Striped Maple Research Articles

Woody Plant Communities after 40 Years of Pollution Control and Restoration in Smelter-Denuded Landscapes

Restoration of degraded ecosystems requires assessing the status of the recovery and identifying key factors limiting the recovery. Nearly 4 decades of the reduction in smelter emissions, soil amelioration, and planting of ∼10 million trees and shrubs have led to extensive revegetation of emission-denuded landscapes in the Sudbury area, ON, Canada. To evaluate the state of recovery and identify factors affecting it, we surveyed woody plants and environmental correlates (soil pH, soil nutrient content, and soil metal content) along gradients of historical smelting impacts. Species richness declined from reference sites to high-impact sites, with impact sites having 23–33% fewer species compared to reference sites. Species composition varied along gradients of historical smelting impacts, with the difference attributable to low abundances or absences of one third of the 43 species found in the reference sites. Species richness and composition were associated with soil toxicity (as measured by metal content and pH) but not soil nutrients. However, the negative relationships between soil toxicity and plant community were attributable to the mediation effect of canopy cover, rather than the direct effect of soil toxicity. Sixty three percent of species that were uncommon or absent in impact sites (Abies balsamea [Balsam Fir], Acer pensylvanicum [Striped Maple], Acer spicatum [Mountain Maple], Betula alleghaniensis [Swamp Birch], Fraxinus nigra [Black Ash], Gaultheria procumbens [American Wintergreen], Linnaea borealis [Twinflower], Lonicera canadensis [Fly Honeysuckle], Lonicera hirsute [Hairy Honeysuckle], and Ostrya virginiana [American Hophornbeam]) were shade-tolerant and declined with declining canopy cover. These species were reported to be absent or uncommon in impact sites nearly 4 decades ago. Together, these results suggest that woody plant community has undergone limited recovery and that the recovery is hampered by poorly developed canopy cover rather than direct soil toxicity or nutrient deficiency. Accordingly, strategic interventions of canopy cover-mediated processes (e.g., shading and soil moisture) is needed to facilitate the recovery of the woody plant community in the smelter-denuded landscapes.

Mating and adult feeding behaviour influence pheromone production in female Asian longhorn beetle Anoplophora glabripennis (Coleoptera: Cerambycidae)

Abstract The Asian longhorn beetle (ALB) Anoplophora glabripennis Motschulsky is a destructive invasive species worldwide. Female ALB produce a pheromone component, α‐longipinene, in the genitalia. However, the origin and factors, such as age, mating, adult feeding and host plant, influencing the production of this compound are unclear. Our results showed that virgin female ALB consistently produced α‐longipinene at various ages after feeding for several days post eclosion, but unfed adult females never produced this compound. Mating significantly reduced the amount of α‐longipinene in female genitalia. α‐Longipinene was the most dominant compound in the volatiles emitted by females, but not in those emitted by males or host twigs (Acer pensylvanicum L.). The proportion of α‐longipinene among the beetle‐released sesquiterpenes that were known to be male antennally active was significantly greater than that emitted by ALB damaged, mechanically damaged or control twigs. These results suggest that ALB females probably derive α‐longipinene or a precursor from hosts via adult feeding, and release it at a significantly different ratio from that found in host volatiles. The various ratios of α‐longipinene produced by beetles and host twigs may encode information pertaining to multiple purposes such as aggregation, mate and host location.

When the going gets tough, the tough turn female: injury and sex expression in a sex-changing tree.

PremisePlant sex is usually fixed, but in rare cases, sex expression is flexible and may be influenced by environmental factors. Theory links female sex expression to better health, but manipulative work involving the experimental change of health via injury is limited, particularly in sexually plastic species. A better understanding of mechanisms influencing shifts in sex is essential to our understanding of life history theory regarding trade‐offs in sex allocation and differential mortality.MethodsWe investigated the relationship between physiological stress and sex expression in sexually plastic striped maple trees (Acer pensylvanicum) by inflicting damage of various intensities (crown pruning, defoliation, and hydraulic restriction). We then monitored the sex expression of injured and control individuals for 2 years to assess the extent to which injury may cue changes in sex expression.ResultsWe found that severe damage such as full defoliation or severe pruning increased odds of changing sex to female and decreased odds of changing to male. In fact, no pruned male trees flowered male 2 years later, while all males in the control group flowered partially or fully male. After full defoliation, trees had 4.5 times higher odds of flowering female. Not all injury is equal; less‐severe physical trauma did not affect the frequency of sex change to femaleness.ConclusionsThis work demonstrates that physical trauma in striped maple appears to exhibit a threshold effect in which only the most stressful of physiological cues instigate changes in sex expression, a phenomenon previously unknown, and that damage stress is strongly correlated with switching to femaleness. These findings have implications for population sex ratios and sustainability within an increasing stressful climate regime.

Leaf chlorophyll plasticity in advanced regeneration of co-occurring Acer pensylvanicum and Fagus grandifolia beneath deciduous forest canopy

The chemical trait ‘total chlorophyll content per unit leaf area’ (CHL) has long been recognized to confer plasticity within a genetically fixed range of phenotypic variance. The plasticity of leaf CHL (PCHL) was assessed with special reference to saplings of the two morphologically divergent tree species Acer pensylvanicum L. (AP) and Fagus grandifolia Ehrh. (FG) which co-occur in the eastern deciduous forest biome of North America. A randomized block design with repeated measures was used to field-test the hypothesis that low leaf display efficiency favoured selection for higher PCHL in FG than in AP. Species were tested in the shade of closed forest canopy at naturally low soil fertility and following applications of mineral NPK to test the second hypothesis that nutrient-poor soils select for high PCHL. Results support the first hypothesis of higher phenotypic PCHL and higher developmental PCHL in FG than in AP. Moreover, a markedly more dynamic CHL increase coincided with more rapid leaf development in FG compared to AP. Differential leaf phenology likely contributed to high PCHL in FG. Results also support, in the case of FG, the second hypothesis that nutrient-poor soils favour phenotypic PCHL. This is, however, not true for AP and confirms a lower shade tolerance rank for AP. Results strongly suggest that the ecological conditions for advanced regeneration in deep shade on nutrient-poor soils maintain high PCHL in FG populations.

Time for a change: patterns of sex expression, health and mortality in a sex-changing tree.

The ability of individuals to change sex during their lifetime is known as environmental sex determination (ESD). This represents a unique life history trait, allowing plants to allocate resources differentially to male and female functions across lifetimes, potentially maximizing fitness in response to changing environmental or internal cues. In this study, Acer pensylvanicum, a species with an unconfirmed sex determination system, was investigated to see what patterns in sex expression existed across multiple years, if there were sex-based differences in growth and mortality, and whether this species conformed to theoretical predictions that females are larger and in better condition. Patterns of sex expression were documented over 4 years in a phenotypically subdioecious A. pensylvanicum population located in New Jersey, USA, and data on size, mortality, health and growth were collected. A machine-learning algorithm known as a boosted classification tree was used to develop a model to predict the sex of a tree based on its condition, size and previous sex. In this study, 54 % of the trees switched sex expression during a 4-year period, with 26 % of those trees switching sex at least twice. Consistently monoecious trees could change relative sex expression by as much as 95 %. Both size and condition were influential in predicting sex, with condition exerting three times more relative influence than size on expressed sex. Contrary to theoretical predictions, the model showed that full female sex expression did not increase with size. Healthy trees were more likely to be male; predicted female sex expression increased with deteriorating health. Growth rate negatively correlated with multiple years of female sex expression. Populations maintained similar male-skewed sex ratios across years and locations and may result from differential mortality: 75 % of dead trees flowered female immediately before death. This study shows conclusively that A. pensylvanicum exhibits ESD and that femaleness correlates with decreased health, in contrast to prevailing theory. The mortality findings advance our understanding of puzzling non-equilibrium sex ratios and life history trade-offs resulting from male and female sex expression.

Down to the wire: late season changes in sex expression in a sexually labile tree species, Acer pensylvanicum (Sapindaceae)

In sexually plastic Acer pensylvanicum, determination of sex can occur extremely late, within three weeks of spring flowering. Physical damage causing complete vascular tissue severance results in increased female expression. Species with environmental sex determination are rare amongst angiosperms but widely distributed across taxa. The timing of floral development in species that change sex based on environmental cues is unexplored. We investigated the timing of differentiation of sexual organs in buds of Acer pensylvanicum, an understory tree in eastern North America with environmental sex determination. We collected branches from individuals at three collection times in the early spring of 2016 and kept them in a warm greenhouse until anthesis. All individuals exhibited complete or partial female inflorescences in the greenhouse in one or more collection. However, none of these same individuals produced only female flowers in the field. Unlike many other woody species that differentiate bud sexual primordia 9–12 months prior to flowering, A. pensylvanicum may differentiate the sexual organs in its flower buds as late as three weeks prior to anthesis. In a separate series of branch collections in 2017, we found that the stress response to cutting leads to increased female sex expression in branches, while earlier warm temperatures (e.g., those caused by growing in a protected greenhouse environment) or increased carbohydrate availability does not. Given the labile sex determination system of A. pensylvanicum, the ability to delay differentiation of buds into male or female until shortly before spring flowering would allow individual trees to respond to sex-determining damage cues as late as mid-spring. This supports the hypothesis that A. pensylvanicum may not exhibit the lag-time characteristic of temperate spring and early-summer flowering woody species and may change sex expression in response to stress.

Evaluating the ecological impacts of salvage logging: can natural and anthropogenic disturbances promote coexistence?

Salvage logging following windthrow is common throughout forests worldwide even though the practice is often considered inimical to forest recovery. Because salvaging removes trees, crushes seedlings, and compacts soils, many warn this practice may delay succession, suppress diversity, and alter composition. Here, over 8 yr following windthrow, we experimentally evaluate how salvaging affects tree succession across 11 gaps in Eastern deciduous forests of Pennsylvania, wherein each gap was divided into salvaged and control (unsalvaged) halves. Our gaps vary in size and windthrow severity, and we explicitly account for this variation as well as variation in soil disturbance (i.e., scarification) resulting from salvaging so that our results would be generalizable. Salvage logging had modest and ephemeral impacts on tree succession. Seedling richness and density declined similarly over time in both salvaged and unsalvaged areas as individuals grew into saplings. The primary impact of salvaging on succession occurred where salvaging scarified soils. Here, salvaging caused 41 to 82% declines in sapling abundance, richness, and diversity, but these differences largely disappeared within 5 yr. Additionally, we documented interactions between windthrow severity and scarification. Specifically, low-severity windthrow and scarification combined reinforced dominance by shade-tolerant and browse-tolerant species (Acer pensylvanicum, Fagus grandifolia). In contrast, high windthrow severity and scarification together reduced the density of a fast-growing pioneer tree (Prunus pensylvanica) and non-tree vegetation cover by 75% and 26%, respectively. This reduction enhanced the recruitment of two mid-successional tree species, Acer rubrum and Prunus serotina, by 2 and 3-fold, respectively. Thus, our findings demonstrate that salvaging creates novel microsites and mitigates competing vegetation, thereby enhancing establishment of important hardwoods and promoting tree species coexistence. Our results, coupled with an assessment of 27 published post-windthrow salvage studies, suggest short-term studies may overestimate the impact of salvaging on regeneration. We conclude that the ecological costs and benefits of salvaging depend upon the variation in canopy and soil disturbance severity as well as the timescale at which effects are evaluated. Thus, our findings are inconsistent with the view that salvaging inexorably undermines plant diversity; rather we suggest salvaging can promote tree species coexistence within various contexts.

Screening natural product extracts against kinetoplastid parasites

The kinetoplastids parasites are a group of flagellated protozoan parasites characterized by the subcellular structure, kinetoplast. Trypanosoma spp and Leishmania spp are the most notable kinetoplastids with major impact on human and animal health. Human African Trypanosomiasis (HAT) caused by Trypansoma brucei and visceral leishmaniasis caused by Leishmania donovani affect mostly neglected segments of the populations. The toxicity and resistance for currently available drugs and depleted drug discovery pipeline, necessitate discovery of new drugs. Natural products are vast source of diverse drug molecules with novel chemotypes. A 384 well plate screening paradigm has been developed that covers the screening of natural products extracts against L. donovani promastigotes, L. donovani axenic amastigote, differentiated THP1 (Human Acute Monocytic Leukemia) cells infected with L. donovani amastigotes and also cytotoxicity against uninfected THP1 cells. In the initial phase 176 plant extracts, prepared from the North American plants, have been screened. Lead extracts Cupressus lawsoniana, Acer pensylvanicum, Verbesina virginica, were identified as new antitrypanosomal leads with significant selectivity. Further follow up evaluation of lead extracts is likely to identify drug leads with novel chemotypes.

Reversing legacy effects in the understory of an oak-dominated forest

Current forests developed under conditions different from original forests, with higher deer densities, reduced fire frequency, denser canopies, and smaller canopy gaps. These alterations have led to understories dominated by species simultaneously browse tolerant, shade tolerant, and fire sensitive leading to difficulties in the regeneration of oak species (Quercus spp.) in some areas. We evaluated how three key processes — understory fire, canopy gaps, and browsing — influenced tree species in east central West Virginia. We were particularly interested in the response of oak species because they are the dominant overstory species and of maple species (Acer spp.), black birch (Betula lenta L.), and yellow-poplar (Liriodendron tulipifera L.) as these are likely to replace the current forest. Single-process effects were significant and significant interactions among processes were numerous. In general, fire caused significant reductions of seedlings and saplings of red maple (Acer rubrum L.) and striped maple (Acer pensylvanicum L.) and increased the seedlings of black birch and yellow-poplar. Canopy gaps increased the abundance of black birch and yellow-poplar seedlings and saplings. Gaps and fire together caused an increase in the relative abundance of yellow-poplar. Excluding browsers and creating canopy gaps together nearly doubled oak sapling importance values versus either treatment alone; however, oak importance values remained low. Given the significant interactions of browse control with the other two processes, browse control should be considered when planning oak regeneration treatments such as canopy gaps or prescribed fire.

Fleshy Saprobic and Ectomycorrhizal Fungal Communities Associated with Healthy and Declining Eastern Hemlock Stands in Great Smoky Mountains National Park

Prior to the loss of Tsuga canadensis (Eastern Hemlock) stands in the Great Smoky Mountains National Park (GRSM), we collected baseline data during 2006–2009 at two locations (Copeland Creek and Gabes Mountain) regarding macrofungi that occur under this tree species. We studied macrofungi in order to understand the current and changing ectomycorrhizal and saprobic fungal community structure associated with healthy (imidicloprid-treated) and dying Eastern Hemlock stands and to contribute data for the All Taxa Biodiversity Inventory (ATBI) in GRSM. A total of 121 taxa representing 75 ectomycorrhizal, 1 pathogenic, and 45 saprobic species, were collected from 92, 59, and 106 sampling locations in 2006, 2007, and 2008, respectively. Macrofungal species richness, diversity, and evenness (E) in Copeland Creek were significantly greater (P = 0.05) in 2006 than 2007. Eighty percent of all fungi collected were found in Copeland Creek (487 m elevation) where trees are <75 years old; the remaining 20% were collected at Gabes Mountain (1158 m elevation) where trees are >150 years old. The most common taxa found across sampling locations included Russula fragrantissima (22.0%), Amanita citrina var. lavendula (Lavender False Death Cap; 17.1%), Austroboletus gracilis (Graceful Bolete; 14.6%), Laccaria laccata (Deceiver; 9.8%), and Russula russuloides (9.8%). Amanita cinereopannosa occurred at a low frequency overall (2.4% of trees sampled) but when present had high abundance. Total macrofungi and ectomycorrhizal fungi at Copeland Creek had significantly greater species richness, density, and evenness than at the Gabes Mountain site. Ectomycorrhizal fungi evenness values following imidicloprid soil-drenching treatments were significantly less uniform for macrofungi collected from within 5 m of trees treated in subplots with full rates of the chemical than for those near untreated trees (E = 0.2 and 0.4, respectively). In addition, there was a numerical trend towards significantly less diversity and evenness at the full chemical application rate compared to the half rate or untreated control plots. There were no differences in the occurrence of saprobic fungi between chemically treated and control trees. Associated vegetation had a significant impact on the occurrence of macrofungi. Across both locations, a total of 37 plant, shrub, or tree species were identified; Acer pensylvanicum (Striped Maple) with an overall abundance of 11.0%, Pyrularia pubera (Buffalo Nut; 10.5%), Ilex opaca (American Holly; 8.2%), Calycanthus floridus (Eastern Sweetshrub; 4.8%), and Rhododendron maximum (Great Rhododendron; 4.7%), were the most common associated species. Species richness, diversity, and evenness of the associated vegetation were significantly different between locations. Evenness data for plant species abundance was not equal, but varied within and across locations.

Indirect Effects of Pandemic Deer Overabundance Inferred from Caterpillar‐Host Relations

Externally feeding phytophagous insect larvae (i.e., caterpillars, here, larval Lepidoptera and sawflies, Hymenoptera: Symphyta) are important canopy herbivores and prey resources in temperate deciduous forests. However, composition of forest trees has changed dramatically in the eastern United States since 1900. In particular, browsing by high densities of white-tailed deer (Odocoileus virginianus) has resulted in forests dominated by browse-tolerant species, such as black cherry (Prunus serotina), and greatly reduced relative abundance of other tree species, notably pin cherry (Prunus pensylvanica) and birches (Betula spp.). To quantify effects of these changes on caterpillars, we sampled caterpillars from 960 branch tips of the 8 tree species that comprise 95% of trees in Allegheny hardwood forests: red maple (Acer rubrum), striped maple (Acer pensylvanicum), sugar maple (Acer saccharum), sweet birch (Betula lenta), yellow birch (Betula allegheniensis), American beech (Fagus grandifolia), black cherry, and pin cherry. We collected 547 caterpillar specimens that belonged to 66 Lepidoptera and 10 Hymenoptera species. Caterpillar density, species richness, and community composition differed significantly among tree species sampled. Pin cherry, nearly eliminated at high deer density, had the highest density and diversity of caterpillars. Pin cherry shared a common caterpillar community with black cherry, which was distinct from those of other tree hosts. As high deer density continues to replace diverse forests of cherries, maples, birches, and beech with monodominant stands of black cherry, up to 66% of caterpillar species may be eliminated. Hence, deer-induced changes in forest vegetation are likely to ricochet back up forest food webs and therefore negatively affect species that depend on caterpillars and moths for food and pollination.

Recruitment and Dominance of Quercus rubra and Quercus alba in a previous Oak-Chestnut Forest from the 1980s to 2008

This study documents 25 y of change in the abundance of Quercus rubra (northern red oak) and Quercus alba (white oak), in a previous chestnut (Castanea castanea)-oak forest in the Southern Appalachians of the eastern U.S.A. Spatially explicit data from 1983–1984 and 2007–2008 of individually mapped trees on two plots in southwestern Virginia were used to examine how the basal area and density of all tree species changed, with specific attention to recruitment, growth, and mortality patterns of Q. rubra and Q. alba. Since the 1980s there has been an increase in the number of shade tolerant trees, primarily Acer pensylvanicum (striped maple), and a decrease in the number of shade intolerant and intermediate shade tolerant trees, including both Q. rubra and Q. alba. We found a negative correlation between A. pensylvanicum abundance and Quercus seedling abundance and a positive correlation between light availability and Quercus seedling abundance. Both Q. rubra and Q. alba have experienced self-thinning, and the previous oak-chestnut forest will likely become increasingly dominated by maples and other shade tolerant species.

Mercury in litterfall and upper soil horizons in forested ecosystems in Vermont, USA

Mercury (Hg) is an atmospheric pollutant that, in forest ecosystems, accumulates in foliage and upper soil horizons. The authors measured soil and litterfall Hg at 15 forest sites (northern hardwood to mixed hardwood/conifer) throughout Vermont, USA, to examine variation among tree species, forest type, and soils. Differences were found among the 12 tree species sampled from at least two sites, with Acer pensylvanicum having significantly greater litterfall total Hg concentration. Senescent leaves had greater Hg concentrations if they originated lower in the canopy or had higher surface:weight ratios. Annual litterfall Hg flux had a wide range, 12.6 to 28.5 µg/m(2) (mean, 17.9 µg/m(2) ), not related to forest type. Soil and Hg pools in the Oi horizon (litter layer) were not related to the measured Hg deposition flux in litterfall or to total modeled Hg deposition. Despite having lower Hg concentrations, upper mineral soil (A horizons) had greater Hg pools than organic soil horizons (forest floor) due to greater bulk density. Significant differences were found in Hg concentration and Hg/C ratio among soil horizons but not among forest types. Overall, our findings highlight the importance of site history and the benefits of collecting litterfall and soils simultaneously. Observed differences in forest floor Hg pools were strongly correlated with carbon pools, which appeared to be a function of historic land-use patterns.

Over-browsing in Pennsylvania creates a depauperate forest dominated by an understory tree: Results from a 60-year-old deer exclosure

Abstract We evaluated the impact of long-term over-browsing by white-tailed deer on the diversity and density of trees in a forest in the Allegheny High Plateau region of central Pennsylvania. We compared tree diversity and density inside a 60 year-old deer exclosure to an adjacent reference site. Browsing caused a 55–100% decline in density of four tree species (Prunus serotina, Acer saccharum, Betula lenta, Cornus alternifolia) and created a forest dominated (> 70% of all stems) by Acer pensylvanicum, an understory tree that is known to be highly browse-tolerant. The total density of trees that are capable of ascending into the canopy (i.e., non subcanopy tree species) declined by 85%. Browsing caused a significant decline in both mean species richness and Shannon diversity and created communities that contrasted significantly in tree species composition (ANOSIM, R = 0.8105, P < 0.0001). Our results suggest that long-term over-browsing can create low density, depauperate communities where dominance is...

Conflicting Phylogenies of Section &lt;I&gt;Macrantha&lt;/I&gt; (&lt;I&gt;Acer&lt;/I&gt; Aceroideae, Sapindaceae) Based on Chloroplast and Nuclear DNA

Abstract Section Macrantha is a monophyletic group with 18–22 species, all of which are distributed in Asia except for Acer pensylvanicum in eastern North America. Nuclear sequences from nrDNA ITS, LEAFY, and GBSSI (two putative copies), along with morphological characters, recognize two clades (series Crataegifolia and Micrantha). However, chloroplast phylogenies based on ndhF, trnL-F, and psbA-trnH are significantly incongruent with the nuclear trees, showing two major clades with species from the Asian continent excluding the northeast (AS - N) in one clade and those from Asian Pacific Islands plus northeast Asia in the other (API + N). Ancient hybridization and chloroplast capture may have occurred in the two series in both geographic areas. The two series diverged at 46.3 mya, which is before the formation of the Japanese Sea in the early Miocene (32–18 mya). The Japanese Sea may be the barrier for the seed exchange between the two geographic areas, and was responsible for the formation of the disjun...

Contrasting patterns and combined effects of moose and insect herbivory on striped maple ( Acer pensylvanicum)

Although both mammalian and insect herbivores can strongly affect plant growth and biomass, interactions between these taxa feeding upon shared plant resources seldom have been studied experimentally in northern forests. In this study, we manipulated density of leaf-chewing insects and took advantage of a natural gradient of moose ( Alces alces) foraging activity to examine their separate and combined effects on sapling striped maple ( Acer pensylvanicum). Winter moose browse was patchy over space and time, but when present it resulted in a median bud loss of 72%. Saplings responded to moose browse by increasing leading shoot growth during the following summer as well as by developing leaves from epicormic buds. However, they did not fully compensate for the loss of biomass, and produced fewer leaves than in the prior year. Leaf-chewing insect herbivory occurred during the summer and was ubiquitous and more uniform than moose browse, but of a lesser magnitude (average 7% leaf area removed). Insect herbivory suppressed shoot growth and leaf production. Leaf damage was greater on browsed than unbrowsed trees, suggesting that browsing may improve leaf quality for insect herbivores, further constraining sapling growth. Although striped maple mortality was low, the average number of leaves produced per sapling declined during the four years of the study, indicating that combined mammalian and insect herbivory coupled with resource limitation will prevent most saplings from reaching maturity.

Tree species and environment associations within hemlock-silverbell stands treated for hemlock woolly adelgid in Great Smoky Mountains National Park1

The hemlock-silverbell (Tsuga canadensis-Halesia tetraptera) association is endemic to several small stands in federally protected lands in the southern Appalachian Mountains and is currently threatened by the hemlock woolly adelgid (Adelges tsugae). Pre-infestation stand structure was still evident at the time of the study but hemlock mortality and associated vegetation responses portend rapid changes in this system. In order to guide potential future restoration efforts and impact assessments, a study was implemented to determine the structure of hemlock-silverbell stands and to identify environmental variables associated with differences in stand composition in areas of Great Smoky Mountains National Park treated to control hemlock woolly adelgid. Halesia tetraptera and T. canadensis exhibited even-aged and uneven-aged stand structures, respectively. Forest composition varied as a function of environmental variables within the hemlock-silverbell association with overstory H. tetraptera relative density positively correlated with higher water availability (Beers aspect and slope) and overstory T. canadensis was negatively correlated with Beers aspect. Relative density of H. tetraptera and T. canadensis in the understory were similarly associated with higher and lower productivity conditions, respectively. In the understory, Acer pensylvanicum relative density was negatively associated with that of understory T. canadensis. The results suggest that partial canopy removal resulting from the loss of T. canadensis due to hemlock woolly adelgid may benefit aggressive tree species such as A. pensylvanicum. The United States Park Service vegetation management policies, here and in other natural areas where non-native invasive species are controlled (but native species responses are unaccounted for), will need to address this phenomenon if T. canadensis restoration is to be accomplished in the event adelgid control can be achieved.

Oak Forest Composition on Contrasting Soil Types at the Mohonk Preserve, Eastern New York

Abstract This research investigated overstory and understory forest composition for 10 sites derived from either shale or sandstone conglomerate parent material on the Shawangunk Ridge in eastern New York. Overstory composition in both soil types was dominated by red oak (Quercus rubra) and chestnut oak (Quercus montana), but the overstory on shale sites was more diverse (14 tree species) and had less oak than sandstone sites (with only 6 tree species). A total of 17 species were recorded as regeneration on shale sites, where seedlings averaged 21,466/ha and saplings averaged 1,833/ha. Dominant seedling on shale sites were chestnut oak (7,100/ha) and red oak (3,583/ha); chestnut oak had significantly more seedlings on shale versus sandstone sites. Saplings on shale sites were predominantly Hamamelis virginiana and Acer pensylvanicum. On sandstone sites, seedlings averaged 6,425/ha (including 2,075 oaks and 2,250 red maple per ha). Sapling numbers for all species were low (1,400/ha) and were mostly red maple. These forests are unique because of the relatively high density of oak seedlings on certain sites and low density of red maple across all sites. This variation in regeneration as well as management strategies to promote additional oak regeneration and canopy recruitment are discussed for these and similar forests.

Effects of bird predation on arthropod abundance and tree growth across an elevational gradient

Considerable uncertainty surrounds the conditions under which birds can cause trophic cascades. In a three‐year experiment, we studied the direct and indirect effects of insectivorous birds on arthropod abundance, herbivory, and growth of striped maple Acer pensylvanicum saplings in a northern hardwood forest of central New Hampshire, USA. We manipulated bird predation by erecting exclosures around saplings and directly manipulated herbivory by removing herbivores. We also examined how climate modifies these interactions by replicating the experiment at three locations along an elevational gradient. Effects of bird predation were variable. Overall, mean arthropod biomass was 20% greater on saplings within bird exclosures than on controls (p&lt;0.05). The mean biomass of leaf‐chewing herbivores, primarily Lepidoptera larvae, was 25% greater within exclosures but not statistically different from controls. To a lesser degree, mean herbivore damage to foliage within exclosures exceeded that of controls but differences were not significant. We also did not detect significant treatment effects on sapling shoot growth. The high understory vegetation density relative to bird abundance, and low rate of herbivory during the study (mean 5% leaf area removed, controls), may have limited the ability of birds to affect sapling growth. Climate effects operated at multiple scales, resulting in a complex interplay of interactions within the food web. Regional synchrony of climatic conditions resulted in annual fluctuations in herbivore abundance and tree growth that were shared across elevations. At the same time, local environmental variation resulted in site differences in the plant, herbivore, and bird communities. These patterns resulted in a mosaic of top–down strengths across time and space, suggesting an overall pattern of limited effects of birds on plant growth, possibly interspersed with hotspots of trophic cascades.

Can the nutrient dynamics of a northern hardwood forest explain variation in its trophic structure?

Abstract Background/Question/Methods: A time series of Lepidoptera larvae (caterpillar) abundance and biomass in the northern hardwood forests of central New Hampshire, USA, shows large interannual fluctuations in aggregated caterpillar biomass (52-fold variation in mg caterpillars/ 8000 leaves) that were spatially correlated across a regional landscape. Primary production of these mature forests has not varied over this period, and many hundreds of Lepidoptera species share comparatively few host plants. Therefore, interannual changes in nutritional quality of even one host plant species may be capable of generating correlated population dynamics for many species in the Lepidoptera community. We tested the hypothesis that variation in soil nutrient availability influences foliar chemistry and ultimately produces a bottom-up force capable influencing the aggregated biomass of the forest's dominant herbivores. Results/Conclusions: Over a period of four years, measures of nutritional quality for herbivores in three of the forest's four dominant understory tree species (Acer saccharum, Acer pensylvanicum, and Viburnum alnifolium) displayed considerable variation that was consistent across the landscape. Foliar nitrogen (N) content and two metrics of secondary metabolite concentration—total phenolics and condensed tannin—all varied by up to 20% among years. Resin bag extracts of NH4+, NO2- /NO3- and PO4+ showed soil mineral nutrient availability displayed six-fold variation that was consistent with the pattern in foliar N, and a whole tree in situ fertilization experimental manipulation produced rapid effects on foliar chemistry. Finally, variation in the forewing lengths of free-flying moths showed an interannual concordance among species within the group of early season feeders that was also consistent with patterns in foliar quality—suggesting collections of species experience correlated variations in larval growth performance.