Testing a non‐equilibrium model of rangeland vegetation dynamics in Mongolia

Abstract

Summary1. Few studies have tested the applicability of current non-equilibrium models of rangeland vegetation dynamics to a particular ecosystem, or across a range of systems that might be expected to respond di erently to grazing. This study assessed the extent to which the non-equilibrium persistent (NEP) model of rangeland vegetation dynamics applies to three distinct Mongolian rangeland ecosystems, the desert-steppe, steppe and mountain-steppe. 2. Standing biomass, vegetation cover and composition, and species richness and diversity were examined along grazing pressure gradients in ecological zones of differing productivity and interannual variability in precipitation. 3. In the desert-steppe, biomass, functional group cover, richness and diversity did not vary along grazing pressure gradients, but all vegetation variables except the cover of weedy annuals and unpalatable forbs varied signi®cantly between years. Vegetation dynamics in this zone largely conformed to the NEP model of rangeland dynamics. 4. In the mountain-steppe, grass and total biomass, total vegetative cover, the cover of grasses, weedy annuals and unpalatable forbs, and richness and diversity varied along grazing pressure gradients. With increasing grazing pressure, grasses decreased and forbs and weedy annuals increased, as the conventional range condition (RC) model predicts. Interannual variation in precipitation in¯uenced total vegetative cover, species and functional group cover, and richness and diversity. 5. In the steppe, forb biomass, grass, forb, unpalatable forb and weedy annual cover, and diversity varied along grazing pressure gradients. Grass biomass and total vegetative cover responded interactively to rainfall and grazing. Forb biomass, grass, forb and weedy annual cover and richness varied between years. Grasses decreased and forbs and weedy annuals increased with increasing grazing pressure, conforming to the RC model. 6. Ecosystem response to rainfall and grazing is complex, and interpretation of the response depends on the speci®c variables examined. The recent paradigm shift in rangeland science from the RC model to non-equilibrium models has been embraced with such enthusiasm by some that the concept of non-equilibrium rangelands may be as much in danger of being misapplied as equilibrium-based models have been.

Environmental change and long-term body mass declines in an alpine mammal

“…It is also possible that density dependence could be mediated by overgrazing; however, no changes in NDVI consistent with overgrazing, such as decreases in maximum NDVI or INDVI [69], were detected. Overgrazing can also encourage the colonisation of grazingtolerant, less palatable species [70], which might not result in detectable changes in productivity. However, such changes would not alter our finding that increases in density appear to have influenced body mass via changes in per-capita resource availability.…”

Monitoring of Khulans and Goitered Gazelles in the Mongolian Gobi – Potential and Limitations of Ground Based Line Transects

“…Average snow cover lasts 97 days. Rain-and snowfall can be highly variable from year to year in space and time and the area is generally considered to follow nonequilibrium dynamics (Fernandez-Gimenez and Allen-Diaz 1999).…”

Plant communities of the Great Gobi B Strictly Protected Area, Mongolia

“…However, we think that dominance relations are subject to pronounced changes in a non-equilibrium system such as the Mongolian Gobi (Fernandez-Gimenez & Allen-Diaz, 1999). This renders communities devised on a dominance approach rather unstable.…”

“…The composition of the vegetation of southern Mongolia indicates a long grazing history (Fernandez-Gimenez, 1999). The number of families using the park has remained fairly stable since the 1970s.…”