Grassland degradation, also called vegetation or steppe degradation, is a biotic disturbance in which grass struggles to grow or can no longer exist on a piece of land due to causes such as overgrazing, burrowing of small mammals, and climate change. Since the 1970s, it has been noticed to affect plains and plateaus of alpine meadows or grasslands, most notably being in the Philippines and in the Tibetan and Inner Mongolian region of China, where of grassland is degraded each year. Across the globe it is estimated that 23% of the land is degraded. It takes years and sometimes even decades, depending on what is happening to that piece of land, for a grassland to become degraded. The process is slow and gradual, but so is restoring degraded grassland. Initially only patches of grass appear to die and appear brown in nature; but the degradation process, if not addressed, can spread to many acres of land. As a result, the frequency of landslides and dust storms may increase. The degraded land's less fertile ground cannot yield crops, nor can animals graze in these fields. With a dramatic decrease in plant diversity in this ecosystem, more carbon and nitrogen may be released into the atmosphere. These results can have serious effects on humans such as displacing herders from their community; a decrease in vegetables, fruit, and meat that are regularly acquired from these fields; and a catalyzing effect on global warming.
Causes
Overgrazing
It is thought that grassland degradation is principally attributed to overgrazing. This occurs when animals consume grass at a faster rate than it can grow back. Lately, overgrazing has become more apparent, partially because of the increase in urbanization, which makes less room for available farmland. With these smaller plots, farmers try to maximize their space and profits by densely packing their land with animals. Another point that comes with the high density of owned animals is that farmers need to be able to provide for them in the winter months, so they must gather much grass since the winter is often harsh and long in alpine meadows. As a result, the grass is given less of a chance to grow back due to either the rapid consumption of grass or the continual stomping of the feet of these animals. This latter suppression also encourages rats and insects to subsist here, both of which further inhibit the growth of grass. Overgrazing is a main cause of shrub and bush encroachment in grasslands and savanna ecosystems.
Small mammals
An increase in some small animal populations has led to some grasslands being degraded. These animals include the Himalayan marmots, the Brandt's and plateau vole, and the plateau pika and zokor. They damage this environment mainly through their burrowing into the ground and gnawing at the grass and other plants. Both of these actions encourage soil erosion and make it more difficult for plants to firmly ground themselves to this poor terrain. Hence grass has a tougher time growing and the terrain becomes spottily doused with grass. However, there are those who do not think that these animals contribute to grassland degradation. They claim that such burrowing aids in the recycling of nutrients in the soil and that the rise in population is only normal since grazing levels in these areas have also risen.
Climate change
Climate change has had a noticeable role in grassland degradation, for its characteristics are not suitable for the growth of grass. The increase in average temperatures of regions makes them less suitable for grass to grow due to the more rapid evaporation of water that was formerly utilized by the grass. Furthermore, neither periods of much rain nor stretches of drought, both of which become more prevalent with climate change, encourage the growing of grass. It is especially harmful when the times of drought are during growing season, as is the case near the Yangtze and Yellow Rivers in China. Additionally, since alpine regions, where degradation typically occurs, are commonly of high elevation, they are more easily affected by climate and its changes. Some scientists, however, write off climate change as an insignificant cause of degradation. Climate change, in particular warmer and drier conditions, brings about suitable conditions for the invasion of non-native grass species.