Mastication is a forest fuel thinning treatment that involves chipping or shredding small trees and shrubs and depositing the material across the forest floor. By decreasing forest density mastication has been shown to lessen crown fire hazard, yet other impacts have only recently started to be studied. Our study evaluates how mastication treatments alter the density and composition of soil see...

Arable land weed seed banks are dynamic and reflect cropping history, current management, and environment. Changes in crop rotation and tillage system can alter weed seed density and species composition. In the semi-arid region of the Pacific Northwest, USA, no-till spring cropping is being studied as an alternative to the traditional winter wheat (Triticum aestivum L.)/dust-mulch fallow (WWF) ...

1. Ambrosia trifida L. (giant ragweed), an aggressive weed of US grain crops and indigenous to North America, colonizes no-tillage crop fields and undisturbed soils despite its large seed size and susceptibility to seed predation. Secondary seed dispersal is critical to seed survival and seedling establishment, yet mechanisms of secondary dispersal are poorly understood for such large-seeded we...

The germination of three cerrado herbaceous species: Bidens gardneri, Vernonia herbacea (Asteraceae) and Psychotria barbiflora (Rubiaceae) was studied using seeds stored in cerrado soil and in refrigerator at 4°C. The field experiment was carried out at a preserved area of cerrado, the Reserva Biológica e Estação Experimental de Mogi-Guaçu, State of São Paulo, Brazil. The soil was collected in ...

Propagule banks are assumed to be able to store considerable genetic variability. Bryophyte populations are expected to rely more heavily on stored propagules than those of seed plants due to the vulnerability of the haploid gametophyte. This reliance has important implications for the genetic structure and evolutionary potential of surface populations. A liverwort, Mannia fragrans, was used to...

Senecio aquaticus, regionally a Red List species in Europe, has become increasingly abundant in agricultural grassland of medium to high management intensity in Switzerland, Southern Germany, and Austria in recent years, where it is a threat for animal and human health due to its toxicity. In this study, we investigated the seed ecology of S. aquaticus to help protection of the species in relic...

Assessing the various mechanisms by which plants revegetate disturbances is important for understanding the effects of disturbances on plant population dynamics, plant community structure, community assembly processes, and ecosystem function. We initiated a 2-yr experiment examining temporal vegetation dynamics and mechanisms of recolonization on different-sized soil disturbances created to sim...

The interdependence of species richness and plant biomass has widely been accepted as a general biodiversity rule. However, there is no information about how relationships are established during colonization and how total biomass is distributed among plants. The main objective of this study was to determine the role of several factors which we have hypothetized as affecting biomass distribution...

An investigation was carried out at the Muda rice fields, Peninsular Malaysia during four consecutive seasons of 2004 and 2005 to study the seasonal variation in the weed seedbank. Species composition with their dominance ranking and similarity between the species were recorded. A total of 577 seeds/sample (3337 seeds/m ) in 1/2004, 970 seeds/sample (5659 seeds/m ) in 2/2004, 928 seeds/sample (...

Population dynamics tries to explain in a simple mechanistic way the variations of the size and structure of biological populations. In this dissertation we use mathematical modeling and analysis to study the various aspects of the dynamics of plant populations and their seed banks. In Chapter 2 we investigate the impact of structural model uncertainty by considering different nonlinear recruit...