Invasive alien species: a major threat for the last remnants of South American grasslands

ZALBA, SERGIO M.; CUEVAS, YANNINA A.; DE VILLALOBOS, ANA ELENA; SANHUEZA, CRISTINA; GERMAIN, PAOLA; AMODEO, MARTÍN; MARTÍNEZ BACCINI, AGUSTÍN; DISPIGNO, LEANDRO

Pirenópolis

Congreso; EMAPI 2013, 12th International Conference on Ecology and Management of Alien Plant Invasions; 2013

Universidade Federal de Brasilia

Introduction The Pampas biome comprises ca. 893,000 km2 of subtropical and temperate grasslands in Southern South America. Climate and soils lead to severe and extensive landscape changes in early colonization times, initially for cattle husbandry and latter for agriculture (Fonseca et al. 2013). Invasive alien plants, especially trees and shrubs, are the main threat for the last remnants of native vegetation growing in areas of low aptitude for agriculture (Zalba and Villamil 2002). Objectives Assess ecological changes associated to the spread of alien woody plant in remnants of native Pampas grasslands. Identify the main drivers of invasion. Design effective control actions. Methods The work was developed at a medium height (up to 1200 mASL) mountains in Southern Pampas (lat 38°S, long 61°W). Some of the most widespread invasive alien woody plants in the area were classified in three groups according to main biological characteristics: pines (wind-dispersed seeds, disturbance dependent recruitment), legume shrubs (fire resistant, long lived seed bank) and rosaceous (seeds dispersed by birds and mammals). An adaptive management strategy was implemented to assess population parameters relevant to the management of the species by the implementation of control actions. Effects of disturbance on invasion and efficiency of different treatments were also tested. Results and Conclusions Invasive alien shrubs and trees are responsible of significant reductions in plant species richness and changes in bird communities, and they also interfere with water runoff in high catchment areas. Invasive pines (Pinus halepensis and P. radiata) increase recruitment in response to wild fires and overgrazing, but prescribed fires could be used for control depending on their frequency. Invasive legumes (Spartium junceum and Genista monspessulana) grow in close association to riparian habitats where they increase fire intensity and frequency. Fire, in turn, promotes massive seed germination. A combination of mechanical and chemical control appears as an appropriate option for their control. Rosaceous invasives (Prunus mahaleb and Rosa spp.) depend on native bird and mammal species for long-distance dispersal and local colonization. P. mahaleb exhibits a lag-phase of 8-18 years between the establishment of the founder individual and local recruitment, representing an opportunity for the prevention further spread. Control efforts resulted in the recovery of grassland structure and composition, without complementary restoration actions. Conclusions Invasive woody plants have proved their ability to spread and colonize pristine grasslands in the Pampas. Their presence is associated to biodiversity losses and alteration of ecosystem services. Effective control is feasible and essential for preserving the last remnants of the biome, with adaptive management as the strongest option for both identifying the key components of the process and reducing its impact. Aknowledgements This work was supported by CONICET (National Research Council, Argentina) and Universidad Nacional del Sur. The main author received the support of Departamento de Ciencias Ecológicas, Universidad de Chile, to attend the congress. Keywords: grasslands, invasive woody plants, adaptive management References Fonseca, C. et al. 2013. Invasive alien plants in the Pampas grasslands: a tri-national cooperation challenge. Biol. Inv. 15: 1751-1763. Zalba, S.M. and C.B. Villamil. 2002. Invasion of woody plants in relictual native grasslands. Biol. Inv, 4: 55-72.