Female Cone Production Research Articles

Variation of Cones Production in a Silver Fir (Abies alba Mill.) Clonal Seed Orchard

The current study is the first to describe fertility dynamics in a Silver fir (Abies alba Mill.) seed orchard and among the few reporting related information from a mature seed orchard. The research aim was to evaluate the female cone production in order to provide support to future management measures. Observations were conducted in a clonal seed orchard from the Eastern Carpathians over six years; all the ramets of 44 clones and the zero-inflated data were analyzed with generalized lineal mixed effects models in a Bayesian framework. The results indicated a higher influence of the year and probably of the sensitivity to climate, and less variability between clones, in both the Poisson and zero-inflated components of cones production. The repeatability of mean annual clone production suggests moderate continuity of cone crops in the production rank of individual clones, while the estimates of heritability were under a moderate genetic control. The values of heritability were influenced by the reporting scale (latent vs. original data scale); therefore, caution in the analysis of non-Gaussian data and in comparisons of heritability between seed orchards is required. The variation of the female cone production was higher than expected for a seed orchard, but with marked variation across years, similar to other related indicators, patterns specific to mature, and productive commercial seed orchards. Several management options to be applied in the future were also discussed.

Climate and size of previous cone crops contribute to large-scale synchronous cone production in balsam fir

Mast year occurrence in trees is often synchronized across large regions. In this study, we used dendrochronological methods based on cone scar characteristics on tree branches in order to reconstruct male and female cone production in balsam fir (Abies balsamea (L.) Mill.) during the period 1988–2018. Results indicate that mast years generally occur every second year and can be synchronized across distances >1000 km. The main predictors of current-year cone abundance were cone abundance during the two previous years, which can be considered a proxy for resource availability for cone bud development during the current year, together with relatively warm temperature during cone bud development. Presence of aborted male cones was positively correlated with the occurrence of relatively cold episodes during cone bud development. This finding suggests that the influence of weather on cone crop abundance is at least partly mediated by growth cessation in the developing cone buds. We also suggest that a change in weather patterns before and after the 2005–2010 period is responsible for a switch in mast years from even to uneven calendar years around that time.

Effects of Light Intensity and Girdling Treatments on the Production of Female Cones in Japanese Larch (Larix kaempferi (Lamb.) Carr.): Implications for the Management of Seed Orchards

To ensure sustainable forestry, it is important to establish an efficient management procedure for improving the seed production capacity of seed orchards. In this study, we evaluated the effects of girdling and increasing light intensity on female cone production in an old L. kaempferi (Lamb.) Carr. seed orchard. We also evaluated whether there is a genotype-specific reproductive response to these factors among clones. The results showed that female cone production was augmented by girdling and increasing light intensity. There was a difference in the effectiveness of girdling treatment levels, and the probability of producing female cones increased markedly at higher girdling levels. At light intensities where the relative photosynthetic photon flux density was higher than 50%, more than half of the trees tended to produce female cones, even in intact (ungirdled) trees, and the genotype-specific response to light intensity was more apparent in less-reproductive clones. These findings suggested that girdling less-reproductive trees combined with increasing light intensity was an effective management strategy for improving cone production in old seed orchards.

Positive coupling between growth and reproduction in young post-fire Aleppo pines depends on climate and site conditions

In fire- and drought-prone Mediterranean forests tree growth and regeneration depend on the moisture regime between fires. Therefore, post-fire tree regeneration will depend on moisture conditions and how they are altered by fire recurrence and climate warming. Aleppo pine forests are the most abundant Circum-Mediterranean ecosystems subjected to frequent wildfires and summer droughts. Because both stressors constrain their reproduction and growth patterns across diverse ecological conditions, these forests represent a suitable system to test how moisture availability drives post-fire regeneration. Aleppo pine is an obligate seeder species that reproduces at an early age after fire. Such precocious behaviour poses the question as to whether post-fire regeneration depends on moisture conditions and the coupling between female cone production and growth. Here, we evaluate if female cone production and radial growth are linked at the tree level in post-fire Aleppo pines by comparing a dry v. a very dry site and considering stands with three different tree densities in south-eastern Spain. We found that trees with higher basal areas produced more female cones and this positive association intensified as the water balance improved. Aleppo pines from the very dry site were more precocious in reproductive terms than pines of the same age from the dry site, but long-term cone production was lower at the very dry site. Lower tree density enhances the resilience of xeric post-fire Aleppo pine forests, in growth and reproduction terms, but this effect can be reversed by droughts. Overall, a more positive water balance improves post-fire regeneration by enhancing growth and cone production. Thus, silvicultural treatments such as thinning should be applied by taking into account the post-fire water balance to maximise growth and cone production in Aleppo pine stands. Our findings illustrate how climate warming could hamper post-fire tree regeneration by aggravating drought stress.

Ecology of whitebark pine populations in relation to white pine blister rust infection in subalpine forests of the Lake Tahoe Basin, USA: Implications for restoration

For over a century, white pine blister rust (WPBR), caused by the introduced fungal pathogen, Cronartium ribicola J.C. Fisch., has affected white pine (Subgenus Strobus) individuals, populations, and associated forest communities in North America. We surveyed eight populations of whitebark pine (Pinus albicaulis Engelm.) across a range of environmental conditions in subalpine forests of the Lake Tahoe Basin, California and Nevada, to determine how WPBR is influencing host fecundity (i.e., female cone production and recruitment), survival, and current population trends. In this region and throughout its range whitebark pine is an important component of subalpine ecosystems. In high-elevation forests of the Lake Tahoe Basin, the primary negative effect of this rust pathogen on whitebark pine is infection and mortality of cone-bearing branches.Mean incidence of WPBR among whitebark pine populations was 35% and ranged from 1% to 65%. Given the high disease incidence, relationships were found between WPBR infection and reproductive output. Percent of individuals infected per population (R2=0.78), average number of WPBR-infected branches per population (R2=0.71), and severity of stem girdling (R2=0.76) were all negatively related with cone production. A positive relationship was found between disease severity (i.e., extent of stem girdling) and available water capacity and a negative relationship was found between disease severity and%sand content. Environmental conditions, including soil properties, may affect pathogen growth and potentially influence the rate at which green infected trees lose the ability to produce female cones. Demographic trends for 7 of 8 whitebark pine populations were stable, with estimates of geometric growth rate (λ)⩾1.0. Population stability is a function of adequate population sizes, mixed-size structure, high survivorship, and moderate fecundity. Results show that WPBR is adversely affecting fecundity but having little effect on survivorship. Restoration strategies are designed to facilitate whitebark pine recruitment and deploy genetically diverse seedling material and potentially WPBR-resistant phenotypes. Our study highlights a need for long-term demographic data and monitoring of WPBR-infection to better understand population consequences and host responses in the future.

Relationships between tree size, crown shape, gender segregation and sex allocation in Pinus halepensis, a Mediterranean pine tree

Sex allocation has been studied mainly in small herbaceous plants but much less in monoecious wind-pollinated trees. The aim of this study was to explore changes in gender segregation and sex allocation by Pinus halepensis, a Mediterranean lowland pine tree, within tree crowns and between trees differing in their size or crown shape. The production of new male and female cones and sex allocation of biomass, nitrogen and phosphorus were studied. The relationship between branch location, its reproductive status and proxies of branch vigour was also studied. Small trees produced only female cones, but, as trees grew, they produced both male and female cones. Female cones were produced mainly in the upper part of the crown, and male cones in its middle and lower parts. Lateral branch density was correlated with the number of male but not female cones; lateral branches were more dense in large than in small trees and even denser in hemispherical trees. Apical branches grew faster, were thicker and their phosphorus concentration was higher than in lateral shoots. Nitrogen concentration was higher in cone-bearing apical branches than in apical vegetative branches and in lateral branches with or without cones. Allocation to male relative to female function increased with tree size as predicted by sex allocation theory. The adaptive values of sex allocation and gender segregation patterns in P. halepensis, in relation to its unique life history, are demonstrated and discussed. Small trees produce only female cones that have a higher probability of being pollinated than the probability of male cones pollinating; the female-first strategy enhances population spread. Hemispherical old trees are loaded with serotinous cones that supply enough seeds for post-fire germination; thus, allocation to males is more beneficial than to females.

The uncoupling of secondary growth, cone and litter production by intradecadal climatic variability in a mediterranean scots pine forest

The relationships between climate variability and canopy dynamics (monthly litter production), chemical composition of the litter, secondary growth and female-cone production were studied in an old growth Scots pine ( Pinus sylvestris) forest over the 1993–2003 period. The forest was located at a Mediterranean mountain site (Valsaín, Segovia, central Spain). The temporally explicit relationships between the mentioned variables were explored by chronological cluster of their time series. Mean air temperature significantly influenced litter production and its seasonal and intradecadal patterns. Seasonal patterns of litter N and P content were negatively correlated with litter production, exhibiting minima of 5.3 g kg −1 (N) and 0.5 g kg −1 (P) by the end of the summer and maxima of 15 g kg −1 (N) and 1.2 g kg −1 (P) during winter; these results are interpreted as retranslocation before needle shedding in summer and loss of green needles in winter respectively. In general the driest and hottest years (1994 and 1995) were associated with significantly decreased secondary growth in the next year, an increased cone production, and an increased nutrient loss due to the combined effect of an increased litter production and an increased nutrient concentration of the litter. Climatic changes during the early stages of cone formation that take place during the spring led to alterations in masting and in the tri-annual process of cone production. Since each parameter studied was differentially affected by climatic variability, the overall effect of the short-term climatic changes experienced by the Scots pine forest studied was an uncoupling of litter production, secondary growth, and reproduction.

Pollen productivity variations. Pollen-ovule ratio and sexual selection in Pinus roxburghii

Total pollen production, pollen-ovule ratio and the production of male-female strobili were recorded in Pinus roxburghii at two different altitudes during two successive years. The values of total pollen production per tree and per hectare varied between 1953.56 to 2727.16 2 10 9 and 2.91 to 4.26 2 10 14 (in 1999) at the lower altitude and 1247.5 to 1673.5 2 10 9 and 2.24 2 10 14 (in 1998) and 1599.89 to 2038.96 2 10 9 and 3.18 2 10 14 (in 1999) at the higher altitude. The pollen-ovule ratio in P. roxburghii has indicated the xenogamous type of breeding system The production of male and female cones per tree and per hectare ranged from 21.7 - 0.34 to 33.6 - 0.71 2 10 3 and 55.16 - 24.08 to 220.85 - 87.75 per tree and 32.55 to 70.56 2 10 5 and 2.76 to 26.50 2 10 3 per hectare respectively. However the production of female cones per 100 male cones oscillated between 0.25 to 0.66, which suggested the intense male competition among trees to pollinate their neighbours. A linear correlation was recorded between diameter and extent of the tree crown to the total production of strobili groups/strobili clusters, strobili, microsporophylls and pollen grains per individual tree. The ratio between the number of strobili per strobili group and the number of strobili groups per tree showed an inverse relationship; thus, the individuals with most strobili groups have the strobili groups with the least strobili and vice-versa. This ratio was also shown between the number of pollen grains per strobilus and the number of strobili per tree, as well as the number of pollen grains per strobili group and the number of strobili groups per tree.

Plant foraging and dynamic competition between branches ofPinus sylvestrisin contrasting light environments

1 The morphological plasticity of sun and shade branches ofPinus sylvestrisgrowing at the edge of a ‘tree‐patch’ created in 1989, when surrounding trees were removed, was compared with that of branches of trees growing in the centre of the patch.2In 1992, we selected 10‐year‐old branches. Yearly growth increments (long‐shoots) and emerging buds were individually marked, architectural parameters measured, the branch topology mapped, and the number of male and female cones counted. In 1993, the survival of growth increments and buds was recorded and the branches were harvested to determine dry mass of growth increments and needles.3The size of growth increments produced after 1989, i.e. their length, total dry mass and needle dry mass, decreased in the order sun branches of edge trees > branches of centre trees > shade branches of edge trees. Thus, the growth increments produced on the shade branches of trees that also had branches in the sun were consistently smaller than the growth increments on the branches of centre trees growing completely in the shade.4The number of new growth increments produced after 1989 was highest in sun branches and lowest in shade branches of edge trees. Survival of growth increments and buds was higher in edge than in centre trees; no difference was found between sun and shade branches of edge trees.5In shade branches of edge trees, branching angles between first‐ and second‐order growth increments were highest and increased from older to younger growth increments. This was interpreted as ‘bending’ towards the edge of the patch.6Production of female cones was almost totally restricted to edge trees and higher in sun than in shade branches.7One prediction of an optimal foraging strategy, i.e. the production of more growth increments and buds in higher light, was supported by the data, whereas the other prediction, i.e. decreased length of growth increments, could only be supported when it was expressed per unit dry mass. Thus, the hypothesis of an adaptive foraging strategy in plants was rejected in favour of a ‘passive’ growth null hypothesis.8The results suggest that both growth increments within branches and branches within trees are physiologically integrated and their ‘foraging behaviour’ can only partly be understood in terms of their local environment. We interpreted the observed differences between shade branches of edge and centre trees as correlative growth inhibition.

Path analysis of natural selection on plant chemistry: the xylem resin of ponderosa pine.

We analyzed the pattern of correlations among fitness components, herbivory, and resin characteristics in a natural all-aged stand of ponderosa pine, to infer the strength and mechanism of natural selection on plant chemistry. Male and female cone production were monitored yearly for 15 years, and levels of herbivory for 9 years in 165 trees. Resin flow rate and monoterpene composition were determined for these same trees. Multiple regression of fitness components on resin characteristics showed significant associations consistent with directional selection for increased resin flow rates and increased proportions of α- and β-pinene, myrcene and terpinolene. However, negative correlations among monoterpene fractions of the resin constrained the overall selection. Selective herbivory by aphids approached statistical significance and monoterpenes showed some (non-significant) effect as deterrents against deer browse. Resin characteristics were not correlated with attack by cone insects or porcupines. However, the association between resin characteristics and fitness is significantly different from that predicted by the path coefficients involving herbivores. Therefore the hypothesis that these herbivores mediate selection on the resin is not supported by the observed pattern of correlations among resin characteristics, herbivory, growth and fecundity. In this population, most of the association between resin characteristics and fitness appears to be mediated by some other factor independent of attack by herbivore species present.

The status and ecology of a Juniperus excelsa subsp. polycarpos woodland in the northern mountains of Oman

Juniperus excelsa subsp. polycarpos (K. Koch) Takhtajan is found in mountain areas from Turkey through to India and as an isolated population on Jebel Akhadar in the northern mountains of Oman. Juniperus is one of the dominant plant species in these mountains and a major landscape feature of several proposed National Nature and Scenic Reserves and of Hayl Juwari, a wooded valley at 2250 m altitude proposed as a Botanical Site of Special Interest. Above 2400 m altitude the Juniperus woodlands generally appear to be regenerating and in good condition, both on exposed slopes and in wadis and sheltered gullies, whereas below 2400 m most stands are in poor condition and exhibit few signs of regeneration. If the apparently poor condition of the lower altitude woodlands is due to any long term change in climatic conditions, both tree status and regeneration would be poorer in relatively more xeric habitats. To test this prediction we have carried out a detailed survey of the status and ecology of a 32 ha area of Hayl Juwari, and analysed differences in tree status and regeneration between wadis (relatively more nesic sites) and non-wadi areas (relatively more xeric). Approximately one third of the trees are dead, and an analysis of the height, condition, regeneration, female cone production, preferred germination sites and spatial distribution of trees indicates the importance of topography, hydrology and microclimate for growth. However, although there are relatively greater numbers of dead and poor-condition trees in the more xeric non-wadi habitat, there is no unequivocal evidence that the present distribution of small, sexually immature trees in both habitats could not form a pattern of larger, sexually mature trees similar to that seen today. We speculate, however, that the climate at this altitude may be marginal for the survival of a J. excelsa subsp. polycarpos woodland and that even small increases in climatic stress could imperil the woodland's present status.

Interactions between Abert's Squirrel and Ponderosa Pine: The Relationship between Selective Herbivory and Host Plant Fitness

Abert's squirrels are highly specialized and selective herbivores and are ecologically dependent on their host species, ponderosa pine. Ponderosa pine trees defoliated as a result of inner bark feeding by Abert's squirrels (target trees) suffered significant reductions in several fitness components including incremental growth, male strobilus production, female cone production, and seed quality. Reproductive output was also depressed in trees defoliated experimentally to mimic squirrel herbivory. In previous work, I have shown that target tree selection is mediated by a suite of host characteristics, some of which are under genetic control. Abert's squirrels may be important agents of natural selection in host ponderosa pine populations because they preferentially attack trees with specific genetically determined traits and because target trees suffer significant reductions in several fitness components.

Relations between reproductive growth and vegetative growth of Pinus radiata

Growth of female cones and male cones of Pinus radiata was measured and compared with vegetative growth in 10- to 14-year-old plantations given a range of water and nutrient supplies on a site near Canberra, Australia. Although P. radiata trees take about 3 years from ‘flower’ initiation to seed maturation, most of the growth in dry weight occurred in two relatively brief periods: male cones grew mainly in the 3 months before shedding their pollen; female cones grew mainly during the 4 months starting about 13 months after the time of pollen shed. As both male cones and foliage fascicles originate as short-shoot initials, each male cone is produced at the expense of one fascicle of foliage. The number of short-shoots produced was positively related to rainfall during their initiation: about September to January. When this period was dry, fewer short-shoots were initiated and a much lower proportion of these was devoted to male cones. The flowering shoots did not compensate for their loss of fascicles by producing more short-shoots or by growing larger needles. On average, about 13% of the potential foliage was diverted to the production of male flowers. Because female cones originate as long-shoot buds (i.e. buds which otherwise would produce branches), they are also produced at some cost in foliage. Reproductive growth also entailed considerable nutrient cost. Even so, there was no evidence that increased reproductive growth caused any decrease in vegetative growth. Within a stand, stem growth per tree during and shortly after the main growth of male cones did not vary with the abundance of male cones on those trees. The weight of matured male and female cones produced by all five treatments from the four flowerings of 1984–1987 averaged 1.1 t ha −1 year −1. This amount was equal to about 10% of stem growth or 5%% of total above-ground growth. The production of both male and female cones was positively related to rainfall during the September to January period in which the male cones were initiated and also to the vegetative growth that occurred during the year of flower initiation.

GENETIC DIFFERENTIATION AND HETEROZYGOSITY IN PINYON PINE ASSOCIATED WITH RESISTANCE TO HERBIVORY AND ENVIRONMENTAL STRESS.

Arizona's Sunset Crater began erupting in 1064 AD and for the next 200 years buried over 2,000 km2 in ash, cinders, and lava. Soil analyses indicate that pinyon pines (Pinus edulis) currently colonizing the cinder fields are faced with a highly stressful environment. Many of these pinyons suffer chronic, intense insect herbivory that reduces plant growth and eliminates female cone production. In contrast, herbivory among pinyons growing in neighboring sandy-loam soils is minimal. Furthermore, numerous trees within the heavily infested cinder field population suffer relatively low herbivory and maintain normal growth and reproduction. We used four polymorphic enzymes to examine the relationship between herbivore attack, environmental stress and genotypes of the adjacent cinder field, and sandy-loam soil pinyon populations. Our results demonstrate that 1) resistant trees display significant genetic differences and are more heterozygous for two enzymes associated with herbivory than susceptible trees; and 2) the cinder-soil pinyons exhibit significant genetic differences and are more heterozygous for an enzyme associated with environmental stress than the neighboring sandy-loam soil pinyons. We conclude that heterozygosity of specific or closely linked loci may facilitate pinyon resistance to herbivory and environmental stress, and that strong selection across narrow geographic boundaries resulted in rapid genetic differentiation of pinyon populations.

Influence of male and female cones on assimilate production of Pinus contorta trees within a forest stand.

Studies on branches of field-grown Pinus contorta Dougl. trees showed that: (i) branches with fully developed male or female cones were heavier than vegetative branches; (ii) the production of female cones decreased neither the number of laterals nor the length of the terminal or lateral shoots on the cone-bearing branches; (iii) the production of male cones decreased both the number of laterals and the number of needles on the cone-bearing branches; (iv) needles on male cone-bearing branches had significantly higher photosynthetic rates and needles on female cone-bearing branches generally also fixed more CO(2) per quantum of light. In addition, both male and female cones refixed a significant proportion of respired CO(2) when illuminated. The simulation model, MAESTRO, was used to estimate light penetration through two stands (3690 and 1845 trees ha(-1)) of P. contorta trees and to calculate the resultant CO(2) assimilation of a vegetative, a male and a female cone-bearing tree on sunny, partly sunny and cloudy days in Scotland. Generally, the CO(2) efflux from female cones was less than 3% of the CO(2) assimilated by the whole tree. The presence of male cones resulted in an average 33% decrease in needle complement, but an increased quantum efficiency of associated needles in the autumn. It was estimated that, on a sunny day, male cone-bearing trees assimilated as much CO(2) as vegetative trees in the high density stand and only 6% less in the low density stand. On cloudy days, the smaller needle complement was beneficial to the carbon economy of the tree because of lower respiration losses compared with a vegetative tree.

The Ontogeny of Gender of Cupressus sempervirens L.

Cupressus sempervirens, known as a monoecious species, is sequentially monoecious. Young trees and new growth are female. Stressed trees are male or show a tendency toward male predominance. Female cone production starts in some plants during year 2 of growth, and male cones are produced in some plants from year 4 on. Monoecy is completed at age 10. Young trees are pollinated only by adults, thus ensuring foreign pollination in the early years of reproduction. Unisexuality in the first years of reproduction reduces the reproductive effort. Under unfavorable conditions, trees are male or show a tendency toward maleness, contributing to the decrease of the reproductive effort.

Cytokinin level and flowering in Douglas-fir

Clones of Douglas-fir [ Pseudotsuga menziesii (Mirb.) Franco] were propagated by cuttings and grown in pots. In 1982, when plants were about 1.5 m high (four years after propagation), they were subjected to a series of treatments known to induce flowering in this species. The apical and basal portions of growing shoots were sampled six weeks after budburst (time of bud differentiation) and analyzed for cytokinin content by immunoaffinity chromatography and radioimmunoassay. Production of male and female cones were recorded for each tree in the subsequent year. Trees with shoots having high concentrations of cytokinins had no female flowers and few male flowers. Female flowers occurred only on plants having low concentrations of cytokinins, although low cytokinin content did not guarantee flowering. Most striking was the polarity of cytokinins in shoots. Apical portions usually contained higher concentrations than basal portions of shoots. A subsequent experiment in which plants were treated with GA and flooding showed that both treatments induced flowering and that the effects were additive.

Preliminary results on gibberellin induction of flowering of seedlings and cuttings of Norway spruce indicate some carry-over effects

In 1983 and 1984 flower induction experiments where conducted on 12-year-old seedlings and 9-year-old cuttings of Norway spruce ( Picea abies (L.) Karst). Potted plants were moved into a greenhouse when the shoot elongation of lateral branches was around 50% completed. Treatments included stem injection or spraying of gibberellins ( GA 4 7 ) with or without girdling. In 1984 few seedlings produced female flowers in response to the 1983 GA treatments. In 1985 abundant flowering (up to 63 and 40% of trees respectively for female and male flowering) was observed on both seedlings and cuttings, exclusively on trees treated with GA in 1983. This demonstrates a strong carry-over effect of these treatments. After treatment in 1984 (only cuttings), male flowering was observed for all treatments, but especially on control trees in the greenhouse. Girdling and GA appeared to reduce male flowering. On the other hand, female flowering (up to 64% of the trees) was exclusively associated with GA treatments, indicating that, at the concentrations we used, GA 4 7 increases the female cone production. For both experiments, girdling alone had no positive effect on flowering.

A review of coning and seed production in Picea sitchensis

SynopsisSitka spruce grown from seed has a juvenile phase of about twenty years before coning commences; mature trees and grafted scions cone intermittently and produce good cone crops every three–five years. These characteristics have lengthened the breeding programme and reduced seed production in orchards. Production of male and female cones can be enhanced by treatments such as heat and drought and by application of a mixture of gibberellins A4 and A7 (GA4/7) to mature grafts. To enhance flowering consistently in container grown grafts the GA4/7 must be applied together with a cultural treatment, but with larger grafts in the field GA4/7 alone is often effective. Attempts to induce cone production in juvenile trees, however, have been less successful. Female cones initiated on field grown trees in response to inductive treatments yield seed of a similar quantity and quality to that from cones on untreated trees. The physiological mechanisms of coning, and cone induction techniques, are discussed.

Floral response of Piceaglauca to gibberellin A4/7, napthaleneacetic acid, root-pruning, and biennial treatment

The floral response of 6-year-old seedling white spruce (Piceaglauca (Moench) Voss.) was evaluated after treatment in 1981 with the gibberellin mixture of A4 and A7 (GA4/7), napthaleneacetic acid (NAA), and root-pruning. To evaluate the effectiveness of biennial treatment, trees treated in 1981 were again treated in 1983 and compared with a second group of trees treated only in 1983. Trees treated in 1981 with 500 mg•L−1 GA4/7 plus 25 mg•L−1 NAA and root-pruning averaged 42 female strobili per tree and control trees remained vegetative. Root-pruning significantly reduced terminal shoot growth and shoot water potential. No male strobili were produced on study trees. Trees treated in 1981 and again in 1983 were as productive (based on female counts) as trees treated only in 1983. Two treatments in 1983 significantly enhanced female strobilus production over the control: (i) 500 mg•L−1 GA4/7 alone and (ii) 250 mg•L−1 GA4/7 plus root-pruning. These treatments averaged 150 and 192 female strobili per tree, respectively; control trees averaged 30. Biennial treatment with GA4/7 and root-pruning can effectively continue to increase female cone production of white spruce.