Unpalatable perennial grass invasion in central-east Argentina native grasslands: processes, implications and recovery.
In temperate semiarid central-east Argentina, unpalatable perennial grasses (UPG) have been steadily invading native grasslands formerly dominated by palatable perennial grasses (PPG). The objective of this contribution is to provide a synthesis of underlying processes and implications of UPG invasion, as well as recovery strategies. Results have shown that heavy selective grazing on PPG reduces their superior competitive ability. Gaps formed due to reduced competition by PPG provide safe sites for UPG establishment. The development of large, long-lived tussock of UPG, in combination with high standing crop accumulation, impairs PPG establishment even in absence of grazing. UPG produce sclerophyllous tissues, high in fibre and lignin and low in protein and mineral content. Senesced tissues of UPG decompose and mineralize nutrients slower than that of PPG, although they show a relatively low potential to cause nutrient immobilization in soil bacteria. UPG are less productive than PPG, which in combination to their low nutritive value commonly reduce carrying capacity and secondary productivity to half or less of potential values. The analysis and interpretation of current available knowledge point out that conservative and flexible stocking, in combination with controlled grazing and fire, should be implemented to recover and maintain a sustainable use of native grasslands in central-east Argentina.