Age Classes Of Foliage Research Articles

Accuracy of Defoliation Estimates from Aerial and Ground Surveys in a Boreal Forest during an Outbreak of the Hemlock Looper, Lambdina fiscellaria (Guenée)

Annual estimates of defoliation are important tools for managing forest insect defoliators such as the hemlock looper, which feeds on conifer needles of all age classes. We tested the accuracy of defoliation classes obtained from aerial surveys by comparing them with ground-based estimates during a recent outbreak of this insect. We used an approach derived from the Fettes method to estimate defoliation on the current-year shoots as well as on the shoots of the four previous years. Defoliation on the current-year shoots provided accurate estimates of the overall defoliation and the strength of the relationship gradually decreasing for one-year-old to four-year-old foliage. The aerial survey provided accurate estimates of light and moderate defoliation during the first year of the outbreak, but accuracy was lower for both ends of the defoliation gradient and was much less reliable after the second year of the outbreak. All levels of defoliation were then observed in stands where defoliation had not been detected by an aerial survey. Cumulative defoliation on all age classes of foliage brings a new challenge to crews assigned to aerial survey programs. Ground-level defoliation estimates on the current-year shoots can help appraise the risk of tree mortality in the following year.

Leaf age and eCO2 both influence photosynthesis by increasing light harvesting in mature Eucalyptus tereticornis at EucFACE

Only a few previous studies have examined how photosynthetically active radiation absorptance, pigments and electron flow change in mature trees exposed to long-term increase in CO2 concentration. We investigated pigment concentrations, leaf optical properties and quantum yield of old and new leaves exposed to ambient (aCO2) and elevated (eCO2) CO2 treatments. Leaf absorptance was around 90% in E. tereticornis trees across both foliage age classes and CO2 treatments. New leaves had 15% higher quantum yield with increased absorptance within the blue spectrum than old leaves; while they reflected and transmitted more photons. In addition, young foliage had increased mass-based concentrations of chlorophyll and carotenoids; however, pigment concentrations were reduced when expressed on area-basis. Quantum yield was 9% higher in eCO2 than aCO2 across both foliage age classes. The CO2 effect was stronger in new leaves where the quantum yield was 17% higher in eCO2 than aCO2, but not different in old leaves between CO2 treatments. New leaves had higher transmittance of photons in eCO2 than aCO2, while there was no change in old leaves. Mass-based concentrations of chlorophyll and carotenoids were reduced in eCO2 compared to aCO2 while concentrations of anthocyanins were higher in response to CO2 treatment. There was a significant effect of Age x CO2 interaction on ratio a/b with larger eCO2-related reductions in old leaves (–5%) but no change in new leaves. Generally, new leaves were more efficient in utilizing the absorbed photons than old leaves, especially under eCO2 which resulted in more carbon fixation. This implies that leaves can adjust their light harvesting capacity to eCO2, particularly in younger leaves which have higher photosynthetic activity.

Evidence of a direct chemical plant defense role for maltol against spruce budworm

AbstractThis study examines the direct chemical defensive role of maltol, a previously identified secondary metabolite found in balsam fir, Abies balsamea (L.) Mill. (Pinaceae), that was detected during herbivory of spruce budworm, Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae). Although used extensively in many industries, in addition to being found in multiple plant species, its functional role in plants remains unknown. The objectives of this study were to quantify the amount of free maltol and its potential conjugated form, maltol glucoside, in various foliage age classes and to evaluate whether constitutive foliage levels of maltol have an impact on spruce budworm fitness in maltol supplementation assays. Gas chromatography–mass spectrometry (GC‐MS) analysis of balsam fir foliage showed that maltol is produced in all foliage age classes tested; however, concentrations were significantly higher in older foliage. Liquid chromatography–mass spectrometry–mass spectrometry (LC‐MS‐MS) analysis showed that maltol also exists in balsam fir in its glucosylated form, a unique discovery in conifers. Similar to maltol, maltol glucoside is also present in current and 1‐year‐old balsam fir foliage and in significantly higher concentration in older foliage. We investigated the impact of maltol‐treated diet on spruce budworm fitness. Maltol additions that reflected constitutive foliage concentrations caused a significant reduction in larval development rate and pupal mass, whereas higher concentrations were required to cause significant mortality. These results suggest that maltol may be an important component of a direct defense strategy in balsam fir against spruce budworm herbivory.

The impact of adhering to sustainable harvesting guidelines on the total photosynthetic capacity ofTaxus Canadensis

Foliage of Canada yew (Taxus canadensis Marsh.) is commercially harvested for extracting taxanes used in anticancer pharmaceutical products. According to New Brunswick harvesting guidelines, only the last three years growth from four out of every five branches should be harvested. A study conducted in the understory of mixedwoods and tolerant hardwoods in northwestern New Brunswick estimated the impact of harvesting foliage on net photosynthetic activity of the residual plant. Net photosynthesis was measured on foliage of current to five-years-old in June, July and August to determine the contribution of each foliage age class to the photosynthetic capacity of a 6-year-old branch segment. Total biomass of each internode age class (0 to 5 and ≥ 6-years-old) was measured to calculate the impact of tip harvesting on percentage of biomass removed and on photosynthetic capacity. When following New Brunswick harvesting guidelines, harvesting removed 15 to 17% of the last three years growth foliage which corresp...

Topkill and stem defects initiated during an uncontrolled spruce budworm outbreak on Cape Breton Island, Nova Scotia

Spruce budworm (SBW; Choristoneura fumiferana [Clem.]) defoliation begins at the top of the crown, and often results in leader death, loss of annual height growth or gradual top dieback, known as topkill. We used regression tree analysis to examine topkill incidences during a severe SBW outbreak in Nova Scotia, Canada in the 1970s–1980s that resulted in 60–100 per cent mortality of merchantable balsam fir (Abies balsamea (L.) Mill.) volume, and re-examined surviving trees for defects 25 years later. At the study outset in 1979, 4–6 years into the SBW outbreak, stand level topkill ranged from 40 to 88 per cent of trees and mean individual-tree topkill probability was 7, 52, 79 and 87 per cent on trees with ≤25, 26–75, 76–90 and 91–100 per cent total defoliation (all age classes of foliage). By 1987, the SBW outbreak had ended and mortality probability of trees was 12, 59, 85 and 98 per cent for classes of peak total defoliation of ≤25, 26–75, 76–90 or 91–100 per cent. Most mortality occurred following 6–8 years of defoliation, but topkill peaked after 4–6 years, indicating that topkill required less cumulative defoliation than death. When the plots were remeasured in 2012, 25 years later, 90 per cent of the surviving trees with documented topkill during the SBW outbreak had stem defects, of which 26 per cent were crooks, 53 per cent forks and 21 per cent sweeps. From 32 to 88 per cent of stem length was located above the point of the defect, resulting in the long-term downgrading of topkill-damaged logs.

Needle longevity of balsam fir is increased by defoliation by spruce budworm

Retention of 10–16-year-old balsam fir needles increased significantly with cumulative spruce budworm defoliation. Mean needle longevity on defoliated 50-year-old fir was almost double that for undefoliated 25-year-old fir. Conifers experiencing environmental change affecting photosynthetic capacity have been observed to compensate by adjusting foliage longevity and increasing retention of old foliage. Defoliation by spruce budworm [Choristoneura fumiferana (Clem.)] is one such change, therefore, it was hypothesized that conifers, such as balsam fir [Abies balsamea (L.) Mill.] may increase foliage life spans to compensate for losses of photosynthetic capacity to defoliation. Understanding foliage longevity is a key component of predicting foliage complement, which is the main driver of effects of defoliation on forest growth and productivity. Defoliation and needle loss were assessed on 16 age classes of foliage on mid-crown branches sampled from 134 mature balsam fir trees near Amqui and Causapscal, Quebec, and related to needle age and cumulative defoliation (summed annual defoliation from 2012 to 2016). A general linear mixed model fitted to the needle survivorship data accounted for 68% of the total deviance. The model interaction term of cumulative defoliation with foliage age indicated that for foliage ages less than about 9 years, increased cumulative defoliation resulted in lower needle survival, possibly because of backfeeding of spruce budworm on 5+-year-old foliage, while in the older age classes, needle survival increased with increasing cumulative defoliation. For the oldest, 11–16-year-old foliage age classes, 10–16% more foliage per age class was retained under severe defoliation than under light defoliation. As a result, median needle age increased from 9.5 to 10.4 years as cumulative defoliation increased from 0 to 500%. Mean needle longevity of 9.5 years for 50-year-old balsam fir with low defoliation observed in this study was considerably higher than the mean of 5.5 years previously observed for 22- to 27-year-old fir in Cape Breton, Nova Scotia. Such differences in needle longevity and retention would cause considerable differences in predictions of tree growth using foliage-based stand growth models.

Adaptive advantages of dietary mixing different‐aged foliage within conifers for a generalist defoliator

AbstractFew herbivores are well adapted to feeding on all foliage age classes available and most have evolved traits that are attuned to the characteristics of either developing or mature foliage; however, recent evidence has shown a number of insect herbivores that may mix different‐aged foliage as a means of enhancing fitness. We carried out a series of laboratory and field experiments to investigate whether larvae of Asian gypsy moth [L. umbrosa (Butler) = L. dispar hokkaidoensis Goldschmidt] (Lepidoptera: Lymantriidae) engage in and benefit from foliage‐age dietary mixing in common conifer species that naturally occur in its native range of Hokkaido, Japan. In a laboratory experiment, early instar larvae were observed on both developing and mature foliage when both age classes were available; however, larval survival and weight were highest on hosts with developing foliage available (larch, fir, and pine), whereas all larvae died on spruce where only mature foliage was available. In contrast, laboratory and field experiments indicated that late‐instar larvae often consumed both developing and mature foliage on all conifer species studied, although there was general preference bias towards mature foliage. Field bioassays indicated that late‐instar larvae provided both foliage age classes (a ‘mixed’ diet) had similar performance to those provided only developing or mature foliage. Results of this study indicate that larvae obtain limited performance benefits from mixing different foliage age‐classes into their diet, other than perhaps the benefits accrued from having a broader resource pool available on a single host tree.

Effect of limited water availability on foliar plant secondary metabolites of two Eucalyptus species

Plant secondary metabolites (PSMs) have many ecological roles such as influencing decomposition, flammability and herbivory. PSM concentrations are genetically determined, but are also affected by environmental factors. Drought periods are predicted to become more frequent in many regions, and may have widespread impacts on PSM-mediated ecological interactions. We used two dominant tree species to investigate the impact of multiple levels of water availability on leaf PSM concentrations. Juvenile Eucalyptus globulus and Eucalyptus viminalis plants were subjected to one of three glasshouse watering regimes (high [control], moderate or low water availability) and the effect on leaf PSMs was investigated between species, treatments, and within-plant foliage age classes. Moderate and low water availability decreased total phenolic concentrations of both species, and decreased the C:N of E. globulus leaves. Low water availability reduced the concentrations of two terpene compounds, but only in specific foliage age classes. Overall, the majority of terpenes were unaffected by decreased water availability, as were two formylated phloroglucinol compounds and condensed tannins. We conclude that water limitation had little impact on overall leaf PSM concentrations, and that juveniles of these two eucalypt species generally maintained PSM concentrations while plant growth declined, eluding to both direct impacts of water limitation and within-plant resource prioritization.

Spatial heterogeneity within an evergreen conifer promotes foliage-age dietary mixing by a specialist herbivore

Dietary mixing of different food items enhances the performance of many animals; however, few studies have tested the mechanisms influencing mixing within individual plants by herbivores. We investigated the mechanisms promoting apparent foliage-age dietary mixing by a specialist sawfly, Pikonema alaskensis (Roh.) (Hymenoptera: Tenthredinidae), within juvenile black spruce (Picea mariana (Mill.) B.S.P.). Field defoliation surveys indicated that larvae generally prefer developing foliage, and most defoliation occurs in the upper crown of trees. However, when upper-crown developing foliage becomes scarce, many larvae consume mature foliage in the upper crown rather than dispersing to lower branches, where preferred developing foliage remains abundant. Manipulative field experiments were conducted to compare the performance of early and late-instar larvae fed mixed versus individual age classes (i.e. developing or mature) of foliage in the upper and lower crown. In contrast to all past studies, foliage-age mixing by P. alaskensis was not associated with nutrient balancing or toxin dilution. Instead, mixing was associated with an expansion of feeding breadth in larvae as they developed, coupled with high levels of variation in resource quality between upper and lower crown levels, which enabled older larvae consuming mature foliage in the upper crown to achieve similar survival as those consuming developing foliage in the lower crown. Our study emphasizes the importance of considering spatial heterogeneity in studies of foliage-age preferenceeperformance relationships for herbivores within trees and demonstrates how a herbivore can use dietary mixing to dramatically expand its resources while simultaneously accounting for heterogeneity within large, architecturally complex plants. Crown Copyright 2010. Published on behalf of The Association for the Study of Animal Behaviour by Elsevier Ltd. All rights reserved.

Estimating cumulative defoliation of balsam fir from hemlock looper and balsam fir sawfly using aerial defoliation survey in western Newfoundland, Canada

Both hemlock looper (Lambdina fiscellaria fiscellaria (Guen.)) and balsam fir sawfly (Neodiprion abietis (Harris)) undergo periodic outbreaks in eastern Canada and cause significant growth and mortality losses to forests. Tree growth and mortality are closely related to cumulative defoliation estimates, which integrate annual defoliation over multiple years. Our objective was to determine a method to estimate cumulative defoliation of balsam fir (Abies balsamea [L.] Mill) due to these insects in western Newfoundland, using aerial defoliation survey data, as an essential input to modeling impacts for Decision Support Systems. Interpretation of aerial defoliation survey data for hemlock looper and balsam fir sawfly is problematic because both insects feed upon multiple age classes of foliage. Current-year (2008) aerial defoliation survey data were compared with ground estimates of defoliation by age class from 45 plots (450 trees and 395 mid-crown branch samples), representing a range of defoliation severity classes for each insect. Cumulative defoliation was calculated using defoliation per foliage age class, weighted by relative foliage mass for a given age of foliage. Three significantly different severity classes were defined based on cumulative defoliation values derived from aerial defoliation survey: (i) 1-year moderate (30–70%) defoliation, (ii) 1-year severe (71–100%) defoliation with calculated cumulative defoliation values of 19 and 39%, respectively, for balsam fir sawfly, 21 and 34% respectively for hemlock looper; and (iii) 2–3 years of moderate–severe defoliation, with cumulative defoliation ranging between 59 and 64% for balsam fir sawfly and 49% for hemlock looper. Defoliation severity from aerial defoliation survey alone hence can be misleading if defoliation measurements are not converted to cumulative defoliation values.

Foliage‐age mixing within balsam fir increases the fitness of a generalist caterpillar

Abstract.1. Manipulative field studies were carried out to evaluate the foliage age preference–performance relationship for an extreme generalist herbivore, the whitemarked tussock moth (Orygia leucostigma Smith) (Lepidoptera: Lymantriidae), within balsam fir [Abies balsamea (L.) Mill].2. Field surveys indicated that early instar caterpillars fed almost exclusively on young (i.e. current‐year) foliage, whereas late instars caterpillars fed on both young and mature (i.e. 1‐ and 2‐year‐old) foliage.3. Survival of early instar caterpillars was highest in treatments where current‐year and/or 1‐year old foliage were available, but decreased significantly on older foliage. In contrast, late instar caterpillars had the highest survival when allowed to feed on all age classes of foliage, whereas potential fecundity was highest for late instars that fed on young foliage.4. Overall, caterpillars had 32–65% higher fitness when able to feed on all rather than just one age class of foliage.5. These results support both the ‘complementary diet' hypothesis, which states that dietary mixing of different‐aged foliage can increase nutrient uptake and/or dilute harmful secondary plant chemicals, and the ‘ontogeny’ hypothesis, which attributes changes in diet to changes in the nutritional needs and/or tolerance to plant defences of juvenile insects as they develop.

Short-term effects of fertilization on photosynthesis and leaf morphology of field-grown loblolly pine following long-term exposure to elevated CO2 concentration

We examined effects of a first nitrogen (N) fertilizer application on upper-canopy needle morphology and gas exchange in approximately 20-m-tall loblolly pine (Pinus taeda L.) exposed to elevated carbon dioxide concentration ([CO(2)]) for 9 years. Duke Forest free-air CO(2) enrichment (FACE) plots were split and half of each ring fertilized with 112 kg ha(-1) elemental N applied in two applications in March and April 2005. Measurements of needle length (L), mass per unit area (LMA), N concentration (N(l)) on a mass and an area basis, light-saturated net photosynthesis per unit leaf area (A(a)) and per unit mass (A(m)), and leaf conductance (g(L)) began after the second fertilizer application in existing 1-year-old foliage (F(O)) and later in developing current-year first-flush (F(C1)) and current-year second-flush (F(C2)) foliage. Elevated [CO(2)] increased A(a) by 43 and 52% in F(O) and F(C1) foliage, respectively, but generally had no significant effect on any other parameter. Fertilization had little or no significant effect on L, LMA, A or g(L) in F(O) foliage; although N(l) was significantly higher in fertilized trees by midsummer. In contrast, fertilization resulted in large increases in L, N(l), and A in F(C1) and F(C2) foliage, increasing A(a) by about 20%. These results suggest that, although both needle age classes accumulate N following fertilization, they use it differently-current-year foliage incorporates N into photosynthetic machinery, whereas 1-year-old foliage serves as an N store. There were no significant interaction effects of elevated [CO(2)] and fertilization on A. Elevated [CO(2)] increased the intercept of the A:N(l) relationship but did not significantly affect the slope of the relationship in either foliage age class.

Seasonal Changes in the Concentration of Major Taxanes in the Biomass of Wild Canada Yew (Taxus canadensis. Marsh.)

Seasonal variations in taxane concentrations in Taxus canadensis. Marsh. (Canada yew) were measured at 15 sampling dates from September 2004 to September 2005 by clipping 3-year-old shoots from the same 15 plants. Four age classes of needles and stems were separated and individually weighed and analyzed for the three major taxanes in T. canadensis.: 10-deacetylbaccatin III (10-DAB III), 9-dihydro-13-acetylbaccatin III (9-DHAB III), and paclitaxel (PAC). The dry weight fraction of each foliage age class decreased with increasing age; that is, proportionately more young than old foliage (current > current + 1 year > current + 2 year) was present in a 3-year-old stem. The ratio of needle:stem dry weight also decreased with increasing foliage age. Taxane concentrations varied widely, depending on the tissue, its age, and time of year. Peak concentrations were observed for a short period at the end of the growing season (August–September). The lowest taxane levels were found during the period of active growth: April through July. PAC and 9-DHAB III concentrations were higher in needles, but young stems contained the highest amounts of 10-DAB III. Levels of all three taxanes were higher in young than in old stems, likely due to increasing amounts of taxane-poor stem wood. Composite taxane concentrations were calculated for 3-year-old foliage from the component needle and stem weights and taxane analyses. It is suggested that summer harvesting between April and July (the low point in annual taxane levels) yields the poorest quality biomass, and harvesting from August onward is preferable.

Sources of within- and between-stand variability in specific leaf area of three ecologically distinct conifer species

Specific leaf area (SLA) is an important ecophysiological variable, but its variability within and between stands has rarely been simultane- ously examined and modeled across multiple species. Extensive datasets on SLA in coastal Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco), hybrid spruce (Picea engelmannii Parry × Picea glauca (Moench) Voss × Picea sitchensis (Bong.) Carr.), and ponderosa pine (Pinus ponderosa Dougl. ex P. & C. Laws.) were used to estimate variability of SLA within a canopy and its relationship to tree- and stand-level covariates, and to predict SLA at various locations in tree crowns. Also, in the case of hybrid spruce, variation in SLA due to different relative horizontal lengths from the bole was examined. In all species, SLA systematically increased from tree tip to crown base and decreased with foliage age class. Cardinal direction did not have a highly significant influence in either Douglas-fir or hybrid spruce, but SLA did significantly decrease from branch tip to bole in hybrid spruce. Tree- and stand-level (e.g. density, site index) factors had relatively little influence on SLA, but stand age did have a significant positive influence .F or ponderosa pine, a significant relationship between canopy mean current-year SLA and carbon isotope discrimination was also found, suggesting the importance of water stress in this species. An equation was fitted to estimate SLA at various points in the canopy for each species and foliage age class using absolute height in the canopy, relative vertical height in the tree, and stand age.

Influence of Swiss needle cast on foliage age-class structure and vertical foliage distribution in Douglas-fir plantations in north coastal Oregon

Swiss needle cast (SNC) causes premature loss of foliage and subsequent growth decline in Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco). Although the mechanisms leading to this growth decline include loss of photosynthetic surface area and physiological disruption of surviving foliage, estimating the relative contribution of these two primary sources requires precise quantification of SNC effects on total foliage mass, foliage age-class structure, and vertical foliage distribution. The effect of SNC severity on these crown structural attributes was tested across a range of stand densities and site qualities in 10- to 60-year-old plantations in north coastal Oregon. Foliage mass in each age-class was sampled at the branch level, and the resulting equations were applied to all live branches on intensively measured sample trees. Vertical distribution of each foliage age-class was described by a beta distribution fitted to each sample tree, and sources of variation in vertical distribution were tested by regressing beta parameter estimates on SNC intensity and other covariates representing tree, stand, and site attributes. Distribution of foliage mass by age-class and by relative height in the crown was significantly affected by SNC severity, in addition to other covariates such as crown size and tree social position. SNC caused a reduction in the amount of foliage in each age-class and greater relative representation of younger needles. SNC also shifted the mode of relative vertical distribution toward the top of the tree for the three youngest foliage age-classes, but toward the base of the crown for 4- and 5-year-old foliage. Quantification of foliage age-class structure and vertical distribution across a range of SNC severity has helped to establish diagnostic criteria for assessing changes in crown structure that precede declines in growth and vigor. The induced changes in crown structure will also help to identify the relative contribution of several mechanisms causing growth losses in diseased trees.

Integrating within-crown variation in net photosynthesis in loblolly and slash pine families.

We examined photosynthetic characteristics of two fast- and two slow-growing half-sib families of both loblolly pine (Pinus taeda L.) and slash pine (Pinus elliottii var. elliottii Engelm.) on two sites in northern Florida to: (1) quantify variation in light-saturated net photosynthesis (Amax) associated with vertical crown position and foliage age; (2) quantify the amount and distribution of leaf area by foliage age class; and (3) determine whether photosynthetic indices, ranging from leaf-level through whole-crown Amax, were related to growth differences among species and families. In both species, leaf-level Amax was higher in more recently formed foliage both within the same year (where Amax in the third flush averaged 10 to 30% higher than Amax in the first flush) and between years (where Amax in current-year foliage averaged 20 to 40% higher than Amax in 1-year-old foliage). When expressed on a leaf area basis, Amax of current-year foliage was higher in slash pine than in loblolly pine, but Amax expressed on a mass basis did not differ between species. Loblolly pine had higher whole-tree leaf area than slash pine, whereas whole-tree Amax did not differ between species. When the mean values for fast-growing families were compared with the mean values for slow-growing families, there were no differences in leaf-level characteristics, whereas at the whole-tree level, fast-growing families had higher leaf area and whole-tree Amax than slow-growing families in both species. When comparisons were made among the individual fast- and slow-growing families, however, results were more variable. In both species, stem volume growth was strongly correlated with whole-tree Amax, with most of the strength of the correlation deriving from the relationship between volume growth and tree leaf area.

Development of gypsy moth larvae feeding on red maple saplings at elevated CO2 and temperature.

Predicted increases in atmospheric CO(2) and global mean temperature may alter important plant-insect associations due to the direct effects of temperature on insect development and the indirect effects of elevated temperature and CO(2) enrichment on phytochemicals important for insect success. We investigated the effects of CO(2) and temperature on the interaction between gypsy moth (Lymantria dispar L.) larvae and red maple (Acer rubrum L.) saplings by bagging first instar larvae within open-top chambers at four CO(2)/temperature treatments: (1) ambient temperature, ambient CO(2), (2) ambient temperature, elevated CO(2) (+300 microl l(-1) CO(2)), (3) elevated temperature (+3.5 degrees C), ambient CO(2), and (4) elevated temperature, elevated CO(2). Larvae were reared to pupation and leaf samples taken biweekly to determine levels of total N, water, non-structural carbohydrates, and an estimate of defensive phenolic compounds in three age classes of foliage: (1) immature, (2) mid-mature and (3) mature. Elevated growth temperature marginally reduced (P <0.1) leaf N and significantly reduced ( P <0.05) leaf water across CO(2) treatments in mature leaves, whereas leaves grown at elevated CO(2) concentration had a significant decrease in leaf N and a significant increase in the ratio of starch:N and total non-structural carbohydrates:N. Leaf N and water decreased and starch:N and total non-structural carbohydrates:N ratios increased as leaves aged. Phenolics were unaffected by CO(2) or temperature treatment. There were no interactive effects of CO(2) and temperature on any phytochemical measure. Gypsy moth larvae reached pupation earlier at the elevated temperature (female =8 days, P <0.07; male =7.5 days, P <0.03), whereas mortality and pupal fresh weight of insects were unrelated to either CO(2), temperature or their interaction. Our data show that CO(2) or temperature-induced alterations in leaf constituents had no effect on insect performance; instead, the long-term exposure to a 3.5 degrees C increase in temperature shortened insect development but had no effect on pupal weight. It appears that in some tree-herbivorous insect systems the direct effects of an increased global mean temperature may have greater consequences for altering plant-insect interactions than the indirect effects of an increased temperature or CO(2) concentration on leaf constituents.

Growth recovery in young, plantation white spruce following artificial defoliation and pruning

Defoliation by the spruce budworm (Choristoneura fumiferana (Clem.)) was simulated by artificially defoliating trees in a plantation of 12-year-old white spruce (Picea glauca (Moench) Voss) over a 2-year period and then allowing the trees to recover for 3 years. Four treatments were applied: control (C); removal of 50% of the current-year foliage (50); removal of all current-year shoots (100P); and removal of all current-year shoots and some older foliage age-classes (100P+). All treatments increased shoot production. Trees in the 100P treatment completely recovered their foliage mass after 1 year, but trees in the 50 treatment were still affected after 3 years of recovery. Trees in the 100P+ treatment showed poor recovery rates in foliage mass. Only the trees in the 50 treatment completely recovered height growth. After 2 years of defoliation, specific volume increment was reduced by 21.3, 58.1, and 75.3% for the 50, 100P, and 100P+ treatments, respectively. After 3 years of recovery, specific volume increment in the 50 treatment recovered completely, while the 100P and 100P+ treatments were reduced by 34.2 and 79.9%, respectively. Because of the release of suppressed buds following both needle loss only and shoot loss, white spruce may be a reforestation candidate for areas having a high probability of budworm outbreaks.

Advantages of a mixed diet: feeding on several foliar age classes increases the performance of a specialist insect herbivore.

Two field studies were carried out to determine the influence of Abies balsamea foliage age on the preference and performance of larvae of Neodiprion abietis, a specialist Diprionid sawfly. Preference was determined by examining N. abietis defoliation on all age classes of foliage. Performance was estimated using larval survival, cocoon weights and the percentage of adults that were females. Neodiprion abietis preference for, and performance on, current-year foliage was very low, peaked on 2 or 3-year-old foliage, and declined on older foliage. Thus, sawfly feeding preference was adaptive. However, survival and cocoon weight were highest when sawflies were allowed to feed on all age classes of foliage, demonstrating that an insect specialist may perform better when feeding on several age classes of foliage from a single host plant species. These results indicate that either different larval instars have different nutritional requirements, or that food mixing provides the best diet, permitting the herbivore to obtain needed nutrients while avoiding ingestion of toxic doses of secondary metabolites. In addition, our results suggest that limited availability of varied foliage has more negative consequences for N. abietis females than for males, as the percentage of survivors that were females decreased when juvenile mortality was high. Our results emphasize the importance of considering non-linear changes in foliar quality as leaves age on herbivore preference and performance, and demonstrate how a herbivore can use this variability to maximize its fitness.

Application of response surface methodology and ANOVA to detect pollution effects on photosynthetic response under varying temperature and light regimes

Studies of air pollution effects on plant physiological responses to diurnal changes in environmental conditions are complex, and thus, require efficient statistical design and valid data analysis. Here, we aim at demonstrating the use of a response-surface methodology (RSM) including least square regression and canonical analyses in combination with a two-way ANOVA to quantify net photosynthetic ( A n) response of ponderosa pine ( Pinus ponderosa Dougl. ex Laws) seedlings to different levels of rain acidity, ozone, temperature, and light conditions. Seedlings were exposed to four combinations of two rain (pH 5.1 and 3) and two ozone (ambient, and twice-ambient) regimes. The rain treatment was applied to foliage only on a weekly basis from January to April 1992. The ozone treatment was applied from September 1991 to November 1992. A n responses of current- and 1-year-old foliage to nine combinations of three temperatures (18, 25, 32°C) and three light regimes (250, 500, 1000 μmol photons m −2 s −1) were measured between 0800 and 1900 h from 18 August to 7 September 1992. A completely randomized design, replicated twice, was used for the assignment of rain-by-ozone combinations (main plots). Foliage age classes were sub-plots within the main plots, temperature levels were sub-plots within foliage age classes, and light levels were sub-plots within temperature levels. Response surface models of A n response to temperature and light levels were constructed per rain-by-ozone combination for each foliage age. β Temp, β Temp 2 , β Light, A n mean , A n max , temperature at A n max , and light at A n max were calculated or estimated. The effects of rain pH and ozone on these variables were then quantified using a two-way ANOVA. No significant rain-by-ozone or ozone effect was detected for any response. Rain of pH 3 decreased A n mean in current-year foliage only.