Differentiation between native and exotic plant species from a dry grassland: fundamental responses to resource availability, and growth rates

Species from a mixed native/exotic dry grassland community in New Zealand were experimentally assessed for three ecophysiological parameters: nutrient response, water response and maximum relative growth rate (RGR max ). These are parameters that relate to factors proposed as important in structuring plant communities in dry environments. Native and exotic species did not differ consistently in water response. Exotic species tended to have a greater response to nutrients, but there was considerable overlap between native and exotic guilds. However, exotic species did have a higher intrinsic growth rate, and this effect was not attributable to differences in life histories. The results suggest that the exotic species are more competitive and more generalist than the native species. These traits are compatible with the concept of the 'ideal invader', and suggest the C-R strategy of Grime's theory. The native species showed characteristics consistent with stress tolerance (sensu Grime). The paucity of evidence for ecophysiological differentiation between the native and exotic guilds, except in intrinsic growth rate, indicates that the exotic species were able to invade not because they had superior adaptation to the physical environment, but because they possessed, by pre-adaptation, the same ways of coping with that environment as the existing species. However, their ability to invade can be related to their growth rates.

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