Almonds are one of the first commercial nut trees to bloom in early spring and thus are susceptible to temperature patterns prior to and during bloom which affect bloom timing, bloom length, pollination and nut set. Data used in this project include yearly dates of 90% bloom from 1996-2006, bloom length in days and final crop yields in pounds per tree for Nonpareil and Mission varieties. Data were collected from the University of California Cooperative Extension reports on the 1993-2006 Regional Almond Variety Trials in Butte, San Joaquin and Kern Counties. Temperature pattern models in the form of Chill Hours (Chill Hour Model), Chill Units (Chill Unit Model), Chill Portions (Chill Portion Model) and Growing Degree Hours (GDH°) (Heat Model) prior to bloom were used to predict the date of 90% bloom for each variety, site and year. Temperature model results were compared to averaged actual dates of 90% bloom by site and variety used to predict bloom timing (Calendar Model). The relationship between bloom length in days and GDH° during bloom and the relationship between bloom length, GDH° during bloom and final crop yields were also evaluated. The average error in predicting the 90% bloom date for both Nonpareil and Mission was smaller using the Calendar Model compared to the four temperature pattern models. The Chill Portion model did not have significantly higher average error in predicting the date of 90% bloom than the Calendar model in Nonpareil. The Chill Unit and Chill Portion models had smaller errors in predicting 90% bloom date than the Chill Hour or GDH° model in Mission. GDH° during bloom was positively correlated with bloom length. GDH° during the first four days of Nonpareil bloom was significantly correlated with crop yields, with each additional GDH° during bloom correlated with a 0.4 lbs./tree increase in crop yield. Further research is needed on specific temperature thresholds and their relationship to physiological changes during almond bloom and pollination. The practice of monitoring chilling and heat accumulation will allow growers to anticipate bloom, prepare to optimize bee activity during bloom, and plan for possible crop yield variations due to adverse weather conditions during bloom in almonds.

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Field and laboratory experiments were conducted to elucidate various factors influencing the temperature-dependent larval eclosion of winter moth, Operophtera brumata L, in New England. We found no difference in duration of the embryonic stage of eggs reared from larvae collected in Massachusetts (MA) and on Vancouver Island, British Columbia (BC), where winter temperatures are rarely below freezing. The number of growing degree days (GDD) required for larval eclosion declined with the number of days chilled in the laboratory and number of days below freezing in the field, confirming the findings of previous studies. Thus, eggs hatched with fewer GDD, when the spring came later than usual. Date of oviposition had no effect on date of hatch. Eggs laid by naturally occurring (feral) females hatched sooner with lower GDD than eggs from laboratory-reared females from MA and BC held on the same trees over the winter. South-facing eggs on the stems of trees hatched on average 1.6 days sooner than north-facing eggs. Growing degree days calculated from bi-hourly measures of temperature were 15% greater than GDD estimates based on the average of daily maximum and minimum temperatures, as used by many GDD estimates made for online sources. Over two years, the mean GDD in ⁰C for hatch of feral eggs based on bihourly temperature measurements, a 1 Jan start date and a 3.9⁰C developmental threshold was 176.53 ± 6.35SE

Research was conducted using the Soil-Plant-Atmosphere-Research (SPAR) units at Mississippi State University, Starkville, MS to investigate temperature effects on warm- and cool-season turfgrasses. Data collected include clipping yield, total root biomass, and relative chlorophyll index (RCI). Cultivars and species in the study included: ‘Latitude 36’, ‘Tifway’, ‘MSB-285’, and ‘TifEagle’ bermudagrass, ‘Meyer’ zoysiagrass, ‘Penn A1/A4’ and ‘Penncross’ creeping bentgrass, ‘Midnight’ Kentucky bluegrass, ‘Fiesta 4’ perennial ryegrass, and ‘Falcon V’ tall fescue. Grasses were grown in the SPAR units at varying day/night temperature regimes. Clipping yield was collected every three days, and regression was used to determine the temperature at which clipping yield equaled zero. Root biomass was collected at the conclusion of the trial, while RCI was taken once weekly. Base temperature for warm-season grasses ranged from 12.5 to 13.2°C. Determined optimum temperatures ranged from 31.8 to 36.1°C for warm-season turfgrasses and 18.8 to 20.6°C for cool-season turfgrasses.

Understanding how climate determines species’ geographic distributions is an important question in ecology with direct implications for predicting climate change-driven range shifts. For Lepidoptera, growing degree-days, a measure of growing season length, has been shown to be an important predictor of species’ distributions in some cases. Most studies use a standardized estimate of base development temperature in their calculations of growing degree-days instead of a species-specific threshold so past investigations of the influence of growing degree-days on Lepidoptera distributions may not have been optimal. Species distribution models (SDMs) are a commonly used approach in ecology that typically only implicitly capture the underlying processes that limit a species’ distribution. A species-specific estimate of growing degree-days should better characterize these processes than standard thermal thresholds and thus improve the accuracy of species distribution models. In this thesis, I use species distribution modelling to model the geographic distribution of 30 moth species native to North America. I ask whether a) growing degree-days are the best climatic predictor of these moth species distributions at broad scales; b) a lab-estimated biological threshold (i.e., BDT) can scale up and improve the predictive ability of SDMs; and c) the quality of experiments used to estimate species-specific BDT influences the predictive accuracy of SDMs. To do so, I compare the predictive accuracy of a correlative model based on a commonly-used thermal threshold to define growing degree-days to a hybrid model with degree-days defined based on a species-specific thermal threshold. I found that the predictive performance of the hybrid models was indistinguishable from the correlative models likely because growing degree-days was not the best climatic predictor of the geographic distributions of the majority of these moth species. I also found that there was no link between the quality of the lab experiments and the difference in performance of the hybrid and correlative models. My findings suggest that lab-estimated thermal thresholds may not always scale up to be predictive at a broad scale and that more work is needed to leverage the data from lab experiments into broad scale SDMs. Determining the ultimate factors that limit species’ distributions will be critical in accurately predicting species’ range shifts response to future climate change.

No description available.

This Thesis presents a framework for modelling species-specific site quality index (SQI) at a spatial resolution of 250 m by integrating biophysical variables of growing degree days (GDD), soil water content (SWC), and incident photosynthetically active radiation (PAR) in descriptions of potential tree growth. Development of GDD maps is based on processing and blending remotely-sensed data acquired with the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor on the Terra satellite and ETM+ sensor on Landsat-7 satellite at spatial resolutions of 250 m and 28.5 m. Descriptions of SWC are based on a temperature-vegetation wetness index (TVWI) that relies on MODIS-based optical and thermal image products. PAR is estimated with an existing solar-radiation distribution model. SQI is defined as a function of species vital attributes and species environmental response to GDD, TVWI, and PAR. The methods are applied to a balsam fir [bF; Abies balsamea (L.) Mill.] dominated region in northwest New Brunswick. Comparisons between SQI and field-based estimates of site index and enhanced vegetation index showed that about 66 and 88% of the values corresponding to a series of Forest Development Survey lines (691 in total) were within 16% of SQI values. On average 92.1% of high bF-content stands (> 50% composition) in the area fell on medium-to-very high SQI values (> 0.50). Based on these agreements, SQI can be perceived as a good predictor of potential tree-species growth in the selection of optimal sites for biomass and wood fibre production.

Berry ripening in lowbush blueberry (Vaccinium angustifolium Ait.) is influenced by developmental, physiological and climatic factors resulting in a heterogenous mix of maturities at harvest. This study characterizes the physico-chemical changes which occur during fruit ontogeny and links ripening patterns to micoclimate. Individual clones in five commercial fiels were followed in the 2006 and 2007 growing seasons. Phenolic acids, flavonols, and flavan-3-ols decreased and anthocyanins increased with maturity. Peak maturity consistently occurred at 1200 accumulated growing degree days (GDD). There was a sharp decline in fruit retention at the end of the growing season suggesting a date after which harvested yield declines but no consistent pattern was detected between years or fields.The consistency of GDD accumulation in relation to ripening pattern suggests GDDs can be used as a predictive ripening index. The physico-chemical nature of ripe berries indicates ripe berries could be harvested earlier than is currently the practice.

Ptilotus nobilis is a short-lived perennial wildflower, native to semi-arid and arid areas of Australia. Propagation by vegetative means is constrained by the early onset and a continuous flowering habit. Despite being defined as the main barrier for vegetative propagation no published research on floral induction and initiation was found. The aim of this study is to provide the first insights into floral evocation in P. nobilis, with the general objectives being to investigate floral induction and initiation, find the means to maintain plants in the vegetative phase, enhance leaf initiation and to gain knowledge of growth and development with an emphasis on light intensity, temperature and daylength. Early experiments aimed to increase the understanding of growth and development. The main cardinal events were identified including the onset of branching (axillary stem growth), visible bud stage, first floret opening and maturity of the inflorescence. To aid future cultivation schedules, four growing degree days (GDD) and one chronological model, using days after sowing (DAS), were established and validated. All GDD models were accurate in predicting first floret opening and maturity, but not in predicting visible bud stage. Best prediction was achieved by using an upper temperature threshold of 18.2 ºC and an own base temperature of 5.0 ºC. Days after sowing were an accurate means of prediction, indicating that temperature and other variables such as light intensity regulate development. A series of defoliation treatments investigated the maintenance of P. nobilis plants in the vegetative phase. Within all treatments, reproductive structures were observed and all plants with more than two true leaves entered the reproductive phase. Plants with less than two true leaves showed a delayed floral bud appearance by up to 20 days. Floral development was affected by most defoliation treatments resulting in vegetative growth within the inflorescences. It is hypothesized that plants have a very short juvenile phase and that a constant floral stimulus may be needed for floral evocation. Using scanning electron and light microscopy a template for the transition from vegetative to reproductive phase was developed. Bract initiation was accompanied by a significant increase in meristem area and diameter, and was defined as the onset of flowering. The established template was used in a subsequent glasshouse trial, which revealed that floral initiation occurred very early and at 25 DAS all plants had entered the reproductive phase. Branching and leaf area expansion were identified as post- initiation processes. Plants were exposed to different light intensities (229.3, 398.6 and 909.3 µmol m-2 s-1) in a glasshouse. Under low light, final leaf number increased by up to three leaves, indicating that the vegetative phase was prolonged. Cardinal events were delayed but all plants reached maturity. It was concluded that a light intensity of 229.3 µmol m-2 s-1 was not low enough to prevent floral initiation and that a further decrease of light intensity in combination with temperature could be more effective. Interactions of light intensity, temperature and daylength were investigated. Plants were grown under high light and low light (< 1.2 MJ m-2) intensities, 25/10 ºC and 35/20 ºC and daylengths of 11 h and 16 h. During the trial period (42 days), low light intensity suppressed floral initiation and high temperatures maintained more plants (70%) in the vegetative phase. However daylength treatments had no effect on the time of bract initiation or the percentage of vegetative plants. After 83 days floral buds and axillary stems were observed on some plants under low light intensity, indicating the onset of the reproductive phase and showing that P. nobilis could not be maintained in the vegetative phase indefinitely. Plants under high light were harvested at maturity and effects of temperature and daylength were analysed. Final leaf number increased under 35/20 ºC supporting the previously established results that floral initiation was delayed and leaf production enhanced by high temperature. Morphological data was collected to classify the photoperiodic response of P. nobilis. Plants under 25/10 ºC and 11 h had the longest inflorescences and greatest number of buds and flowers, which was also reflected in the buds and flowers dry weight, with an increase of up to 3.4 fold under these conditions. The difficulty of classifying some plants accordingly to their photoperiodic response and the proposal that P. nobilis may be a facultative short day plant under 25/10 ºC is discussed. In summary, this study presents the first evidence that P. nobilis has a very short juvenile phase and that growth and development are mainly driven by light intensity and temperature. It was possible to enhance vegetative growth by defoliation, low light intensity and high temperatures, however this did not fully prevent flowering, which indicates that P. nobilis has a very strong flowering response or signal.

Ptilotus nobilis is a short-lived perennial wildflower, native to semi-arid and arid areas of Australia. Propagation by vegetative means is constrained by the early onset and a continuous flowering habit. Despite being defined as the main barrier for vegetative propagation no published research on floral induction and initiation was found. The aim of this study is to provide the first insights into floral evocation in P. nobilis, with the general objectives being to investigate floral induction and initiation, find the means to maintain plants in the vegetative phase, enhance leaf initiation and to gain knowledge of growth and development with an emphasis on light intensity, temperature and daylength. Early experiments aimed to increase the understanding of growth and development. The main cardinal events were identified including the onset of branching (axillary stem growth), visible bud stage, first floret opening and maturity of the inflorescence. To aid future cultivation schedules, four growing degree days (GDD) and one chronological model, using days after sowing (DAS), were established and validated. All GDD models were accurate in predicting first floret opening and maturity, but not in predicting visible bud stage. Best prediction was achieved by using an upper temperature threshold of 18.2 ºC and an own base temperature of 5.0 ºC. Days after sowing were an accurate means of prediction, indicating that temperature and other variables such as light intensity regulate development. A series of defoliation treatments investigated the maintenance of P. nobilis plants in the vegetative phase. Within all treatments, reproductive structures were observed and all plants with more than two true leaves entered the reproductive phase. Plants with less than two true leaves showed a delayed floral bud appearance by up to 20 days. Floral development was affected by most defoliation treatments resulting in vegetative growth within the inflorescences. It is hypothesized that plants have a very short juvenile phase and that a constant floral stimulus may be needed for floral evocation. Using scanning electron and light microscopy a template for the transition from vegetative to reproductive phase was developed. Bract initiation was accompanied by a significant increase in meristem area and diameter, and was defined as the onset of flowering. The established template was used in a subsequent glasshouse trial, which revealed that floral initiation occurred very early and at 25 DAS all plants had entered the reproductive phase. Branching and leaf area expansion were identified as post- initiation processes. Plants were exposed to different light intensities (229.3, 398.6 and 909.3 µmol m-2 s-1) in a glasshouse. Under low light, final leaf number increased by up to three leaves, indicating that the vegetative phase was prolonged. Cardinal events were delayed but all plants reached maturity. It was concluded that a light intensity of 229.3 µmol m-2 s-1 was not low enough to prevent floral initiation and that a further decrease of light intensity in combination with temperature could be more effective. Interactions of light intensity, temperature and daylength were investigated. Plants were grown under high light and low light (< 1.2 MJ m-2) intensities, 25/10 ºC and 35/20 ºC and daylengths of 11 h and 16 h. During the trial period (42 days), low light intensity suppressed floral initiation and high temperatures maintained more plants (70%) in the vegetative phase. However daylength treatments had no effect on the time of bract initiation or the percentage of vegetative plants. After 83 days floral buds and axillary stems were observed on some plants under low light intensity, indicating the onset of the reproductive phase and showing that P. nobilis could not be maintained in the vegetative phase indefinitely. Plants under high light were harvested at maturity and effects of temperature and daylength were analysed. Final leaf number increased under 35/20 ºC supporting the previously established results that floral initiation was delayed and leaf production enhanced by high temperature. Morphological data was collected to classify the photoperiodic response of P. nobilis. Plants under 25/10 ºC and 11 h had the longest inflorescences and greatest number of buds and flowers, which was also reflected in the buds and flowers dry weight, with an increase of up to 3.4 fold under these conditions. The difficulty of classifying some plants accordingly to their photoperiodic response and the proposal that P. nobilis may be a facultative short day plant under 25/10 ºC is discussed. In summary, this study presents the first evidence that P. nobilis has a very short juvenile phase and that growth and development are mainly driven by light intensity and temperature. It was possible to enhance vegetative growth by defoliation, low light intensity and high temperatures, however this did not fully prevent flowering, which indicates that P. nobilis has a very strong flowering response or signal.