Review: Keystone issues in ruminant science II. Environmental impact of ruminants: methane emissions and rangeland degradation.

Since the publication of the UN-FAO report on the environmental impact of livestock production in 2006, negative headlines seem to rule the public perception of ruminant livestock production. Two themes dominate this discussion: the emission of greenhouse gases, and the worldwide degradation of grazing resources. We show that currently used methods for source strength estimation in global methane budget models cannot produce independent estimates and therefore do not qualify as support of policy decisions. We further submit that there is no justification for the view that methane output by ruminants is a key priority area of research in ruminant nutrition. We review the history of methodology and application of vegetation monitoring on rangelands and its interaction with grazing management. We discuss some of the reasons why rangeland conservation management has become globally so divergent in its application scope and success, with widespread resource degradation observed worldwide. This is a critically relevant topic affecting a natural space occupying more than half of the global landmass, and constituting the most important feed resource for global livestock production. Achieving sustainable management of rangelands has been a challenge around the world throughout recorded history. The integrated management of grazing and prescribed fire as the keystone practices should be based on sound ecological principles and be supported by management-oriented decision-support tools. This has not been accomplished yet. In the past couple of centuries, historic grazing and fire regimes have been significantly disrupted worldwide, often in conjunction with excessive grazing, causing widespread rangeland degradation. These problems are linked to increasing human and livestock populations and changing cultures. Increasing human populations are also the key factor in the ever-expanding conversion of historic rangelands into rainfed crop production areas. These occur on semi-arid lands not allowing long-term sustainable use for crop production and consequently, they lead to extremely detrimental consequences for the environment and for the climate. With this paper, we introduce key concepts in rangeland monitoring to animal scientists in order to facilitate a deeper understanding of the current problems in conservation management of one of the most important resources for livestock production. We explore the problem of rangeland degradation related to livestock grazing and the role of rangeland management in providing solutions. We discuss how rangeland and animal management must be integrated to ensure long-term use of this resource, without which global livestock production would not be feasible.