Alien grass invasion of Renosterveld : influence of soil variable gradients
Date
2008-12
Authors
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Publisher
Stellenbosch : Stellenbosch University
Abstract
This thesis examines the role of agricultural activity in the process of invasion of west
coast renosterveld fragments by annual alien grass species. This highly endangered
vegetation type has less than 5% remaining, it is vital to understand the mechanisms
allowing invasion of annual alien grasses in order to effectively prevent the loss of the
many rare and endemic species found in west coast renosterveld. This study was
divided into three major components.
Firstly the distribution of indigenous and alien plant species in relation to fence lines,
separating active agricultural fields from untransformed vegetation, was described.
Regression analysis was used to test for relationships between distances from
agricultural fields and soil physical and chemical characteristics in natural vegetation.
Cover by annual alien invasive grasses in untransformed vegetation decreased
significantly with distance away from agricultural land.
Secondly alien and indigenous grass seed banks were sampled along the transects, at
the same sites, in order to establish whether the seed banks correlated with above
ground cover. Results varied among sites and seed banks were correlated with the
vegetation cover at only one site. It appears that there are a multitude of factors
determining the distribution of annual alien grass cover.
Thirdly a greenhouse experiment established the role that nitrogen plays in the success
of the alien grass Avena fatua. This species was grown in competition with three
indigenous species, an annual forb (Dimorphotheca pluvialis), a geophyte (Oxalis
purpurea) and an indigenous perennial grass (Tribolium uniolae) at three levels of soil
nitrogen. The geophyte was largely unaffected, while growth of the annual and
indigenous perennial grasses was negatively affected by competition with A. fatua.
Nitrogen did not seem to affect competitive interactions. Management of these renosterveld patches, in order to conserve them effectively, will
require a multi-faceted approach, including prevention of further invasion and removal
of invasive grasses already present.
Description
Thesis (MScConsEcol (Conservation Ecology and Entomology))--Stellenbosch University, 2008.
Keywords
Annual alien grass, Edge effect, Renosterveld, Soil physical and chemical characteristics, Alien invasion, Theses -- Conservation ecology and entomology, Dissertations -- Conservation ecology and entomology