Seed dormancy and dormancy-breaking conditions of 12 West African woody species with high reforestation potential in the forest-savanna ecotone of Côte d'Ivoire

Information on the regeneration ecology of native woody species of the forest-savanna ecotone of West Africa is scarce, which is a major impediment to their optimal utilization in large-scale restoration programmes. The scattered information that is available for some of these species reveals that freshly matured seed are dormant. However, environmental heterogeneity among different habitats may results in inter-population seed dormancy variation. Thus, our objective was to re-examine the dormancy of 12 species from the forest-savanna ecotone that have been targeted for reforestation. Specifically, we aimed to examine the water-permeability of the seeds and explore the effectiveness of acid scarification and heat treatment to alleviate dormancy. Four species belonging to families other than Fabaceae and Malvaceae had water-permeable seeds. Two of them had nondormant (ND) seeds, and seeds of the other two species had a mixture of ND and other kinds of dormancy (possibly physiological dormancy, PD). Most species of Fabaceae and Malvaceae had water-impermeable seeds. All seeds of three species had physical dormant (PY), and some seeds of the remaining species had PY, while others were ND or had PD. Acid-scarification was effective in breaking PY and in augmenting imbibition and germination of non-PY seeds, while heat treatment was moderately effective in breaking dormancy. In general, acid scarification for 1-30 minutes and heat treatment for one hour at 55-75°C were optimal to enhance seed germination, depending on species. The present study has wide practical implications for park conservationists and restoration ecologists interested in producing bulk quantities of high-quality planting stocks of native woody species for large-scale restoration programmes.

Habitat distribution modeling for reintroduction and conservation of Aristolochia indica L. - a threatened medicinal plant in Assam, India

A detailed study on the regeneration ecology of Aristolochia indica L. was carried out to prevent this threatened medicinal plant from its future extirpation in Assam, India. The population stock of the species has been depleting fast in its natural habitats as a consequence of certain factors such as habitat fragmentation, over-exploitation due to its high medicinal properties, and other anthropogenic activities. For improving the conservation status of the species, potential area and habitat for its reintroduction were predicted using Maximum Entropy distribution modelling algorithm. The model was developed using environmental parameters and locality data in the natural range of Karbi Anglong District of Assam, India. The model predicted that the suitable habitats for the reintroduction of A. indica L. were restricted to parts of Assam, Nagaland, Meghalaya, and Arunachal Pradesh which have been identified to offer suitable environmental conditions for persistence of the species. Population status was positively correlated with higher model thresholds in the undisturbed habitats confirming the usefulness of the habitat model in population monitoring, particularly in predicting the successful establishment of the species.

Determinants of survival over 7 years for a natural cohort of sugar maple seedlings in a northern hardwood forest

The regeneration ecology of sugar maple (Acer saccharum Marsh.) has been impacted by acid rain leaching of base cations from the soils throughout much of its range. We tracked the survival and causes of death for a natural cohort of sugar maple seedlings across 22 sites in the Hubbard Brook Valley in New Hampshire, USA, where soil acidification has been documented. Survival over 7 years averaged 3.4%; however, significant differences in survival were observed among sites, which were classified into three main groups based on the shape of their survival curves. These site groups differed in position on the landscape, seedling nutrition and leaf size, and the prevalence of damage agents, but not in soil Ca. First-season mortality was high (71%), and the main damage agents were fungal infection (Rhizoctonia spp.) and caterpillar herbivory (Geometridae). Other principal causes of mortality in order of importance were winter injury, mechanical damage, and rodent (Myodes gapperi Vigors, 1830) tunneling, and all damage agents varied significantly in severity between years. This study highlights the importance of landscape-level variation in biotic factors for predicting sugar maple regeneration success. Predictions of sugar maple regeneration will require a better understanding of controls on initial seedling growth and the suite of biotic agents that damages seedlings.

Changing perspectives on regeneration ecology and genetic diversity in western quaking aspen: implications for silviculture

A conventional view of regeneration ecology of quaking aspen ( Populus tremuloides Michx.) in western North American holds that reproduction is strictly vegetative and, except on some marginal sites, only successful following high-severity disturbance. This view has strongly influenced silvicultural treatment of western aspen and has led to low expectations concerning genetic diversity of stands and landscapes. However, recent discoveries are fundamentally altering our understanding of western aspen regeneration ecology and genetics. For example, there are clearly multiple pathways of aspen regeneration and stand development. Research on a variety of fronts indicates that seedling establishment is common enough to be ecologically important and that genetic diversity is substantially greater than previously thought. We review conventional understanding of western aspen and put this into the context of silvicultural practice. We then review recent developments in aspen research and assess the silvicultural implications of these insights.