Vegetation regime shifts in Yamal-Nenets
The Yamal-Nenets social-ecological system comprises about 5000 nomadic reindeer herders and 300 000 semi-domestic reindeers, moving with the seasons in 21 different brigades from the southern tree limit up north, across the Arctic tundra. Shrub encroachment has been observed during the last three decades, but has been controlled by reindeer grazing. These changes have produced two regime states: shrubland without reindeer herding, and open land with reindeer herding. The first regime is mainly caused by temperature increase, which has produced warmer winters, summers and extended growing seasons. These temperature changes have altered the controlling feedbacks of the tundra, such as slow growth of shrubs, microbial activity, and decomposition litter rates. This regime is hence seen as the undesirable regime for the Yamal-Nenets social-ecological system.
Type of regime shift
- Rock and Ice
- Extensive livestock production (natural rangelands)
Spatial scale of the case study
- Local/landscape (e.g. lake, catchment, community)
Continent or Ocean
- Yamal Peninsula, Northwest Siberia
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Key direct drivers
- Vegetation conversion and habitat fragmentation
- Infrastructure development
- Extensive livestock production (rangelands)
- Rock and Ice
Key Ecosystem Processes
- Soil formation
- Primary production
- Nutrient cycling
- Water cycling
- Wild animal and plant products
- Climate regulation
- Regulation of soil erosion
- Aesthetic values
- Knowledge and educational values
- Spiritual and religious
- Food and nutrition
- Livelihoods and economic activity
- Cultural, aesthetic and recreational values
- Social conflict
- Cultural identity
Spatial scale of RS
Time scale of RS
- Readily reversible
- Contemporary observations
Confidence: Existence of RS
- Well established – Wide agreement in the literature that the RS exists
Confidence: Mechanism underlying RS
- Well established – Wide agreement on the underlying mechanism
The Yamal Peninsula consists entirely of low Arctic tundra and contains a variety of lichen, moss, graminoid, and shrub species. Although vegetation shifts can be described in other low tundra areas, the Yamal peninsula is unique due to the delayed exploitation of hydrocarbons as a result of the Soviet Union collapse (Kumpula et al. 2012). The Yamal Peninsula nomadic Nenets and reindeer, the largest reindeer-herder society in the world (Zeng et al. 2013), both rely on this landscape for their livelihood while simultaneously shaping the state of the landscape (Walker et al. 2009). This report views the Yamal Peninsula and Nenets society as a social-ecological system; however, emphasis is placed on changes in the ecosystem.
Open land with reindeer herding
In this regime the landscape consists of lichen, moss, and graminoid species. The density of reindeer and intensity of grazing determines whether lichen, moss, or graminoid species dominate the landscape (van der Wal 2005). Small deciduous shrubs can also be found in this regime; however, they will only be found in small patches. A key feature of this regime is that it is an open landscape and allows the Nenets and their reindeer herds to roam across the land. The vegetation existing in this regime is palatable for reindeers, and thus, reindeer grazing largely maintains this open landscape (Yu et al. 2011; Walker et al. 2009).
Shrubland without reindeer herding
This regime is dominated by deciduous and evergreen shrubs. A defining feature of this regime is that the shrubs are densely packed on the landscape, making it difficult for reindeer and Nenets to roam across the land. Dense shrubland has the potential to form near areas where gas infrastructure has been built (Forbes et al. 2009), making it difficult for Nenets and their reindeer herds to reach this land. Alternatively, dense shrubland can also form due to overgrazing from a high density of reindeer (Yu et al. 2011). Reinforcing feedback mechanism allows for shrub encroachment to expand (Myers-Smith 2005). Rising temperatures and longer summers as a result of climate change are having large effects on vegetation, with thawing permafrost, landslides, and shrub encroachment (Forbes et al. 2009, Kumpala et al. 2012).
Drivers and causes of the regime shift
Shift from open land with reindeer herding to shrubland without reindeer herding
Currently, the dominant vegetation in low Arctic tundra is composed of mosses, lichens and graminoids. However, it has been observed a transition from these growth forms to shrubs during the last three decades in Eurasia (Kullman 2002; Aune et al. 2011; Yu et al. 2011; Macias-Fauria et al. 2012) and five decades in North America (Sturm et al. 2005; Tape et al. 2006; Myers-Smith 2007). Temperature is considered a key factor in controlling vegetation growth in this ecosystem (Grace et al. 2002; Zeng et al. 2013).
The main driver of this regime shift is the rate of warming; -1 to 2oC during the last five decades in the tundra (Aune et al. 2011). The temperature rise has caused mild winters (Sturm et al. 2005), warmer summers (Kullman 2002; Macias-Fauria et al. 2012), and longer growing seasons (Zeng et al. 2013).
The temperature rise in the tundra has changed controlling feedbacks such as vegetation growth rates, microbial activity, and nutrient cycling (Myers-Smith 2007; Yu et al. 2011). The new conditions have benefited the establishment, survival and growth of seedlings and saplings, which are the most vulnerable reproduction phases of trees and shrubs in this ecosystem (Kullman 2002). These changes in the current tundra regime lead to shrub encroachment, which in turn decreases the presence of mosses, grasses, and lichens by shading them.
Shift from Shrubland without reindeer herding to open land with reindeer herding
Shrub encroachment in the Arctic Tundra caused by temperature rise is controlled by large herbivore grazing (Olofsson et al. 2009). Yu et al. (2011) found that reindeers in Yamal peninsula graze mosses, lichens, deciduous shrubs and grasses, except evergreen shrubs because of its low nitrogen concentration and poor digestibility. However, reindeer trampling could decline the evergreen shrubs because they have the slowest growth rate in the tundra vegetation (Yu et al. 2011), which make its recovery from this type of disturbance difficult. Heavy grazing could lead to a shift from shrub dominated tundra to moss graminoid-dominated tundra because the latter have faster growth rates than shrubs (Yu et al. 2011).
How the regime shift worked
Shift from open land with reindeer herding to shrubland without reindeer herding
Open land with reindeer herding regime is largely maintained by the reindeer grazing and trampling activities (Yu et al. 2011; van der Wal 2005). Maintaining open land with a reindeer herding regime is largely dependent on the density and abundance of reindeer on the Yamal Peninsula. If there were a sudden decline in the reindeer population, the grazing/trampling-nutrient restoring reinforcing feedback loop would no longer be strong enough to maintain an open land regime (Yu et al. 2011). Alternatively, as grazing intensity reaches overgrazing, shrubs start to dominate the landscape (Bråthen et al 2007; Yu et al. 2011). Thus, if the density of reindeer exceed the land’s carrying capacity, it can also lead to a shift to a shrub-dominated regime. Indirectly, the Nenets impact the open land regime; the number of reindeer herding Nenets loosely determines how many reindeer will be able to use the land (Kumpala et al. 2012). A main driver of change impacting Nenets-reindeer relations comes from gas exploitation on the Yamal Peninsula. An increase in gas exploitation infrastructure (ex. pipelines, etc.) has the potential to fragment the land (Forbes et al. 2009), and therefore disrupt the reindeer driven reinforcing feedback loop.
Once the land enters a shrub-dominated regime without reindeer herding, a reinforcing feedback loop promotes the establishment of more shrubs (Myers-Smith 2007). In addition, there is an established link between Arctic warming and an increase in deciduous shrub biomass (Macias-Fauria et al. 2012), which further interacts with the establishment of a self-reinforcing shrub-dominated regime.
Shift from shrubland without reindeer herding to open land with reindeer herding
To shift from a shrubland to open land would require shrubs to be removed from the field. This could be done through clearing shrubland to build roads or pipelines in relation to gas exploitation development on the Yamal Peninsula (Forbes et al. 2009). Although this would initially cause a shift to more open land, one could speculate that this would fragment the land, contributing to a shift back to shrubland. A more persistent force to shift the land from shrubland to open land would come from the reindeer. Although it is difficult for reindeer to move through dense shrubland, and only some shrubs are part of reindeer diet, reindeer help convert shrub land to open land through grazing and trampling (Yu et al. 2011).
Impacts on ecosystem services and human well-being
Shrubs to grass:
When shrubland shifts to open land, biodiversity and connectivity go down, with fewer habitats for birds (Henden et al. 2013). In the long run, a shift towards open land could diminish biodiversity as an ecosystem service for the Yamal-Nenets, possibly leading to a degraded landscape and loss of productive reindeer herding land (Bråthen et al. 2007). The reindeers graze on dwarf shrubs, like willows. When shrubs are replaced by grass, Nenets lose provisional ecosystem services, such as food sources for the reindeers, and more importantly stocks of firewood (Walker et al. 2009, Degteva & Nellemann 2013). Gains from the shift for the Nenets are the graminoid-dominated pastures, which lead to an increase in provisioning ecosystem services. In Yamal the loss of shrubs has been compensated for by the net increases in productivity among highly nutritious and digestible forage species (Forbes et al. 2009). This has given way for more reindeers, which means more resources to be able to access provisional ecosystem services: food, clothing and antlers to trade with the gas company employees (Forbes et al. 2009, Kumpala et al. 2012, Forbes et al. 2013, Degteva & Nellemann 2013). As for regulating services, increased abundance of reindeers leads to a reinforcing feedback, which keeps the grass state by trampling, grazing, and addition of nutrients (Forbes et al. 2009).
Grassland has been suggested to dampen global warming, due to increased albedo in winter (Zimov et al. 1995). The graminoid landscape state could thus be beneficial for human wellbeing in Yamal, since it could dampen temperature and lead to less thawing of permafrost, and less problems such as landslides and erosion. Cultural ecosystem services increase in that nomadic life is based on herding, so aesthetic, spiritual and recreational services will increase from the shift. Nenets clearly benefit in the short run from this regime shift. No other groups of humans lose or gain anything substantial.
Shift from open land to shrubs:
If large patches, and eventually whole areas, of the tundra shift into the shrub state, reindeer herding would be hard to maintain since reindeer only graze shrubs up to a certain size, and with warmer climate shrub size will increase (Walker et al. 2011). Regulating services from reindeers, such as grazing and trampling, would decline. With this shift - especially if combined with the expected severe land use change due to Yamal gas exploitation (Kumpala et al. 2012) - provisional services for the Nenets would decrease due to the lower abundance of reindeers. This would in turn diminish a wide array of cultural and spiritual ecosystem services, such as lost sense of place, practices of the everyday life on the tundra, and holy places (Forbes et al. 2009, Kumpala et al. 2012).
Increased shrubland would, on the other hand, be beneficial for biodiversity, opening up for larger populations of birds (Henden et al. 2013), herbivores other than reindeers, and predators such as wolves and wolverines (Golovatin et al. 2012). With this succession, in combination of the expected influx of thousands of migrant oil and gas workers, there could be increased possibilities for hunting and recreation.
The shrub dominated regime is seen as an undesirable regime since the vegetation is unfavorable for the Nenets nomads’ traditional reindeer herding lifestyle. If there would be an aim of keeping the landscape in a shrub dominated state there cannot be any reindeers or few reindeers in the area. The shrubs are growing at a slow pace which means that if there are no grazing animals disturbing this growth process there will be a maintained regime of mature shrubs (Bråthen et al. 2007). To shift from a shrubland to open land would require shrubs to be removed from the field. This could be done through clearing shrubland to build roads or pipelines in relation to gas exploitation development on the Yamal Peninsula (Forbes et al. 2009).
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