Tipping points and resilience in Mongolian grasslands
Submitted by Brandon Bestelmeyer on Wed, 06/04/2014 - 16:03
The future of Mongolian rangelands is at a crossroads. The decision is whether to try to control livestock numbers or to allow (or encourage) numbers to increase. Many believe that the latter will result in irreversible changes, including those called ‘desertification’.
Before 1993, while still under the influence of the Soviet Union, nationwide livestock numbers hovered around 50 million animals*. Beginning in 1993, livestock numbers marched upward about 30%, then crashing during consecutive harsh winters combined with drought conditions, known as a dzuds. These are terrible disasters in which vulnerable herders lose their livelihoods. Numbers rose again and crashed again in the next dzud, and have risen yet again to about 75 million. And there are proposals that the true carrying capacity is still distant at 90 million animals.
In this context, I was asked the question: “How far are we from passing the tipping point of turning our rangelands into desert?” The question was asked by Green Gold Mongolia, a Swiss supported donor organization focused on poverty reduction. The response below was published in the June 2014 issue of Монгол малчин (Mongolian Herder) magazine in anticipation of a conference on rangeland management occurred on June 16 in Ulaanbaatar. I will have a report later on that, but for now, here was my response to the question. I’d be interested to hear reactions to it.
“Ecological science, particularly with regard to Mongolian rangelands, is not able to estimate when a tipping point will be passed. Nonetheless, it does provide a framework for responding to the threat of desertification tipping points.
Desertification involves several kinds of changes. Some of these changes, such as reductions of desired plant species, can be reversed over relatively short periods of time. Other changes, such as the loss of plant species or dominance of unpalatable plants, may take decades or more to reverse, and therefore require interventions such as species removal and active restoration. Finally, plant cover loss associated with soil degradation can cause changes that take many decades to recover or are irreversible—this is true desertification. The studies by Green Gold and others suggest that irreversible degradation is occurring in some places due to plant species loss and soil erosion and these processes should be cause for great concern. But the good news is that while some places already appear to have crossed tipping points in response to mismanagement, many others are expected to be recoverable with reductions to livestock numbers and changes to the timing of grazing.
Desertification processes are difficult to detect and are patchy (variable in space). This is an important problem because it makes assessment difficult—how will we know when we are approaching a possible tipping point? The solution to this problem is to use science-based understanding to define early warning indicators based on clear conceptual models of how rangeland ecosystems change. Then to use ground assessment, monitoring, and remote sensing to detect these indicators and respond to instances of desertification. In general, persistent low vegetation cover and high bare ground cover signal an increased vulnerability to desertification. Because plant cover in Mongolian rangelands is highly variable due to weather variations, low cover of key plants or all vegetation does not necessarily mean that a persistent change is imminent, but it is a necessary condition for persistent change. Based on the current conceptual models and data collected for the Ecological Site Core Group by Green Gold, many sampling points exhibit reduced cover of key species relative to healthy conditions that indicate where changes in grazing management could initiate recovery.
Given the difficulty in assessing tipping points, it is prudent to avoid them by increasing resilience. In arid parts of the United States, for example, historical grazing management was oriented toward using as much of the available forage as possible. The goal was to get livestock through the droughts until rainfall came again. Then in the 1950s the Great Drought occurred, seven consecutive years with below average rainfall, sometimes far below average. During this period many patches of grassland were lost and never recovered their former composition and grazing value. As a consequence of the learning during these and previous drought episodes, stocking rates are now low and flexible. Good years are viewed as an opportunity to add surplus stock, but the starting point is to use conservative stocking rates. During droughts, stocking rates are not so high as to contribute to significant animal mortality and persistent loss of valued forage plants.
In addition, conservative grazing can gradually improve forage quality and makes drought effects less severe. Conservative grazing means that we try to distance ourselves as much as we can from a possible tipping point (that is, increase resilience). One important reason for resilience-based management is that we cannot know exactly how far we are (in terms of stocking rates or vegetation cover) from a tipping point. This is because multiple factors are involved. Climate variability, including drought periods or other weather extremes, is predicted to increase in frequency. In addition to allowing for increases in forage quality, conservative grazing serves as a form of insurance against extreme events (such as dzuds) over which we have little control. This is the concept of resilience: management that allows human communities and ecosystems to persist and recover from extreme events and human errors. An even better question than “how far are we from a tipping point” is “how can we build resilience for herding communities, vegetation, and biodiversity in Mongolian rangelands”?
The good news is, based on the data I have seen to this point, Mongolia has ample opportunity to build resilience. How long this opportunity will last will depend on the interaction of weather and management in the coming years. We cannot say how long this opportunity will last because we cannot predict the weather and because our knowledge of management is usually delayed. All should be aware of the desertification episodes in other parts of the world, including my home in the southwestern United States. These past episodes were not predicted. There is no better time for change than the present."
*actually Mongolian sheep units, a measure that standardizes across multiple livestock species