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Species Regeneration (species + regeneration)

Distribution by Scientific Domains

Life Sciences	50%

Selected Abstracts

Postdispersal seed predation and seed viability in forest soils: implications for the regeneration of tree species in Ethiopian church forests

AFRICAN JOURNAL OF ECOLOGY, Issue 2 2010
Alemayehu Wassie
Abstract Almost all dry Afromontane forests of Northern Ethiopia have been converted to agricultural, grazing or scrub lands except for small fragments left around churches (,Church forests'). Species regeneration in these forests is limited. We investigated (i) how intense postdispersal seed predation was in church forest, and if this seed predation varied with species and/or habitat, and (ii) for how long tree seeds maintained their viability while buried in forest soil. In the seed predation experiment, we monitored seeds of six tree species in four habitats for a period of 14 weeks (the peak seeding season). In the seed viability experiment, we assessed seed viability of five species in four habitats after being buried 6, 12, or 18 months. Ninety-two percent of the tree seeds were predated within 3.5 months. Predation was mainly dependent on species whereas habitat had a weaker effect. Seed viability decreased sharply with burial time in soil for all species except for Juniperus. To minimize seed availability limitation for regeneration of such species in the forest, the standing vegetation needs to be persistently managed and conserved for a continuous seed rain supply. Additional seed sowing, and seed and seedling protection (by e.g. animal exclosures) may increase successful regeneration of important species in these forests. Résumé Presque toutes les forêts afromontagnardes sèches du nord de l'Ethiopie ont été converties en terres agricoles, pâturages ou broussailles, à l'exception de petits fragments laissés autour des églises (« Forêts d'églises »). La régénération des espèces dans ces fragments reste limitée. Nous avons étudié (1) l'intensité de la prédation sur les semences après leur dispersion dans ces forêts et si cette prédation variait selon les espèces et/ou les habitats, (2) combien de temps les semences d'arbres gardaient leur viabilité lorsqu'elles étaient enterrées dans le sol d'une forêt. Dans l'expérience sur la prédation des semences, nous avons suivi des semences de six espèces d'arbres dans quatre habitats pendant 14 semaines (le pic de la saison des semences). Dans l'expérience sur la viabilité des semences, nous avons évalué la viabilité de semences de cinq espèces dans quatre habitats après avoir été enterrées depuis 6, 12 ou 18 mois. 92% des semences avaient été consommées en 3,5 mois. La prédation dépendait principalement de l'espèce, et l'habitat avait un effet moins important. La viabilité des semences diminuait fortement avec l'allongement de la durée d'enfouissement pour toutes les espèces sauf Juniperus. Pour diminuer autant que possible la limitation de la disponibilité des semences destinées à la régénération de telles espèces dans la forêt, il faut gérer continuellement la végétation présente et la conserver pour une production continue de semences. Un ensemencement supplémentaire ainsi que la protection des semences et des jeunes plants (par exemple en les clôturants pour écarter les animaux) pourraient améliorer la régénération des espèces importantes de ces forêts. [source]

Strategic light manipulation as a restoration strategy to reduce alien grasses and encourage native regeneration in Hawaiian mesic forests

APPLIED VEGETATION SCIENCE, Issue 3 2010
S. McDaniel
Abstract Question: Is there a light level at which alien grass biomass is reduced while still supporting growth and survival of native woody species, allowing for native species regeneration in abandoned pastures? Location: Island of Hawaii, USA. Methods: In a two-part study we examined the effect of light availability on common native woody and alien grass species found in secondary forests in Hawaii. A field survey was conducted to examine the relationship between light availability and canopy type (open pasture, planted canopy and secondary forest) on understory grass biomass and litter accumulation. We then experimentally manipulated light levels to determine the effect of light availability on growth and survival of six native woody species and three alien grasses. Low-light (5%), medium-light (10%) and high-light (20-30%) treatments were created using shade structures erected beneath the existing secondary koa canopy. Results: In the field survey, alien grass biomass was greatest under the open pasture and lowest in the secondary forest. There was a positive correlation between understory light availability and alien grass biomass. In the experimental study, large reductions in relative growth rates were documented for all of the grass species and four of the six woody species under the lowest light level. Although growth at 5% light is substantially reduced, survival is still high (84-100%), indicating that these species may persist under closed canopy. Conclusion: Low-light conditions result in the greatest reduction in alien grass biomass while creating an environment in which native woody species can grow and survive. [source]

Effects of invasive alien kahili ginger (Hedychium gardnerianum) on native plant species regeneration in a Hawaiian rainforest

APPLIED VEGETATION SCIENCE, Issue 1 2010
V. Minden
Abstract Questions: Does the invasive alien Hedychium gardnerianum (1) replace native understory species, (2) suppress natural regeneration of native plant species, (3) increase the invasiveness of other non-native plants and (4) are native forests are able to recover after removal of H. gardnerianum. Location: A mature rainforest in Hawai'i Volcanoes National Park on the island of Hawai'i (about 1200 m a.s.l.; precipitation approximately 2770 mm yr,1). Study sites included natural plots without effects of alien plants, ginger plots with a H. gardnerianum -dominated herb layer and cleared plots treated with herbicide to remove alien plants. Methods: Counting mature trees, saplings and seedlings of native and alien plant species. Using non-parametric H -tests to compare impact of H. gardnerianum on the structure of different sites. Results: Results confirmed the hypothesis that H. gardnerianum has negative effects on natural forest dynamics. Lower numbers of native tree seedlings and saplings were found on ginger-dominated plots. Furthermore, H. gardnerianum did not show negative effects on the invasive alien tree species Psidium cattleianum. Conclusions: This study reveals that where dominance of H. gardnerianum persists, regeneration of the forest by native species will be inhibited. Furthermore, these areas might experience invasion by P. cattleianum, resulting in displacement of native canopy species in the future, leading to a change in forest structure and loss of other species dependent on natural rainforest, such as endemic birds. However, if H. gardnerianum is removed the native Hawaiian forest is likely to regenerate and regain its natural structure. [source]

Variation in the impact of exotic grasses on native plant composition in relation to fire across an elevation gradient in Hawaii

AUSTRAL ECOLOGY, Issue 5 2000
Carla M. D'Antonio
Abstract The impact that an exotic species can have on the composition of the community it enters is a function of its abundance, its particular species traits and characteristics of the recipient community. In this study we examined species composition in 14 sites burned in fires fuelled by non-indigenous C4 grasses in Hawaii Volcanoes National Park, Hawaii. We considered fire intensity, time since fire, climatic zone of site, unburned grass cover, unburned native cover and identity of the most abundant exotic grass in the adjacent unburned site as potential predictor variables of the impact of fire upon native species. We found that climatic zone was the single best variable for explaining variation in native cover among burned sites and between burned and unburned pairs. Fire in the eastern coastal lowlands had a very small effect on native plant cover and often stimulated native species regeneration, whereas fire in the seasonal submontane zone consistently caused a decline in native species cover and almost no species were fire tolerant. The dominant shrub, Styphelia tameiameia, in particular was fire intolerant. The number of years since fire, fire intensity and native cover in reference sites were not significantly correlated with native species cover in burned sites. The particular species of grass that carried the fire did however, have a significant effect on native species recovery. Where the African grass Melinis minutiflora was a dominant or codominant species, fire impacts were more severe than where it was absent regardless of climate zone. Overall, the impacts of exotic grass-fuelled fires on native species composition and cover in seasonally dry Hawaiian ecosystems was context specific. This specificity is best explained by differences between the climatic zones in which fire occurred. Elevation was the main physical variable that differed among the climatic zones and it alone could explain a large percentage of the variation in native cover among sites. Rainfall, by contrast, did not vary systematically with elevation. Elevation is associated with differences in composition of the native species assemblages. In the coastal lowlands, the native grass Heteropogon contortus, was largely responsible for positive changes in native cover after fire although other native species also increased. Like the exotic grasses, this species is a perennial C4 grass. It is lacking in the submontane zone and there are no comparable native species there and almost all native species in the submontane zone were reduced by fire. The lack of fire tolerant species in the submontane zone thus clearly contributes to the devastating impact of fire upon native cover there. [source]