Woody plant encroachment

Woody plant encroachment is when bushes, shrubs and woody plants grow more and take over the area where there used to be grass and other plants. It happens mostly in grasslands, savannas and woodlands and can change the area from being open to being closed. The causes of this include things like people using the land too much, not having fires, and climate change. It can be bad for nature and for people who use the land. Some countries try to stop this by doing things like cutting down some of the bushes, using fire and managing the land. Sometimes, this type of land is good for the climate because it can take in carbon. But, it is not always good and more research is needed to understand the effects on the climate.
Explanation.
Woody plant encroachment is when bushes and shrubs grow more and take over the area where there used to be grass and other plants. This happens in grasslands and shrublands and can change the area from being open to being closed. It is different from invasive species which are plants that are brought from other places. It can happen because of things like people using the land too much, not allowing natural fires, and because of climate change. This can be bad for nature and for people who use the land. Some research has been done on this topic, but more is needed to understand it better.
Reasons.
Woody encroachment has probably started thousands of years ago, when Earth started warming, but it has happened much faster during the last 50 years. There are different possible reasons for woody encroachment, some directly linked to the action of people, others linked to climate change. The reasons for woody encroachment are very different between dry grasslands and wet grasslands. Once the bushes and shrubs have grown and taken over an area, they make it harder for grass to grow. This makes the problem of woody encroachment continue.
Land use.
When people abandon land, that means when they stop using the land for agriculture, bushes often start growing. This happens for example in the Alps in Southern Europe, because more and more people leave their farms and move to cities.
Also when people use land very intensively, bush encroachment can happen. For example when farmers bring many cows to areas where wild animals lived before, these cows eat up most of the grass quickly, but do not touch the bushes. The result is that bushes occupy more and more of the land, while grasses start to disappear. Once woody encroachment has started, it is hard to stop it, even when the number of cows is made less.
Climate Change.
While changes in how people use the land is often seen as the main reason for woody encroachment, some studies suggest that global factors like climate change and rainfall patterns also play a role. Climate change can make it easier for bushes and shrubs to grow because of things like more CO2 in the air and changes in temperature and rainfall. Once the bushes and shrubs are established, they can make it harder for grass to grow and the problem of woody encroachment can continue. According to the Intergovernmental Panel on Climate Change (IPCC) report, high latitude tundra and boreal forests are particularly at risk of woody encroachment due to climate change.
Results.
Woody encroachment is a big change for nature in areas where it happens. Often, the encroachment is seen as harmful to nature. It can make the number of different plant species less, it allows less water to go into the ground and animals have less to eat. For that reason woody encroachment is often called a form or land degradation. But this is not always the case, encroachment can also lead to good changes in nature. That is why one must study woody encroachment in each area where it happens, becore making conclusions.
How woody encroachment changes nature depends on different things:
Many scientists see woody encroachment as a form of land degradation and think it can even lead to the creation of new deserts. Because bushes make nature look more green, the encroachmetn is sometimes called "green desertification".
Biodiversity.
Woody encroachment can have negative effects on the variety of plants and animals in that area (biodiversity). In Africa, the number of different plants and animals usually decreases when woody encroachment happens. In North America, the number of different plants and animals may increase or decrease depending on the area. In Brazil, one third of the different plant species are lost because of woody encroachment.
The following list shows what species are affected by woody encroachment: