Polypropylene netting erosion control blankets protect the ground by acting as a temporary barrier that prevents soil erosion and helps vegetation establish. They do this by holding the soil in place, reducing the impact of rainfall, and creating a stable environment for new plant growth. 

Here's a more detailed explanation of how they work:

Soil Stabilization:

The netting, typically made of polypropylene, is woven or stitched together to form a matrix that helps to hold the soil particles in place. This prevents the soil from being washed away by rain or wind. 

Reduced Impact of Rainfall:

By providing a surface layer, the blanket intercepts raindrops and reduces their force, preventing the soil from being compacted and eroded. 

Protection from Wind Erosion:

The netting also provides some protection from wind erosion by creating a barrier that reduces wind speed and prevents soil particles from being blown away. 

Support for Vegetation Establishment:

The netting provides a stable, protected environment for seeds and young plants to establish their roots and grow. 

Gradual Degradation:

Many erosion control blankets are designed to degrade over time, typically as vegetation becomes established and its root system takes over the task of soil stabilization.