Is Cotoneaster franchetii invasion in Central Argentina facilitated by Eurasian livestock?

VILLADÉ, E; TECCO, PA; RENISON, D; LETT, I; HENSEN, I

Leipzig (Alemania)

Congreso; EURECO – 11th European Ecological Conference of the European Ecological Federation jointly with the GFOE – 38th Annual Conference of the Ecological Society of Germany; 2008

EURECO-GFOE

Grazing in areas with long evolutionary histories of large herbivores is supposed to reduce biotic invasion, while grazing exclusion is supposed to promote invasion, particularly in nutrient rich habitats [1]. However, grazing induced invasion resistance may be reduced when invasive species complexes are introduced, for example, large herbivores and the plants with which they most likely have co-evolved. A case in point is the Asian woody shrub Cotoneaster franchetti in its invasion into the mountains of central Argentina which have been grazed by Eurasian livestock for over 400 years while native large herbivores have become completely extinct. We studied C. franchetti regeneration along a fence-line separating an area of 200 ha with and without livestock. We sampled 30 C. franchetti seeder trees and their surroundings on each side of the fence-line and recorded any signs of browsing, number of seedlings shorter or larger than 5 cm as well as the microsite characteristics surrounding sites with or without seedlings. We recorded 892 seedlings, of which only 8% showed any signs of browsing. Small seedlings were found at similar densities with and without livestock influence. In contrast, large seedling density was significantly higher in the area with livestock, irrespective of shrub canopy cover. Seedling density under and out of the canopy of the seeder shrubs were 7 and 0.3 seedlings/m2, respectively. Seeder shrub size exerted a positive effect on seedling density. Microsite characteristics were important out of the shrub canopy only on sites where seedlings were usually more shaded and more south oriented than on sites without seedlings, irrespective of livestock presence. We conclude that livestock produce both some negative effects on C. franchetti through browsing and positive effects on large seedling recruitment possibly through a reduction of competition with native species which are heavily browsed and grazed. It is also possible that C. franchetti avoids browsing by producing secondary chemical compounds. Large seedlings of a similar native shrub/tree (Polylepis australis) which dominated the area prior to livestock introduction are highly browsed which strongly reduces adult recruitment [2]. As such, the presence of Eurasian livestock favours the recruitment of the Asian shrub and hinders the native shrub/tree. Our study therefore suggests that the Eurasian plant/herbivore complex is more successful in its invasive potential than the plant alone. Given the high C. franchetti seedling densities both in areas with and without livestock, livestock management does not seem to be suitably effective in controlling C. franchetti invasion in Central Argentina and should be modified accordingly, especially for shady south facing areas.