Genetic erosion is due to shifting cultivation.

Shifting cultivation, also known as slash-and-burn agriculture, is a traditional farming system in which land is cleared, cultivated for a few years, and then left fallow for a period of time to restore its fertility. This practice involves the repeated clearing and burning of forests, which leads to the loss of genetic diversity in plant species.

Explanation:

1. Shifting cultivation and genetic erosion:
Shifting cultivation involves the continuous clearing and burning of forests, which results in the destruction of natural habitats and the loss of biodiversity. The process of clearing the land involves cutting down trees and burning vegetation, which eliminates the natural habitat for many plant species. As a result, the genetic diversity within these plant species is reduced, leading to genetic erosion.

2. Loss of genetic diversity:
Genetic erosion refers to the loss of genetic diversity within a particular species or population. Genetic diversity is crucial for the long-term survival and adaptation of species to changing environmental conditions. It provides the raw material for evolution and allows species to respond to new challenges, such as diseases, pests, and climate change.

3. Impact of shifting cultivation on genetic erosion:
Shifting cultivation practices often involve the use of landraces, which are local varieties of crops that have adapted to specific environmental conditions over time. These landraces often possess unique genetic traits that make them resistant to diseases, pests, and other environmental stresses.

However, when forests are cleared for shifting cultivation, these landraces are often replaced with genetically uniform varieties of crops that are more productive but lack genetic diversity. These genetically uniform varieties are often selected for their high yield potential and uniformity, but they may be more susceptible to diseases and other environmental stresses.

4. Consequences of genetic erosion:
Genetic erosion can have serious consequences for agricultural sustainability and food security. The loss of genetic diversity reduces the ability of crops to adapt to changing environmental conditions, making them more vulnerable to pests, diseases, and climate change.

Furthermore, the loss of genetic diversity reduces the availability of genetic resources for crop improvement and breeding programs. This hampers the development of new crop varieties that are resistant to diseases, pests, and other environmental stresses.

In conclusion, shifting cultivation is a major cause of genetic erosion. The repeated clearing and burning of forests associated with shifting cultivation lead to the loss of genetic diversity within plant species, resulting in reduced adaptability and increased vulnerability to pests, diseases, and climate change.