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Abstract: Assimilated non-structural carbohydrates (NSC) can be stored as reserves in plants and remobilized during periods of asynchrony between carbon acquisition and carbon demand to fuel essential metabolic functions and growth. However, the framework of NSC allocation to reserves and their remobilization remains unclear, especially for mature trees which potentially can store large quantities of reserves. Here, I characterize the seasonal dynamics of NSC reserves in mature boreal Betula papyrifera and relate them to seasonal growth processes (first study), as well as determine the patterns and potential constraints of between-organ reserve remobilization. I used different patterns of stem phloem girdling to separate crown, stem and root NSC storage and their remobilization in response to induced C stress (second study). In the first study, I found that whole-tree NSC pools increased seasonally by 72% from a spring minimum to a maximum during late summer bud-set — greatly exceeding the relative change in reserves reported for more temperate conspecifics. At the organ level, the branches were the largest and most dynamic storage pool, suggesting that storage changes at the branch level largely drive whole-tree storage dynamics in these trees. In the second study, I found evidence that the crown of birch trees could store nearly double the reserves of what was observed under normal conditions, and that the stored NSC in the stem may not be universally available for remobilization to other organs (here roots) under C stress. Together, these results suggest that seasonal NSC allocation patterns appear to be highly regulated to ensure adequate distribution (allocation) of NSC to reserves throughout organs over time to support organ-level processes — however, if organs are constrained by carbon limitations, it appears that the remobilization of the organ reserve storage pools are regulated somewhat autonomously which could potentially limit the sharing of reserves within the large organism.

Post-agricultural forests are characterized by low species diversity, structural homogeneity, and have many invasive species. These conditions present unique challenges to land managers, who are increasingly looking for ways to achieve multiple land management goals including ecosystem enhancement and the potential for moderate timber harvesting. Given these broadened goals, management options that result in less ‘intense’ disturbances are increasingly sought after. Girdling is one such method that results in the slow death (3-5 years) of affected trees, whose implementation and effects upon post-agricultural forests remains undertested. At the Working Woods area in Holden Arboretum up to 20% of the canopy was girdled between 2018 and 2019. The canopy structure and growth of 457 target trees that received varying amounts of nearby girdling were measured from 2018 through the end of 2020. To assess canopy structure, hemispherical photos were used to provide a measure of canopy openness around the target tree, and a LI-COR LAI 2200C was used to measure both Leaf Area Index (LAI) and Diffuse Non-Interceptance (DIFN). Canopy structure metrics were assessed in a mixed effect model that showed the presence of girdling treatment and time since girdling appeared to only marginally influence LAI measurements. Growth was assessed with both yearly diameter at breast height (dbh) and weekly dendrometer band window increment measurements. Growth was assessed in several growth periods consisting of pre-treatment growth, post-treatment growth, and the overall growth throughout the experiment. Pre-treatment growth was assessed through linear regression and ANOVA models that found it to be very dependent on initial size and species. Post treatment growth in similar models showed that initial size is still important, but species trends results in inconsistent growth rates as elm trees were the only species to exhibit greater growth rates with increased nearby girdling.These results suggest that the three years of measurements have seen only minimal changes as a result of girdling treatment both in canopy structural changes and residual focal tree growth. Additional yearly assessments would be needed as girdling results in a slow release from competition.

The mixed deciduous forests of the upper Midwest, USA are approaching an ecological threshold in which early successional dominant aspen and birch trees are reaching maturity and beginning to senesce. At the University of Michigan Biological Station in northern Michigan, we are combining long-term carbon (C) cycling measurements with a large-scale experimental manipulation to forecast how net ecosystem production will change in response to ongoing succession, disturbance, and climate variation. Our goal is to elucidate biophysical mechanisms that will constrain C storage in future forests. In the spring of 2008, we began the Forest Accelerated Succession ExperimenT (FASET), in which all aspen and birch (~35% canopy LAI) within 39 ha of an 85 yr old forest were stem girdled to accelerate mortality. The adjacent, untreated forest serves as a control. I hypothesized that, 1) aspen-birch senescence would decrease C allocation to root and microbial pools, resulting in increased root mortality and reduced root respiration, 2) that the treatment effect on soil respiration (Rs) would become more severe as time since girdling increased, and 3) the magnitude of the treatment effect would be proportional to the percent basal area of girdled aspen and birch. Sites with high percent basal area of girdled aspen and birch would yield lower Rs, while sites with low percent basal area of girdled aspen and birch and control sites would have higher Rs. We measured Rs continuously using arrays of automated soil respiration chambers in the treatment and control sites. We also quantified above and below-canopy radiation, precipitation, air and soil temperature, and soil moisture. At the ecosystem scale, we calculated gross primary production from measurements of net CO2 exchange between forest and atmosphere using eddy-covariance methods. Soil respiration was significantly reduced in the treatment relative to the control site in the first and second years after girdling, supporting my first hypothesis. However, the treatment effect occurred faster than anticipated, because root C stores were expected to maintain Rs despite girdling in the first treatment year. I modeled the automated chamber Rs data using a piece-wise linear regression and found that the magnitude of the treatment effect was significantly greater in 2009 compared to 2008, supporting my second hypothesis. Results from the basal area gradient study showed no significant difference between treatment and control site Rs. However, percent basal area of aspen and birch was a significant explanatory parameter in the model, revealing that as percent basal area of aspen and birch increased in the control site, so did Rs. The treatment site showed no relationship between Rs and basal area, suggesting the treatment is beginning to deteriorate normal forest belowground functioning. My results provide an estimate of Rs after a species specific disturbance and can be extrapolated to other such disturbances such as those caused by stem girdling insects or diseases. My Rs estimates can also be applied to calculations of net ecosystem productivity, because Rs is the main component of ecosystem respiration.

Viticultural practices such as trunk girdling and shoot topping along with defoliation, shading and node number per vine treatments were used to alter the carbohydrate physiology of mature Chardonnay grapevines growing in the cool climate of Canterbury, New Zealand. The timing of vine defoliation in the season previous to fruiting decreased concentrations of over-wintering carbohydrate reserves (mostly starch) in both the trunks and roots of grapevines. Roots were particularly sensitive, with defoliation as early as 4 weeks after bloom in the previous season reducing starch concentrations to 1.5%Dwt at bud burst compared with 17%Dwt in non-defoliated vines. In contrast, partial vine defoliation as early as bloom in the previous season reduced root starch concentrations to 4-7%Dwt at bud burst compared with 15%Dwt in non-defoliated vines. Vine shading and trunk girdling treatments at bloom in the previous season, resulted in small reductions in root starch concentrations (16%Dwt) compared with non-shaded and non-girdled vines (19%Dwt), but shoot topping did not. Study across three growing seasons established that higher concentrations of over-wintering trunk and root carbohydrate reserves were associated with warmer and sunnier weather in the previous growing season. Individual shoot leaf removal at either the beginning or towards the end of the inflorescence initiation period, reduced shoot starch concentrations to 3-6%Dwt compared with 11 %Dwt for no leaf removal, such reductions persisted through to the following season. Shoot topping at the start of the initiation period had no effect on shoot carbohydrate accumulation, but trunk girdling temporarily increased shoot starch concentrations during the first 31 days after treatment. Reductions in over-wintering trunk and root carbohydrate reserves were associated with a reduction in inflorescences per shoot and flowers per inflorescence in the following season, the reduction as much as 50% compared with non carbohydrate stressed vines. While there were strong linear or curvilinear relationships between the concentration of starch in trunks and roots at bud burst and inflorescences per shoot and flowers per inflorescence, in case the of inflorescences per shoot, there was not an immediate cause and effect because inflorescences were initiated in the previous season. Individual shoot leaf removal during the inflorescence initiation period illustrated that leaf removal directly inhibited the initiation of inflorescences in latent buds. Shoot carbohydrate measurements showed a strong curvilinear relationship to the number of inflorescences per shoot, with a threshold starch concentration of 10-12%Dwt during the inflorescence initiation period required for a maximum number of inflorescences per shoot. Furthermore, examination of individual node positions emphasised the importance of the subtending leaf on the initiation of inflorescences within the latent bud. The number of inflorescences per shoot post bud burst was reduced on vines that were both carbohydrate reserve stressed (by previous season's defoliation) and had a high node (108) number retained per vine after winter pruning compared with little or no reduction in inflorescences per shoot on carbohydrate reserve stressed vines that had a low (20) node number per vine. The reduction in inflorescences per shoot on high node vines was associated with reduced carbohydrate reserves and reduced shoot vigour (thinner and lighter shoots). Flowers per inflorescence were reduced by as much 50% in response to lower overwintering carbohydrate reserves. Fewer flowers per inflorescence were attributed to a reduction in primary branching of the inflorescence and also a reduction in flowers per branch. Strong linear relationships between the concentrations of starch in trunks and roots and flowers per inflorescence indicate that the determination of flowers per inflorescence, unlike inflorescences per shoot, may be dependent on the level of overwintering carbohydrate reserves. This is most likely due to changes in branching of the inflorescence and individual flower formation occurring during the bud burst period. Per cent fruitset was not affected by reductions in carbohydrate reserves, so fewer inflorescences per shoot and flowers per inflorescence resulted in reduced vine yield. The findings of this thesis indicate that changes in the level of carbohydrate production and partitioning in response to a range of viticultural management practices and seasonal weather contribute to seasonal variation in grapevine flowering and yields in New Zealand's cool climate environment. The relationships between carbohydrate reserves and flowering illustrate the potential to use this information to predict grapevine flowering and forecast yields. The practical implications of this research illustrate that the viticulturist must manage grapevines not only for the current crop, but also for subsequent crops by maintaining sufficient carbohydrate reserves for balanced growth flowering and fruiting from season to season.

There has been an increased interest in characterizing and interpreting ecological heterogeneity over space and time in the past two decades. This is mainly due to the renewed recognition of the significance of heterogeneity in ecological theories. However, studies that have combined both spatial and temporal aspects of heterogeneity have been rare. A unified approach to define and quantify heterogeneity has also been lacking. Designed to overcome these problems, this study was conducted in a 40-year-old Pinus elliottii Engelm. forest at the Savannah River Site near Aiken, SC, USA with the following specific objectives: 1) to characterize the spatial patterns of soil and forest floor variables (moisture, pH, soil available nitrogen and phosphate, forest floor and soil carbon and nitrogen), 2) to examine the dynamics of these spatial patterns in response to two types of disturbance: whole-tree harvesting and girdling, and 3) to evaluate some of the current methods for quantifying ecological heterogeneity. In response to both disturbance treatments, spatial heterogeneity measured by sample variance showed a marked "increase and then decline" temporal pattern in soil moisture, soil available nitrogen and phosphorus. Similar patterns were not found in total soil C and N, and total litter C and N. Harvesting resulted in greater and more drastic changes in the variations of soil nutrients and water than did girdling. Despite the popularity of semivariogram analysis in recent ecological studies, the technique did not provide consistent results on patterns of heterogeneity in our system. A simulation experiment demonstrated that semivariogram analysis may suffer from many problems when it is used to characterize patchiness, one form of heterogeneity. The results from this study have a number of implications. First, spatial patterns of soil resources are high dynamic. The dynamics of patterns in soil resources may partly account for the weak correlation between vegetation and soil observed in ecological literature. Second, heterogeneity may be most effectively quantified by first identifying quantifiable components and then quantifying these components individually. A common pattern can be sought by comparing patterns of different components of heterogeneity for a given ecological property and by comparing patterns of different ecological variables for a given component of heterogeneity. Third, compared to surveys, field manipulative experiments can provide information that link patterns with ecological processes. As such, this study adds to ecological literature valuable information on temporal changes of soil heterogeneity following disturbance and conceptual advances in the quantification of ecological heterogeneity.

Two experimental trials were conducted on apple trees between 1994 and 1996 in order to assess the effect of different girdling and bridge grafting treatments on vegetative and reproductive growth and physiology of apple trees and the apples they produced. The treatments were chosen to assess the possible utility of bridge grafting and girdling as methods to control apple tree vigour while maintaining production and quality of the apples. Physiological measurements were also taken to see whether organ carbohydrate levels could give at least a partial explanation of the effects induced. In the first trial, four apple cultivars ('Granny Smith', 'Cox's Orange Pippin', 'Oregon Red Delicious' and 'Gala') on three rootstocks, (MM106, M793 and Northern Spy) were used. The trees were interstock bridge grafted with segments of either M9 dwarfing rootstocks or with cuttings from the same variety or were left alone as controls. The trees were in a 12 year old apple orchard, planted at moderate density. In the second trial three apple cultivars ('Braeburn', 'Royal Gala' and 'Fuji') growing under an ultra high density planting system on rootstock MM106 (ranging from 5000 to 40,000 tree/ha) were used. The trees were 6 years old at the start of the trial. The trees were treated with three different girdling techniques (Ring, Guillotine or none) in order to investigate the effects of girdling relative to uncut controls on vegetative growth, reproductive growth, organ carbohydrate levels, fruit quality parameters and fruit storage potentials. In general the bridge grafting treatments reduced vegetative growth, but increased flower number, fruit set and total yield. They also changed the carbohydrate levels above and below the cut. The treatment reduced average shoot length by 20% while increasing flower density (143%) flowers per spur (17%), fruit set (70%), and total yield (31.7%) the year after the treatment. Similar results were found in the second trial where trees were girdled without bridges grafted in. The greater effect was found in the second year, with the more severe ring girdling treatment having a greater effect. In this second trial the different varieties and populations produced substantial variation in all parameters but few significant interactions with the girdling treatments. This leads to the conclusion that girdling has a consistent main effect as described. In general the girdling treatments reduced trunk diameter, branches per tree and shoot length by 7.2%, 10.2% and 10.9% respectively. At the same time girdling increased flower number (11.1 %), fruit set (25%) and total yield (62%) in the second growing season. Fruit were picked as specified by the New Zealand Apple and Pear Marketing Board. They were then evaluated at harvest and during storage at 10°C after periods of 40 and 60 days. In both trials the treatments reduced mean fruit weight and fruit LID ratio, while there were significant increases in flesh firmness, brix value, and seed number. There were more severe effects from M9 bridge grafting and ring girdling treatments in both growing seasons. In both trials storage for 40 and 60 days at 10°C significantly enhanced weight loss, flesh colour and brix value while there was a highly significant reduction in flesh firmness with increasing storage time, for both growing season. Fruit tissue samples were taken from both trials after 40 days and analysed 'for calcium, potassium and magnesium content for the second season only. There was a highly significant increase in calcium level associated with the girdling and grafting treatments while potassium and magnesium levels were lower in both trials. As with other parameters, in the first trial the bridge grafting M9 treatment had the greater effect while in the second trial the ring girdling treatment showed greater differences compared to the control. These data and evidence from reports of other workers indicate that girdling is effective in controlling the vegetative growth of apple trees. The observed increase in reproductive growth was greater in the second year after treatment. There was a reduction in fruit size with girdling but this might have been due to crop load rather than reduced vigour. The reduction in shoot growth may be determined by hormonal signals rather than CRO (Carbohydrate) concentration a possibility not examined here. However, the hormonal signals may themselves be affected by CRO transport within the tree. Reduced transport to the roots of CRO may in turn reduce hormone signals to promote vegetative growth and consequently result in the correlations demonstrated between CRO levels and treatments reported on here. The data generally supported the model of organ carbohydrate level effects on growth, yield and quality of apple trees proposed by Khan et ai., (1998), with the added benefit of indicating both bridge grafting and girdling can reduce tree vigour while maintaining yields and apple quality.