Low-vigor Trees Research Articles

The Relative Importance of Crown Position and Vigor in Determining the Growth and Mortality of Sugar Maple Trees

Abstract In northern hardwood forests, selection silviculture aims to remove low-vigor trees that are likely to die or grow slowly to increase the growth of the remaining high-vigor trees, particularly those afforded more exposure to direct light. However, few studies have quantified the relative importance of crown position and vigor in determining growth and mortality. In this article, we did so for the most common species, sugar maple (Acer saccharum Marsh.), and we quantified the difference in growth and mortality between each of four crown classes to determine whether fewer classes can be used to describe competition-related variation in growth. Our results show that mortality is primarily determined by vigor, competition reduces growth more than the defects used to assess vigor, and there is only a modest difference in growth between dominant and co-dominant trees, indicating that these two classes can be merged because they are effectively released, unlike trees that are surrounded by competitors. Based on these results, we conclude that stand improvement should not be prioritized over crown spacing, and that tree markers should release surrounded trees to whatever extent possible, including as many trees as possible and low-vigor trees where necessary. Study Implications: We identified three ways to balance stand improvement and crown spacing in selection-managed northern hardwood forests. First, tree markers should not only release high-vigor trees, but also low-vigor trees that will be retained. Second, tree markers should focus on releasing trees surrounded by competitors rather than dominant and co-dominant trees. Third, rather than maximizing lateral light exposure for a few select trees, tree markers should release trees to whatever extent possible, including as many trees as possible and low-vigor trees where necessary. Finally, we provide a heuristic method for classifying crown position and implementing our spacing recommendations.

Spatial patterns of vigor by stand density across species groups and its drivers in a pre-harvest ponderosa pine-dominated landscape in northern California

Information on spatial patterns of forest health and stand vigor in historical forests is quite limited, particularly for forests of North America, which have been subsequently harvested. We used forest inventory data from 1934, which pre-dated early 20th century timber harvest, to reconstruct patterns of vigor in overstory trees. Across 4,000 ha of ponderosa pine-dominated forests in the Blacks Mountain Experimental Forest (BMEF), we described the spatial patterns of pre-harvest (1934) forests using a stand density index (SDI) and accounting for different species and vigor classes. We then identified topo-edaphic variables associated with pre-harvest SDI. To do so, we first calculated SDI for two species groups: 1) ponderosa pine (Pinus ponderosa Laws.) and Jeffrey pine (Pinus jeffreyi Grev. & Balf.), and 2) incense-cedar (Calocedrus decurrens (Torr.) Florin) and white fir (Abies concolor (Grod. and Glend.)) as well as for seven vigor classes within these two groups. Second, using Moran’s I, we found four spatially aggregated clusters (Moran’s I = 0.35): 1) ponderosa pine-high vigor, 2) ponderosa pine-low vigor, 3) mixed species-high vigor, and 4) mixed species-low vigor. Most of the pre-harvest landscape consisted of high vigor ponderosa pine clusters with low SDI (relative density (RD) < 0.25). High elevation sections consisted of mixed species clusters of both high and low vigor with high SDI (RD > 0.35). Using classification and regression tree analysis, we identified elevation (m), surface-soil depth (cm), and sub-soil depth (cm) were related to the clusters. A multinominal logistic regression model (kappa = 0.44; classification accuracy = 64.4 %) identified surface stoniness, available water capacity at 150 cm depth and its interaction with sub-soil depth as important variables that were related to clusters. Within ponderosa pine-dominated forests, managers consider dense stands of low vigor trees to be at-risk of insect, disease, and fire. Thus, our results can be used by managers as representative baselines for characterizing (pre-harvest) stand conditions to guide management treatments to support high vigor and low density forest conditions.

A Study of Shoot Growth, Leaf Photosynthesis, and Nutrients in ‘Lingfengjing’ Litchi Grafted onto Seedlings of Different Cultivars

Litchi (Litchi chinensis Sonn.) is one of the important fruit crops in southern China. ‘Lingfengnuo’ (LFN) is a new late-maturing litchi variety which has gained great popularity among consumers and growers due to its high quality and reliable productivity. However, there has been limited research on the graft compatibility of LFN on different rootstocks, which is important for selecting the optimal rootstocks for propagation, and thus application of this new cultivar. In this study, LFN scions were grafted onto one-year-old seedlings from 13 cultivars including ‘Heiye’ (HY), ‘Shakeng’ (SK), ‘Hehuadahongli’ (HHDHL), ‘Maguili’ (MGL), ‘Xiaojinzhong’ (XJZ), ‘Huaizhi’ (HZ), ‘Chenzi’ (CZ), ‘Shangshuhuai’ (SSH), ‘Baitangying’ (BTY), ‘Shuangjianyuhebao’ (SJYHB), ‘Jingganghongnuo’ (JGHN), ‘Baila’ (BL), and ‘Shuidong’ (SD). Graft success, morphology of the graft joint, shoot growth, leaf photosynthetic rate, and nutrients were compared. Graft success was highest for XJZ, HZ, BL and JGHN. Tree vigor, reflected by flush growth, was highest for HZ, followed by JGHN and BTY, but weakest for HY, SD, SJYHB, and XJZ. The stem significantly swelled above the graft joint in trees with rootstocks of HY, SD, and SJYHB seedlings; however, this did not occur in XJZ. Leaf photosynthesis displayed a similar pattern to tree vigor, and was highest for HZ and lowest for HY, SD, and XJZ. These low vigor trees produced flowers the next year after grafting. The result suggested that HZ, JGHN, and BTY seedlings as rootstock are highly compatible with LFN, while those of HY, SD, and SJYHB are poorly compatible. Rootstocks did not significantly influence the leaf N, P, and Fe, but showed significant differences in other minerals. The leaf Ca, Mg, Zn and B were lowest in the trees graft onto HZ seedlings. Based on these results, HZ seedlings are recommended as the best rootstock for the propagation of LFN; however, a supply of Ca, Mg, B and Zn fertilizers a especially needed for LFN trees on HZ seedling rootstock.

Assessment of Ponderosa Pine Vigor Using Four-Band Aerial Imagery in South Central Oregon: Crown Objects to Landscapes

Ponderosa pine is an integral part of the forested landscape in the western US; it is the dominant tree species on landscapes that provide critical ecosystem services. Moderate drought tolerance allows it to occupy the transition zone between forests, open woodlands, and grasslands. Increases in stand density resulting from wildfire suppression, combined with lengthening, intensifying, and more frequent droughts have resulted in reduced tree vigor and stand health in dry ponderosa pine throughout its range. To address a management need for efficient landscape-level surveys of forest health, we used Random Forests to develop an object-oriented classification of individual tree crowns (ITCs) into vigor classes using existing, agency-acquired four-band aerial imagery. Classes of tree vigor were based on quantitative physiological and morphological attributes established in a previous study. We applied our model across a landscape dominated by ponderosa pine with a variety of forest treatments to assess their impacts on tree vigor and stand health. We found that stands that were both thinned and burned had the lowest proportion of low-vigor ITCs, and that stands treated before the 2014–2016 drought had lower proportions of low-vigor ITCs than stands treated more recently (2016). Upland stands had significantly higher proportions of low-vigor trees than lowland stands. Maps identifying the low-vigor ITCs would assist managers in identifying priority stands for treatment and marking trees for harvest or retention. These maps can be created using already available imagery and GIS software.

Relationships between Tree Vigor Indices and a Tree Classification System Based upon Apparent Stem Defects in Northern Hardwood Stands

Many northern hardwood stands include several low-vigor trees as a result of past management. To restore these degraded stands, partial cuts are applied with partly validated tree classification systems that are based upon apparent stem defects. We sampled 214 sugar maple (Acer saccharum Marsh.) and 84 yellow birch (Betula alleghaniensis Britt.) trees from six sites covering the northern hardwood forest zone of the Province of Quebec, Canada. We evaluated their vigor with a four-class system, and quantified the growth efficiency index and several indices that were based solely upon radial growth. The growth efficiency index increased non-significantly with increasing tree vigor class. The five-year basal area increment (BAI-1-5) was significantly different between the lowest and highest tree vigor classes. Yet, temporal changes in BAI-1-5 helped classify correctly only 16% of high-vigor trees that became poorly vigorous 8–10 years later. Overall, these results suggest that the tree classification system is weakly related to actual tree vigor and its application likely generates few significant gains in future stand vigor. Modifying and simplifying the tree vigor system must be considered to facilitate the tree marking process that is required to improve the vigor of degraded stands.

Appraisal of Urban Trees Using Twelve Valuation Formulas and Two Appraiser Groups

Monetary valuation using urban tree appraisals can be performed with formulas, a common practice in many countries. This study compares twelve parametric type formulas: Amenity Valuation of Tree and Woodlands (Helliwell), Standard Tree Evaluation Method (STEM), French Method, Italian Method, Tedesco, Norma Granada, Trunk Replacement Formula (CTLA), Burnley Method, Danish Method, Swiss Method, and two Chilean formulas used in Municipalities of Concepción, La Pintana, and Maipú (COPIMA Method), and Peñalolén Method. Formulas were then applied to 30 trees located in Santiago, Talca and Concepción, Chile. Researchers used eight appraisers divided into two groups, according to senior-level and junior-level experience. Statistical differences were determined using the Kruskal-Wallis test of non-parametric variance, while Fisher’s least significant difference test was used to identify homogeneous groups. The results show a wide dispersion of values that were high for “emblematic” trees and low for young or low-vigor trees. Formula, type of appraisers, and inter-appraiser differences formed nine, two, and three groups, respectively. The lowest-appraised trees were obtained using the Danish and French Method, while the highest values were obtained with the Burnley, Helliwell, and STEM formulas. Although there were differences in tree value according to the type of appraiser, when comparing difference among appraisers, researchers found these were not due to experience level. Given the wide range of values found, the study authors cannot recommend any specific formula(s) for assessing urban trees, as results will depend on the variables of interest used in the formulas and their intended application and use.

Fuel Properties of Sugar Maple and Yellow Birch Wood in Relation with Tree Vigor

The fuel properties of wood obtained from sugar maple (SM) and yellow birch (YB) of temperate hardwood stands located in the Province of Quebec, Canada were studied to see how tree vigor affects the chemical composition and calorific value of the wood. This study focused on the physical and chemical properties of wood with the aim of using the material for the production of solid biofuels. Specific items measured included the wood’s calorific values, and the levels of extractives, ash, and lignin. Changes in chemical composition were found among tree vigor classes. The low vigor trees had higher extractives, ash, and lignin contents than the vigorous trees. Total extractives ranged between 4.88 and 7.32% in SM, and between 3.35 and 5.12% in YB. Klason lignin ranged between 21.46 and 23.53% in SM, and between 18.60 and 21.51% in YB. Ash content ranged between 0.38 and 0.97% in SM, and between 0.26 and 0.47% in YB. The combined effects of higher lignin content that could contribute to a better self-bonding of particles and of higher extractives content that could facilitate the pelletization process makes the low vigor trees more suitable for conversion into solid biofuels. The higher amounts of extractives and lignin present in the low vigor sugar maple and yellow birch trees could also have a positive role in maintaining the high calorific values of this wood despite higher ash content.

Integrating standing value estimations into tree marking guidelines to meet wood supply objectives

The identification of low-vigor trees with potential for sawlog production is a key objective of tree marking guidelines used for partial cuts in northern hardwoods. The aim of this study was to measure the impact of various vigor-related defects on the monetary value of hardwoods. To achieve this, we sampled 64 sugar maple (Acer saccharum Marshall) and 32 yellow birch (Betula alleghaniensis Britton) trees from two locations in southern Quebec, Canada. We identified over 420 defects, which were grouped into 8 categories. The trees were then harvested and processed into lumber, and the value per unit volume of each stem was calculated from the value of the product assortment (lumber, chips, and sawdust). We found that visible evidence of fungal infections (sporocarps and (or) stroma) and cracks had the largest negative influence on value in both species. A model that included these defects was almost as good at predicting value as one that included a specifically designed quality classification. A more accurate assessment of value could be achieved using wood decay assessment tools and (or) by considering site-specific variables. Results from this study showed that visual identification of fungal infections and cracks could be used to enhance tree marking guidelines for hardwoods. This would meet both the silvicultural objective of selection cuts, by removing low-vigor trees, and the wood supply objective, by improving stem quality assessment prior to harvest.

Breeding Oil and Table Olives for Mechanical Harvesting in Spain

The olive (Olea europaea) and table olive industries worldwide are almost entirely supported by low-density rain-fed orchards planted with local cultivars empirically selected by farmers for centuries. New early and high-bearing plantation systems adapted to mechanical harvesting have been designed and developed during the past 50 years. Only certain traditional cultivars are well suited for these new olive plantations. The new orchards therefore require new cultivars. A long-term effort on the exploration, conservation, and sustainable use of olive genetic resources starting in Spain in 1970 has been followed by breeding programs developed since the early 1990s by the University of Cordoba, the University of Seville, and the Andalusia Institute for Agricultural, Food and Fisheries Research. We are trying to use crossbreeding to obtain new early bearing cultivars adapted to mechanically harvested orchards. Objectives related to shortening the juvenile period (JP) and developing early tests of selection, early bearing, high cropping, resistance to chief diseases (particularly verticillium wilt caused by Verticillium dahliae), industrial suitability, high oil content, diversity of olive oil composition for oil cultivars, and fruit size and quality for table olive are being pursued. Specific criteria for the adaptation of oil olive and table olive cultivars to mechanical harvesting, such as low-vigor trees with a compact growth habit, the force needed for fruit removal, natural fruit abscission, resistance to bruising, and extending the harvest time in cultivars showing homogeneous ripening are evaluated in the progenies. To date, more than 19,000 seedlings have been initially evaluated, 481 preselections are on intermediate field trials, and 31 advanced selections are being established in a network of field trials. A new protected cultivar Sikitita (Chiquitita in the United States), selected for very-high-density narrow hedgerows, was released in 2008. Recently, a first project on olive genomics is heralding the use of marker-assisted selection in the midterm phase of development. Cultivars adapted to the new mechanical harvest systems will be progressively released in the future.

Growth, yield and fruit quality of ‘Tropic Snow’ peach on size-controlling rootstocks under dry Mediterranean climates

A six-year trial was carried out to evaluate the vegetative and productive performance of low-chill, early-ripening ‘Tropic Snow’ peach grown on five peach×almond rootstocks, different for their vigor. The study was conducted in south-western Sicily using 45 V-trained peach trees planted in 2005 and grafted on GF677, the most common rootstock in Sicily, and four low-vigor rootstocks selected at the Department of Agricultural, Food and Environmental Sciences, University of Pisa, namely IS5/8 (Polluce), IS5/19 (Castore), IS5/23, and IS5/29. Trunk circumference, winter and summer pruning weight, total number and weight of fruits per tree, and major fruit quality traits were recorded starting at the 3rd leaf. After fruit harvest in the 5th leaf, irrigation was withheld during the dry summer period (July–September). All IS selections reduced trunk cross-sectional area (TCSA) and pruning weight compared to GF677, with IS5/23 reducing TCSA by 62% and Castore, Polluce and IS5/29 by 32% by the 8th leaf. Yield efficiency was inversely related to tree vigor, with IS5/23 inducing the highest increase over GF677. Trees on IS5/23 exhibited 24–28% reductions of crop load and yield, whereas only IS5/29 increased fruit size compared to GF677. Postharvest water deficit induced significant yield declines in GF677, IS5/29 and IS5/23 in the following year. Low-vigor trees on Castore, Polluce and IS5/23 were more sensitive to changes in stomatal conductance in terms of carbon fixation, performing better than trees on GF677 and IS5/29 under non-limiting water conditions. Only minor rootstock effects on fruit quality were observed, with IS5/23 reducing significantly the final grower's profit. Overall, all low-vigor rootstocks performed decently, and in particular IS5/29 exhibited a good compromise between growth reduction, yield and fruit size, whereas Castore and Polluce may represent valid alternatives to GF677 for early peach production in dry Mediterranean areas.

Improving tree selection for partial cutting through joint probability modelling of tree vigor and quality

Tree classification systems are generally designed to predict the supply of high-quality logs for the wood processing industries and to mark defective trees for removal with the aim of improving both the vigor and quality of future stands. Although these two objectives are generally inversely related, their joint consideration could enable the development of robust criteria for improved tree selection in partial cuttings of northern hardwood stands by targeting low-vigor (LV) trees of high quality (HQ). In this study, we used a copula approach to model the joint probability distribution of trees characterized by both vigor and quality, which accounts for the statistical dependence between the different classes of both classification systems. The relationships between the probability of occurrence of a tree in each joint category and tree diameter at breast height (DBH) were quite similar among the three studied species: yellow birch (Betula alleghaniensis Britt.), sugar maple (Acer saccharum Marsh.), and American beech (Fagus grandifolia Ehrh.). In particular, the probability of occurrence of LV–HQ trees was characterized by a parabolic curve with a maximum value attained at the mid-DBH range, whereas that of LV and low-quality (LQ) trees increased with increasing DBH. This suggests that instead of harvesting large and mostly LV–LQ trees, partial cutting should target smaller LV–HQ trees, so that the volume of harvested HQ trees would increase without compromising the silvicultural objective of improving the vigor of future stands.

Composition of ethanolic extracts of wood and bark from Acer saccharum and Betula alleghaniensis trees of different vigor classes

The forest populations of Acer saccharum Marsh and Betula alleghaniensis Britton of south west Québec contain a significant proportion of low vigor trees, which are prioritized for harvesting as part of a forest restoration plan. Ethanol extractions of bark and wood collected from vigorous and non-vigorous trees were performed in order to compare their chemical compositions and thus evaluate the potential of adding value to the processing of low-vigor trees. Two methods – maceration and ultrasound assisted solvent extractions – were applied. Total content of phenols, proanthocyanidins, hydroxycinnamic acids and flavonoids were determined in the extracts by spectrophotometric methods. Concentrations of selected triterpenes and sterols were evaluated by GC–MS. While some variation in extract yields, polyphenol and lipophilic content was detected between vigorous and non-vigorous trees, the overall composition of extracts remained similar across vigor classes. The two extraction methods yielded very similar results while the advantage of the ultrasound assisted method was a much shorter extraction time. Ultrasound assisted ethanolic extraction of potentially valuable compounds could therefore be considered as an option to add value to the processing of low vigor A. saccharum and B. alleghaniensis trees.

The Role of Autumn Infections in the Progression of Fire Blight Symptoms in Perennial Pear Branches.

The role of autumn infections in the progression of fire blight (caused by Erwinia amylovora) symptoms in perennial pear branches was studied in orchard-grown trees in Israel. The extent of symptom progression and the final length of fire blight cankers in perennial branches were variably affected by the vigor of the trees and the season of infection. Following spring infections, when all trees supported active shoot growth, fire blight symptoms progressed more rapidly and to longer distances in trees that exhibited high vigor (i.e., with numerous annual shoots on most terminal branches) than in low-vigor trees (i.e., few or no annual shoots on terminal branches). Irrespective of the vigor of the trees, the progression of fire blight symptoms in perennial branches ceased between mid-May and mid-July, and only a small proportion (0 to 14.2%) of the infections had invaded main limbs or trunks of trees. Progression of fire blight symptoms following autumn infections was related to the preceding summer (August to No-vember) shoot regrowth: in trees in which the shoots did not restore their growth in the summer, the rate of symptom progression in perennial branches was higher in trees with a low vigor than in those with a high vigor, whereas for those with summer regrowth the relationship between rates of symptom expression was reversed. Irrespective of the vigor group and of whether there was summer regrowth, symptoms in perennial branches continued to progress through the winter until the following spring. Most of the autumn infections (50 to 78.5%) that developed in susceptible trees had invaded main limbs or trunks of trees. The results of this study indicate that factors related to host phenology and physiology, rather than factors related to environmental influences (such as temperature), govern the extent, rate, and duration of fire blight progression in perennial pear branches. Furthermore, it turned out that autumn infections play a substantial role in fire blight epidemiology in Israel.

Modeling individual tree mortality for Austrian forest species

Individual tree mortality models were developed for the six major forest species of Austria: Norway spruce ( Picea abies), white fir ( Abies alba), European larch ( Larix decidua), Scots pine ( Pinus sylvestris), European beech ( Fagus silvatica), and oak ( Quercus spp.); a joint model for the remaining broadleaf species was also developed. Data came from 5-year remeasurements of the permanent plot network of the Austrian National Forest Inventory. Parameters of the logistic equation were estimated using maximum likelihood methods. For all species, we found the hyperbolic transformation of diameter ( D −1 ) to be highly significant in predicting the high mortality rates for small diameter trees and decreasing mortality rates for larger diameters. For spruce, a quadratic transformation in D was needed to accurately model the increase in mortality observed for large, low-vigor trees with diameter >70 cm, which resulted in a U-shaped distribution. Crown ratio was also consistently significant, except for oak. We likewise found basal-area-in-larger-trees ( BAL) to be a highly significant predictor of mortality rate for all species except fir and oak. Predicted mortality rate increases as the basal area in larger trees increases and as crown ratio decreases. The resulting logistic mortality model had the same general form for all species, with the signs of all parameters conforming to expectations. In general, chi-square statistics indicate that the most important variable is D −1, the second most important is crown ratio, and the third most important predictor is BAL. The relative importance of crown ratio appears to be greater for shade tolerant species (fir, beech, spruce) than for shade intolerant species (larch, Scots pine, oak). Examination of graphs of observed vs. predicted mortality rates reveals that the species-specific mortality models are all well behaved, and match the observed mortality rates quite well. The D −1 transformation is flexible, as can be seen by comparing the rather different mortality rates of larch and Scots pine. Predicted and observed mortality rates with respect to crown ratio are quite close to the observed mortality rates for all but the smallest crown ratios ( CR<20%), a class with very few observations. Finally, the logistic mortality models passed a validation test on independent data not used in parameter estimation. The key ingredient for obtaining a good mortality model is a data set that is both large and representative of the population under study, and the Austrian National Forest Inventory data satisfy both requirements.

COMPARISON OF PRUNING TECHNIQUES TO INVIGORATE LOW-VIGOR ALMOND TREES

Some precocious almond varieties often produce little vegetative growth once they reach full maturity. A pruning trial was established using 11 year old `Harvey' trees that were healthy but making little or no new growth. The four treatments were: 1) severe heading or dehorning trees to six foot in height (first year only), 2) heading one third of the tree for three years, 3) making 20 small heading cuts all over the tree each year, and 4) normal thinning cuts (or control). All heading treatments caused more shoot growth than did the conventional thinning cuts (or control). The dehorning treatment (#1) responded with the most vigorous growth but much lower yields during the next two years compared to the control (#4). Yields were comparable between the two treatments during years three to five however. The heading treatments #2 and #3 had comparable yields with the control by the second year. They also showed more shoot growth. Tree yields from treatment #2 tended to lag below treatment #3 and the control, even though they were statistically the same. This trend may indicate that three years of moderately severe pruning is too much. Treatment #3 may be the best technique for invigorating healthy low vigor trees while minimizing yield losses, but will be the most expensive.

Characteristics of high- and low-vigor lodgepole pine trees in old-growth stands.

Lodgepole pine (Pinus contorta var. latifolia Engelm.) trees in an old stand differed widely in appearance. Some appeared healthy, with deep crowns, high leaf areas, nearly conical-shaped crown tops, and branches with live needles extending well back from the tip. Others with similar-sized boles appeared to be in a state of decline, having much shallower crowns, lower leaf areas, crowns that were flattened at the top, and "tufted" branches with needles only near the ends of the branches. Ten trees, five each in these two apparent vigor classes, were selected from a one-hectare area of a mature stand. Trees in the two groups were found to have similar height, diameter at breast height, age, and total volume. As expected from the selection criteria, high-vigor trees had much deeper crowns (P = 0.01) and higher leaf areas (P = 0.10). The volume of heartwood in the bole was higher in the low-vigor trees (P = 0.08), and the volume of the sapwood was higher in the high-vigor trees (P = 0.13). Sapwood and heartwood ages were similar in both classes. This suggests that, in earlier years, low-vigor trees reached a larger volume, represented by the present heartwood, than did the high-vigor trees (i.e., the current vigor rankings are the reverse of what they had been). The ratio of sapwood volume to total leaf area was not significantly higher in the low-vigor trees (P = 0.24), although this ratio varied tenfold among the data. Results suggest that a physiological basis for assessing vigor involving leaf area, sapwood, heartwood, age, and incremental growth data would identify a continuum of response from high- to low-vigor trees rather than discrete groups based on visual appearance.

Effect of Natural Inbreeding on Variance Structure in Tests of Wind-Pollination Douglas-Fir Progenies

Abstract Studies of the mating habits of Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) have shown that wind-pollination families contain a small proportion of very slow-growing natural inbreds. The effect of these very small trees on means, variances, and variance ratios was evaluated for height and diameter in a 16-year-old plantation by systematically deleting from analyses the shortest individuals in wind-pollination (W) and diallel (D) progenies of six parent trees. The progenies were growing together in a common field test. The D population served as a control (no inbreds). The low-vigor trees in the W population type gave a downward bias to means and an upward bias to within-plot and family x block variance estimates. Amount of bias differed among W families. Before deletion, estimates of additive genetic variance and heritability for height in the W test were about one-third and one-sixth the estimates from the D test. Deleting the shortest 5 to 8% of the trees from the W population did not remove all the discrepancy, but it did result in much closer agreement between W and D tests. For the D test alone, deletion of the smallest trees had a negligible effect on estimates of additive genetic variance and heritability. For. Sci 34(1):102-118.

Attacks of Mountain Pine Beetle as Related to Tree Vigor of Ponderosa Pine

The relationship between tree vigor, measured as stem growth per unit of leaf area, and susceptibility to mountain pine beetle attacks was examined in a stocking-level experiment of ponderosa pine (Pinus ponderosa Laws.) in central Oregon. Vigor decreased as both tree density (basal area) and leaf area index increased. Low vigor trees were more often attacked by beetles than high vigor trees. Attacks increased below a vigor threshold of about 100 g of wood produced per square meter of leaf area per year, corresponding in this study to a basal area of 21 m 2 ha - or a leaf area index of 2.9 m 2 m -2. For management of ponderosa pine, maintaining vigor through thinning will reduce the risk of mountain pine beetle attacks. FOREST Sex. 29:395-402.

Carry Over Effect of Ethephon on Fruit Shape of ‘Delicious’ Apples1

Abstract (2-Chloroethyl)phosphonic acid (ethephon) applied to ‘Delicious’ apples before harvest to improve fruit quality can change fruit shape (length/diameter ratio) the next year. The change is magnified when ethephon follows a summer application of succinic acid-2,2-dhnethylhydrazide (SADH) and is most evident on low vigor trees.

Laboratory Rearing of the Lesser Peach Tree Borer, Synanthedon pictipes1, on Artificial Diets2, 3

The lesser peach tree borer, Synanthedon pictipes (Grote and Robinson), is a pest in low-vigor cherry trees in northern Wisconsin. Females oviposit especially in tree wounds, which are often produced by mechanical shakers or wind and storm damage. While investigating chemical and physical factors which influence female preference of wounds as ovipositional sites, and studying factors involved in early-instar feeding responses, a dependable daily emergence of adults was required. For this reason we began rearing the insect on artificial diets, and this note describes our laboratory culture techniques.