Patterns of exotic plant invasions in fragmented urban and rural grasslands across continents |
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Authors: | Sarel S Cilliers Nicholas S G Williams Francois J Barnard |
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Institution: | (1) School of Environmental Sciences and Development, North-West University (Potchefstroom Campus), Potchefstroom, South Africa;(2) Department of Resource Management and Geography, The University of Melbourne, Burnley Campus, 500 Yarra Boulevard, Richmond, VIC, 3121, Australia |
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Abstract: | Linear native grassland remnants in fragmented landscapes are usually at a great risk of exotic species invasion from their
edges. Changes in species distribution near habitat edges are extensively studied in ecology as knowledge about edge responses
is important to understand the development of patterns and processes in landscapes. However, elucidating robust general principles
for edge effects has been difficult as species responses to habitat edges are highly variable and dependent on a large number
of attributes which affect the function and structure of edges and therefore the distance that edge effects penetrate into
fragmented natural vegetation. The objective of this study was to investigate the generality of exotic species invasion patterns
from edges in native grassland patches surrounded by urban and rural landscapes. This was done by comparing the results of
research from Victoria, Australia with a similar study from North-West Province, South Africa. Despite their occurrence on
different continents, the grasslands are floristically and structurally similar and are dominated by the same grass species.
Invasion patterns were quantified using two spatial statistics methods; block kriging and spatially constrained clustering.
Two distinct patterns of exotic species invasion were identified in native grassland remnants in South Africa and Australia,
namely exotic species invasion from the edge where the cover of exotic species increased with increasing proximity to the
edge and a pattern that suggests that gap phase vegetation dynamics may also drive exotic species invasion at urban grasslands.
Although urbanization and weed invasions are complex processes similar patterns of exotic species invasion in urban grasslands
were found in two different continents suggesting that general patterns may occur. Implications of this for the conservation
of native grasslands in contrasting landscapes are discussed. |
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Keywords: | Urban Grasslands Rural Exotic species invasion Edge effects Gap dynamics |
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