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Seedling Populations (seedling + population)

Distribution by Scientific Domains

Life Sciences	75%

Selected Abstracts

Mortality in seedling populations of Silver Birch: genotypic variation and herbivore effects

FUNCTIONAL ECOLOGY, Issue 5 2003
K. Prittinen
Summary 1Variation among mature plants reflects mortality that has occurred during the seedling phase. Our earlier studies have shown variation in resistance to insect and vole herbivory among Silver Birch genotypes that represent variation in a naturally regenerated birch stand. The aim of this study was to examine whether seedling mortality varied among these genotypes, and whether insect and field vole herbivory affected mortality. The 20 genotypes studied competed with each other in dense stands, which were randomly assigned to insect and vole exposure and fertilization treatments. 2Insect herbivory and fertilization increased mortality significantly (by 98 and 68%, respectively). The fertilization effect was probably due to accelerated self-thinning among fast-growing seedlings. Although vole browsing removed considerable biomass, it did not affect seedling mortality. 3Mortality was context-dependent. The genotypes differed both in their overall mortality and in their response to insect herbivory. However, the effect of insects on a genotype depended more on its success in competition than on its resistance: even small amounts of feeding were detrimental to short, shaded seedlings, while taller seedlings in the canopy were affected less, although they were eaten more. 4It is concluded that moderate levels of insect herbivory can increase seedling mortality considerably. Furthermore, herbivory can change the genetic structure of birch populations through selective mortality, which in dense stands is dependent on competitive traits. [source]

Long-term effects of prescribed early fire, grazing and selective tree cutting on seedling populations in the Sudanian savanna of Burkina Faso

AFRICAN JOURNAL OF ECOLOGY, Issue 1 2009
Didier Zida
Abstract Annual early fire, selective tree cutting and exclusion of grazing are currently used as management tools in the Sudanian savanna of Burkina Faso although their long-term effects on seedling recruitment are poorly documented. A factorial experiment involving fire, grazing and cutting, each with two levels, was established in 1992 to study the effects of these management regimes and their interactions on the regeneration of woody species, and examine whether their effects varied temporally. Species richness, density and the morphology of seedlings were assessed in 1997 and 2002, and their relative changes were determined. The change in species richness of multi-stemmed individuals was significantly higher (P = 0.018) on plots that received fire × cutting treatment than the control plots. Significantly more species with single-stem were found on unburnt than on burnt plots (P < 0.001). Grazing tended to reduce the change in total density while fire (P < 0.001) and grazing (P = 0.029) significantly reduced the change in density of single-stemmed individuals. Selective cutting did not affect the total seedling density, but tended to reduce the change in single-stemmed seedling density. Principal component analysis revealed species-specific responses to treatments, particularly the relatively high abundance of lianas compared with other species. Résumé Les feux annuels précoces, la coupe sélective d'arbres et l'exclusion du pâturage sont des moyens actuellement utilisés dans la gestion de la savane soudanienne du Burkina Faso, mais leurs effets à long terme sur le recrutement de jeunes plants sont encore mal documentés. Une expérience factorielle impliquant le feu, le pâturage et la coupe, chacun à deux niveaux, a été mis en place en 1992 pour étudier les effets de ces régimes de gestion et leurs interactions sur la régénération d'espèces ligneuses et pour voir si ces effets variaient de façon temporelle. La richesse spécifique, la densité et la morphologie des jeunes plants furent évaluées en 1997 et en 2002, et l'on a leurs changements relatifs déterminés. Le changement de la richesse spécifique des individus multicoles était significativement plus important (P = 0.018) dans les parcelles qui avaient subi le traitement feu × coupe que dans les parcelles témoins. On a trouvé significativement plus d'espèces à tige unique dans les parcelles non brûlées que dans les parcelles brûlées (P < 0.001). Le pâturage avait tendance à réduire le changement de densité totale alors que le feu (P < 0.001) et le pâturage (P = 0.029) réduisaient significativement le changement de densité des individus à tige unique. La coupe sélective n'affectait pas la densité totale des jeunes plants mais avait tendance à réduire le changement de la densité des plants à tige unique. L'analyse en composantes principales a révélé que les réponses aux différents traitements étaient spécifiques aux espèces, particulièrement l'abondance de lianes, relativement grande par rapport aux autres espèces. [source]

United States Department of Agriculture,Agricultural Research Service research on pest biology: weeds,,

PEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 6-7 2003
Frank Forcella
Abstract Over 125 permanent full-time scientists conduct research within the USDA Agricultural Research Service (ARS) on issues related to weeds. The research emphasis of most of these scientists involves ecology and management or biological control of weeds. Many scientists perform research on weed biology as components of their primary projects on weed control and integrated crop and soil management. Describing all ARS projects involved with weed biology is impossible, and consequently only research that falls within the following arbitrarily chosen topics is highlighted in this article: dormancy mechanisms; cell division; diversity of rangeland weeds; soil resources and rangeland weeds; poisonous rangeland plants; horticultural weeds; weed traits limiting chemical control; aquatic and semi-aquatic weeds; weed/transgenic wheat hybrids; seedbanks, seedling emergence and seedling populations; and weed seed production. Within these topics, and others not highlighted, the desire of ARS is that good information on weed biology currently translates or eventually will translate into practical advice for those who must manage weeds. Published in 2003 for SCI by John Wiley & Sons, Ltd. [source]

Components of genetic variation for resistance of strawberry to Phytophthora cactorum estimated using segregating seedling populations and their parent genotypes

PLANT PATHOLOGY, Issue 2 2008
D. V. Shaw
Strawberry (Fragaria × ananassa) seedlings from 50 bi-parental crosses among 20 elite genotypes were evaluated for resistance to Phytophthora cactorum after artificial inoculation. Plots of seedlings or runner plants were rated using a disease severity score and the percentage of stunted plants per plot. The distribution of cross means for percentages of plants with stunting was highly skewed; 79% of the inoculated seedlings showed some level of stunting compared to non-inoculated control seedlings, and all but one of the crosses had 50% or more stunted plants. Disease severity scores for the bi-parental crosses were normally distributed and expressed a range of variation not reflected by the percentage of visibly stunted plants. Factorial analysis based on seedling plot means demonstrated significant additive genetic variance for the disease severity score, and the additive genetic variance was 1·9 times greater than the estimated dominance variance. The cross-mean heritability was for the severity score. Estimates of the additive genetic variance component using the covariance of severity scores obtained from the seedling analysis and with severity scores for their parents evaluated in a commercial environment were similar, and 0·30, respectively. Most of the selection response obtained through genotypic selection would thus be transferred to segregating offspring. [source]