Abstract
Abstract Two successive shrub invasions of a short tussock grassland induced by grazing and burning were examined in montane South Island, New Zealand. The first invasion was by a native shrub, matagouri ( Discaria toumatou Raoul). The second invasion was by an exotic shrub, Scotch broom ( Cytisus scoparius (L.) Link), which invaded the matagouri shrubland that had developed over the grassland. The invasions were investigated using analysis of spatial patterns of both shrubs and tussocks, and age, growth rates and size structure of the shrubs. Competition between the two shrub species was examined using spatial patterns and comparing allometric relationships. After initial invasion by matagouri of the grasslands, stand density increased by consolidation about its initial colonization points. Current matagouri distribution is often negatively associated with tussocks. Scotch broom occurs most frequently in a dense sward of introduced grasses and occasionally in tussocks in interstices among matagouri shrubs. Despite the palatability of Scotch broom to sheep that graze the site, there was no evidence that the spiny matagouri facilitates invasion by protecting Scotch broom seedlings; rather there was negative association between the shrub species. The two species probably compete for above‐ground space. However, diameter and height growth rates of Scotch broom far exceed those of matagouri so Scotch broom is likely to increase in biomass rapidly at the site. The autogenic organization and disturbance history of the resident plant communities have rendered each vulnerable to successive invasions.
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Claims 9
Claim · model-written summary
Matagouri density increased by consolidation around initial colonization points.
Verbatim
e0“After initial invasion by matagouri of the grasslands, stand density increased by consolidation about its initial colonization points”
Claim · model-written summary
Current matagouri distribution was often negatively associated with tussocks.
Verbatim
e0“Current matagouri distribution is often negatively associated with tussocks”
Claim · model-written summary
Scotch broom occurred most often in dense introduced grass sward.
Not reportedDirection
Verbatim
e0“Scotch broom occurs most frequently in a dense sward of introduced grasses”
Claim · model-written summary
Scotch broom occasionally occurred among tussocks in matagouri interstices.
Not reportedDirection
Verbatim
e0“occasionally in tussocks in interstices among matagouri shrubs”
Claim · model-written summary
The shrubs were negatively associated rather than showing evidence of seedling protection.
Verbatim
e0“there was no evidence that the spiny matagouri facilitates invasion by protecting Scotch broom seedlings; rather there was negative association between the shrub species”
Claim · model-written summary
The authors inferred competition for above-ground space between the shrub species.
Verbatim
e0“The two species probably compete for above‐ground space”
Claim · model-written summary
Scotch broom diameter and height growth rates far exceeded matagouri rates.
Verbatim
e0“diameter and height growth rates of Scotch broom far exceed those of matagouri”
Claim · model-written summary
Scotch broom was expected to increase rapidly in biomass at the site.
Verbatim
e0“Scotch broom is likely to increase in biomass rapidly at the site”
Claim · model-written summary
Community organization and disturbance history were inferred to make the communities vulnerable to successive invasions.
Verbatim
e0“The autogenic organization and disturbance history of the resident plant communities have rendered each vulnerable to successive invasions”