diversity and abundance of herbaceous vegetation and tree seedlings. We used a 3 x 2 factorial design (L. maackii present/absent/removed and O. virginianus present/excluded) to assess individual and interactive effects of these species on survival of sugar maple (Acer saccharum) seedlings in a deciduous forest in southwestern Ohio. Survival of seedlings was negatively affected by presence of honeysuckle and browsing by deer, but there was no significant deer x honeysuckle interaction. Negative effects on survival and, hence abundance, of sugar maple seedlings could affect the relative dominance of species of canopy trees in these forests. Because there was no honeysuckle x deer interaction, control measures that target Amur honeysuckle and white-tailed deer separately could be employed without producing unintended effects on sugar maple seedlings.

Determinants of survival over 7 years for a natural cohort of sugar maple seedlings in a northern hardwood forest

The regeneration ecology of sugar maple (Acer saccharum Marsh.) has been impacted by acid rain leaching of base cations from the soils throughout much of its range. We tracked the survival and causes of death for a natural cohort of sugar maple seedlings across 22 sites in the Hubbard Brook Valley in New Hampshire, USA, where soil acidification has been documented. Survival over 7 years averaged 3.4%; however, significant differences in survival were observed among sites, which were classified into three main groups based on the shape of their survival curves. These site groups differed in position on the landscape, seedling nutrition and leaf size, and the prevalence of damage agents, but not in soil Ca. First-season mortality was high (71%), and the main damage agents were fungal infection (Rhizoctonia spp.) and caterpillar herbivory (Geometridae). Other principal causes of mortality in order of importance were winter injury, mechanical damage, and rodent (Myodes gapperi Vigors, 1830) tunneling, and all damage agents varied significantly in severity between years. This study highlights the importance of landscape-level variation in biotic factors for predicting sugar maple regeneration success. Predictions of sugar maple regeneration will require a better understanding of controls on initial seedling growth and the suite of biotic agents that damages seedlings.

Spatial coexistence of American beech and sugar maple regeneration in post-harvest northern hardwood forests

Fine scale regeneration patterns of coexistent species are influenced by regeneration mechanisms and microsite requirements. Spatial patterns may be either disjunct or overlapping, which will determine competitive effects and microsite dominance, and future forest composition. Using American beech (Fagus grandifolia Ehrh.) and sugar maple (Acer saccharum Marshall) as an example, three hypotheses were tested: (1) random beech spatial patterns, (2) clumped spatial patterns of small sugar maple seedlings, and (3) disjunct beech and sugar maple patterns. Individual stems were sampled in a contiguous grid of 1-m2 quadrats across a 576-m2 area at three sites. Densities were separated into three height classes (≤30 cm, 30–90 cm, and > 90 cm, ≤4 cm diameter at breast height). Spatial statistics and regression were used to analyze spatial patterns and correlations. Beech and seedling sugar maple patterns were patchy, rejecting the first and not rejecting the second hypotheses. Hypothesis three was rejected because patches of the two species overlapped with advance regeneration beech overtopping sugar maple. Patchy patterns of advance regeneration beech and post-harvest sugar maple establishment suggest spatiotemporal niche partitioning. Beech had a competitive height advantage following harvest, but sugar maple still occurred in beech-free patches and beneath overtopping beech at a fine scale. Self-replacing beech patterns will ensure the species will continue dominance unless a selective chemical or manual treatment is applied that removes beech and releases sugar maple.

Effects of an invasive herbivore at the single plant scale do not extend to population-scale seedling dynamics

A complex of nine invasive weevils has established in the northern hardwood forests of the Great Lakes Region. These weevils have become the numerically dominant arthropod fauna in the lower vegetation strata of this ecosystem. Effects of these folivorous adults and rhizophagous larvae on seedling survival and density are unknown. We measured the impact of adult weevil defoliation on individual sugar maple (Acer saccharum Marshall) seedlings, the numerically dominant flora in these stands. Over 14 500 seedlings were measured to examine the effects of larval abundance, adult abundance, and adult defoliation on seedling dynamics during 2005–2009. Heavy defoliation led to individual sugar maple seedling mortality. However, at the stand level there was no measureable net effect of invasive weevils against the high natural background rates of seedling mortality. Seedling growth and biomass were reduced by high adult or larval populations, which were associated with heavy leaf and root herbivory, but not by moderate adult or larval populations. We conclude that high levels of redundancy and compensatory processes in this environment allow sugar maple seedling populations to tolerate high levels of weevil damage, although additional stresses could reduce this resilience.

Experimental reversal of soil acidification in a deciduous forest: Implications for seedling performance and changes in dominance of shade-tolerant species

Acer saccharum Marsh. (sugar maple) and the less valuable Fagus grandifolia Ehrh. (American beech) are the dominant shade-tolerant canopy species over large forest tracts in northeast North America. Negative effects of soil acidification on sugar maple could favor greater dominance of beech in the “zero-sum game” dynamics of closed-canopy forests. A watershed-level Ca addition experiment, reversing some effects of acidification (including pH and Ca availability), provided an opportunity to test effects on beech and sugar maple seedling performance over 5yrs, under different canopy species. Ca addition almost doubled leaf area of sugar maple and increased that of beech by over 40%. However extension growth was increased only in sugar maple. Both the direction of effects and the relative performance of maple and beech were consistent across canopy species. We combine our results and other evidence into a conceptual model of how soil acidification and Ca depletion is shifting the competitive balance in the seedling stage toward beech, implying an increase in beech relative abundance in the canopy, unless compensated by other factors, such as beech bark disease. These findings, and mounting evidence of other negative effects of soil acidification, suggest re-examination of the cost-effectiveness of chemical remediation in some poorly buffered forested watersheds.

Effects of Acidic Deposition and Soil Acidification on Sugar Maple Trees in the Adirondack Mountains, New York

We documented the effects of acidic atmospheric deposition and soil acidification on the canopy health, basal area increment, and regeneration of sugar maple (SM) trees across the Adirondack region of New York State, in the northeastern United States, where SM are plentiful but not well studied and where widespread depletion of soil calcium (Ca) has been documented. Sugar maple is a dominant canopy species in the Adirondack Mountain ecoregion, and it has a high demand for Ca. Trees in this region growing on soils with poor acid-base chemistry (low exchangeable Ca and % base saturation [BS]) that receive relatively high levels of atmospheric sulfur and nitrogen deposition exhibited a near absence of SM seedling regeneration and lower crown vigor compared with study plots with relatively high exchangeable Ca and BS and lower levels of acidic deposition. Basal area increment averaged over the 20th century was correlated (p < 0.1) with acid-base chemistry of the Oa, A, and upper B soil horizons. A lack of Adirondack SM regeneration, reduced canopy condition, and possibly decreased basal area growth over recent decades are associated with low concentrations of nutrient base cations in this region that has undergone soil Ca depletion from acidic deposition.

Geographical variation in reproductive capacity of sugar maple (Acer saccharum Marshall) northern peripheral populations

AbstractAimSeveral models have predicted that, with climate change, Northern Hemisphere species will migrate northwards from their present distribution ranges. Sugar maple (Acer saccharum Marshall) reaches its northern continuous distributional limit in north‐eastern North America at the transition between boreal mixed‐wood and temperate deciduous forest. Our objective was to determine whether lower sugar maple recruitment potential accounts for this gradual transition between the continuous and discontinuous zones of the distribution.LocationThe northern limit of sugar maple in eastern Canada.MethodsWe analysed the reproductive capacity of sugar maple populations along three latitudinal transects (located in the west, centre and east of Québec) in 24 sites located between 45°51′–48°59′ N and 70°21′–79°27′ W. The study area was divided into two zones, continuous and discontinuous, based on sugar maple stand abundance. We examined stand structure, sugar maple seed abundance and germination, and sugar maple seedling density and age structure.ResultsSugar maple regeneration was uneven‐aged and similar between continuous (south) and discontinuous (north) zones. For the western transect, more filled seeds and more seedlings were recorded in the continuous zone than in the discontinuous zone. Sugar maple seedling density was positively influenced by (1) basal area of mature sugar maple and saplings of all species, and (2) July mean temperature and precipitation. Four mast seed years were identified that were well synchronized across all sites; mast seeding covaried significantly with July mean temperature and July mean precipitation of the previous year.Main conclusionsOur study clearly demonstrated an effect of climatic variables and stand characteristics on sugar maple regeneration. However, these factors did not explain the transition from a continuous to a discontinuous distribution for this species. Most of our northern sites exhibited constant sugar maple recruitment over time. These results highlight the importance of including non‐climatic factors in models predicting species change in abundance.

Chronic nitrogen deposition reduces the abundance of dominant forest understory and groundcover species

Humans have altered the global nitrogen (N) cycle, greatly increasing atmospheric nitrogen deposition in industrialized regions of the world. Groundcover plants can be sensitive indicators of nitrogen deposition impacts. Here, we report results from repeated measurements over a 7year period of groundcover (plants<1.4m tall) and understory (plants with a diameter<5cm at 1.4m in height) vegetation in four mature northern hardwood forests in the north-central United States receiving experimental additions of N (3gm−2year−1 as NaNO3 for 18years). Experimental N deposition reduced the average abundance of sugar maple (Acer saccharum Marsh.) seedlings in the groundcover by>50% (P<0.001). This reduction occurred at all four sites, but was only statistically significant at the two sites where these seedlings were most abundant (site×nitrogen: P<0.001). Our observations of mortality within a large cohort of sugar maple seedlings across three sites provide further evidence of this effect. For these seedlings, experimental N deposition significantly (P<0.05) increased mortality in the weeks following germination, as well as over the longer term, reducing overall survival after 5years by almost 90%. Although groundcover plants accounted for<0.5% of aboveground plant biomass, they contributed up to 10% of ecosystem leaf area and 5% of aboveground litter. At the two sites where sugar maple seedlings were infrequent, understory vegetation was more abundant and dominated by hop-hornbeam (Ostrya virginiana (Miller) K. Koch; 42% of all stems). At these two sites, experimental N deposition significantly reduced the abundance of understory hop-hornbeam by more than 75% (site×nitrogen: P=0.008). The effects of experimental N deposition on the understory and groundcover vegetation occurred without significant decreases in reproductive litter or increases in canopy leaf area. Instead, the negative effects are more likely a by-product of other documented changes caused by the experimental N deposition: increased forest floor mass, decreased mycorrhizal abundance, and increased production of potentially alleopathic phenolic compounds. Because the late-successional species in these forests rely upon groundcover and understory plants for regeneration, the effects of added N on this vegetation have potential implications for future forest composition, particularly given the likely loss of some species in these forests due to exotic pests and pathogens.

Interactive Effects of Canopy Gap, Liming and Understory Control on Aboveground Growth of Yellow Birch and Sugar Maple Seedlings

Environmental changes influence seedling establishment and growth simultaneously and sequentially. However, the complex effects of environmental changes on understory seedlings in temperate forests are not well explored. Thus, a 4-year field experiment was conducted at Riviere a Pierre, Quebec, Canada, with two species of yellow birch (Betula alleghaniensis Britton.) and sugar maple (Acer saccharum Marsh.) in three levels of canopy gaps (<= 50 m(2), 101-300 m(2), and 701-1200 m(2)), two competition patterns (neighbor vegetation weeded and unweeded), and two liming treatments (liming and non-liming). We measured the height and height increment, crown features, and the aboveground biomass of the two species. Our results indicated that seedlings grow taller and represent higher new growth and biomass in large canopy gaps, weeded neighbour vegetation also increased the seedling height and new growths but suppressed stern biomass, and liming had no effect on the two species. The interactions of the canopy gaps, liming, and competition exhibited complex effects on growth and biomass allocation. The interactive effect was found to be positive in a large canopy gap, but not in small and intermediate gaps. It suggested that creation of a large canopy gap accelerates seedling growth and promotes an interactive effect with other factors in the changing environment. In a large canopy gap, the crown length and leaf biomass increased in the weeded and limed plot, but the biomass allocation was different between yellow birch and sugar maple in weeded plots, indicating that weeding the neighbor vegetation leads the two species dynamics in opposite directions.

Simulated N deposition negatively impacts sugar maple regeneration in a northern hardwood ecosystem

Summary1. During the next century, atmospheric nitrogen (N) deposition is projected to more than double, potentially leading to a decline in plant diversity as well as a change in plant community composition and structure.2. In a decade‐long field experiment, simulated atmospheric N deposition has slowed litter decay, resulting in an accumulation of forest floor (i.e. Oi &amp; Oe horizons). We reasoned that a greater forest floor mass under simulated N deposition would impose a physical barrier to sugar maple Acer saccharum seedling establishment, thereby reducing seedling populations of an ecologically and economically important tree species.3. To test this idea, we first quantified sugar maple seedling abundance in replicate northern hardwood forest stands receiving ambient atmospheric N (7–12 kg N ha−1 year−1) and experimental atmospheric N deposition, simulating future amounts in eastern North America (ambient plus 30 kg NO3− N ha−1 year−1). Then, we experimentally manipulated forest floor mass under ambient and simulated N deposition treatments. Finally, we transplanted first‐year established seedlings into areas receiving ambient and simulated N deposition and quantified their mortality after 1 year.4. First‐year seedling abundance did not differ under ambient and simulated N deposition; however, there were greater abundances of second‐ and third‐to‐fifth‐year seedlings under ambient N deposition (P &lt; 0·001). In all cases, experimental manipulation to increase forest floor mass, equivalent to that under simulated N deposition, resulted in significantly (P = 0·001) fewer established individuals, regardless of whether the greater forest floor mass occurred under ambient or simulated N deposition. Finally, fewer 1‐year‐old transplanted seedlings survived when grown under simulated N, albeit that result was not statistically significant.5. Synthesis and applications. The slowing of decay and the accumulation of forest floor under anthropogenic N deposition can negatively impact seedling survival and potentially alter stand development and structural diversity. As atmospheric N deposition increases globally, it becomes necessary to understand the mechanisms that lead to population changes for ecologically important tree species. The responses we document should be considered in simulations of future of forest’dynamics, as atmospheric N deposition continues to increase, specifically when sugar maple life‐history traits are included to simulate regeneration, structural diversity and stand development.

Gap-, stand-, and landscape-scale factors contribute to poor sugar maple regeneration after timber harvest

Natural regeneration in canopy gaps is a key process affecting long-term dynamics of many forests, including northern hardwood forests. The density and composition of regenerating trees are often highly variable, reflecting sensitivity to a suite of driving factors operating at different scales (e.g., harvest gap to regional landscape), including production of seeds, physical characteristics of gaps and stands, competition with non-tree vegetation, and browsing by animals. Multivariate analyses over broad geographic areas provide insights into the relative effects of these factors and permit exploration of spatial patterns in regeneration. We examined the effects of gap-, stand-, and landscape-scale factors on densities of tree seedlings (<1 m tall) and saplings (1–2 m tall) in 59 selection-harvested northern hardwood stands located across a 4500 km 2 region of Michigan's Upper Peninsula. We used Bayesian multilevel modeling to account for the hierarchical structure of the data and assess uncertainty in parameter estimates. Sugar maple ( Acer saccharum) saplings were absent from 61% of 154 m 2 plots centered in harvest gaps ( n = 347) despite its high shade tolerance and overstory dominance, but densities were high in other gaps. Densities of sugar maple seedlings and/or saplings were negatively associated with a combination of greater stand-scale densities of white-tailed deer ( Odocoileus virginianus), greater gap-scale cover of non-tree vegetation, and lower gap-scale light availability, with deer density having the greatest effect. Densities of unpalatable and commercially less valuable ironwood ( Ostrya virginiana), the second most common regeneration species, were positively related to gap-scale seed-production potential but were unrelated to factors affecting sugar maple. Ironwood tended to replace sugar maple saplings in areas with high deer density. At the landscape scale, densities of sugar maple seedlings and saplings decreased with decreasing latitude and snow depth and increasing winter deer densities. These inverse spatial patterns suggest that deer herbivory can lead to landscape-scale variation in regeneration success. However, the spatial distribution of habitat types (a proxy for soil moisture and nutrient conditions) confound this observation, with higher densities of sugar maple generally located on stands with less nutrient-rich habitat types. Results demonstrate that combinations of factors operating at different scales, and with different relative magnitudes of impact, contribute to high variation in regeneration composition and density following timber harvest. Selection silvicultural practices, as currently applied, do not ensure regeneration of desirable species; practices might require modifications in general (e.g., increasing gap size) and to match them to regionally varying factors like deer density.

Responses of sugar maple and hemlock seedlings to elevated carbon dioxide under altered above- and belowground nitrogen sources

Various human-induced changes to the atmosphere have caused carbon dioxide (CO₂), nitrogen dioxide (NO₂) and nitrate deposition (NO₃⁻) to increase in many regions of the world. The goal of this study was to examine the simultaneous influence of these three factors on tree seedlings. We used open-top chambers to fumigate sugar maple (Acer saccharum) and eastern hemlock (Tsuga canadensis) with ambient or elevated CO₂ and NO₂ (elevated concentrations were 760 ppm and 40 ppb, respectively). In addition, we applied an artificial wet deposition of 30 kg ha⁻¹ year⁻¹ NO₃⁻ to half of the open-top chambers. After two growing seasons, hemlocks showed a stimulation of growth under elevated CO₂, but the addition of elevated NO₂ or NO₃⁻ eliminated this effect. In contrast, sugar maple seedlings showed no growth enhancement under elevated CO₂ alone and decreased growth in the presence of NO₂ or NO₃⁻, and the combined treatments of elevated CO₂ with increased NO₂ or NO₃⁻ were similar to control plants. Elevated CO₂ induced changes in the leaf characteristics of both species, including decreased specific leaf area, decreased %N and increased C:N. The effects of elevated CO₂, NO₂ and NO₃⁻ on growth were not additive and treatments that singly had no effect often modified the effects of other treatments. The growth of both maple and hemlock seedlings under the full combination of treatments (CO₂ + NO₂ + NO₃⁻) was similar to that of seedlings grown under control conditions, suggesting that models predicting increased seedling growth under future atmospheric conditions may be overestimating the growth and carbon storage potential of young trees.

Litter layers (Oie) as a calcium source of sugar maple seedlings in a northern hardwood forest

The role of the Oie horizon in calcium supply of sugar maple (Acer saccharum Marsh.) seedlings was evaluated. Forest floor Oie horizon was reciprocally transplanted on 1 m2 quadrats between a Ca-treated (W1) and a reference (W3) watershed, and sugar maple seeds were planted on the quadrats. The Oie horizon in W1 exhibited a greatly increased Ca:Sr molar ratio compared with the reference W3 (550 vs. 220), allowing distinction of this Ca source in seedling tissues. Foliage and fine roots of maple seedlings growing on quadrats in W3 with Oie transplanted from W1 exhibited Ca:Sr ratios intermediate between the Oie and underlying native soil horizons, demonstrating the role of Oie in seedling Ca nutrition. However, apparently strong and temporally changing discrimination of Ca and Sr in seedling uptake and internal transport confounded quantitative evaluation.

Differences in arbuscular mycorrhizal fungal communities associated with sugar maple seedlings in and outside of invaded garlic mustard forest patches

Garlic mustard (Alliaria petiolata) is a Eurasian native that has become invasive in North America. The invasive success of A. petiolata has been partly attributed to its production of allelopathic compounds that can limit the growth of arbuscular mycorrhizal fungi (AMF). Although such effects are well known, specific effects on the richness and community composition of AMF associated with woody species have not been explored. We collected sugar maple (Acer saccharum) seedlings from eight natural forest sites in Ohio and Massachusetts, containing areas either invaded or uninvaded by A. petiolata. We measured AMF root colonization of seedlings, isolated DNA from the roots and performed PCR-TRFLP analysis to assess the richness and community composition of AMF. As expected, we found reduced AMF colonization in A. petiolata invaded patches. A. petiolata did not alter the detected TRF richness, but was associated with significant changes in the composition of AMF communities in half of the sites monitored in each region. Our results suggest that although AMF colonization was reduced in A. petiolata patches, many indigenous AMF communities include AMF that are tolerant to allelopathic effects of A. petiolata.

Regeneration ecology of sugar maple (Acer saccharum): seedling survival in relation to nutrition, site factors, and damage by insects and pathogens

The possible regeneration failure of sugar maple ( Acer saccharum Marsh.) as part of their decline has been not well explored using field studies. We sought to clarify the roles of maternal effects and dynamics of early-season survival in contributing to the previously documented pattern of larger seedlings and higher seedling densities on a Ca-treated watershed (CAL) at Hubbard Brook Experimental Forest. We used a reciprocal seed planting experiment at four sites, two sites per watershed blocked by elevation. Regardless of maternity, sugar maple seedlings planted in CAL had higher survival than seedlings in the reference watershed. However, this advantage was not as clearly linked to the Ca amendment as in our previous work, probably, in part, because Ca availability has decreased over time. Maternal effects on seed chemistry and some seedling traits were detected, but these were not strong determinants of survival. Site was a good predictor of early seedling survival with litter layer depth, pathogen prevalence, and soil chemistry all contributing to the explanatory power of site. The strength of Ca,addition effects on sugar maple regeneration from seed depends on initial soil characteristics, application amounts, and interactions of the amendment with other factors such as leaf litter cycling, weather, and pathogens.

Sugar maple seedling carbon assimilation at the northern limit of its range: the importance of seasonal light

Using in situ light curves and understory seasonal light measurements the importance of canopy avoidance was evaluated for a population of sugar maple ( Acer saccharum Marsh.) seedlings living at the boreal ecotone in Lake Superior Provincial Park, Ontario, Canada. At higher latitudes, the time period associated with canopy avoidance is shorter and occurs at cooler temperatures, increasing the risk of frost damage. In 2008, leaf-out began 5 days prior to the last frost of the season. By modeling the potential carbon gain of seedlings, it is clear that the short time period prior to canopy leaf-out still contributes a disproportionate amount of carbon to the overall budget of seedlings. Of the total seasonal carbon gain, 80.6% was assimilated in the initial 15 days following sugar maple seedling leaf-out. Based on our model, by leafing out only 6 days earlier than the average seedling leaf-out date, ∼200% more carbon could be assimilated during the course of the growing season. Vegetation phenology is cued by climatic triggers — as climate changes so too will phenological responses. These mechanisms add to the overall carbon budget of seedlings; recognizing these mechanisms is essential to thoroughly understand the natural history of this species.

Desiccation Tolerance of Green Ash and Sugar Maple Fine Roots

Abstract Exposed fine roots are subject to desiccation, which may affect their survival as well as new root growth following bare root transplanting. Fine roots of dormant 1-year-old green ash (Fraxinus pennsylvanica) and sugar maple (Acer saccharum) seedlings, subjected to desiccation treatments of 0, 1, 2, or 3 hours in December and March, lost up to 82 percent of their water. Root electrolyte leakage, a measure of cell damage, tripled after three hours of desiccation. The increase was moderately, but significantly, greater in March for both species. Desiccation treatments had no effect on fine root survival. Growth of new roots (RGP) was also unaffected by desiccation treatments. RGP of maple was greater in March than December, but not ash.

Nutrient concentrations in roots, leaves and wood of seedling and mature sugar maple and American beech at two contrasting sites

Differences in sensitivity to soil conditions across tree species and developmental stage are important to predicting forest response to environmental change. This study was conducted to compare elemental concentrations in leaves, stems, and roots of (1) sugar maple ( Acer saccharum Marsh.) seedlings vs. mature trees and (2) mature sugar maple vs. mature American beech ( Fagus grandifolia Ehrh.) in two sites that differ in soil base saturation and pH. Both sites are located in Huntington Forest, NY, USA; one site (hereafter ‘H’) has higher soil pH and Ca, Mg, and Mn concentrations than the other site (hereafter ‘L’). Sugar maple growth at H (14.8 cm 2 year −1 per tree) was much greater than at L (8.6 cm 2 year −1 per tree), but the growth of beech was not different between the two sites. Leaves, roots, and stem wood of mature beech trees and sugar maple seedlings and mature trees were sampled for nutrient analysis. Foliar Ca, K, and Al concentrations were positively correlated with soil elements, but Mn concentrations were negatively correlated. Sugar maple differed more than beech between sites in foliar K and Mn concentrations. Root Mg and P concentrations reflected soil chemistry differences, in contrast to foliar concentrations of Mg and P, which were indistinguishable between the sites. In sugar maple, seedlings differed more than in mature trees in nutrient concentrations in roots, especially for Mg and Mn. Although beech was not as responsive to nutrient availability as sugar maple in foliar and root nutrient concentrations, Ca and Mg concentrations in beech wood were higher in H (52% higher for Ca and 68% higher for Mg), while sugar maple did not differ between sites. Sugar maple regeneration failure on acidic soils in the same region is consistent with our finding that sugar maple seedlings were very sensitive to nutrient availability. This sensitivity could ultimately contribute to the replacement of sugar maple by American beech in regions of low pH and base cations if base cation leaching by anthropogenic deposition and tree harvesting continues.

Influence of overstory density on ecophysiology of red oak (Quercus rubra) and sugar maple (Acer saccharum) seedlings in central Ontario shelterwoods

A field experiment was established in a second-growth hardwood forest dominated by red oak (Quercus rubra L.) to examine the effects of shelterwood overstory density on leaf gas exchange and seedling water status of planted red oak, naturally regenerated red oak and sugar maple (Acer saccharum Marsh.) seedlings during the first growing season following harvest. Canopy cover of uncut control stands and moderate and light shelterwoods averaged 97, 80 and 49%, respectively. Understory light and vapor pressure deficit (VPD) strongly influenced gas exchange responses to overstory reduction. Increased irradiance beneath the shelterwoods significantly increased net photosynthesis (P(n)) and leaf conductance to water vapor (G(wv)) of red oak and maple seedlings; however, P(n) and G(wv) of planted and naturally regenerated red oak seedlings were two to three times higher than those of sugar maple seedlings in both partial harvest treatments, due in large part to decreased stomatal limitation of gas exchange in red oak as a result of increased VPD in the shelterwoods. In both species, seedling water status was higher in the partial harvest treatments, as reflected by the higher predawn leaf water potential and seedling water-use efficiency in seedlings in shelterwoods than in uncut stands. Within a treatment, planted and natural red oak seedlings exhibited similar leaf gas exchange rates and water status, indicating little adverse physiological effect of transplanting. We conclude that the use of shelterwoods favors photosynthetic potential of red oak over sugar maple, and should improve red oak regeneration in Ontario.