Vegetative Ramets Research Articles

Ramet demography in a ring‐forming clonal sedge

1 In a calcareous dry grassland community in central Europe genets of the clonal sedge Carex humilis form very distinct rings of densely aggregated ramets. As genet growth form is generated by ramet population dynamics, ramet demography must be studied in order to understand how rings develop. We analysed how ramet demography in C. humilis depends on ramet position within the ring and how this is linked to ramet size. 2 The per ramet population growth rate was > 1 at the periphery of rings but < 1 in the interior, meaning that the population increases at the periphery but decreases in the interior. The population growth rate differed mainly because ramets were smaller in the interior and because smaller ramets produced fewer vegetative ramets. It is unlikely that the smaller ramet size is caused by negative density dependence, interspecific competition, internal control or resource depletion. 3 The study covered four growing seasons and we found considerable variation in ramet demography between years. The net result for the 4 years was that the total number of C. humilis ramets in the population increased. However, both production of vegetative ramets and ramet size decreased during the study period and if this trend continues population size will instead decrease.

Large‐scale spatial dynamics of plants: a response to Freckleton &amp; Watkinson

Metapopulation theory (summarized by Hanski 1999) is one of the most influential developments in ecology of recent decades, for example as a cornerstone of conservation biology, and as a theoretical basis for studies of dispersal and of the distribution and abundance of species. A synthesis of metapopulation theory and landscape ecology has been regarded as a key to analyses of the ecological consequences of ongoing landscape changes (Wiens 1997). Although successfully applied to many regional systems of animal populations, the usefulness of metapopulation theory for studies of plants is still open to debate. As Husband & Barrett (1996) and Eriksson (1996) concluded, rather few studies have documented metapopulations in plants, and the same holds for other forms of regional dynamics, e.g. source-sink populations and remnant populations. In a recent paper, Freckleton & Watkinson (2002) have critically reviewed studies of plant metapopulations, with the objectives of assessing whether regional populations of plants really are metapopulations, and suggesting a new typology for different forms of plant regional dynamics. Freckleton & Watkinson stress, and we agree, that these issues are not merely semantic. The concepts of regional dynamics not only determine the ways in which empirical studies are performed, but also influence the interpretation of data (illustrated by Freckleton & Watkinson with studies claiming, but not showing, the existence of metapopulations) and the modelling of spatial dynamics of plant populations. Freckleton & Watkinson (2002) begin by listing four criteria that must be fulfilled in order to regard a regional population as a metapopulation: (i) suitable habitat occurs as discrete patches that may be occupied or unoccupied; (ii) all local populations have a measurable extinction risk; (iii) habitat patches are interconnected by dispersal, allowing the possibility of re-colonization; and (iv) local populations are not completely synchronized in their dynamics. If these criteria are met, regional dynamics cannot be inferred from local processes, and local dynamics cannot be understood without referring to regional patterns or processes. Freckleton & Watkinson (2002) conclude that, given these criteria, very few cases exist where plant metapopulations have been documented. Indeed, there are a number of reasons why plants may not develop metapopulations in the same way as short-lived mobile animals. The existence of long-lived life cycle stages (e.g. seeds or vegetative ramets) means that a local population may persist for a long time even though the patch has become unsuitable. Successful dispersal and recruitment may be very sporadic, and therefore recolonization is unlikely after local population extinction. Dispersal over long distances may be governed by chance events. The definition of 'long distance' may differ between species, but in many cases it may be no more than a few hundred metres (Cain et al. 2000). Suitable habitat is difficult to define, and suitability is likely to be a continuous function of abiotic and biotic environmental factors. Freckleton & Watkinson propose that, using a metapopulation concept for describing regional populations, many plant regional populations would be described as non-equilibrium metapopulations, a conclusion we also reached for plants in fragmented habitats (Eriksson & Ehrl~n 2001). We agree with Freckleton & Watkinson (2002) that it is difficult to assess whether plants in general fulfil the criteria for metapopulations. However, we disagree with their suggestions on a new typology for regional dynamics. We also believe that their conclusions concerning the difficulties in documenting metapopulations in plants may be interpreted as indicating that local processes are sufficient for understanding regional patterns of plant populations, although we acknowledge that this may not have been their intention. We have three objectives here: (i) to comment on the typology of regional dynamics suggested by Freckleton & Watkinson (2002); (ii) to suggest how regional processes might be of importance to plant distributions irrespective of whether plants have metapopulations; and (iii) to argue that metapopulation theory should be developed further as a tool for studies of plants, rather than being replaced by other concepts.

Small‐scale turnover in a calcareous grassland, its pattern and components

Abstract. We studied small‐scale turnover in a calcareous grassland community in 2 cm × 2 cm subplots within 46 10 cm × 10 cm plots from 1996 to 1999. In different years, 73–84% of the subplots were occupied by rooted plant individuals, but the location of empty subplots varied considerably between years. Seedlings were the most mobile components in subplots – during one year (from July to July), seedlings either appeared or disappeared in on average 85% of all subplots where seedlings had occurred during that year. Within a one‐year period, vegetative ramets appeared or disappeared in an average of 30% of all subplots that had rooted plants at either the beginning or the end of that year. When only previously empty subplots were taken into account, 80% of appearances were due to clonal growth and 20% due to seedling establishment. Ca. 75% of the seedlings, however, established in subplots that already contained a rooted plant individual. There were significantly less generative appearances when a moist summer was followed by a dry one, and significantly more vegetative appearances when a dry summer was followed by a moist one. 24–33% of the established seedlings survived the first year; from the second year onwards the annual survival was greater than 50%. Seedling survival was higher among shortlived species. Generative turnover varied between species, but we found no correlation with life history characteristics or frequency. Vegetative turnover of species was dependent on the year and on species traits. Sedges had a significantly higher turnover than grasses. Species potentially able to move clonally &gt; 10 cm per year had a higher turnover than slower species. Turnover was not dependent on species frequency in the community. Forbs with more seedlings also had a higher vegetative turnover. There were no evident links between spatial mobility and species coexistence; predominating species exhibited contrasting turnover rates, subordinate species had contrasting turnover rates as well. Turnover is important in more general terms as a process resulting in free gaps – arenas for recruitment of whatever species.

Small-scale turnover in a calcareous grassland, its pattern and components

Abstract We studied small-scale turnover in a calcareous grassland community in 2 cm × 2 cm subplots within 46 10 cm × 10 cm plots from 1996 to 1999. In different years, 73–84% of the subplots were occupied by rooted plant individuals, but the location of empty subplots varied considerably between years. Seedlings were the most mobile components in subplots – during one year (from July to July), seedlings either appeared or disappeared in on average 85% of all subplots where seedlings had occurred during that year. Within a one-year period, vegetative ramets appeared or disappeared in an average of 30% of all subplots that had rooted plants at either the beginning or the end of that year. When only previously empty subplots were taken into account, 80% of appearances were due to clonal growth and 20% due to seedling establishment. Ca. 75% of the seedlings, however, established in subplots that already contained a rooted plant individual. There were significantly less generative appearances when a moist su...

Roles of succession, light, nutrients and disturbance on population vigor and maintenance of the rare plant Solidago shortii (Asteraceae)

Results of field and glasshouse experiments on Solidago shortii, and our observations on this species over many years, were used to construct a conceptual model of the roles of succession, light, soil nutrients and disturbance on population vigor and maintenance of this federal-endangered species. As cover of woody vegetation increased at a population site between 1986 and 1992, number of flowering ramets of S. shortii significantly decreased but number of vegetative ramets remained nearly constant. Adult plants transplanted into a redcedar thicket and those shaded in a glasshouse produced many fewer flowering ramets and capitula per flowering ramet and less biomass and had higher mortality than those in the open. Seedlings/juveniles shaded in a glasshouse had significantly less dry biomass; lower RGR, NAR, leaf area and root/shoot ratio and higher LAR, SLA and LWR than nonshaded ones. In a field site and glasshouse, fertilized plants (NPK) consistently had more flowering ramets and capitula per flowering ramet than nonfertilized ones. Hierarchy of dry weight of plants grown in a glasshouse in soils derived from five types of bedrock was phosphatic limestone > calcareous shale > sandstone > black shale = dolomite. Flowering and biomass production in the field-fertilizer and soil-type experiments were associated closely with levels of P. Number of flowering ramets significantly increased in plants transferred from shaded to nonshaded glasshouse conditions, but no such increase occurred after opening the canopy above plants in a thicket. Both high light and high nutrient levels apparently are necessary to maintain high vigor of S. shortii. In areas subject to invasion by woody plants, periodic high intensity disturbance may be required to prevent population extirpation.

Effects of Fire, Browsers and Gallers on New Jersey Tea (Ceanothus herbaceous) Growth and Reproduction

Abstract Woody plant species in grassland ecosystems can be subjected to damage from fire and multiple herbivore species, but interactions between fire and herbivory can modify their separate impacts on woody plant life histories. We studied how galling (by Periploca ceanothiella, Lepidoptera: Cosmopterigidae), deer browsing (Odocoilius virginianus) and fire affected the growth and reproduction of the woody shrub Ceanothus herbaceous (Rhamnaceae) on a burned and an unburned site at Konza Prairie Research Natural Area in eastern Kansas. Fire was the major influence on C. herbaceous growth, causing plants to produce long unbranched vegetative ramets from protected belowground meristems, while unburned plants were heavily branched and bore shorter shoots and numerous inflorescences. Unburned plants experienced higher gall frequencies, more galls on their longest shoots, but similar deer browsing compared to burned plants. Ramets with herbivore damage had more branches and inflorescences than undamaged ramets...

Surfgrass (Phyllospadix Torreyi) Reproduction: Reproductive Phenology, Resource Allocation, and Male Rarity

Little is known about the reproductive ecology of aquatic angiosperms, despite their wide distribution and ecological importance. Surfgrass (Phyllospadix torreyi) is a clonal marine angiosperm that lives on turbulent rocky shores. Surfgrass exhibits a strongly female—biased sex ratio in flowering shoots throughout its distribution along the Pacific coast of North America. The ecological causes for this biased sex ratio were examined over 3 yr in a surfgrass population off Catalina Island in southern California, USA. Abundances, biomass, and C:N content of male and female flowering ramets were measured, and the reproductive phenology, reproductive losses to abortions, herbivore damage to fruits and seeds, and clonal survival and growth were quantified. Each year, a quarter of the vegetative ramets reproduced sexually and seed production in the population was prolific. The population sex ratio was female biased across the entire depth distribution of surfgrass, but males were more abundant deeper in the bed. Despite male rarity, pollen was abundant in the population, and virtually all ovules were fertilized, with few losses to abortions or herbivory before seed release. Potential female fitness (seeds produced) was highest at shallow depths where light availability was greatest and abortions were reduced. The spatial segregation of the sexes was not due to environmental sex lability but to greater ramification of female vs. male clones in shallow depths. Female flowering shoots had significantly higher biomass than males across water depth, despite no obvious cost in terms of vegetative growth, or advantage in terms of plant size. If current theory on sex allocation than the sex ratio should be biased toward the gender with the lower reproductive cost is true for surfgrass, then surfgrass provides an example of how a subtle resource allocation difference can result in a dramatic population bias. An alternative explanation for the female bias in surfgrass population is greater male mortality due to significantly weaker attachment to the substratum. This study demonstrates the potential role hydrodynamics can play in aquatic plant reproduction and in structuring their population.

Environmental constraints on the growth, photosynthesis and reproductive development of Dryas octopetala at a high Arctic polar semi-desert, Svalbard.

Opportunities exist in high Arctic polar semidesert communities for colonisation of unvegetated ground by long-lived clonal plants such as Dryas octopetala. This can be achieved by lateral spread of vegetative ramets, or by sexual reproduction and seedling recruitment. The objectives of this study were (1) to determine whether these two means of proliferation show differential sensitivity to contrasting components of the abiotic environment (temperature, soil nutrient and water availability) and (2) to evaluate the potential for D. octopetala to respond to climate change by an increase in cover and biomass in polar semi-desert communities. Factorial environmental manipulations of growing season temperature, soil nutrient and water status were conducted over 3 years at a polar semi-desert community in Svalbard, Norway (78°56.12'N, 11°50.4'E) and both clonal and sexual reproductive performance, together with instantaneous net photosynthesis (Pn), were recorded during the third season (1993). D. octopetala capitalised rapidly on an amelioration in the availability of inorganic nutrients (N, P and K) by an expansion in leaf area and biomass supported by increased Pn per unit leaf weight, and by apparent luxury uptake of nutrients (particularly P). Several facets of sexual reproductive development and seed viability were markedly improved by elevated temperatures or soil nutrient availability. Thus although D. octopetala is a long-lived clonal plant, with many traits characteristic of stress resistance syndrome, it showed considerable phenotypic plasticity in response to environmental manipulations. The results support the hypothesis that clonal growth confers survival potential during unfavourable years, together with the ability to capitalise on nutrient flushes and recycle nutrients internally. Continued investment in sexual reproduction ensures that seed setting is successful during favourable years, even if these occur infrequently. Cimate warming in the high Arctic could thus result in changes in the cover, biomass and the relative significance of clonal versus sexual proliferation of D. octopetala (and thus the genetic diversity of the population) but the long-term responses will probably be constrained by lack of available nutrients.

Allozymic uniformity in Iris lacustris (dwarf lake iris) in Wisconsin

Iris lacustris Nutt. is a federally listed threatened species in Canada and the United States and is currently under consideration for active conservation management. The species is restricted to the shores of the western Great Lakes region and to a very narrow habitat type. Reproduction is almost exclusively by vegetative ramets. Limited sexual reproduction occurs after primarily geitonogamous pollination, although the plant is primarily selfed. Enzyme electrophoresis was used to determine the extent of genetic variation within and between Wisconsin populations. Ten enzymes coded by 22 putative genetic loci were examined. All nine populations were found to be monomorphic at the 22 loci for the same suite of isozymes. Heterozygosity was not detected at any loci. The apparent genetically depauperate nature of the species is addressed with regard to life history and reproductive biology. Implications for conservation management are addressed. Key words: Iris lacustris, threatened, isozyme, monomorphic.

Plants as Mosaics: Leaf-, Ramet-, and Gender-Level Variation in the Physiology of the Dwarf Willow, Salix arctica

Plant ecophysiological investigations often fail to account for age-specific, tissue-or organ-specific, or life-history-specific effects on overall performance. To address this issue, aspects of gas exchange and water relations of a deciduous and dioecious dwarf willow, Salix arctica, were examined. The degree of physiological variation that occurred as leaves aged was investigated, within and among vegetative and reproductive ramets of a plant's canopy, and between the sexes. Significant differences were observed in rates of photosynthetic carbon assimilation, dark respiration and stomatal conductance, as well as in bulk tissue water relations of leaves at different ages, between reproductive and vegetative ramets within an individual, and between male and female individuals (...)

Size‐Structures and Reproductive Characteristics in Diploid and Triploid Populations of Disporum sessile D. Don (Liliaceae)

Abstract Disporum sessile (Liliaceae), a perennial herb of temperate forests is composed of diploid (2n=16) and triploid (2n=24) populations. The size structure differed remarkably as triploid populations had few small plants and no seedlings. Triploid flowering plants were considerably larger than diploids. Triploids that flowered were 2.5 times larger than diploids that flowered and the size of vegetative ramets produced by triploids was twice as large. In triploids, fruiting rates were quite low only with inviable seeds and vegetative propagule size was greater than that of diploids. As regards growth parameters that help to increase plant size, triploids were superior to diploids. Differences in growth and reproductive parameters between diploids and triploids may contribute to forming different patch sizes.

Genet and Ramet Demography of Oenocarpus Mapora SSP. Mapora, a Clonal Palm of Panamanian Tropical Moist Forest

This study analyses the demography of a clonal plant species explicitly at the genet level. The tropical palm Oenocarpus mapora ssp. mapora produces vegetative ramets that root and are capable of independent survival; its growth from results in clones (genets) that are readily distinguishable as clumps in the field. The importance of clonal growth to the dynamics of the population of genetic individuals is evaluated and the influence of the clonal habit upon the demographic variation among O. mapora populations growing in heterogeneous forest habitats is examined

Revegetation of Artificial Disturbances in Grasslands of the Serengeti National Park, Tanzania: I. Colonization of Grazed and Ungrazed Plots

(1) The effects of small, physical disturbances on the structure and species composition and of grazing on colonization and regrowth of tropical grasslands were investigated in four communities in the Serengeti National Park, Tanzania. The species composition and densities of seedlings, surviving sprouts and invading ramets were recorded throughout the first growing season following disturbance. Soils, seed banks and natural disturbances were also investigated. (2) All species that grew in the disturbed plots were present prior to the.treatments and, in most cases, the most abundant colonizing species were previously abundant also. (3) Seedlings were more abundant than vegetative sprouts and ramets on disturbed plots in all communities. (4) The densities of seedlings, sprouts and invading ramets decreased along a gradient of increasing rainfall and soil moisture. This decrease in revegetating plants was not correlated with soil type, persistent seed bank (which was negligible in all sites), or frequency of disturbance, but it was partially correlated with the composition of the undisturbed vegetation. (5) The depth of disturbance affected significantly 28% of the species; seedlings were more abundant in the deeply disturbed and sprouting species were more abundant in shallowly disturbed plots. (6) Grazing affected significantly 23% of the species. Most species escaped the effects of grazing by being prostrate, resprouting from ground-level or underground organs, or by growing before or after the periods of heaviest grazing. (7) Large mammals were not responsible for the rich community pattern found in most Serengeti grasslands.