Rangeland ecology: Global Issues and Questions Key global research issues & questions in Rangeland Ecology • Despite the focus here on global issues, we need to recognize that Mongolia is the home of many of the advancements in our knowledge about rangelands Robin Reid1 and Maria Fernandez-Gimenez2 1Director, Center for Collaborative Conservation 1Senior Research Scientist, Natural Resource Ecology Lab 2Associate Professor Colorado State University, Fort Collins, Colorado, USA What we will cover today Bio-physical constraints History & social context Rainfall /snow, soil fertility, Land-use history, current biodiversity, hydrology land tenure, governance In this short presentation, we cannot cover all of the global questions about rangeland ecology Underlying causes of change Institutions, economic development, climate, livestock and human pop change, governance, We will focus on: policy • Causes of rangeland change Proximate causes of change Cropland and settlement expansion, • General viewpoints (paradigms) of the dynamics of overstocking, sedentarisation, fencing rangelands (equilibrium / non-equilibrium) Positive feedback Rangeland Negative feedback • Models of how rangelands change (range succession that accelerates change that slows/stops degradation and state-and-transition models) degradation Ecol. change Social change • A possible future for Mongolia? Landscape +/- Biodiversity +/- Migration fragmentation in rangelands +/- Soil fertility +/- Poverty +/- Rainfall +/- Equity Reid et al. 2006 Why should we seek to understand the Two main viewpoints in the debate about how dynamics of pastoral ecosystems? rangeland systems function The equilibrium view / paradigm ‘Unless pastoral ecosystem dynamics are considered and • Every rangeland has a set vegetation ‘carrying used as guidelines for development policies, interventions capacity’, determined by rainfall and soils, which are likely to be random activities which comprise determines how many livestock it can support development by trial and error, a practice with unfortunate implications for the ecosystems and people on which • Vegetation response to grazing is linear and reversible, these "development experiments" are performed.’ and herders can manage vegetation by changing the number of animals they graze • When grazing is too heavy, it can decrease the ability of the range vegetation to support livestock in the future p. 458, Ellis and Swift 1988 1 Two main viewpoints in the debate about how Linear and non-linear change, and rangeland systems function thresholds in rangelands The non-equilibrium view / paradigm • Dry rangelands have no set ‘carrying capacity’; this varies widely according to rainfall threshold high high • Vegetation response to grazing can be non-linear and s Linear s s t s t a n a irreversible, and herders cannot manage vegetation by n a m a l m l o P o i P changing the number of animals they graze i b b • Grazing rarely becomes too heavy because frequent droughts low low or winter storms prevent livestock populations from growing low high low high too large Livestock Livestock grazing intensity grazing intensity • Because of this, livestock rarely decrease the ability of the range vegetation to support livestock in the future What is the most controversial part of these So, do livestock degrade rangelands or do viewpoints? they not? • In wet, semi-arid rangelands, much research suggests degradation is possible, but, if reversible, these If rangelands follow the non-equilibrium viewpoint, then rangelands can recover quickly herders and their livestock rarely degrade rangelands • In arid rangelands, research is mixed, sometimes livestock do and sometimes they do not degrade rangelands. Degradation may occur more often in wetlands or riverine corridors. Here, it often depends on how heavy and continuous the grazing is. Some of these rangelands are quite resilient to grazing. • But, this also depends on how ‘degradation’ is defined, from whose viewpoint, the scale under consideration, and by what measure For example, human values affect what observers think is degradation in rangelands The human-centered point of view Models that explain how rangelands change This alone is not degradation Rangeland vegetation productivity Range succession / condition model Livestock production …unless this happens too State-and-transition model The ecosystem-centered point of view Rangeland productivity This alone can indicate degradation Rangeland plant cover Rangeland soil nutrients /erosion Livestock production Rangeland native plant diversity This is an additional Rangeland hydrology thing to worry about Reid in prep 2 Problems with the range succession / Range succession / condition model condition model • Assumes that vegetation change is linear, continuous • Sometimes, it fails to predict what happens when a grazing or fire or another disturbance is removed and reversible • It predicts only one vegetation endpoint, rather than the • Assumes that all disturbances /stresses that modify vegetation have similar effects (like grazing, fire, multiple vegetation endpoints that are often possible in a drought, winter storms) particular place • Does not tell us about many other aspects of rangelands that are important like water, biodiversity, erosion Increased rain /snow Fire, Drought Vegetation potential, nutrient cycling No grazing Grazing • Change is measured against an historical mature Young Mature plant plant (climax) community that with climate change may not community Vegetation succession community exist Vegetation retrogression • Grazing was considered to be an external disturbance rather than part of the rangeland Dyksterhuis 1949 Here, a fire threshold separates a grassland and a State & Transition Model woodland state. Transitions among the three grassland communities on left are reversible by changing grazing Threshold intensity. Community 1 transition 1 Community 2 Community 3 Vegetation State A Vegetation State B transition 2 Vegetation State C Bestelmeyer et al. 2003 Fuhlendorf and Smeins 1997 Different states of rangelands, as measured by State & Transition Models: the cover of woody plants, the types of grass and the amount of soil erosion • Improve on the Range Succession / Condition model because: – Non-linear change is possible – Irreversible change is possible – Multiple vegetation states are possible – Different causes of change (like grazing, fire, drought, winter storms) can have different effects • Do not replace range succession / condition models, but provide another tool that strengthens these models • Are very useful for bringing together local, traditional and scientific knowledge Briske 2005, Bestelmeyer 2003, Stringham 2001 3 There are multiple and interacting causes and Intact landscape Intact consequences of rangeland conversion and fragmentation landscapes Causes Processes Consequences allow livestock to Livestock population Rangeland / habitat conversion growth • Cropland Population loss or species move to • Settlement (rural and urban) extinction reach Human population growth • Infrastructure (roads, railways) (intrinsic, migration) • Impermeable fencing Change in hydrology diverse • Land tenure rules vegetation • Protected area establishment Change in the movement Human development of individuals and types that Rangeland / habitat modification pathogens they need Land tenure and • Wood collection Fragmented landscape settlement policies • Charcoal making Change in genetic in different • Hunting variation in populations seasons. Technology • Grazing • Permeable fencing Intact • Fires Change in primary and Conflict and revolution • Droughts secondary productivity landscapes support Markets Rangeland / habitat fragmentation Change in nutrient and • Permanent fragmentation as a water cycling more Disease result of processes under loss livestock above Change in greenhouse per Climate (drought, CC) • Temporary fragmentation as a gas emissions and carbon result of processes under sequestration hectare. modification above Reid et al 2004 Galvin et al. 2008 Over time, people can both fragment and un- Global Questions in Rangeland Ecology (1) fragment rangelands • What are the major causes of rangeland change and how do these causes interact? • What are the management objectives of users of rangelands? Does livestock grazing causes undesirable change in rangelands (like lower plant productivity, fewer native plants, reduced stream flow)? • Do these feedback on the livestock? In other words, does livestock grazing affect rangeland productivity to the extent that future livestock grazing suffers? • At what level of grazing do these changes begin to occur? Lackett et al 2008 Global Questions in Rangeland Ecology (2) Literature in this presentation (1) Bestelmeyer, B. T., J. R. Brown, et al. 2003. "Development and use of • If grazers are removed, does the rangeland recover to state-and-transition models for rangelands." Journal of Range Management 56(2): 114-126. the pre-grazed state or are grazers causing irreversible change? Is this change undesirable (= degradation) and Briske, D. D., S. D. Fuhlendor, et al. 2005. "State-and-transition models, from whose point of view? thresholds, and rangeland health: A synthesis of ecological concepts and perspectives." Rangeland Ecology & Management 58(1): 1-10. • How does livestock grazing interact with climate and land use to influence the state of rangelands? Ellis, J. and D. M. Swift (1988). "Stability of African pastoral ecosystems: Alternative paradigms and implications for development." Journal