Root growth dynamics of Aleppo pine (Pinus halepensis Mill.) seedlings in relation to shoot elongation, plant size and tissue nitrogen concentration

Large and high nitrogen (N) concentration seedlings frequently have higher survival and growth in Mediterranean forest plantations than seedlings with the opposite traits, which has been linked to the production of deeper and larger root systems in the former type of seedlings. This study assessed the influence of seedling size and N concentration on root growth dynamics and its relation to shoot elongation in Aleppo pine (Pinus halepensis Mill.) seedlings. We cultivated seedlings that differed in size and tissue N concentration that were subsequently transplanted into transparent methacrylate tubes in the field. The number of roots, root depth, and the root and shoot elongation rate (length increase per unit time) were periodically measured for 10 weeks. At the end of the study, we also measured the twig water potential (ψ) and the mass of plant organs. New root mass at the end of the study increased with seedling size, which was linked to the production of a greater number of new roots of lower specific length rather than to higher elongation rate of individual roots. Neither plant size nor N concentration affected root depth. New root mass per leaf mass unit, shoot elongation rate, and pre-dawn ψ were reduced with reduction in seedling size, while mid-day ψ and the root relative growth rate were not affected by seedling size. N concentration had an additive effect on plant size on root growth but its overall effect was less important than seedling size. Shoot and roots had an antagonistic elongation pattern through time in small seedlings, indicating that the growth of both organs depressed each other and that they competed for the same resources. Antagonism between shoot and root elongation decreased with plant size, disappearing in large and medium seedlings, and it was independent of seedling N concentration. We conclude that root and shoot growth but not rooting depth increased with plant size and tissue N concentration in Aleppo pine seedlings. Since production of new roots is critical for the establishment of planted seedlings, higher absolute root growth in large seedlings may increase their transplanting performance relative to small seedlings. The lack of antagonism between root and shoot growth in large seedlings suggests that these plants can provide resources to sustain simultaneous growth of both organs.     

Vertebrate frugivory and seed dispersal of a Chihuahuan Desert cactus

Vertebrate frugivory of fleshy-fruited plants may be very important for the recruitment of sexually derived seedlings if it represents the main mechanism of primary seed-dispersal.Opuntia rastrera produces fleshy fruits rich in water and sugars that are attractive to vertebrate frugivores. However, there is a very low rate of seedling recruitment in natural conditions. One of the causes that can influence this low recruitment is an insufficient seed dispersal due to a low fruit removal even under different resource (fruits) availability. To test this prediction, we studied the production and consumption of fruits in two consecutive years in two vegetation types: nopaleras (dense Opuntia-dominated scrublands) and grasslands with sparse populations of O. rastrera. Plant cover, fruit production and removal, and frugivore identity were recorded within each vegetation type in four randomly selected circular plots (7854 m²). Fruit production per area was higher in nopaleras in both years whereas per cladode production did not differ between vegetation types but differed between years in response to variation in precipitation. Fruit consumption by vertebrates was high (100%) and independent of spatial and temporal fruit availability. The intensity of fruit removal was inversely related to resource availability: it was faster in the less dense community (grassland) and in the driest year. Contrary to other studies with similar cacti, fruit removal by small mammals was insignificant whereas main consumers were birds and large mammals. Vertebrate frugivory represents the only mechanism of primary dispersal of seeds as all fruits are removed in about one month. Despite the high quantity of viable seeds (more than one million per ha in nopaleras and a tenth of that in grasslands) that are dispersed by frugivores after the consumption of about 300 kg of fruit per ha in nopaleras and a tenth of that in grasslands, the rare establishment of seedlings (about one seedling per three million of seeds produced) reported in the literature indicates that the interaction between O. rastrera and the disperser guild is indeed very asymmetrical. We speculate that the harsh conditions for cactus establishment found in this ecosystem demand a high investment in disperser rewards (fleshy fruits) to allow a very modest rate of sexually-derived seedling establishment.     

Density‐dependent demographic responses of a semelparous plant to natural variation in seed rain

The link between reproductive and vegetative ecology of flowering plants is rarely explored, despite its importance for understanding population processes and fitness. This link can be studied by using experimental or natural variation in seed input to the soil to assess how reproductive success affects vital rates of offspring. We previously reported for Ipomopsis aggregata that per‐seed probability of germinating is insensitive to density of seeds sown into plots, whereas per capita flower production among adults that grow from the seedlings declines in nonlinear fashion with density. Here we describe a parallel non‐experimental study. We related seedling emergence to estimated natural seed input (‘seed rain’) in three populations across ten summers and monitored seedlings that emerged in the first two summers throughout their life histories. Seedling emergence in 1996 was linearly related to seed rain from plants that flowered in 1995. This density independent seed‐to‐seedling transition recurred over the next nine summers, but the slope varied with springtime precipitation. Total numbers of 1996 seedlings that survived to flower and numbers of flowers they produced increased linearly with seed rain in one population, but did not vary detectably in the other two, consistent with negative density dependence. In consequence λ (the dominant eigenvalue of a population projection matrix) decreased from high values at low densities of seed rain to a relatively constant low value with greater seed rain. We also detected density dependence in the 1995 seedling cohort in survival and flower production. The similarity of results from natural and experimental studies supports a conclusion of nonlinear density dependence and shows that characterizing it requires the full life history. For this plant species and others, studies of pollination and fecundity alone may not suffice to draw conclusions about population change or fitness.     

Phytochrome Action in Oryza sativa L: IV. Red and Far Red Reversible Effect on the Production of Ethylene in Excised Coleoptiles

Excised apical segments of etiolated rice (Oryza sativa L.) coleoptiles produced ethylene. Increasing the number of cut sites per coleoptile increased the rate of ethylene formation. Ethylene produced by an etiolated-intact seedling in the dark was about a half of that by the excised coleoptile segment. Red light of low energy as well as of continuous irradiation inhibited the production of ethylene. The inhibition by a low energy dose of red light was partly relieved, if the red light was followed immediately by a small dose of far red light. The effect of red and far red light was repeatedly reversible, indicating that ethylene production was regulated by a phytochrome system. If the exposure to far red light was preceded by a period of darkness, this photoreversibility disappeared; 50% of the initial reversibility was lost within 5 hours. Applied ethylene (10 microliters per liter) significantly promoted the growth of intact coleoptiles of either totally etiolated or red light-treated seedlings, but had no effect on the excised apical segment of coleoptile.     

Heat Shock Increases the Tolerance of Plants to UV-B Radiation: 2. Ethylene and Carbon Dioxide Evolution

The effects of heat shock (HS, 45°C) and UV-B radiation (280–320 nm, 18.3 kJ/(m²h)) and the consecutive action of the combination of these factors on ethylene production, gas exchange, and the growth of intact melon (Melo sativusSager.) seedlings were investigated. The changes in ethylene production and carbon dioxide exchange were described by a single-peaked curve. In the course of UV-B irradiation, the time of maximum ethylene and CO₂evolution coincided (the first 5 min) and comprised 0.36 nl/(seedling h) for ethylene and 146.2 l/(seedling h) for carbon dioxide. After HS, the maximum of ethylene production (0.37 nl/(seedling h)) was reached within 10 min, and that of carbon dioxide production (313 l/(seedling h)), within 45 min. The rate of ethylene production (0.22 nl/(seedling h)), carbon dioxide production (97.7 l/(seedling h)), and oxygen consumption (162.5 l/(seedling h)) in the control seedlings did not change in the course of experiment. Throughout the experiment, the respiratory quotient of seedlings was ca. 0.6 regardless on the nature and duration of the acting factor. Preliminary heating at 45°C for 1 h increased the tolerance of seedlings to the subsequent UV-B radiation for 1 h. The protective effect of HS manifests itself in alleviating the inhibiting action of UV-B radiation on seedling growth and development, and this effect was preceded by an increase in ethylene production and respiration. The possible mechanisms of cross-tolerance of plants to overheating and UV-B radiation are discussed.     

Seed dispersal and population structure in Vriesea gigantea,a bromeliad from the Brazilian Atlantic Rainforest

Seed dispersal, population structure and the mating system of plant species can have great consequences on the genetic structure of populations. Vriesea gigantea is a bromeliad from southeastern Brazil which is self‐compatible and pollinator dependent for fruit set. Its populations are fertile in terms of the production of flowers, pollen, fruits and seeds. To assess the importance of seed supply for gene flow, colonization and distribution of adult individuals, the seed dispersal and population structure of V. gigantea were studied. Seeds are dispersed over short distances; most seeds land close to the mother plant. This pattern coincides with the reported aggregate distribution of bromeliad seedlings. Population structure results showed high seedling recruitment, because 51.3% developed into adults, although few juveniles reached this stage. This result is different from that for other bromeliad species from different habitat conditions. Seed dispersal and population structural patterns are consistent with previous molecular studies, revealing that V. gigantea populations are genetically structured, with low gene flow and a moderate outcrossing rate. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 164 , 317–325.     

The Effect of Age, Pre-conditioning, and Water Stress on the Transpiration Rates of Douglas-Fir (Pseudotsuga menziesii) Seedlings of Several Ecotypes

Seedlings of Douglas-fir from seed of a number of mesic and xeric origins were grown in growth chambers and a nursery to various ages up to 16 weeks. Measurements were made to determine the effect of seedling age, growth chamber and nursery pre-conditioning, and seed source on transpiration rates under closely controlled laboratory conditions. Additional experiments were conducted on seedlings of two contrasting ecotypes to determine the effect of different pre-conditioning combinations of plant and soil water potential on seedling transpiration rates. Results show that well-watered seedlings of two mesic ecotypes show no decline in transpiration rates per unit leaf area up to 16 weeks of age while corresponding seedlings of three exeric ecotypes do decline. The growth chamber pre-conditioning results in lower seedling transpiration rates and more decline in seedling transpiration rates with increasing plant water stress than for nursery pre-conditioning. In a similar way, the xeric ecotype seedlings have more decline in transpiration rates with increasing plant water stress than do the mesic ecotype seedlings. Soil water potential influences transpiration rates through pre-conditioning effects. Seedlings which have experienced prior soil moisture stress decrease transpiration more in response to low plant water potentials than do plants which have experienced no soil moisture stress. These behavioral characteristics illustrate adaptive means by which seedlings conserve water through the interaction of genetic and preconditioning mechanisms.     

Importance of Time Constants in an Open Flow System: Mathematical Correction of Fast Ethylene Kinetics in Physiological Studies

A mathematical analysis for fast changes of ethylene concentration in an open flow system (non-steady-state conditions) is presented and experimentally tested. In this way it becomes possible to determine true values of ethylene production in the minute range following physiological and environmental changes which influence ethylene evolution. By this procedure ethylene kinetics can also be compared in absolute values independent of flow rate and plant chamber volume.     

Characterization of plant-growth promoting diazotrophic bacteria isolated from field grown Chinese cabbage under different fertilization conditions

Diazotrophic bacteria isolated from the rhizosphere of Chinese cabbage were assessed for other plant growth promoting characteristics viz., production of IAA, ethylene, ACC deaminase, phosphate solubilization, and gnotobiotic root elongation. Their effect on inoculation to Chinese cabbage was also observed under growth chamber conditions. A total of 19 strains that showed higher nitrogenase activity identified by 16S rRNA gene sequence analysis were found to be the members of the genera Pseudomonas and Agrobacterium belonging to α- and γ-Proteobacteria groups. These strains were also efficient in producing IAA and ACC deaminase though they produced low levels of ethylene and no phosphate solubilization. In addition, inoculation of selected diazotrophic bacterial strains significantly increased seedling length, dry weight, and total nitrogen when compared to uninoculated control. The colonization of crop plants by diazotrophic bacteria can be affected by many biotic and abiotic factors, and further studies are oriented towards investigating the factors that could influence the establishment of a selected bacterial community.     

Ethylene Production by Attached Leaves or Intact Shoots of Tobacco Cultivars Differing in Their Speed of Yellowing during Curing

Using an open air flow system, differences in the yellowing rate of leaves during curing were assessed in relation to ethylene production by shoots of intact seedlings or attached mature leaves of 60 day old tobacco (Nicotiana tabacum L.) plants. The rate of ethylene evolution from the leaves of the fast yellowing cultivars was significantly higher than in the slow yellowing ones. The same differences were obtained with shoots of intact seedlings. The findings suggest that it is possible to use ethylene production by seedlings as a selection criterion in screening for genotypic differences in the rate of yellowing. The ability of carbon dioxide (1%) to enhance ethylene production by attached leaves was significant in a slow, but not in a fast yellowing cultivar. However, similar amounts of ethylene were produced on administration of 1-aminocyclopropane-1-carboxylic acid to a slow and a fast yellowing cultivar. Exposure of attached leaves to exogenous ethylene (0.1 microliter per liter) accelerated the loss of chlorophyll and protein. This treatment was effective only for slightly yellow leaves and not for fully expanded green ones. The significance and possible use of ethylene in the flue-curing process are discussed.     

Ungulate browsing on introduced pines differs between plant communities: Implications for invasion process and management

The effects of herbivory on plant invasions are broadly discussed, and many studies have led to widely debated theories. In particular, the effects of herbivores on pine invasion found in different studies vary; in some cases, they controlled their expansion, and in others, they promoted it. On the other hand, vulnerability to invasion by pines differs between community types. Sites with dunes and bare ground are the most heavily invaded, followed by grasslands, while shrublands and forests are least invaded. Because current evidence is mostly observational, some of the varying responses of pine invasions to herbivory should be examined further through replicated experiments. Here, we address experimentally the extent to which preference for the non‐native invasive Pinus contorta by domestic sheep (Ovis aries) depends on the vegetation type. We installed experimental enclosures within two adjacent communities, grassland and shrubland, and in each one, we planted seedlings of P. contorta Douglas and established a sheep density typically recommended for the study area. The number of browsed seedlings, the number and type of branches browsed per seedling, the reduction in height and probability of survival immediately after browsing period were recorded. The number of browsed seedlings and damage to the terminal bud were higher in grassland than in shrubland, while the number of browsed branches per seedling was higher in shrubland than grassland. The reductions in height and probability of survival immediately after browsing were similar in both communities. These results show that moderate levels of sheep herbivory could reduce 20% seedling survival in both communities; nevertheless, the damage patterns differ between them. The sheep browsed more substantial number of seedlings in grasslands than in shrublands. However, if sheep find the seedlings, they damage it more in shrublands. These results suggest that experimental studies comparing communities are important for pine invasion management.     

Slugs, willow seedlings and nutrient fertilization: intrinsic vigor inversely affects palatability

This study evaluates how preference by a generalist slug herbivore Arion subfuscus changes inversely with seedling size across three levels of fertilization for three full‐sib families of willow seedlings. We analyzed seedlings for condensed tannin and protein concentration, and related these data to changes in palatability. In preference tests over time, leaf discs from more fertilized seedlings experienced an extended window of vulnerability compared to discs from less fertilized seedlings, which were also more tannin‐rich. In a whole seedling selection study, slugs readily attacked smaller seedlings (<5 cm) but rarely attacked taller seedlings (>10 cm). However, a general difference in risk of damage close to 50% existed when comparing shorter and taller individuals within each family and level of fertilizer. The decrease in palatability with height of the seedlings was positively correlated with an increase in condensed tannin concentration. We found no effect of seedling size on protein concentration. Akaiki index criterion model comparisons suggested that only main effects were important for explaining seedling choice by slugs as well as the ratio between proteins and condensed tannins. Seedling size, had the largest effect, followed by fertilizer level and family. Surprisingly, seedling size and fertilizer treatment had opposite effects on palatability to slugs. Size decreased probability of damage, whereas fertilization extended the window of susceptibility. Because the seedlings were even‐aged, differences in size are interpreted as differences in growth rate or vigor. The positive phenotypic correlation found between size and tannin production in the less preferred willow seedlings confirms that several plant defense traits may be selected for simultaneously, because fast growth may allow an early development of plant defenses. We discuss these results in the light of plant‐defense theories that predict a negative correlation between the allocation to growth and the production of secondary defense compounds.     

Reproductive capacity,germination and survivorship of Lithospermum caroliniense on Lake Huron sand dunes

Summary The flowering of pin (long-styled) and thrum (short-styled) plants in populations of Lithospermum caroliniense (Walt.) McMill. was synchronized and both morphs had an extended period of flowering. The plants produced a large number of flowers that did not set seeds — hence the seed production per plant was very low. The seeds showed strong dormancy. Even under natural conditions, only 19% of the seeds produced seedlings. However, seedling survival was relatively high probably due to rapid root growth to deeper layers where moisture was not limiting. The probability of survival of seedlings increased with age; survival of seedlings, juveniles and adults after 2 years was 39, 68 and 98%, respectively. The dry weight of roots increased from 10% in June to 42% in September whereas the proportion of biomass contained in leaves, stems and hypocotyls decreased with age.     

广西多穗柯叶片性状变异及幼苗生长量研究

多穗柯是一种珍贵天然野生药用植物,可以开发出保健食品色素和天然医用药品,广西的资源较丰富,该研究采集巴马、那坡、德保及田林等4个产地的多穗柯种子进行播种育苗,并跟踪调查测定一年生幼苗的叶片性状及幼苗生长量,并进行相关性分析。结果表明:(1)不同产地间叶片性状及幼苗生长指标均存在不同程度的差异,其中巴马与那坡、德保、田林在叶长、叶宽、叶面积、叶脉间距、叶鲜重、叶片干物质含量、叶片组织密度等叶片性状上的差异均达到显著水平,在株高、地径、单株干重、主根长、单株根干重及单株叶干重等生长指标上亦存在显著差异,且生长量是后3个产地的1~2倍;通过比较各产地的叶片保水力及植株净生长量,巴马的多穗柯植株耐旱性及生长速度优于其他三地。综合各性状表现,认为巴马的多穗柯苗期表现比较好,生长速度快,长势好,抗旱性较强,可作为多穗柯优良种源的初步选择。(2)8月份是多穗柯株高、地径的生长高峰期,建议此时应加强肥水管理,调节适宜的水肥光热条件,尽量延长幼苗的快速生长时间,以获得苗木的最大累积生长量。(3)叶片性状与幼苗生长量的相关性分析结果显示,叶面积与株高、地径、单株干重、单株根干重以及单株叶干重等呈极显著正相关,叶脉间距、叶绿素相对含量(SPAD)与株高、单株干重呈显著或极显著正相关,比叶面积与株高、地径呈显著负相关。因此,在以后的优株表型选择中,要优先考虑叶子大、叶脉间距宽、中老熟叶片叶色浓绿的植株。该研究结果为多穗柯优良种质资源的早期筛选提供了一定的依据。     

Episodic recruitment of the seedling banks in balsam fir and white spruce

• Premise of the study: In ecosystems where seed production is low and masting years are sporadic, or with species that have short-lived seeds, regeneration is assured by seedling banks rather than seed banks. Seedling establishment and survival play a critical role in determining the composition of these plant communities by supplying new individuals for their maintenance. Seedling emergence and mortality were investigated to test the hypothesis that recruitment into the seedling bank is periodic. • Materials and methods: Seed production and seedling emergence and survival was monitored during 1994-2007 in balsam fir (Abies balsamea) and white spruce (Picea glauca) in four pristine stands of the boreal forest of Quebec, Canada. Measurements were collected twice per month by sampling one permanent plot of 20 × 20 m per stand. • Key results: Seed-rain abundance reached 9 × 10³ seeds m⁻² year⁻¹, and was characterized by synchronous sequences of low and high seed production. New seedlings appeared only during the year following a seed production of at least 1 × 10³ and 1.5 × 10² seeds m⁻² year⁻¹ for balsam fir and white spruce, respectively. Seedlings emerged in July and survived 34-52 d on average, with balsam fir showing a longer lifespan and lower mortality, although 85–99% of seedlings died before completing one year of life. • Conclusions: The emergence of young seedlings was coupled with massive seed rains, which allowed synchronous replenishment of the seedling banks among stands and species, and generated different cohorts, yielding a discontinuous age structure.     

Growth Reduction of Apple Seedlings by Pratylenchus penetrans as Influenced by Seedling Age at Inoculation

Apple seedlings of different ages (1, 3, and 5 weeks) were inoculated with 6,900 Pratylenchus penetrans per seedling in 10-cm-diam pots in a growth chamber. Rate of growth suppression and total growth suppression of seedlings by P. penetrans were inversely proportional to seedling age at time of nematode inoculation. Younger seedlings were found to contain a higher number of nematodes per gram root.     

Ethylene and the growth of rice seedlings

Etiolated whole rice seedlings enclosed in sealed vials produced ethylene at a rate of 0.9 picomole per hour per seedling. When 2-centimeter-long shoots were subdivided into 5-millimeter-long sections, the sections containing the tip of the shoot evolved 37% of the total ethylene with the remaining 63% being produced along a gradient decreasing to the base of the shoot. The tip of the coleoptile also had the highest level of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid and of the ethylene-forming enzyme activity. Ethylene is one of the factors controlling coleoptile elongation. Decapitation of the seedling reduced ethylene evolution to one-third its original level and inhibited coleoptile growth. In short-term experiments, the growth rate of decapitated seedlings was restored to almost that of intact seedlings by application of ethylene at a concentration of 10 microliters per liter. Apart from ethylene, O₂ also participates in the control of coleoptile growth. When rice seedlings were grown in a gas mixture of N₂ and O₂, the length of the coleoptiles reached a maximum at a concentration of 2.5% O₂. Lower and higher concentrations of O₂ reduced coleoptile growth. The effect of exogenous ethylene on coleoptile growth was also O₂ dependent.     

The role of ethylene in the regeneration of Helianthus annuus (sunflower) plants from callus

Hypocotyl-derived callus from the Helianthus annuus L. inbred line SS415B regenerated significantly more plants if the seedlings were grown in the light. The difference between light- and dark-grown seedlings was not correlated with differences in seedling ethylene production, but seemed to be due to a difference in sensitivity to ethylene at a specific time during seedling growth. Treating 3-day-old dark-grown seedlings with 10 μ M aminoethoxyvinylglycine (AVG) effectively inhibited ethylene production for at least 7 days. Hypocotyl callus derived from AVG-treated seedlings gave the same amount of regeneration as callus from light-grown seedlings. Promotion of regeneration by AVG was not seen unless the 3-day-old seedlings were grown for 4 additional days prior to culturing hypocotyl explants. The effects of AVG could be reversed by treatment with 1-aminocyclopropane-1-carboxylic acid (ACC) during these 4 days. After the 4 days, ACC was no longer effective.     

Contrasting effects of ethylene perception and biosynthesis inhibitors on germination and seedling growth of barley (Hordeum vulgare L.)

The effects of the plant growth regulator ethylene, and of ethylene inhibitors, on barley (Hordeum vulgare L.) germination and seedling growth were investigated. Exogenous 1-aminocyclopropane-1-carboxylic acid (ACC) at 100 microM enhanced ethylene production by barley seedlings and stimulated shoot growth, whereas both germination and seedling growth were inhibited by antagonists of ethylene perception (75 microM silver ions, 100 microM 2,5-norbornadiene (NBD)). In contrast, germination was unaffected by, and root and shoot growth of seedlings was strongly stimulated by inhibitors of ethylene biosynthesis (10 microM cobalt chloride, 10 microM aminoethoxyvinylglycine (AVG)). Since the ethylene and polyamine biosynthetic pathways are linked through S:-adenosylmethionine, this prompted further explorations into the role of polyamines in germination and seedling growth. Exogenous polyamines (putrescine, spermidine and spermine) at 1 microM concentration stimulated barley seedling growth in a similar fashion to the ethylene biosynthetic inhibitors. Both polyamines and ethylene biosynthetic inhibitors reversed the inhibitory effects of ethylene perception inhibitors on germination and seedling growth. Blocking endogenous ethylene production with aminoethoxyvinylglycine enhanced the free putrescine and spermidine content of germinating barley grains. Thus endogenous polyamines may play a complementary, growth-promotive, role to ethylene in the normal course of barley germination. Further, experiments that have been carried out using inhibitors of ethylene biosynthesis may have to be re-evaluated to take the possible effect of polyamines into account.     

Structure and Dynamics of Populations of Japanese Barberry (Berberis Thunbergii DC.) in Deciduous Forests of New Jersey

Japanese barberry, Berberis thunbergii DC., has become a prominent exotic species in deciduous forests throughout the eastern and midwestern US. Populations range from small plants occurring at low densities to dense, impenetrable thickets of plants with up to 40 stems/individual. A study was undertaken at Morristown National Historical Park in New Jersey to document plant densities, plant size, recruitment through vegetative processes of new shoot initiation and clonal spread and recruitment from seedling establishment, and mortality of stems and plants. Nearly 2000 shoots on 370 plants were individually marked and followed for two growing seasons, and over 1000 seedlings were also individually marked and followed. Populations vary much more in total shoots/area than they do in plant individuals/area, or in mean plant size (shoots/plant), as even the sparse populations have a few large individuals. Shoot mortality is less than new shoot initiation, but most plants do not change in size or change by small numbers of stems. However, the number of new shoots per plant increases as plant size increases. Once plants have three stems, they suffer little or no mortality. Seedling establishment is proportional to the density of shoots, so that as plants grow in size, local recruitment from seed increases. Large numbers of seedlings, and a survival rate of 10%, combine to make seedling recruitment a major component of population increase. The combination of multiple forms of vegetative and seed-based population growth, and the very low rates of plant mortality due to the multi-stemmed growth form explains the ability of this invasive species to rapidly produce dense, persistent populations.