Clonal Shrub Research Articles

Reproductive Biology of the Monoecious Clonal Shrub Taxus canadensis

WILSON, P. (Department of Biology, California State University, 18111 Nordhoff Street, Northridge, CA 91330-8303), M. BUONOPANE (Department of Biology, Bates College, Lewiston, ME 04240) AND T D. ALLISON (Department of Forestry and Wildlife, University of Massachusetts, Amherst, MA 01002). Reproductive biology of the monoecious clonal shrub Taxus canadensis. Bull. Torrey Bot. Club 123: 7-15 1996.-Strobilus production, pollination, and maturation were studied in Taxus canadensis, a procumbent clonally-spreading shrub. Plants that produced many cones had greater shoot growth; no obvious tradeoff between sexual effort and vegetative growth was observed. T canadensis is monoecious, but plants showed considerable variation in phenotypic gender. Because related species are dioecious, we hypothesize that T. canadensis evolved from a dioecious ancestor. Monoecy may have been favored as a means of assuring pollination via selfing; the proportion of ovules pollinated was positively correlated with the number of male cones on a plant. Selfing may be at the cost of inbreeding depression; 26% of the female cones aborted, about twice the percentage of the dioecious Taxus cuspidata. Application of nutrient fertilizer did not reduce the abortion percentage. Seed and aril maturation in T. canadensis occurred over a three month period, much more gradually than in T cuspidata. Removal of the seeds, probably by antagonistic rodents, was very rapid and thorough in T canadensis. Asynchronous ripening and monoecy may help reduce seed predation by rodents by reducing the conspicuousness of fruiting displays relative to the dioecious species.

Responses to harvesting intensity in a clonal dwarf shrub, the bilberry (Vaccinium myrtillus L.)

The effects of herbivory were simulated on stands of bilberry (Vaccinium myrtillus L.) in a boreal Empetrum-Myrtillus type forest. Five harvesting intensities were used (0% (A), 25% (B), 50% (C), 100% (D) of the bilberry ramets or all the ramets of all species (E)). Density and biomass of the stands, and growth of the ramets were monitored for five growth seasons, from 1986 to 1990. After damage new ramets emerged rapidly from dormant buds at the base of removed ramets. Between 70 and 97% of the density relative to the control level was regained by the final harvest. However, only between 11 and 64% of the biomass relative to the control level was recovered. Clipping reduced the branch growth, both in the new ramets and in the new parts of the old, unclipped ramets. Severe treatments (D and E) decreased the growth more than did light harvesting (B and C). Survival and fecundity of the ramets were not affected. The result therefore suggested that the bilberry is not able to recover totally from severe herbivory damage between the years of peak rodent population that shows a 3–4 year cycle. Nevertheless, extreme grazing pressure is rare in boreal ecosystems as alternative food is available for herbivores, and predators also limit the herbivore population. Hence the bilberry exhibits moderate tolerance of the usual level of herbivory damage.

Canopy Gap Closure in Thickets of the Clonal Shrub, Cornus racemosa

DICKINSON, M. B. (Department of Biological Science, Florida State University, Tallahassee, FL 32306), F. E. PUTZ (Department of Botany, University of Florida, Gainesville, FL 326112009), AND C. D. CANHAM (Institute of Ecosystem Studies, The New York Botanical Garden, Box AB, Millbrook, NY 12545). Canopy gap closure in thickets of the clonal shrub, Cornus racemosa. Bull. Torrey Bot. Club 120: 439-444. 1993.-We investigated the rates and mechanisms of canopy gap closure and changes in thicket age, stem density, crown size, and canopy closure with height in thickets of the clonal shrub, Cornus racemosa Linnaeus. We conducted the study in a well drained upland old field with nutrient-poor soil and a poorly drained lowland old field with more nutrient-rich soil in New York's Hudson Valley. As thickets grow taller, canopy closure tends to decrease because lateral growth of canopy stem crowns does not completely offset decreases in canopy stem density. When stems die, they generally die standing and singly, forming gaps in the canopy. Single stem gaps formed by standing-dead stems were closed predominantly by lateral growth of the branches in the crowns of stems surrounding the gaps. Mean closure rates of experimentally created gaps were greater on average in the wetter and more nutrient-rich lowland site (15.0 cm/yr) than in the upland site (5.0 cm/yr). Gaps closed by 85%/yr at the lowland site and 21%/yr at the upland site. The fates of understory stems differed between sites, more understory stems reached the canopy in upland thickets. Stem lean contributed to both the opening and closing of individual gaps at both sites. On average, lean opened gaps in upland thickets and had no effect on lowland gap closure rates. Stem lean after gap creation increased with canopy stem density. Larger gaps should take longer to close, allowing more opportunity for understory stems to contribute to gap closure.

Sprout demography and intraclonal competition inLycium barbarum, a clonal shrub, during an early phase of revegeeation

A demographic study of post-fire revegetation in a clonal shrubLycium barbarum is presented. Spontaneous development of the sprout population was estimated using both nondestructive and destructive methods and compared to the data from experimentally thinned plots. Relationships between growth parameters (height, biomass, leaf area) and their changes in the course of development are analysed. Description of the seasonal dynamics of the sprout population is given. Intraclonal competition among individual sprouts was observed. Results of the growth analysis are presented for populations of different age.

Variation in growth rate in shoot populations of the clonal dwarf shrub Linnaea borealis

This study was based on two years of field observations of a Linnaea borealis population in a coniferous forest in Sweden. Detailed information on performance and survivorship of shoots were gathered from consecutively made drawings of 90 individually marked shoot systems of Linnaea distributed among 15 plots in the forest. Branching of the shoot systems was correlated to growth of the main shoot. Increasing light flux negatively affected growth of Linnaea. A tendency for a competitive effect on Linnaea of Vaccinium spp. was also found. In contrast, the surrounding mosses, and intraspecific density of Linnaea had no significant effect on the shoot systems. The growth rate of the shoot population was analysed by matrix models. Population growth rate was most dependent on survivorship and growth of main shoots in Linnaea, while the survivorship of lateral shoots was of less importance. In spite of an average decrease in the population size as revealed by the matrix model simulation, the incorporation of the observed spatial variation in shoot growth increment, branching and shoot survivorship, yielded varying population growth rates. Parts of the population increased in size. The importance of choice of spatial scale in population analyses of forest understory plants is emphasized.

SEXUAL DIMORPHISM IN BIOMASS ALLOCATION AND CLONAL GROWTH OF XANTHOXYLUM AMERICANUM

Reproduction can have a high resource cost. It has been suggested that greater investments in sexual reproduction by female dioecious plants leads to a lower rate of vegetative growth in females than in males. In this study, we investigated sexual dimorphism in biomass allocation and genet growth of the dioecious clonal shrub, northern prickly ash (Xanthoxylum americanum). The allocation of biomass over the course of one growing season to reproductive tissue, leaves, and growth of aboveground first‐year wood, was compared in 18 clones growing in fields and six clones in woods in southeastern Wisconsin during 1985 and 1986. In addition, the number of shoots per clone, and weight of nonfirst‐year wood (accumulated biomass) above‐ and below‐ground were estimated. In open field sites, male clones allocated more biomass to new wood and less to reproduction than females, although males allocated more to flowers alone. Accordingly, male clones had significantly more shoots and more accumulated biomass both above‐ and below‐ground than female clones. In the woods, where fruit set was near zero, there were few significant differences between male and female clones in either biomass allocation or accumulated biomass. These results support the hypothesis that the high resource investment in fruit production by females reduces their vegetative growth relative to males.

Sexual Dimorphism in Biomass Allocation and Clonal Growth of Xanthoxylum americanum

Reproduction can have a high resource cost. It has been suggested that greater investments in sexual reproduction by female dioecious plants leads to a lower rate of vegetative growth in females than in males. In this study, we investigated sexual dimorphism in biomass allocation and genet growth of the dioecious clonal shrub, northern prickly ash (Xanthoxylum americanum). The allocation of biomass over the course of one growing season to reproductive tissue, leaves, and growth of aboveground first-year wood, was compared in 18 clones growing in fields and six clones in woods in southeastern Wisconsin during 1985 and 1986. In addition, the number of shoots per clone, and weight of nonfirst-year wood (accumulated biomass) above- and below-ground were estimated. In open field sites, male clones allocated more biomass to new wood and less to reproduction than females, although males allocated more to flowers alone. Accordingly, male clones had significantly more shoots and more accumulated biomass both above- and below-ground than female clones. In the woods, where fruit set was near zero, there were few significant differences between male and female clones in either biomass allocation or accumulated biomass. These results support the hypothesis that the high resource investment in fruit production by females reduces their vegetative growth relative to males.

Modules of Production and Reproduction in a Dioecious Clonal Shrub

Modules of Production and Reproduction in a Dioecious Clonal Shrub

Modules of Production and Reproduction in a Dioecious Clonal Shrub, Rhus Typhina

The hypothesis that male—biased sex ratios result from the greater costs of reproduction for females was examined at various modular levels in a study of the dioecious clonal shrub, staghorn sumac (Rhus typhina). The population of flowering trunks was male—biased, though male and female clones proved to be of similar ages. Trunks within apparent female clones were more likely to be vegetative or dead than in male clones, though the density of living plus dead trunks was comparable in male and female clones. Females of given ages had the same mean trunk diameter as similarly aged males. Overall, the average female trunk diameter was the same as the average male diameter. Differential costs and patterns of reproduction for males and females were revealed through destructive harvests and separate analysis of trunks and branches. An abrupt discontinuity n the performance (growth) of male trunks and branches. An abrupt discontinuity in the performance (growth) of male trunks was found; those with a diameter less than °4 cm had greater total numbers of leaves, branches, and inflorescences than females of comparable diameter, whereas larger males and females did not differ from each other. Flowering males branches had significantly fewer leaves than those of flowering females. The number of leaves per branch was highly correlated with the number of fruits produced in the corresponding terminal inflorescence. The average (±SE) male inflorescence had 4099 ± 312 flowers, whereas the average female inflorescence bore 1575 ± 67.2 fruits. There was a sixfold difference in the biomass of these terminal reproductive units (female infructescences being heavier.) This study suggests the importance in a clonal species of defining the modular level at which costs are assessed. The hypothesis that females suffer greater reproductive costs as a consequence of fruit production is supported by the finding of diminished survivorship of daughter trunks in female clones. However, it is not supported by data on annual trunk diameter increments. Reproductive costs in sumac are shown at the level of the clone (ramet survivorship) or the branch, rather than at the level of the flowering trunk module.

Stem Dynamics of the Shrub Alnus Incana SSP. Rugosa: Transition Matrix Models

We constructed transition matrices from observed rates of sprout production and stem growth in two New York state populations of a clonal shrub, Alnus incana ssp. rugosa. The largest real eigenvalue of the transition matrix, l, summarized current population rates of growth. An old—field alder thicket showed slow population decline over all 3 yr of study. The other population, in an undisturbed natural swamp, showed decline in each year but overall increase when data from all 3 yr were combined. Sensitivity matrices were calculated from the stable size distributions and reproductive value vectors for each 3 yr matrix. Sensitivity of population growth rates to specific transitions was illustrated by changing values of the matrix elements and calculating resultant 1 values. Population growth rates were least affected by changes in survivorship of small stems, and most affected by altering sprout production rates and large stem survivorship. Annual variations in demographic rates, and comparisons between actual stem size class distributions and the stable distributions predicted by the matrix models, confirmed the inadequacy of assuming constant transition probabilities. In such a case, transition matrix models are best viewed not as projections of long—term population behavior, but as indicators of current demographic trends.

Spatial Distribution of Genetic Individuals in Thickets of Alnus incana ssp. Rugosa, a Clonal Shrub

Spatial Distribution of Genetic Individuals in Thickets of Alnus incana ssp. Rugosa, a Clonal Shrub

An Ecologic Study of the Flora of Mountainous North Carolina (Concluded)

Previous articleNext article FreeAn Ecologic Study of the Flora of Mountainous North Carolina (Concluded)John W. HarshbergerJohn W. Harshberger Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by Volume 36, Number 5Nov., 1903 Article DOIhttps://doi.org/10.1086/328418 Views: 99Total views on this site Citations: 5Citations are reported from Crossref Journal History This article was published in the Botanical Gazette (1876-1991), which is continued by International Journal of Plant Sciences (1992-present). PDF download Crossref reports the following articles citing this article:James T. Donaldson, Zachary C. Dinkins, Foster Levy, Arpita Nandi Surface-soil Properties of Alder Balds with Respect to Grassy and Rhododendron Balds on Roan Mountain, North Carolina—Tennessee, Southeastern Naturalist 13, no.22 (Jun 2014): 377–395.https://doi.org/10.1656/058.013.0218J.R. Webster, K. Morkeski, C.A. Wojculewski, B.R. Niederlehner, E.F. Benfield, K.J. Elliott Effects of Hemlock Mortality on Streams in the Southern Appalachian Mountains, The American Midland Naturalist 168, no.11 (Jul 2012): 112–131.https://doi.org/10.1674/0003-0031-168.1.112Katherine J. Elliott, James M. Vose Age and distribution of an evergreen clonal shrub in the Coweeta Basin: Rhododendron maximum L. 1, The Journal of the Torrey Botanical Society 139, no.22 (Apr 2012): 149–166.https://doi.org/10.3159/TORREY-D-11-00076.1Ronald L. Stuckey Phytogeographical outline of aquatic and wetland angiosperms in continental eastern North America, Aquatic Botany 44, no.2-32-3 (Jan 1993): 259–301.https://doi.org/10.1016/0304-3770(93)90073-6 H. D. Clayberg Upland Societies of Petoskey-Walloon Lake Region, Botanical Gazette 69, no.11 (Oct 2015): 28–53.https://doi.org/10.1086/332607