Post by Admin on Nov 9, 2020 23:55:07 GMT
4.4 Results
Below we go through each area designated by local pastoralists as having a specific usage, briefly elaborating on the vegetation growth cycles and the snow fall patterns as well as any issues with our simplified modelling approach. We group these areas into the seasonal movement stages they belong to in order to see whether they do show commonalities or disparities.
4.4.1 Winter grazing grounds.
As expected, the main requirement for a winter pasture is limited snow cover during the cold months of the year, so animals can access food. In all three areas we see little snow in the months of December through March. For Adunqiaolu there is some thicker snow cover in February 2017, but then the next year sees almost no snow in the same month. Kazan shows snow in December of 2016 but is completely free of snow in December 2017. Crucially, there is no month during the year which sees complete thick or moderate snow cover. Some parts of the pasture always remain open or are at most temporarily covered with a thin layer of snow. Clearly the significance of observations made during two consecutive years is limited, but neither of the years was considered extreme by the locals. Neither black nor white disasters were recorded for the time period the underlying data of the model date to (December 2016 –February 2018). Hence, the time period covered can be assumed to lie within the range of normal years where no shocks to the pastoralist system and therefore no changes in herding patterns are observed.
The limited snow cover during the winter months is connected to the low quality of the pasture in the following months. Even during the peak of the vegetation cycle in July the average NDVI value barely exceeds 0.3 for the Adunqiaolu winter pasture and its core area and 0.25 for the Kazan winter pasture. The grazing grounds dry off quickly in summer and the NDVI values decline. It is important to note that the NDVI values for barren areas, rock, and snow lie around 0.1 to -0.1. Considerable snow cover therefore impacts the average NDVI values and these averages are not directly connected to the quality of the grazing during the winter months. Slightly higher grazing qualities can be expected since snow cover biases the NDVI of a pasture area towards 0. Average NDVI values for winter pastures during the months of usage seem to hover around a value of 0.1.
4.4.2 Spring/autumn grazing grounds.
Spring/autumn pastures are more difficult to identify, since they serve a transitional function and are usually only used during six to eight weeks from late March to early May and from late September to early December. In terms of snow cover the data showed a still considerable snow cover in March. With the beginning of April, the vegetation saw rapid development which is consistent with the first movement of pastoralists during the year. However, both Husta, including its core area, as well as the Wenquan spring/autumn pasture showed characteristics that need to be further elaborated upon since they demonstrate the limits of a pasture classification approach based on NDVI averages and snow cover. Wenquan, whereas consistent with the melting period and the first move of the year, showed very low NDVI averages over the entire year, even trailing the overgrazed and dried off winter pastures. The topographic location of the Wenquan spring/autumn pasture offered explanations beyond the simplistic assumptions of the model.
The Wenquan pasture seemed to only provide meagre grazing throughout the entire year. The area lies to both sides of a river. Water has a very low NDVI value approaching -1 and could considerably influence an average. However, even when excluding the river and the denuded surfaces of the riverbed, the NDVI average stayed low. Therefore, other explanations needed to be considered. According to ethnographic data, the most important reason for the usage of Wenquan as a spring pasture was the early temperature increase which allows for a shortening of the winter camping time. These range lands provided a convenient location within the landscape as a transition area for heading up to the summer pastures as soon as snow started to melt there. It also had small areas of lush vegetation next to the riverbank which were too small in area size to influence the overall NDVI average much but provided ideal grazing for a limited amount of time. The abundant availability of water next to the river was convenient for herders and even allowed for limited agricultural activity including fodder crops and sometimes vegetables. Beyond environmental factors, Wenquan served as a place for exchange of animals and goods and stacking supplies for winter/summer periods.
The Husta grazing lands are not only used in spring and autumn but also in summer. The reason for this lies in the favourable topographic location of the pasture. Its lower elevation starts around 1400 m a.s.l. and the highest areas lie at 2200 m a.s.l. This allows for slow movements inside the pasture area itself, depending on where the grazing is best. To the south, the Husta pasture is framed by a small ridge of around 1600–1900 m a.s.l. The north side is backed by the mountain range which defines the Bortala valley [38]. This creates a topographic situation where seasonal springs and small creeks provide water for the vegetation throughout the growing season from spring to autumn and create one of the best grazing grounds in the entire valley.
4.4.3 Summer grazing grounds.
The summer pastures are characterized by late snow melt in the spring, usually in the month of April, with a good chance of considerable quantities of snow by October. Harnur East and West, as well as the summer pasture west of the Sarimu Lake, clearly fit this pattern. Harnur East, one of the highest lying summer pastures, shows consistent snow cover of between 70% and 100% from October through April, with most areas displaying thick or moderate snow cover. The Adunqiaolu Northwest summer pasture and its core area can experience full snow cover during the winter months (December 2016), but otherwise see relatively little snow during the study period. We think that the chance of a full moderate or thick snow cover excludes this area from safe usage during the winter, but there may be sociocultural and practical factors at play as well. As discussed earlier, less snow cover is not the only condition to be considered in defining a suitable winter pastureland. Winter camping grounds also require specific landforms such as a small hill or depression for shelter as well as easy external access. At an elevation of 2900 m a.s.l. the Adunqiaolu Northwest summer pasture is extremely cold in winter and the landforms offer no places for good shelter from the wind. The track leading up to the pastures is difficult, particularly in winter when it would be necessary to climb or descend steep, potentially snow-covered slopes.
All summer pastures show a late but accelerated start to vegetation growth in the month of May. This fits with the second movement of the year in early May. The herds arrive on the summer pastures around the time when vegetation growth is spiking up from its low level in April. The average NDVI values for the summer pastures peaks in July with values around 0.7. These average values are extremely high for grassland and speak for the excellent quality of the grazing on these summer pastures. NDVI has been shown to correlate with productivity [50, 51]. The interrelations are certainly more complex, but as an approximation the summer pastures can be seen as roughly twice as productive as the winter pastures in our case. This has clear implications for the calorie intake of the animals over the course of the year and demonstrates why these seasonal movements are worthwhile.
4.5 Summary
The general model does provide insights into potential usage patterns of the landscape (Fig 11). The combination of snow cover and grazing quality seems to show relatively clearly what a particular area is best used for and the results match up with the ethnographically assigned usage. The Kazan winter pasture, for example, has relatively low pasture quality, but it is almost free of snow in the harshest winter months of January and February, thus guaranteeing access of animals to food. On the Wenquan spring pasture, the growth phase starts early and when the first seasonal movements are made by pastoralists, the pasture is already relatively lush, seeing additional growth throughout the months of April and May. The quality of the grass then stays fairly consistent throughout the summer. The herds, however, are moved to the summer pastures like, for example, Sarimu. These have been under thick snow all winter, but as soon as it melts in late April / early May, the intensive growth phase starts. These pastures provide the best grazing throughout the summer into early fall. Before the first snow starts covering the ground in October, the animals are moved back to the autumn pasture where they can graze on the grass that was left untouched throughout the summer for a few more weeks before eventually the move to the winter pasture completes the year.
Fig 11. Idealised pastoralist movements based on ethnographic and remote sensing data.
Left y-axis: snow cover in % displayed as a bar diagram distinguishing thin/moderate/thick snow cover. Right y-axis: average NDVI value.
Below we go through each area designated by local pastoralists as having a specific usage, briefly elaborating on the vegetation growth cycles and the snow fall patterns as well as any issues with our simplified modelling approach. We group these areas into the seasonal movement stages they belong to in order to see whether they do show commonalities or disparities.
4.4.1 Winter grazing grounds.
As expected, the main requirement for a winter pasture is limited snow cover during the cold months of the year, so animals can access food. In all three areas we see little snow in the months of December through March. For Adunqiaolu there is some thicker snow cover in February 2017, but then the next year sees almost no snow in the same month. Kazan shows snow in December of 2016 but is completely free of snow in December 2017. Crucially, there is no month during the year which sees complete thick or moderate snow cover. Some parts of the pasture always remain open or are at most temporarily covered with a thin layer of snow. Clearly the significance of observations made during two consecutive years is limited, but neither of the years was considered extreme by the locals. Neither black nor white disasters were recorded for the time period the underlying data of the model date to (December 2016 –February 2018). Hence, the time period covered can be assumed to lie within the range of normal years where no shocks to the pastoralist system and therefore no changes in herding patterns are observed.
The limited snow cover during the winter months is connected to the low quality of the pasture in the following months. Even during the peak of the vegetation cycle in July the average NDVI value barely exceeds 0.3 for the Adunqiaolu winter pasture and its core area and 0.25 for the Kazan winter pasture. The grazing grounds dry off quickly in summer and the NDVI values decline. It is important to note that the NDVI values for barren areas, rock, and snow lie around 0.1 to -0.1. Considerable snow cover therefore impacts the average NDVI values and these averages are not directly connected to the quality of the grazing during the winter months. Slightly higher grazing qualities can be expected since snow cover biases the NDVI of a pasture area towards 0. Average NDVI values for winter pastures during the months of usage seem to hover around a value of 0.1.
4.4.2 Spring/autumn grazing grounds.
Spring/autumn pastures are more difficult to identify, since they serve a transitional function and are usually only used during six to eight weeks from late March to early May and from late September to early December. In terms of snow cover the data showed a still considerable snow cover in March. With the beginning of April, the vegetation saw rapid development which is consistent with the first movement of pastoralists during the year. However, both Husta, including its core area, as well as the Wenquan spring/autumn pasture showed characteristics that need to be further elaborated upon since they demonstrate the limits of a pasture classification approach based on NDVI averages and snow cover. Wenquan, whereas consistent with the melting period and the first move of the year, showed very low NDVI averages over the entire year, even trailing the overgrazed and dried off winter pastures. The topographic location of the Wenquan spring/autumn pasture offered explanations beyond the simplistic assumptions of the model.
The Wenquan pasture seemed to only provide meagre grazing throughout the entire year. The area lies to both sides of a river. Water has a very low NDVI value approaching -1 and could considerably influence an average. However, even when excluding the river and the denuded surfaces of the riverbed, the NDVI average stayed low. Therefore, other explanations needed to be considered. According to ethnographic data, the most important reason for the usage of Wenquan as a spring pasture was the early temperature increase which allows for a shortening of the winter camping time. These range lands provided a convenient location within the landscape as a transition area for heading up to the summer pastures as soon as snow started to melt there. It also had small areas of lush vegetation next to the riverbank which were too small in area size to influence the overall NDVI average much but provided ideal grazing for a limited amount of time. The abundant availability of water next to the river was convenient for herders and even allowed for limited agricultural activity including fodder crops and sometimes vegetables. Beyond environmental factors, Wenquan served as a place for exchange of animals and goods and stacking supplies for winter/summer periods.
The Husta grazing lands are not only used in spring and autumn but also in summer. The reason for this lies in the favourable topographic location of the pasture. Its lower elevation starts around 1400 m a.s.l. and the highest areas lie at 2200 m a.s.l. This allows for slow movements inside the pasture area itself, depending on where the grazing is best. To the south, the Husta pasture is framed by a small ridge of around 1600–1900 m a.s.l. The north side is backed by the mountain range which defines the Bortala valley [38]. This creates a topographic situation where seasonal springs and small creeks provide water for the vegetation throughout the growing season from spring to autumn and create one of the best grazing grounds in the entire valley.
4.4.3 Summer grazing grounds.
The summer pastures are characterized by late snow melt in the spring, usually in the month of April, with a good chance of considerable quantities of snow by October. Harnur East and West, as well as the summer pasture west of the Sarimu Lake, clearly fit this pattern. Harnur East, one of the highest lying summer pastures, shows consistent snow cover of between 70% and 100% from October through April, with most areas displaying thick or moderate snow cover. The Adunqiaolu Northwest summer pasture and its core area can experience full snow cover during the winter months (December 2016), but otherwise see relatively little snow during the study period. We think that the chance of a full moderate or thick snow cover excludes this area from safe usage during the winter, but there may be sociocultural and practical factors at play as well. As discussed earlier, less snow cover is not the only condition to be considered in defining a suitable winter pastureland. Winter camping grounds also require specific landforms such as a small hill or depression for shelter as well as easy external access. At an elevation of 2900 m a.s.l. the Adunqiaolu Northwest summer pasture is extremely cold in winter and the landforms offer no places for good shelter from the wind. The track leading up to the pastures is difficult, particularly in winter when it would be necessary to climb or descend steep, potentially snow-covered slopes.
All summer pastures show a late but accelerated start to vegetation growth in the month of May. This fits with the second movement of the year in early May. The herds arrive on the summer pastures around the time when vegetation growth is spiking up from its low level in April. The average NDVI values for the summer pastures peaks in July with values around 0.7. These average values are extremely high for grassland and speak for the excellent quality of the grazing on these summer pastures. NDVI has been shown to correlate with productivity [50, 51]. The interrelations are certainly more complex, but as an approximation the summer pastures can be seen as roughly twice as productive as the winter pastures in our case. This has clear implications for the calorie intake of the animals over the course of the year and demonstrates why these seasonal movements are worthwhile.
4.5 Summary
The general model does provide insights into potential usage patterns of the landscape (Fig 11). The combination of snow cover and grazing quality seems to show relatively clearly what a particular area is best used for and the results match up with the ethnographically assigned usage. The Kazan winter pasture, for example, has relatively low pasture quality, but it is almost free of snow in the harshest winter months of January and February, thus guaranteeing access of animals to food. On the Wenquan spring pasture, the growth phase starts early and when the first seasonal movements are made by pastoralists, the pasture is already relatively lush, seeing additional growth throughout the months of April and May. The quality of the grass then stays fairly consistent throughout the summer. The herds, however, are moved to the summer pastures like, for example, Sarimu. These have been under thick snow all winter, but as soon as it melts in late April / early May, the intensive growth phase starts. These pastures provide the best grazing throughout the summer into early fall. Before the first snow starts covering the ground in October, the animals are moved back to the autumn pasture where they can graze on the grass that was left untouched throughout the summer for a few more weeks before eventually the move to the winter pasture completes the year.
Fig 11. Idealised pastoralist movements based on ethnographic and remote sensing data.
Left y-axis: snow cover in % displayed as a bar diagram distinguishing thin/moderate/thick snow cover. Right y-axis: average NDVI value.
