Epicormic Research Articles

USING HIDDEN SEMI-MARKOV CHAINS TO COMPARE THE SHOOT STRUCTURE OF THREE DIFFERENT ALMOND CULTIVARS

Shoot structure, resulting from lateral branching and flowering patterns, determines final tree form, fruit bearing habit, and cropping potential. The genetic make-up of different cultivars controls vegetative and reproductive growth, but few structural studies have been done to systematically describe almond shoot structure. A specific class of Markovian models, referred to as hidden semi-Markov chains (HSMC), has been proposed to identify and characterize branching and flowering patterns in fruit trees. This type of model is particularly appropriate when the shoot structure is organized as a succession of homogeneous branching zones and captures the variable character of the observed patterns. This study reports the first almond HSMC analysis of shoot structure based on data collected from epicormic shoots and five length categories of proleptic shoots in three almond cultivars with distinctly different tree architecture. 'Nonpareil' is the most important cultivar grown in California and has a relatively spreading tree habit. 'Aldrich' is a newer cultivar with an upright growth habit, and 'Winters' has a spreading habit with a high tendency for sylleptic branching on proleptic shoots. Shoots of these three cultivars were analyzed to determine different zones that could be classified according to lateral bud fates and the number of flower buds at each node. This modeling technique showed that almond shoot structures are highly organized and predictable. Substantial differences were found in the structure of the proleptic shoots of similar length, among the cultivars, but fewer differences were found among epicormic shoots. For long shoots, 'Aldrich' had the highest probability of flower buds and 'Winters' had the greatest lateral branching distributed along shoots. 'Nonpareil' had similar branching probabilities as 'Aldrich' and its probability of flower buds was similar to 'Winters'. It is anticipated that these HSMC will be useful for identifying desirable shoot structures for cultivar improvement and will help to explain the differences in tree architecture and cropping potential among cultivars. (Resume d'auteur)

Structural development of redwood branches and its effects on wood growth

Redwood branches provide all the carbohydrates for the most carbon-heavy forests on Earth, and recent whole-tree measurements have quantified trunk growth rates associated with complete branch inventories. Providing all of a tree's photosynthetic capacity, branches represent an increasing proportion of total aboveground wood production as trees enlarge. To examine branch development and its effects on wood volume growth, we dissected 31 branches from eight Sequoia sempervirens (D. Don) Endl. and seven Sequoiadendron giganteum Lindl. trees. The cambium-area-to-leaf-area ratio was maintained with size and age but increased with light availability, whereas the heartwood-deposition-area-to-leaf-area ratio increased with size and age but was insensitive to light availability. The proportion of foliage mass arrayed in <1-cm-diameter epicormic shoots increased with decreasing light and was higher in Sequoia (20-60%) than in Sequoiadendron (3-16%). Well-illuminated branches concentrated leaves higher and distally, while shaded branches distributed leaves lower and proximally. In similar light environments, older branches distributed leaves lower and more proximally than younger branches. Branch size, light, species, heartwood area, a heartwood-area-species interaction, and ovulate cone mass predicted 87.5% of the variability in wood volume growth of branches. After accounting for the positive effects of size and light, wood volume growth declined with heartwood area and age. The effect of age was trivial compared to the effect of heartwood area, suggesting that heartwood expansion caused the age-related decline in wood volume growth. Additionally, Sequoiadendron branches of similar size and light environment with more ovulate cones produced less wood, even though these cones were long-lived and photosynthetic, reflecting the energetic cost of seed production. These results contributed to a conceptual model of branch development in which light availability, injury, heartwood content, gravity, and time interact to produce the high degree of branch structural variation evident within redwood crowns.

Changes in evapotranspiration following wildfire in resprouting eucalypt forests

ABSTRACTForests that recover from disturbance predominately via vegetative resprouting may be expected to have different catchment water balance dynamics following wildfire than forests recovering from seed. However, the impacts of wildfire on forest water use are largely unknown in resprouting forest types. This is despite their dominance across the majority of southern Australia's forested catchments and the large areas burnt in recent years. We hypothesized that postfire changes in evapotranspiration (Et) would be a function of fire severity and topography and that partitioning of Et would change after fire because of altered stand structure. We tested these hypotheses by monitoring Et and component fluxes across different topographic positions and fire severities in a mixed eucalypt species forest located in water supply catchments for the city of Melbourne. For this forest type, wildfire triggers vegetative resprouting from lignotubers and epicormic shoots on the bole and branches of the overstorey trees, in addition to prolific seedling germination. Monitoring was undertaken over 1–3 years following the 2009 Black Saturday wildfires. We found that Et was on average 41% lower in forest burnt at high severity compared with unburnt forest, whereas Et from forest burnt at moderate severity was only 3% lower than unburnt forest over 1–2 years postfire but on average 9% higher over 2–3 years postfire. Et losses were driven by tree and shrub mortality in conjunction with lower transpiration in surviving trees. Lower Et was partially offset by regenerating seedlings that drove increases in forest floor Et and interception loss. Finally, we found that topography, through its effects on evaporative demand and forest structure, was a strong determinant of total Et but did not affect the nature of postfire recovery. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Vegetative propagation of mature dragon trees through epicormic shoots

cEmbrapa, Centro Nacional de Pesquisa de Florestas, Colombo-PR, Brazil. SUMMARY Epicormic shoots were induced in stumps and detached branches of adult Paulownia fortunei var. mikado plants to evaluate rooting potential. Stem cuttings obtained from shoots of stump were prepared with 12 cm in length and two leaves reduced to 78.5 cm² (10 cm diameter). Cuttings from shoots of branches were prepared with 8-10 cm in length, and two leaves reduced to 50 % of the original size. Anatomical analysis was performed to evaluate possible barriers to rhizogenesis. After disinfestation, indolebutyric acid (IBA) was applied (0, 500, 1,000, 1,500 and 2,000 mg L -1 ). Installation was made in plastic pots with a volume of 170 cm³ and 53 cm³, respectively for each type of cuttings, with fine vermiculite and carbonized rice hulls (1:1 v/v) as substrate. After 60 days in a greenhouse, cuttings from epicormic shoots of branches presented rooting (58.12 %) and the average length of the three longest roots/ cutting (4.76 cm) was higher than in cuttings from stumps. The highest number of roots/cutting (7.66) and percentage of cuttings with callus (27.50) was observed in cuttings from stumps. There were no anatomical barriers observed harming the roots formation in the two types of cuttings. The use of indolebutyric acid is not required to induce rooting.

Proposed pre-selection method for identification of dwarfing peach rootstocks based on rapid shoot xylem vessel analysis

The association between a genotype's dwarfing ability and a genetic, physiological, or anatomical trait would be of great value for selecting dwarf rootstocks at an early stage of development. Dwarfing peach rootstocks have been associated with decreased hydraulic conductance due to smaller xylem vessel diameters compared to invigorating rootstock genotypes. We evaluated tentative anatomical criteria for selecting dwarfing peach rootstocks based on measurements of the diameter of the largest xylem vessels and the number of xylem vessels surrounding the largest vessels in cross sections of shoots. Epicormic and proleptic shoots were collected from trees of the standard, invigorating ‘Nemaguard’ peach rootstock and a series of dwarfing rootstocks: ‘Controller 9.5’ ™ (HBOK 50), ‘Controller 9’ ™ (P30-135), ‘Controller 8’ ™ (HBOK 10), ‘Controller 7’ ™ (HBOK 32), ‘Controller 6’ ™ (HBOK 27) and ‘Controller 5’ ™ (K146-43). Transverse sections were cut from 2, 3, and 4mm diameter stems of proleptic shoots and from 4, 5, and 6mm diameter stems of epicormic shoots. The samples were fresh sectioned to a thickness of about 150μm, stained with Toluidin-Blue-O and photographed on a light microscope. The largest xylem vessel was visually identified in each microscopic view field, and the surrounding circle of vessels with a diameter of ∼164 micrometers were counted. Rootstock genotype, shoot diameter, and the interactions between rootstock×shoot diameter significantly affected the diameters of the largest vessels of both proleptic and epicormic shoots. Most of the evaluations of the largest vessel diameter were able to distinguish the lowest vigor rootstock from the vigorous, but the intermediate vigor rootstocks were not clearly distinguished by this criterion. The less vigorous rootstocks showed a tendency for having more vessels. The larger vessel diameters in more vigorous rootstocks appeared to be related with fewer vessels. For rootstock screening purposes epicormic shoots appeared to be better for evaluation than proleptic shoots. Young, vigorous seedlings are in the vegetative phase of plant growth, and probably more similar to epicormic shoots than to proleptic onesshoots that are physiologically more related to fruit bearing than to rapid vegetative growth. We propose that the evaluation of the largest vessel of a microscopic view field associated with the number of vessels around the largest vessel, measured on 5mm vigorous shoots would be useful as a criterion for selecting dwarfing peach rootstock genotypes.

Vegetative propagation of adult Ilex paraguariensis trees through epicormic shoots

The difficulty and length of time required for seed germination of mate (Ilex paraguariensis), as well as the pressing need for clonal multiplication of improved genetic material, has resulted in several studies related to vegetative propagation in an effort to obtain rooted cuttings more quickly and with better genetic quality. Currently, the biggest challenge is propagating and rooting adult plants selected in the field without requiring clear cutting to generate conditions for the basal induction of juvenile sprouts. Therefore, the objective of this study was to develop a method to rescue adult mate plants through the generation of epicormic sprouts. To accomplish this, tree branches of mate that were at least 19 years of age were collected and packed in trays with sand for sprouting. Different solutions containing a mixture of sucrose and indole-3-butyric acid (IBA) were sprayed in branches at 29, 22, 15, 8 and 1 day(s) before collection. We conclude that the vegetative propagation of adult mate trees is technically efficient and requires no treatment with sucrose or IBA and results in the formation of plants suitable for planting or serving as mother plants for continuous multiplication via cloning.

Differences in proleptic and epicormic shoot structures in relation to water deficit and growth rate in almond trees (Prunus dulcis).

Shoot characteristics differ depending on the meristem tissue that they originate from and environmental conditions during their development. This study focused on the effects of plant water status on axillary meristem fate and flowering patterns along proleptic and epicormic shoots, as well as on shoot growth rates on 'Nonpareil' almond trees (Prunus dulcis). The aims were (1) to characterize the structural differences between proleptic and epicormic shoots, (2) to determine whether water deficits modify shoot structures differently depending on shoot type, and (3) to determine whether shoot structures are related to shoot growth rates. A hidden semi-Markov model of the axillary meristem fate and number of flower buds per node was built for two shoot types growing on trees exposed to three plant water status treatments. The models segmented observed shoots into successive homogeneous zones, which were compared between treatments. Shoot growth rates were calculated from shoot extension measurements made during the growing season. Proleptic shoots had seven successive homogeneous zones while epicormic shoots had five zones. Shoot structures were associated with changes in growth rate over the season. Water deficit (1) affected the occurrence and lengths of the first zones of proleptic shoots, but only the occurrence of the third zone was reduced in epicormic shoots; (2) had a minor effect on zone flowering patterns and did not modify shoot or zone composition of axillary meristem fates; and (3) reduced growth rates, although patterns over the season were similar among treatments. Two meristem types, with different latency durations, produced shoots with different growth rates and distinct structures. Differences between shoot type structure responses to water deficit appeared to reflect their ontogenetic characteristics and/or resource availability for their development. Tree water deficit appeared to stimulate a more rapid progression through ontogenetic states.

Diplodia corticola and Phytophthora cinnamomi: the main pathogens involved in holm oak decline on Caprera Island (Italy)

SummarySince 2008, severe and widespread tree decline and mortality has been observed at the main growing Quercus ilex L. (holm oak) forest on Caprera Island, Italy. To clarify the symptomatology and aetiology of this phenomenon, field surveys and isolations from symptomatic trees were carried out in summer 2010. Affected trees exhibited crown thinning, branch dieback, sunken cankers, epicormic shoots, exudates on branches and trunk, root losses and sudden death symptoms. Four fungal species belonging to Botryosphaeriaceae family, namely Botryosphaeria dothidea, Diplodia corticola, D. seriata and Neofusicoccum parvum, were isolated from cankers on trunk and branches, whereas three species of Phytophthora, namely P. cinnamomi, P. cryptogea and P. gonapodyides, were isolated from fine roots and rhizosphere soil samples. Isolates were identified using both morphological analysis and DNA‐based techniques. Pathogenicity trials on holm oak seedlings showed that all the isolated species are pathogenic. D. corticola proved to be the most aggressive species. Our results provide the first evidence for a combined involvement of D. corticola and P. cinnamomi in the aetiology of holm oak decline in Italy and suggest that these pathogens are not only important contributing factors in the onset of long‐term tree decline, but also may cause the rapid devastation of extensive oak ecosystems.

PM 7/117 (1) Hymenoscyphus pseudoalbidus

Specific scopeThis Standard describes a diagnostic protocol for Hymenoscyphus pseudoalbidus (anamorph Chalara fraxinea).Specific approval and amendmentApproved as an EPPO Standard in 2013‐09.

Does woodland condition influence the diversity and abundance of small mammal communities?

Loss of mammal species in Australia in the last 200 years has been attributed to many factors including habitat removal and altered fire regimes. Decline in tree condition could contribute further to the ongoing decline of mammals. Eucalyptus wandoo trees are currently undergoing a decline in condition that can result in a loss of canopy and other changes to the habitat. This paper examines the relationships between E. wandoo tree condition, habitat characteristics and small mammal species richness and abundance. Live-capture trapping was conducted at 24 E. wandoo sites at Dryandra State Forest and Wandoo Conservation Park, Western Australia. Condition and microhabitat variables of E. wandoo were recorded for each site. Generalised additive mixed models revealed a range of habitat and tree condition characteristics that influenced small mammal abundance and species richness, including site litter cover, crown dieback, understorey vegetation cover and tree density. The availability of coarse woody debris played a large role in explaining the abundance of Cercartetus concinnus and Antechinus flavipes, along with other microhabitat and tree condition variables, such as tree leaf litter and crown dieback. Epicormic growth, crown density and the distance to the drift fence from E. wandoo trees were the common variables in the best model for the abundance of Sminthopsis griseoventer. The decline in condition of E. wandoo and the subsequent modifications to the microhabitat are correlated with changes in the small mammal community. A better understanding of how the decline of E. wandoo impacts small mammal communities could improve management practices in E. wandoo woodlands.

Effects of pruning and stand density on the productionof new epicormic shoots in young stands of pedunculate oak (Quercus robur L.)

Avoidance or control of epicormic shoots is among the major silvicultural challenges for the production of high-quality oak timber. In northern Europe, contemporary oak silviculture aims to produce valuable timber on a relatively short rotation, applying early, heavy thinning combined with artificial pruning. The aim of this study was to analyse the effects of pruning and stand density on the production of new epicormic shoots on young trees of pedunculate oak (Quercus robur L.). The study was based on two field experiments in even-aged stands of pedunculate oak subjected to different thinning practices and early selection of potential future crop trees. From ages 13 to 15 years, stem density was reduced to 300 trees ha−1, 1,000 ha−1 or stands remained unthinned. Pruning was conducted on selected trees at ages 22–24 years. At that age, the stem density in unthinned control plots ranged from 2,500 to 3,100 ha−1. All treatments were replicated twice within each experiment. Pruning led to an overall increase in the total production of new epicormic shoots. More epicormic shoots were produced in the lower part of the stem (0–3 m in height) than in the upper part (3–6 m). The number of new epicormic shoots increased with increasing stand density. Early, heavy thinning combined with high pruning at regular intervals may help shorten the rotation length for pedunculate oak without further reduction in wood quality than that which is caused by wider annual growth rings.

Restoration of lapsed beech pollards: Evaluation of techniques and guidance for future work

We examined the impact of two pollard restoration techniques on 38 ancient, lapsed beech pollards in the Basque Country (northern Spain) in four locations from 2007 to 2009. In 2007, prior to the trials, the trees were generally in good condition. Trials involved recutting the branches of trees with axes and/or chainsaws, and compared traditional Basque-style cuts, immediately above the bolling (main stem) close to the site of previous pollarding cuts, with gradual restoration techniques involving significantly smaller reductions of the canopy branches.Although one tree died following cutting, the responses of 36 pollards in 2009 (the third full season of regrowth), were generally good across the sites. Responses measured included the production of new shoots from dormant buds below the cuts and increases in the annual extension growth of retained branches. Stub length of cut branches was important with stubs longer than 500 mm producing significantly more new shoots from dormant buds. This finding supports results from recutting ancient beech pollards in England. The Basque-style cuts promoted more and longer epicormic growth. In addition, axe cuts encouraged more new shoots on cut branches, although the sample size and the possible confounding factor of stub length requires that this result be investigated further.

Effects of volcanic and hydrologic processes on forest vegetation: Chaitén Volcano, Chile

The 2008-2009 eruption of Chaiten Volcano (Chile) involved a variety of volcanic and associated hydro- logic processes that damaged nearby forests. These processes included coarse (gravel) and fine (silt to sand) tephra fall, a laterally directed blast, fluvial deposition of remobilized tephra, a variety of low-temperature mass-movement processes, and a pyroclastic flow. Each of these geophysical processes constitutes a type of ecosystem disturbance which involves a distinctive suite of disturbance mechanisms, namely burial by tephra and sediment, heating, abrasion, impact force, and canopy loading (accumulation of tephra in tree crowns). Each process affected specific areas, and created patches and disturbance gradients in the forest landscape. Coarse tephra ('gravel rain', >5 cm depth) abraded foliage from tree canopies over an area of approximately 50 km 2 north-northeast of the vent. Fine tephra (>10 cm depth) accumulated in tree crowns and led to breakage of branches in old forest and bowing of flexible, young trees over an area of about 480 km 2 . A directed blast down the north flank of the volcano damaged forest over an area of 4 km 2 . This blast zone included an area of tree removal near the crater rim, toppled forest farther down the slope, and standing, scorched forest around the blast perimeter. Fluvial deposition of >100 cm of remobilized tephra, beginning about 10 days after initiation of the erup- tion, buried floodplain forest in distinct, elongate streamside patches covering 5 km 2 of the lower 19 km of the Rayas River and several km 2 of the lower Chaiten River. Across this array of disturbance processes the fate of affected trees varied from complete mortality in the tree removal and pyroclastic flow areas, to no mortality in areas of thin tephra fall deposits. Tree damage included defoliation, loss of branches, snapping of tree trunks, abrasion of bark and ephiphytes, and uprooting. Damaged trees sprouted from epicormic buds located in trunks and branches, but sprouting varied over time among disturbance mechanisms and species. Although some effects of the Chaiten eruption are very similar to those from the 1980 eruption of Mount St. Helens (USA), interactions between biota and geophysical processes at Chaiten produced some unique effects. Examination of vegetation response helps interpret geophysical processes, and disturbance mechanisms influence early stages of biotic response to an eruption.

Growth and form of Quercus robur and Fraxinus excelsior respond distinctly different to initial growing space: results from 24-year-old Nelder experiments

Initial growing space is of critical importance to growth and quality development of individual trees. We investigated how mortality, growth (diameter at breast height, total height), natural pruning (height to first dead and first live branch and branchiness) and stem and crown form of 24-year-old pedunculate oak (Quercus robur [L.]) and European ash (Fraxinus excelsior [L.]) were affected by initial spacing. Data were recorded from two replicate single-species Nelder wheels located in southern Germany with eight initial stocking regimes varying from 1,020 to 30,780 seedlings·ha−1. Mortality substantially decreased with increasing initial growing space but significantly differed among the two species, averaging 59% and 15% for oak and ash plots, respectively. In contrast to oak, the low self-thinning rate found in the ash plots over the investigated study period resulted in a high number of smaller intermediate or suppressed trees, eventually retarding individual tree as well as overall stand development. As a result, oak gained greater stem dimensions throughout all initial spacing regimes and the average height of ash significantly increased with initial growing space. The survival of lower crown class ashes also appeared to accelerate self-pruning dynamics. In comparison to oak, we observed less dead and live primary branches as well as a smaller number of epicormic shoots along the first 6 m of the lower stem of dominant and co-dominant ashes in all spacing regimes. Whereas stem form of both species was hardly affected by initial growing space, the percentage of brushy crowns significantly increased with initial spacing in oak and ash. Our findings suggest that initial stockings of ca. 12,000 seedlings per hectare in oak and 2,500 seedlings per hectare in ash will guarantee a sufficient number of at least 300 potential crop trees per hectare in pure oak and ash plantations at the end of the self-thinning phase, respectively. If the problem of epicormic shoots and inadequate self-pruning can be controlled with trainer species, the initial stocking may be reduced significantly in oak.

Buds, bushfires and resprouting in the eucalypts

Eucalypts encounter a wide range of severe disturbances such as extensive defoliation by insects, major structural damage from cyclonic winds, as well as foliage and bark loss during drought and fire. Most healthy, mature eucalypts are not killed by these events, but regenerate vegetatively. With increasing intensity of disturbance, resprouting first occurs from the accessory buds in the small-diameter branchlets of the crown, followed by the epicormic buds in the medium- and large-diameter branches and stems, and then from the buds of the lignotuber. All these modes of regeneration are ultimately dependent on preventitious buds and, thus, the present review concentrates on axillary buds, their subsequent development into epicormic or lignotuber buds and their degree of protection from fire. The eucalypts have remarkably abundant, well protected and anatomically distinctive bud-forming structures in their leaf axils, branches, stems and lignotubers. These structures are quite consistent across this large genus, but are generally different from resprouting structures in many other plants. From an anatomical perspective, these structures seem best adapted to regeneration after fire, rather than damage from insects, storms or drought and this also correlates with ecological observations. On a worldwide basis, the eucalypts are some of the most successful post-fire resprouters, especially epicormic resprouting after medium- and high-intensity fires. Given the apparent ecological advantages of epicormic resprouting (the rapid reestablishment of extensive leaf area while simultaneously shading basal resprouters and seedlings) this could be an important factor in the success of eucalypts in Australia. Recent phylogenetic analysis has indicated a long relationship between eucalypts, fire and bud structures that facilitate resprouting.

Sawn timber grade recovery from a planted coast redwood stand growing in New Zealand

Timber from old-growth stands of coast redwood (Sequoia sempervirens (D.Don) Endl.) is dimensionally stable, resistant to surface checking and splitting, and has been widely used for outdoor purposes such as decking and cladding. Restrictions on the supply of redwood timber from Californian stands have increased the focus on timber from plantations grown elsewhere in comparatively short rotations. Little is known about the quality of timber produced from plantations of redwood in New Zealand. In this study trees from a 38-year-old pruned stand in Mangatu Forest near Gisborne, New Zealand, selected to cover the range of stem diameters present, were cross-cut into logs. Each log was then sawn into boards and each board was graded according to a simplified United States redwood grading system. Total timber volume (50 logs) was 16.2 m3, valued at USD 7,835 (2008 prices). This was less than might be expected in a well-managed stand. The 13 pruned logs accounted for 38% of the total volume recovered and 50% the total financial value of the timber. Pruned log quality assessed according to a pruned log index (PLI) was low, due to untimely pruning and the presence of epicormic shoots. Only 12% of the timber was graded clear and 32% of this came from pruned logs. Despite low PLI scores, the relationships between PLI, proportion of clear timber and pruned log value were reasonably strong. Recoveries from individual stems were variable. The most important determinants of log value were log size, which affected timber recovery; pruning quality, which governed the volume of clear wood; the proportion of heartwood, (valued for durability and appearance); and to a lesser extent, mid-stem branch vitality. High incidence of dead (bark-encased) knots in most of the unpruned logs contributed to the poor timber grade recovery results. Other defects (insect tunnels, rot and traumatic resin pockets) were associated with a 7% reduction in financial value. Accurate prediction of the pattern of distribution of heartwood inside a redwood log could play a major role in maximising the value of recovered timber.

USING CONCEPTS OF SHOOT GROWTH AND ARCHITECTURE TO UNDERSTAND AND PREDICT RESPONSES OF PEACH TREES TO PRUNING

One definition of horticulture is art of cultivating garden plants and pruning is a horticultural practice that is traditionally approached as more of an art than a science. This is largely because of the complexity of tree growth and development and a lack of general understanding and appreciation about the processes involved in governing shoot and tree growth and development. However recent tree architectural studies have provided systematic analyses of the shoot growth and statistical and dynamic simulation models have been developed that predict tree development and responses to pruning based on scientific concepts. These concepts include apical dominance (and its subcomponents; correlative inhibition, apical control and shoot epinasty); prolepsis and syllepsis; preformation and neoformation; epicormic shoot formation and plastochron (leaf emergence rates). In this paper we will discuss how many of these concepts can be combined with hidden semi-Markov chain models of shoot bud fates and a simulation model of source-sink interactions in peach trees (L-PEACH) to understand and predict natural development of peach trees and their responses to pruning. The results of these modeling efforts help explain the architectural and physiological basis of several common, empirically-based pruning systems used in California. These concepts also provide an understanding of the limitations of relying primarily on the use of pruning to control size of trees growing on commonly used invigorating rootstocks. This research demonstrates how computer simulation modeling can be used to test and analyze interactions between environmental factors and management practices in determining patterns of tree growth and development.

Fagus sylvatica trunk epicormics in relation to primary and secondary growth.

European beech epicormics have received far less attention than epicormics of other species, especially sessile oak. However, previous work on beech has demonstrated that there is a negative effect of radial growth on trunk sprouting, while more recent investigations on sessile oak proved a strong positive influence of the presence of epicormics. The aims of this study were, first, to make a general quantification of the epicormics present along beech stems and, secondly, to test the effects of both radial growth and epicormic frequency on sprouting. In order to test the effect of radial growth, ten forked individuals were sampled, with a dominant and a dominated fork of almost equal length for every individual. To test the effects of primary growth and epicormic frequency, on the last 17 annual shoots of each fork arm, the number of axillary buds, shoot length, ring width profiles, epicormic shoots and other epicormics were carefully recorded. The distribution of annual shoot length, radial growth profiles and parallel frequencies of all epicormics are presented. The latter frequencies were parallel to the annual shoot lengths, nearly equivalent for both arms of each tree, and radial growth profiles included very narrow rings in the lowest annual shoots and even missing rings in the dominated arms alone. The location of the latent buds and the epicormics was mainly at branch base, while epicormic shoots, bud clusters and spheroblasts were present mainly in the lowest annual shoots investigated. Using a zero-inflated mixed model, sprouting was shown to depend positively on epicormic frequency and negatively on radial growth. Support for a trade-off between cambial activity and sprouting is put forward. Sprouting mainly depends on the frequency of epicormics. Between- and within-tree variability of the epicormic composition in a given species may thus have fundamental and applied implications.

Effect of auxins on axillary and de novo shoot regeneration from in vitro shoot cultures derived from forced epicormic buds of teak (Tectona grandis L.)

In this presentation, we report on de novo and axillary shoot regeneration and rooting of shoots maintained over a long term, from cultures of Tectona grandis L. Shoot-tips of teak shoots forced from epicormic buds were used as the starting material for axenic shoot-culture establishment. Long term maintenance of such axenic shoot cultures was carried out by regular sub-culturing on MS media supplemented with N6-benzyleadenine (BA, 8.8 μmol·L−1) and indole-3-butyric acid (IBA, 2 μmol·L−1) for 24 months. Vigorously growing shoot tips (2–3 cm long) were inoculated on the MS basal medium supplemented with different concentrations (0, 1, 2, 4, 6, 8 or 10 μmol·L−1) of either IBA or α-naphthaleneacetic acid (NAA) for rooting. Axillary and de novo shoots were developed from axillary and cut basal ends of shoots, respectively. Shoots growing on auxins were further sub-cultured (every 15 days) and maintained for 45 days. The greatest number of de novo (5.06) as well as axillary shoots (2.85) was observed on the MS medium supplemented with 10 μmol·L−1 NAA or 8 μmol·L−1 IBA, respectively, after 45 days. The combinations of both IBA (μmol·L−1) + NAA (μmol·L−1) were tested at different concentrations (4 + 4, 6 + 6, 8 + 8) supplemented to a half strength MS basal medium with 0.1% activated charcoal for rooting of decapitated and non-decapitated de novo and axillary shoots. Rooting from non-decapitated de novo shoots was highest (93.33%) with a mean number of roots of 4.61 on this medium, supplemented with 6 μmol·L−1 IBA + 6 μmol·L−1 NAA, after 36 days of initial culture. Individual auxin, however, was not effective for root induction. Rooted shoots were acclimatized in a green house and after four weeks plantlets were transferred to the field.

Observation of Quercus petraea epicormics with X-ray CT reveals strong pith-to-bark correlations: Silvicultural and ecological implications

Our knowledge about oak epicormics has considerably increased in recent years, particularly thanks to the external recording of all epicormic types (suppressed buds, bud clusters, sprouts, picots and burls) and to internal observations made using X-ray computed tomography (CT). Several stages of epicormic ontogeny have been identified. The aims of this study were to provide the quantification of oak epicormic ontogeny and to identify the relationships between epicormics present near the trunk pith and epicormics present at the surface of the bark, based on data recovered from X-ray CT scanning. One to three 1-m-long logs per tree were recovered from crop trees felled in five experimental stands located in four forests in northern France. The manual interpretation of the images provided by X-ray CT makes it possible to identify the origin and fate of every rameal trace, i.e., branch knot, epicormic shoot or trace of suppressed buds. The fate of branches and the origin and the fate of suppressed buds and sprouts were quantified. A strong relationship between the number of epicormics at the surface of the bark and the number of epicormics near the pith was highlighted. This could result in important silvicultural recommendations in terms of the necessary early selection of crop trees with the lowest number of epicormics possible, especially suppressed buds. From a broader ecological point of view, this paves the way to a better understanding of the variability of the sprouting response induced by disturbances, which is assumed to develop at an early stage in the tree life.