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University of Otago (2011)

The role of shrubs and rabbit herbivory in the ecological restoration of the drylands of south-central New Zealand

Camara Amadou

Titre : The role of shrubs and rabbit herbivory in the ecological restoration of the drylands of south-central New Zealand

Auteur : Amadou Camara

Université de soutenance : University of Otago

Grade : Doctor of Philosophy 2011

Résumé partiel
The net outcome of the interaction between woody and herbaceous plant species can be positive or negative depending on plant species and environmental conditions. Positive interactions (facilitation) are postulated to be more prevalent and negative interactions (competition) less prevalent, under high environmental severity. Positive interactions have been attributed to the so-called ‘fertile islands’ and ‘nurse plant’ effects. The ‘fertile islands’ and the ‘nurse plant’ effects are suggested mechanisms for plant interactions in arid and semi-arid environments worldwide. Some indigenous plants in dryland New Zealand are postulated to have grown under a woody canopy and may benefit from the restoration of the woody habitat. However, restoration of indigenous plants may be impeded by mammalian herbivory. In this study, the ‘fertile islands’ and the ‘nurse plant’ effects and their possible role in the ecological restoration of a predominantly indigenous dryland mixed woody and herbaceous vegetation, were investigated, in the presence and absence of rabbit herbivory, in the dry sub-humid Central Otago by field experiments and by glasshouse ecophysiological experiments. The fertile islands effect was investigated by comparing soil properties under four shrub species to those of the adjacent grassland. Soils under Kunzea ericoides and Coprosma propinqua were more fertile compared to those of the grassland. Soils under two other species Discaria toumatou and Rosa rubiginosa were not significantly different in fertility from soils in the grassland.
The nurse plant effect was tested in the field by comparing the height growth and survival of five planted herbaceous plant species as well as the natural recruitment of herbaceous species under a shrub canopy to those of the adjacent grassland, with or without grazing. In general there was no significant difference in height growth or survival between plants under a shrub canopy and those in the grassland. Grazing had a negative effect on the height growth and survival of herbaceous plant species. Herbaceous plant species richness under a canopy differed with shrub species and season of measurement. Effects of a shrub canopy on herbaceous plant species richness ranged from mainly positive (Rosa rubiginosa) to mainly positive but inconsistent (Coprosma propinqua and Discaria toumatou) and mainly negative but scale-dependent (Kunzea ericoides). However, herbaceous plant species composition was not significantly different between areas under a shrub canopy and the adjacent grassland.

Présentation

Page publiée le 31 décembre 2011, mise à jour le 7 août 2017