PhD defence: Mona Chor Bjørn

Mona Chor Bjørn defends her PhD thesis: 

Between Design and Ecology – Innovative herbaceous vegetation

Assessment Committee

Associate professor Marten Sørensen (chairman)
External members Professor P. Lindemann-Matthies and Professor N. Kühn.

Principal supervisor:

Associate Professor Marian Ørgaard, Department of Plants and Environmental
Sciences, University of Copenhagen, Denmark

Co-supervisors:

Professor Jacob Weiner, Department of Plants and Environmental Sciences, University of Copenhagen, Denmark

Professor Johannes Kollmann, Restoration Ecology, Department of Ecology and Ecosystem Management, Technische Universität München, Germany

Abstract

Urban green space offers more than recreation – it is a resource and a habitat for flora and wildlife. Since 2000 numerous articles have documented an increased public awareness of urban nature and biodiversity. As a result there has been increased interest in new vegetation types in urban and suburban environments. Colourful species-rich forb vegetation may be one possible way to link recreational values, aesthetical preferences and herbaceous vegetation with habitat requirements for diverse flora and fauna in urban and suburban environments.

The overall aim of this thesis is to improve our current understanding, both theoretical and practical, of the design and dynamical changes in low resource requiring, colourful forb vegetation. Through literature and an experimental field study, this thesis contributes to new perspectives on the possibilities for and limitations of creating and managing such vegetation, based on concepts and theories in plant community ecology. If these communities are based on local forbs there is a continuum in anthropogenic intervention from designed and intensively maintained to semi-natural herbaceous vegetation.

Results from a large field experiment show that, after three years, bare soil re-vegetates to become grass-dominated herbaceous vegetation with plant density and standing biomass similar to that of experimental species-rich forb vegetation. Standing biomass can be used as a measure to predict community development after disturbance. For a given biomass production, however, species-richness may be low or high. Some perennial forb species show good persistence in the face of competition from grasses and other weeds, while other species disappear quickly. Unexpected longevity of some monocarpic and polycarpic species may explain forb survivorship and a negative response to mowing during the summer. Predicting the growth of herbaceous plant communities is challenging. Our results show that, when grown at the same density, the biomass production of forbs is highly variable and species specific.

Plants are dynamic organisms, which respond physically to changes in the environment. There is a need to investigate the use of strategic interventions to secure persistence and regeneration of species-rich colourful forb vegetation. Disturbance is important to facilitate recruitment from seed as well as vegetative spread. Without some disturbance, forb vegetation will become colonised by grasses and eventually woody species.

This thesis adds useful basic knowledge in plant community ecology and species-specific growth, which are relevant to research and planning in landscape architecture and ecology.