Intermediate disturbance on rangelands : Management applicability of the intermediate disturbance hypothesis across Mongolian rangeland ecosystems

The current growing body of evidence for diversity-disturbance relationships suggests that the peaked pattern predicted by the intermediate disturbance hypothesis (IDH) may not be the rule. Even if ecologists could quantify the diversity-disturbance relationship consistent with the IDH, the applicability of the IDH to land management has rarely been addressed. We examined two hypotheses related to the generality and management applicability of the IDH to Mongolian rangeland ecosystems: that the diversity-disturbance relationship varies as a function of landscape condition and that some intermediate scales of grazing can play an important role in terms of sustainable rangeland management through a grazing gradient approach. We quantified the landscape condition of each ecological site using an ordination technique and determined two types of landscape conditions, relatively benign and harsh environmental conditions. At the ecological sites characterized by relatively benign environmental conditions, diversity-disturbance relationships were generally consistent with the IDH and maximum diversity was observed at some intermediate distance from the source of the grazing gradient. In contrast, the IDH was not supported at most but not all sites characterized by relatively harsh environmental conditions. The intermediate levels of grazing were generally located below the ecological threshold representing the points or zones at which disturbance should be limited to prevent drastic changes in ecological conditions, suggesting that there is little “conundrum” with regard to intermediate disturbance in the studied systems in terms of land management. We suggest that the landscape condition is one of the primary factors that cause inconsistencies in diversity-disturbance relationships. The ecological threshold can extend its utility in rangeland management because it also has the compatibility with the maintenance of species diversity. This study thus suggests that some intermediate scales of grazing and ecological thresholds are mutually supportive tools for sustainable management of Mongolian rangelands

Threshold Dynamics of Vegetation and Their Management Implications in a Mongolian Shrubland

The concept of ecological threshold has spurred important advances in understanding the nonlinear behavior of ecosystems to various disturbances (Groffman et al. 2006, Suding and Hobbs 2009). Studies on lakes, coral reefs, and arid grasslands have shown that structural attributes of ecosystems can change abruptly along a disturbance gradient (Scheffer and Carpenter 2003, Mumby et al. 2007, Sasaki et al. 2008). Yet, such nonlinear response patterns are implicitly assumed to reflect the modification of system feedbacks and interactions. We know little about mechanistic linkages between nonlinear response patterns and underlying feedback mechanisms, and the irreversibility of nonlinear responses. Consequently, in many applied settings, the threshold concept is being adopted without sufficient evaluation of evidence. Here, we present initial work towards the understanding of threshold dynamics of vegetation in a Mongolian shrubland. Our study should enhance the conceptual development of ecological threshold as well as human decision-making

Resource Variations across the Landscape Mediate the Impact of Grazing on Vegetation in Mongolian Rangeland under High Climatic Variability

Assessment of grazing-induced degradation of arid and semi-arid rangelands with stochastic rainfall regimes is challenging. For the last two decades, rangeland ecologists have been discussing the relative importance of biotic and abiotic factors in controlling vegetation dynamics. According to the non-equilibrium concept, which emerged as a new paradigm to describe ecosystems in highly variable and poorly predictable environments, vegetation dynamics are driven primarily by abiotic factors such as rainfall, rather than by internal biotic regulation (e.g. grazing impact). Although a number of studies have emphasized the non-equilibrium nature of most rangelands, they have produced inconsistent results and there is still no consensus on the relative importance of grazing impact. Alternatively, recent studies have suggested that a continuum of systems exists, rather than a stark dichotomy between equilibrium and non-equilibrium rangelands. Moreover, theoretical studies have predicted that, in addition to climatic variability, resource variations occurring in space and time as a result of landscape heterogeneity should be taken into account in assessments of grazing impact. However, there have been few empirical studies of the role of resource variations in either mitigating or enhancing the impacts of grazing on vegetation. This study explores the impact of grazing strategies on vegetation in Mongolian rangelands under high climatic variability. Specifically, it is focused on key resource areas, defined in terms of the key factor determining livestock population, and thus the ability to forage during drought. Based on the prediction proposed by Illius and O’Connor (1999) that animal numbers are regulated in a density-dependent manner by the limited forage availability in key resource areas, we established and examined the hypothesis that grazing impacts would be greater in key resource areas than in other areas even in Mongolian rangelands

The Linkage Between Pastoralists\u27 Perspectives and Vegetation Threshold Changes in Mongolian Rangelands (Advanced Studies on Sustainable Animal Production: Interrelationships among Human, Animal and Environment, 8th International Symposium of Integrated Field Science)

Poster Sessio

How to measure response diversity

The insurance effect of biodiversity—that diversity enhances and stabilises aggregate ecosystem properties—is mechanistically underlain by inter- and intraspecific trait variation in organismal responses to environmental change. This variation, termed response diversity, is therefore a potentially critical determinant of ecological stability. However, response diversity has yet to be widely quantified, possibly due to difficulties in its measurement. Even when it has been measured, approaches have varied.Here, we review methods for measuring response diversity and from them distil a methodological framework for quantifying response diversity from experimental and/or observational data, which can be practically applied in lab and field settings across a range of taxa.Previous empirical studies on response diversity most commonly invoke functional response traits as proxies aimed at capturing functional responses to the environment. Our approach, which is based on environment-dependent functional responses to any biotic or abiotic environmental variable, is conceptually simple and robust to any form of environmental response, including nonlinear responses. Given its derivation from empirical data on functional responses, this approach should more directly reflect response diversity than the trait-based approach dominant in the literature.By capturing even subtle inter- or intraspecific variation in environmental responses, and environment-dependencies in response diversity, we hope this framework will motivate tests of the diversity-stability relationship from a new perspective, and provide an approach for mapping, monitoring, and conserving this critical dimension of biodiversity

Socio-ecological Interactions in a Changing Climate: A Review of the Mongolian Pastoral System

Coping with climate change in socio-ecological systems is one of the most urgent issues facing the world. This is particularly true in socio-ecological systems, where climate not only influences social and ecosystem dynamics, but also modulates their interaction. In this paper, we presented a conceptual framework through a literature review and a trend analysis for assessing the impact of climate change that incorporates socio-ecological interactions. In particular, we focused on the Mongolian pastoral system, which has tightly coupled socio-ecological interactions, as a model for describing the framework. Our framework suggests that the flexibility in mobility of herders is the principal factor in determining the vulnerability of the socio-ecological system to climate change. The flexibility varies along a climatic gradient and socio-ecological interactions in each region have evolved to be suited to its local climate regime. Herders in northern and central regions of Mongolia move shorter distances, and less flexible, than those in southern (Gobi) region. Climatic hazards, on the other hand have been increasing across Mongolia with a trend toward warmer and drier conditions since the 1960s. We suggest that further warming and drying would have the greatest impact on northern and central regions due to lower flexibility in mobility among herders there coupled with the much higher livestock density in the regions. The findings support that maintaining flexibility of mobile herding will likely be crucial to reducing the vulnerability of the Mongolian pastoral system to climate change