Facilitation by unpalatable weeds may conserve plant diversity in overgrazed meadows in the Caucasus Mountains

Abstract

Positive interactions among plants have been demonstrated in many communities around the world, and appear to play important roles in maintaining species coexistence, productivity, and species diversity. However, the potential for positive interactions to conserve biological diversity in ecosystems that are disturbed by humans is poorly understood and often overlooked. One of the most important positive effects one plant can have on another is protection from herbivory. By associating with an unpalatable neighbor, a tasty species may avoid being eaten and increase in size and reproductive fitness. We examined the role of two highly unpalatable plants, Cirsiumobvalatum and Veratrum lobelianum, in subalpine meadow plant communities of the central Caucasus Mountains in the Republic of Georgia, where intense livestock grazing has occurred for over two thousand years. These two species are avoided by livestock because of spines and toxicity, respectively, and have increased dramatically in abundance recently due to seasonal trans‐Caucasus migrations of vast herds of domestic sheep during the Soviet era. The Gudauri region, bisected by the Russian‐Georgian Military Road, was a focal point of these migrations, and there we found that plant communities associated with Cirsium and Veratrum were very different in composition than open meadows. Forty‐four percent (15/34) of all species at our site were found at only “trace” (<1.0%) cover values in the open meadow, but at significantly higher covers under Cirsium or Veratrum. Of the 38 species that were reproducing sexually at our site, eight were found only under the unpalatable invaders. Communities associated with Cirsium and Veratrum had 78–128% more species in flower or fruit than open meadow communities, respectively, than open meadow sites. Furthermore, community composition and reproductive output differed substantially between Cirsium and Veratrum, indicating some degree of species‐specificity in their effects. These results indicate that unpalatable plants, which are generally indicators of unhealthy rangelands, have the potential to preserve plant diversity in overgrazed plant communities.

Remote Sensing for Grassland Management in the Arid Southwest

“…The weeds Veratrum lobelianum and Cirsium obvallatum, which have been reported in grazing areas in the Caucasus (Callaway et al 2000), primarily occur in the subalpine zone in areas with dense vegetation cover.…”

Short-Term Effects of Cattle Browsing on Tree Sapling Growth in Mountain Wooded Pastures

“…Tree regeneration has been shown to occur most often in safe sites (Harper 1977), such as on rocky outcrops or near unpalatable plants providing protection against browsers (Callaway et al 2000;Milchunas and Noy-Meir 2002;Bakker et al 2004;Smit et al 2005). Overall, browsing reduced both the biomass of current-year shoots and total aboveground biomass for all tree species and size classes.…”

Restoration of woodpasture on former agricultural land: The importance of safe sites and time gaps before grazing for tree seedlings

“…Evidence for these succession mechanisms in the initial stages is accumulating (e.g. Callaway and Davis, 1998;Callaway et al, 2000;Bokdam and Gleichman, 2000;Rousset and Lepart, 2003;Bossuyt et al, 2005), although experimental work is rather sparse (Callaway et al, 2005;Callaway, 1992;Rousset and Lepart, 2000;Bakker et al, 2004;Smit et al, 2006).…”