			Home About us Contact

Established Seedlings (established + seedling)

Distribution by Scientific Domains

Life Sciences	100%

Selected Abstracts

Realized gene flow within mixed stands of Quercus robur L. and Q. petraea (Matt.) L. revealed at the stage of naturally established seedling

MOLECULAR ECOLOGY, Issue 10 2010
I. J. CHYBICKI
Abstract The estimates of contemporary gene flow assessed based on naturally established seedlings provide information much needed for understanding the abilities of forest tree populations to persist under global changes through migration and/or adaptation facilitated by gene exchange among populations. Here, we investigated pollen- and seed-mediated gene flow in two mixed-oak forest stands (consisting of Quercus robur L. and Q. petraea [Matt.] Liebl.). The gene flow parameters were estimated based on microsatellite multilocus genotypes of seedlings and adults and their spatial locations within the sample plots using models that attempt to reconstruct the genealogy of the seedling cohorts. Pollen and seed dispersal were modelled using the standard seedling neighbourhood model and a modification,the 2-component seedling neighbourhood model, with the later allowing separation of the dispersal process into local and long-distance components. The 2-component model fitted the data substantially better than the standard model and provided estimates of mean seed and pollen dispersal distances accounting for long-distance propagule dispersal. The mean distance of effective pollen dispersal was found to be 298 and 463 m, depending on the stand, while the mean distance of effective seed dispersal was only 8.8 and 15.6 m, which is consistent with wind pollination and primarily seed dispersal by gravity in Quercus. Some differences observed between the two stands could be attributed to the differences in the stand structure of the adult populations and the existing understory vegetation. Such a mixture of relatively limited seed dispersal with occasional long distance gene flow seems to be an efficient strategy for colonizing new habitats with subsequent local adaptation, while maintaining genetic diversity within populations. [source]

Effects of large herbivores and fire on the regeneration of Acacia erioloba woodlands in Chobe National Park, Botswana

AFRICAN JOURNAL OF ECOLOGY, Issue 4 2001
Myra E. Barnes
Abstract Acacia erioloba woodlands provide important forage and shade for wildlife in northern Botswana. Mortality of mature trees caused by browsing elephants has been well documented but the lack of regeneration of new trees has received little attention. Annual growth of new shoots and changes in height were measured to determine the influence of elephants and small ungulate browsers, rainfall and fire on the growth and survival of established A. erioloba seedlings from 1995 to 1997 in the Savuti area of Chobe National Park. All above-ground vegetation was removed from 40% of established seedlings in 1995 and 28% in 1997 by browsing elephants, and the mean height of remaining seedlings decreased from >550 mm to <300 mm. When seedlings browsed by kudu, impala and steenbok but not elephants are considered, mean seedling height increased <50 mm per year, even though mean new shoot growth remaining at the end of the dry season was 100,200 mm. Fires burned portions of the study area in 1993 and 1997, killing above-ground vegetation, but most established A. erioloba seedlings survived, producing coppice growth from roots. While elephants and fire caused the greatest reduction in established seedling height and number, small browsers suppressed growth, keeping seedlings vulnerable to fire and delaying growth to reproductive maturity. Résumé Les forêts d'Acacia erioloba procurent une nourriture et des abris importants pour la faune au nord du Botswana. On connaît bien la mortalité des grands arbres due aux éléphants mais on n'a accordé que peu d',attention au manque de régénération de nouveaux arbres. On a mesuré la croissance annuelle des jeunes pousses et le changement de hauteur pour déterminer l'influence des éléphants et des petits ongulés, des chutes de pluies et des feux sur la croissance et la survie des semis connus d',A. erioloba, de 1995 à 1997 dans la zone de Savuti au Parc National de Chobe. Toute la végétation au-dessus du sol a été supprimée sur 40% des semis connus en 1995, et 28% en 1997 par le broutage des éléphants, et la hauteur moyenne des plants restants a baissé de > 550 mm à < 300 mm. Lorsqu'on considère les pousses broutées par les koudous, les impalas et les steenbocks, mais pas par les éléphants, la hauteur moyenne des jeunes pousses augmentait de moins de 50 mm par an même si la croissance moyenne des nouvelles pousses subsistant à la fin de la saison sèche était de 100 à 200 mm. Les feux ont brûlé des portions de la zone étudiée en 1993 et en 1997, tuant toute la végétation au-dessus du sol, mais les pousses d',A. erioloba les mieux situées ont survécu, produisant de nouveaux taillis au départ des racines. Alors que les éléphants et les feux causaient les plus fortes réductions de la hauteur et du nombre des pousses établies, les petits ruminants en supprimaient la croissance, ce qui les laissait vulnérables aux feux et retardait la croissance jusqu'à la maturité. [source]

Seed limitation in a Panamanian forest

JOURNAL OF ECOLOGY, Issue 5 2005
JENS-CHRISTIAN SVENNING
Summary 1The role of seed limitation in tropical forests remains uncertain owing to the scarcity of experimental evidence. We performed seed addition experiments to assess seed limitation for 32 shade-tolerant tropical forest species and monitored the natural seed rain of 25 of these species for 17 years. 2One, two or five seeds were sown into 0.0079-m2 plots for large- (n = 5 species), medium- (n = 5) and small-seeded species (n = 22), respectively. The experiment was replicated at 69 sites, placed in groups of three at 23 locations. Seedling establishment was evaluated after 1 and 2 years in paired seed addition and control plots. Natural seedling emergence and understorey plant density were also measured. 3Median natural seed rain was 0.31 seeds m,2 year,1 per focal species. 4Seed addition enhanced seedling establishment in 31 and 26 of the 32 species after 1 and 2 years, respectively. Mean number of focal species' seedlings after 2 years was 0.002 seedlings in control plots and 0.12, 0.37 and 0.60 seedlings in seed addition plots for large-, medium- and small-seeded species, respectively. 5A 25 seeds added treatment increased seedling establishment by , 2.0-fold over the five seeds added treatment after 2 years. 6Community-wide recruitment and understorey plant density were strongly seed-limited. The natural density of understorey plants averaged 12 plants m,2 and was significantly less than for seedlings of the single focal species in plots with , 2 seeds added 2 years earlier. 7The number of established seedlings per seed added was independent of seed size. 8Treatment (adding zero or five seeds), species identity and location all affected seedling establishment for the 11 small-seeded species represented at all sites, with treatment and its interactions accounting for 86% of the explained variation. 9Our results suggest that seed limitation plays a dominant role in seedling recruitment and understorey plant community assembly in tropical forests. Although strong seed limitation may set the stage for species-neutral community assembly, the species differences in seedling establishment rate and its spatial variation demonstrate an important role for species-specific processes. [source]

Realized gene flow within mixed stands of Quercus robur L. and Q. petraea (Matt.) L. revealed at the stage of naturally established seedling

Destination-based seed dispersal homogenizes genetic structure of a tropical palm

MOLECULAR ECOLOGY, Issue 8 2010
JORDAN KARUBIAN
Abstract As the dominant seed dispersal agents in many ecosystems, frugivorous animals profoundly impact gene movement and fine-scale genetic structure of plants. Most frugivores engage in some form of destination-based dispersal, in that they move seeds towards specific destinations, resulting in clumped distributions of seeds away from the source tree. Molecular analyses of dispersed seeds and seedlings suggest that destination-based dispersal may often yield clusters of maternal genotypes and lead to pronounced local genetic structure. The long-wattled umbrellabird Cephalopterus penduliger is a frugivorous bird whose lek mating system creates a species-specific pattern of seed dispersal that can potentially be distinguished from background dispersal processes. We used this system to test how destination-based dispersal by umbrellabirds into the lek affects gene movement and genetic structure of one of their preferred food sources Oenocarpus bataua, a canopy palm tree. Relative to background dispersal processes, umbrellabird mating behaviour yielded more diverse seed pools in leks that included on average five times more seed sources and a higher incidence of long-distance dispersal events. This resulted in markedly lower fine-scale spatial genetic structure among established seedlings in leks than background areas. These species-specific impacts of destination-based dispersal illustrate how detailed knowledge of disperser behaviour can elucidate the mechanistic link driving observed patterns of seed movement and genetic structure. [source]

Fat-tailed gene flow in the dioecious canopy tree species Fraxinus mandshurica var. japonica revealed by microsatellites

MOLECULAR ECOLOGY, Issue 10 2006
S. GOTO
Abstract Pollen flow, seed dispersal and individual reproductive success can be simultaneously estimated from the genotypes of adults and offspring using stochastic models. Using four polymorphic microsatellite loci, gene flow of the wind-pollinated and wind-seed-dispersed dioecious tree species, Fraxinus mandshurica var. japonica, was quantified in a riparian forest, in northern Japan. In a 10.5-ha plot, 74 female adults, 76 male adults and 292 current-year seedlings were mapped and genotyped, together with 200 seeds. To estimate dispersal kernels of pollen and seeds, we applied normal, exponential power, Weibull, bivariate t -distribution kernels, and two-component models consisting of two normal distribution functions, one with a small and one with a large variance. A two-component pollen flow model with a small contribution (26.1%) from short-distance dispersal (, = 7.2 m), and the rest from long-distance flow (, = 209.9 m), was chosen for the best-fitting model. The average distance that integrated pollen flows inside and outside the study plot was estimated to be 196.8 m. Tree size and flowering intensity affected reproduction, and there appeared to be critical values that distinguished reproductively successful and unsuccessful adults. In contrast, the gene flow model that estimated both pollen and seed dispersal from established seedlings resulted in extensive seed dispersal, and the expected spatial genetic structures did not satisfactorily fit with the observations, even for the selected model. Our results advanced small-scale individual-based parentage analysis for quantifying fat-tailed gene flow in wind-mediated species, but also clarified its limitations and suggested future possibilities for gene flow studies. [source]