Our purpose is to discuss the impact of alien plants on rangeland ecosystems of the Great Basin in terms of their effects on biological functions. The sagebrush/bunchgrass ranges of western North America are used as a model ecosystem for the impact of alien plants. Alien weed species have been introduced in successive waves, with the success of each new introduction dependent on how well adapted to the environment and how competitive the new weed is with those previously introduced. Annual species have been successful across extensive areas of Great Basin rangelands. Biennial and short- and long-lived perennial introductions have been restricted to much more specific habitats. Alien plants impact rangelands through stand renewal and successional processes. Alien weeds can cause such processes to be accelerated and/or truncated depending on the species and range site.

Postdispersal weed seed predation by animals during the summer fallow period may lead to a reduction in the number of weeds that grow in the following winter cropping season. In this study, we investigated the patterns of weed seed removal, the influence of crop residue cover on seed removal, the types of granivores present and their seed preferences in a 16-ha postharvest cropping field in Western Australia during the summer months over 2 yr. Seed removal from caches was extremely variable (from 0 to 100%). Removal rates were generally highest along the edges of the field near bordering vegetation and lowest in the center of the field and within the bordering vegetation. However, there were many deviations from this general pattern. There was no change in rates of predation with different levels of residue cover. Ants or other small invertebrates were found to remove the most seeds. However, seed removal by other animals, such as rodents, was also evident. Annual ryegrass seeds were preferred over wild oat seeds, followed by wild radish pod segments. Seed harvesting was lowest in late January, peaked in February, and decreased in March. Results from this study suggest seed harvesters could reduce the number of surface seeds in the field, reducing the weed seed bank. Management options that increase the activity of the seed harvesters may lead to less variability in seed predation and could, therefore, be incorporated into an integrated weed management program.

Depending on the mosaic of habitats that is created, forest fragmentation can reduce the abundance and diversity of forest birds. Temperate deciduous forests in South America are rapidly being replaced by pine plantations, causing changes in habitats for both breeding and migrant birds. We examined differences in avian species richness and abundance in three areas: a reserve with continuous tracts of native forest, forest fragments and pine plantations. Four species were negatively affected by fragmentation, with their abundance declining from continuous forest to pine plantations. Fourteen species were not affected by fragmentation and eight had significantly increased abundance in pine plantations compared to continuous forest. Overall abundance in pooled and ground/understorey birds was higher in forest fragments and pine plantations compared to continuous forest. The abundance of granivorous species was higher in the pine plantations than in the forest reserve, but the abundance of insectivorous species was higher in the forest reserve and in forest fragments than in pine plantations. Thus, forest fragmentation affects birds differentially according to their feeding ecology.