Maple Foliage Research Articles

Propagating Uncertainty in Predicting Individuals and Means Illustrated with Foliar Chemistry and Forest Biomass

Quantifying uncertainty is important to establishing the significance of comparisons, to making predictions with known confidence, and to identifying priorities for investment. However, uncertainty can be difficult to quantify correctly. While sampling error is commonly reported based on replicate measurements, the uncertainty in regression models used to estimate forest biomass from tree dimensions is commonly ignored and has sometimes been reported incorrectly, due either to lack of clarity in recommended procedures or to incentives to underestimate uncertainties. Even more rarely are the uncertainty in predicting individuals and the uncertainty in the mean both recognized for their contributions to overall uncertainty. In this paper, we demonstrate the effect of propagating these two sources of uncertainty using a simple example of calcium concentration of sugar maple foliage, which does not require regression, then the mass of foliage and calcium content of foliage, and finally an entire forest with multiple species and tissue types. The uncertainty due to predicting individuals is greater than the uncertainty in the mean for studies with few trees—up to 30 trees for foliar calcium concentration and 50 trees for foliar mass and calcium content in the data set we analyzed from the Hubbard Brook Experimental Forest. The most correct analysis will take both sources of uncertainty into account, but for practical purposes, country-level reports of uncertainty in carbon stocks can safely ignore the uncertainty in individuals, which becomes negligible with large enough numbers of trees. Ignoring the uncertainty in the mean will result in exaggerated confidence in estimates of forest biomass and carbon and nutrient contents.

Effects of larval host and natural microsporidian infection on adult life history traits of the forest tent caterpillar (Lepidoptera: Lasiocampidae).

Host affiliation and entomopathogenic infections play a major role in shaping population dynamics of the forest tent caterpillar (FTC), Malacosoma disstria Hübner (Lepidoptera: Lasiocampidae). The effect of these individual factors has been studied, but it is unknown whether interactions between these factors significantly impact FTC life history traits. In the laboratory, we investigated a tritrophic interaction among larval diet, larval microsporidian infection, and FTC life history traits. Larvae were reared on foliage of trembling aspen, Populus tremuloides Michx (Malpighiales: Salicaceae) or sugar maple, Acer saccharum Marshall (Sapindales: Sapindaceae), or an artificial diet. Natural levels of microsporidian infection were assessed through microscopy and categorized as none (0 spores), low (1-100 spores), or high (>100 spores). Microsporidian infection and larval diet individually, but not interactively, impacted FTC life history traits. Moths with high infection had smaller wings, but infection did not increase the probability of wing malformations. Wings of FTC reared on fresh maple foliage were significantly smaller, had a higher probability of wing malformation, and a lower likelihood of cocoon production than FTC reared on other diets, but displayed higher overall survival. While microsporidian infection did not influence FTC-diet interactions, we provide further evidence on how these main effects may individually contribute to shaping FTC adult life history traits, and, ultimately, cyclical population dynamics. Future research should consider how larval mortality, distinct infection levels, and geographical source of FTC populations affect this tritrophic interaction.

Rapid tannin profiling of tree fodders using untargeted mid-infrared spectroscopy and partial least squares regression

BackgroundThe presence of condensed tannins (CT) in tree fodders entails a series of productive, health and ecological benefits for ruminant nutrition. Current wet analytical methods employed for full CT characterisation are time and resource-consuming, thus limiting its applicability for silvopastoral systems. The development of quick, safe and robust analytical techniques to monitor CT’s full profile is crucial to suitably understand CT variability and biological activity, which would help to develop efficient evidence-based decision-making to maximise CT-derived benefits. The present study investigates the suitability of Fourier-transformed mid-infrared spectroscopy (MIR: 4000–550 cm−1) combined with multivariate analysis to determine CT concentration and structure (mean degree of polymerization—mDP, procyanidins:prodelphidins ratio—PC:PD and cis:trans ratio) in oak, field maple and goat willow foliage, using HCl:Butanol:Acetone:Iron (HBAI) and thiolysis-HPLC as reference methods.ResultsThe MIR spectra obtained were explored firstly using Principal Component Analysis, whereas multivariate calibration models were developed based on partial least-squares regression. MIR showed an excellent prediction capacity for the determination of PC:PD [coefficient of determination for prediction (R2P) = 0.96; ratio of prediction to deviation (RPD) = 5.26, range error ratio (RER) = 14.1] and cis:trans ratio (R2P = 0.95; RPD = 4.24; RER = 13.3); modest for CT quantification (HBAI: R2P = 0.92; RPD = 3.71; RER = 13.1; Thiolysis: R2P = 0.88; RPD = 2.80; RER = 11.5); and weak for mDP (R2P = 0.66; RPD = 1.86; RER = 7.16).ConclusionsMIR combined with chemometrics allowed to characterize the full CT profile of tree foliage rapidly, which would help to assess better plant ecology variability and to improve the nutritional management of ruminant livestock.

Chlorophyll fluorescence parameters, leaf traits and foliar chemistry of white oak and red maple trees in urban forest patches.

The provisioning of critical ecosystem services to cities of the eastern USA depends on the health and physiological function of trees in urban areas. Although we know that the urban environment may be stressful for trees planted in highly developed areas, it is not clear that trees in urban forest patches experience the same stressful environmental impacts. In this study, we examine chlorophyll fluorescence parameters, leaf traits, foliar nutrients and stable isotope signatures of urban forest patch trees compared with trees growing at reference forest sites, in order to characterize physiological response of these native tree species to the urban environment of three major cities arranged along a latitudinal gradient (New York, NY; Philadelphia, PA; Baltimore, MD). Overall, white oaks (Quercus alba L.) show more differences in chlorophyll fluorescence parameters and leaf traits by city and site type (urban vs reference) than red maples (Acer rubrum L.). The exceptions were δ13C and δ15N, which did not vary in white oak foliage but were significantly depleted (δ13C) and enriched (δ15N) in urban red maple foliage. Across all sites, red maples had higher thermal tolerance of photosynthesis (Tcrit) than white oaks, suggesting a greater ability to withstand temperature stress from the urban heat island effect and climate change. However, the highest average values of Tcrit were found in the Baltimore urban white oaks, suggesting that species suitability and response to the urban environment varies across a latitudinal gradient. Stomatal pore index (SPI) showed inter-specific differences, with red maple SPI being higher in urban trees, whereas white oak SPI was lower in urban trees. These results demonstrate that differences in native tree physiology occur between urban and reference forest patches, but they are site- and species-specific. Data on local site characteristics and tree species performance over time remain necessary to gain insight about urban woodland ecosystem function.

Impact of climate-related changes to the timing of autumn foliage colouration on tourism in Japan

This study introduces plant phenophase as a “bridge” to assessing the impact of climate change on autumn foliage viewing tourism in Japan. The results showed that from 1978 to 2016, the autumnal foliage colouration of four cities in Japan was delayed, the duration of the autumnal leaf discolouration was significantly shortened, and only one city experienced a significant delay in leaf-falling. The delay in the autumn foliage colouration and leaf-falling periods on average increase the December maple viewing tourism volume by 3.64% and 3.02%, respectively. The impact on autumn maple foliage viewing tourism volume also has a 1-year delay effect, and the maple foliage phenophase of different cities have significantly varied influence on maple foliage viewing tourism volume. Overall, the change in the timing of maple leaf discolouration has been advantageous to the Japanese maple tourism industry.

Long-Term Effects of Forest Liming on Soil, Soil Leachate, and Foliage Chemistry in Northern Pennsylvania

Sugar maple (Acer saccharum Marsh.) decline disease, decreased growth, and regeneration failure have been related to a low supply of Ca and Mg. There is increased interest in augmenting cation availability via liming, but there is little information on the amounts of lime required and the longevity of the lime treatment. A single application of 22.4 Mg ha-1 of dolomitic limestone in 1985 at four forested sites in Potter County, PA has shown that soil, soil water, and sugar maple foliage chemistry are significantly altered by liming and the changes in soils and foliage persist as long as 21-yr post-treatment. By 2001, only 3 kg ha-1 of lime remained undissolved while increases in exchangeable Ca and Mg, and pH continued through 2006 at depths up to 35 to 45 cm. Exchangeable Mn and Al concentrations were significantly reduced by lime application, though effects were slower to develop at deeper depths. Soil solution chemistry from 1996 was highly variable but reflected the changed soil nutrients. On limed plots, sugar maple foliage had elevated concentrations of Ca and Mg in 2006 samples, indicating the persistence of the lime treatment. Comparison of Ca/Al ratios in soil solution, soils, and foliage show inconsistencies from previous published risk thresholds. Species-specific thresholds of Ca and Mg availability in soil and foliage have better potential management application and should be more rigorously tested as stress indicators.

Analytical Study of Azadirachtin and 3-Tigloylazadirachtol Residues in Foliage and Phloem of Hardwood Tree Species by Liquid Chromatography–Electrospray Mass Spectrometry

A rapid and sensitive LC-ESI-MS method has been developed and validated for the quantitation of azadirachtin and 3-tigloylazadirachtol in deciduous tree matrices. The method involves automated extraction and simultaneous cleanup using an accelerated solvent technique with the matrix dispersed in solid phase over a layer of primary-secondary amine silica. The limits of quantification were 0.02 mg/kg for all matrices with the exception of Norway maple foliage (0.05 mg/kg). Validation at three levels (0.02, 0.1, and 1 mg/kg), demonstrated satisfactory recoveries (71-103%) with relative standard deviation <20%. Two in-source fragment ions were used for confirmation at levels above 0.1 mg/kg. Over a period of several months, quality control analyses showed the technique to be robust and effective in tracking the fate of these natural botanical insecticides following systemic injection into various tree species for control of invasive insect pest species such as the emerald ash borer and Asian longhorned beetle.

Air pollution and the changing biogeochemistry of northern forests

Industrialization has greatly affected the biogeochemistry of northern forests by increasing the atmospheric deposition of acid and nitrogen (N). In 1990, the US Congress amended the Clean Air Act to include tighter emissions regulations; this reduced acid deposition (by &gt;50% in this study), but did not effectively lower N deposition. Here, we demonstrate that since this legislation was enacted, there have been marked decreases in sulfur (−16%), calcium (−17%), and aluminum (−42%) concentrations in sugar maple (Acer saccharum) foliage across the Upper Great Lakes region of the US, signaling a declining influence of acid deposition. In contrast, N deposition has persistently been over 75% greater than the amount of N needed to offset annual plant N sequestration, creating increases in N availability and soil N leaching. Recent emissions regulations will reduce N deposition somewhat, but further increases in soil N availability and leaching are likely. Policy decisions regarding N deposition will have to weigh increased carbon storage against negative impacts on water quality and species diversity.

Long-term impact of liming on growth and vigor of northern hardwoods

Sugar maple (Acer saccharum Marsh.) is a keystone species in the northern hardwood forest, and decline episodes have negatively affected the growth and health of sugar maple in portions of its range over the past 50+ years. Crown health, growth, survival, and flower and seed production of sugar maple were negatively affected by a widespread decline event in the mid-1980s on the unglaciated Allegheny Plateau in northern Pennsylvania. A long-term liming study was initiated in 1985 to evaluate responses to a one-time application of 22.4 Mg·ha–1 of dolomitic limestone in four northern hardwood stands. Over the 23-year period ending in 2008, sugar maple basal area increment (BAINC) increased significantly (P ≤ 0.05) in limed plots from 1995 through 2008, whereas American beech (Fagus grandifolia Ehrh.) BAINC was unaffected. For black cherry (Prunus serotina Ehrh.), the third principal overstory species, BAINC and survival were reduced in limed plots compared with unlimed plots. Foliar Ca and Mg remained significantly higher in sugar maple foliage sampled 21 years after lime application, showing persistence of the lime effect. These results show long-term species-specific responses to lime application.

Host Plant Phenology Affects Performance of an Invasive Weevil,Phyllobius oblongus(Coleoptera: Curculionidae), in a Northern Hardwood Forest

We investigated how host plant phenology and plant species affected longevity, reproduction, and feeding behavior of an invasive weevil. Phyllobius oblongus L. (Coleoptera: Curculionidae) is common in northern hardwood forests of the Great Lakes Region. Adults emerge in spring, feed on foliage of woody understory plants, and oviposit in the soil. Preliminary data indicate that adults often feed on sugar maple, Acer saccharum Marshall, foliage early in the season, then feed on other species such as raspberry, Rubus spp. Whether this behavior reflects temporal changes in the quality of A. saccharum tissue or merely subsequent availability of later-season plants is unknown. We tested adult P. oblongus in laboratory assays using young (newly flushed) sugar maple foliage, old (2-3 wk postflush) sugar maple foliage, and raspberry foliage. Raspberry has indeterminate growth, thus always has young foliage available for herbivores. Survival, oviposition, and leaf consumption were recorded. In performance assays under no-choice conditions, mated pairs were provided one type of host foliage for the duration of their lives. In behavioral choice tests, all three host plants were provided simultaneously and leaf area consumption was compared. Adults survived longer on and consumed greater amounts of young maple and raspberry foliage than old maple foliage. P. oblongus preferred young maple foliage to old maple foliage early in the season, however, later in the growing season weevils showed less pronounced feeding preferences. These results suggest how leaf phenology, plant species composition, and feeding plasticity in host utilization may interact to affect P. oblongus population dynamics.

Performance of the invasive weevil Polydrusus sericeus is influenced by atmospheric CO2 and host species

Natural forest systems constitute a major portion of the world's land area, and are subject to the potentially negative effects of both global climate change and invasion by exotic insects. A suite of invasive weevils has become established in the northern hardwood forests of North America. How these insects will respond to increasing CO2 or O3 is unknown. The present study examined the effects of elevated atmospheric CO2 and O3 on the invasive weevil Polydrusus sericeus Schaller at the Aspen Free Air CO2 Enrichment (FACE) site near Rhinelander, Wisconsin. A performance assay was conducted in the laboratory during the summer of 2007 using mated pairs of P. sericeus fed a combination of aspen, birch and maple foliage. We recorded leaf area consumption, oviposition and adult longevity. We also conducted visual abundance surveys in the field from 2004 to 2007 on aspen and birch at Aspen FACE. Elevated CO2, but not O3, significantly affected P. sericeus performance. Female, but not male, longevity was reduced under elevated CO2. Polydrusus sericeus also produced fewer eggs under elevated CO2 conditions compared with ambient conditions. Adult P. sericeus strongly preferred birch over both aspen and maple, regardless of fumigation treatment. The effects of elevated CO2 on P. sericeus populations at Aspen FACE were minimal, and varied among years and host tree species. Polydrusus sericeus abundance was significantly greater on birch than aspen. Over the long term, elevated CO2 may reduce adult female longevity and fecundity of P. sericeus. Further studies are needed to evaluate how this information may scale to ecosystem impacts.

Impact of Host Tree on Forest Tent Caterpillar Performance and Offspring Overwintering Mortality

One of the most damaging insect pests in deciduous forests of North America is the forest tent caterpillar, Malacosoma disstria Hübner. It can feed on a variety of plants, but trembling aspen (Populus tremuloides Michaux) is its preferred host and sugar maple (Acer saccharum Marshall) serves as a secondary one in the northern part of its distribution. Because host plant characteristics influence insect performance and survival, we evaluated the impact of trembling aspen and sugar maple foliage on M. disstria performance. Host effects on insect cold hardiness and overwintering survival of offspring were also studied. Forest tent caterpillar reared on aspen leaves had a shorter development time, higher pupal weights and fecundity, and superior egg parameters (length and weight) compared with those reared on sugar maple leaves. Larvae from the two food treatments had low glucose levels during diapause, whereas glycerol content of insects reared on maple was significantly higher during diapause than larvae fed on aspen. Lower glycerol content may explain the higher overwinter mortality of pharate larvae from aspen-reared parents even though their supercooling points were as low as -36 degrees C. This study shows the influence of host plant on insect life history and the need to consider overwintering success and offspring performance in studies to understand and predict population growth and cycling.

Stem girdling manipulates leaf sugar concentrations and anthocyanin expression in sugar maple trees during autumn

To better understand the effects of sugar accumulation on red color development of foliage during autumn, we compared carbohydrate concentration, anthocyanin expression and xylem pressure potential of foliage on girdled versus non-girled (control) branches of 12 mature, open-grown sugar maple (Acer saccharum Marsh.) trees. Half of the study trees were known to exhibit mostly yellow foliar coloration and half historically displayed red coloration. Leaves from both girdled and control branches were harvested at peak color expression (i.e., little or no chlorophyll present). Disruption of phloem export by girdling increased foliar sucrose, glucose and fructose concentrations regardless of historical tree color patterns. Branch girdling also increased foliar anthocyanin expression from 50.4 to 66.7% in historically red trees and from 11.7 to 54.2% in historically yellow trees, the latter representing about a fivefold increase compared with control branches. Correlation analyses indicated a strong and consistent relationship between foliar red coloration and sugar concentrations, particularly glucose and fructose, in both girdled and control branches. Measures of xylem pressure potentials confirmed that girdling was a phloem-specific treatment and had no effect on water transport to distal leaves. Results indicate that stem girdling increased foliar sugar concentrations and enhanced anthocyanin expression during autumn in sugar maple foliage. Native environmental stresses (e.g., low autumn temperatures) that reduce phloem transport may promote similar physiological outcomes.

Use of foliar Ca/Sr discrimination and 87Sr/86Sr ratios to determine soil Ca sources to sugar maple foliage in a northern hardwood forest

Calcium/strontium and 87Sr/86Sr ratios in foliage can be used to determine the relative importance of different soil sources of Ca to vegetation, if the discrimination of Ca/Sr by the plant between nutrient sources and foliage is known. We compared these tracers in the foliage of sugar maple (Acer saccharum) to the exchange fraction and acid leaches of soil horizons at six study sites in the White Mountains of New Hampshire, USA. In a previous study, sugar maple was shown to discriminate for Ca compared to Sr in foliage formation by a factor of 1.14 ± 0.12. After accounting for the predicted 14% shift in Ca/Sr, foliar Ca/Sr and 87Sr/86Sr ratios closely match the values in the Oie horizon at each study site across a 3.6-fold variation in foliar Ca/Sr ratios. Newly weathered cations, for which the Ca/Sr and 87Sr/86Sr ratios are estimated from acid leaches of soils, can be ruled out as a major Ca source to current foliage. Within sites, the 87Sr/86Sr ratio of the soil exchange pool in the Oa horizon and in the 0–10 cm and 10–20 cm increments of the mineral soil are similar to the Oie horizon and sugar maple foliar values, suggesting a common source of Sr in all of the actively cycling pools, but providing no help in distinguishing among them as sources to foliage. The Ca/Sr ratio in the soil exchange pool, however, decreases significantly with depth, and based on this variation, the exchange pool below the forest floor can be excluded as a major Ca source to the current sugar maple foliage. This study confirms that internal recycling of Ca between litter, organic soil horizons and vegetation dominate annual uptake of Ca in northern hardwood ecosystems. Refinement of our understanding of Ca and Sr uptake and allocation in trees allows improvement in the use of Ca/Sr and 87Sr/86Sr ratios to trace Ca sources to plants.

Aerial dispersal and host plant selection by neonate Thyridopteryx ephemeraeformis (Lepidoptera: Psychidae)

Abstract. 1. Neonate evergreen bagworms, Thyridopteryx ephemeraeformis (Haworth) (Lepidoptera: Psychidae), disperse by dropping on a strand of silk, termed silking, and ballooning on the wind. Larvae construct silken bags with fragments of plant foliage. This species is highly polyphagous, feeding on more than 125 species of woody plants of 45 families. The larvae commonly infests juniper (Juniperus spp.) and arborvitae (Thuja spp.), but rarely feed on deciduous hosts such as maples. The hypothesis is proposed that polyphagy in T. ephemeraeformis is maintained by variation among larvae in dispersal behaviour, and time constraints on the opportunity to disperse, but patterns of host species preference result from a predisposition for larvae to settle on arborvitae and juniper but disperse from other hosts.2. Consistent with that hypothesis, laboratory experiments revealed: (a) starved larvae varied in their tendency to disperse from paper leaf models; (b) starved larvae readily silked only during their first day; (c) larvae became increasingly sedentary the longer they were exposed to plant foliage; (d) when provided with several opportunities to silk, larvae became sedentary after exposure to arborvitae foliage, but repeatedly silked after exposure to maple (Acer species) foliage or paper; and (e) larvae were less inclined to silk from foliage of arborvitae than from maple.3. Field experiments supported the hypothesis by demonstrating that: (a) neonates tended to disperse from maple leaves while larvae older than 1 day tended to settle and remain; and (b) neonates were less likely to disperse from arborvitae and juniper trees than from maples.

Photosynthetic and antioxidant enzyme responses of sugar maple and red maple seedlings to excess manganese in contrasting light environments.

Manganese (Mn) toxicity may be a significant constraint to forest health on acidic, non-glaciated soils. We hypothesised that sugar maple (Acer saccharum Marsh.) and red maple (Acer rubrum L.) seedlings differ in their tolerance to excess Mn, and that photosynthetic sensitivity to excess Mn is exacerbated at higher light intensities through photo-oxidative stress. To test these hypotheses, we assessed photosynthesis and antioxidant enzyme responses of sugar maple and red maple seedlings at variable Mn and light levels in a greenhouse study. In both species, high Mn treatments impaired photosynthetic function, particularly in high light conditions. Responses to Mn and light depended on the developmental stage of the leaves. All sugar maple leaves were sensitive to Mn toxicity except shaded young leaves. For red maple, only mature leaves exposed to high light were prone to Mn toxicity. Antioxidant enzyme and ФPSII / ФCO2 data suggested that photo-oxidative stress did not explain the observed photosynthetic responses to treatment variables. Our results indicate that in natural forest environments, sugar maple and red maple foliage exposed to high light intensity (outer canopy, canopy gaps) may be more prone to Mn toxicity.

Effects of prescribed fire on canopy foliar chemistry and suitability for an insect herbivore

We assessed the effects of a prescribed fire on the phytochemical characteristics and vigor of overstory chestnut oak, scarlet oak, and red maple, and measured the impact of potential changes on herbivore fitness. We compared foliar carbohydrates, tannins, nutrients, and fiber concentrations in foliage from burned and non-burned forest canopies. There were significant differences in most foliar characteristics between tree species. Total non-structural carbohydrate concentrations in scarlet oak and red maple foliage, and calcium levels in red maple foliage, were significantly lower in burned plots, but other phytochemical characteristics were largely unaffected by burning. Tree growth also varied with species. Burning increased chestnut oak relative growth, decreased scarlet oak growth, and had no affect on red maple growth. Scarlet oak and red maple foliage from burned and non-burned forest canopies were assayed for gypsy moth performance. Caterpillars fed foliage from scarlet oak, the preferred host, grew larger and developed more rapidly than did those fed red maple foliage. There were no significant burn treatment differences in caterpillar development within either tree species, suggesting that managers using prescribed fire to promote oak regeneration need not worry about enhancing forest stand susceptibility to gypsy moth. However, the fire in this study was of low to moderate intensity; more intense fires may alter foliar palatability.

Impacts of Ammonium Sulfate Treatment on the Foliar Chemistry of Forest Trees at the Bear Brook Watershed in Maine

Foliar chemistry was examined in mature sugar maple (Acer saccharum Marsh), red maple (Acer rubrum L.), American beech (Fagus grandifolia Ehrh.), and red spruce (Picea rubens Sarg.) in response to chronic, watershed-level additions of ammonium sulfate [(NH4)2SO4]. Following four years of treatment, N concentrations were significantly higher in foliage from the treated watershed for all four species, with increases ranging from 6% in American beech to 33% in sugar maple. Sugar maple foliage from the treated watershed had significantly lower Ca concentrations (18%). Concentrations of K were significantly lower in beech (13%) and red spruce (9%) from the treated watershed. Foliar Mg was not different between watersheds. Aluminum concentrations were significantly higher in the foliage from the treated watershed for beech (18%), red maple (33%), and sugar maple (65%), but no differences in Al concentration occurred in current year red spruce foliage. Red spruce foliage resampled following a fifth year of treatment contained higher concentrations of N and Al and lower concentrations of Ca and Mg in the treated watershed. Despite these differences in red spruce foliar chemistry, wood production and density did not appear to be affected by the treatment.

Food-chain chemistry, reproductive success, and foraging behaviour of songbirds in acidified maple forests of central Ontario

We examined the breeding success of two insectivorous bird species, the resident black-capped chickadee (Parus atricapillus) and the Neotropical migrant chestnut-sided warbler (Dendroica pensylvanica), in relation to food-chain chemistry at a healthy and a declining forest site in central Ontario, Canada. The health of sugar maples (Acer saccharum) was poorer and the pH of both soil and throughfall was lower at the declining site than at the healthy site. The calcium and magnesium concentrations and the calcium:aluminum ratio in the soil were also lower at the declining site than at the healthy site. The calcium, magnesium, and phosphorus concentrations and the calcium:aluminum ratio in sugar maple foliage were lower at the declining site than at the healthy site, indicating extensive acid leaching of the soil and foliage at the declining site. Caterpillars (Geometridae) at the declining site had a lower calcium concentration and beetles had a lower magnesium concentration than these groups at the healthy site. The calcium:aluminum ratios in the tissues of insects in both groups were lower at the declining site than at the healthy site, paralleling the foliar and soil chemical differences. There were, however, no differences in clutch or brood sizes, or percent hatch, for either bird species between the healthy and declining sites. Chickadees consistently foraged lower in the canopy at the declining site, a possible compensatory behaviourial response to canopy dieback and (or) lower food quality in the upper canopy.

Photostabilization of the botanical insecticide azadirachtin in the presence of lecithin as UV protectant

Abstract The phytochemical insecticide, azadirachtin (AZ), undergoes UV‐induced photodegradation. Using the isomer AZ‐A as a standard, its photochemical stability was studied with and without adding lecithin surfactant as a UV protectant. Standard solutions of pure AZ‐A and Margosan‐O® were prepared in methanol‐hexane with (AZ‐A:lecithin, 1:2 by weight) and without lecithin, applied separately onto glass plates and maple (Acer L.) foliage and exposed to radiant energy under controlled conditions. Noticeable photostabilization of AZ‐A was achieved in the samples containing lecithin compared to AZ‐A samples without the lecithin additive. First‐order kinetic evaluation of the data showed that the DTy50 (half‐life) and C (rate constant) values for AZ‐A with and without lecithin on glass plates were 5.68 d and 0.122, and 5.42 d and 0.128, respectively. The corresponding values for the Margosan‐0 formulation were 7.37 d and 0.094, and 6.24 d and 0.111. The DT50 and C values for the pure AZ‐A on maple foliage wi...