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How carbohydrate reserves change in conifers during drought and bark beetle attacks are poorly understood. We investigated changes in carbohydrate reserves and carbon-dependent terpene defenses in ponderosa pine trees experimentally subjected to two levels of drought stress (via root trenching) and two types of biotic challenge treatments (pheromone-induced bark beetle attacks or inoculations with crushed beetles that include beetle-associated fungi) for two consecutive years. Our results showed that trenching did not influence carbohydrates whereas both biotic challenges reduced amounts of starch and sugars of trees. However, only the trenched-beetle attacked trees depleted carbohydrates and died within the first year of bark beetle attacks. While live trees contained higher carbohydrates than dying trees, amounts of constitutive and induced terpenes produced did not vary between live and beetle-attacked dying trees, respectively. Based on these results we propose that reallocation of carbohydrates to terpenes during the early stages of beetle attacks is limited in drought-stricken trees, and that the combination of biotic and abiotic stress leads to tree death. The process tree death is subsequently aggravated by beetle girdling of phloem, occlusion of vascular tissue by bark beetle-vectored fungi, and potential exploitation of host carbohydrates by beetle symbionts as nutrients.

スターフルーツ（Averrhoa carambola L.）は沖縄や鹿児島などで栽培されている熱帯果樹である。本研究では，スターフルーツの着花数の増加と開花期の調節を目的として，環状剥皮，結縛，摘心および環状剥皮の幅の違いが着花に及ぼす影響について調査した。1年生の直立枝と下垂枝に分け，環状剥皮，結縛，摘心処理をそれぞれ行った結果，環状剥皮による着花促進がみられた。直立枝では花房数の有意な差はみられなかったが，下垂枝では花房数および小花数が最大であったことから，環状剥皮はスターフルーツにおいて着花促進効果が最も高い方法であると考えられた。さらに環状剥皮の幅の違いについて，1年生の枝に2.5mm, 5mm, 10mm幅でそれぞれ処理を行った。その結果，環状剥皮で着花促進効果がみられ，処理5週後の枝あたりの花房数が2.5mm幅区で最も多くなった。花房が着生している枝の割合は2.5mm, 5mm, 10mm幅区で90%以上に達した。これらの結果から，着花数増加のためにスターフルーツの枝に環状剥皮を行う場合，処理幅は2.5mmで十分であることが示された。, Star fruit (Averrhoa carambola L.) is a tropical fruit tree indigenous to Java and the Moluccas Islands that bears fruit throughout the year when cultivated under tropical conditions. In Japan, it is cultivated in Okinawa and the Kyushu region and has two annual flowering periods : one from May to June and the other from September to October. Cultivation of this species has been hindered by the lack of established cultivation methods, and because it produces few flowers. Consequently, controlling the flowering period and increasing the number of flowers would be advantageous for improving star fruit production. The influence of girdling, strapping, and pinching treatments to increase flower setting were investigated in different treatment plots in a vinyl greenhouse at Tokyo University of Agriculture, Kanagawa, Japan. The treatments were performed on upright and descending branches of starfruit. Descending branches had larger numbers of flower clusters than upright branches. Compared to the control, girdling significantly increased the number of flower clusters on descending branches, but no such effect was observed on upright branches. In addition, the influence of girdling width (2.5, 5, and 10 mm) on flower setting on horizontal branches was examined. Compared to the control, the number of flower clusters increased for all girdling widths. The largest numbers of flower clusters and small flowers were observed in the 2.5 mm width girdling plot at 5 weeks after treatment. For the 2.5, 5, and 10 mm width girdling plots, more than 90% of branches had flower clusters at 5 weeks after treatment, compared to 30% in the control plot. The findings demonstrate that girdling improves flower setting in star fruit.

The present study was carried out during two successive of 2016 and 2017 on 10 years old Balady mandarin (Citrus reticulate Blanco) trees budded on sour orange rootstock (Citrus aurantium L. Osbeck) and spaced 3.5×3.5 meters apart. Trees have been treated with girdling and gibberellic acid and were grown in sandy soil under drip irrigation system in a private orchard at Al-kamal region- Ismalia Governorate, Egypt, in July and December. The aim of this work was to study the effect of girdling and gibberellic acid on the vegetative growth, yield and fruit quality. The chosen trees girdled with 2 mm, 4 mm width and gibberellic acid was sprayed (at 50 and 100 ppm) alone or in combination with girdling in each season. Results showed that, girdling 4 mm+100 ppm gibberellic acid have given the best enhanced vegetative growth parameters in terms of leaf area, carbohydrate and chlorophyll contents in the leaves of Balady mandarin trees in both seasons. Moreover, treatment of girdling 4 mm in December and girdling 4 mm+50 ppm GA3gave the best fruit length, diameter as compared to control treatment. Yield and fruit quality of the chosen trees were significantly increased by all treatments as compared to control in both seasons.

Girdling is an ancient agronomic technique that causes a change in the distribution of photosynthates, mineral nutrients and plant hormones. The aim of this study was to assess the effect of girdli...

In North America, notodontid caterpillars feed predominantly on hardwood trees; some cause significant economic damage with periodic outbreaks. The late instars of several species cut girdles around the petiole, rachis, or stem before feeding on distal leaf blades. Little is known about the benefits or costs of girdling for caterpillars. In this paper, we analyzed the energetic cost of girdling by comparing final instars of a girdling notodontid, Oedemasia leptinoides, with two non-girdling notodontids, Cecrita guttivitta and Lochmaeus manteo. Time allocated to four behaviors (girdling, feeding, walking, and inactive) was measured in the field with 3-h observations each day over three days. We also measured metabolic rates for the four behaviors using flow-through respirometry. The metabolic rate for each behavior was multiplied by the time spent over the 9 h of observation to estimate the total energetic cost of each behavior. In the field, O. leptinoides on black hickory (Carya texana) spent 4.6 ± 0.9% of their time girdling. They cut girdles primarily on the first day and fed on leaves mostly on days 2 and 3. Their metabolic rate during girdling was similar to feeding and walking, but greater than inactivity. Overall, the larvae utilized 6.4 ± 1.2% of their total energy while girdling. Relative to non-girdlers, O. leptinoides larvae spent significantly less time and energy feeding on leaves suggesting a trade-off between girdling and feeding. To our knowledge, this study is the first to quantify the energetic cost of an insect behavior for modifying host plants before feeding.

Robinia pseudoacacia L. has been widely planted worldwide for a variety of purposes, but it is an aggressive invader in many regions. To control invasion by the species, we examined the effectiveness of girdling young trees to ground level to kill trees and preclude sprout development through comparison among girdling, clearcut and control treatments on the Tama river terrace, Tokyo. More than 99% of R. pseudoacacia trees were killed by girdling. The number of sprouts that developed from roots and stumps after girdling was distinctly reduced compared with that observed after clearcutting. We also conducted girdling of young trees of Ailanthus altissima (Mill.) Swingle, which shows similar developmental and ecological characteristics to R. pseudoacacia, and the two species are often sympatric. More than 98% of A. altissima trees were killed, but a higher number of sprouts developed from A. altissima stumps compared with that from R. pseudoacacia stumps. These results indicate that girdling young trees to ground level is an effective method of controlling R. pseudoacacia by killing the stem and precluding sprout development. The girdling method is simple to apply and imposes a low burden on the surrounding environment.

The effect of cane girdling on grape skin phenolic composition and concentration was examined on three Hungarian table grape varieties, i.e. noir-skinned 'Esther', rose-skinned 'Lidi', and blanc-skinned 'Fanny'. Girdling was conducted at the BBCH 75 phenological growth stage (pea-sized berries). A significant increase was observed in anthocyanin-glycosides in the treated berry skins irrespective of the cultivar. Other phenolic substances (gallic acid, trans-resveratrol, (+)-catechin, quercetin-3-glucuronide) were less sensitive to the treatment, but noticeable differences were found between the genotypes.

The present investigation was carried out at farmer’s field, Sainik Farm, Patharchatta, Pantnagar, District Udham Singh Nagar, Uttarakhand. The experiment was conducted to study the effect of girdling on growth, flowering and fruiting attributes in Litchi cv. Late Bedana. Twenty-year-old litchi trees consisted of seven treatments with two level of girdling severity of 25% and 50% primary branches in combination of girdling width of 2 mm, 4 mm and 6 mm, along with ungirdled control which were tested with randomized block design with three replications. The results indicated that all the litchi trees which were subjected to different severity and width of girdling had more flowering intensity (%) fruit set (%) and fruit retention (%) and girdling also reduced fruit drop as compared to control. However, the treatment girdling of 50% of primary branches + 4 mm wide had significant effect on improving fruit set (38.44%) and fruit retention (14.07%). Girdling blocks the downward flow of carbohydrate from leaves to roots thus the carbohydrate may accumulate above the girdled portion which resulted in additional supply of carbohydrates from leaves to fruits, therefore, the fruit yield and fruit quality of litchi may increase.

As we know auxins were the first class of plant hormones to be discovered that use to kill weeds, promote growth and fruit quality of particular plant.in this review paper I have compile the summary of Auxin as important hormone required to carry any essential function in plant viz., delaying, early maturation, help in rooting etc. I have categorized crop in accordance with role of auxin with tropical and temperate crops, which I hope could help scientist for further breeding programme, to acknowledge the role with its pros and cons. In mango it mainly influence the girdling effect, fruit repining process, and in grape it helps in the maturation and quality maintenance of berries on the other hand in apple with the appropriate concentration it triggers the production of ethylene which eventually promotes ripening accompany it helps in the translocation of calcium which maintain the fruit quality. In guava auxin is immensely used in the form IAA and IBA which operates as a rooting hormone in this crop to hasten the growth during layering on the other hand in pear and peach its application influence the growth of primary and secondary shoot.

African mahogany (Khaya spp.) produces high-value wood, and its cultivation is expanding in tropical regions. The silvopastoral system is an alternative method for growing timber trees, but may involve cattle stripping bark from trees, which limits its usefulness. We evaluated cattle bark-stripping rates in two African mahogany species, K. grandifoliola and K. senegalensis, in a silvopastoral system with Guinea grass, Panicum maximum, in South-eastern Brazil. Cattle had free access to plantations of both tree species for 2 weeks in May 2018 and July 2019, when trees were 5 and 6 years old, respectively. In 2018, we found bark-stripping only in K. grandifoliola, but in 2019 both species were bark-stripped. The proportion of bark-stripped trees was higher for K. grandifoliola than for K. senegalensis. Considering both years, 29/155 (18.7%) K. senegalensis trees and 106/153 (69.3%) K. grandifoliola trees had some of their bark-stripped by cattle. Bark-stripped trees had lower trunk diameter growth than unaffected trees, and their growth was affected by the degree of bark-stripping. Some trees were girdled by bark-stripping. These trees dried up, and some of them fell down 1 year after girdling. In 2019, despite the high herbage mass, levels of crude protein in the pasture were very low, which may have stimulated bark-stripping. Although we could not identify the reasons for bark-stripping, we recommend avoiding the use of silvopastoral systems with cattle and African mahogany in times of the year when pasture has a low quality.

The pre-disturbance vegetation characteristics that predict carbon (C) cycling responses to disturbance are not well known. To address this gap, we initiated the Forest Resilience Threshold Experiment, a manipulative study in which more than 3600 trees were stem girdled to achieve replicated factorial combinations of four levels (control, 45, 65, and 85% gross defoliation) of disturbance severity and two disturbance types (targeting upper or lower canopy strata). Applying a standardized stability framework in which initial C cycling resistance to disturbance was calculated as the first-year natural log response ratio of disturbance and control treatments, we investigated to what extent pre-disturbance levels of species diversity, aboveground woody biomass, leaf area index, and canopy rugosity—a measure of structural complexity—predict the initial responses of subcanopy light-saturated leaf CO2 assimilation (Asat), aboveground wood NPP (ANPPw), and soil respiration (Rs) to phloem-disrupting disturbance. In the year following stem girdling, we found that above-ground C cycling processes, Asat and ANPPw, were highly resistant to increases in disturbance severity, while Rs resistance declined as severity increased. Disturbance type had no effect on first-year resistance. Pre-disturbance aboveground woody biomass, and canopy rugosity were positive predictors of ANPPw resistance and, conversely, negatively related to Rs resistance. Subcanopy Asat resistance was not related to pre-disturbance vegetation characteristics. Stability of C uptake processes along with Rs declines suggest the net C sink was sustained in the initial months following disturbance. We conclude that biomass and complexity are significant, but not universal, predictors of initial C cycling resistance to disturbance. Moreover, our findings highlight the utility of standardized stability measures when comparing functional responses to disturbance.

Grapevine red blotch virus (GRBV) is the causal agent of grapevine red blotch disease, which affects wine grapes and leads to reduced crop yield and quality. While some virus spread can be attributed to the propagation of infected plant material, a greenhouse assay recently demonstrated that the threecornered alfalfa hopper (Membracidae: Spissistilus festinus Say) can transmit GRBV between grapevines. While S. festinus is not considered an economic pest of wine grapes, this species is present in California vineyards and their feeding can cause petiole girdling. Recent surveys have noted a correlation between S. festinus populations and GRBV-positive vines in vineyard areas adjacent to riparian habitat. Here, S. festinus populations were monitored over a 2-yr period at multiple vineyard sites adjacent to riparian habitats. At each site, insects were sampled from ground covers and the vine canopy at the vineyard edge and interior, and vines in both locations were evaluated for petiole girdling. Results indicate that there was no difference in abundance of S. festinus at the vineyard edge and interior. Populations in the vine canopy were highest in the late spring and early summer, and this was followed by the appearance of petiole girdling, indicating a key period of potential GRBV transmission. Furthermore, activity in the vine canopy appears to be amplified when the quality of ground covers is reduced as the season progresses. That said, overall populations of S. festinus were relatively low and additional work is needed to characterize the timing and efficiency of transmission under field conditions.

The experiment conducted in the Kampinos National Park since 2015 was aimed at assessing the sprouting ability of black cherry (Prunus serotina Ehrh.) in response to different measures of mechanical control and mycobiota colonizing the dying trees. Basal cut-stump, cutting at ca. 1 m above the ground and girdling were performed on 4 terms, two plots and applied to 25 trees, 600 trees in total. Sprouts were removed every 8 weeks since the initial treatment for 4 consecutive growing seasons, except winter-treated trees. At the end of the fourth season of control, 515 out of 600 trees were dead (86%): 81% on Lipków and 90% on Sieraków plot. Among 18 experiment variants with sprouts removal, 17 showed more than 80% of dead trees. The lowest, 76% share, concerned summer cut-stump at the base of the tree. For winter measures, the share of dead trees was lower in all cases and ranged from 28% to 64% proving that sprouts removal contributes to the drop of sprouting strength and quicker dying of the trees. Almost 80% of trees showed sporocarps that represented 51 taxa of macrofungi in total, including 6 Ascomycota and 45 Basidiomycota. The group of six most frequently encountered fungi includes: Hyphoderma setigerum, Bjerkandera adusta, Peniophora cinerea, Armillaria ostoyae, Nectria cinnabarina, Stereum hirsutum. Both plots had similar share of black cherry individuals with sporocarps of macrofungi, that is, 81% and 78% for Sieraków and Lipków respectively. The share of colonized trees and the number of reported macrofungal taxa increased significantly compared to the year following the treatment. In addition, the composition of macrofungi changed with the progressing dying of trees. These results broaden the knowledge about macroscopic fungi colonising and living on black cherry within its secondary range of distribution. Moreover, one macrofungus and two microfungi new for KNP are reported.

We monitored six healthy dominant trees and six girdled Scots pine trees for two successive growing seasons (2014 and 2015) to investigate the seasonal dynamics, cambial activity, and morphology of the new xylem and phloem cells formed under environmental stress when girdling was applied during the dormant period (15 January 2014). Microcore (1.8 mm) samples were collected weekly using a Trephor tool above and below the girdling area, and weather data were measured on site. Drought stress in combination with girdling reduced the total number of differentiation days cell formation. In 2014, no significant differences in tracheid dimensions were observed between the girdled area and the control trees, while in 2015, the control trees showed significantly smaller cell wall thickness and radial dimensions of the latewood tracheids (LW) compared to 2014 and girdled trees had no occurrence of LW. Under stressful heat waves and prolonged periods of no precipitation, the trees tended to reduce the number of tracheids that were formed and exhibited smaller radial dimensions (narrower tree rings) to increase their hydraulic efficiency. Trees responded to limited water availability by forming intra-annual density fluctuations (IADFs L) in the zone of the LW to overcome stressful conditions. Although xylem cell differentiation was affected by stressful conditions, no significant variability in phloem cell dimensions was observed. Thus, the phloem tissue was less sensitive to exogenous factors.

Entre las dificultades que presenta la producción de aguacate ‘Hass’ en Nayarit, están los bajos precios debido a la estacionalidad de la cosecha en los meses de septiembre a noviembre. El objetivo de la investigación fue identificar la fecha de anillado capaz de adelantar la floración y con ello adelantar la época de cosecha. Se evaluaron cuatro fechas de anillado (tratamientos) con diez repeticiones en un diseño experimental de bloques completamente al azar, generando los siguientes tratamientos (T): T1 = 15 de agosto, T2 = 15 de septiembre, T3 = 15 de octubre, T4 = 15 de noviembre en el año 2017 y T5 (sin anillar). Cada anillado fue de 0.5 cm de ancho en el 50% de las ramas. Las variables evaluadas fueron: concentración N, P, K, Ca y Mg en etapa vegetativa y floración, días a inicio de floración, número de brotes florales por m3 de dosel, días a inicio de fructificación, largo de panícula, grosor de panícula, producción de fruto por árbol y materia seca de mesocarpio. El análisis de varianza mostró diferencias significativas para días a inicio de floración, días a inicio de fructificación, largo de panícula, materia seca en mesocarpio y producción de fruto. No se presentaron diferencias en concentración nutrimental en las etapas fenológicas. Se concluyó que la fecha de anillado del 15 de agosto adelantó la floración 52 días comparado contra el testigo sin anillado y permitió adelantar la cosecha al mes de mayo.

Summary Experimental evidence that nonstomatal limitations to photosynthesis (NSLs) correlate with leaf sugar and/or leaf water status suggests the possibility that stomata adjust to maximise photosynthesis through a trade-off between leaf CO2 supply and NSLs, potentially involving source-sink interactions. However, the mechanisms regulating NSLs and sink strength, as well as their implications for stomatal control, remain uncertain. We used an analytically solvable model to explore optimal stomatal control under alternative hypotheses for source and sink regulation. We assumed that either leaf sugar concentration or leaf water potential regulates NSLs, and that either phloem turgor pressure or phloem sugar concentration regulates sink phloem unloading. All hypotheses lead to realistic stomatal responses to light, CO2 and air humidity, including conservative behaviour for the intercellular-to-atmospheric CO2 concentration ratio. Sugar- and water-regulated NSLs are distinguished by the presence/absence of a stomatal closure response to changing sink strength. Turgor- and sugar-regulated phloem unloading are distinguished by the presence/absence of stomatal closure under drought and avoidance/occurrence of negative phloem turgor. Results from girdling and drought experiments on Pinus sylvestris, Betula pendula, Populus tremula and Picea abies saplings are consistent with optimal stomatal control under sugar-regulated NSLs and turgor-regulated unloading. Our analytical results provide a simple representation of stomatal responses to above- and below-ground environmental factors and sink activity. Experimental evidence that nonstomatal limitations to photosynthesis (NSLs) correlate with leaf sugar and/or leaf water status suggests the possibility that stomata adjust to maximise photosynthesis through a trade-off between leaf CO2 supply and NSLs, potentially involving source-sink interactions. However, the mechanisms regulating NSLs and sink strength, as well as their implications for stomatal control, remain uncertain. We used an analytically solvable model to explore optimal stomatal control under alternative hypotheses for source and sink regulation. We assumed that either leaf sugar concentration or leaf water potential regulates NSLs, and that either phloem turgor pressure or phloem sugar concentration regulates sink phloem unloading. All hypotheses led to realistic stomatal responses to light, CO2 and air humidity, including conservative behaviour for the intercellular-to-atmospheric CO2 concentration ratio. Sugar-regulated and water-regulated NSLs are distinguished by the presence/absence of a stomatal closure response to changing sink strength. Turgor-regulated and sugar-regulated phloem unloading are distinguished by the presence/absence of stomatal closure under drought and avoidance/occurrence of negative phloem turgor. Results from girdling and drought experiments on Pinus sylvestris, Betula pendula, Populus tremula and Picea abies saplings are consistent with optimal stomatal control under sugar-regulated NSLs and turgor-regulated unloading. Our analytical results provide a simple representation of stomatal responses to above-ground and below-ground environmental factors and sink activity.

Natural habitats increasingly face the introduction and spread of non-native species. Under the right conditions, non-native species can become invasive over time. This issue is now being addressed by many experts and researchers who are using and developing various approaches and methods to limit and eliminate or suppress problematic plant species. Many invasive plants are already spreading uncontrollably in urban and forestry areas, causing health hazards, environmental and economic damage and negatively impacting natural ecosystems. The use of chemical agents is generally limited, so our only option to control and suppress the problematic species is mechanical removal. In this research suppression by tree stem wounding, i.e., incomplete girdling, was used. This type of injury causes the plant to lose its vitality, become weaker after first year and then die within a few years. Using a research approach, we chronologically monitored the response of cherry laurel (Prunus laurocerasus L.) stem tissue to mechanical wounding of the incomplete girdling. Magnetic resonance imaging (MRI) and light microscopy were used for monitoring moisture content and anatomical changes in different periods after injury. The results of the study showed that cherry laurel, with an intense wound tissue response and other changes, is a species with good compartmentalization potential. The rapid and intense tissue response to injury requires high energy and nutrient consumption and consequently leads to a loss of vigour and mechanical stability, which may result in plant destruction. Results revealed that mechanical wounding by incomplete girdling is a successful method for suppression of non-native and invasive cherry laurel.

Impacts of forest management practices on soil carbon (C) and nitrogen (N) dynamics remain under debate due to complex interactions between belowground biogeochemical processes. To optimize practices that minimize soil C and N losses, we investigated the effects of management practices on soil C and N fluxes, including the leaching of dissolved organic C (DOC) and N, by comparing clearcutting, stem girdling (removal of the bark and phloem tissue), and control treatments in a Japanese cedar plantation. Canopy opening by clearcutting is hypothesized to have a greater effect on soil C loss and the leaching of nitrate-N relative to girdling. Results showed that clearcutting increased soil heterotrophic respiration (organic matter decomposition) and lead to a loss of soil organic C (2.9–3.7 Mg C ha−1 yr−1). Higher litter inputs from girdled tree dieback caused an increase in DOC fluxes from the organic horizon, whereas the loss of fresh litter inputs decreased DOC fluxes from the organic horizon following clearcutting. Clearcutting increased nitrate-N leaching by 3.3–4.8 kg N ha−1 yr−1 due to the loss of plant N uptake and the increased mineralization of soil organic matter, but high C/N ratios in dissolved organic matter limited nitrate leaching in the girdled treatment. Effects of forest management practices on soil C loss and nitrate leaching loss could be variable, but the slash application in clearcutting and the slow dieback in stem girdling could mitigate soil C loss and nitrate leaching loss.

To investigate the importance of shoot-to-root communication in modulating tissue phytohormone balance as the soil dries, root and leaf hormonal profiles were determined in soybean plants (Glycine max L. Merr. cv. Siverka) exposed to factorial girdling (achieved surgically on Day 0 by excising the phloem with a sharp razor blade thereby disrupting basipetal hormone transport) and soil drying treatments. Plants were randomized into 2 groups: girdled and intact plants, and each girdled group was further separated into two groups: well-watered and soil drying. Thus the experiment was a two (± girdling) x two (± soil drying) factorial experiment. Within 26 h while the soil was still moist, girdling increased root ACC (by 11-fold) and decreased root ABA concentrations (by 28 %), decreased foliar iP, tZ and GA concentrations (by up to 90 %), and increased foliar ABA and JA concentrations (by 1.6- and 4.9-fold respectively) compared to intact plants, but only leaf ABA concentration correlated with partial stomatal closure. Two days of soil drying increased root ABA and JA concentrations in intact plants, and both hormones significantly decreased in roots of girdled plants compared to intact plants. Soil drying increased foliar iP, ABA, JA and SA concentrations by 1.3-, 2.5-, 1.3- and 1.4-fold respectively compared to well-watered intact plants by the end of the experiment, but girdling prevented this foliar iP, ABA, JA accumulation compared to droughted intact plants. Thus, girdling affects the co-ordination of root and leaf phytohormone concentrations such as JA and ABA, which may transiently modulate stomatal closure. However, leaf ABA concentration varied consistently with root ABA concentration across all treatments, and explained more of the variation in stomatal conductance than any other hormone or leaf water potential., PC thanks the SEW-REAP Project (EuropeAid ECRIP ICI+/2014/348- 010) and a Lancaster University Faculty studentship for supporting his PhD research

Cone development in conifer species is crucial to ensure sexual regeneration. A better understanding of carbon (C) source-sink relations at the branch level can guide strategies for improving resource allocation to reproduction. In particular, the evaluation of C relations between vegetative and reproductive branches is helpful to test whether tree branches are carbon autonomous. With this aim, we integrated girdling and defoliation treatments with 13C pulse labeling in situ to evaluate C autonomy in cone-bearing branches of P. koraiensis during the growing season. Girdling significantly reduced branch volumetric development, branch biomass, and non-structural carbohydrates across foliar, twig, and cone tissues, it also arrested cone development. Defoliation effects on these variables were minor, although they tended to increase with defoliation intensity. In addition, 13C increased by 4.5% and 45.4% after 4 h and 24 h of 13C labeling in unlabeled cone-bearing branches, respectively, indicating the C translocation from labeled vegetative branches. These results indicate that the cone-bearing branches are not C autonomous and that the development of female cones relies to a great extent on C import from neighboring branches. However, the amount of C translocated was largely dependent on manipulative alterations of the source-sink balance, thereby denoting extensive plasticity in the degree of branch C autonomy. These results shed light on the reproductive physiology of P. koraiensis.

The use of well-feathered nursery trees on dwarfing rootstocks is crucial for establishing high-density apple orchards to ensure early production. Training trees to develop a tall spindle canopy architecture has gained popularity in high-density orchards during the past decade. However, commercially produced nursery trees often lack feathers or are unevenly branched, making initial training decisions difficult and delaying precocious fruiting. In this project, we studied the vegetative meristem activation response to partial scoring or partial girdling of the bark cambium above the bud, with and without application of 500 ppm Promalin (gibberellin4+7 + benzyladenine), tip removal of the tree leader at the silver tip stage on April 23, 2019, Promalin spray at 500 ppm at post-bloom stage on May 7, 2019, and nitrogen (N) as UAN-32 (32% N) application at five levels (60, 80, 100, 120, or 140 g actual N/tree) on June 20, 2019, in newly planted un-feathered or unevenly branched “Aztec Fuji” trees on Budagovsky 9 (Bud 9) in southwest Idaho, USA. Grower’s Short Cut trees received a heading cut to the leader at 60 cm above the ground and resulted in the emergence of 5 - 6 strong branches near the heading cut. These trees had larger trunk cross-sectional areas than scored or girdled trees. Scoring or girdling, with or without Promalin, significantly improved branching by increasing the number of branches and bourse shoots. In many cases, the effects of partial scoring, with or without Promalin, were similar to those of bark girdling which is a more risky and time-consuming process. Branches induced by scoring and girdling had sharper crotch angles relative to the vertical leader. Spraying Promalin during the post-bloom stage at 500 ppm was not as effective as scoring or girdling to initiate branches. Additional N rates or removal of the leader tip did not significantly impact branch induction.

Understanding short- and long-term responses of forest nutrient cycling to disturbance is vital to predicting future forest function. Mortality of ash trees (Fraxinus spp.) due to emerald ash borer [EAB, Agrilus planipennis (Coleoptera: Buprestidae)] invasion is likely to alter ecosystem processes within infested stands throughout North America. In particular, the loss of Fraxinus nigra (black ash) from F. nigra-dominated swamps may significantly impact the biogeochemical cycles within these ecologically important wetlands. A multiyear manipulative study of nine F. nigra-dominated wetlands in Michigan, USA was undertaken to investigate the potential response of above- and belowground biogeochemical processes to EAB. Short- and long-term changes to site conditions following infestation were emulated by respectively girdling or felling F. nigra saplings and overstory trees. Following disturbance, a short-term reduction in demand for soil nitrogen (N) by dominant canopy species was hypothesized to result in increased soil N availability and a subsequent increase in N uptake by retained species. Though reduced total N return via litterfall indicated decreased demand, this resulted in minimal impacts to soil N availability following treatment. Additionally, increased N uptake by co-dominant Acer rubrum (red maple) and Betula alleghaniensis (yellow birch) was not observed; these combined responses may be attributable to increased immobilization of N by soil microbes. In the 3 years following treatment, the response of foliar characteristics of residual stems—including decreased N concentrations and increased leaf mass per area—appeared to be driven primarily by aboveground conditions and a change from shade- to sun-acclimated leaves. While increased microbial immobilization of N may reduce long-term changes in site fertility, these responses may also limit the potential for short-term positive growth responses of extant woody vegetation. In the longer term, replacing N-rich F. nigra leaf litter with that of A. rubrum and B. alleghaniensis, which have lower N content, is likely to have important feedback effects on soil processes.

Hazelnut (Corylus avellana L.) is an important nut crop with clear mast seeding behaviour leading to alternate yield and, thus, to management issues. It was hypothesized that masting is associated to accumulation/depletion of carbon within storage tissues (i.e. stem, large branches, roots). We hypothesized that fruit yield depends both on carbon fixed by leaves on the same branch and carbon stored in the main stem. We therefore conducted a manipulation of carbon sink-source resources on fruit-bearing branches of C. avellana cv. ‘Tonda di Giffoni’ by combining girdling and defoliation on a set of branches. We measured the number and diameter of nuts and leaves, the dry weight of fruits and seeds and the amount of blanks over the growing season. We also estimated the whole tree leaf area by allometric equations and the tree yield by collecting all nuts separately on 15 trees at maturity. The average seed dry mass in the un-defoliated girdled treatment was significantly lower than the control (0.5 vs. 0.9 g) suggesting that the fruit-bearing branches need to import carbon from the main stem and that the carbon autonomy of fruit-bearing branches is not supported during kernel maturation process. We also observed that the correlation at whole tree level between leaf area and seed mass is strong in non-masting years, while it becomes weaker in masting years reinforcing the hypothesis that the productivity of masting yields also relies on stored resources.

The prolonged absence of fire in Oregon white oak (Quercus garryana) woodlands and savannas of the Pacific Northwest has resulted in substantial conifer encroachment over the past century. Use of low intensity prescribed burns often lacks sufficient intensity to kill larger encroached trees, requiring alternative approaches. In the Bald Hills region of Redwood National Park, managers have implemented girdling treatments to kill Douglas-fir (Pseudotsuga menziesii) over the past two decades with the objective of recovering remnant oaks and restoring historical woodland area. We surveyed 258 girdled Douglas-fir to examine the effectiveness of girdling treatments to create snags and the impacts of girdling on tree regeneration and fuel recruitment over a 17 year time since girdling chronosequence. Girdling was successful in killing 91% of the treated Douglas-fir independent of the method used (axe or chainsaw). Larger trees with a low girdle width-to-tree diameter ratio tended to survive girdling. Trees with a girdle width-to-tree diameter ratio ≥1 were most effective at killing trees. Snags generated through girdling decayed over time but did not significantly reduce in height over the time period examined. Bird activity was observed on 19% of snags across the chronosequence but 88% of 10 y old snags had signs of bird foraging. Fine woody fuel loading and fuelbed depths were potentially elevated 7 years after treatment but did not persist through the time period examined. Regeneration of Douglas-fir and oaks were highly variable and did not seem to be clearly linked to girdling activity. Our results indicate that girdling is a highly effective treatment to kill Douglas-fir and aid restoration of Oregon oak woodlands with limited negative impacts on surface fuel hazards or regeneration.