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Fraxinus nigra Marsh. (black ash), a dominant tree species of wetland forests in northern Minnesota, USA, is imperiled by the invasive insect emerald ash borer (EAB; Agrilus planipennis Fairmaire, 1888). Regeneration of associated tree species is generally low in F. nigra forests and could be impacted further by climate change. Proactive management may be critical to maintaining tree cover and ecosystem function following EAB invasion. We investigated the mean height and diameter relative growth rate (RGR) of seedlings of 10 potential replacement tree species, including two from the next southern climate zone projected to be adapted to the future northern Minnesota climate. Seedlings were planted in F. nigra wetlands under four canopy treatments: unharvested control, clearcut, girdling F. nigra to emulate EAB-induced mortality, and group selection. Mean height and diameter RGR was fastest overall in the clearcut treatment, followed by the girdling, group selection, and control treatments. Depending on species, treatment significantly influenced RGR. Several species projected to be adapted to the future northern Minnesota climate had moderate to rapid mean RGR, including one from the next southern climate zone. Our results suggest that seedling plantings and overstory treatment represent an effective strategy for establishing F. nigra replacement tree species as EAB approaches, while reducing future risk from climate change.

As global climatic changes increase plant susceptibility to large-scale disturbances such as drought and pathogens, understory responses to these disturbances will become increasingly important to long-term forest dynamics. To better understand understory responses to canopy disturbance, we measured changes in the growth and physiology of the dominant understory shrub, American witch-hazel (Hamamelis virginiana L.), in response to girdling of canopy oaks in a temperate hardwood forest of the northeastern United States. Changes in the growth and physiology of H. virginiana may be important to the regeneration of northeastern temperate forests, as this common shrub largely shapes the microenvironment for seedlings on the forest floor where it occurs. Canopy disturbance by girdling resulted in significant increases in light and soil nitrogen availability. In response to these environmental changes, basal-area growth of H. virginiana increased by an average 334%. This growth increase corresponded to significant increases in foliar nitrogen, respiration, and leaf chlorophyll and carotenoid concentrations. These findings indicate improved environmental conditions and increased growth for this understory shrub following the loss of dominant canopy trees. This study suggests that following large-scale canopy disturbance, H. virginiana and shrubs like it may play an important role in competing for soil N and shading seedlings of regenerating canopy species.

To investigate the effects of girdling on the water relation of trees, we measured a number of water-status parameters and morphological features following trunk and branch girdling of Chamaecyparis pisifera Siebold & Zucc. Girdling caused a marked reduction in the water-conduction area of the trunk cross section at the girdled part. Some girdled trees generated intense acoustic emissions (AE), simultaneously decreased leaf water potentials (LWP), and then died within 1 year. However, others lived for more than 2 years after girdling. In these survivors, the water-conduction area of the trunk cross section was reduced but not entirely blocked, and LWP decreases did not occur. Consequently, we conclude that girdling affects xylem water conductivity and sometimes causes short-term (within 1 year) tree death by blocking water uptake from soil to leaves. The results of this study on whether tree death from girdling occurs sooner or later could be important in the use of girdling for thinning management.

Black ash wetlands are seriously threatened because of the invasive emerald ash borer (EAB). Wetland hydrology is likely to be modified following ash mortality, but the magnitude of hydrological impact following loss via EAB and alternative mitigation harvests is not clear. Our objective was to assess the water table response to simulated EAB and harvesting to determine if management actions will be needed to maintain ecosystem functions following EAB infestation. We applied four replicated treatments to 1.6 ha plots as follows: (1) control, (2) girdling of all black ash trees to simulate loss via EAB mortality, (3) group selection harvests (20% of stand in 0.04 ha gaps), and (4) clear-cut harvest. Water table (WT) elevations were monitored for 1 year pre-treatment and two years post-treatment. Clear-cutting delayed WT drawdown in both years of the study, and the WT was significantly higher than the control treatment, predominantly when WT depth was below 30 cm. The effect of the group selection treatment on WT response was muted compared to clear-cutting and also limited to periods when the WT depth was below 30 cm. These responses were attributed to establishment of shallow-rooted vegetation in cut areas, which would have limited influence on WT dynamics as depth increased. There was little effect of girdling on the WT in the first year post-treatment, but effects on the WT were very similar to clear-cutting in the second year and more pronounced when the WT was within 30 cm of the soil surface. These effects were attributed to reduced transpiration coupled with the presence of a partial canopy following girdling, which would have reduced vegetation establishment and evaporation compared to clear-cutting. Given the large influence of WT depth on vegetation dynamics and associated feedbacks to altered hydrology, these early results indicate a greater risk of ecosystem alteration following EAB mortality compared to clear-cut harvesting. Depending on local hydrologic regime, variation in precipitation patterns, and time for complete canopy loss, it may be necessary for managers to implement active mitigation strategies (e.g., group selection coupled with planting of alternative species) prior to EAB infestation to maintain ecosystem processes in these forested wetland systems.

Ringbarking is a girdling technique that is used prior to timber harvesting to reduce losses to Armillaria root disease in some parts of the world. The technique had not previously been evaluated in British Columbia, Canada. Small plots of primarily Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees that were ringbarked prior to timber harvesting had approximately 50% lower levels of Armillaria root disease caused tree mortality in young trees after 15 years than plots of trees that were not ringbarked. Ringbarking did not reduce Armillaria root disease in this trial as much as has been reported in other research. This could be attributable to the centre of the small plots being within 5–10 m of live and dead Armillaria-infected trees in the surrounding forest. The treatment did reduce the severity of the disease by both statistically and biologically significant amounts and, therefore, warrants further investigation as a possible treatment where timber harvesting is conducted in Armillaria root disease affected stands.

We assessed the effectiveness of different management strategies against the non-native invasive tree species black cherry ( Prunus serotina Ehrh.). The species causes substantial management problems in European forest ecosystems, like the Valle del Ticino Biosphere Reserve in Italy, by suppressing the regeneration of native tree species. This can modify ecological key processes and cause biodiversity loss. Since chemical and biological control has mainly been abandoned in European forest ecosystem management, mechanical control measures are presently the preferred option to proceed against the black cherry but have shown very limited results in the reserve. The aim was to control the success of felling the species and to test other mechanical control methods such as girdling and snapping the trees with regard to their efficiency by quantifying the species’ growth reactions. For this purpose, observational studies were conducted in two forest stands of which one was treated in 1996 and the other more recently in 2009. A subsample of resprouting stumps was treated a second time in 2010 to observe the effect of a direct second cutback. An experimental study was implemented in a third forest stand also in 2010 to compare three different mechanical control methods. The results suggest that felling black cherry is ineffective if the objective is to reduce the species’ abundance because resprouts occur on 100% of the treated trees and biomass increment is not reduced in the long term. Girdling proved to be the most effective treatment across the diameter classes considered.

The emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is a devastating, invasive insect pest of ash trees, Fraxinus spp., in North America. Using a simulation model, we evaluated three potential management options to slow the spread of A. planipennis in discrete outlier sites: (i) removing ash trees to reduce available host phloem resource, (ii) girdling ash trees to attract ovipositing female beetles and destroying the trees before larvae complete devel- opment, and (iii) applying a highly effective systemic insecticide. Simulations indicate that systemic insecticide applica- tions provided the greatest reduction in the radial spread of A. planipennis. In simulations in which management options were applied only within a 300 m radius from the origin of the infestation, insecticide applications reduced the radial spread by 30% and larval consumption of ash phloem by 40% beyond the treated area. In contrast, girdling ash trees re- duced the radial spread by 15% and larval consumption of ash phloem by 20% beyond the treated area. Both of these management options significantly reduced the spread of A. planipennis when treatments were applied 1 to 4 years after in- festations were initiated. Reducing ash phloem by removing ash trees decreased population size within treated areas but did not reduce the radial spread, population size, or larval consumption of ash phloem beyond treated areas. Resume´ : L'agrile du frene, Agrilus plenipennis Fairmaire (coleoptere, buprestides), est un insecte nuisible envahissant qui est devastateur pour le frene, Fraxinus spp., en Amerique du Nord. Al'aide d'un modele de simulation, nous avons evalue ´

New infestations of emerald ash borer, Agrilus planipennis Fairmaire, an invasive pest native to Asia, are difficult to detect until densities build and symptoms appear on affected ash ( Fraxinus spp). We compared the attraction of A. planipennis to ash trees stressed by girdling (bark and phloem removed from a 15 cm wide band around the tree (2003–2005)), vertical wounding (same area of bark and phloem removed in a vertical strip (2004)), herbicide treatment (Pathway applied with a Hypo-Hatchet tree injector (2003) or basal bark application of Garlon 4 (2004, 2005)), exposure to the volatile stress elicitor methyl jasmonate (2005), or left untreated (2003–2005). The number and density of captured adults and density of larvae were recorded for 24, 18, and 18 replicates of each treatment at four, three, and five sites in 2003, 2004, and 2005, respectively. Girdled trees generally captured more adult A. planipennis and consistently had higher larval densities than untreated trees, and at most sites, than trees stressed by other treatments. Differential attraction to girdled trees was more pronounced at sites with lower densities of A. planipennis. Rates of capture of adults and densities of larvae were higher on trees in full or nearly full sun than on shaded trees. Girdled trees could be a useful tool for use in operational programs to detect or manage localized A. planipennis infestations.

We studied flower stimulation in two young miniaturized seed orchards of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) in Oregon. In experiment 1, female and male flowering were substantially enhanced when the trees were treated 2–4 years after grafting with stem girdling plus stem-injected gibberellin A4/7 (GA 0.25× rate = ProCone(tm) at 0.084 µL·mm–2 scion cross-sectional area). Comparable results were obtained the following year when the same trees were retreated with 1× GA. In experiment 2, female and male flowering were significantly enhanced when 3-year-old trees were treated with girdling plus either 1× GA, 1.5× GA, or 2× GA. Some treatments had higher mortality and less height growth than the control in the year of cone development. We recommend using a combination of girdling and 1× GA biennially once trees are large enough to produce large per-hectare seed yields and withstand the stress of flower stimulation. At the study orchards, this seems to be about 5 years postgrafting, just before the sixth growing season. Yields were estimated to be 272 963 seeds·ha–1 at age 4 years, or 143 095 seeds·ha–1 annually with stimulation occurring every 2 years. Yields should increase as orchards age, with full stocking, and with higher planting densities.

Broadleaf trees are routinely removed from conifer plantations during vegetation management treatments, but whether the removal increases tree productivity or affects root disease and plant diversity is unknown. The effects of manual and chemical reduction of paper birch (Betula papyrifera Marsh.) and trembling aspen (Populus tremuloides Michx.) on conifer survival, growth, root disease incidence, and plant community diversity were investigated for 5 years in Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) and lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) plantations in southern interior British Columbia. Broadleaves were reduced by manual, girdling, and cut-stump glyphosate treatments for 5 years but most severely following cut-stump glyphosate and with a delay due to slow death following girdling. Conifer survival was reduced for 3–5 years following manual cutting or girdling of birch because of a 1.5- to 4-fold increase in mortality due to Armillaria ostoyae (Romagn.) Herink, but this did not occur following cut-stump glyphosate treatment of birch or manual cutting of aspen. Conifer diameter increased with treatment intensity and productivity of the vegetation complex. Competition thresholds were identified for diameter but not survival, although Armillaria-caused mortality tended to increase near the minimum growth threshold. Structural diversity increased following manual cutting and cut-stump glyphosate because birch dominants were removed and understory layers increased, but species richness and diversity were unaffected. Forest managers can expect increased conifer growth with birch removal but also small increases in mortality due to Armillaria ostoyae root disease following manual treatments and loss of large birch trees in all treatments.

Controlled, localized heating was applied to the trunks of young Aleppo pines (Pinushalepensis Mill.) during the winter. Three levels of burning were applied to the circumference of the trunks (zero, partial, or total), and the effects on tree physiology and growth were monitored during the 7 months following heating. Effects of the heat treatment on tree physiology were assessed by measuring predawn water potential, sap flux density, microvariations in trunk diameter, electrical resistance of the cambium, and gas exchanges from the needles (photosynthesis and stomatal conductance). Morphological response measurements included height and radial growth of the trees and morphological characteristics of the needles. The amount of chlorotic foliage was also measured. Aleppo pine was highly resistant to trunk injury, surviving when 80% of the trunk circumference was destroyed by fire. The behaviour of partially burnt pines was not significantly different from that of controls, for all variables studied. Trees whose trunks were totally burnt died from 1 to 5 months after treatment. Sap flux density of totally burnt trees was already significantly lower than that of other trees in the first week following the treatment. A decrease in net photosynthesis and stomatal conductance in the still surviving totally burnt trees was also recorded during the first measurements made in July. Treatment differences in predawn water potential, microvariations in trunk diameter, and electrical resistance of the cambium only appeared a few days before death of the totally burnt trees.

Field-grown European larch (Larixdecidua Mill.) and Japanese larch (Larixkaempferi (Lamb.) Carr.) grafts were treated with main-stem girdling applied with or without injection of gibberellin A4/7 (GA4/7). The level of female coning was low in the untreated trees and was significantly increased by girdling; the mean number of seed cones per tree, on trees receiving girdling alone, was 71 for the European larch and 50 for the Japanese larch. There was considerable male flowering on the untreated trees, (701 and 1208 cones per tree on the European and Japanese larch, respectively), and on trees receiving girdling alone there were 1356 pollen cones per tree on the European larch, and 2035 on the Japanese larch, representing increases of 94 and 68%, respectively, compared with the untreated trees. The overall girdling effect on male flowering, however, was not statistically significant for either species. GA4/7 application produced no significant increases in coning, and in fact fewer pollen cones were observed on GA4/7-treated grafts than on grafts without GA4/7. Between 6 and 12% of the pollen-cone buds on untreated trees did not flush successfully, and the GA4/7 application significantly increased this proportion of unflushed buds. Girdling is an easy and effective treatment to increase female coning of European and Japanese larch and may also result in increases in pollen cones; thus, it would be a useful treatment to assist in the breeding of these species and the production of their hybrid (Larix ×eurolepis A. Henry).

Gibberellin A4/A7 (GA4/7) was injected into the main stem of container-grown Larixdecidua Mill, and Larixkaempferi (Lamb.) Carr. grafts, using different quantities and times of application of GA4/7 and applying it both alone and in combination with heat, drought, girdling, or root pruning. The GA4/7 did not increase flowering, and girdling and root pruning alone were ineffective. In contrast, flowering was substantially increased when grafts were placed in a polythene house from May (beginning of long-shoot elongation) to June or early September (depending on experiments), in three separate experiments, with mean maximum temperatures of 29–30 °C. This heat treatment significantly increased both seed- and pollen-cone production, and drought treatment significantly increased seed-cone production. Treatment means of up to 143 seed cones and between 250 and 1000 pollen cones per graft, on 1.5 m tall grafts, were observed. In one experiment heat treatment in the polythene house did not increase flowering. In that experiment vegetative buds reflushed during treatment in the polythene house, which could have reduced potential flowering sites; the reflushing may have been associated with needle damage possibly caused by higher than usual temperatures, of over 40 °C.

Fourteen treatments expected to promote and regulate flowering were administered to 7-year-old seedlings of Chinese pine (Pinustabulaeformis Carr.), and three were administered to 11-year-old grafted propagules. The cultural treatments, including root pruning, stem girdling, polyethylene mulching, and injection of gibberellin A3 (GA3) significantly increased male cone bud production of the young seedlings. For female flowering, however, only GA4 injection, alone and in combination with root pruning, had a statistically significant positive effect. N6-benzyladenine (BA) injection significantly decreased both male and female cone-bud production. There was no synergistic effect between the cultural and the hormonal treatments on flowering of the seedlings. Treatments with naphthaleneacetic acid dramatically enhanced male cone bud production of the grafted propagules, but did so at the expense of female cone bud production. The hormonal treatments (GA3, GA4, and BA injection) all promoted vegetative shoot growth of the treated seedlings. The cultural treatments generally inhibited shoot length growth and had no significant effect on diameter growth.

Leader growth and radial increment on the stem and main lateral roots during three consecutive years following partial girdling treatment were analyzed on 25- to 30-year-old lodgepole pine (Pinuscontorta Dougl. var. latifolia Engelm.) from a natural stand in west-central Alberta. Simulation of the larval feeding wounds of the weevil, Hylobiuswarreni Wood, consisted of the removal of a 7-mm-wide band of bark from 0% (control), 20%, 40%, 60%, 80%, and 90% of the root-collar circumference of 58 sample trees.Partial girdling reduced leader elongation and radial increment of the leader and lateral roots. Leader height decreased with increased girdling of the root-collar during each of the three post-treatment years. Below the leader, partial girdling of the root-collar did not affect radial increment in the first year, caused an increase during the second year, and a decrease in the third year. At 2 cm above the partial girdles, radial growth above the girdled side of stems was always less than that on the nongirdled side and showed a trend of increase with increased girdling on both girdled and nongirdled sides of the stem. Radial increment was considerably reduced on lateral roots extending below girdle wounds during the three post-treatment years. Two graphs are prepared which can be used to estimate height and radial increment losses in young pine stands infested by H. warreni.

Soil samples and black walnut (Juglansnigra L.) measurements were taken in plots of a 14-year-old plantation combining two walnut spacings with four interplanted nitrogen-fixing species and a control, lnterplantings of walnut with black locust (Robiniapseudoacacia L.) and autumn-olive (Elaeagnusumbellata Thunb.) had the highest total soil nitrogen concentrations in the top 30 cm of soil, followed by European alder (Alnusglutinosa L. [Gaertn.]), lespedeza clover (Lespedezastriata [Thunb.] Hook & Arn.), and control plots. Soil nitrogen concentrations were greatest in the surficial 6 cm of soil. At the closer, 3.7- by 4.9-m spacing in autumn-olive plots where walnut growth and competition were greatest, and at both spacings in plots with girdled black locust, nitrogen concentrations in the soil were especially high. This is consistent with speculation that recent stress on autumn-olive from walnut competition and stress on locust from past stem girdling resulted in increased inputs of nitrogen into soil. Walnut size was greatest by far in autumn-olive plots, where the spreading form of the shrub afforded soil shading and weed control. Walnut size was generally greater in mixed plots at the wider 3.7 m by 9.8 m spacing, where walnut competition with itself was least. However, walnut basal area was not strongly correlated with mean total soil nitrogen concentration of the top 30 cm of soil in a plot (r2 = 0.32 at closer walnut spacings), suggesting that the net accretion of nitrogen in soil accounted only in part for measured differences in walnut growth in mixed plantings with nitrogen-fixing plants.

Slash pine (Pinuselliottii Engl.) shoots collected from 30 ortets, approximately 8 years from seed, were girdled for different lengths of time and treated at the time they were girdled with one of five rooting powders varying in indolebutyric acid concentration. Girdling 2, 4, or 6 weeks prior to placement in the rooting bench significantly promoted rooting, but girdling times did not significantly differ from one another. Treatment with 1 or 2% IBA also promoted rooting, with 2-weeks' girdling plus 1 or 2% indolebutyric acid yielding the best results (70 and 73%, respectively). Shoots treated with 2% IBA produced significantly more primary roots than the other auxin treatments.

Two experiments were undertaken in 1977 and 1979 to promote flowering of 5- and 7-ycar-old field-grown seedlings of Larixleptolepis Gord. and L. decidua Mill. A gibbcrellin A4/7 mixture (GA4/7) was applied alone or in combination with GA3 and naphthalene acetic acid (NAA) to both girdled and nongirdled trees or branches by two methods, perfusion into the xylem and spraying with an aqueous cationic surfactant solution. Perfusion was most effective, especially on girdled branches, although spraying was reasonably effective for male flowering in L. decidua. Only GA4/7 alone significantly increased flowering. Male flowering was doubled and female flowering increased eightfold by GA4/7 in the best treatments, over all application dates. Generally, male flowering doubled and female flowering increased eightfold by GA4/7. Even more flowering was obtained at optimal application dates. May and June applications were best, especially for treatments associated with girdling. However, some flowering occurred with applications as late as August and September. More strobili of both sexes develop in the upper crown. However GA4/7 treatment induced seed cone buds to appear in the lower crown, an abnormal location. An unusual effect occurred in that a positive flowering response of the 1977 experiment occurred only in 1979, whereas the 1979 experiment yielded enhanced flowering in 1980. Soil mulching with a plastic film, with or without hormone treatment, was a very effective adjunct treatment for both male and female flowering.

Mature 14-year-old grafted Piceasitchensis (Bong.) Carr. which were field grown and 6 m tall were given stem injections of gibberellin A4/7 (GA4/7) alone and in combination with girdling. The GA4/7 was applied twice, at 100 or 250 mg per application. GA4/7 alone produced a large and significant stimulation of the numbers of both pollen and seed cones, with means of about 200 pollen and 90 seed cones per tree, and 90% of the clones flowering; both levels of GA4/7 application stimulated flowering to approximately the same extent. The girdling treatment enhanced flowering when environmental conditions facilitated light flowering of the controls, and also increased the response to 100 mg GA4/7. The stimulation of flowering was carried over into the 2nd year after treatment, but only when both girdling and GA4/7 had been applied together.

Healthy lodgepole pine trees (Pinuscontorta Dougl. var. latifolia Engelm.) were girdled on the lower trunk in patterns designed to selectively eliminate the influence of materials transported from the roots, lateral tissues, and crown. Titres of soluble sugars and starch observed in areas isolated by girdling were significantly lower than those observed in areas open to the upper bole and crown. Corresponding decreases were observed in the numbers of Dendroctonusponderosae Hopkins attacking those areas.

Balsam fir (Abiesbalsamea (L.) Mill.) trees lived from 2 to 30 months following girdling in five regions of eastern Canada. Girdled trees died fastest in the eastern Ontario plot (2 to 16 months), whereas in Newfoundland all of the 22 girdled trees were still alive 1 year after girdling; these regional variations were related to precipitation during the growing season, the length and mean temperature of the growing season, and to the level of bark beetle populations. Once dead, the sapwood of balsam fir in the three easternmost provinces developed sap stain more extensively than in western and eastern Ontario; however, the sapwood of trees in the latter areas was affected by sap rot far more rapidly than those in New Brunswick, Quebec, and Newfoundland. The principal cause of these observed differences appears to be regional differences in intensity of attack by the three major insects that invade weakened and dead balsam fir, which in turn may at least partly be due to regional climatic differences. The results of this study can be used as an aid in predicting the rate and pattern of deterioration of killed balsam fir in connection with salvage operations in eastern Canada.

In intact grafted Piceasitchensis (Bong.) Carr., which had about 10 whorls of main branches, the seed cones were largely confined to the upper 4 whorls; pollen cones were broadly distributed throughout the tree, though they were most numerous in the same region as the seed cones. Girdling plus gibberellin A4/7 application to the stem did not greatly alter the distribution of seed cones, but the zone of densest pollen cones occurred lower down. When the treatments were applied directly to branches in the lower crown, very few seed cones were produced on the treated branches but the number of pollen cones was enhanced. The lower crown of intact trees thus appears to be a zone that does not normally produce seed cones. However, when trees were top pruned (decapitated at whorl 6) and treated at the stem, numerous seed cones were produced on whorls previously in the nonproducing zone in the lower crown. Top-pruned trees became bushier and, in a good flowering year, 3 years after pruning, they produced as many seed cones as intact trees. Top pruning thus greatly improved the accessibility of seed cones and appears to be a practical management technique for Sitka spruce breeding programmes and seed orchards.

Flowering (production of seed cone buds) of white spruce (Piceaglauca (Moench) Voss) grafts and of 55-year-old trees was significantly promoted by the application of gibberellin A4/7 (GA4/7). Use of GA4/7 accompanied by the adjunct cultural treatment of nondestructive girdling was especially effective. When GA4/7 was injected into a branch, the flowering stimulus was translocated upwards, thereby yielding up to a fivefold increase (72 female cone buds per propagule) in flowering. Clonal propagules sprayed to drip off with GA4/7 + auxin (naphtaleneacetic acid) averaged 116 female cone buds per propagule (a 12-fold increase over controls) with a 100% frequency of flowering. Pollen cone bud production and number of male flowering plants also tended to increase with the most successful flowering treatments. When GA4/7 was applied to 55-year-old trees with nondestructive, overlapping stem girdles and auxin, treatments were significantly effective (6- to 27-fold increases, respectively). When GA4/7 + Ca(NO3)2 was applied to 55-year-old trees, there was a tendency (nonsignificant) to increase (4- to 16-fold) flowering, relative to GA4/7 alone. White spruce, because of its very sporadic flowering and usually nominal response to GA4/7 alone, should be classed as a "recalcitrant conifer species." Use of the GA4/7 plus appropriate adjunct cultural treatments (high temperature, water stress, girdling) and (or) auxin is, thus, recommended if significant flowering and seed cone production is desired.

Three species of 11-year-old pine trees were inoculated with Bursaphelenchusxylophilus in the field. Four branches in single whorls on red, Scots, and jack pine trees were wounded and inoculated with 10 000 nematodes each or with water extracts from Botrytiscinerea cultures. Prior to field inoculations, the pathogenicity of the nematode isolate was confirmed on seedlings in the greenhouse. Fourteen weeks after inoculation, 27 of 80 and 13 of 52 branches were dead or dying on Scots and jack pine trees, respectively. No symptoms were observed on red pine trees inoculated with B. xylophilus or on any controls. Branch death was attributed to the formation of girdling cankers resulting from inoculation. An average of 9.14, 10.39, and 0.02 nematodes were extracted per gram of wood from branch samples collected from Scots, jack, and red pine trees at 14 weeks, respectively, and at 58 weeks an average of 13.82, 1.01, and 0.05 nematodes per gram of wood sampled were recovered. Proportions of branch samples with nematodes declined from 14 to 58 weeks after inoculation. Although limited mortality of branches occurred, the pine wood nematode was not found to cause tree death following inoculation.

Coniferous trees resist invasion of their phloem and xylem by microorganisms through an induced defence reaction; resin-filled reaction zones are formed around the infections to stop the intrusion. The efficacy of the reaction is supposedly dependent on an ample supply of carbohydrates. Two hypotheses were formulated: (i) phloem starch reserves are consumed by the defence reaction; (ii) trees low in phloem starch are vulnerable to infection. To test the hypotheses, stem sections of Piceaabies trees were mass inoculated with a pathogenic blue-stain fungus, Ceratoscystispolonica, associated with the spruce bark beetle Ipstypographus. Stem starch concentration was manipulated through girdling. Mass inoculation lead to a significant decrease in phloem starch concentration. Starch reserves of single trees were not correlated to their resistance to infection. Translocation capacity of the phloem is suggested critical for the defence reaction.

Gibberellic acid (GA) and naphthaleneacetic acid (NAA) were applied alone and in combination to both girdled and nongirdled branches of Douglas-fir in four seed orchards (two containing seedlings and two containing grafts). GA significantly increased seed-cone buds and cones and caused a nonsignificant increase in pollen-cone buds. Cone production was not significantly affected by girdling or the application of NAA. Trees treated with the combination of GA + NAA responded similarly to those treated with GA alone. Cone production response to GA varied according to the orchard locations, with better response in the normally more productive orchards. The percentage of trees flowering was increased by GA. Hormone treatments had no effect on seeds per cone but they significantly reduced filled seed per cone. Owing to increased cone number, however, the GA treatments greatly increased the yield of viable seed. NAA increased the percentage of seed germinating and the rate of seed germination, while GA had no effect.

Results of three girdling experiments in operational Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) seed orchards, spanning a period of 12 years are summarized. Saw-cut girdles were superior to band girdles for stimulating a cone crop because they were easier to perform, healed faster, and resulted in lower abortion rates in the stimulated crop. Both annual and biennial saw-cut girdle regimens resulted in improved cone yields relative to untreated controls in four successive years. Over that same period of time, cumulative response to annual girdling was greater than to biennial girdling, but in certain response years biennial girdling was best. Girdling had no significant effect on filled seed per cone, filled seed weight, and germination of existing or stimulated crops. There was some indication that repeated girdling increased abortion rates in existing crops but decreased the rate of abortion in the stimulated crop. The long-term effect of repeated girdling on vegetative health and vigor was minor. Flower promotion treatments such as girdling probably improve the genetic quality of orchard seed by creating near-random mating conditions and by preempting unwanted pollen sources.

Norway spruce stems were artificially weakened by cutting a hole through them. The wood subsequently formed near the discontinuity was observed after six growing seasons following the cutting. Enhanced xylem development persisted in the zone of the discontinuity long after wounding and partial girdling stimuli could be considered to have an effect. This evidence supports the mechanistic hypothesis of stem-form development because mechanical stress level along the stem, originating from wind loading, would be greatest in the region of the discontinuity.

Diurnal circumferential fluctuations were measured during late summer at different locations on the stems of several Douglas-fir trees.In one study, devices were installed to record periodically circumferential changes at five levels on the stems of study trees. The results indicated that the amplitude of diurnal fluctuation is considerably greater in a zone adjacent to midcrown than at levels above or below. Within this zone, shrinkage and subsequent dimensional recovery begin sooner and proceed at the greatest rates. The more dynamic fluctuation within this zone may relate to transpirational patterns in the crown and to factors determining "stem elasticity".In a related study, a tree was girdled. Results indicated that circumferential fluctuations are primarily seated in peripheral tissues removed in the process of girdling. Possible explanations and implications of the reported patterns are discussed.

In six experiments over a 3-year period with 96 12- to 14-year-old Pinuselliottii var. elliollii Engelm. ortets, cuttings from shoots girdled and treated with a special rooting powder (containing 1% each indolebutyric acid, 1-phenyl-3-methyl-5-pyrazolone, and n-dimethylaminosuccinamic acid, plus 10% each powdered sucrose and captan) rooted faster, had larger root systems, and survived better both before and after rooting than nongirdled cuttings given the same powder. About 33% of cuttings taken 2 months after a June or July girdle rooted, but only 1% of the nongirdled ones did. Rooting success increased from January girdling to a June–July peak, then decreased to a low in late October.