Invasion of introduced conifers is shaped by mammalian herbivores: Evidence from a literature review

RELVA, M.A.; NUÑEZ, M.

Portland, Oregon

Congreso; ESA 97th Meeting; 2012

Ecological Society of America

Invasion of introduced conifers is shaped by mammal herbivores: Evidence from a literature review María A. Relva, Laboratorio Ecotono, INIBIOMA (Universidad Nacional del Comahue and Conicet), Bariloche, Argentina Martín A. Nuñez, Ecology and Evolutionary Biology, The University of Tennessee, Knoxville, TN a) Background/Questions/Methods Invading conifer species, introduced originally for forestry, are increasingly recognized as serious problems in many parts of the southern hemisphere, where it is having a vast ecological and economical impact. Understanding the factors that trigger invasion and that can control them is key for their management. Grazing by mammal herbivores have been indicated as one of the mechanisms halting conifer invasions. However, contrasting effects have been also reported (e.g. positive, negative or no effect of grazing on invasion). This could be due to the fact that herbivores may prefer to consume competitive vegetation releasing the trees. In this study we attempt to identify situations were these contrasting situations occur and aim to find factors that may explain these different responses. We conducted a search of articles focused on the spreading of conifer species (introduced and native) under broad grazing situations (domestic cattle or wildlife). From this search we obtained 268 records, and after selections for articles with enough data for comparisons we kept 18 records. We used a discriminant function with the aim to predict the conifer invasion responses based on the identity of the conifer species, the recipient plant community as well as the herbivore attributes. b) Results/Conclusions The results showed that the species? identity is the best predictor to the invasion responses (positive, negative or no effect) while the herbivore density is also a variable with high explanatory power. As expected, some conifer species tended to be more invasive than others and this was also moderated by herbivory. At intermediate levels of herbivory invasion by conifers seem to be more aggressive, and at high levels of herbivory invasion cannot occur. These results suggest that herbivore can mediate the invasion of invasive trees. In some locations this information can be use by managers to control the spread of exotic buy simply increasing the density of herbivores (e.g. sheep or cattle) to reach high levels in areas near the source of invasive trees, for example in areas adjacent to pine plantations.