Floral Bud Production Research Articles

Flowering, floral visitors and climatic drivers of reproductive phenology of two endangered magnolias from neotropical Andean forests

AbstractDepressed fruit and seed production and scant seedling recruitment appear to be imperiling natural populations of Colombian Magnolia species. From February 2015 to April 2017, we recorded data on flowering, pollen limitation, floral visitors, and the reproductive phenology of Magnolia jardinensis and Magnolia yarumalensis, two threatened and endemic species from Colombian Andean cloud forests. Both species are protogynous with anthesis lasting two consecutive days—with M. jardinensis flowers opening in the evening, while M. yarumalensis flowers open early in the morning. Fruit abortion in both bagged flowers and open pollination experiments suggests that both species exhibit considerable reproductive limitations. There was a lower percentage of pollen germination in M. jardinensis (3–26%) than in M. yarumalensis (60–86%), suggesting more limitations in the former species. Magnolia yarumalensis was a prolific fruit producer compared to M. jardinensis, which produced only one ripe fruit during the study, in spite of its high production of floral buds. Despite sharing the same locality, these species did not share pollinators, thus further increasing their vulnerability to extinction. Floral buds in both species were negatively correlated with minimum temperature and precipitation, while ripe fruits in both species were positively correlated with increases in precipitation and temperature. Our results provide information about how climate change could affect the various phenophases of these species. Knowledge about reproductive phenology and life history traits such as flowering and pollinators is crucial for specific and efficient conservation efforts to protect these endangered species under the current climate change scenarios.

CO2 Enrichment with Higher Light Level Improves Flowering Quality of Phalaenopsis Queen Beer ‘Mantefon’

We investigated the flowering and photosynthetic responses of Phalaenopsis Queen Beer ‘Mantefon’ to CO2 enrichment and light level. Potted plants at the flowering stage were supplied with low light level (LL; 90 ± 10 μmol m−2 s−1) or high light level (HL; 260 ± 40 μmol m−2 s−1) using three−wave cool white fluorescent lamps and metal halide lamp and different levels of CO2. Carbon dioxide was supplied to the plants, which perform crassulacean acid metabolism, during their dark period at three concentrations: 400 (control), 800, and 1200 μmol mol−1 CO2. More flowers and lateral branches were produced by plants grown under HL than the control plants grown under LL, and there were more visible floral buds in the plants grown under HL than those grown LL, regardless of CO2 concentration. Net CO2 assimilation rate was higher in plants exposed to 800 and 1200 μmol mol−1 CO2 under LL and 1200 μmol mol−1 CO2 than the control plants under LL and HL. We conclude that photosynthesis is enhanced in CO2-enriched plants, and lateral branch and floral bud production are maximized at the high light level used here in Phalaenopsis Queen Beer ‘Mantefon’.

Growth and carbon balance are differently regulated by tree and shoot fruiting contexts: an integrative study on apple genotypes with contrasted bearing patterns.

In plants, carbon source-sink relationships are assumed to affect their reproductive effort. In fruit trees, carbon source-sink relationships are likely to be involved in their fruiting behavior. In apple, a large variability in fruiting behaviors exists, from regular to biennial, which has been related to the within-tree synchronization vs desynchronization of floral induction in buds. In this study, we analyzed if carbon assimilation, availability and fluxes as well as shoot growth differ in apple genotypes with contrasted behaviors. Another aim was to determine the scale of plant organization at which growth and carbon balance are regulated. The study was carried out on 16 genotypes belonging to three classes: (i) biennial, (ii) regular with a high production of floral buds every year and (iii) regular, displaying desynchronized bud fates in each year. Three shoot categories, vegetative and reproductive shoots with or without fruits, were included. This study shows that shoot growth and carbon balance are differentially regulated by tree and shoot fruiting contexts. Shoot growth was determined by the shoot fruiting context, or by the type of shoot itself, since vegetative shoots were always longer than reproductive shoots whatever the tree crop load. Leaf photosynthesis depended on the tree crop load only, irrespective of the shoot category or the genotypic class. Starch content was also strongly affected by the tree crop load with some adjustments of the carbon balance among shoots since starch content was lower, at least at some dates, in shoots with fruits compared with the shoots without fruits within the same trees. Finally, the genotypic differences in terms of shoot carbon balance partly matched with genotypic bearing patterns. Nevertheless, carbon content in buds and the role of gibberellins produced by seeds as well as the distances at which they could affect floral induction should be further analyzed.

EFFECT OF FIRE ON FLOWERING AND FRUITING OF ANACARDIUM HUMILE (ANACARDIACEAE) IN CERRADO STRICTO SENSU

ABSTRACT Knowledge about the effects of fire on sexual reproduction of Cerrado woody species is fundamental for elaborating public policies and management plans for its conservation. The present study evaluated the effect of a controlled burning on flowering and fruiting of Anacardium humile in an Cerrado stricto sensu environment, in Cavalcante, GO. An area with no fire records for five years was submitted to controlled burning in May 2016, used as the experimental area and its adjacent areas protected from fire as control area. In each area, 16 reproductive individuals were selected and their production of floral buds, flowers and fruits, followed up for 17 months. In 2016 the production of reproductive structures was higher in the control area, since the majority of individuals of the burned area invested in the recovery of vegetative structures (branches) damaged by fire. Only three individuals flowered in the burned area in 2016 and presented greater effort in the production of buds and flowers per panicle than the individuals in the control area, however, the fruit set was equal between the areas. One year after fire, the production of reproductive structures became equal between areas. The control area presented higher fruit production in 2017 in comparison to 2016, indicating a variable pattern in annual fruit production. The impact of fire on the reproductive structures of A. humile is greater in the same year of fire and its reproductive potential can be normalized in the subsequent year.

Effects of an accidental dry-season fire on the reproductive phenology of two Neotropical savanna shrubs.

Fire is a recurrent disturbance in savanna vegetation and savanna species are adapted to it. Even so, fire may affect various aspects of plant ecology, including phenology. We studied the effects of a spatially heterogeneous fire on the reproductive phenology of two dominant woody plant species, Miconia albicans (Melastomataceae) and Schefflera vinosa (Araliaceae), in a savanna area in South-eastern Brazil. The study site was partially burnt by a dry-season accidental fire in August 2006, and we monitored the phenolology of 30 burnt and 30 unburnt individuals of each species between September 2007 and September 2008. We used restricted randomizations to assess phenological differences between the burnt and unburnt individuals. Fire had negative effects on the phenology of M. albicans, with a smaller production of reproductive structures in general and of floral buds, total fruits, and ripe fruits in burnt plants. All unburnt but only 16% of the burnt M. albicans plants produced ripe fruits during the study. Fire effects on S. vinosa were smaller, but there was a greater production of floral buds and fruits (but not ripe fruits) by burnt plants; approximately 90% of the individuals of S. vinosa produced ripe fruits during the study, regardless of having been burnt or not. The differences between the two species may be related to S. vinosa's faster growth and absence from the seed bank at the study site, whereas M. albicans grows more slowly and is dominant in the seed bank.

A tool for identifying potential Eucalyptus nitens seed orchard sites based on climate and topography

Shy seed production in orchards of Eucalyptus nitens is a major barrier to the deployment of genetic gain in South African plantations. A machine learning method was used to identify optimal sites for the establishment of E. nitens seed orchards within the plantation forestry landscape of the summer rainfall region of South Africa. The ensemble classifier random forests (RF) was used to identify the environmental factors conducive to E. nitens floral bud production, and, based on these, build a predictive model deployable to the plantation forestry landscape for identifying suitable areas for E. nitens seed orchards. The RF model predicted site suitability likelihood for floral bud production with a high level of accuracy (area under the receiver operating characteristic curve = 0.83). Within the climatically optimal range for growing E. nitens, flower bud production was more abundant and consistent on cold slopes, i.e. sites experiencing lower minimum air temperatures during spring and autumn. The model was applied to the commercial plantation forestry landscape for the purpose of indicating sites climatically optimal for floral bud production in E. nitens and the establishment of breeding and seed production orchards of the same species.

Conditional outcomes in ant–plant–herbivore interactions influenced by sequential flowering

Mechanisms that affect a host plant’s ability to face herbivory are subjects of ongoing interest. Plant reproductive phenology plays a key role in the dynamics of communities in many ways. In ant–plant–herbivore interactions, host-plant phenology affects traits of its herbivores which in turn determine what traits ants must have to benefit the host-plant. Diversity of plant phenological traits could influence the ecological diversity of coevolved ant–plant mutualisms.In the Brazilian savanna, members of several plant families resprout and bloom simultaneously. However, some shrubs of the family Malpighiaceae exhibit sequential flowering, and four of these species also present extrafloral nectaries that attract ants. Here we determine whether their phenological patterns results in a shared herbivore guild and if this may be harmful to these plant species, making the association with ants critical to the plant optimal development and reproductive success. Plant phenology, herbivory, and the richness and abundance of ants and herbivores were recorded on control (with unrestricted ant access) and treatment (ant-excluded) shrubs. Floral-bud production and fruit set were also quantified. The plants flowered sequentially with brief periods of overlap, benefitting the guild of generalist herbivores. A cluster analysis indicated that 32 herbivore species were associated with these Malpighiaceae, with substantial species overlap. In all species, ants reduced leaf-area loss but not the damage to reproductive structures. Some floral herbivores presented adaptations to avoid or appease ants. We suggest that plant phenology directly influences the outcomes of these ant–plant–herbivore interactions and the related ecological networks.

Overhead irrigation increased winter chilling and floral bud production in Eucalyptus nitens

Eucalyptus nitens requires a sufficiently cold winter to produce flower buds. In areas in South Africa where E. nitens commercial plantations as well as breeding and production seed orchards are located, winter chilling is often insufficient for floral bud initiation. Hence, under such conditions, E. nitens floral bud and seed crops are poor and inconsistent. The local industry is almost entirely dependent on paclobutrazol (PBZ) applications for encouraging flowering in E. nitens seed orchards. Between 2008 and 2010, an experiment was conducted to investigate the potential of overhead irrigation (sprinkling) as a means of supplementing winter chilling to improve floral bud production in E. nitens. The treatments included three levels of sprinkling (nil, 10 weeks and 16 weeks duration), two levels of PBZ (nil, 0.025 g a.i. per mm basal stem circumference) and two grafted clones (prolific flowerer and shy-flowerer). Sprinkling reduced E. nitens daytime bud temperatures by as much as 16.2 °C on warm, dry winter days. In 2009 (cold winter) and 2010 (warm winter), sprinkling increased chilling accumulation by 44% and 72% (nil versus maximum sprinkling), respectively. In 2009, in the absence of PBZ, sprinkling resulted in a higher percentage of trees of either clone producing umbels (flower buds) compared with the control. In the warmer 2010 winter, sprinkling again increased flowering, with the number of flowering shoots and umbels per tree being significantly higher than the control at p < 0.05. In both 2009 and 2010, PBZ showed a strong additive effect to winter chilling on E. nitens floral bud production. The E. nitens clone × chilling × PBZ flowering interaction was complex and warrants more detailed investigation in future. Overhead sprinkling offers a practical method of supplementing winter chilling and improving floral bud production in high-chill-requiring temperate eucalypt species such as E. nitens.

Floral Phenology of Upper Amazon Cocoa Trees: Implications for Reproduction and Productivity of Cocoa

A study of the floral phenology of cocoa trees was carried out between 2006 and 2008 at Kubease in the Ashanti Region of Ghana, using one hundred cocoa trees from ten farm plots. The objective was to assess the contribution of floral phenology to the productivity of cocoa. Cocoa like all tropical tree species exhibited seasonally-related phenological patterns involving overlapping cycles under both intrinsic and extrinsic controls. However, unlike most tropical plants, flowering was in the rainy season. The production of new pods or cherelles increased during the major rainy season (June, July, and August), but was evenly distributed from the minor to the dry season. Production of small and medium pods peaked in August whereas production of large pods peaked in October. There was a positive correlation between new pod production and pods abortion (r = 0.69; n = 100; P &lt; 0.05). Temperature, light intensity, and rainfall positively affected production of floral buds and production of open flowers. However, rainfall had the greatest influence on the phenological cycle of the cocoa plant. The floral phenological pattern also coincided with the activity of the main pollinators of cocoa which resulted in enhanced reproductive capacity for increased production of cocoa.

Tolerating castration by hiding flowers in plain sight

A key challenge in the study of inter-specific cooperation, or mutualisms, is to understand the mechanisms that prevent cheating. However, many mutualisms are still invaded by parasites, and we propose that plant ‘tolerance strategies’, which allow an individual to re-grow and/or reproduce after damage, might have evolved to recover some of the fitness lost to parasitism. We focus on the ant plant Cordia nodosa and its protecting ant symbionts Allomerus octoarticulatus and Azteca spp. Allomerus is a castration parasite, destroying host flowers. However, some flowers are produced on new branch shoots, where they escape castration. Here, we ask whether C. nodosa tolerates castration by directing floral growth to new shoots. We find that C. nodosa produces four times more floral buds on the new shoots of Allomerus-inhabited plants, compared to Azteca-inhabited plants. Additionally, on Allomerus-inhabited plants, the production of floral buds is three times greater on new than on mature shoots, and more floral buds are grown on plants with new shoots than on those without. We conclude therefore that C. nodosa tolerates castration by re-allocating floral resources to new shoots. We also test whether tolerance exploits behavioural differences between the brood-tending ‘nurse’ ant worker caste, which is active on mature shoots, and the new shoot-protecting ‘patroller’ caste. Behavioural assay experiments reveal that nurse ants are strongly attracted to extracts of flowers, whereas patrollers are not, suggesting that nurses are the primary castrating caste. Thus, producing flowers on new shoots avoids the castrating caste. We finish by proposing that tolerance strategies can promote the evolution and maintenance of mutualism.

Effect of winter chilling and paclobutrazol on floral bud production in Eucalyptus nitens

Flower bud production of Eucalyptus nitens is comparatively abundant at specific high altitude sites in the South African summer rainfall region. This suggests that cumulative cold may be implicated in the floral induction process. Therefore, three chill models were used to investigate whether winter temperature data can be related to E. nitens flower bud production at sites differing in chill accumulation. Amount of accumulated winter chill, in conjunction with paclobutrazol treatment, was able to explain between 66 and 72% of the variation in E. nitens flower bud production. Although the potential chilling requirement of E. nitens can be calculated with similar accuracy by each of the chill models tested, the Dynamic Model performed best under the particular range of experimental conditions. At low to moderate levels of winter chill (43 to 81 Chilling Portions (CPs) of the Dynamic Model), paclobutrazol application hastened first flowering and increased the percentage reproductive trees by between 5–27% in the case of seedlings, and between 2–62% in the case of grafts. At high levels of winter chill (> 87 CPs), paclobutrazol had a negligible effect on the percentage reproductive trees in the case of either seedlings or grafts. At four and five years after planting, very high levels of accumulated winter chill (96 CPs) stimulated a high percentage of seedlings (25–50%) and grafts (55–64%) to produce flower buds. Considerable variation in precocity and chilling requirement (for floral induction) is evident within the South African E. nitens breeding population. A better accuracy in relating E. nitens floral bud production to amount of prior winter chilling could be achieved by further experimentation involving fewer genotypes and a wider range of chilling conditions.

The effects of temperature and lighting on flowering of lavender (Lavandula angustifolia ‘Hidcote’)

SummaryA series of three experiments was conducted to determine the effects of temperature and lighting on bud initiation and flower expression in lavender. A period of nine weeks at 4°C was shown to satisfy the vernalization requirement for all plants, and after five weeks at 4°C, 50% of plants flowered. Vernalization was shown to occur more slowly at temperatures above 4°C and was observed up to 16°C. Following vernalization, a higher temperature advanced bud appearance, with an optimum temperature of 20°C, but reduced the number of buds. When vernalization was incomplete, a higher temperature delayed bud appearance and reduced the number of buds. A daylength of 15 h compared with 8 h either during or after cold treatment increased the number of buds produced, suggesting that additional lighting may be needed for the winter production of plants in flower. Whilst it was possible to model flower development after bud appearance, unexplained variation between experiments in the time to first visible bud prevented satisfactory mathematical description of floral bud production. It was concluded that the “environmental history” of commercially micro-propagated material had a significant effect on the duration of cold required for vernalization, and that differences in the vernalization requirement of individual meristems led to variation in the cold requirements of plants within a crop. The commercial significance of these conclusions is discussed.

Inter- and intra-generic differences in growth, reproduction, and fitness of nine herbaceous annual species grown in elevated CO2 environments.

In assessing the capacity of plants to adapt to rapidly changing global climate, we must elucidate the impacts of elevated carbon dioxide on reproduction, fitness and evolution. We investigated how elevated CO2 influenced reproduction and growth of plants exhibiting a range of floral morphologies, the implications of shifts in allocation for fitness in these species, and whether related taxa would show similar patterns of response. Three herbaceous, annual species each of the genera Polygonum, Ipomoea, and Cassia were grown under 350 or 700 ppm CO2. Vegetative growth and reproductive output were measured non-destructively throughout the full life span, and vegetative biomass was quantified for a subsample of plants in a harvest at first flowering. Viability and germination studies of seed progeny were conducted to characterize fitness precisely. Early vegetative growth was often enhanced in high-CO2 grown plants of Polygonum and Cassia (but not Ipomoea). However, early vegetative growth was not a strong predictor of subsequent reproduction. Phenology and production of floral buds, flowers, unripe and abscised fruits differed between CO2 treatments, and genera differed in their reproductive and fitness responses to elevated CO2. Polygonum and Cassia species showed accelerated, enhanced reproduction, while Ipomoea species generally declined in reproductive output in elevated CO2. Seed "quality" and fitness (in terms of viability and percentage germination) were not always directly correlated with quantity produced, indicating that output alone may not reliably indicate fitness or evolutionary potential. Species within genera typically responded more consistently to CO2 than unrelated species. Cluster analyses were performed separately on suites of vegetative and reproductive characters. Some species assorted within genera when these reproductive responses were considered, but vegetative responses did not reflect taxonomic affinity in these plants. Congeners may respond similarly in terms of reproductive output under global change, but fitness and prognoses of population persistence and evolutionary performance can be inferred only rarely from examination of vegetative characters alone.

Entomofauna visitante de Belamcanda chinensis (L.) DC (Iridaceae) durante o período de floração

A study of the reproductive biology of B. chinensis (L.) DC. (Iridaceae) was realized comprising floral biology and breeding systems. The floral biology studies included analyses of nectar production, occurence of osmophores, corolla pigments, ultraviolet reflexion and absortion patterns, viability of pollen, pollinators and flower visitors. The breeding systems were studied taking into account the results of manual pollinators tests. B. chinensis is self-compatible bul cross-pollination is more frequent. The effective pollinators are Plebeia droryana (Friese, 1906) (45,7%), Trigona spinipes (Fabricius, 1793) (27,3%), Tetragonisca angustula (Latreille, 1811) (9,3%). Others insects visitors are considered nectar and pollen thieves. The flowering begins generally in January and February. The complete reproductive cicle, as here considered, begining with floral bud production ending with development of mature fruits, lasts January to June. Seed dispersion is ornitocoric.

Architecture and Gender Allocation: Floral Sex Expression Along Branches of the Monoecious cucurbit, Apodanthera undulata

Floral sex expression along branches of the monoecious species Apodanthera undulata follows a typical cucurbit pattern: staminate buds are common at early nodes and become less frequent as branches elongate, while pistillate buds are more common at the more distal nodes of a branch. However, this developmental sequence is not sufficiently canalized to explain the male-phase plants in this species. Male-phase plants have shorter internodes than monoecious-phase plants and also produce and mature fewer flower buds. These data indicate that male plants probably experience less favorable growing conditions than monoecious plants. Finally, the distributions of staminate and pistillate buds along branches and the length of their associated internodes indicate that floral bud production is affected by the same factors that determine branch growth. Consequently, seasonal changes in growth conditions are hypothesized to affect both flower bud production and sex expression.

Out-of-season Prickly Pear: Fruit Characteristics and Effect of Fertilization and Short Droughts on Productivity

Field experiments were conducted to examine the effect of fertilization and short periods of drought on the out-of-season winter crop in prickly pear [Opuntia ficus-indica (L.) Mill.]. In addition, the winter and summer crops were compared regarding floral bud production and fruit characteristics. Under both continuous fertigation (N, P, K applied with the irrigation water) and continuous irrigation, the number of floral buds per plant was much lower in the winter than in the summer crop. Fertilization increased production of floral buds in both crops, but to a greater extent in the winter crop. The increase in floral bud production in fertilized plants was associated with an increase in NO3-N content in the cladodes. Suspension of fertigation for 4 or 8 weeks immediately after the summer harvest decreased cladode water content and delayed and reduced floral bud emergence as compared with continuous fertigation (control) or late drought (4 or 8 weeks) applied 4 weeks after the summer harvest. The plants subjected to early drought suffered from high mortality of floral buds. The fruits of the winter crop ripened in early spring, following the pattern of floral bud emergence the previous autumn. Mean fresh weight and peel: pulp ratio (w/w) were higher in fruits that ripened in the spring (winter crop) than in fruits that ripened in the summer.

Effectiveness of Liothrips urichi (Thysanoptera: Phlaeothripidae) Introduced for Biological Control of Clidemia hirta in Hawaii

The effectiveness of Liothrips urichi Karny introduced to control the noxious weed Clidemia hirta (L.) D. Don was studied at three sites on Oahu, Hawaii. Vegetative C. hirta infested with L. urichi showed greater mortality after 1 mo and significantly shorter internode diameters among the survivors at 4 mo than uninfested plants. L. urichi had no effect on plant height in the field but stunted the growth of young potted C. hirta in greenhouse studies and caused a significant increase in terminal leaf drop. No effect on production of floral buds, flowers, or berries occurred at any field site over 11 mo. L. urichi was restricted to sunny or partly sunny sites and never occurred in heavily shaded areas. Higher thrips infestations occurred during the fall and winter and lower infestations during the summer. Percentage of damaged tips also fluctuated seasonally, but the degree of damage to individual leaves was not seasonal.

Influence of Water Stress on Flowering and Seed Production of Macroptilium atropurpureum cv. Siratro

Macroptilium atropurpureum cv. Siratro was grown in large soil beds with a constant water table below, developing a dawn leaf water potential of --0.25 MPa. Water stresses equivalent to -0.7 or -1.0 MPa were developed over 14 d, causing reduced stem and bud elongation, leaf expansion, and bud differentiation and survival. Apex size, the proportion of buds which were floral or vegetative, the early phases of floral initiation, and seed formation on advanced inflorescences were little affected during the water deficit period.Upon rewatering previously stressed plants showed increases relative to control plants in the rates of shoot appearance, leaf expansion and new node appearance. The ratio of buds becoming floral was independent of watering treatment, and the enhanced rate of floral bud production in the previously-stressed treatments was due to higher rates of total bud differentiation which persisted for up to six weeks after rewatering. Survival of floral buds was reduced by previous stress, but number of flowers per inflorescence, pod setting, seed number per pod and 100-seed weight were independent of treatment. Seed production was controlled by inflorescence density. Rate of seed production was independent of treatment during water deficit and four weeks subsequently, and was then enhanced by 46 and 54 per cent relative to the control in the -0.7 and -1.0 MPa treatments respectively.

Effects of night temperature on floral initiation and raceme development in macadamia

The effects of night temperature on floral initiation and raceme development in macadamia ( Macadamia integrifolia Maiden and Betche) were examined under controlled-environment conditions. Warm nights (20°C compared with 15 °C or less) just prior to and after floral initiation, followed by low ambient night temperatures (mean 10.5 °C) prior to anthesis, promoted floral bud production over an extended period of time. The rate and extent of early raceme elongation, and hence the number of flowers produced per raceme, was greater under warm nights. Despite differences in the number of racemes (and flowers) produced, the number of nuts set per tree were not significantly different. It is suggested that excess flower production may represent a waste of metabolic activity.

Variation in Population Growth Rate in the Woodland Annual Impatiens pallida (Balsaminaceae)

Variation in population growth rate over environmental gradients was determined for the annual Impatiens pallida (Balsaminaceae), by monitoring age- and size-specific survivorship and fecundity in five populations of this summer-flowering and primarily woodland species. All I. pallida seedlings emerged within a few days of each other and a size hierarchy was established within a month, and remained unchanged thereafter. Light and initial seedling density together explained 67% of the variance in mean adult plant size. As a result of differences among populations in the amount of disturbance, survivorship to the time of floral bud production ranged from 39% to 93% of the initial seedling total. Survivorship during the reproductive period was most affected by plant size and soil moisture. For plants surviving to flowering time, the probability of setting seed, the type of seed and the number of seeds produced per plant were significantly positively correlated with plant size. More than 82% of all seeds were produced by plants greater than or 1 m tall. Cleistogamy was the major form of reproduction in 4 out of 5 populations monitored. The net reproductive rate (R0) differed greatly among populations, ranging from 1.23 to 16.27. Population growth rate increased with increasing resource availability and decreasing disturbance during the growing season. The magnitude of R0 depended primarily on 1) timing, intensity and frequency of disturbance, 2) length of the reproductive period, and 3) population size structure.